Steel 31CrMo12
EN 31CrMo12
31CrMo12 (1.8515) is a high-chromium, aluminium-free low-alloy nitriding steel from the European nitriding-steel family, relying on chromium and molybdenum for deep hardenability and a hard nitrided case.
Reference datasheet — 31CrMo12 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 +QT condition
31CrMo12 tempers and conditions
31CrMo12 is supplied in 8 conditions, soft to hard. +QT 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 |
|---|---|---|---|---|---|---|
Annealed | Choose the soft annealed bar (≤ 248 HB) when rough machining or cold working comes first, then quench, temper and nitride afterwards; yield is only 470 MPa in this state. | 470 | 800 | 18 | 230 HB | — |
Hot rolled | Order untreated hot-rolled or forged stock only when you will anneal or quench and temper in house; hardness near 270 HB is not controlled and machining response varies. | 550 | 900 | 14 | 27 HRC | 6.9 % IACS |
Normalized | Pick normalized forgings or billets for a refined, uniform microstructure at 600 MPa yield and 280 HB — between annealed and quenched-and-tempered — as an intermediate stage before final Q&T. | 600 | 950 | 15 | 29 HRC | 6.9 % IACS |
+QT | Specify for 250-500 mm forgings and bar, where deep hardenability still holds 740 MPa yield and Rm 880-1080 MPa at the core; strength drops further as section size grows. | 740 | 980 | 15 | 31 HRC | 6.6 % IACS |
+QT | Use for 100-250 mm sections quenched and tempered to Rm 980-1180 MPa; the slower cooling of medium bar leaves core strength at 850 MPa yield, slightly below thin sections. | 850 | 1,060 | 13 | 34 HRC | 6.6 % IACS |
+QTDefault Quenched and tempered | Choose oil quenched and high-temperature tempered bar up to 100 mm diameter (Rm 1030-1230 MPa) as the usual stock condition for finish machining before gas nitriding. | 900 | 1,100 | 13 | 35 HRC | — |
+QT + gas nitrided | Select the finished state — quenched and tempered, then gas nitrided to 800-950 HV with a 0.3-0.6 mm case — for maximum wear and fatigue resistance; no machining is possible after nitriding. | 900 | 1,100 | 12 | 66 HRC | — |
Peeled/turned and cold-drawn or ground bar | Pick peeled, cold-drawn or ground bright bar when tight diameter tolerance and surface quality let you go straight to finish machining and nitriding; core is annealed or quenched and tempered. | 900 | 1,100 | 11 | 35 HRC | 6.6 % IACS |
What is 31CrMo12?
31CrMo12 (1.8515) is a high-chromium, aluminium-free low-alloy nitriding steel from the European nitriding-steel family, relying on chromium and molybdenum for deep hardenability and a hard nitrided case. It is used for heavily stressed nitrided components in large sections, supplied as Q&T bar and forgings at about 900 MPa yield, 1100 MPa tensile, 13 % elongation and 340 HB (35 HRC), with service to 480 °C. Weldability is poor, machinability is low (score 40), and the base steel has no corrosion resistance without nitriding or plating. 41CrAlMo7-10 gives a harder case where slightly lower core strength is acceptable. 31CrMo12 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). 31CrMo12 has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Elongation at break is 13% and the elastic modulus is 210 GPa (30.5 Msi).
What is 31CrMo12 used for?
- heavy machinery shafts
- gears
- high-wear tooling components
Advantages
- High strength — 900 MPa (131 ksi), better than 90% of steel grades
- High service temperature — 480°C (896 °F), better than 88% of steel grades
Limitations
- Limited formability — 20/100, worse than 80% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
- Poor heat conductor — 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
31CrMo12 properties
Typical room-temperature values for 31CrMo12-+QT; bars are the position among steel grades.
Physical3
31CrMo12 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
31CrMo12 has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Elongation at break is 13% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
31CrMo12 is rated for continuous service to 480°C (896 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
31CrMo12 conducts electricity at 6.6 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of 31CrMo12 takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
31CrMo12's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (25/100); formability poor (20/100).
