Steel 31CrMoB2-1 +QT 40-45 HRC (+QT high strength)
Hardness band
EN 31CrMoB2-1
High-strength temper for property-class 10.9/12.9 bolts and highly loaded shafts; needs plating bake-out to avoid hydrogen embrittlement.
Values for the +QT 40-45 HRC condition
Other 31CrMoB2-1 tempers and conditions
31CrMoB2-1 is listed in 11 conditions; see the grade overview at 31CrMoB2-1.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Softest condition, chosen for multi-station cold heading/extrusion of bolt and screw blanks before quench & temper. | 370 | 570 | 23 | 170 HB | — |
Annealed | General soft-annealed bar for machining or as a starting stock before quench and temper. | 390 | 600 | 22 | 11 HRC | 8.4 % IACS |
Restricted (core) hardenability band, Jominy-guaranteed | Order this when heat-treat response must sit inside a narrow Jominy band so the core hardness of quenched fasteners/parts is reproducible batch to batch. | 400 | 620 | 20 | 10 HRC | 8.5 % IACS |
Treated to hardness range | Ordered when the mill must certify a delivered hardness window (e.g. ≤207 HB) rather than a specific heat treatment route. | 400 | 610 | 20 | 10 HRC | 8.5 % IACS |
Specified hardenability | Standard hardenability-guaranteed supply condition; pick when parts are hardened in-house and the end-quench curve must be certified. | 410 | 640 | 19 | 14 HRC | 8.2 % IACS |
Hot rolled | Cheapest mill condition; only for parts that will be fully re-heat-treated after forming or forging. | 430 | 680 | 18 | 16 HRC | 8.2 % IACS |
Normalized | Uniform fine-grained structure after hot forming; used to homogenize forgings before final hardening. | 450 | 700 | 18 | 17 HRC | 8.2 % IACS |
Spheroidize annealed and cold drawn | Most common wire/bar supply for cold-heading lines: spheroidized softness plus drawn size tolerance, straightness and clean surface. | 540 | 650 | 12 | 200 HB | — |
Cold drawn | Bright drawn bar for automatic machining where tight tolerance and higher as-supplied strength are wanted without spheroidizing. | 600 | 720 | 10 | 19 HRC | 8 % IACS |
+QTDefault Quenched and tempered | Standard delivered/finished strength condition for bolts, shafts and machine parts needing ~1000 MPa with good toughness. | 850 | 1,000 | 14 | 31 HRC | — |
+QT 40-45 HRCThis page +QT high strength | High-strength temper for property-class 10.9/12.9 bolts and highly loaded shafts; needs plating bake-out to avoid hydrogen embrittlement. | 1,150 | 1,300 | 10 | 42 HRC | — |
What is 31CrMoB2-1 +QT 40-45 HRC?
31CrMoB2-1 +QT 40-45 HRC is 31CrMoB2-1 heat treated to +QT 40-45 HRC — high-strength temper for property-class 10.9/12.9 bolts and highly loaded shafts; needs plating bake-out to avoid hydrogen embrittlement. 31CrMoB2-1 +QT 40-45 HRC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi). 31CrMoB2-1 +QT 40-45 HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). +QT is the default condition FabDigit quotes; +QT 40-45 HRC is available on request or by drawing note.
Advantages
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
- Limited formability — 15/100, worse than 87% of steel grades
- Difficult to machine — 35/100, worse than 84% of steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 78% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
31CrMoB2-1 +QT 40-45 HRC properties
Typical room-temperature values for 31CrMoB2-1 +QT 40-45 HRC; 16 are specific to this condition. Other listed values are 31CrMoB2-1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
31CrMoB2-1 +QT 40-45 HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
31CrMoB2-1 +QT 40-45 HRC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
31CrMoB2-1 +QT 40-45 HRC is rated for continuous service to 300°C (572 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
31CrMoB2-1 +QT 40-45 HRC 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 31CrMoB2-1 +QT 40-45 HRC takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability6
31CrMoB2-1 +QT 40-45 HRC's machinability is fair (35/100, worse than 84% of steel grades); weldability poor (30/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 31CrMoB2-1 +QT 40-45 HRC
Is 31CrMoB2-1 easy to machine?
