SCM440 / AISI 4140 / 42CrMo4 Alloy Steel Guide: Properties, Hardness, Heat Treatment, Machining Applications

Introducing Belinker Manufacturing

Belinker Manufacturing is a Korea-based machining partner specializing in automation equipment, industrial machinery, and plant components.
With a 4,300 m² machining center in Cheonan and a network of over 200 partner shops, we provide end-to-end solutions that cover material selection, heat treatment, precision machining, and quality inspection.

We have extensive experience with alloy steels such as SCM440, SKD11, S45C, and stainless steels. Our facility is equipped with large CNC and MCT machines capable of handling shafts up to 5,300 mm, and we are experienced in grinding and dimensional correction for high-hardness materials above HRC 50. Through our trusted heat-treatment partners, we also support Q&T and induction hardening processes.

At Belinker, we focus on being a partner who understands the real challenges of the shop floor and delivers practical solutions, not just a machining vendor.

What is SCM440?

SCM440 is a chromium-molybdenum alloy steel, often referred to as Cr-Mo steel. It is known by different names in different standards: SCM440 in JIS, 42CrMo4 in EN, and AISI 4140 in ASTM. Despite the differences in nomenclature, they share nearly identical properties.

The addition of chromium and molybdenum provides a balance of strength, toughness, wear resistance, and reliable heat-treatment performance. This makes SCM440 one of the most widely used alloy steels in automotive, machinery, and plant applications.

Chemical Composition

This composition enables SCM440 to maintain uniform hardness and high fatigue resistance after heat treatment.

Mechanical Properties

Before heat treatment:

• Tensile strength: 600–800 MPa

• Yield strength: 350–500 MPa

• Hardness: around HB 200

• Elongation: about 20%

After quenching and tempering:

• Tensile strength: 850–1000 MPa

• Yield strength: 650–800 MPa

• Hardness: HRC 28–32, with potential up to HRC 50

• Excellent fatigue resistance under cyclic loads

The key advantage is that both strength and toughness can be tailored through heat treatment, making it a versatile material.

Machining Characteristics

Cutting and milling:

• Cutting speed: 60–120 m/min depending on hardness

• Feed rate: 0.1–0.3 mm/rev

• Tools: Carbide with TiN or TiCN coating

• Cutting fluid: Water-soluble with high lubrication

After heat treatment, medium to low cutting speeds are recommended to extend tool life.

For parts above HRC 40, grinding or CBN tools are preferred. Weldability is limited, requiring preheating at 200–400℃ and post-weld heat treatment to prevent cracking.

Heat Treatment

• Quenching at 830–870℃ with oil or water cooling

• Tempering at 500–650℃ depending on required properties

• Induction hardening for surface hardness above HRC 50

This combination allows the surface to remain hard while maintaining core toughness, ideal for components under heavy loads and shocks.

Applications

SCM440 is used across multiple industries:

• Automotive: crankshafts, camshafts, gears, drive shafts

• Industrial machinery: spindles, couplings, rollers, shafts

• Plant and energy: high-temperature bolts, pressure vessels, power plant components

• Tooling: mold bases and heavy-duty tool parts

It is particularly effective for components exposed to high stress, repeated fatigue, and elevated temperatures.

Belinker Manufacturing’s SCM440 Expertise

Many of our clients request SCM440 parts, and these projects often involve more than simple machining. Large shafts, precision gears, and heat-treated components require dimensional correction, grinding, and careful control of heat treatment.

Belinker Manufacturing provides end-to-end SCM440 solutions, from raw material sourcing to final inspection. With large-capacity CNC and MCT equipment, high-hardness grinding experience, and a robust heat-treatment network, we deliver components that meet strict specifications and demanding schedules.

Conclusion

SCM440 is a balanced alloy steel, offering strength, toughness, wear resistance, and heat-treatability. To fully leverage these properties, it is important to work with a partner who understands both the material and the practical challenges of machining and heat treatment.

Belinker Manufacturing has consistently delivered SCM440 solutions for automotive, industrial, and plant applications. Our combination of equipment, expertise, and reliable process control makes us a trusted partner for companies seeking quality and efficiency in SCM440 machining.