Steel 55SiMnVB-QT520
Heat-treated state
GB 55SiMnVB
QT520 = oil quenched 860 °C, tempered ~520 °C
Pick when impact toughness and crack tolerance in thick leaf sections matter more than peak spring load capacity.
Values for the QT520 condition
Other 55SiMnVB tempers and conditions
55SiMnVB is listed in 7 conditions; see the grade overview at 55SiMnVB.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Choose when the bar must be cold-sheared, punched, straightened or machined before heat treatment. | 430 | 720 | 18 | 215 HB | — |
Hot rolled | Mill delivery condition for spring flats and rounds that the spring maker will hot-form, quench and temper in-house. | 550 | 900 | 13 | 27 HRC | — |
Normalized | Grain-refining pre-treatment after forging or hot forming, before final quench and temper. | 600 | 950 | 12 | 30 HRC | 7 % IACS |
Cold drawn | Small-diameter rod and wire supplied cold drawn to size for wound springs that are hardened and tempered after coiling. | 780 | 950 | 9 | 30 HRC | 7 % IACS |
QT520This page Oil quenched 860 °C, tempered ~520 °C | Pick when impact toughness and crack tolerance in thick leaf sections matter more than peak spring load capacity. | 1,130 | 1,280 | 11 | 40 HRC | — |
QT460Default Oil quenched 860 °C, tempered 460 °C | Standard spring service condition and the basis of the GB/T 1222 property minima; best strength–toughness balance for heavy leaf springs. | 1,320 | 1,500 | 8 | 45 HRC | — |
Oil quenched 860 °C, tempered ~400 °C | Highest strength/relaxation resistance for coil springs and torsion bars where toughness demand is moderate. | 1,550 | 1,750 | 6 | 50 HRC | — |
What is 55SiMnVB-QT520?
55SiMnVB-QT520 is 55SiMnVB heat treated to QT520 — pick when impact toughness and crack tolerance in thick leaf sections matter more than peak spring load capacity. 55SiMnVB-QT520 has a yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 93% of steel grades. Elongation at break is 11% and the elastic modulus is 206 GPa (29.9 Msi). 55SiMnVB-QT520 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). QT460 is the default condition FabDigit quotes; QT520 is available on request or by drawing note.
Advantages
- High strength — 1,130 MPa (164 ksi), better than 93% of steel grades
Limitations
- Limited formability — 10/100, worse than 95% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Difficult to machine — 30/100, worse than 89% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
55SiMnVB-QT520 properties
Typical room-temperature values for 55SiMnVB-QT520; 12 are specific to this condition. Other listed values are 55SiMnVB reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
55SiMnVB-QT520 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
55SiMnVB-QT520 has a yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 93% of steel grades. Elongation at break is 11% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
55SiMnVB-QT520 is rated for continuous service to 250°C (482 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 12.5 µm/m·K (6.94 µin/in·°F).
Electrical3
55SiMnVB-QT520 conducts electricity at 6.4 % IACS, worse than 77% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 55SiMnVB-QT520 takes about 27 MJ of energy and emits 2.1 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 30%.
Manufacturability6
55SiMnVB-QT520's machinability is poor (30/100, worse than 89% of steel grades); weldability poor (20/100); formability not recommended (10/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 55SiMnVB-QT520
Is 55SiMnVB easy to machine?
Machine in the annealed condition (carbide, 80–120 m/min); after quench and temper at 45 HRC expect grinding or CBN turning only, and keep decarburised skin off finished spring surfaces.
Can 55SiMnVB be welded?
Not recommended for load-bearing joints — 0.55 %C plus boron gives high hardenability and cold cracking; if unavoidable, preheat 250–350 °C, low-hydrogen consumables and immediate post-weld temper.
Can 55SiMnVB be formed, bent or molded?
Hot form/roll leaf ends and coil at 900–1000 °C, then oil quench from 850–870 °C and temper 400–520 °C; cold bending is only feasible in the annealed state.
What surface finishes work on 55SiMnVB?
Shot peen springs after tempering for fatigue life, then phosphate + epoxy/powder paint or zinc-rich primer; avoid acid pickling and electroplating on the hardened part unless followed by a 200 °C hydrogen bake-out.
55SiMnVB 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 | 0.52 – 0.6 | 0.56 |
| Si | 0.7 – 1 | 0.85 |
| Mn | 1 – 1.3 | 1.15 |
| Vgrain refinement, temper resistance | 0.08 – 0.16 | 0.12 |
| Bhardenability booster; requires low free N | 5×10⁻⁴ – 0 | 0 |
| Crresidual | ≤ 0.35 | — |
| Niresidual | ≤ 0.35 | — |
| Curesidual | ≤ 0.25 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.02 | — |
| Fe | balance | — |
55SiMnVB-QT520 — frequently asked
What is 55SiMnVB-QT520 used for?
55SiMnVB-QT520 is typically used for truck leaf springs, heavy vehicle suspension springs, parabolic trailer springs, off-highway and agricultural machinery springs, heavy coil springs and spring plates and clamp bands. In short: low-cost Cr-V spring substitute; high hardenability from boron; highest hardness of the spring pair.
What is the yield strength of 55SiMnVB-QT520?
55SiMnVB-QT520 has a typical yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 55SiMnVB-QT520 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 89% of steel grades). Machine in the annealed condition (carbide, 80–120 m/min); after quench and temper at 45 HRC expect grinding or CBN turning only, and keep decarburised skin off finished spring surfaces.
Can 55SiMnVB-QT520 be welded?
Not readily — weldability is rated poor (20/100). Not recommended for load-bearing joints — 0.55 %C plus boron gives high hardenability and cold cracking; if unavoidable, preheat 250–350 °C, low-hydrogen consumables and immediate post-weld temper.
What surface finishes work on 55SiMnVB-QT520?
Shot peen springs after tempering for fatigue life, then phosphate + epoxy/powder paint or zinc-rich primer; avoid acid pickling and electroplating on the hardened part unless followed by a 200 °C hydrogen bake-out.
Can 55SiMnVB-QT520 be formed, bent or molded?
Hot form/roll leaf ends and coil at 900–1000 °C, then oil quench from 850–870 °C and temper 400–520 °C; cold bending is only feasible in the annealed state.
What is the maximum service temperature of 55SiMnVB-QT520?
55SiMnVB-QT520 is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 55SiMnVB-QT460 and 55SiMnVB-A?
QT460 is the default condition — standard spring service condition and the basis of the GB/T 1222 property minima; best strength–toughness balance for heavy leaf springs. A: choose when the bar must be cold-sheared, punched, straightened or machined before heat treatment. Yield strength is 1,320 MPa in QT460 versus 430 MPa in A.
Sources
- GB/T 1222 (Spring steels) (2016)
- (Handbook of Iron and Steel Materials) (2009)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- (Spring Design Handbook) (2008)
- Hardness conversion tables for metals — ASTM E140 (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.