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SUS420J2 Material: Full Guide to Martensitic Stainless Steel

Three core values including C 0.26-0.40%, Cr 12-14% and martensitic structure define SUS420J2 material. This article analyzes this JIS martensitic stainless steel from three aspects: chemical makeup, metallographic structure and mechanical & physical performance.

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SUS420J2 Material
SUS420J2 Material
SUS420J2 HRC
SUS420J2 HRC

Chemical Composition of SUS420J2 Material

 
Carbon and chromium serve as the core elements of SUS420J2 material composition.
ElementContent in SUS420J2 (%)Content in 420J1 (%)Function
C (Carbon)0.26-0.40≤0.15Creates hardness and tensile strength
Cr (Chromium)12.00-14.0012.00-14.00Improves corrosion resistance and hardenability
Si (Silicon)≤1.00≤1.00Deoxidizer, boosts material strength
Mn (Manganese)≤1.00≤1.00Removes oxide, enhances hardening capacity
P (Phosphorus)≤0.040≤0.040Harmful impurity, lower value is better
S (Sulfur)≤0.030≤0.030Minor impurity, optimizes cutting performance
Ni (Nickel)≤0.60≤0.60Raises toughness and anti-corrosion ability

Carbon and chromium decide the core property of SUS420J2 material. 0.26-0.40% carbon forms high-carbon martensite after heat treatment, with maximum hardness over 55 HRC. 12-14% chromium forms a passive film to meet the standard for stainless steel (steel with Cr ≥ 10.5% counts as stainless steel). To verify genuine SUS420J2 material: steel with Cr below 12% or C below 0.26% is non-standard grade.

Metallographic Structure of SUS420J2 Material

 
  • Annealed state: Spheroidized pearlite, hardness ≤235 HB
  • Quenched state: Lath martensite, tiny retained austenite and undissolved carbide
  • Tempered state: Tempered martensite plus scattered carbide. Carbide shape changes from needle-like to spherical as tempering temperature rises.
 

Physical & Mechanical Performance of SUS420J2 Material

 
Below lists key performance data of JIS SUS420J2 material.
 
CategoryPropertyValueNote
PhysicalDensity7.75 g/cm³Slightly lighter than carbon steel (7.85 g/cm³)
PhysicalThermal expansion coefficient10.3×10⁻⁶/K (0-100°C)Similar to carbon steel
PhysicalThermal conductivity24.9 W/(m·K) (100°C)Around 1/16 of copper’s conductivity
Mechanical (Quenched & Tempered)Tensile strength≥740 MPaEquals around 108 ksi
Mechanical (Quenched & Tempered)Yield strength≥540 MPaEquals around 78 ksi
Mechanical (Quenched & Tempered)Elongation≥12%Medium-low ductility
Mechanical (Quenched & Tempered)Reduction of area≥40%—
Mechanical (Annealed)Hardness≤235 HBRoughly ≤20 HRC

Core features of SUS420J2 material properties: high tensile strength (over 740 MPa), medium hardness and limited toughness. It is not suitable for parts under heavy impact, yet it balances wear resistance and anti-corrosion better than other 420 series martensitic stainless steel.

Core Differences: SUS420J2 Material vs 304 & 316

 
Do not mix martensitic and austenitic stainless steel — their performance gaps are huge.
 
IndexSUS420J2 (Martensitic)SUS304 (Austenitic)SUS316 (Austenitic)
Cr Content12-14%18-20%16-18%
Ni Content≤0.60%8-10.5%10-14%
Mo ContentNoneNone2-3%
Hardness50-55 HRC (quenched)≤90 HRB (cannot harden via quenching)≤90 HRB (cannot harden via quenching)
MagnetismMagneticWeakly non-magneticWeakly non-magnetic
Corrosion ResistanceMediumGoodExcellent (with molybdenum)
Typical UseCutters, molds, valvesFood equipment, chemical tanks, constructionMarine equipment, medical parts
420 material properties excel in hardness, while 304 and 316 stand out in corrosion resistance. Pick 420J2 for cutting tools; choose 316 for parts exposed to seawater. These grades cannot replace each other. Quenching 304 will not create martensite, as nickel content above 8% stabilizes its austenitic structure.
 

Supply Forms & Specifications of SUS420J2 Material

 

Supply Forms and Specification

 
  1. Round bar: Φ10-300mm (annealed or quenched & tempered)
  2. Steel plate: 3-100mm thick (mostly annealed)
  3. Steel strip: 0.1-3mm thick (cold rolled bright surface)
  4. Forged piece: Customized per technical drawing
  5. Steel wire: Φ0.5-12mm (for springs and cutters)
 

MTC Data of SUS420J2 Material:

 
  1. Chemical component (C, Si, Mn, P, S, Cr)
  2. Hardness (≤235 HB for annealed stock, 28-34 HRC for QT delivery condition)
  3. Mechanical properties (annealed – no, QT – yes)
  4. Heat treatment state (annealed / quenched & tempered)
  5. Grain size (normally 6-8)
  6. UT test (D/d or E/e)
  7. Surface condition(black surface, bright surface, grinded surface, polished surface)

FAQ:

Q1: Can SUS420J2 material be used for food contact parts?

A: Not recommended for direct contact with acidic food. 420J2 only contains 12-14% chromium, far less anti-corrosion capacity than 304 (18% Cr + 8% Ni). It can be used for dry, non-acidic food contact parts; select 304 or 316 for wet or acidic working conditions.

A: Their chemical makeup is very close (3Cr13: C 0.26-0.35%, Cr 12-14%), so interchange works for most common scenarios. JIS standard sets stricter limits for P and S (≤0.030-0.040%) compared with GB standard (≤0.035%). Purchase steel matching the original drawing standard for high-demand applications.

A: Minimum carbon 0.26% (carbon over 0.40% causes brittleness; carbon below 0.26% leads to insufficient hardness), minimum chromium 12% (low chromium weakens anti-corrosion), P ≤0.040% (high phosphorus brings cold brittleness), delivery hardness (annealed ≤235 HB, quenched 50-55 HRC).

Conclusion

If you confused about material selection or SUS420J2 heat treatment? Talk with engineers from Keyspark Steel. We have 20 years of manufacturing experience with martensitic stainless steel, and help you make data-backed material choices to avoid mistakes.

 

 

📧 Email: Sales@keysparksteel.com
📱 Mobile/WhatsApp: +86 150 2405 6480

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