Essential Guide To Common Metal Types And Uses

I. Non-alloy Steel

Non-alloy steel refers to an iron-carbon alloy with w_c <2.11%, containing small amounts of impurities such as Si, Mn, S, P, etc. Before the implementation of the new steel classification standards, it was called carbon steel (abbreviated as carbon steel). It is a commonly used material in various industrial sectors.

1. Classification of Non-alloy Steel

There are three main methods for classifying non-alloy steel:

(1) Based on carbon content

Divided into low carbon steel (w_c <0.25%), medium carbon steel (0.25%≤w_c ≤0.60%), and high carbon steel (w_c >0.60%).

(2) Based on main quality grades

Divided into ordinary quality non-alloy steel (w_s ≤0.040%, w_p≤0.040%), high-quality non-alloy steel excluding ordinary quality non-alloy steel and special quality non-alloy steel, and special quality non-alloy steel (w_s ≤0.020%, w_p ≤0.020%).

(3) Based on the use of steel

Divided into carbon structural steel, non-alloy tool steel, and cast carbon steel.

In addition, according to the degree of deoxidation of the molten steel during smelting, it is divided into rimmed steel, killed steel, and special killed steel.

2. Grades, Properties, and Main Uses of Non-alloy Steel

(1) Carbon Structural Steel Non-alloy Mechanical Structural Steel

1) Ordinary Carbon Structural Steel

The grade of ordinary carbon structural steel is represented by “Q+number+quality grade+deoxidation method symbol”. “Q” is the initial letter of the Chinese pinyin for “yield strength”, the “number” indicates its minimum yield strength, and the quality grades are represented by A, B, C, D, with grade A being the lowest and grade D being the highest.

The deoxidation method symbols are F, Z, TZ for rimmed steel, killed steel, and special killed steel, respectively. Usually, the symbols for killed steel and special killed steel (Z and TZ) can be omitted. For example, the grade Q235AF indicates grade A rimmed steel with a yield strength ≥235MPa. The grades, properties, and main uses of ordinary carbon structural steel are shown in Table 1.

Table 1 Grades, Main Properties, and Uses of Ordinary Carbon Structural Steel

New Grade	Old Grade	Main Properties	Example Uses
Q195	A1, B1	High plasticity, toughness, good welding performance, good pressure processing performance, but low strength	Used for making anchor bolts, plowshares, chimneys, roofing panels, rivets, low carbon steel wires, thin plates, welded pipes, tie rods, hooks, brackets, welded structures
Q215	A2, C2
Q235	A3, C3	Good plasticity, toughness, and welding performance, good cold stamping performance, certain strength, good cold bending performance	Widely used for parts and welded structures with general requirements, such as tie rods, pins, shafts, screws, nuts, collars, brackets, bases, building structures, bridges, etc.

2) High-quality Carbon Structural Steel

The grade of high-quality carbon structural steel is generally represented by two digits, which indicate the average mass fraction of carbon in ten-thousandths. For example, 35 steel indicates high-quality carbon structural steel with an average carbon mass fraction of 0.35%.

If the mass fraction of manganese in the steel is high (0.7%≤W_Mn ≤1.2%), the chemical element symbol for manganese (Mn) is added after the grade, for example, 35Mn. The grades, properties, and main uses of high-quality carbon structural steel are shown in Table 2.

Table 2 Grades, Properties, and Main Uses of High-quality Carbon Structural Steel

Grade	Main Performance Characteristics	Example Uses
08	Low strength and hardness, excellent plasticity. Good deep drawing and deep drawing properties, good cold workability and weldability. High tendency to segregation of components, high sensitivity to aging, so during cold working, stress relief heat treatment or water toughening treatment can be used to prevent cold working fractures.	Easy to roll into thin plates, thin strips, cold-deformed profiles, cold-drawn steel wires, used for stamping parts, deep drawing parts, various non-load-bearing covering parts, carburizing, nitriding, making various sleeves, templates, brackets, etc.
20	Strength and hardness slightly higher than 15 steel, good plasticity and weldability, good toughness after hot rolling or normalizing.	Used to make less important small and medium-sized carburized, carbonitrided parts, forged parts, such as lever shafts, transmission forks, gears, heavy machinery tie rods, hooks, etc.
30	Higher strength and hardness, good plasticity, good weldability, can be used after normalizing or tempering, suitable for hot forging and hot pressing. Good machinability.	Used for low-load parts with low stress and temperatures below 150°C, such as lead screws, tie rods, shaft keys, gears, shaft sleeves, etc. Carburized parts have good surface wear resistance and can be used as wear-resistant parts.
45	The most commonly used medium carbon quenched and tempered steel, with good comprehensive mechanical properties, poor hardenability, and prone to cracking during water quenching. Small parts should be tempered, and large parts should be normalized.	Mainly used to manufacture high-strength moving parts, such as turbine impellers, compressor pistons, shafts, gears, racks, worms, etc. For welded parts, preheating before welding and stress relief annealing after welding should be noted.
65	After heat treatment or cold work hardening, it has high strength and elasticity. Poor weldability, prone to cracking, poor machinability, low cold deformation plasticity, poor hardenability, generally oil quenched. The characteristic is that its fatigue strength can be comparable to alloy spring steel under the same configuration.	Suitable for making flat or spiral spring parts with simple cross-sections and shapes and low stress, such as valve springs, spring rings, etc.; also suitable for making high wear resistance parts, such as rollers, crankshafts, cams, and wire ropes, etc.
85	The highest carbon content structural steel, with higher strength and hardness than other high carbon steels, but slightly lower elasticity, other properties are similar to 65 steel. Poor hardenability.	Railway vehicles, flat plate springs, round spiral springs, steel wires, steel strips, etc.
40Mn	Slightly higher hardenability than 40 steel. After heat treatment, strength, hardness, and toughness are slightly higher than 40 steel, medium plasticity during cold deformation, good machinability, low weldability, with overheating sensitivity and temper brittleness, prone to cracking during water quenching.	Fatigue-resistant parts, crankshafts, rollers, shafts, connecting rods, screws, and nuts working under high stress, etc.
65Mn	Higher strength, hardness, elasticity, and hardenability than 65 steel, with overheating sensitivity and temper brittleness tendency, prone to cracking during water quenching. Machinability in annealed state is acceptable, low cold deformation plasticity, poor weldability.	Medium load leaf springs, 7~20mm diameter spiral springs and spring washers, spring rings. High wear resistance parts, such as grinding machine spindles, spring collets, precision machine tool lead screws, plows, cutters, rings on spiral roller bearings, railway rails, etc.

