SCM-420H alloy steel

Introduction

We manufacture forging ingots, billets, and blooms in alloy steel specifically for SCM-420H, tailored for high-performance engineering and case hardening applications. SCM-420H is a low carbon chromium-molybdenum alloy steel designed with controlled hardenability, making it ideal for components requiring uniform heat treatment response and consistent mechanical properties.

The “h” designation indicates controlled hardenability limits, ensuring predictable hardness distribution during quenching and tempering. Chromium enhances hardenability and wear resistance, while molybdenum improves fatigue strength and resistance to temper brittleness. SCM-420H provides excellent machinability in the annealed condition and superior performance after carburizing, making it highly suitable for automotive and precision engineering applications.

This steel provides an excellent balance of surface hardness, core toughness, and process consistency.

Chemical composition

Element	Content (%)	Function / effect
Carbon (c)	0.18 – 0.23	Provides core toughness and supports carburizing
Manganese (mn)	0.60 – 0.85	Improves hardenability and strength
Silicon (si)	0.15 – 0.35	Improves strength and elasticity
Chromium (cr)	0.90 – 1.20	Enhances hardenability and wear resistance
Molybdenum (mo)	0.15 – 0.30	Improves fatigue resistance and temperature stability
Phosphorus (p)	Max 0.030	Impurity; lower content improves toughness
Sulphur (s)	Max 0.030	Impurity; controlled content improves machinability

Mechanical properties (typical, depending on condition & heat treatment)

• Tensile strength: 700 – 950 MPa (core, heat treated)
• Yield strength: 450 – 650 MPa
• Surface hardness (after carburizing): 58 – 62 HRC
• Core toughness: High
• Fatigue resistance: Excellent

Heat treatment

• carburizing: heating in a carbon-rich atmosphere to develop high surface hardness.
• quenching: rapid cooling after carburizing to achieve hard martensitic surface structure.
• tempering: reheating to relieve internal stresses and improve core toughness while maintaining required hardness.
• annealing: performed prior to machining to improve workability.

Controlled hardenability in SCM-420H ensures consistent heat treatment performance across different section sizes.

Key features and benefits

• controlled hardenability for uniform hardness distribution
• excellent carburizing response for high surface hardness
• tough and ductile core for impact and shock resistance
• high wear resistance for extended component life
• superior fatigue strength under cyclic loading
• good machinability in annealed condition
• dimensional stability after heat treatment
• ideal for high-precision engineering applications

Typical applications

• automotive transmission gears and pinions
• shafts, splined shafts, and axle components
• camshafts and crankshaft components
• differential gears and couplings
• forged and case-hardened automotive components
• high-precision engineering parts requiring controlled hardenability

Equivalent steel grades

SCM-420H has several international near equivalents, including:

• 20crmo4h (en standard) – controlled hardenability european grade
• AISI 4120h – american hardenability controlled carburizing steel
• din 1.7243h – german hardenability controlled equivalent

Why choose SCM-420H for your application?

SCM-420H is specially developed for applications requiring consistent heat treatment results and uniform mechanical properties. Its controlled hardenability ensures reliable performance, reduces distortion during heat treatment, and improves product quality. Additionally, its excellent carburizing response provides long service life and high wear resistance.

Comparison table for similar grades

Grade	Carbon (%)	Key applications	Heat treatment	Comments
SCM-420H	0.18 – 0.23	Gears, shafts, automotive parts	Carburizing, quenching & tempering	Controlled hardenability steel
20crmo4h	0.17 – 0.24	Automotive and engineering components	Carburizing	European equivalent
Aisi 4120h	0.18 – 0.23	Transmission and machinery parts	Carburizing	American equivalent
Din 1.7243h	0.18 – 0.23	Precision engineering components	Carburizing	German equivalent

Summary

SCM-420H is a high-quality chromium-molybdenum carburizing alloy steel designed for case hardening applications where controlled hardenability is required. It provides excellent surface hardness, core toughness, and reliable performance for automotive and engineering components.