4130 Steel vs 4120 Steel

4130 steel and 4120 steel both belong to the 41xx series of chromium-molybdenum steel (commonly known as chromium-molybdenum steel). However, the difference in their carbon content leads to significant differences between them.This article will start with the differences in chemical composition, analyzing the core differences between the two in terms of heat treatment, mechanical properties, processing performance, and applications, helping people to better understand these two materials.

Chemical Composition:4130 Steel vs 4120 Steel

Grade	C	Si	Mn	P	S	Cr	Mo
4130	0.28-0.33	0.15-0.35	0.4-0.6	≤0.035	≤0.04	0.8-1.1	0.15-0.25
4120	0.18-0.23	0.15-0.35	0.9-1.2	≤0.035	≤0.04	0.4-0.6	0.13-0.20

The biggest difference between 4130 steel and 4120 steel is their carbon content.

The higher carbon content gives 4130 steel greater strength and hardness than 4120 steel, but 4120 steel has better toughness, ductility, and weldability.Additionally, the higher chromium content in 4130 steel helps improve its hardenability and corrosion resistance.

Heat Treatment & Mechanical Property:4130 Steel vs 4120 Steel

Typical Heat Treatment Process:Quenching & Tempering

4130 steel		4120 steel
Quenching	Tempering	Quenching	Tempering
850-880°C/oil	540-650°C/Air	870-890°C/Water	540-680°C/Air
Tensile Strength	950-1000 Mpa	Tensile Strength	750-800 Mpa
Yield Strength	800-850 Mpa	Yield Strength	620-670 Mpa
Elongation	16-18%	Elongation	20-22%
Reduction of Area	50-55%	Reduction of Area	60-65%
Impact toughness	70-80J	Impact toughness	100-120J

As we can see from the table above, 4130 steel is more suitable for quenching and tempering than 4120 steel, achieving good strength and toughness, making it suitable for high-load structural components.

Meanwhile, quenched and tempered 4120 steel is more suitable for parts requiring medium strength and good toughness. To fully utilize its properties, it typically requires carburizing followed by quenching and tempering, resulting in a surface hardness significantly higher than in the quenched and tempered state.

4120 Steel:Carburizing +Quenching & Tempering

Carburizing	Quenching	Tempering
920-940°C	810-830°C	160-200°C
Core Tensile strength	≥885 MPa
Core Yield strength	≥685 MPa
Core Impact toughness	≥78 J
Surface hardness	58-64 HRC

After carburizing, the surface hardness of 4120 steel is significantly improved, and its wear resistance far exceeds that of 4130 steel,while the core still maintains high toughness.

Machining & Welding Performance:4130 Steel vs 4120 Steel

Machining

Both 4130 and 4120 steels are easy to machine in the annealed state.However, after final heat treatment, the hardness of 4120 steel increases further due to carburizing, making it significantly more difficult to machine than the quenched and tempered 4130 steel.

Weldability

4130 steel has a carbon equivalent of approximately 0.5 (based on the formula CE = C + Cr/5 + Mo/4). Preheating to 150-200°C is required during welding to prevent cracking, and post-weld stress relief annealing (650°C) is required to prevent cracking. 4120 Steel has a lower carbon equivalent (approximately 0.4), offers better weldability, and requires less stringent preheating.

How to Choose: 4130 Steel or 4120 Steel?

If you need to manufacture a structural component that withstands high stress, requiring good overall material properties and weldability, then 4130 is a more suitable choice.

If you need to manufacture a part that requires extremely high surface wear resistance while its core must withstand impact, then 4120, with its excellent carburizing capabilities, is a more suitable material selection.