Steel SUJ3-BQ (Austempered)
Heat-treated state
JIS SUJ3
Preferred for large railway, rolling-mill and thick-section bearings: compressive surface residual stress, better toughness and less risk of quench cracking than martensitic hardening.
Values for the BQ condition
Other SUJ3 tempers and conditions
SUJ3 is listed in 8 conditions; see the grade overview at SUJ3.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | The condition bearing bar and tube are normally bought in: soft, uniform spheroidal carbides, ready for turning and subsequent hardening. | 400 | 660 | 21 | 195 HB | 44 W/m·K |
Hot rolled | As-supplied bar or forging before spheroidising; too hard and carbide-networked for machining, an intermediate state only. | 600 | 980 | 10 | 30 HRC | 8 % IACS |
Cold drawn | Choose for close-tolerance, bright small-diameter bar and rollers where limited stock removal is wanted before hardening. | 640 | 820 | 10 | 24 HRC | 8 % IACS |
Normalized | Used after forging on heavy sections to break up network carbides; always followed by spheroidising, not a delivery condition. | 650 | 1,050 | 9 | 34 HRC | 8 % IACS |
BQThis page Austempered | Preferred for large railway, rolling-mill and thick-section bearings: compressive surface residual stress, better toughness and less risk of quench cracking than martensitic hardening. | 1,550 | 1,950 | 4 | 59 HRC | — |
Hardened, stabilising temper 240–260 °C | Dimensional-stability (S1-type) temper for bearings running continuously up to about 180 °C, at the cost of a few HRC. | 1,600 | 1,900 | 3 | 58 HRC | — |
Oil hardened, tempered 180–200 °C | Standard bearing temper: slightly lower hardness than QT160 with better toughness and stability to ~150 °C. | 1,700 | 2,050 | 2 | 61 HRC | 35 W/m·K |
Oil hardened, tempered 150–170 °C | Maximum hardness and rolling-contact fatigue life for rings and rollers running below ~120 °C. | 1,800 | 2,200 | 1 | 62 HRC | 34 W/m·K |
What is SUJ3-BQ?
SUJ3-BQ is SUJ3 heat treated to BQ — preferred for large railway, rolling-mill and thick-section bearings: compressive surface residual stress, better toughness and less risk of quench cracking than martensitic hardening. SUJ3-BQ has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 97% of steel grades. Elongation at break is 4% and the elastic modulus is 208 GPa (30.2 Msi). SUJ3-BQ 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; BQ is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Difficult to machine — 6/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- Limited ductility — 4%, worse than 98% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
SUJ3-BQ properties
Typical room-temperature values for SUJ3-BQ; 11 are specific to this condition. Other listed values are SUJ3 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUJ3-BQ 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
SUJ3-BQ has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 97% of steel grades. Elongation at break is 4% and the elastic modulus is 208 GPa (30.2 Msi).
Thermal6
SUJ3-BQ is rated for continuous service to 180°C (356 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SUJ3-BQ conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SUJ3-BQ takes about 31 MJ of energy and emits 2.2 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 30%.
Manufacturability7
SUJ3-BQ's machinability is not recommended (6/100, worse than 100% of steel grades); weldability not recommended (8/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUJ3-BQ
Is SUJ3 easy to machine?
Machine only in the spheroidise-annealed state (≈40 % of AISI 1212) with sharp carbide tooling and rigid setups; hardened parts require CBN hard turning or grinding.
Can SUJ3 be welded?
Effectively unweldable — high carbon plus Si/Mn gives quench cracking; if unavoidable, preheat 300–400 °C, use low-hydrogen filler and immediate post-weld temper.
Can SUJ3 be formed, bent or molded?
Hot forge 1050–1150 °C (stop above 850 °C) then normalise and spheroidise; cold ring rolling or upsetting only from the annealed condition, and expect ~0.05 % oil-quench growth to be ground out.
What surface finishes work on SUJ3?
Grind and superfinish to Ra <0.05 µm for raceways; protect with oil, phosphate, black oxide or thin chrome/zinc plating since bare surfaces rust quickly — no anodising.
SUJ3 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 |
|---|---|---|
| CGCr15SiMn per GB/T 18254: 0.95–1.05 | 0.95 – 1.1 | 1.02 |
| Siraised vs SUJ2 for hardenability; GCr15SiMn 0.45–0.75 | 0.4 – 0.7 | 0.55 |
| MnGCr15SiMn 0.95–1.25 | 0.9 – 1.15 | 1.02 |
| Crnote: GCr15SiMn specifies 1.40–1.65 Cr, so the two grades are close but not identical | 0.9 – 1.2 | 1.05 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Moresidual max | ≤ 0.08 | — |
| Niresidual max | ≤ 0.25 | — |
| Curesidual max | ≤ 0.25 | — |
| Ototal oxygen, vacuum-degassed bearing quality (typ ≤8 ppm) | ≤ 0 | — |
| Fe | balance | — |
SUJ3-BQ — frequently asked
What is SUJ3-BQ used for?
SUJ3-BQ is typically used for large diameter bearing rings, heavy rollers and needle rollers, tapered roller bearing cups and cones, thrust bearing washers, cam followers and track rollers and precision spindle bearing components. In short: deeper-hardening SUJ2; large-bearing JIS grade; finish by grinding only.
What is the yield strength of SUJ3-BQ?
SUJ3-BQ has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SUJ3-BQ easy to machine?
Not especially — machinability is rated not recommended (6/100, worse than 100% of steel grades). Machine only in the spheroidise-annealed state (≈40 % of AISI 1212) with sharp carbide tooling and rigid setups; hardened parts require CBN hard turning or grinding.
Can SUJ3-BQ be welded?
Not readily — weldability is rated not recommended (8/100). Effectively unweldable — high carbon plus Si/Mn gives quench cracking; if unavoidable, preheat 300–400 °C, use low-hydrogen filler and immediate post-weld temper.
What surface finishes work on SUJ3-BQ?
Grind and superfinish to Ra <0.05 µm for raceways; protect with oil, phosphate, black oxide or thin chrome/zinc plating since bare surfaces rust quickly — no anodising.
Can SUJ3-BQ be formed, bent or molded?
Hot forge 1050–1150 °C (stop above 850 °C) then normalise and spheroidise; cold ring rolling or upsetting only from the annealed condition, and expect ~0.05 % oil-quench growth to be ground out.
What is the maximum service temperature of SUJ3-BQ?
SUJ3-BQ 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 SUJ3-A and SUJ3-QT160?
A is the default condition — the condition bearing bar and tube are normally bought in: soft, uniform spheroidal carbides, ready for turning and subsequent hardening. QT160: maximum hardness and rolling-contact fatigue life for rings and rollers running below ~120 °C. Yield strength is 400 MPa in A versus 1,800 MPa in QT160.
Sources
- JIS G 4805 High carbon chromium bearing steels — Japanese Standards Association (2019)
- GB/T 18254 High-carbon chromium bearing steel — SAC (China) (2016)
- ISO 683-17 Ball and roller bearing steels — ISO (2014)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (52100/bearing steels) — ASM International (1990)
- Heat Treater's Guide: Practices and Procedures for Irons and Steels — ASM International (1995)
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.