Steel SMn420-CH (Carburized and hardened)
Heat-treated state
The service condition for gears and shafts: hard wear-resistant case with a tough, ductile core.
Values for the CH condition
Other SMn420 tempers and conditions
SMn420 is listed in 6 conditions; see the grade overview at SMn420.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition, chosen for cold forming, deep machining or before cold heading. | 300 | 490 | 30 | 143 HB | — |
HRDefault Hot rolled | Standard mill supply condition for bar destined for machining and subsequent carburizing. | 350 | 560 | 25 | 160 HB | — |
Normalized | Grain refinement and uniform structure before carburizing or rough machining. | 380 | 590 | 24 | 175 HB | 8.6 % IACS |
Cold drawn | Pick for tight tolerance, bright surface bar for automatic-lathe parts and pins. | 560 | 660 | 12 | 197 HB | — |
Quenched and tempered | Through-hardened core condition used for the JIS G4053 acceptance test and for uncarburized parts. | 600 | 780 | 19 | 23 HRC | — |
CHThis page Carburized and hardened | The service condition for gears and shafts: hard wear-resistant case with a tough, ductile core. | 800 | 1,080 | 11 | 60 HRC | — |
What is SMn420-CH?
SMn420-CH is SMn420 heat treated to CH — the service condition for gears and shafts: hard wear-resistant case with a tough, ductile core. SMn420-CH has a yield strength of 800 MPa (116 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 86% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi). SMn420-CH has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; CH is available on request or by drawing note.
Advantages
- High strength — 800 MPa (116 ksi), better than 86% of steel grades
Limitations
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
SMn420-CH properties
Typical room-temperature values for SMn420-CH; 12 are specific to this condition. Other listed values are SMn420 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SMn420-CH has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical13
SMn420-CH has a yield strength of 800 MPa (116 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 86% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMn420-CH is rated for continuous service to 180°C (356 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
SMn420-CH conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of SMn420-CH takes about 26 MJ of energy and emits 2.1 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability7
SMn420-CH's machinability is not recommended (12/100, worse than 99% of steel grades); weldability poor (15/100); formability good (55/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMn420-CH
Is SMn420 easy to machine?
Machines readily in the annealed/normalized state (≈65 % of AISI 1212) but is gummy — use positive rake carbide, good chip control and coolant; finish-grind after carburizing.
Can SMn420 be welded?
Weldable with low-hydrogen electrodes at CE ≈ 0.45; preheat 150–250 °C on heavy sections and never weld carburized surfaces.
Can SMn420 be formed, bent or molded?
Good cold heading and bending in the spheroidize-annealed condition; hot forge 1100–1200 °C and normalize afterwards to refine grain before carburizing.
What surface finishes work on SMn420?
Not anodizable — protect with phosphate + oil, black oxide or zinc/nickel plating; bake after plating to avoid hydrogen embrittlement of the hardened case.
SMn420 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.17 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mnprincipal hardenability element | 1.2 – 1.5 | 1.35 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Curesidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.25 | — |
| Crresidual | ≤ 0.35 | — |
| Fe | balance | — |
SMn420-CH — frequently asked
What is SMn420-CH used for?
SMn420-CH is typically used for gears, shafts and small pins. In short: economical carburizing steel; nickel-free Mn hardenability; medium-duty gear grade.
What is the yield strength of SMn420-CH?
SMn420-CH has a typical yield strength of 800 MPa (116 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 86% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SMn420-CH easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machines readily in the annealed/normalized state (≈65 % of AISI 1212) but is gummy — use positive rake carbide, good chip control and coolant; finish-grind after carburizing.
Can SMn420-CH be welded?
Not readily — weldability is rated poor (15/100). Weldable with low-hydrogen electrodes at CE ≈ 0.45; preheat 150–250 °C on heavy sections and never weld carburized surfaces.
What surface finishes work on SMn420-CH?
Not anodizable — protect with phosphate + oil, black oxide or zinc/nickel plating; bake after plating to avoid hydrogen embrittlement of the hardened case.
Can SMn420-CH be formed, bent or molded?
Good cold heading and bending in the spheroidize-annealed condition; hot forge 1100–1200 °C and normalize afterwards to refine grain before carburizing.
What is the maximum service temperature of SMn420-CH?
SMn420-CH is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SMn420-HR and SMn420-CH?
HR is the default condition — standard mill supply condition for bar destined for machining and subsequent carburizing. CH: the service condition for gears and shafts: hard wear-resistant case with a tough, ductile core. Yield strength is 350 MPa in HR versus 800 MPa in CH.
Sources
- JIS G4053 — Low-alloyed steels for machine structural use — JSA (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals and Processes (carburizing) — ASM International (2013)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- GB/T 3077 — Alloy structural steels (comparable 20Mn2 grade) — SAC (2015)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.