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SUS420J2 HRC: Full Analysis of Quenched & Tempered Hardness

After quenching, SUS420J2 HRC can exceed 55 HRC, dropping 3-4 HRC for every 100°C rise in tempering temperature. This article explains how to balance performance and covers full hardness changes from annealing, quenching to tempering.

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SUS420J2 HRC
SUS420J2 HRC

Quenching Process for SUS420J2 HRC

 

Martensite transformation of SUS420J2 occurs after quenching at 1000–1050°C. Take oil quenching as an example: heat to 1000°C → rapidly immerse in oil for cooling. The finished structure consists of lath martensite plus a small amount of retained austenite, with hardness ranging 54–57 HRC.

 

Quenching at 1050°C delivers 1–2 extra HRC, but leads to coarse grain structure and reduced toughness. Quenching medium also affects hardness uniformity: oil quenching offers ±1 HRC tolerance, while air quenching only reaches ±3 HRC.

 
The complete SUS420J2 HRC range covers annealed state ≤235 HB (around 20 HRC) up to maximum quenched hardness 57 HRC. Standard delivery hardness from suppliers sits at 47–55 HRC after full quenching and tempering.
 

Precise Tempering Temperature Control for SUS420J2 HRC

 
Adjusting tempering temperature directly changes SUS420J2 hardness HRC. Core rule for SUS420J2 HRC tempering: higher tempering temperature accelerates martensite decomposition and carbide precipitation, lowering hardness while boosting toughness.
Tempering Temp (°C)Hardness (HRC)Microstructure ChangeTypical Application
200–25054–56Minor epsilon carbide precipitationCutters, scissors, surgical instruments
300–35050–53Carbides start spheroidizingBearings, precision shafts, heavy wear parts
400–45045–49Full carbide spheroidizationValves, pump bodies, general molds
500–55038–44Massive martensite decompositionHigh-toughness impact-resistant components
Key rule of the SUS420J2 HRC chart: hardness falls 3–4 HRC per 100°C temperature rise between 200°C and 500°C. A secondary hardening zone appears at 450–500°C from molybdenum carbide precipitation, slowing the hardness decline temporarily.
 

SUS420J2 HRC vs 420J1

 

At identical tempering temperatures, 420J2 holds 2–4 HRC higher hardness than 420J1, caused by carbon content gap. JIS 420J2 contains 0.26–0.40% carbon, while 420J1 has maximum 0.15% carbon.

 

A 0.1% carbon difference creates around 5 HRC gap in quenched martensite, narrowing to 2–4 HRC after tempering.

 

Maximum quenched hardness of 420J1 is roughly 52 HRC, dropping to 48–50 HRC after 200°C tempering. Under the same heat treatment, 420J2 hits 54–56 HRC. Only 420J2 meets requirements above 50 HRC, making it the highest hardness grade within the 420 stainless HRC series.

 

Inspection Method for JIS SUS420J2 HRC

  1. Use bench Rockwell hardness tester (C scale, 150kgf diamond indenter), take average of five test points. Deviation over ±1.5 HRC indicates uneven quenching or tempering.
  2. Portable Leeb hardness tester for quick screening. A 2–3 HRC reading offset is normal; retest abnormal samples on bench equipment.
  3. Remove a 0.2–0.3mm decarburized surface layer before testing. Decarburized surfaces read 3–5 HRC lower; reporting unground test results leads to quality disputes.
 
Batch sampling rule: test 3 points on each piece, all must fall within specification range. If one point fails on any part, double inspection volume for the whole batch. Standard delivery tolerance for JIS SUS420J2 HRC is 50–55 HRC. Reject all stock below 48 HRC or above 57 HRC.
 

Mechanical Properties of SUS420J2 HRC

Hardness (HRC)Tensile Strength (MPa)Yield Strength (MPa)Toughness Feature
55~1800~1500Low toughness, high brittleness, only for cutting tools
50~1500~1200Medium toughness, general wear-resistant parts
45~1200~950Good toughness, molds and valves
40~1000~780High toughness, impact-resistant workpieces

FAQ:

Q1: Can SUS420J2 HRC reach over 60?

A: Hard to achieve. Theoretical maximum quenched hardness for its 0.40% carbon limit is around 58 HRC. Cryogenic treatment at -80°C adds 1–2 HRC up to 58–59 HRC. For hardness above 60 HRC, select higher-carbon martensitic steel such as 440C (0.95–1.20% carbon, 60+ HRC achievable).

A: Deviation within ±1.5 HRC is normal. Request replacement if offset exceeds 2 HRC, which signals unstable tempering control from suppliers. Long-term partners can lock tighter tolerance at ±1 HRC.

A: Low tempering (200–300°C) retains high hardness yet leaves heavy internal stress and unstable dimensions. High tempering (500–550°C) lowers hardness but improves dimensional stability and impact resistance. High-precision components prefer high-temperature tempering.

Conclusion

Unsure about proper heat treatment hardness targets? Consult engineers from Keyspark Steel. We own 20 years of martensitic stainless steel heat treatment experience, customizing quenching and tempering parameters to guarantee consistent batch hardness. If you want to purchase SUS 420J2, welcome to contact us!

 

 

 

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

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