Steel SMnB443H
SMnB443H is a higher-carbon JIS G4053 manganese-boron steel supplied to the guaranteed H hardenability band, used where the case depth and core strength available from SMnB420H are insufficient.
Reference datasheet — SMnB443H is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the QT28-32HRC condition
SMnB443H tempers and conditions
SMnB443H is supplied in 10 conditions, soft to hard. QT28-32HRC is the default FabDigit quotes; the values on this page are for it.
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 | — |
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?
SMnB443H is a higher-carbon JIS G4053 manganese-boron steel supplied to the guaranteed H hardenability band, used where the case depth and core strength available from SMnB420H are insufficient. It is stocked as hot-rolled, annealed, spheroidized, normalized, cold-drawn and quenched-and-tempered bar; the default Q&T condition gives 780 MPa yield, 950 MPa tensile, 14% elongation and 293 HB (30 HRC), with service to 400 °C. Weldability is poor (Ceq ≈0.7–0.8) and there is no corrosion resistance. Where welded joints are required, drop back to SMnB420H. SMnB443H 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). SMnB443H has a yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi).
What is SMnB443H used for?
- Automotive transmission gears
- Differential ring and pinion gears
- Transmission and countershafts
- Axle shafts
- Heavy-duty sprockets
- Planetary gear carriers
- Induction-hardened pins
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 780 MPa (113 ksi), better than 86% of steel grades
Limitations
- Limited ductility — 14%, worse than 75% of steel grades
SMnB443H properties
Typical room-temperature values for SMnB443H-QT28-32HRC; bars are the position among steel grades.
Physical3
SMnB443H 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 has a yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SMnB443H 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 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 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's machinability is fair (48/100, worse than 57% of steel grades); weldability poor (30/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SMnB443H is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SMnB443H
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
How much does SMnB443H cost?
SMnB443H is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SMnB443H — frequently asked
What is SMnB443H used for?
SMnB443H 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?
SMnB443H has a typical yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is SMnB443H easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% 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 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?
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 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?
SMnB443H 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.
How much does SMnB443H cost?
SMnB443H is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.