Steel GCr9-BQ
Heat-treated state
GB GCr9
BQ = bainite hardened (austempered), 58–62 HRC
Isothermal salt-bath quench to lower bainite: lower distortion, compressive surface stresses and better toughness for contaminated-lubrication or impact-loaded bearings.
Values for the BQ condition
Other GCr9 tempers and conditions
GCr9 is listed in 8 conditions; see the grade overview at GCr9.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stocked condition (179–207 HB) for turning, cold forming and ring rolling before hardening. | 390 | 640 | 23 | 190 HB | 44 W/m·K |
Hot rolled | As-rolled bar stock before spheroidizing; cheapest form, hard and coarse-structured, normally re-annealed before machining. | 550 | 900 | 12 | 27 HRC | 7 % IACS |
Normalized | Used to break up carbide networks in forgings before spheroidizing; not a delivery condition for finished parts. | 600 | 1,000 | 10 | 31 HRC | 7 % IACS |
Cold drawn | Precision-size bright bar for automatic-lathe production of rollers, pins and small races. | 600 | 750 | 10 | 20 HRC | 7 % IACS |
Induction hardened | Local surface hardening of larger shafts/raceways where a tough unhardened core is wanted. | 1,000 | 1,200 | 2 | 60 HRC | 6.5 % IACS |
Quenched & tempered, 58–62 HRC | Slightly softer, tougher and more dimensionally stable variant for shock-loaded or warmer-running components. | 1,600 | 1,950 | 2 | 60 HRC | — |
BQThis page Bainite hardened (austempered), 58–62 HRC | Isothermal salt-bath quench to lower bainite: lower distortion, compressive surface stresses and better toughness for contaminated-lubrication or impact-loaded bearings. | 1,650 | 2,000 | 2.5 | 60 HRC | — |
Quenched & low-temperature tempered, 60–64 HRC | Standard bearing-service condition: oil/martempered from ~830–850 °C and tempered 150–180 °C for maximum wear and rolling-contact fatigue life. | 1,750 | 2,150 | 1 | 62 HRC | 38 W/m·K |
What is GCr9-BQ?
GCr9-BQ is GCr9 heat treated to BQ — isothermal salt-bath quench to lower bainite: lower distortion, compressive surface stresses and better toughness for contaminated-lubrication or impact-loaded bearings. GCr9-BQ 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 2.5% and the elastic modulus is 210 GPa (30.5 Msi). GCr9-BQ has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,425°C (2,597 °F). A is the default condition FabDigit quotes; BQ 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
- Limited ductility — 2.5%, worse than 99% of steel grades
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
GCr9-BQ properties
Typical room-temperature values for GCr9-BQ; 10 are specific to this condition. Other listed values are GCr9 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
GCr9-BQ has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical15
GCr9-BQ 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 2.5% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
GCr9-BQ 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 12 µm/m·K (6.67 µin/in·°F).
Electrical3
GCr9-BQ conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of GCr9-BQ takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability7
GCr9-BQ's machinability is not recommended (12/100, worse than 99% of steel grades); weldability poor (15/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with GCr9-BQ
Is GCr9 easy to machine?
Machine only in the spheroidize-annealed state (179–207 HB) with coated carbide; after hardening use CBN hard turning or grinding.
Can GCr9 be welded?
Effectively unweldable — 1 % C causes quench cracking; if unavoidable, preheat >300 °C, low-hydrogen filler and immediate stress relief.
Can GCr9 be formed, bent or molded?
Cold heading and ring rolling are done after spheroidizing; hot forging at 1050–1100 °C followed by controlled cooling and re-annealing to avoid carbide networks.
What surface finishes work on GCr9?
Rust-preventive oil, black oxide, phosphate or thin hard chrome; hardened surfaces lap and superfinish to mirror Ra < 0.05 µm for raceways.
GCr9 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 |
|---|---|---|
| Chigh carbon for martensite hardness and carbides | 0.95 – 1.05 | 1 |
| Crlower than GCr15 → shallower hardenability | 0.9 – 1.2 | 1.05 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.2 – 0.4 | 0.3 |
| Pimpurity limit | ≤ 0.03 | — |
| Simpurity limit | ≤ 0.02 | — |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| Moresidual | ≤ 0.1 | — |
| Fe | balance | — |
GCr9-BQ — frequently asked
What is GCr9-BQ used for?
GCr9-BQ is typically used for small ball bearing rings and balls, needle roller bearing components, light-duty rollers and pins, cam followers, linear guide balls and small wear bushings and sleeves. In short: economical alternative to GCr15; for small bearing sections; through-hardens to 64 HRC.
What is the yield strength of GCr9-BQ?
GCr9-BQ 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 8 listed tempers.
Is GCr9-BQ easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machine only in the spheroidize-annealed state (179–207 HB) with coated carbide; after hardening use CBN hard turning or grinding.
Can GCr9-BQ be welded?
Not readily — weldability is rated poor (15/100). Effectively unweldable — 1 % C causes quench cracking; if unavoidable, preheat >300 °C, low-hydrogen filler and immediate stress relief.
What surface finishes work on GCr9-BQ?
Rust-preventive oil, black oxide, phosphate or thin hard chrome; hardened surfaces lap and superfinish to mirror Ra < 0.05 µm for raceways.
Can GCr9-BQ be formed, bent or molded?
Cold heading and ring rolling are done after spheroidizing; hot forging at 1050–1100 °C followed by controlled cooling and re-annealing to avoid carbide networks.
What is the maximum service temperature of GCr9-BQ?
GCr9-BQ 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 GCr9-A and GCr9-BQ?
A is the default condition — standard stocked condition (179–207 HB) for turning, cold forming and ring rolling before hardening. BQ: isothermal salt-bath quench to lower bainite: lower distortion, compressive surface stresses and better toughness for contaminated-lubrication or impact-loaded bearings. Yield strength is 390 MPa in A versus 1,650 MPa in BQ.
Sources
- ASTM A295 / A295M High-Carbon Anti-Friction Bearing Steel (51100, 52100) — ASTM International (2014)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- 100Cr6 / 52100 bearing steel bar datasheet — Ovako / (2022)
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.