Steel SMn438-QT (Quenched and tempered)
Heat-treated state · default condition
Standard supply condition for shafts, axles and gear blanks needing ≥785 MPa with good toughness.
Values for the QT 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 | — |
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 | — |
QTDefaultThis page 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-QT?
SMn438-QT is SMn438 heat treated to QT — standard supply condition for shafts, axles and gear blanks needing ≥785 MPa with good toughness. SMn438-QT has a yield strength of 690 MPa (100 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 80% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi). SMn438-QT 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).
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 690 MPa (100 ksi), better than 80% of steel grades
SMn438-QT properties
Typical room-temperature values for SMn438-QT; 11 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-QT 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-QT has a yield strength of 690 MPa (100 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 80% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMn438-QT 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-QT 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-QT 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-QT's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); formability fair (35/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMn438-QT
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-QT — frequently asked
What is SMn438-QT used for?
SMn438-QT 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-QT?
SMn438-QT has a typical yield strength of 690 MPa (100 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SMn438-QT 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-QT 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-QT?
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-QT 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-QT?
SMn438-QT 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.