Steel 100CrMo7-4 +B (Bainite hardened)
Heat-treated state
EN 100CrMo7-4
Austempered lower-bainite condition for heavy-section, shock- or contamination-loaded bearings: compressive surface stresses, better toughness and crack resistance than martensite.
Values for the +B condition
Other 100CrMo7-4 tempers and conditions
100CrMo7-4 is listed in 7 conditions; see the grade overview at 100CrMo7-4.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACDefault Spheroidize annealed | Standard stock condition for bearing-ring blanks: soft, globular carbide structure giving the best machinability and cold-forming behaviour before hardening. | 410 | 680 | 20 | 207 HB | 44 W/m·K |
Annealed | General soft-annealed delivery condition when a full spheroidized carbide structure is not contractually required. | 420 | 700 | 18 | 17 HRC | 6.6 % IACS |
Hot rolled | Mill-supplied as-rolled bar for re-heating/forging; hardness too high and structure too banded for direct machining. | 560 | 950 | 10 | 30 HRC | 6.4 % IACS |
Spheroidize annealed and cold drawn bar | Choose for close-tolerance bright bar (rollers, pins, small rings) where the drawn surface and size accuracy save a turning operation. | 620 | 780 | 11 | 235 HB | — |
+BThis page Bainite hardened | Austempered lower-bainite condition for heavy-section, shock- or contamination-loaded bearings: compressive surface stresses, better toughness and crack resistance than martensite. | 1,650 | 2,000 | 1.5 | 60 HRC | — |
+QT 58–61 HRC | Higher-temper condition for rings that must stay dimensionally stable at elevated running temperature (up to ~180 °C) at slight hardness cost. | 1,750 | 2,050 | 1 | 60 HRC | 36 W/m·K |
+QT 61–64 HRC | Standard finished-bearing condition: maximum hardness and rolling-contact fatigue life for raceways and rolling elements up to ~150 °C. | 1,950 | 2,250 | 0.7 | 62 HRC | 34 W/m·K |
What is 100CrMo7-4 +B?
100CrMo7-4 +B is 100CrMo7-4 heat treated to +B — austempered lower-bainite condition for heavy-section, shock- or contamination-loaded bearings: compressive surface stresses, better toughness and crack resistance than martensite. 100CrMo7-4 +B has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 99% of steel grades. Elongation at break is 1.5% and the elastic modulus is 210 GPa (30.5 Msi). 100CrMo7-4 +B has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F). +AC is the default condition FabDigit quotes; +B is available on request or by drawing note.
Advantages
- High strength — 1,650 MPa (239 ksi), better than 99% of steel grades
- Polishes to a fine finish — 85/100, better than 99% of steel grades
Limitations
- Difficult to machine — 6/100, worse than 100% of steel grades
- Difficult to weld — 4/100, worse than 100% of steel grades
- Limited ductility — 1.5%, worse than 99% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low electrical conductivity — 6.5 % IACS, worse than 77% of steel grades
100CrMo7-4 +B properties
Typical room-temperature values for 100CrMo7-4 +B; 13 are specific to this condition. Other listed values are 100CrMo7-4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
100CrMo7-4 +B has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
100CrMo7-4 +B has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 99% of steel grades. Elongation at break is 1.5% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
100CrMo7-4 +B is rated for continuous service to 200°C (392 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
100CrMo7-4 +B conducts electricity at 6.5 % IACS, worse than 77% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 100CrMo7-4 +B takes about 33 MJ of energy and emits 2.3 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 25%.
Manufacturability8
100CrMo7-4 +B's machinability is not recommended (6/100, worse than 100% of steel grades); weldability not recommended (4/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 100CrMo7-4 +B
Is 100CrMo7-4 easy to machine?
Machine only in the spheroidized (+AC) state with coated carbide at moderate speed; after hardening use CBN hard turning or grinding.
Can 100CrMo7-4 be welded?
Effectively non-weldable at ~1 %C — any fusion welding cracks; use shrink fits, bolting or friction welding with full post-weld heat treatment on non-critical joints.
Can 100CrMo7-4 be formed, bent or molded?
Cold ring rolling / cold heading possible only in fully spheroidized bar; hot forge 1050–1100 °C and cool slowly to avoid network carbides and flakes.
What surface finishes work on 100CrMo7-4?
Hardened raceways are ground and superfinished to Ra <0.05 µm; protect with preservative oil, phosphate, black oxide or thin dense chrome — no anodizing.
100CrMo7-4 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 | 0.92 – 1.05 | 0.98 |
| Si | 0.2 – 0.4 | 0.3 |
| Mn | 0.6 – 0.8 | 0.7 |
| Cr | 1.65 – 1.95 | 1.8 |
| MoMo addition gives deep hardenability in heavy sections | 0.4 – 0.6 | 0.5 |
| P | ≤ 0.03 | — |
| S | ≤ 0.02 | — |
| Niresidual, max | ≤ 0.25 | — |
| Curesidual, max | ≤ 0.3 | — |
| Alresidual, max | ≤ 0.05 | — |
| O≤15 ppm total oxygen for bearing quality | ≤ 0 | — |
| Fe | balance | — |
100CrMo7-4 +B — frequently asked
What is 100CrMo7-4 +B used for?
100CrMo7-4 +B is typically used for large-diameter rolling bearings, slewing ring bearings and heavy industrial bearing races. In short: heavy-section bearing steel; deep through-hardenability; bainite-hardened option available.
What is the yield strength of 100CrMo7-4 +B?
100CrMo7-4 +B has a typical yield strength of 1,650 MPa (239 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 100CrMo7-4 +B easy to machine?
Not especially — machinability is rated not recommended (6/100, worse than 100% of steel grades). Machine only in the spheroidized (+AC) state with coated carbide at moderate speed; after hardening use CBN hard turning or grinding.
Can 100CrMo7-4 +B be welded?
Not readily — weldability is rated not recommended (4/100). Effectively non-weldable at ~1 %C — any fusion welding cracks; use shrink fits, bolting or friction welding with full post-weld heat treatment on non-critical joints.
What surface finishes work on 100CrMo7-4 +B?
Hardened raceways are ground and superfinished to Ra <0.05 µm; protect with preservative oil, phosphate, black oxide or thin dense chrome — no anodizing.
Can 100CrMo7-4 +B be formed, bent or molded?
Cold ring rolling / cold heading possible only in fully spheroidized bar; hot forge 1050–1100 °C and cool slowly to avoid network carbides and flakes.
What is the maximum service temperature of 100CrMo7-4 +B?
100CrMo7-4 +B is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 100CrMo7-4 +AC and 100CrMo7-4-HR?
+AC is the default condition — standard stock condition for bearing-ring blanks: soft, globular carbide structure giving the best machinability and cold-forming behaviour before hardening. HR: mill-supplied as-rolled bar for re-heating/forging; hardness too high and structure too banded for direct machining. Yield strength is 410 MPa in +AC versus 560 MPa in HR.
Sources
- ISO 683-17 Heat-treatable steels, alloy steels and free-cutting steels — Part 17: Ball and roller bearing steels — ISO (2014)
- EN 10027-2 Designation systems for steels — Steel numbers (1.3538) — CEN (2015)
- ASM Handbook Vol. 1: Properties and Selection — Bearing Steels — ASM International (1990)
- Bearing steel bar datasheets (100Cr6 / 100CrMo7 / 100CrMo7-4 family) — Ovako / Sandvik / Böhler (2023)
- Machinery's Handbook — machinability ratings for high-carbon chromium steels — 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.