Steel 51B60 QT-56HRC
Hardness band
EN 51B60 · UNS G51601
QT-56HRC = q&T 205–315 °C
Choose the low 205–315 °C temper at 55–58 HRC for blades, plowshares and wear parts needing maximum hardness and 2100 MPa tensile; toughness drops sharply to 5 % elongation.
Values for the QT-56HRC condition
Other 51B60 tempers and conditions
51B60 is listed in 8 conditions; see the grade overview at 51B60.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Choose the spheroidized or fully annealed bar as the softest state for machining, cold forming or before hardening; 197 HB gives the best machinability at only 276 MPa yield. | 276 | 725 | 17 | 197 HB | — |
Hot rolled | Order hot rolled bar or flat spring stock as the lowest-cost supply state at 860 MPa tensile and 248 HB; it still has to be quenched and tempered before it can be put into service. | 490 | 860 | 15 | 24 HRC | 7.6 % IACS |
Normalized | Normalize at 855 °C and air cool after forging or rough machining to refine grain and homogenize the structure in preparation for hardening; gives 957 MPa tensile at 269 HB. | 531 | 957 | 17.5 | 27 HRC | — |
Cold drawn | Use cold drawn bright bar, cold worked after annealing, when tight tolerance, good surface finish and a lift to 660 MPa yield suit machining parts directly from stock. | 660 | 800 | 12 | 229 HB | — |
Q&T 650 °C | Pick the oil quench with a 650 °C temper, about 26 HRC, as the toughest hardened state for structural parts that must still be machined yet hold 895 MPa yield and 17.5 % elongation. | 895 | 1,005 | 17.5 | 26 HRC | — |
Q&T 540 °C | Use the oil quench with a 540 °C temper to about 40 HRC as the balanced general-purpose hardened state for torsion bars and wear-resistant structural parts at 1310 MPa tensile. | 1,160 | 1,310 | 12.5 | 42 HRC | — |
Q&T 425 °C | Specify the 425 °C spring temper at 47–50 HRC as the standard in-service state for leaf and coil springs, giving the best elastic limit and fatigue life at 1570 MPa yield. | 1,570 | 1,730 | 9 | 48 HRC | — |
QT-56HRCThis page Q&T 205–315 °C | Choose the low 205–315 °C temper at 55–58 HRC for blades, plowshares and wear parts needing maximum hardness and 2100 MPa tensile; toughness drops sharply to 5 % elongation. | 1,780 | 2,100 | 5 | 56 HRC | — |
What is 51B60 QT-56HRC?
51B60 QT-56HRC is 51B60 heat treated to QT-56HRC — choose the low 205–315 °C temper at 55–58 HRC for blades, plowshares and wear parts needing maximum hardness and 2100 MPa tensile; toughness drops sharply to 5 % elongation. 51B60 QT-56HRC has a yield strength of 1,780 MPa (258 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Elongation at break is 5% and the elastic modulus is 205 GPa (29.7 Msi). 51B60 QT-56HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,415°C (2,579 °F). A is the default condition FabDigit quotes; QT-56HRC is available on request or by drawing note.
Advantages
- High strength — 1,780 MPa (258 ksi), better than 99% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Difficult to weld — 5/100, worse than 100% of steel grades
- Difficult to machine — 10/100, worse than 99% of steel grades
- Limited ductility — 5%, worse than 98% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Low fracture toughness — 35 MPa·√m (31.9 ksi·√in), worse than 94% of steel grades
51B60 QT-56HRC properties
Typical room-temperature values for 51B60 QT-56HRC; 14 are specific to this condition. Other listed values are 51B60 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
51B60 QT-56HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,415°C (2,579 °F).
Mechanical16
51B60 QT-56HRC has a yield strength of 1,780 MPa (258 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Elongation at break is 5% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
51B60 QT-56HRC is rated for continuous service to 180°C (356 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
51B60 QT-56HRC conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 51B60 QT-56HRC takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
51B60 QT-56HRC's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (5/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 51B60 QT-56HRC
Is 51B60 easy to machine?
Machining is most economical in the annealed or spheroidized condition (≤220 HB) using carbide tooling at low speed with heavy feed. Above 45 HRC only grinding or CBN is practical.
Can 51B60 be welded?
The carbon equivalent is high (about 0.9) and weldability is poor: 150–300 °C preheat, low-hydrogen consumables and immediate post-weld tempering are required. Avoid welding finished springs altogether.
Can 51B60 be formed, bent or molded?
Leaf and coil springs are usually hot formed at 850–950 °C and quenched directly after forming. Annealed material can be warm bent; cold bend radii should be at least 3t to avoid cracking.
What surface finishes work on 51B60?
Shot peening substantially increases spring fatigue life. Protect surfaces with phosphate plus paint, zinc-flake coating or zinc plating, and de-embrittle electroplated parts at 190–220 °C for 4 h or more.
51B60 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 | 0.56 – 0.64 | 0.6 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.7 – 0.9 | 0.8 |
| Beffective B; Ti/Al must fix N to ensure hardenability | 5×10⁻⁴ – 0 | 0 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
51B60 QT-56HRC — frequently asked
What is 51B60 QT-56HRC used for?
51B60 QT-56HRC is typically used for coil springs, leaf springs and wear components. In short: high-carbon spring steel; hardens to 56 HRC; effectively non-weldable.
What is the yield strength of 51B60 QT-56HRC?
51B60 QT-56HRC has a typical yield strength of 1,780 MPa (258 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 51B60 QT-56HRC easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machining is most economical in the annealed or spheroidized condition (≤220 HB) using carbide tooling at low speed with heavy feed. Above 45 HRC only grinding or CBN is practical.
Can 51B60 QT-56HRC be welded?
Not readily — weldability is rated not recommended (5/100). The carbon equivalent is high (about 0.9) and weldability is poor: 150–300 °C preheat, low-hydrogen consumables and immediate post-weld tempering are required. Avoid welding finished springs altogether.
What surface finishes work on 51B60 QT-56HRC?
Shot peening substantially increases spring fatigue life. Protect surfaces with phosphate plus paint, zinc-flake coating or zinc plating, and de-embrittle electroplated parts at 190–220 °C for 4 h or more.
Can 51B60 QT-56HRC be formed, bent or molded?
Leaf and coil springs are usually hot formed at 850–950 °C and quenched directly after forming. Annealed material can be warm bent; cold bend radii should be at least 3t to avoid cracking.
What is the maximum service temperature of 51B60 QT-56HRC?
51B60 QT-56HRC 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 51B60-A and 51B60-CD?
A is the default condition — choose the spheroidized or fully annealed bar as the softest state for machining, cold forming or before hardening; 197 HB gives the best machinability at only 276 MPa yield. CD: use cold drawn bright bar, cold worked after annealing, when tight tolerance, good surface finish and a lift to 660 MPa yield suit machining parts directly from stock. Yield strength is 276 MPa in A versus 660 MPa in CD.
Sources
- SAE J404 / J1249 — Chemical Compositions of SAE Alloy Steels (51B60, UNS G51601) — SAE International (2021)
- ASTM A29/A29M — General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM International (2020)
- ASTM A689 — Carbon and Alloy Steel Bars for Springs — ASTM International (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (5160/51B60 ) — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals — ASM International (2013)
- Machining Data Handbook / ASM Vol.16 — ASM International (1989)
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.