Steel 20MnB-HR (Hot rolled)
Supply condition · default condition
GB 20MnB
Standard stock condition for GB/T 3077 20MnB round bar and wire rod, to be heat treated by the part maker.
Values for the HR condition
Other 20MnB tempers and conditions
20MnB is listed in 10 conditions; see the grade overview at 20MnB.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold-heading bolts and screws: spheroidal carbides give the lowest work-hardening and best die life. | 300 | 480 | 30 | 140 HB | 9 % IACS |
Solution annealed | Pick for maximum machinability and stress-free blanks before carburizing or quench-and-temper. | 330 | 540 | 26 | 155 HB | — |
HRDefaultThis page Hot rolled | Standard stock condition for GB/T 3077 20MnB round bar and wire rod, to be heat treated by the part maker. | 400 | 620 | 22 | 170 HB | — |
Normalized | Use to refine forging/rolling structure and give uniform machinability before final hardening. | 420 | 640 | 21 | 180 HB | 8 % IACS |
Cold drawn | Choose for close-tolerance bright bar with higher as-supplied strength for pins and shafts machined without heat treatment. | 600 | 720 | 12 | 17 HRC | 8 % IACS |
quenched + tempered ~600 °C | Softest quench-and-temper option: maximum toughness and easy final machining for larger sections. | 660 | 830 | 19 | 24 HRC | — |
quenched + tempered ~500 °C | Tough medium-hardness condition for shafts, tie rods and machined parts needing good impact strength. | 780 | 950 | 16 | 30 HRC | — |
Carburized and hardened | The main service condition for gears, splines and sprockets: hard wear-resistant case on a tough boron-hardened core. | 850 | 1,100 | 10 | 60 HRC | — |
Quenched 860 °C + tempered 200 °C | The standard property-verification condition of GB/T 3077 and the practical state for high-strength pins, links and 9.8/10.9-class fasteners. | 950 | 1,150 | 12 | 38 HRC | — |
As-quenched | Intermediate condition only — must be tempered; shows the full martensite hardness the boron addition delivers. | 1,150 | 1,450 | 6 | 45 HRC | 7 % IACS |
What is 20MnB-HR?
20MnB-HR is 20MnB supplied in the HR condition — standard stock condition for GB/T 3077 20MnB round bar and wire rod, to be heat treated by the part maker. 20MnB-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi). 20MnB-HR 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).
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
Limitations
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
20MnB-HR properties
Typical room-temperature values for 20MnB-HR; 12 are specific to this condition. Other listed values are 20MnB reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
20MnB-HR 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
20MnB-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
20MnB-HR is rated for continuous service to 300°C (572 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
20MnB-HR conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 20MnB-HR takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
20MnB-HR's machinability is good (60/100, better than 83% of steel grades); weldability good (62/100); formability good (65/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 20MnB-HR
Is 20MnB easy to machine?
Best machined annealed or normalized (~150–190 HB) with carbide at 120–180 m/min; gummy in the as-rolled ferrite-pearlite state, so finish-machine before carburizing and allow 0.2–0.4 mm grind stock for distortion.
Can 20MnB be welded?
Weldable with low-hydrogen electrodes at CE ≈ 0.40; preheat 100–150 °C above 20 mm and post-weld temper, but avoid welding after carburizing or quench-hardening due to hard HAZ cracking.
Can 20MnB be formed, bent or molded?
Excellent cold-heading and upsetting behaviour when spheroidize annealed; hot forge 1150–850 °C followed by normalizing to restore grain size before hardening.
What surface finishes work on 20MnB?
No inherent corrosion resistance — specify zinc/zinc-nickel plating (with 190–220 °C bake to avoid hydrogen embrittlement above 1000 MPa), phosphate + oil, Dacromet or black oxide.
20MnB 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 |
|---|---|---|
| C | 0.17 – 0.24 | 0.2 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 0.8 – 1.1 | 0.95 |
| Beffective (acid-soluble) boron; usually Ti/Al protected against N | 8×10⁻⁴ – 0 | 0 |
| Pmax, high-grade quality | ≤ 0.03 | — |
| Smax, high-grade quality | ≤ 0.03 | — |
| Crresidual max | ≤ 0.3 | — |
| Niresidual max | ≤ 0.3 | — |
| Curesidual max | ≤ 0.25 | — |
| Fe | balance | — |
20MnB-HR — frequently asked
What is 20MnB-HR used for?
20MnB-HR is typically used for gears, shafts and carburized pins. In short: low-cost 20Cr substitute; good cold-heading carburizing steel; boron-boosted hardenability.
What is the yield strength of 20MnB-HR?
20MnB-HR has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 20MnB-HR easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% of steel grades). Best machined annealed or normalized (~150–190 HB) with carbide at 120–180 m/min; gummy in the as-rolled ferrite-pearlite state, so finish-machine before carburizing and allow 0.2–0.4 mm grind stock for distortion.
Can 20MnB-HR be welded?
Yes — weldability is rated good (62/100). Weldable with low-hydrogen electrodes at CE ≈ 0.40; preheat 100–150 °C above 20 mm and post-weld temper, but avoid welding after carburizing or quench-hardening due to hard HAZ cracking.
What surface finishes work on 20MnB-HR?
No inherent corrosion resistance — specify zinc/zinc-nickel plating (with 190–220 °C bake to avoid hydrogen embrittlement above 1000 MPa), phosphate + oil, Dacromet or black oxide.
Can 20MnB-HR be formed, bent or molded?
Excellent cold-heading and upsetting behaviour when spheroidize annealed; hot forge 1150–850 °C followed by normalizing to restore grain size before hardening.
What is the maximum service temperature of 20MnB-HR?
20MnB-HR 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.
What is the difference between 20MnB-HR and 20MnB-Q?
HR is the default condition — standard stock condition for GB/T 3077 20MnB round bar and wire rod, to be heat treated by the part maker. Q: intermediate condition only — must be tempered; shows the full martensite hardness the boron addition delivers. Yield strength is 400 MPa in HR versus 1,150 MPa in Q.
Sources
- GB/T 699 (comparison grades) — SAC (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Machinery's Handbook (machinability and boron steel data) — 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.