(2) Non-alloy Tool Steel

The mass fraction of carbon in carbon tool steel is between 0.65% and 1.35%, all of which are of high-quality or high-grade high-quality carbon steel. This type of steel has high hardness and high wear resistance, mainly used for making tools, measuring tools, and molds, such as making hand saw blades, files, etc.

The grade of non-alloy tool steel is represented by “T + number”. Among them, “T” is the initial letter of the Chinese pinyin for “carbon”, and the number represents the thousandth of the average mass fraction of carbon in the steel. If it is high-grade high-quality non-alloy tool steel, the symbol “A” is added after the number.

For example, T8 indicates high-quality non-alloy tool steel with an average carbon mass fraction of 0.8%, and T8A indicates high-grade high-quality non-alloy tool steel with an average carbon mass fraction of 0.8%. The common grades, properties, and main uses of non-alloy tool steel are shown in Table 3.

Table 3 Common Grades, Properties, and Main Uses of Non-alloy Tool Steel

Grade	Main Properties	Hardness			Example Uses
		Annealed State	Quenched Sample
		HBW	Quenching Temperature/°C Cooling medium	HRC
T7 T7A	After heat treatment, it has high strength, toughness, and considerable hardness, but poor hardenability and hot hardness, and deforms during quenching	≤187	800~820 Water	≥62	Used to manufacture various tools that withstand impact and vibration, requiring good toughness, moderate hardness, and low cutting ability, such as small pneumatic tools, woodworking chisels and saws, tin snips, hand hammers, machinist hammer heads, and pins
T8 T8A	After quenching and tempering, it has high hardness, good wear resistance, but low strength and plasticity, and poor hardenability Poor, prone to overheating during heating, easy to deform, low hot hardness, and low impact resistance	≤187	780~800 Water	≥62	Used to manufacture tools with cutting edges that do not heat up during work, with high hardness and wear resistance, such as axes, chisels, saw blades for woodworking, simple molds and punches, vise jaws, spring sheets, and pins
T8Mn T8MnA	Performance is similar to T8 and T8A, but manganese improves its hardenability compared to T8 and T8A, with a deeper hardened layer Deeper	≤187	780~800 Water	≥62	Uses are similar to T8 and T8A
T10 T10A	Good toughness, high strength, better wear resistance than T8 and T8A, low hot hardness, poor hardenability, and large quenching deformation	≤197	760～780 Water	≥62	Used to manufacture tools with poor cutting conditions, high wear resistance, not subject to strong vibration, requiring certain toughness and sharpness, such as milling cutters, turning tools, drills, taps, machine woodworking tools, wire drawing dies, and punching dies
T12 T12A	High hardness and wear resistance, low toughness, poor hot hardness, poor hardenability, and large quenching deformation	≤207		≥62	Used to manufacture tools with small impact, low cutting speed, and high hardness, such as milling cutters, turning tools, drills, taps, dies, saw blades, small cold cutting dies, and punching dies, as well as high hardness, low impact mechanical parts
T13 T13A	The best non-alloy tool steel in carbon steel for hardness and wear resistance, but poor toughness and cannot withstand impact	≤217		≥62	Used to manufacture tools requiring extremely high hardness but not subject to impact, such as scrapers, razors, wire drawing tools, tools for engraving file patterns, engraving tools, drills, and files

(3) Cast carbon steel

The grade of cast carbon steel (referred to as “cast steel”) is indicated by “ZG + two groups of numbers”. “ZG” is the abbreviation of the Chinese pinyin for “cast steel”, the first group of numbers indicates its minimum yield strength value, and the second group of numbers indicates its minimum tensile strength value. For example, ZG230-450 indicates cast carbon steel with a yield strength of not less than 230MPa and a tensile strength of not less than 450MPa.

The mass fraction of carbon in cast carbon steel for general engineering use is between 0.15% and 0.60%. Cast carbon steel is mainly used to make cast steel parts that require high strength and toughness, have complex shapes, and are difficult to form by pressure processing methods. The grades, chemical composition, mechanical properties, and main uses of cast steel are shown in Table 4.

Table 4 Grades, chemical composition, mechanical properties, and main uses of cast carbon steel

Grade	Main chemical composition Mass fraction (%)						Room temperature mechanical properties					Performance characteristics and examples of use
	C	Si	Mn	P		S	R_eL (R_r0.2) MPa	R_m MPa	A_11.3 (%)	Z (%)	K/J [a_K/ (J/cm²)]
	Not more than						Not less than
ZG200-400	0.20	0.60	0.80		0.035		200	400	25	40	30(60)	Good plasticity, toughness, and weldability. Used for various mechanical parts that are not heavily stressed and require good toughness, such as machine bases and transmission housings.
ZG230-450	0.30	0.60	0.90		0.035		230	450	22	32	25(45)	Certain strength and good plasticity, toughness, and weldability. Used for various mechanical parts that are not heavily stressed and require good toughness, such as anvils, bearing caps, base plates, valve bodies, etc.
ZG270-500	0.40	0.60	0.90		0.035		270	500	18	25	22(35)	High strength and good hardness, good castability, good weldability, and good machinability. Used for rolling mill frames, bearing seats, connecting rods, housings, crankshafts, etc. Cylinder blocks, etc.
ZG310-570	0.50						310	570	15	21	15(30)	Good strength and machinability, low plasticity, and toughness. Used for parts with large loads, such as large gears, cylinder blocks, brake wheels, rollers, etc.
ZG340-640	0.60						340	640	10	18	10(20)	High strength, hardness, and wear resistance, good machinability, poor weldability, good fluidity, and high crack sensitivity. Used for gears, ratchets, etc.

II. low alloy steel and alloy steel

Steel obtained by intentionally adding a certain amount of alloy elements to carbon steel is called low alloy steel and alloy steel. In alloy steel, commonly added alloy elements include: manganese (w ≥1%), silicon (w ≥0.5%), chromium, tungsten, nickel, molybdenum, vanadium, aluminum, copper, titanium, niobium, and rare earth elements.

These elements can improve the mechanical properties and hardenability of steel, improve the process performance of steel, or obtain certain special physical and chemical properties, thereby greatly expanding its application range. Alloy steel can be divided into: alloy structural steel, alloy tool steel, and special purpose steel.

1. Low alloy high strength structural steel

It is a steel made by adding a small amount (≤5%) of alloy elements on the basis of low carbon steel (w_c <0.2%), and its grade is also represented by “Q+number”. Its meaning is the same as that of ordinary carbon structural steel, for example, Q345 indicates low alloy high strength structural steel with a minimum yield strength of 345MPa.

