Knowledge about Stainless Steel 420

Stainless Steel 420 is a high-carbon martensitic stainless steel with 12–14% chromium. It is valued for its excellent heat-treatability, achieving higher hardness and wear resistance than 410. Its balance of corrosion resistance and edge retention makes it a top choice for cutting tools and precision components.

Chemical Composition (Key, % ASTM A240) C: 0.15–0.40; Cr: 12.00–14.00; Mn: ≤1.00; Si: ≤1.00

Mechanical Properties (Heat-Treated) Tensile Strength: ≥760 MPa; Yield Strength: ≥550 MPa; Elongation: ≥12%; Hardness: Up to 50 HRC (heat-treated)

Performance & Uses Advantages: Exceptional edge retention, high hardness, good corrosion resistance for martensitic grades. Applications: Knife blades, scissors, surgical scalpels, valve seats, mold parts.

Equivalent Grades: EN 1.4021, JIS SUS420J1/J2, DIN X20Cr13/X30Cr13

5 Quick Q&As

1. Why does 420 have better edge retention than 410? 420's higher carbon content (0.15–0.40% vs. 0.08–0.15% for 410) is the key. During heat treatment, carbon combines with chromium to form more chromium carbides, which are hard particles that resist wear. When sharpened, 420's surface retains these carbides, preventing the edge from dulling quickly-critical for knife blades and scalpels. 410, with fewer carbides, loses its edge faster, making it less suitable for cutting applications where sharpness longevity is needed.

2. What are the different subtypes of 420 (J1/J2), and how do they differ? 420J1 has a lower carbon range (0.15–0.25%) and is more ductile, making it easier to form into complex shapes like scissors. 420J2 has higher carbon (0.25–0.40%) and achieves higher hardness (up to 50 HRC vs. 45 HRC for J1), ideal for heavy-duty cutting tools like hunting knives. Both have the same chromium content (12–14%), so corrosion resistance is similar. The choice depends on formability needs: J1 for easier fabrication, J2 for maximum hardness and wear resistance.

3. Can 420 be welded, and what precautions are needed? Welding 420 is possible but challenging due to its high carbon content and martensitic structure. It is prone to cold cracking (after welding) because rapid cooling forms hard, brittle martensite. To prevent this, preheat the steel to 200–300°C before welding, use low-heat input (slow travel speeds), and post-weld temper immediately at 250–300°C to soften the weld zone. Use 410 or 420 filler wire to match composition. Avoid welding thick sections of 420J2, as it is more crack-prone than J1.

4. How does 420's corrosion resistance hold up in food contact applications? 420 is suitable for food contact (e.g., kitchen knives) because its chromium oxide layer resists corrosion from food acids (e.g., tomatoes, citrus). It is easy to clean, and its smooth surface prevents bacterial buildup. However, it requires proper care: after use, it should be dried immediately to avoid rusting from water and food residues. Unlike austenitic grades like 304 (which are more corrosion-resistant), 420 may develop light rust if left wet, but this can be removed with a polish.

5. Why is 420 used for mold parts instead of 304? Mold parts (e.g., injection mold cores) require high hardness to resist wear from repeated plastic injection and good dimensional stability. 420, when heat-treated, achieves 45–50 HRC, making it much harder than 304 (which maxes out at 217 HB, too soft for mold use). 420 also has better machinability for precision mold shapes, and its corrosion resistance is sufficient to withstand plastic resins and mold cleaning agents. 304, while more corrosion-resistant, lacks the strength and wear resistance needed for long-term mold service.