Chromium-Molybdenum Alloy Steel:4145 Steel vs 4140 Steel

4145 steel and 4140 steel are both medium carbon chromium-molybdenum alloy steels (ASTM A29 standard). 4145 steel can be considered an “upgraded version” of 4140 steel,the slight difference in carbon content results in significant differences in their properties.

So what are the specific differences? This article will compare them in terms of chemical composition, performance, and typical applications.

Chemical Composition:4140 Steel vs 4145 Steel

	C	Si	Mn	Cr	Mo
4140 steel	0.38-0.43	0.15-0.35	0.75-1.0	0.8-1.1	0.15-0.25
4145 steel	0.43-0.48	0.15-0.35	0.75-1.0	0.8-1.1	0.15-0.25

The essential difference between 4140 and 4145 steel lies in their carbon content: 4145 has about 0.05% more carbon than 4140, resulting in higher strength, hardness, and hardenability, but sacrificing some toughness and weldability.

Mechanical Property:4140 Steel vs 4145 Steel

4140 steel		4145 steel
Tensile strength	850-1000 MPa	Tensile strength	900-1100 MPa
Yield strength	650-800 MPa	Yield strength	750-900 MPa
Impact Charpy-V-20℃	45-60 J	Impact energy (20℃)	35-50 J
Elongation	15-20%	Elongation	12-18%
Hardness	28-32 HRC	Hardness (HRC)	30-36HRC

The higher carbon content allows 4145 steel to achieve higher tensile strength and yield strength, and its hardness is also correspondingly higher, but its toughness is slightly sacrificed compared to 4140.

Machining & Welding Performance:4140 Steel vs 4145 Steel

Weldability

Both 4140 and 4145 steels have poor weldability. Relatively speaking, 4140 has slightly better weldability. Due to the high carbon content and hardening tendency of 4145 steel, it is very prone to cracking during welding, so strict preheating and post-weld heat treatment are usually required.

Machining

Both 4140 and 4145 exhibit good machinability in the annealed state. However, once 4145 steel undergoes quenching and tempering to achieve high hardness, the machining difficulty increases significantly.

How to Choose Between 4140 and 4145?

The choice between 4140 and 4145 mainly depends on the application requirements.

If you need a balance of strength and toughness, good weldability and machinability, 4140 steel is a good choice.Typical applications:automotive crankshafts, drive shafts, connecting rods.

If you need to withstand extremely high static loads or wear and have requirements for hardenability,choose 4145 without hesitation.Typical applications:Oil drilling tools, high-pressure vessels, heavy shafts.

The choice between 4145 and 4140 is essentially a trade-off between strength and toughness. In extreme conditions such as oil and military applications, 4145 is a mandatory requirement due to its superior hardness; while in the automotive and general machinery sectors, 4140 offers a more balanced performance.

Interactive topic: In your industry, which material would you prefer, 4140 or 4145?Welcome to discuss with us!