If there are letters A, B, C, D, E after the grade, it also indicates the quality grade, for example, Q345B indicates B-grade low alloy high strength structural steel with a minimum yield strength of 345MPa.

Low alloy steel is usually used in the state of hot rolling annealing (or normalizing). Its strength is 10% to 20% higher than that of ordinary low carbon steel, so it is called low alloy high strength steel.

It has good plasticity, toughness, and good weldability and corrosion resistance. It is currently widely used in bridges, vehicles, ships, buildings, containers, etc. The main purpose is to reduce the weight of the structure itself and ensure the reliability and durability of use. The grades, chemical composition, mechanical properties, and uses of commonly used low alloy high strength structural steels are shown in Table 1-7.

Table 5 Common grades, chemical composition, mechanical properties, and main uses of low alloy high strength structural steels

Grade		Chemical composition (mass fraction) (%)				Steel Thickness /mm	Mechanical properties			Cold bending test	Example of use
New standard	Old standard	C	Si	Mn	Others	Steel Thickness /mm	R_m /MPa	R_eL /MPa	A (%)	a – Specimen thickness d – Mandrel diameter	Example of use
Q345	14MnNb	0.12~ 0.18	0.20~ 0.50	0.80~ 1.20	0.15~ 0.50Nb	≤16	500	360	20	180℃ (d=2a)	Oil tanks, boilers, bridges, etc.
	16Mn	0.12~ 0.20	0.20~ 0.50	1.2~ 1.60	——	≤16	520	350	21		Bridges, ships, vehicles, Pressure vessels, building structures, etc.
	16MnRE	0.12~ 0.20	0.20~ 0.50	1.2~ 1.50	0.2~ 0.35Cu	≤16	520	350	21		Bridges, ships, vehicles, Pressure vessels, building structures etc.
Q390	15MnT 15MnV	0.12~ 0.18	0.20~ 0.50	1.25~ 1.50	0.12~ 0.20Ti	≤25	540	400	19	180℃ (d=3a)	Ships, pressure vessels, power station equipment, etc. Ship sides, pressure vessels, bridges, vehicles, lifting machinery, etc.
Q390	15MnT 15MnV	0.12~ 0.18	0.20~ 0.50	1.25~ 1.50	0.04~ 0.14V	≤25	540	400	18	180℃ (d=3a)	Bridges, ships, vehicles, Pressure vessels, building structures, etc.

2. Alloy structural steel

Alloy structural steel mainly includes alloy carburizing steel, alloy quenched and tempered steel, alloy spring steel, rolling bearing steel, etc.

(1) Alloy carburizing steel

Alloy carburizing steel is made by adding alloy elements such as chromium, manganese, nickel, titanium, vanadium, etc., to low carbon steel. Its grade is represented by “two digits + alloy element symbol + number”.

The first two “digits” indicate the ten-thousandth of the average carbon mass fraction in the steel, the element symbol indicates the alloy elements contained in the steel, and the “number” after the element symbol indicates its average content percentage. It is stipulated that when the average content of alloy elements is <1.5%, only the element symbol is marked, and the number is not marked; when the average mass fraction of alloy elements is between 1.5% and 2.5%, 2.5% and 3.5%, etc., 2, 3, etc., are marked accordingly after the element.

For example, 20Mn2 indicates that the average carbon mass fraction is 0.20% and the average manganese mass fraction is 2% in the alloy carburizing steel. If it is high-quality alloy structural steel, the symbol “A” is added at the end of the grade, such as 18Cr2Ni4WA.

Alloy carburizing steel is usually used after carburizing, quenching, and low-temperature tempering. It is mainly used for parts that require high surface hardness, high strength, high wear resistance, and high toughness in the core, and can withstand impact loads (such as transmission gears, gear shafts, piston pins, etc.). The grades, compositions, mechanical properties, and uses of commonly used alloy carburizing steels can be found in GB/T3077—2015 (Alloy Structural Steel).

(2) Alloy Quenched and Tempered Steel

Alloy quenched and tempered steel usually refers to medium carbon alloy steel used after quenching and tempering treatment, with a carbon mass fraction between 0.25% and 0.50%. The grade representation method of alloy quenched and tempered steel is the same as that of alloy carburizing steel, also using “two digits + alloy element symbol + number”.

Alloy quenched and tempered steel is mainly used for important parts that require high hardness, good plasticity, and toughness, such as main shafts, crankshafts, connecting rod bolts, important gears, etc. If some parts also require high surface hardness and wear resistance, they can be subjected to surface induction heating quenching and low-temperature tempering after quenching and tempering treatment.

The grades, compositions, heat treatments, and properties of commonly used alloy quenched and tempered steels can be found in GB/T3077—2015 (Alloy Structural Steel). Widely used alloy quenched and tempered steels include 40Cr, 40MnVB, 30CrMnSi, 20MnVB, 12CrNi3, etc.

(3) Alloy Spring Steel

Alloy steel used to manufacture various springs or elastic parts is called alloy spring steel, with a carbon mass fraction generally between 0.45% and 0.70%. The grade representation method of alloy spring steel is the same as that of alloy carburizing steel, also using “two digits + element symbol + number”.

The grades, compositions, heat treatments, properties, and uses of commonly used alloy spring steels can be found in GB/T1222—2007 (Spring Steel). The most widely used is silicon-manganese alloy spring steel, such as 60Si2Mn, which is widely used to manufacture coil springs and leaf springs for automobiles, tractors, locomotives, and other important springs working under high stress.

(4) Rolling Bearing Steel

Alloy steel used to manufacture rolling elements (balls, rollers, needles) and rings in rolling bearings is called rolling bearing steel, with a carbon mass fraction generally between 0.95% and 1.15%, to obtain high-carbon martensite after quenching, ensuring that rolling bearing steel has high hardness and high strength.

The grade of rolling bearing steel is represented by “G + Cr + number”. “G” is the first letter of the Chinese pinyin for “rolling”, “Cr” is the element symbol for chromium, and the “number” indicates the thousandth of the average chromium mass fraction in the steel. For example, GCr15 indicates that the average chromium mass fraction is 1.5% in rolling bearing steel.

The chromium mass fraction in rolling bearing steel is generally between 0.40% and 1.65%. Its function is to improve the hardenability of the steel and form dispersed carbides, thereby improving the wear resistance and contact fatigue strength of the steel. For large bearings, elements such as manganese and silicon are also added to further improve the hardenability of the steel.

Currently, the most widely used grades of rolling bearing steel in China are GCr15 (mainly used to manufacture small and medium-sized bearings) and GCr15SiMn (mainly used to manufacture larger bearings).

