SCM420 Alloy Steel-JIS G4053

SCM420 is a chromium-molybdenum alloy steel (Cr-Mo steel) in the Japanese JIS standard (JIS G4053).

SCM420 steel also belongs to the category of carburizing steel, so it is widely used in the automotive and machinery manufacturing fields due to its high cost performance and good carburizing performance. It is often used in mechanical parts that require high surface hardness and good core toughness.

SCM420 STEEL CHEMICAL COMPOSITION

Grade	C	Si	Mn	P	S	Cr	Mo
SCM420	0.18-0.23	0.15-0.35	0.6-0.85	≤0.03	≤0.03	0.9-1.2	0.15-0.30

Features: The addition of chromium (Cr) and molybdenum (Mo) significantly improves hardenability, wear resistance and fatigue resistance. The carbon content is moderate and suitable for carburizing treatment.

SCM420 STEEL RELATED STANDARD & EQUIVALENT GRADE

China: 20CrMo (GB/T 3077)
USA: SAE 4120 (similar, but slightly different in composition)
Germany: 20CrMo4 (DIN 17210)

SCM420 STEEL FORGING

Initial Forging Temperature：1200℃
Final Forging Temperature：800℃
Forging Ratio：above 4:1
Post-Forging Treatment:SCM420 steel should be slowly cooling in sand after forged.

SCM420 STEEL HEAT TREATMENT

Normalizing
– Temperature: 880–920°C, air cooling
Annealing
– Temperature: 850–860°C, furnace cooling
Carburizing treatment
– Temperature: 900–950°C (the depth of the carburized layer is usually 0.5–2.0 mm).
– Medium: gas carburizing (such as CO/CH₄) or solid carburizing.
Quenching
– Temperature: oil quenching after carburizing (800–850°C).
Tempering
– Low temperature tempering: 150–200°C (eliminate internal stress and maintain high hardness).
Secondary quenching (optional): refine core grains and improve overall performance.

SCM420 STEEL MATERIAL CHARACTERISTICS

Carburizing performance: Through surface carburizing (Carburizing) and subsequent heat treatment, a high hardness surface layer (HRC 58-62) and a tough core (HRC 25-35) can be formed, which is suitable for parts that withstand impact and wear.
Strength and toughness: The core maintains good toughness, and has excellent impact and fatigue resistance.
Processability: The machinability is good in the annealed state, but the weldability is poor (preheating and post-heat treatment are required).

Comparison with other carburizing steels

Grade	Standard	Features comparison
SCM420	JIS G4053	Moderate chromium and molybdenum content, balanced comprehensive performance, and low cost.
8620	ASTM A322	Higher nickel content, better core toughness, suitable for heavy-duty parts.
20MnCr5	EN 10084	High manganese content, slightly better hardenability than SCM420, commonly used in Europe.

SCM420 Steel Typical Applications

Automotive industry: gears (such as transmission gears, differential gears), drive shafts, camshafts, etc.
Mechanical parts: bearings, shafts, mold guides, chain pins, etc.
Engineering machinery: hydraulic components, gearbox components.