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. 31CrMo12 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 31CrMo12
Is 31CrMo12 easy to machine?
In the quenched and tempered condition (~340 HB) it turns and mills normally with coated carbide at roughly 0.7–0.8 times the cutting speed used for 42CrMo4. After nitriding only grinding or honing is possible, and stock removal must stay below 0.05 mm per face to preserve the case.
Can 31CrMo12 be welded?
Weldability is poor because of the high carbon equivalent: preheat to 250–350 °C, use low-hydrogen or matching Cr-Mo consumables and temper immediately after welding below the original tempering temperature. Nitrided parts should not be welded.
Can 31CrMo12 be formed, bent or molded?
Warm or hot forge annealed material at 1100–850 °C followed by slow cooling or annealing. In the Q&T condition cold forming is not practical, and bending or stamping do not apply.
31CrMo12 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 | 0.28 – 0.35 | 0.31 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.4 – 0.7 | 0.55 |
| Pimpurity limit | ≤ 0.03 | |
| Simpurity limit; free-machining variant may be 0.020–0.040 | ≤ 0.04 | |
| Cr | 2.8 – 3.3 | 3.05 |
| Mo | 0.3 – 0.5 | 0.4 |
| Fe | balance |
What surface finishes work on 31CrMo12?
Stress relieve at approximately 550–600 °C after rough machining to limit nitriding distortion; anodizing does not apply. Final surfaces can be black-oxided, phosphated, hard chrome plated, or left as the nitrided layer with optional post-oxidation for wear and corrosion resistance.
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
Equivalent designations
Standards and trade names that resolve to Steel 31CrMo12 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- EN / DIN / Werkstoff-Nr.
- 1.8515
How much does 31CrMo12 cost?
31CrMo12 is a standard-cost steel ($$), cheaper than about 71% 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.
31CrMo12 — frequently asked
What is 31CrMo12 used for?
31CrMo12 is typically used for heavy machinery shafts, gears and high-wear tooling components. In short: aluminium-free nitriding steel; highest core strength here; deep hardenability, large sections.
What is the yield strength of 31CrMo12?
31CrMo12 has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 31CrMo12 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). In the quenched and tempered condition (~340 HB) it turns and mills normally with coated carbide at roughly 0.7–0.8 times the cutting speed used for 42CrMo4. After nitriding only grinding or honing is possible, and stock removal must stay below 0.05 mm per face to preserve the case.
Can 31CrMo12 be welded?
Not readily — weldability is rated poor (25/100). Weldability is poor because of the high carbon equivalent: preheat to 250–350 °C, use low-hydrogen or matching Cr-Mo consumables and temper immediately after welding below the original tempering temperature. Nitrided parts should not be welded.
What surface finishes work on 31CrMo12?
Stress relieve at approximately 550–600 °C after rough machining to limit nitriding distortion; anodizing does not apply. Final surfaces can be black-oxided, phosphated, hard chrome plated, or left as the nitrided layer with optional post-oxidation for wear and corrosion resistance.
Can 31CrMo12 be formed, bent or molded?
Warm or hot forge annealed material at 1100–850 °C followed by slow cooling or annealing. In the Q&T condition cold forming is not practical, and bending or stamping do not apply.
What is the maximum service temperature of 31CrMo12?
31CrMo12 is rated for continuous use to about 480°C (896 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 31CrMo12 cost?
31CrMo12 is a standard-cost steel ($$), cheaper than about 71% 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
- EN 10085 — Nitriding steels — Technical delivery conditions — CEN (2001)
- DIN 17211 (withdrawn, historical nitriding steel data) — DIN (1987)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals (nitriding) — ASM International (2013)
- Nitriding steel 1.8515 / 31CrMo12 bar datasheet — Böhler / Ovako / Lucchini (typical mill data) (2022)
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.