Steel 30MoB1 +QT 8.8 (+QT to property class 8.8)
Hardness band
EN 30MoB1
Fastener heat treatment for class 8.8 bolts — tempered high for maximum ductility and low hydrogen-embrittlement risk.
Values for the +QT 8.8 condition
Other 30MoB1 tempers and conditions
30MoB1 is listed in 9 conditions; see the grade overview at 30MoB1.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Pick for severe multi-station cold heading and cold extrusion — lowest flow stress and best die life. | 320 | 520 | 23 | 152 HB | — |
Annealed | General soft-annealed bar for machining or light upsetting before hardening. | 340 | 570 | 20 | 165 HB | — |
Hot rolled | Mill as-rolled coil, the cheapest input when the fastener maker does its own spheroidizing. | 410 | 660 | 17 | 195 HB | — |
+AC+CDefault Spheroidized and cold drawn to size | The standard cold-heading wire delivery condition: drawn to gauge with a phosphate/lubricant coating, ready to head and then quench & temper. | 530 | 620 | 11 | 185 HB | — |
Cold drawn | Straight, size-accurate bar for machined shafts that will be hardened afterwards. | 610 | 710 | 8 | 210 HB | — |
+QT 8.8This page +QT to property class 8.8 | Fastener heat treatment for class 8.8 bolts — tempered high for maximum ductility and low hydrogen-embrittlement risk. | 720 | 900 | 13 | 27 HRC | — |
Quenched and tempered | Balanced strength/toughness condition for medium-strength shafts, pins and studs up to ~20 mm section. | 850 | 1,000 | 14 | 31 HRC | — |
+QT to property class 10.9 | Main commercial reason for the grade: 10.9 bolts and wheel studs at lower alloy cost than 42CrMo4. | 990 | 1,100 | 10 | 34 HRC | — |
Guaranteed hardenability, supplied/used in the hardened (quenched +… | Order +H when the Jominy band matters; in the as-hardened (oil/water quench + 180–250 °C temper) state it gives maximum hardness and wear resistance but low toughness. | 1,250 | 1,550 | 8 | 46 HRC | — |
What is 30MoB1 +QT 8.8?
30MoB1 +QT 8.8 is 30MoB1 heat treated to +QT 8.8 — fastener heat treatment for class 8.8 bolts — tempered high for maximum ductility and low hydrogen-embrittlement risk. 30MoB1 +QT 8.8 has a yield strength of 720 MPa (104 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 82% of steel grades. Elongation at break is 13% and the elastic modulus is 210 GPa (30.5 Msi). 30MoB1 +QT 8.8 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F). +AC+C is the default condition FabDigit quotes; +QT 8.8 is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 720 MPa (104 ksi), better than 82% of steel grades
Limitations
- Limited ductility — 13%, worse than 78% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
30MoB1 +QT 8.8 properties
Typical room-temperature values for 30MoB1 +QT 8.8; 11 are specific to this condition. Other listed values are 30MoB1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
30MoB1 +QT 8.8 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F).
Mechanical14
30MoB1 +QT 8.8 has a yield strength of 720 MPa (104 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 82% of steel grades. Elongation at break is 13% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
30MoB1 +QT 8.8 is rated for continuous service to 300°C (572 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
30MoB1 +QT 8.8 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 30MoB1 +QT 8.8 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
30MoB1 +QT 8.8's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (50/100); formability good (60/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 30MoB1 +QT 8.8
Is 30MoB1 easy to machine?
Machines like a 0.30 % C low-alloy steel (~60–65 % of AISI 1212) in +AC/+AC+C; spheroidized structure is gummy, so use sharp coated carbide, positive rake and good chip breaking, and machine before hardening wherever possible.
Can 30MoB1 be welded?
Weldable with low-hydrogen consumables but boron plus 0.25 Mo make the HAZ air-hardening: preheat 150–250 °C, control interpass, and post-weld temper; welding after Q&T destroys the fastener strength class.
Can 30MoB1 be formed, bent or molded?
Designed for cold heading and cold extrusion in the +AC condition with phosphate+soap or polymer lubricant; upsetting ratios typical of 30MnB4-class steel are achievable, hot forging 1100–1200 °C, finish above 900 °C.
What surface finishes work on 30MoB1?
No anodizing — protect with zinc or zinc-nickel electroplate (bake 200 °C ≥4 h to de-embrittle parts ≥1000 MPa), zinc-flake (Dacromet/Geomet) for 10.9 fasteners, or phosphate and oil.
30MoB1 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 | 0.27 – 0.33 | 0.3 |
| Silow Si for cold heading | ≤ 0.3 | 0.15 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Motemper-resistance and hardenability | 0.2 – 0.3 | 0.25 |
| Beffective (soluble) boron; needs Ti/Al nitrogen fixing | 8×10⁻⁴ – 0.01 | 0 |
| Algrain refinement / N fixing | 0.02 – 0.06 | 0.04 |
| Tioptional, to protect boron from N | ≤ 0.05 | 0.03 |
| Crresidual | ≤ 0.3 | 0.1 |
| Niresidual | ≤ 0.3 | 0.08 |
| Curesidual | ≤ 0.25 | 0.1 |
| Fe | balance | — |
30MoB1 +QT 8.8 — frequently asked
What is 30MoB1 +QT 8.8 used for?
30MoB1 +QT 8.8 is typically used for fasteners, shafts and structural bolts. In short: boron hardenability, low alloy cost; reaches 8.8 and 10.9 classes; cold-heading fastener steel.
What is the yield strength of 30MoB1 +QT 8.8?
30MoB1 +QT 8.8 has a typical yield strength of 720 MPa (104 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 82% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 30MoB1 +QT 8.8 easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machines like a 0.30 % C low-alloy steel (~60–65 % of AISI 1212) in +AC/+AC+C; spheroidized structure is gummy, so use sharp coated carbide, positive rake and good chip breaking, and machine before hardening wherever possible.
Can 30MoB1 +QT 8.8 be welded?
With care — weldability is rated fair (50/100). Weldable with low-hydrogen consumables but boron plus 0.25 Mo make the HAZ air-hardening: preheat 150–250 °C, control interpass, and post-weld temper; welding after Q&T destroys the fastener strength class.
What surface finishes work on 30MoB1 +QT 8.8?
No anodizing — protect with zinc or zinc-nickel electroplate (bake 200 °C ≥4 h to de-embrittle parts ≥1000 MPa), zinc-flake (Dacromet/Geomet) for 10.9 fasteners, or phosphate and oil.
Can 30MoB1 +QT 8.8 be formed, bent or molded?
Designed for cold heading and cold extrusion in the +AC condition with phosphate+soap or polymer lubricant; upsetting ratios typical of 30MnB4-class steel are achievable, hot forging 1100–1200 °C, finish above 900 °C.
What is the maximum service temperature of 30MoB1 +QT 8.8?
30MoB1 +QT 8.8 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- EN 10263-4 Steel rod, bars and wire for cold heading and cold extrusion — Part 4: quench and temper steels — CEN (2017)
- EN ISO 898-1 Mechanical properties of fasteners — bolts, screws and studs — ISO (2013)
- EN 10083-3 Steels for quenching and tempering — alloy steels — CEN (2006)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Stahlschlüssel / Key to Steel — material 1.5408 — Verlag Stahlschlüssel Wegst (2019)
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.