Rolling bearing steel can also be used to manufacture parts with high wear resistance and high fatigue strength, such as grinder spindles, cold punching dies, lead screws, precision measuring tools, etc. The grades, compositions, heat treatments, and properties of commonly used rolling bearing steels can be found in GB/T 18254—2016 (High Carbon Chromium Bearing Steel).

3. Alloy Tool Steel

Alloy steel used to manufacture various tools is called alloy tool steel. It is steel made by adding an appropriate amount of alloy elements to non-alloy tool steel. This type of steel has higher hardness, wear resistance, and toughness than non-alloy tool steel, especially better hardenability, hardenability, hot hardness, and tempering stability. Therefore, it can be used to manufacture tools with large cross-sections, complex shapes, and high-performance requirements.

Alloy tool steel is divided into measuring tool steel, impact-resistant tool steel, hot work die steel, cold work die steel, plastic mold steel, etc., according to its use. The grade representation method is similar to that of alloy structural steel, except that the carbon content representation method is different. When w _c ≥1%, the carbon content is not marked; when w_c <1%, a single digit is used to indicate the thousandth of the average carbon content in the steel.

For example, Cr12MoV indicates that w_c ≥1%, w_Cr =12%, and w _Mo , w_v <1.5% in alloy tool steel. Another example is 9SiCr, which indicates that w_c =0.9%, and w_Si , w_Cr <1.5% in alloy tool steel. Alloy tool steels are all high-quality steels, so the symbol “A” is not marked at the end of the grade.

(1) Cold Work Die Steel

Refers to the steel used to manufacture molds for cold stamping, cold extrusion, and cold drawing of metal in cold conditions. It has high hardness, high wear resistance, sufficient strength, and toughness, and requires good hardenability and small quenching deformation. This type of steel is used after quenching and tempering. The grades, heat treatments, properties, and uses of commonly used cold work die steels are shown in Table 6.

Table 6 Commonly Used Cold Work Die Steel Grades, Heat Treatments, Properties, and Uses

Grade	Delivery Condition Hardness HBW	Quenching		Hardness HRC (Not less than)	Example of use
Grade	Delivery Condition Hardness HBW	Temperature/℃	Quenching cooling medium	Hardness HRC (Not less than)	Example of use
9Mn2V	≤229	780~810	Oil	62	Punching die, cold pressing die
CrWMn	207~255	800~830	Oil	62	Complex shape, high precision punching die
Cr12	217~269	950~1000	Oil	60	Cold punching die, punch, drawing die, powder metallurgy die
Cr12MoV	207~255	950~1000	Oil	58	Punching die, trimming die, drawing die

(2) Hot work die steel

Hot work die steel refers to the steel used for making hot forging dies, hot extrusion dies, and die-casting dies, which form hot metal or alloy under pressure. Hot work die steel works at high temperatures (400～600℃) and, during operation, it not only bears large impact loads but also endures significant compressive stress, tensile stress, bending stress, and intense friction caused by the flow of hot metal in the die cavity.

Therefore, hot work die steel is required to maintain sufficient hardness, strength, toughness, and wear resistance at high temperatures. Additionally, this type of steel is repeatedly heated by hot metal and cooled by cooling media (water, oil, air) during operation, causing volume changes and making it prone to thermal fatigue.

The mass fraction of carbon in hot work die steel is generally between 0.3% and 0.6%, making it medium carbon alloy steel. Common grades of hot work die steel include 5CrMnMo and 5CrNiMo. The latter has better hardenability than the former, with similar other properties. 5CrMnMo is suitable for making small to medium-sized hot forging dies, while 5CrNiMo is suitable for making medium to large-sized hot forging dies. Common grades of die-casting die steel include 3Cr2W8V, etc.

(3) Plastic mold steel

Plastic mold steel refers to the steel used for making molds that press fine powder or granular plastic into shape under low-temperature heating conditions not exceeding 200℃. According to the molding method of plastic products, plastic molding molds can be divided into die-casting molds, extrusion molds, injection molds, forming molds, blow molding molds, etc.

During operation, the mold is continuously heated, pressed, and subjected to a certain degree of friction and corrosion by harmful gases. Therefore, plastic mold steel is required to have sufficient strength and toughness at 200℃, high wear resistance and corrosion resistance, good machinability, polishability, weldability, and heat treatment process performance. Currently, commonly used plastic mold steels include 3Cr2Mo, 3Cr2MnNiMo.

(4) Steel for measuring tools and cutting tools

Measuring tools are measurement tools used in mechanical engineering to control machining accuracy, such as micrometers, gauge blocks, plug gauges, calipers, etc. Since measuring tools often come into contact with the parts being measured during use, they are subject to wear and impact. Therefore, the working parts of measuring tools are required to have high hardness (62~65HRC), high wear resistance, high dimensional stability, and sufficient toughness.

9SiCr and other steels are often used to make precision measuring tools with high accuracy and complex shapes, such as gauge blocks and plug gauges. In addition, alloy carburizing steel or bearing steel (GCr15) can be used to make measuring tools that do not require high precision but need to be impact-resistant after carburizing and quenching treatment; sometimes cold work tool steel (CrWMn) is also used to make precision measuring tools.

4. Grades, properties, and uses of special performance steels

Special purpose steel refers to alloy steel with special physical and chemical properties, as well as certain mechanical properties. It includes stainless steel, heat-resistant steel, and wear-resistant steel, among others.

(1) Stainless steel

Stainless steel refers to alloy steel that can resist atmospheric corrosion, acid, alkali corrosion, or other media corrosion. The main characteristics of stainless steel are its resistance to rust and corrosion, with a chromium content of at least 10.5% and a carbon content not exceeding 1.2%.

Stainless steel is classified into different types based on its metallographic structure: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, austenitic-ferritic stainless steel, and precipitation-hardening stainless steel. The grades, compositions, heat treatments, and properties of commonly used stainless steels can be found in GB/T1220—2007 (Stainless Steel Bars). The most widely used types and grades of stainless steel include the following:

1) Ferritic stainless steel

Ferritic stainless steel has three types:

Cr12 type, Cr13 type, such as 06Cr13Al, 022Cr12, etc., are commonly used as heat-resistant steel, such as for automobile exhaust valves.
Cr17 type, such as 10Cr17, 10Cr17Mo, etc., are mainly used for containers and pipelines in chemical equipment.
Cr27~30 type, such as 008Cr27Mo, 008Cr30Mo2, etc., are steels resistant to strong acid corrosion.

