Steel SMn438-HR (Hot rolled)
Supply condition
Cheapest mill condition for parts that will be heat treated after rough machining.
Values for the HR condition
Other SMn438 tempers and conditions
SMn438 is listed in 8 conditions; see the grade overview at SMn438.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition — pick it for heavy machining, deep boring or cold forming before hardening. | 340 | 580 | 26 | 170 HB | — |
HRThis page Hot rolled | Cheapest mill condition for parts that will be heat treated after rough machining. | 380 | 640 | 22 | 190 HB | — |
Normalized | Uniform fine grain and stable machining response for forgings before final Q&T. | 420 | 680 | 22 | 14 HRC | 8.2 % IACS |
Cold drawn | Straight, close-tolerance bright bar for as-supplied shafting where no heat treatment follows. | 640 | 760 | 12 | 20 HRC | — |
QTDefault Quenched and tempered | Standard supply condition for shafts, axles and gear blanks needing ≥785 MPa with good toughness. | 690 | 860 | 20 | 25 HRC | — |
Induction hardened | Choose when journals, splines or gear teeth need a wear-resistant 50–58 HRC skin over a tough core. | 700 | 880 | 16 | 55 HRC | 7.4 % IACS |
Q&T to 28–32 HRC | Higher-strength tempering band for loaded shafts and connecting parts still machinable with carbide. | 790 | 950 | 17 | 30 HRC | — |
Q&T to 33–38 HRC | Maximum useful through-hardness for small sections where wear and strength beat toughness. | 950 | 1,130 | 14 | 35 HRC | — |
What is SMn438-HR?
SMn438-HR is SMn438 supplied in the HR condition — cheapest mill condition for parts that will be heat treated after rough machining. SMn438-HR has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 68% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). SMn438-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). QT is the default condition FabDigit quotes; HR is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
SMn438-HR properties
Typical room-temperature values for SMn438-HR; 10 are specific to this condition. Other listed values are SMn438 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SMn438-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
SMn438-HR has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 68% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMn438-HR 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
SMn438-HR conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of SMn438-HR takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
SMn438-HR's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMn438-HR
Is SMn438 easy to machine?
Machines like Q&T 1541 at roughly 60 % of 1212; use rigid setups, carbide inserts and 120–180 m/min in the 235–285 HB condition — soften by annealing for heavy stock removal.
Can SMn438 be welded?
CE ≈ 0.7, so preheat 200–300 °C, use low-hydrogen consumables and temper after welding; avoid welding fully hardened parts.
Can SMn438 be formed, bent or molded?
Hot forge 1050–1200 °C then normalize; cold bending is limited — anneal first and keep generous bend radii.
What surface finishes work on SMn438?
No anodizing (ferrous); protect with oil, phosphate + oil, black oxide or zinc plating, and bake after plating to avoid hydrogen embrittlement above 1000 MPa.
SMn438 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 |
|---|---|---|
| CJIS G4053 SMn438 | 0.35 – 0.41 | 0.38 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 1.35 – 1.65 | 1.5 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Crresidual limit | ≤ 0.35 | — |
| Niresidual limit | ≤ 0.25 | — |
| Curesidual limit | ≤ 0.3 | — |
| Fe | balance | — |
SMn438-HR — frequently asked
What is SMn438-HR used for?
SMn438-HR is typically used for shafts, gears and sprockets. In short: low-cost hardenable alloy bar; 1541 manganese-steel equivalent; chromium-free shaft steel.
What is the yield strength of SMn438-HR?
SMn438-HR has a typical yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 68% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SMn438-HR easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like Q&T 1541 at roughly 60 % of 1212; use rigid setups, carbide inserts and 120–180 m/min in the 235–285 HB condition — soften by annealing for heavy stock removal.
Can SMn438-HR be welded?
With care — weldability is rated fair (40/100). CE ≈ 0.7, so preheat 200–300 °C, use low-hydrogen consumables and temper after welding; avoid welding fully hardened parts.
What surface finishes work on SMn438-HR?
No anodizing (ferrous); protect with oil, phosphate + oil, black oxide or zinc plating, and bake after plating to avoid hydrogen embrittlement above 1000 MPa.
Can SMn438-HR be formed, bent or molded?
Hot forge 1050–1200 °C then normalize; cold bending is limited — anneal first and keep generous bend radii.
What is the maximum service temperature of SMn438-HR?
SMn438-HR 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 SMn438-QT and SMn438-A?
QT is the default condition — standard supply condition for shafts, axles and gear blanks needing ≥785 MPa with good toughness. A: softest condition — pick it for heavy machining, deep boring or cold forming before hardening. Yield strength is 690 MPa in QT versus 340 MPa in A.
Sources
- JIS G 4053 — Low-alloyed structural steels for machine structural use — JSA (2016)
- SAE J404 / J1268 — Chemical compositions and hardenability of SAE alloy steels (1541/1541H) — SAE International (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- GB/T 3077 — Alloy structural steels (comparable 40Mn2) — 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.