Steel SMnB443H QT40-45HRC
Hardness band
Maximum through-hardened strength for small sections; toughness and machinability drop sharply.
Values for the QT40-45HRC condition
Other SMnB443H tempers and conditions
SMnB443H is listed in 10 conditions; see the grade overview at SMnB443H.
- SA
- A
- HR
- N
- CD
- QT22-26HRC
- QT28-32HRC
- IH
- QT32-36HRC
- QT40-45HRC
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold heading/forging of bolts and gear blanks before quench and temper. | 340 | 600 | 25 | 170 HB | 8.6 % IACS |
Solution annealed | Softest condition for heavy machining or cold work before hardening. | 370 | 650 | 22 | 10 HRC | 8.5 % IACS |
Hot rolled | Mill supply condition for bars that will be re-heat-treated by the part maker. | 430 | 760 | 18 | 17 HRC | 8.2 % IACS |
Normalized | Uniform fine pearlitic structure for stable machining and pre-hardening grain refinement. | 480 | 810 | 17 | 21 HRC | 8 % IACS |
Cold drawn | Bright, size-accurate bar for parts machined near final size and hardened afterwards. | 660 | 820 | 12 | 22 HRC | 7.9 % IACS |
quenched and high-temperature tempered | Tough, easily machined condition for large shafts where toughness beats peak strength. | 660 | 830 | 17 | 24 HRC | — |
QT28-32HRCDefault quenched and tempered (standard supply) | Default balance of strength and toughness for gears, shafts and connecting rods. | 780 | 950 | 14 | 30 HRC | — |
Induction hardened | Pick for gear teeth, journals and splines needing a hard wear surface with a tough core. | 780 | 950 | 13 | 57 HRC | 7.5 % IACS |
quenched and low-temperature tempered | Higher-strength condition for heavily loaded gear blanks and high-tensile fasteners. | 910 | 1,080 | 12 | 34 HRC | — |
QT40-45HRCThis page quenched and tempered high strength | Maximum through-hardened strength for small sections; toughness and machinability drop sharply. | 1,180 | 1,350 | 10 | 42 HRC | — |
What is SMnB443H QT40-45HRC?
SMnB443H QT40-45HRC is SMnB443H heat treated to QT40-45HRC — maximum through-hardened strength for small sections; toughness and machinability drop sharply. SMnB443H QT40-45HRC has a yield strength of 1,180 MPa (171 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi). SMnB443H QT40-45HRC 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). QT28-32HRC is the default condition FabDigit quotes; QT40-45HRC is available on request or by drawing note.
Advantages
- High strength — 1,180 MPa (171 ksi), better than 94% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
- Difficult to machine — 28/100, worse than 91% of steel grades
SMnB443H QT40-45HRC properties
Typical room-temperature values for SMnB443H QT40-45HRC; 11 are specific to this condition. Other listed values are SMnB443H reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SMnB443H QT40-45HRC 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
SMnB443H QT40-45HRC has a yield strength of 1,180 MPa (171 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMnB443H QT40-45HRC is rated for continuous service to 400°C (752 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
SMnB443H QT40-45HRC 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 SMnB443H QT40-45HRC takes about 26 MJ of energy and emits 1.9 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability6
SMnB443H QT40-45HRC's machinability is poor (28/100, worse than 91% of steel grades); weldability poor (30/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SMnB443H QT40-45HRC
Is SMnB443H easy to machine?
Machine in the annealed or ≤30 HRC condition with coated carbide, moderate speed and rigid setup; boron does not embrittle chips but Q&T above 34 HRC cuts tool life sharply.
Can SMnB443H be welded?
Poor weldability (Ceq ≈ 0.7–0.8) — preheat 250–350 °C, low-hydrogen consumables and immediate stress-relief/temper, otherwise martensitic HAZ cracking.
Can SMnB443H be formed, bent or molded?
Cold head or bend only after spheroidize annealing; otherwise hot forge 1100–1200 °C and normalize before hardening.
What surface finishes work on SMnB443H?
No inherent corrosion resistance — use black oxide, phosphate + oil, zinc plate (with bake to avoid hydrogen embrittlement above 32 HRC), nitriding or paint.
SMnB443H 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 widened range | 0.39 – 0.46 | 0.43 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 1.1 – 1.5 | 1.3 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Beffective boron; requires Ti/Al for N fixing | 8×10⁻⁴ – 0 | 0 |
| Curesidual max | ≤ 0.3 | — |
| Niresidual max | ≤ 0.25 | — |
| Crresidual max | ≤ 0.35 | — |
| Fe | balance | — |
SMnB443H QT40-45HRC — frequently asked
What is SMnB443H QT40-45HRC used for?
SMnB443H QT40-45HRC is typically used for automotive transmission gears, differential ring and pinion gears, transmission and countershafts, axle shafts, heavy-duty sprockets and planetary gear carriers. In short: deep-hardening boron gear steel; higher carbon than SMnB420H; poor weldability.
What is the yield strength of SMnB443H QT40-45HRC?
SMnB443H QT40-45HRC has a typical yield strength of 1,180 MPa (171 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is SMnB443H QT40-45HRC easy to machine?
Not especially — machinability is rated poor (28/100, worse than 91% of steel grades). Machine in the annealed or ≤30 HRC condition with coated carbide, moderate speed and rigid setup; boron does not embrittle chips but Q&T above 34 HRC cuts tool life sharply.
Can SMnB443H QT40-45HRC be welded?
Not readily — weldability is rated poor (30/100). Poor weldability (Ceq ≈ 0.7–0.8) — preheat 250–350 °C, low-hydrogen consumables and immediate stress-relief/temper, otherwise martensitic HAZ cracking.
What surface finishes work on SMnB443H QT40-45HRC?
No inherent corrosion resistance — use black oxide, phosphate + oil, zinc plate (with bake to avoid hydrogen embrittlement above 32 HRC), nitriding or paint.
Can SMnB443H QT40-45HRC be formed, bent or molded?
Cold head or bend only after spheroidize annealing; otherwise hot forge 1100–1200 °C and normalize before hardening.
What is the maximum service temperature of SMnB443H QT40-45HRC?
SMnB443H QT40-45HRC 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 SMnB443H QT28-32HRC and SMnB443H-SA?
QT28-32HRC is the default condition — default balance of strength and toughness for gears, shafts and connecting rods. SA: choose for cold heading/forging of bolts and gear blanks before quench and temper. Yield strength is 780 MPa in QT28-32HRC versus 340 MPa in SA.
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) — ASM International (2013)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- Mysteel / SMM special bar steel price quotations (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.