Steel 15MnB
GB 15MnB
15MnB is a low-carbon manganese-boron case-hardening steel that uses boron to reach hardenability levels otherwise requiring chromium-molybdenum carburizing grades.
Reference datasheet — 15MnB 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 HR condition
15MnB tempers and conditions
15MnB is supplied in 8 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold-forged bolts, nuts and rivets where maximum cold upsettability is required. | 270 | 450 | 30 | 135 HB | 8.5 % IACS |
Solution annealed | Pick for maximum softness and dimensional stability before heavy machining or deep drawing. | 310 | 510 | 26 | 156 HB | 8.5 % IACS |
HRDefault Hot rolled | Default mill stock condition for bar and plate before machining and heat treatment. | 380 | 590 | 21 | 187 HB | — |
Normalized | Standard pre-treatment for uniform fine grain and predictable case-hardening response. | 400 | 610 | 22 | 190 HB | 8 % IACS |
Cold drawn | Pick for close-tolerance, bright-finish shafting where strength is raised by drawing rather than heat treatment. | 560 | 680 | 11 | 210 HB | 8 % IACS |
Quenched and tempered | Use for through-hardened shafts, links and structural parts needing balanced strength and toughness. | 660 | 830 | 16 | 24 HRC | — |
Carburized and hardened | Primary service condition for gears, pins and sprockets: hard 0.6–1.2 mm case on a tough low-carbon core. | 780 | 1,000 | 11 | 60 HRC | — |
Quenched and low-temperature tempered | Direct-hardened condition for thin wear parts, tines, blades and chain links needing high hardness at low cost. | 950 | 1,250 | 10 | 41 HRC | — |
What is 15MnB?
15MnB is a low-carbon manganese-boron case-hardening steel that uses boron to reach hardenability levels otherwise requiring chromium-molybdenum carburizing grades. It is supplied as hot-rolled, annealed, spheroidize-annealed, normalized, cold-drawn, quench-tempered and cold-heading quality bar and wire, with default values of 380 MPa yield, 590 MPa tensile, 21 % elongation and 187 HB, weldability 72 and formability 62. Boron hardenability is destroyed by soaking above about 1200 °C, and the steel has no natural corrosion resistance. 20MnB is the higher-carbon step up when more core strength is needed. 15MnB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). 15MnB has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 68% of steel grades. Elongation at break is 21% and the elastic modulus is 210 GPa (30.5 Msi).
What is 15MnB used for?
- small gears
- pins
- bushings
Advantages
- Forms and bends easily — 62/100, better than 78% of steel grades
- Readily welded — 72/100, better than 75% of steel grades
15MnB properties
Typical room-temperature values for 15MnB-HR; bars are the position among steel grades.
Physical3
15MnB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
15MnB has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 68% of steel grades. Elongation at break is 21% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
15MnB is rated for continuous service to 350°C (662 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
15MnB conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 15MnB takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
15MnB's machinability is good (58/100, better than 75% of steel grades); weldability very good (72/100); formability good (62/100).
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. 15MnB is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 15MnB
Is 15MnB easy to machine?
Machine in the annealed or normalized state (~160–200 HB) with carbide at 120–180 m/min; the gummy low-carbon matrix needs positive rake and good chip control, and finish-machining after case hardening requires grinding.
Can 15MnB be welded?
Weldable by MIG/MAG, SMAW or resistance welding with CE(IIW) ≈ 0.40; preheat 100–150 °C on sections over ~20 mm, use low-hydrogen consumables, and avoid welding after carburizing.
Can 15MnB be formed, bent or molded?
Excellent cold heading and bending in the spheroidize-annealed condition; hot forge 1150–850 °C and avoid soaking above ~1200 °C or repeated high-temperature austenitising, which destroys the boron hardenability effect.
15MnB 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 |
|---|---|---|
| Ccase-hardening carbon level | 0.12 – 0.18 | 0.15 |
| Si | 0.17 – 0.37 | 0.27 |
| Mnmain hardenability element | 1 – 1.4 | 1.2 |
| Beffective (acid-soluble) boron | 8×10⁻⁴ – 0 | 0 |
| AlAlt, added to fix nitrogen and protect boron | 0.02 – 0.06 | 0.04 |
| Tioptional nitrogen fixer in some mill practices | ≤ 0.05 | |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.02 |
| Crresidual | ≤ 0.25 | |
| Niresidual | ≤ 0.3 | |
| Curesidual | ≤ 0.25 | |
| Fe | balance |
What surface finishes work on 15MnB?
No natural corrosion resistance — specify zinc or zinc–nickel plating, phosphate + oil, black oxide, hot-dip galvanizing (avoid for hardened parts due to hydrogen/temper risk) or painting; bake after plating to prevent hydrogen embrittlement in hardened conditions.
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 15MnB cost?
15MnB 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.
15MnB — frequently asked
What is 15MnB used for?
15MnB is typically used for small gears, pins and bushings. In short: economical Cr-Mo case-hardening substitute; high weldability for boron steel; cold-heading quality available.
What is the yield strength of 15MnB?
15MnB has a typical yield strength of 380 MPa (55.1 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 68% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 15MnB easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machine in the annealed or normalized state (~160–200 HB) with carbide at 120–180 m/min; the gummy low-carbon matrix needs positive rake and good chip control, and finish-machining after case hardening requires grinding.
Can 15MnB be welded?
Yes — weldability is rated very good (72/100). Weldable by MIG/MAG, SMAW or resistance welding with CE(IIW) ≈ 0.40; preheat 100–150 °C on sections over ~20 mm, use low-hydrogen consumables, and avoid welding after carburizing.
What surface finishes work on 15MnB?
No natural corrosion resistance — specify zinc or zinc–nickel plating, phosphate + oil, black oxide, hot-dip galvanizing (avoid for hardened parts due to hydrogen/temper risk) or painting; bake after plating to prevent hydrogen embrittlement in hardened conditions.
Can 15MnB be formed, bent or molded?
Excellent cold heading and bending in the spheroidize-annealed condition; hot forge 1150–850 °C and avoid soaking above ~1200 °C or repeated high-temperature austenitising, which destroys the boron hardenability effect.
What is the maximum service temperature of 15MnB?
15MnB is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 15MnB-HR and 15MnB QT-LT?
HR is the default condition — default mill stock condition for bar and plate before machining and heat treatment. QT-LT: direct-hardened condition for thin wear parts, tines, blades and chain links needing high hardness at low cost. Yield strength is 380 MPa in HR versus 950 MPa in QT-LT.
How much does 15MnB cost?
15MnB 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
- GB/T 3077 (alloy structural steels, boron grades) (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4: Heat Treating (boron steels, carburizing) — ASM International (1991)
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.