Steel SMnB420H-HR (Hot rolled)
Supply condition
Cheapest mill condition for forging stock and parts that will be normalized or carburized later.
Values for the HR condition
Other SMnB420H tempers and conditions
SMnB420H is listed in 6 conditions; see the grade overview at SMnB420H.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stocked condition for machining or cold heading before carburizing. | 355 | 560 | 26 | 170 HB | — |
HRThis page Hot rolled | Cheapest mill condition for forging stock and parts that will be normalized or carburized later. | 400 | 620 | 22 | 187 HB | — |
Normalized | Use to refine forging grain and stabilise distortion before carburizing or final machining. | 430 | 640 | 22 | 190 HB | — |
Cold drawn | Choose for close-tolerance bright bar for automatic screw-machine pins and shafts. | 580 | 700 | 12 | 210 HB | — |
Quenched and tempered | Reference condition for the JIS mechanical acceptance test and for parts used without a case. | 700 | 900 | 17 | 30 HRC | — |
Carburized, quenched and low-temperature tempered | Final service condition for gears and splined shafts needing a hard wear surface with a tough core. | 780 | 1,000 | 12 | 60 HRC | — |
What is SMnB420H-HR?
SMnB420H-HR is SMnB420H supplied in the HR condition — cheapest mill condition for forging stock and parts that will be normalized or carburized later. SMnB420H-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi). SMnB420H-HR 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). A is the default condition FabDigit quotes; HR is available on request or by drawing note.
SMnB420H-HR properties
Typical room-temperature values for SMnB420H-HR; 11 are specific to this condition. Other listed values are SMnB420H reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SMnB420H-HR 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).
Mechanical14
SMnB420H-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SMnB420H-HR is rated for continuous service to 350°C (662 °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
SMnB420H-HR conducts electricity at 8.2 % IACS, better than 61% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of SMnB420H-HR takes about 27 MJ of energy and emits 2 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 30%.
Manufacturability6
SMnB420H-HR's machinability is good (58/100, better than 75% of steel grades); weldability good (55/100); formability fair (52/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMnB420H-HR
Is SMnB420H easy to machine?
Machine in the annealed/normalized state with carbide at ~150–220 m/min; the Mn-rich matrix is gummy, so use positive rake and generous coolant, and finish-grind after carburizing.
Can SMnB420H be welded?
CE ≈0.45–0.50 — weldable with low-hydrogen consumables, 150–250 °C preheat and slow cooling; never weld after carburizing.
Can SMnB420H be formed, bent or molded?
Good hot forgeability at 1100–1200 °C and acceptable cold heading when spheroidize annealed; normalize forgings before case hardening to control grain size and distortion.
What surface finishes work on SMnB420H?
No inherent corrosion protection — use phosphating plus oil, black oxide, or zinc/zinc-nickel plating (bake to avoid hydrogen embrittlement on hardened parts); shot peening markedly raises gear-tooth bending fatigue.
SMnB420H 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 |
|---|---|---|
| CH-steel range slightly wider than SMnB420 | 0.17 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 1.15 – 1.6 | 1.35 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Beffective (soluble) boron; Al/Ti added to fix nitrogen | 5×10⁻⁴ – 0.01 | 0 |
| Curesidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.25 | — |
| Crresidual | ≤ 0.2 | — |
| Fe | balance | — |
SMnB420H-HR — frequently asked
What is SMnB420H-HR used for?
SMnB420H-HR is typically used for carburized gears, shafts and pins. In short: chromium-free hardenability; low-cost carburizing steel; guaranteed H hardenability band.
What is the yield strength of SMnB420H-HR?
SMnB420H-HR has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SMnB420H-HR easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machine in the annealed/normalized state with carbide at ~150–220 m/min; the Mn-rich matrix is gummy, so use positive rake and generous coolant, and finish-grind after carburizing.
Can SMnB420H-HR be welded?
Yes — weldability is rated good (55/100). CE ≈0.45–0.50 — weldable with low-hydrogen consumables, 150–250 °C preheat and slow cooling; never weld after carburizing.
What surface finishes work on SMnB420H-HR?
No inherent corrosion protection — use phosphating plus oil, black oxide, or zinc/zinc-nickel plating (bake to avoid hydrogen embrittlement on hardened parts); shot peening markedly raises gear-tooth bending fatigue.
Can SMnB420H-HR be formed, bent or molded?
Good hot forgeability at 1100–1200 °C and acceptable cold heading when spheroidize annealed; normalize forgings before case hardening to control grain size and distortion.
What is the maximum service temperature of SMnB420H-HR?
SMnB420H-HR is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SMnB420H-A and SMnB420H CARB?
A is the default condition — standard stocked condition for machining or cold heading before carburizing. CARB: final service condition for gears and splined shafts needing a hard wear surface with a tough core. Yield strength is 355 MPa in A versus 780 MPa in CARB.
Sources
- JIS G 4052 — Structural steels with specified hardenability bands — JSA (2016)
- JIS G 4053 — 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 (boron hardenability, carburizing) — ASM International (2013)
- GB/T 3077 / GB/T 5216 — / (20MnB comparison) — SAC (2015)
- Mysteel / SMM (2025)
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.