2) Martensitic stainless steel

The main grades of martensitic stainless steel are 12Cr13, 20Cr13 (with lower carbon content), mainly used for parts requiring high mechanical properties and low corrosion resistance, such as turbine blades and medical instruments; 30Cr13, 40Cr13 (with higher carbon content) are mainly used for hydraulic press valves and hard, wear-resistant medical surgical tools, measuring tools, stainless steel bearings, and springs.

3) Austenitic stainless steel

Austenitic stainless steel includes 06Cr19Ni10, 12Cr18Ni9, mainly used for making parts requiring high corrosion resistance and light load parts that need welding after cold deformation, such as in chemical equipment and pipelines. It can also be used to make non-magnetic corrosion-resistant parts in the instrumentation and power generation industries. This type of steel mainly increases its strength through cold deformation processing and cannot be strengthened by heat treatment.

(2) Heat-resistant steel

Heat-resistant steel refers to special performance steel with good chemical stability or high strength at high temperatures. Common grades of heat-resistant steel include: 10Cr17, which can be used to make parts resistant to oxidation below 900°C, such as radiators, furnace parts, and oil nozzles. 42Cr9Si2 and 40Cr10Si2Mo are commonly used to make exhaust valves and other parts that are subject to high-temperature exhaust gas corrosion and impact and wear (hence also called valve steel).

06Cr19Ni10 and 45Cr14Ni14W2Mo, due to their high chromium and nickel content, are widely used heat-resistant steels, commonly used in parts of boilers, turbines, internal combustion engines, and heat treatment furnaces.

(3) Wear-resistant steel

Wear-resistant steel refers to steel with high wear resistance. For example, high manganese steel, which hardens only under strong impact loads, generally has a carbon content of 1.0% to 1.3% and a manganese content of 11% to 14%.

When high manganese steel is heated to 1000~1100°C and subjected to solution treatment, a single-phase austenite structure can be obtained. At this time, the hardness is not high (about 180~220HBW). When it undergoes strong friction or impact under high pressure, the austenite on the surface of the workpiece will quickly undergo plastic deformation, causing strain hardening and martensitic transformation, significantly increasing the surface hardness (about 550HBW or higher) and enhancing wear resistance.

When the surface hardened layer wears off, the newly exposed surface will undergo the same transformation and gain wear resistance. The pressure processing and cutting processing of high manganese steel are very difficult, so it is generally directly cast into parts and used after solution treatment.

High manganese steel is mainly used for parts that work under severe friction and strong impact conditions, such as tracks for tanks and tractors, excavator bucket teeth, bulldozer blades, railway turnouts, and crusher jaws. Its grades are specified in GB/T 5680—2010 “Austenitic Manganese Steel Castings,” such as ZG100Mn13.

III. Cast iron

Cast iron refers to a group of iron-carbon-silicon alloys with high carbon and silicon content, and also contains a considerable amount of impurities such as manganese, sulfur, and phosphorus. In cast iron, carbon mainly exists in the form of graphite. The process of carbon precipitating in the form of graphite is called graphitization, commonly represented by the symbol G. Different degrees of graphitization result in different types, structures, and properties of cast iron.

The mechanical properties of cast iron are inferior to steel, but cast iron with a composition close to eutectic has a low melting point and good fluidity, so it has excellent casting properties, good wear resistance, vibration damping, and machinability. Additionally, the production process and equipment are simple, and the cost is low, making cast iron one of the most widely used metal materials.

1. Classification of cast iron

According to the different forms of carbon in cast iron, cast iron can be divided into the following three categories:

(1) Gray cast iron

Carbon is entirely or mostly in the form of graphite, without ledeburite structure, and its fracture surface is dark gray. Most of the cast iron used in industry is this type of cast iron.

(2) White cast iron

The graphitization process of this type of cast iron is completely suppressed. Except for a small amount of carbon dissolved in ferrite, all carbon exists in the form of Fe₃C. Its fracture surface is silvery white, hard, and brittle, making it difficult to machine. Therefore, it is rarely used directly in industry. Currently, white cast iron is mainly used as raw material for steelmaking and for producing malleable cast iron blanks.

(3) Mottled cast iron

The graphitization process of this type of cast iron is only partially realized. Part of the carbon exists in the form of graphite, and the other part exists in the form of Fe₃C. Its fracture surface is mottled black and white, also very hard and brittle, making it difficult to machine. Therefore, it is rarely used in industry.

Gray cast iron is commonly used in industry. Its performance is related not only to its composition and matrix structure but also to the shape and size of the graphite. According to the different forms of graphite in cast iron, cast iron can be divided into the following four types:

1) Gray cast iron

Its graphite is flake-shaped, with poor mechanical properties, but its production process is simple, cost is low, and casting performance is excellent, making it widely used in industry.

2) Malleable cast iron

Its graphite is in the form of clusters, with better mechanical properties than gray cast iron, but the production cycle is long and the cost is high. It is generally used to manufacture some important small castings.

3) Ductile cast iron

Its graphite is spherical, with the highest mechanical properties, and its strength is close to that of non-alloy steel. The production process is simpler than that of malleable cast iron. Ductile cast iron can replace some non-alloy steel and alloy steel in manufacturing certain important parts.

4) Vermicular cast iron

Its graphite is vermicular, with mechanical properties between gray cast iron and ductile cast iron. It is a new type of cast iron with a relatively short development history.

2. Gray cast iron

(1) Structure and properties of gray cast iron

The microstructure of gray cast iron is characterized by flake graphite distributed on various matrix structures. According to the different matrix structures, it is divided into:

Ferritic gray cast iron (flake graphite distributed on a ferritic matrix).

Ferritic + pearlitic gray cast iron (flake graphite distributed on a ferritic and pearlitic matrix).
Pearlitic gray cast iron (flake graphite distributed on a pearlitic matrix).

The structure of gray cast iron is equivalent to flake graphite distributed on a steel matrix. Since the strength, plasticity, and toughness of graphite are extremely low, it acts as cracks and voids in the cast iron, destroying the continuity of the matrix metal and causing stress concentration at the tips of the flake graphite.

Therefore, the mechanical properties of gray cast iron are significantly lower than those of non-alloy steel. It is a brittle material, not suitable for forging and stamping, and has poor weldability. However, the compressive strength of gray cast iron is less affected by graphite, and its compressive strength is close to that of steel, making it suitable for making compression parts but not tension parts.

The presence of graphite gives gray cast iron better castability, wear resistance, vibration damping, and machinability than non-alloy steel, with lower notch sensitivity, making it widely used in industry.

