V.S. Heat Treatment
Heat treatment & metal finishing experts
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V.S. Heat Treatment
Heat treatment & metal finishing experts
Our engineers reply with a tailored quote within 24 hours.
Pick your grade to see the right process, realistic hardness, and what to put on the order — based on the small parts we harden every day.
Medium-grade bolts and nuts, pins, small shafts and general machine parts
The most common hardening grade in Thailand; service hardness tunes over a wide band via tempering temperature.
Not sure of your grade, or want the spec confirmed before ordering? Send us your drawing for a free check — reply within 24 h.
Grades respond to hardening very differently. Carbon content sets the ceiling (more carbon → harder), while alloying elements such as chromium, molybdenum or boron improve hardenability — how deep the hardness reaches. Below roughly 0.3% carbon, direct hardening barely works; the standard route is carburizing, which adds carbon to the surface first.
As-quenched hardness and in-service hardness are not the same number. Freshly quenched steel is at its hardest but brittle, so it is tempered — trading some hardness for toughness. The "in-service" column shows the ranges drawings actually specify.
The numbers on this page are typical for small parts (screws, nuts, bolts, springs, pins), which through-harden easily. Real results still depend on section size, quench medium and heat chemistry — send us your drawing and we confirm the spec before any work starts.
Typical ranges for small parts (screws, nuts, bolts, springs, pins) after the recommended process.
| Grade | Carbon (%) | Recommended process | As-hardened surface (HRC) | Typical in-service (HRC) | Typical uses |
|---|---|---|---|---|---|
| S20CAISI 1020 / DIN C22 | 0.18–0.23 | Carburizing (case hardening) | 55–62 | 55–60 | Self-tapping screws, machine screws, rivets and parts needing a wear-resistant case over a tough core |
| S45CAISI 1045 / DIN C45 | 0.42–0.48 | Quench & temper (Q&T) | 50–58 | 40–55 | Medium-grade bolts and nuts, pins, small shafts and general machine parts |
| SCM435AISI 4135 / DIN 34CrMo4 | 0.33–0.38 | Quench & temper (Q&T) | 48–55 | 33–44 | Grade 10.9 high-tensile bolts, studs and load-bearing screws |
| SCM440AISI 4140 / DIN 42CrMo4 | 0.38–0.43 | Quench & temper (Q&T) | 50–58 | 28–48 | Grade 12.9 bolts, high-load pins and torque-carrying parts |
| SCr440AISI 5140 / DIN 41Cr4 | 0.38–0.43 | Quench & temper (Q&T) | 50–57 | 28–45 | Load-bearing bolts and pins, small automotive parts |
| SWCH10B21AISI 10B21 | 0.18–0.23 + B | Quench & temper (Q&T) | 40–48 | 28–40 | Cold-headed self-tapping screws and grade 8.8–10.9 bolts |
| SWCH10B33AISI 10B33 | 0.30–0.36 + B | Quench & temper (Q&T) | 45–52 | 32–42 | Grade 10.9 bolts, wheel nuts and cold-headed high-strength screws |
| SUP9AISI 5155 / DIN 55Cr3 | 0.52–0.60 | Quench & temper (Q&T) / Austempering | 50–58 | 40–50 | Leaf springs, coil springs, spring washers and automotive spring parts |
| SK85 (SK5)AISI 1084–1086 / DIN C85 | 0.80–0.90 | Quench & temper (Q&T) / Austempering | 58–64 | 45–60 | Flat springs, clips, spring washers and small blades |
| SUJ2AISI 52100 / DIN 100Cr6 | 0.95–1.10 | Quench & temper (Q&T) | 60–64 | 58–64 | Small bearings, rollers, hardened pins and gauge pins |
| SKS3AISI O1 (近) / DIN 100MnCrW4 | 0.90–1.00 | Quench & temper (Q&T) | 58–63 | 56–62 | Small punches, dies, gauges and small cutting tools |
| SUS420J2AISI 420 / DIN X30Cr13 | 0.26–0.40 | Quench & temper (Q&T) | 48–55 | 45–52 | Stainless parts that must be hard: special screws, small blades, small valve stems |
| SUS304AISI 304 / DIN X5CrNi18-10 | ≤ 0.08 | Not hardenable by heat treatment | — | — | General stainless nuts, screws and washers where corrosion resistance matters more than hardness |
Figures are typical ranges for small, thin-section parts, based on JIS specifications and our production experience. Actual results depend on section size, quench medium, tempering temperature and the heat's actual chemistry — treat as guidance, not a guarantee.
No — SUS304 is austenitic stainless; its structure does not transform to martensite on quenching, so heat treatment will not harden it. It only work-hardens from cold forming. If you need a hardenable stainless, use a martensitic grade such as SUS420J2 (about 48–55 HRC).
Below roughly 0.3% carbon, too little martensite forms and the hardness gain is minimal. The standard route is carburizing — diffusing carbon into the surface before quenching — giving a 55–62 HRC case over a tough core. Ideal for self-tapping screws and wear parts.
At minimum: steel grade, target hardness as a range (e.g. 38–44 HRC), where it is measured (surface or core), case depth for carburizing work, and quantity or weight. A drawing or photo helps — send it through our quote form.
It depends on section size, quench medium, tempering temperature and the heat's actual chemistry. These ranges assume small parts that through-harden easily. We confirm the spec together before accepting the job and ship in-house lab readings with every lot.