DIN	AISI	JIS	Chemical Composition
			C	Si	Mn	P	S	Co	Cr	Mo	Ni	V	W	Cu
42CrMo4	4140H	SCM 440H	0.37 to 0.44	0.15 to 0.35	0.65 to 1.10	≤ 0.04	≤ 0.03	-	0.75 to 1.20	0.15 to 1.25	≤ 0.25	-	-	≤ 0.35

 

Heat Treatment

Annealing

Heat to 800 ^oC - 850 ^oC, hold until temperature is uniform throughout the section and cool in furnace.

Flame or Induction Hardening

4140 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50.

Parts should be heated as quickly as possible to the austenitic temperature range (840 C - 870 C) and "required case depth followed by an immediate oil or water quench, depending upon hardness required, workpiece" size/shape and quenching arrangements.

"Following quenching to hand warm, most components should be tempered between 150 C - 200 C to remove" quenching stresses in the case. This will have little effect on case hardness and will reduce the risk of grinding cracks.

Hardening

Heat to 840 ^oC - 875 ^oC, hold until temperature is uniform throughout the section, soak for 10 - 15 minutes per 25 mm section, and quench in oil, water, or polymer as required.
*Temper immediately while still hand warm.

Nitriding

4140 hardened and tempered bar can also be successfully nitrided, giving a surface hardness of up to Rc 60. Nitriding is carried out at 490 ^oC - 530 ^oC, followed by slow cooling (no quench) reducing the problem of distortion. Parts can therefore be machined to near final size, leaving a grinding allowance only. The tensile strength of the core is usually not affected since the nitriding temperature range is generally below the original tempering temperature employed.

Normalizing

Heat to 870 ^oC - 900 ^oC, hold until temperature is uniform throughout the section, soak for 10 - 15 minutes and cool in still air.

Stress Relieving

Heat to 680 ^oC - 700 ^oC, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.

Tempering

Re-heat to 550 ^oC - 700 ^oC as required, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.

Notes on Heat Treatment

Re-heat to 550 ^oC - 700 ^oC as required, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.

 

Machining

4140 in the hardened and tempered as supplied condition has good to very good machinability and operations such as sawing, turning, drilling, broaching, hobbing, milling and tapping can be carried out satisfactoraly using machine manufacturers recommendations for suitable tool type - feeds and speeds.

 

Welding

Welding of 4140 in the hardened and tempered condition (as normally supplied), is not recommended and should be avoided if at all possible, as the mechanical properties will be altered within the weld heat affected zone. It is preferred that welding be carried out on 4140 while in the annealed condition, and that the work piece, immediately on cooling to hand warm, is then stress relieved at 595 ^oC - 620 ^oC prior to hardening and tempering.
If welding in the hardened and tempered condition is really necessary, then the work piece, immediately on cooling to hand warm, should be if possible stress relieved at 15 ^oC below the original tempering temperature (if known).