Project Description

SCM420 is a chromium-molybdenum low-alloy case-hardening steel specified under JIS G 4053. Designed for carburizing applications, it delivers surface hardness of 58–62 HRC combined with core toughness in the HRC 32–42 range after heat treatment. Equivalent to GB 20CrMo, DIN 25CrMo4 (1.7218), and AISI 4120 / 4118, SCM420 is widely specified for heavy-duty transmission components and oilfield equipment requiring high surface wear resistance with a strong, ductile core.

SCM420 Equivalent Grades

Standard Designation
JIS G 4053 SCM420 / SCM420H
GB/T 3077 20CrMo / 20CrMoH
DIN EN 10084 20CrMo4 (1.7321) / 18CrMo4 (1.7243)
DIN 25CrMo4 (1.7218)
AISI/SAE 4120 / 4118
ISO 683-11 20MnCr5
GOST 20ХМ

SCM420 Applications in Oil & Gas

Drill Collar Connection Subs
High-Pressure Fasteners
Mud Pump Pinion Shafts
Valve Body & Stem Components
Top Drive Transmission Gears
Drawworks Brake Drum Shafts
Rotary Table Gears
BOP Ram Shafts
Downhole Motor Shafts
Cementing Pump Plungers
Swivel Stem Shafts
Kelly Drive Bushings

SHUNFU METAL SCM420 Supply Range

Hot-Rolled Round
Φ 10 – 500 mm
Length 5–12 m
Forged Round
Φ 100 – 800 mm
Up to 12,000 mm
Hot-Rolled Flat
T 3 – 150 × W 20 – 610 mm
Mill edge / Sheared
Forged Flat / Block
T 50 – 500 × W 100 – 1200 mm
Rough machined available
SCM420H hardenability-guaranteed grade available. Surface finishes: black, turned, ground, or as specified.

SCM420 Chemical Composition (JIS G 4053)

SCM420 alloy steel round bar
SCM420 Steel Round Bar
Element Content (wt%)
C 0.18 – 0.23
Si 0.15 – 0.35
Mn 0.60 – 0.90
P ≤ 0.030
S ≤ 0.030
Cr 0.90 – 1.20
Mo 0.15 – 0.25
Ni ≤ 0.25
Cu ≤ 0.30

SHUNFU METAL melts SCM420 via EAF + LF + VD route, with optional ESR for premium cleanliness. Residual elements (P, S, Cu, Ni) are tightly controlled below JIS limits to ensure consistent carburizing response.

SCM420 Mechanical Properties

Quenched & Tempered (880°C Q + 500°C T)

Property Value
Tensile Strength ≥ 885 MPa
Yield Strength ≥ 685 MPa
Elongation (δ₅) ≥ 12%
Reduction of Area ≥ 50%
Impact (Akv) ≥ 78 J
Hardness ≤ 197 HBW

Carburized + Quenched + Low-Temp Tempered

Location Hardness
Case (surface) 58 – 62 HRC
Core 32 – 42 HRC

Typical case depth: 0.75–1.25 mm at 926°C × 4h gas carburizing. SCM420 achieves 3–5 HRC higher core hardness than SCM415 under identical quench conditions. Hardenability verified by Jominy end-quench per JIS G 0561.

SHUNFU METAL Manufacturing & Quality Control for SCM420

Melting
EAF + LF + VD triple refining. Oxygen ≤ 15 ppm, hydrogen ≤ 2 ppm. Optional ESR for superior micro-cleanliness. Every heat undergoes full optical emission spectrometry with 21-element sweep.
Forging
6,000-ton hydraulic press and GFM radial forging machine. Hot-forming at 1,050–1,200°C, finish-forge above 850°C. Post-forge normalizing at 880–920°C to refine grain structure and ensure uniform carburizing response.
Heat Treatment
Computer-controlled batch furnaces ±5°C uniformity. Annealing at 850°C furnace cool; normalizing at 880–920°C air cool. Jominy end-quench testing per JIS G 0561 for SCM420H grade hardenability band verification.
Inspection & Certification
100% ultrasonic testing per SEP 1921 / EN 10228-3. Dimensional verification with laser micrometer. Certification to EN 10204 3.1 (standard) or 3.2 (TUV/SGS witness). Surface quality to EN 10221 Class A.

SCM420 Heat Treatment & Processing Guide

Carburizing
Gas carburizing at 900–930°C. Effective case depth 0.5–2.0 mm depending on cycle time and carbon potential. Mask non-case areas with copper plating or anti-carburizing paste before treatment.
Quenching
Oil quench from 820–870°C after carburizing. For thin-walled or long-shaft parts, marquenching (stepped quench) helps minimize distortion. Post-quench hardness typically HRC 58–62 at case.
Tempering
Low-temperature temper at 150–200°C air cool after carburize-quench. For Q+T structural condition: austenitize at 880°C (water/oil quench), temper at 500°C (water/oil cool). No temper brittleness.