Steel 20MnB-CH (Carburized and hardened)
Heat-treated state
GB 20MnB
The main service condition for gears, splines and sprockets: hard wear-resistant case on a tough boron-hardened core.
Values for the CH 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 | — |
HRDefault 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 | — |
CHThis page 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-CH?
20MnB-CH is 20MnB heat treated to CH — the main service condition for gears, splines and sprockets: hard wear-resistant case on a tough boron-hardened core. 20MnB-CH has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 88% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi). 20MnB-CH 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). HR is the default condition FabDigit quotes; CH is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 850 MPa (123 ksi), better than 88% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
Limitations
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
20MnB-CH properties
Typical room-temperature values for 20MnB-CH; 11 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-CH 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-CH has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 88% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
20MnB-CH is rated for continuous service to 180°C (356 °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-CH 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-CH 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-CH's machinability is not recommended (12/100, worse than 99% of steel grades); weldability poor (15/100); formability good (65/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 20MnB-CH
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-CH — frequently asked
What is 20MnB-CH used for?
20MnB-CH 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-CH?
20MnB-CH has a typical yield strength of 850 MPa (123 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 88% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 20MnB-CH easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% 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-CH be welded?
Not readily — weldability is rated poor (15/100). 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-CH?
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-CH 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-CH?
20MnB-CH is rated for continuous use to about 180°C (356 °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.