SUS420J2 (JIS G4303) is the high-carbon upgrade of the martensitic stainless family — 0.26–0.40% C combined with 12–14% Cr enables hardening to 50–56HRC, roughly 10HRC higher than SUS410. The carbon increase raises hardness and wear resistance at the cost of reduced corrosion resistance and toughness. This is the grade for kitchen knife blades, surgical scissors, mold cavities for plastics, and precision gauge blocks where stainless behavior and edge retention must coexist. Understanding its heat treatment window — and the chromium carbide precipitation mechanism that simultaneously creates hardness and reduces corrosion resistance — is essential to specifying it correctly.
- International Equivalent Grades
- Chemical Composition: SUS420J2 vs SUS410
- Mechanical Properties
- Heat Treatment
- Corrosion Resistance
- Machinability
- Common Mistakes
- When to Choose SUS420J2
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4303 | SUS420J2 | Japan | Reference |
| ASTM A276 | AISI 420 / Type 420 | USA | ✅ Nearest Exact |
| EN 10088-1 | 1.4028 / X30Cr13 | Europe | ✅ Nearest Exact |
| DIN 17440 | X30Cr13 | Germany | ✅ Nearest Exact |
| ISO 15510 | X30Cr13 | International | ✅ Nearest Exact |
| GB/T 4237 | 30Cr13 | China | ✅ Nearest Exact |
2. Chemical Composition: SUS420J2 vs SUS410
| Element | SUS420J2 (JIS) | SUS410 (JIS) | 1.4028 (EN) |
|---|---|---|---|
| C | 0.26–0.40% | 0.08–0.15% | 0.26–0.35% |
| Si | ≤ 1.00% | ≤ 1.00% | ≤ 1.00% |
| Mn | ≤ 1.00% | ≤ 1.00% | ≤ 1.50% |
| Cr | 12.00–14.00% | 11.50–13.50% | 12.00–14.00% |
| Ni | ≤ 0.60% | ≤ 0.60% | ≤ 1.00% |
| Mo | — | — | — |
Source: JIS G4303:2012, ASTM A276/A276M-17, EN 10088-1:2014. The 0.26–0.40% C range is the defining feature — it forms more martensite per unit volume on quenching, directly increasing hardness from SUS410’s ~44HRC ceiling to SUS420J2’s ~50–56HRC.
3. Mechanical Properties
| Condition | Tensile Strength | 0.2% Proof Stress | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | ≥ 540 MPa (78 ksi) | ≥ 345 MPa (50 ksi) | ≥ 15% | ≤ 235HBW |
| Hardened + low temper (150–180°C) | ~1700–1900 MPa (247–276 ksi) | ~1400 MPa (203 ksi) | ~3–5% | 52–56HRC |
| Hardened + mid temper (300°C) | ~1400–1600 MPa (203–232 ksi) | ~1200 MPa (174 ksi) | ~8–10% | 46–50HRC |
| Hardened + high temper (600°C) | ~900–1100 MPa (131–160 ksi) | ~700 MPa (102 ksi) | ~15% | 28–34HRC |
4. Heat Treatment
Annealing
Full anneal: 800–900°C (1472–1652°F), furnace cool at ≤ 25°C/hr through 600°C, then air cool. Sub-critical anneal: 740–780°C (1364–1436°F), air cool. Used to restore machinability after cold work or between forming operations.
Hardening
Austenitize at 1000–1050°C (1832–1922°F) for 20–30 min, quench in oil (preferred) or air for thin sections. The austenitizing temperature is critical: too low leaves undissolved carbides and limits hardness; too high causes grain growth and reduces toughness. Target as-quenched hardness: 55–58HRC.
