Steel SUJ4-BH (Bainite hardened)
Heat-treated state
JIS SUJ4
Lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting.
Values for the BH condition
Other SUJ4 tempers and conditions
SUJ4 is listed in 7 conditions; see the grade overview at SUJ4.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard supply condition for machining rings, rollers and blanks before hardening. | 420 | 700 | 22 | 190 HB | 45 W/m·K |
Hot rolled | Cheapest mill condition for forging or ring-rolling stock; must be spheroidize annealed before machining. | 550 | 950 | 12 | 27 HRC | 3.5 % IACS |
Cold drawn | Bright-drawn bar and cold-heading wire for small rollers, pins and turned parts with good size tolerance. | 620 | 800 | 12 | 21 HRC | 3.5 % IACS |
high-temperature tempered (300–350 °C) for elevated-temperature service | Choose for bearings and rolls running up to ~250 °C, where the Mo addition preserves hardness after high tempering. | 1,650 | 1,950 | 1 | 57 HRC | 3 % IACS |
BHThis page Bainite hardened | Lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting. | 1,750 | 2,100 | 2 | 60 HRC | 3.2 % IACS |
tempered 200–250 °C (dimensionally stabilized, S1/TS class) | Pick when the part sees 150–200 °C and dimensional stability matters more than peak hardness. | 1,800 | 2,150 | — | 60 HRC | 35 W/m·K |
oil/salt quenched, tempered 150–180 °C (standard martensitic hardening) | Standard finished-bearing condition: maximum contact fatigue life and wear resistance for service below ~120 °C. | 1,900 | 2,350 | 1 | 62 HRC | 34 W/m·K |
What is SUJ4-BH?
SUJ4-BH is SUJ4 heat treated to BH — lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting. SUJ4-BH has a yield strength of 1,750 MPa (254 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Elongation at break is 2% and the elastic modulus is 208 GPa (30.2 Msi). SUJ4-BH has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,400°C (2,552 °F). A is the default condition FabDigit quotes; BH is available on request or by drawing note.
Advantages
- High strength — 1,750 MPa (254 ksi), better than 99% of steel grades
- Polishes to a fine finish — 85/100, better than 99% of steel grades
Limitations
- Difficult to machine — 5/100, worse than 100% of steel grades
- Difficult to weld — 3/100, worse than 100% of steel grades
- Limited formability — 2/100, worse than 100% of steel grades
- Limited ductility — 2%, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
SUJ4-BH properties
Typical room-temperature values for SUJ4-BH; 22 are specific to this condition. Other listed values are SUJ4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUJ4-BH has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
SUJ4-BH has a yield strength of 1,750 MPa (254 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Elongation at break is 2% and the elastic modulus is 208 GPa (30.2 Msi).
Thermal6
SUJ4-BH is rated for continuous service to 180°C (356 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SUJ4-BH conducts electricity at 3.2 % IACS, worse than 87% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SUJ4-BH takes about 33 MJ of energy and emits 2.4 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 25%.
Manufacturability7
SUJ4-BH's machinability is not recommended (5/100, worse than 100% of steel grades); weldability not recommended (3/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUJ4-BH
Is SUJ4 easy to machine?
Machine only in the spheroidize-annealed condition (≈40% of AISI 1212) with coated carbide and rigid setups; hardened 60+ HRC parts require grinding, honing or CBN hard turning.
Can SUJ4 be welded?
Essentially unweldable — ~1% C gives severe quench cracking; if repair is unavoidable use 300–400 °C preheat, low-hydrogen consumables and immediate post-weld temper.
Can SUJ4 be formed, bent or molded?
Hot forge/ring-roll at 1050–1100 °C (stop above ~900 °C) then spheroidize anneal at 780–800 °C with slow cooling; cold heading and cold ring rolling need fully spheroidized structure.
What surface finishes work on SUJ4?
Not anodizable; protect with rust-preventive oil, phosphate, black oxide or thin dense chrome, and superfinish/lap raceways to Ra ≤0.05 µm for bearing life.
SUJ4 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 | 0.95 – 1.1 | 1.02 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | ≤ 0.5 | 0.35 |
| Cr | 1.3 – 1.6 | 1.45 |
| Mothe distinguishing addition vs SUJ2; raises hardenability | 0.1 – 0.25 | 0.18 |
| Pimpurity limit | ≤ 0.03 | — |
| Simpurity limit | ≤ 0.03 | — |
| Niresidual | ≤ 0.25 | — |
| Curesidual | ≤ 0.25 | — |
| Ototal oxygen, vacuum-degassed bearing quality | ≤ 0 | 8×10⁻⁴ |
| Fe | balance | — |
SUJ4-BH — frequently asked
What is SUJ4-BH used for?
SUJ4-BH is typically used for large bearing rings and races, heavy-duty cylindrical rollers, thick-section tapered roller cups and cones, spherical roller bearing outer rings, gearbox and wind turbine bearing components and cam followers and track rollers. In short: deeper-hardening SUJ2 alternative; mo-alloyed bearing steel; for thick bearing sections.
What is the yield strength of SUJ4-BH?
SUJ4-BH has a typical yield strength of 1,750 MPa (254 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is SUJ4-BH easy to machine?
Not especially — machinability is rated not recommended (5/100, worse than 100% of steel grades). Machine only in the spheroidize-annealed condition (≈40% of AISI 1212) with coated carbide and rigid setups; hardened 60+ HRC parts require grinding, honing or CBN hard turning.
Can SUJ4-BH be welded?
Not readily — weldability is rated not recommended (3/100). Essentially unweldable — ~1% C gives severe quench cracking; if repair is unavoidable use 300–400 °C preheat, low-hydrogen consumables and immediate post-weld temper.
What surface finishes work on SUJ4-BH?
Not anodizable; protect with rust-preventive oil, phosphate, black oxide or thin dense chrome, and superfinish/lap raceways to Ra ≤0.05 µm for bearing life.
Can SUJ4-BH be formed, bent or molded?
Hot forge/ring-roll at 1050–1100 °C (stop above ~900 °C) then spheroidize anneal at 780–800 °C with slow cooling; cold heading and cold ring rolling need fully spheroidized structure.
What is the maximum service temperature of SUJ4-BH?
SUJ4-BH 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 SUJ4-A and SUJ4-BH?
A is the default condition — standard supply condition for machining rings, rollers and blanks before hardening. BH: lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting. Yield strength is 420 MPa in A versus 1,750 MPa in BH.
Sources
- JIS G 4805 High carbon chromium bearing steels — JSA (2019)
- ISO 683-17 Heat-treatable steels — Ball and roller bearing steels — ISO (2014)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels (bearing steels) — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- Bearing steel grades 100Cr6 / 100CrMo7 data sheets — Sanyo Special Steel / Ovako (2022)
- GCr15/GCr15SiMo — Mysteel / 1688 (2025)
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.