Machine in +AC/+A/+TH (≤210 HB) with carbide inserts; in Q&T above 40 HRC switch to coated carbide or CBN with rigid setups and reduced feeds.
Can 31CrMoB2-1 be welded?
Boron and ~0.31 %C give CE ≈0.55 — preheat 150–250 °C, low-hydrogen consumables and post-weld temper; welded joints in the Q&T state lose local strength.
Can 31CrMoB2-1 be formed, bent or molded?
Cold heading and extrusion only from +AC or +AC+C wire with phosphate+soap or polymer lube; hot forge 1100–1200 °C and re-normalize before hardening.
What surface finishes work on 31CrMoB2-1?
No anodizing (steel). Protect with zinc, zinc-nickel or zinc-flake coating, phosphate or black oxide; bake at 200 °C within 4 h after electroplating parts above ~1000 MPa.
31CrMoB2-1 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 |
|---|---|---|
| Cgrade-defining carbon level | 0.28 – 0.34 | 0.31 |
| Si | ≤ 0.3 | 0.2 |
| Mn | 0.5 – 0.8 | 0.65 |
| P | ≤ 0.03 | 0.02 |
| Smax; S-resulphurized versions exist for machining | ≤ 0.03 | 0.01 |
| Crdesignation digit 2 = 0.5 % Cr | 0.4 – 0.6 | 0.5 |
| Modesignation digit 1 = 0.1 % Mo | 0.08 – 0.15 | 0.1 |
| Beffective (soluble) boron for hardenability | 8×10⁻⁴ – 0.01 | 0 |
| Tiadded to fix nitrogen and protect boron effect | 0.02 – 0.06 | 0.04 |
| Algrain refining / deoxidation | 0.02 – 0.06 | 0.03 |
| Fe | balance | — |
31CrMoB2-1 +QT 40-45 HRC — frequently asked
What is 31CrMoB2-1 +QT 40-45 HRC used for?
31CrMoB2-1 +QT 40-45 HRC is typically used for high-strength bolts and fasteners, shafts, structural pins and automotive suspension components. In short: boron-boosted hardenability; low-cost fastener steel; cold-headable in +AC.
What is the yield strength of 31CrMoB2-1 +QT 40-45 HRC?
31CrMoB2-1 +QT 40-45 HRC has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 31CrMoB2-1 +QT 40-45 HRC easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Machine in +AC/+A/+TH (≤210 HB) with carbide inserts; in Q&T above 40 HRC switch to coated carbide or CBN with rigid setups and reduced feeds.
Can 31CrMoB2-1 +QT 40-45 HRC be welded?
Not readily — weldability is rated poor (30/100). Boron and ~0.31 %C give CE ≈0.55 — preheat 150–250 °C, low-hydrogen consumables and post-weld temper; welded joints in the Q&T state lose local strength.
What surface finishes work on 31CrMoB2-1 +QT 40-45 HRC?
No anodizing (steel). Protect with zinc, zinc-nickel or zinc-flake coating, phosphate or black oxide; bake at 200 °C within 4 h after electroplating parts above ~1000 MPa.
Can 31CrMoB2-1 +QT 40-45 HRC be formed, bent or molded?
Cold heading and extrusion only from +AC or +AC+C wire with phosphate+soap or polymer lube; hot forge 1100–1200 °C and re-normalize before hardening.
What is the maximum service temperature of 31CrMoB2-1 +QT 40-45 HRC?
31CrMoB2-1 +QT 40-45 HRC 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 10083-3 Steels for quenching and tempering — Alloy steels — CEN (2006)
- EN 10263-4 Steel rod, bars and wire for cold heading and cold extrusion — Steels for quenching and tempering (delivery conditions +A, +AC, +C, +AC+C, +TH) — CEN (2018)
- EN 10084 / EN 10250-3 (hardenability designations +H, +HH, +HL, +CH) — CEN (2008)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A: Steel Heat Treating Fundamentals (boron hardenability) — ASM International (2013)
- GB/T 3077 (comparable 30CrMoB-type boron grades) — SAC (2015)
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.