Tempering
| Application | Temper Temperature | Hardness Target | Notes |
|---|---|---|---|
| Kitchen knife blades | 150–180°C (302–356°F) | 54–58HRC | Maximum edge retention; lower toughness |
| Surgical scissors, scalpels | 180–220°C (356–428°F) | 50–54HRC | Balance of hardness and toughness |
| Plastic injection molds | 180–220°C (356–428°F) | 50–54HRC | High wear resistance for abrasive polymers |
| General engineering | 550–650°C (1022–1202°F) | 28–34HRC | Maximum toughness |
5. Corrosion Resistance
Higher carbon is a double-edged sword: it raises hardness but reduces corrosion resistance. Some Cr bonds to C as chromium carbides, lowering the effective Cr available for passivation. SUS420J2’s corrosion resistance in the hardened condition is lower than SUS410 and significantly below the austenitic grades.
| Condition | Corrosion Resistance | Reason |
|---|---|---|
| Annealed | Moderate (PREN ~12–14) | Cr mostly in solution |
| Hardened + low temper | Lower (~PREN 10–12) | Carbide precipitation reduces free Cr |
| Hardened + high temper (>600°C) | Moderate (PREN ~12–14) | Carbides partially dissolved back into matrix |
In practice, SUS420J2 kitchen knives corrode faster than SUS316 medical instruments when stored wet. The corrosion resistance is adequate for dry food contact and indoor environments but requires maintenance (drying after use, oiling for storage) in the hardened condition.
6. Machinability
In the annealed condition, SUS420J2 machines at approximately 55–65% of AISI 1212. The higher carbon versus SUS410 increases cutting tool wear slightly. After hardening to 50+HRC, conventional machining is impractical — grinding becomes the primary finishing operation. Sequence for mold work: rough machine in annealed state → harden → finish grind to final dimensions and surface finish.
7. Common Mistakes
8. When to Choose SUS420J2
Hardness above 44HRC is required with basic stainless behavior: kitchen and professional knife blades, scissors, surgical instruments, plastic injection mold cavities (abrasive polymer grades), precision gauges, and bearing surfaces in mild corrosive environments. The combination of 50–56HRC and 12% Cr is the defining niche.
44HRC is sufficient and better corrosion resistance or toughness is needed: pump shafts, valve internals, turbine blades, fasteners in steam service. SUS410 has higher toughness and marginally better corrosion resistance at equivalent temper conditions.
Wear resistance and hardness take priority over corrosion resistance: cold-work dies, cutting tools, forming punches. Tool steels achieve higher hardness (58–65HRC) with much better wear resistance — the “stainless” benefit of SUS420J2 is not needed for enclosed tooling environments.
9. FAQ
Q: What is the difference between SUS420J1 and SUS420J2?
Carbon content: SUS420J1 is C 0.16–0.25%; SUS420J2 is C 0.26–0.40%. SUS420J2 achieves higher maximum hardness (50–56HRC vs 45–50HRC for J1) and is the standard choice for knife blades and mold cavities. SUS420J1 is an intermediate grade sometimes used where moderate hardness and better toughness are balanced.
Q: Can SUS420J2 be used for food contact?
Yes — SUS420J2 complies with food-contact material regulations (FDA, EU) for dry food and food without prolonged water contact. Kitchen knives made from SUS420J2 are food-safe. However, the grade requires drying after washing — leaving it wet causes surface staining and can initiate pitting in the hardened condition where effective Cr content is reduced.
Q: Is SUS420J2 the same as 1.4028?
Essentially yes. EN 1.4028 (X30Cr13) specifies C 0.26–0.35%, which overlaps the lower part of JIS SUS420J2’s 0.26–0.40% C range. Material certified to 1.4028 will behave like SUS420J2; at the upper end of the JIS C range (0.35–0.40%), hardness and wear resistance are slightly higher than typical 1.4028.
Summary
- SUS420J2 = AISI 420 (high-C range) = EN 1.4028: 13% Cr, 0.26–0.40% C martensitic stainless
- Hardens to 50–56HRC — ~10HRC higher than SUS410, making it the blade and mold steel in the stainless family
- Corrosion resistance is lower than SUS410 in the hardened state due to carbide formation tying up Cr
- Temper within 1 hour of quench — delayed tempering causes hydrogen-assisted cracking
- Avoid tempering 400–600°C (temper embrittlement range)
- Applications: kitchen knives, surgical scissors, plastic mold cavities, precision gauges in mild environments
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