(2) Grades and uses of gray cast iron

The grade of gray cast iron consists of “HT + number”. “HT” is the abbreviation of “gray iron” in Chinese pinyin, and the number represents the minimum tensile strength value (MPa) of a single cast test bar with a diameter of Φ30mm. Common grades, mechanical properties, and uses of gray cast iron are shown in Table 7.

Table 7 Grades, mechanical properties, and uses of gray cast iron (excerpted from GB/T 9439—2010)

Category of cast iron	Grade	Casting wall thickness/mm	Tensile strength R_m /MPa	Hardness HBW	Microstructure		Example of use
Category of cast iron	Grade	Casting wall thickness/mm	Tensile strength R_m /MPa	Hardness HBW	Matrix	Graphite	Example of use
Ferritic gray cast iron	HT100	5~40	≥100	≤170	F+P (small)	Coarse flakes	Low load and unimportant parts, such as covers, housings, handwheels, brackets, counterweights, etc.
Ferritic-pearlitic gray cast iron	HT150	5~300	≥150	125~205	F+P	Coarser flakes	Parts subjected to moderate stress, such as columns, bases, gearboxes, worktables, tool holders, end covers, valve bodies, pipe fittings, and parts with general working condition requirements
Pearlitic gray cast iron	HT200	5~300	≥200	150~230	P	Medium Flaky	Parts subjected to greater stress and more important parts, such as cylinder blocks, gears, machine bases, flywheels, beds, cylinder liners, pistons, brake wheels, couplings, gearboxes, bearing seats, hydraulic cylinders, etc.
Pearlitic gray cast iron	HT250	5~300	≥250	180~250	P	Finer Flaky
Inoculated cast iron	HT300	10~300	≥300	200~275	Sorbite Or troostite	Fine Flaky	Important parts subjected to high bending stress and tensile stress, such as gears, cams, lathe chucks, shearing machine and press bodies, beds, high-pressure hydraulic cylinders, slide valve housings, etc.
Inoculated cast iron	HT350	10~300	≥350	220~290	Sorbite Or troostite	Fine Flaky

(3) Inoculation treatment of gray cast iron

Inoculation treatment refers to the method of adding a small amount of inoculant (such as ferrosilicon, calcium-silicon alloy, etc.) to the molten iron during pouring to change the crystallization conditions of the molten iron, so as to obtain fine, uniformly distributed flaky graphite and fine pearlitic structure.

Inoculation treatment makes the structure and performance of each section of the casting uniform and consistent, improves the strength, plasticity, and toughness of the cast iron, and also reduces the section sensitivity of gray cast iron. Cast iron after inoculation treatment is called inoculated cast iron, and HT300 and HT350 in Table 7 belong to inoculated cast iron.

(4) Heat treatment of gray cast iron

Since heat treatment can only change the matrix structure of gray cast iron and cannot change the shape and distribution of graphite, it has little effect on improving the mechanical properties of gray cast iron.

Therefore, the heat treatment of gray cast iron is mainly used to eliminate internal stress in castings, improve their machinability, and increase the surface hardness and wear resistance of castings. Common heat treatment methods include stress relief annealing (aging treatment), softening annealing (graphitization annealing), and surface quenching.

3. Ductile Iron

Ductile iron is a type of cast iron in which a spheroidizing agent and an inoculant are added before the molten iron is poured, causing the graphite in the cast iron to be distributed in a spherical shape, either entirely or mostly.

(1) Structure and Properties of Ductile Iron

Depending on the chemical composition, cooling rate, and heat treatment method, ductile iron can have different microstructures, mainly including ferrite, ferrite + pearlite, and pearlite matrix structures. Ferritic ductile iron has good plasticity and toughness, while pearlitic ductile iron has high tensile strength and hardness (more than 50% higher than ferritic ductile iron). The properties of ductile iron with a ferrite + pearlite matrix are intermediate between the two.

Replacing non-alloy steel with ductile iron for parts subjected to static loads is safe and reliable. Currently, the application of ductile iron in industrial and agricultural production is becoming increasingly widespread.

(2) Grades and Uses of Ductile Iron

The grade of ductile iron is composed of “QT + numbers-numbers”. “QT” is the abbreviation of “ductile iron” in Chinese pinyin, the first set of numbers represents its tensile strength value (MPa), and the second set of numbers represents the elongation value after fracture. Common grades, mechanical properties, and uses of ductile iron are shown in Table 8.

Table 8 Grades, Mechanical Properties, and Uses of Ductile Iron (excerpted from GB/T 1348—2009)

Grade	Basic Structure	Mechanical Properties				Example Uses
		R_m/MPa	R_p0.2/MP₈	A(%)	Hardness HBW
		Not Less Than			Hardness HBW
QT400-8	Ferrite	400	250	18	120~175	Parts subjected to impact and vibration, such as hubs, drive axle housings, differential housings, shift forks of automobiles and tractors, agricultural machinery parts, medium and low pressure valves, water and gas pipelines, high and low pressure cylinders on compressors, motor housings, gearboxes, flywheel housings, etc.
QT400-5		400	250	15	120~180
QT450-10		450	310	10	160~210
QT500-7	Ferrite +Pearlite	500	320	7	170~230	Machine bases, drive shafts, flywheels, oil pump gears of internal combustion engines, axle bearings of railway locomotives, etc.
QT600-3	Pearlite +Ferrite	600	370	3	190~270	Parts with large loads and complex forces, such as crankshafts, connecting rods, camshafts, cylinder liners of automobiles and tractors, main spindles of some grinders, milling machines, lathes, machine tool worms, worm gears, rolling mill rolls, large gears, small hydroturbine main shafts, cylinder blocks, bridge crane rollers, etc.
QT700-2	Pearlite	700	420	2	225~305
QT800-2	Pearlite or Tempered Structure	800	480	2	245~335
QT900-2	Bainite or Tempered Martensite	900	600	2	280~360	High-strength gears, such as hypoid gears of automobile rear axles, large reducer gears, crankshafts, camshafts of internal combustion engines, etc.

(3) Heat Treatment of Ductile Iron

Since the spheroidal graphite has a small splitting effect on the matrix, the mechanical properties of ductile iron mainly depend on the matrix structure. Therefore, improving the matrix structure through heat treatment can significantly improve the mechanical properties of ductile iron. The heat treatment methods are basically the same as those for steel, mainly including annealing, normalizing, quenching and tempering, and isothermal quenching.

4. Malleable Cast Iron

Malleable cast iron is cast iron with flocculent graphite obtained by graphitization annealing of white cast iron. The production process involves first casting white cast iron, and then decomposing the cementite through high-temperature graphitization annealing (also called malleable annealing) to obtain flocculent graphite.

