Steel 55SiMnVB-QT400
Heat-treated state
GB 55SiMnVB
QT400 = oil quenched 860 °C, tempered ~400 °C
Highest strength/relaxation resistance for coil springs and torsion bars where toughness demand is moderate.
Values for the QT400 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 |
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 | — |
QT400This page 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-QT400?
55SiMnVB-QT400 is 55SiMnVB heat treated to QT400 — highest strength/relaxation resistance for coil springs and torsion bars where toughness demand is moderate. 55SiMnVB-QT400 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi). 55SiMnVB-QT400 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; QT400 is available on request or by drawing note.
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Limited formability — 5/100, worse than 99% of steel grades
- Limited ductility — 6%, worse than 97% of steel grades
- Difficult to machine — 18/100, worse than 97% of steel grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 90% of steel grades
- Limited service temperature — 230°C (446 °F), worse than 88% of steel grades
55SiMnVB-QT400 properties
Typical room-temperature values for 55SiMnVB-QT400; 14 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-QT400 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-QT400 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
55SiMnVB-QT400 is rated for continuous service to 230°C (446 °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-QT400 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-QT400 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-QT400's machinability is poor (18/100, worse than 97% of steel grades); weldability poor (20/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 55SiMnVB-QT400
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-QT400 — frequently asked
What is 55SiMnVB-QT400 used for?
55SiMnVB-QT400 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-QT400?
55SiMnVB-QT400 has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 55SiMnVB-QT400 easy to machine?
Not especially — machinability is rated poor (18/100, worse than 97% 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-QT400 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-QT400?
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-QT400 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-QT400?
55SiMnVB-QT400 is rated for continuous use to about 230°C (446 °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.