Best Materials For Shafts: Carbon Steel, Alloy Steel, Ductile Iron

Best Materials for Shafts: Carbon Steel, Alloy Steel, Ductile Iron

What makes certain materials ideal for manufacturing shafts? This question is crucial for anyone involved in mechanical design or engineering. This article explores the characteristics of carbon steel, alloy steel, and ductile iron, detailing their mechanical properties, suitability for various loads, and specific applications. By reading, you’ll gain insights into why these materials are preferred for different shaft types, helping you make informed decisions in your engineering projects.

Last updated:

June 28, 2024

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The common materials for shafts are carbon structural steel, alloy steel, and ductile iron. Steel shaft blanks are mostly rolled round steel or forgings.

I. Carbon Steel

High-quality medium carbon steel 30~50 is commonly used for relatively important or heavily loaded shafts, among which 45 steel is the most widely used. For such materials, their mechanical properties can be improved and enhanced through heat treatment methods such as quenching and tempering or normalizing.

Ordinary carbon steel Q235, Q275, etc. can be used for unimportant light load low-speed shafts or general transmission shafts.

II. Alloy Steel

Alloy steel has higher comprehensive mechanical properties and better heat treatment performance. Therefore, for important shafts that carry a large load and are limited in weight and size or have high wear resistance and corrosion resistance requirements, alloy steel can be used and subjected to certain heat treatments.

It must be noted that:

Alloy steel is more sensitive to stress concentration and is more expensive;

Since the elastic modulus of carbon steel and alloy steel is almost the same at normal temperatures, using alloy steel instead of carbon steel cannot achieve the purpose of improving the stiffness of the shaft;
Various heat treatments, chemical treatments, and surface strengthening treatments (such as shot peening, rolling, etc.) can significantly improve the fatigue strength or wear resistance of the shaft, but have little effect on its stiffness.

III. Ductile Iron

Ductile iron is suitable for manufacturing shafts with complex shapes such as crankshafts, camshafts, etc., and has the advantages of being inexpensive, having relatively high strength, good wear resistance, vibration absorption, machinability, and lower sensitivity to stress concentration. However, the quality of castings is not easy to control, and reliability is relatively poor.

The common materials for shafts and their main mechanical properties are shown in the table below.

Table: Common Materials for Shafts and Their Main Mechanical Properties

Material		Heat Treatment	Blank Diameter/mm	Hardness HBW	Mechanical Properties/MPa				Remarks
Category	Grade	Heat Treatment	Blank Diameter/mm	Hardness HBW	Ultimate Strength σ_b	Yield Point σ_s	Bending Fatigue Limit σ_-1	Shear Fatigue Limit τ_-1	Remarks
Carbon Structural Steel	Q235	Air cooled after hot rolling or forging	≤100	—	400～420	225	170	105	Used for shafts that are not important or carry a small load
	Q235	Air cooled after hot rolling or forging	>100～250	—	375～390	215	170	105
	45	Normalizing	≤100	170～217	600	300	275	140	Most widely used
	45	Tempering	≤200	217 ～ 255	650	360	300	155	Most widely used
Alloy steel	40Cr	Tempering	≤100	241 ～ 266	750	550	350	200	Used for important shafts carrying larger loads without significant impact
	40Cr	Tempering	>100 ～ 300	241 ～ 266	700	550	340	185
	35SiMn (42SiMn)	Tempering	≤100	229 ～ 286	800	520	400	205	Performance close to 40Cr, used for medium and small shafts
	35SiMn (42SiMn)	Tempering	>100 ～ 300	217 ～ 269	750	450	350	185	Performance close to 40Cr, used for medium and small shafts
	40MnB	Tempering	25		1000	800	485	280	Performance close to 40Cr, used for important shafts
	40MnB	Tempering	≤200	241 ～ 286	750	500	335	195	Performance close to 40Cr, used for important shafts
	20Cr	Carburizing Quenching Tempering	15	Surface 50 ～ 60HRC	850	550	375	215	Used for shafts requiring both high strength and toughness
	20Cr		≤60	Surface 50 ～ 60HRC	650	400	280	160
	20CrMnTi		15	Surface 50 ～ 62HRC	1100	850	525	300
Ductile cast Malleable iron	QT400-15		—	156 ～ 197	400	300	145	125	Used for manufacturing shafts with complex shapes
Ductile cast Malleable iron	QT600-3		—	197 ～ 269	600	420	215	185	Used for manufacturing shafts with complex shapes