(1) Structure and Properties of Malleable Cast Iron

Malleable cast iron is classified into blackheart malleable cast iron (also known as ferritic malleable cast iron), pearlitic malleable cast iron, and whiteheart malleable cast iron based on the matrix structure obtained after annealing.

The graphite in malleable cast iron is flocculent. Compared to gray cast iron, malleable cast iron has better strength and plasticity, especially better low-temperature impact performance. Compared to ductile iron, it has the advantages of lower cost, stable quality, simple molten iron treatment, and suitability for organized production.

The wear resistance and vibration damping of malleable cast iron are superior to ordinary non-alloy steel, and its machinability is close to that of gray cast iron. It is suitable for making complex-shaped thin-walled small and medium-sized parts and parts that require high toughness due to vibration during operation. Malleable cast iron is named for its high strength, plasticity, and impact toughness, but it cannot actually be forged.

(2) Grades and Applications of Malleable Cast Iron

The commonly used grades of malleable cast iron are composed of “KTH+number-number”, “KTZ+number-number”, or “KTB+number-number”. “KT” is the abbreviation of the Chinese pinyin for “malleable iron”. “KTH” stands for blackheart malleable cast iron, “KTZ” stands for pearlitic malleable cast iron, and “KTB” stands for whiteheart malleable cast iron. The first set of numbers after the symbol indicates the tensile strength value (MPa), and the second set of numbers indicates the elongation value after fracture. The grades, mechanical properties, and applications of commonly used malleable cast iron are shown in Table 9.

Table 9 Grades, Mechanical Properties, and Applications of Malleable Cast Iron (excerpted from GB/T 9440—2010)

Type	Grade	Sample Diameter/mm	Mechanical Properties				Example Applications
			R_m/MPa	R_p0.2/MPa	A(%)	HBW
			Not Less Than			HBW
Blackheart Malleable Cast Iron	KTH300-06	12 or 15	300		6	≤150	Elbows, Tee Fittings, Medium and Low Pressure Valves Gates, etc.
	KTH330-08		330		8		Wrenches, Plow Blades, Plow Columns, Wheel Housings, etc.
	KTH350-10		350	200	10		Automobile and Tractor Front and Rear Wheel Housings, Differential Housings, Steering Knuckle Housings, Brakes, and Railway Parts, etc.
	KTH370-12		370		12
Pearlitic Malleable Cast Iron	KTZ450-06	12 or 15	450	270	6	150~200	High Load and Wear-Resistant Parts, such as Crankshafts, Camshafts, Connecting Rods, Gears, Piston Rings, Bushings, Harrow Discs, Universal Joints, Ratchets, Wrenches, Drive Chains, etc.
	KTZ550-04		550	340	4	180~230
	KTZ650-02		650	430	2	210~260
	KTZ700-02		750	530	2	240~290

5. Compacted Graphite Iron

Compacted graphite iron is cast iron with worm-like graphite obtained by adding an appropriate amount of vermicularizing agent and inoculant to molten iron of a certain composition. Its production method and procedure are basically the same as those of ductile iron.

(1) Grades, Properties, and Applications of Compacted Graphite Iron

Since most of the graphite in compacted graphite iron is worm-like, its structure and properties are between those of ductile iron and gray cast iron with the same matrix structure. Its strength, toughness, fatigue strength, wear resistance, and thermal fatigue resistance are higher than those of gray cast iron, and its section sensitivity is also small. However, its plasticity and toughness are lower than those of ductile iron. The castability, vibration damping, thermal conductivity, and machinability of compacted graphite iron are better than those of ductile iron, and its tensile strength is close to that of ductile iron.

The grades of compacted graphite iron are composed of “RuT+number”, where “RuT” is the abbreviation of the Chinese pinyin for “compacted iron”, and the number indicates its tensile strength value (MPa). The grades, mechanical properties, and applications of compacted graphite iron are shown in Table 10.

Table 10 Grades, Mechanical Properties, and Applications of Vermicular Graphite Cast Iron (Excerpt from GB/T 26655—2011)

Grade	Mechanical Properties				Example Applications
	R_m/MPa	R_p0.2/MPa	A(%)	HBW
	Not less than			HBW
RuT300	300	210	2.0	140~210	Exhaust pipes, gearbox housings, cylinder heads, hydraulic parts, textile machine parts, ingot molds, etc.
RuT350	350	245	1.5	160~220	Heavy machine tool parts, large gearbox housings, covers, bases, flywheels, lifting machine drums, etc.
RuT400	400	280	1.0	180~240	Piston rings, cylinder liners, brake discs, steel ball grinding discs, dredge pump bodies, etc.
RuT450	450	315	1.0	200~250

(2) Heat Treatment of Vermicular Graphite Cast Iron

The heat treatment of vermicular graphite cast iron is mainly to adjust its matrix structure to meet different mechanical property requirements. Common heat treatment processes include normalizing and annealing. The purpose of normalizing is to increase the amount of pearlite, thereby improving strength and wear resistance; annealing is to obtain a matrix with more than 85% ferrite or to eliminate free cementite in thin-walled areas.

6. Alloy Cast Iron

Alloy cast iron is cast iron in which some alloying elements are intentionally added during smelting to improve its physical, chemical, and mechanical properties or to obtain certain special properties, such as wear-resistant cast iron, heat-resistant cast iron, and corrosion-resistant cast iron.

(1) Wear-Resistant Cast Iron

Wear-resistant cast iron can be roughly divided into anti-friction cast iron and wear-resistant cast iron based on its working conditions.

Anti-friction cast iron requires low wear, low friction coefficient, good thermal conductivity, and good processing technology during operation. Common anti-friction cast irons include: gray cast iron with a pearlitic matrix (with good anti-friction properties) and high-phosphorus cast iron (with significant wear resistance, commonly used for lathe, milling machine, and boring machine beds and worktables).

Anti-wear cast iron is used for castings that work under dry friction conditions without lubrication, requiring a structure with uniform high hardness. Common anti-wear cast irons include: chilled cast iron (which has high strength and wear resistance and can withstand certain impacts), anti-wear white cast iron (widely used to manufacture wear-resistant parts such as rolls and wheels), and medium manganese ductile iron (widely used to manufacture parts that work under impact loads and wear conditions, such as plowshares, grinding balls for ball mills, and tractor track plates).

(2) Heat-resistant cast iron

The heat resistance of cast iron mainly refers to its ability to resist oxidation and thermal growth at high temperatures. The so-called “thermal growth” refers to the irreversible expansion of the volume of cast iron at high temperatures, which can expand by about 10% in severe cases.

