Steel SMn420
SMn420 is a JIS manganese-alloyed case-hardening steel (near AISI 5120) that draws its hardenability from manganese rather than nickel, giving an economical carburizing grade.
Reference datasheet — SMn420 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the HR condition
SMn420 tempers and conditions
SMn420 is supplied in 6 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
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 | — |
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?
SMn420 is a JIS manganese-alloyed case-hardening steel (near AISI 5120) that draws its hardenability from manganese rather than nickel, giving an economical carburizing grade. Hot-rolled and annealed properties are 350 MPa yield, 560 MPa tensile, 25 % elongation and 160 HB, with machinability 60, weldability 60 and formability 55; bar and cold-drawn stock are the normal forms. Core hardenability is lower than 20MC5 or 18NCD6, so it suits medium-duty sections only, and it offers no corrosion resistance. Move to 20MnCr5 for larger or more heavily loaded gears. SMn420 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). SMn420 has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
What is SMn420 used for?
- gears
- shafts
- small pins
Advantages
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
SMn420 properties
Typical room-temperature values for SMn420-HR; bars are the position among steel grades.
Physical3
SMn420 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 has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMn420 is rated for continuous service to 400°C (752 °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 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 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's machinability is good (60/100, better than 83% of steel grades); weldability good (60/100); formability good (55/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SMn420 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SMn420
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SMn420 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 5120
How much does SMn420 cost?
SMn420 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SMn420 — frequently asked
What is SMn420 used for?
SMn420 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?
SMn420 has a typical yield strength of 350 MPa (50.8 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 74% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SMn420 easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% 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 be welded?
Yes — weldability is rated good (60/100). 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?
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 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?
SMn420 is rated for continuous use to about 400°C (752 °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.
How much does SMn420 cost?
SMn420 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.