Steel 70Mn4 +QT40 (+QT 40–45 HRC)
Heat-treated state
EN 70Mn4 · GB 70Mn
Tempered around 450–500 °C — pick for tough, high-strength wear parts where some ductility is still needed.
Values for the +QT40 condition
Other 70Mn4 tempers and conditions
70Mn4 is listed in 8 conditions; see the grade overview at 70Mn4.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ADefault Annealed | Softest supply condition — pick for machining, deep blanking/forming or cold drawing before hardening. | 400 | 650 | 15 | 205 HB | 47 W/m·K |
Treated for improved shearability | Controlled lamellar/partly spheroidised structure with a capped hardness band — pick when bars or strip are cold-sheared, cropped or blanked to slug/blank with clean cut faces. | 480 | 800 | 10 | 24 HRC | — |
Normalized | Uniform fine pearlitic structure — pick to reset grain size after hot forming and before hardening. | 520 | 900 | 9 | 26 HRC | — |
Hot rolled | Cheapest supply form — pick when the part will be fully re-heat-treated anyway. | 550 | 950 | 8 | 29 HRC | 9 % IACS |
Cold drawn | Work-hardened strip or patented drawn wire — pick for flat springs, shims and clips used without further hardening. | 1,000 | 1,150 | 3 | 36 HRC | — |
+QT40This page +QT 40–45 HRC | Tempered around 450–500 °C — pick for tough, high-strength wear parts where some ductility is still needed. | 1,200 | 1,400 | 8 | 42 HRC | 44 W/m·K |
+QT 48–52 HRC | Classic oil-hardened-and-tempered spring/blade condition — pick for flat springs, retaining rings and cutting blades. | 1,550 | 1,750 | 5 | 50 HRC | 43 W/m·K |
Hardened | Maximum surface hardness for wear and rolling contact — pick for induction-hardened tracks, pins and wear plates; brittle and must not be shock-loaded. | 1,800 | 2,100 | 1 | 60 HRC | 42 W/m·K |
What is 70Mn4 +QT40?
70Mn4 +QT40 is 70Mn4 heat treated to +QT40 — tempered around 450–500 °C — pick for tough, high-strength wear parts where some ductility is still needed. 70Mn4 +QT40 has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Elongation at break is 8% and the elastic modulus is 207 GPa (30 Msi). 70Mn4 +QT40 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). +A is the default condition FabDigit quotes; +QT40 is available on request or by drawing note.
Advantages
- High strength — 1,200 MPa (174 ksi), better than 94% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to weld — 8/100, worse than 99% of steel grades
- Limited formability — 8/100, worse than 97% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
- Difficult to machine — 25/100, worse than 93% of steel grades
- Low fracture toughness — 40 MPa·√m (36.4 ksi·√in), worse than 92% of steel grades
70Mn4 +QT40 properties
Typical room-temperature values for 70Mn4 +QT40; 18 are specific to this condition. Other listed values are 70Mn4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
70Mn4 +QT40 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
70Mn4 +QT40 has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Elongation at break is 8% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
70Mn4 +QT40 is rated for continuous service to 300°C (572 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
70Mn4 +QT40 conducts electricity at 9 % IACS, better than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 70Mn4 +QT40 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
70Mn4 +QT40's machinability is poor (25/100, worse than 93% of steel grades); weldability not recommended (8/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 70Mn4 +QT40
Is 70Mn4 easy to machine?
Machine only in the +A or +S condition with sharp carbide tooling and generous coolant; above ~45 HRC switch to grinding, CBN turning or EDM.
Can 70Mn4 be welded?
Effectively non-weldable for structural joints (CE ≈ 0.9); if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and post-weld temper immediately.
Can 70Mn4 be formed, bent or molded?
Bend and blank only from the annealed strip with bend radii ≥ 2–3 t across the rolling direction; hot form 850–1050 °C, then normalize before hardening — harden 800–830 °C in oil, temper 160–500 °C to the required hardness.
What surface finishes work on 70Mn4?
No inherent corrosion protection — phosphate + oil, black oxide, zinc or Zn-Ni plating (bake 190 °C ≥ 4 h after plating to avoid hydrogen embrittlement); shot peening markedly improves spring fatigue life.
70Mn4 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 |
|---|---|---|
| Cgrade-defining carbon level | 0.65 – 0.75 | 0.7 |
| Si | 0.15 – 0.35 | 0.25 |
| Mnraises hardenability vs plain C70 | 0.9 – 1.2 | 1 |
| Pimpurity limit | ≤ 0.03 | — |
| Simpurity limit | ≤ 0.03 | — |
| Crresidual | ≤ 0.4 | — |
| Niresidual | ≤ 0.4 | — |
| Curesidual | ≤ 0.3 | — |
| Fe | balance | — |
70Mn4 +QT40 — frequently asked
What is 70Mn4 +QT40 used for?
70Mn4 +QT40 is typically used for induction-hardened bearing components, springs, wear plates and cutting tools. In short: hardenable spring and wear steel; higher carbon than 56Mn4; essentially non-weldable.
What is the yield strength of 70Mn4 +QT40?
70Mn4 +QT40 has a typical yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 70Mn4 +QT40 easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine only in the +A or +S condition with sharp carbide tooling and generous coolant; above ~45 HRC switch to grinding, CBN turning or EDM.
Can 70Mn4 +QT40 be welded?
Not readily — weldability is rated not recommended (8/100). Effectively non-weldable for structural joints (CE ≈ 0.9); if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and post-weld temper immediately.
What surface finishes work on 70Mn4 +QT40?
No inherent corrosion protection — phosphate + oil, black oxide, zinc or Zn-Ni plating (bake 190 °C ≥ 4 h after plating to avoid hydrogen embrittlement); shot peening markedly improves spring fatigue life.
Can 70Mn4 +QT40 be formed, bent or molded?
Bend and blank only from the annealed strip with bend radii ≥ 2–3 t across the rolling direction; hot form 850–1050 °C, then normalize before hardening — harden 800–830 °C in oil, temper 160–500 °C to the required hardness.
What is the maximum service temperature of 70Mn4 +QT40?
70Mn4 +QT40 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- DIN 17222 — Cold rolled steel strip for springs — DIN (1979)
- EN 10132-4 — Cold rolled narrow steel strip for heat treatment: spring steels — CEN (2000)
- EN 10083-2 — Steels for quenching and tempering: non-alloy steels (delivery conditions +A, +S, +N, +QT) — CEN (2006)
- Stahlschlüssel / Key to Steel — material No. 1.1244 (70Mn4) — Verlag Stahlschlüssel Wegst (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Machinery's Handbook (machinability ratings, heat-treat practice) — Industrial Press (2020)
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.