The main reasons are that oxidizing gases penetrate into the cast iron to form oxides with low density and large volume; carbides decompose at high temperatures to produce graphite with low density and large volume; and phase changes occur in the cast iron matrix during heating and cooling. The final result of thermal growth can lead to deformation, warping, cracking, or even breaking of parts.

The grades, compositions, operating temperatures, and applications of commonly used heat-resistant cast irons can be found in the national standard (GB/T 9437—2009).

(3) Corrosion-resistant cast iron

Corrosion-resistant cast iron not only has certain mechanical properties but also requires high corrosion resistance when working in corrosive media.

Corrosion-resistant cast iron is widely used in industries such as petrochemicals and shipbuilding to manufacture parts such as pipes, valves, pumps, and containers that frequently work in media such as atmosphere, seawater, acids, alkalis, and salts. However, each type of corrosion-resistant cast iron has a certain applicable range, and it is necessary to select reasonably based on the corrosive medium and working conditions. The compositions and application ranges of commonly used corrosion-resistant cast irons can be found in relevant metal material manuals.

IV. Non-ferrous metals and their alloys

Non-ferrous metals refer to all other metals except steel and cast iron, also known as non-iron metals. There are many types of non-ferrous metals, mainly including copper (Cu), aluminum (Al), titanium (Ti), magnesium (Mg), tungsten (W), molybdenum (Mo), and their alloys. The smelting of non-ferrous metals is relatively difficult and costly, and their production and usage are far less than those of steel materials.

However, non-ferrous metals have certain special physical and chemical properties that steel materials do not possess. Therefore, non-ferrous metals have become indispensable materials in modern industry. The following is a brief introduction to aluminum alloys and copper alloys, which are widely used in industrial production.

1. Aluminum and its alloys

(1) Industrial pure aluminum (referred to as pure aluminum)

Pure aluminum is currently the most widely used non-ferrous metal in industry. The purity of industrial pure aluminum is 98.8% to 99.7%. Pure aluminum has a low density of only 2.72g/cm³; it has high electrical and thermal conductivity, second only to silver, copper, and gold, ranking fourth.

Aluminum has good atmospheric corrosion resistance in the atmosphere but cannot resist corrosion by acids, alkalis, and salts. Pure aluminum has low strength, high plasticity, and no ferromagnetism. It can be processed into various profiles (such as wires, rods, and tubes) through cold and hot deformation but cannot be used as load-bearing structural parts.

(2) Aluminum alloys

Aluminum alloys are obtained by adding appropriate amounts of alloying elements such as Cu, Si, Mg, Zn, and Mn to aluminum and using methods such as solid solution strengthening. Aluminum alloys have high strength while maintaining the low density, good electrical conductivity, and thermal conductivity of pure aluminum. Some aluminum alloys can also be further strengthened through cold deformation or heat treatment, making them suitable for manufacturing mechanical parts that bear certain loads.

1) Classification of aluminum alloys

According to the composition and processing characteristics, commonly used aluminum alloys can be divided into wrought aluminum alloys and cast aluminum alloys. Wrought aluminum alloys have good plasticity and are suitable for pressure processing, while cast aluminum alloys have a eutectic structure, low melting point, good fluidity, and are suitable for casting.

2) Heat treatment of aluminum alloys

The principles of heat treatment for aluminum alloys are different from those for steel because aluminum alloys do not have allotropic transformations and cannot be strengthened through martensitic transformation like steel. Aluminum alloys can obtain a single-phase solid solution structure after heating, and there are changes in solubility in the solid state. Therefore, aluminum alloys can be strengthened by quenching and aging treatment (called solution aging treatment).

The strength of aluminum alloys is not high after quenching and must be placed at room temperature for a period of time before the strength and hardness increase significantly. This phenomenon is called age hardening. Aging at room temperature is called natural aging, while aging under heating conditions (100~200℃) is called artificial aging. Quenching and aging treatment is not only the main way to strengthen aluminum alloys but also an important means to strengthen other non-ferrous metals.

2. Copper and its alloys

(1) Industrial pure copper

Industrial pure copper, referred to as pure copper, has a melting point of 1083℃. It has good electrical and thermal conductivity (second only to silver), good corrosion resistance in the atmosphere and fresh water, and is non-magnetic.

Pure copper has low strength and hardness, good plasticity, toughness, and weldability. It can be processed into various profiles suitable for the electrical industry (such as wires, cables, and copper tubes), communication equipment, and anti-magnetic and non-magnetic instruments through cold and hot deformation.

(2) Copper alloys

Copper alloys are obtained by adding appropriate amounts of elements such as silicon, zinc, and aluminum to copper and undergoing alloying treatment. These alloys have strength and toughness that meet usage requirements. According to their chemical composition, copper alloys are divided into brass, cupronickel, and bronze. According to their production methods, copper alloys are divided into wrought copper alloys and cast copper alloys. The most widely used in industry are brass and bronze.

1) Brass

Brass is a copper alloy with zinc (Zn) as the main alloying element, named for its golden color. Brass is divided into ordinary brass and special brass based on its composition. Ordinary brass is a binary alloy composed of copper and zinc.

When w_Zn <32%, as the mass fraction of zinc increases, the strength and hardness of brass increase, and it has good plasticity, commonly used for cold deformation processing;
When w_Zn is between 30% and 32%, its plasticity is the highest;

When w_Zn is between 32% and 45%, while the strength continues to increase, the plasticity decreases somewhat, this type of brass is suitable for hot deformation processing;
When w_Zn >45%, the strength and plasticity of brass both decrease sharply, and it has no practical value in production.

Ordinary brass is divided into processed brass and cast brass according to different production methods.

Special brass is a copper alloy formed by adding elements such as lead (Pb), aluminum (Al), tin (Sn), and silicon (Si) to ordinary brass, and is correspondingly called lead brass, aluminum brass, tin brass, silicon brass, etc.

The addition of lead can improve machinability and wear resistance;
The addition of aluminum can improve strength, hardness, and corrosion resistance, and also reduce the tendency of brass to crack;

The addition of silicon can improve casting performance and help increase its strength and corrosion resistance;
Tin can improve corrosion resistance and reduce the tendency of stress corrosion cracking;
If the special brass contains fewer alloying elements and has higher plasticity, it is called processed special brass;

If it contains more alloying elements and has better strength and castability, it is called cast special brass.

2) Bronze

Bronze is a copper alloy other than brass and cupronickel (copper-nickel alloy). According to different production methods, it can be divided into processed bronze and cast bronze; according to different compositions, it can be divided into ordinary bronze and special bronze.

Essential Guide to Common Metal Types and Uses