Steel 56Si7 +QT+SP (+QT + shot peened)
Finish state
EN 56Si7
Q&T springs that are shot- or stress-peened to add compressive surface stress — the standard choice for high-cycle automotive suspension springs.
Values for the +QT+SP condition
Other 56Si7 tempers and conditions
56Si7 is listed in 8 conditions; see the grade overview at 56Si7.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Softest, most ductile delivery state — pick it for cold coiling, deep drawing or heavy cold upsetting before hardening. | 420 | 720 | 20 | 205 HB | — |
Treated for high shearability | Bar/coil heat treated to a low, uniform hardness so blanks can be cold sheared or cropped without cracking before hot/warm forming. | 440 | 760 | 18 | 17 HRC | 6 % IACS |
Annealed | Choose for machining, straightening or bar/strip stock that will be hardened after forming. | 470 | 800 | 16 | 230 HB | 42 W/m·K |
Treated to a specified core hardenability band | Same soft delivery state as +H but with the hardenability band certified on the core of heavy sections such as thick leaf-spring or torsion-bar stock. | 510 | 880 | 14 | 23 HRC | 5.9 % IACS |
Treated to a specified hardenability band | Order this when the mill must certify an end-quench (Jominy) hardenability band; supplied soft/hot-rolled and hardened by the spring maker. | 520 | 900 | 14 | 25 HRC | 5.9 % IACS |
Hot rolled | Cheapest mill state for hot-coiled springs that will be austenitized straight from the forming heat; hardness and decarburization vary. | 570 | 1,000 | 12 | 29 HRC | 5.8 % IACS |
+QTDefault Quenched and tempered | Standard finished spring condition: oil-quenched from ~860 °C and tempered 400–480 °C for maximum elastic limit and fatigue life. | 1,450 | 1,650 | 7 | 48 HRC | — |
+QT+SPThis page +QT + shot peened | Q&T springs that are shot- or stress-peened to add compressive surface stress — the standard choice for high-cycle automotive suspension springs. | 1,450 | 1,650 | 6 | 49 HRC | 5.7 % IACS |
What is 56Si7 +QT+SP?
56Si7 +QT+SP is 56Si7 supplied in the +QT+SP condition — q&T springs that are shot- or stress-peened to add compressive surface stress — the standard choice for high-cycle automotive suspension springs. 56Si7 +QT+SP has a yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi). 56Si7 +QT+SP has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F). +QT is the default condition FabDigit quotes; +QT+SP is available on request or by drawing note.
Advantages
- High strength — 1,450 MPa (210 ksi), better than 97% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to weld — 10/100, 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
- Limited formability — 8/100, worse than 97% of steel grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 90% of steel grades
56Si7 +QT+SP properties
Typical room-temperature values for 56Si7 +QT+SP; 22 are specific to this condition. Other listed values are 56Si7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
56Si7 +QT+SP has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
56Si7 +QT+SP has a yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
56Si7 +QT+SP 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 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
56Si7 +QT+SP conducts electricity at 5.7 % IACS, worse than 80% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 56Si7 +QT+SP takes about 28 MJ of energy and emits 2.1 kg of CO₂ — less than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
56Si7 +QT+SP's machinability is poor (18/100, worse than 97% of steel grades); weldability not recommended (10/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 56Si7 +QT+SP
Is 56Si7 easy to machine?
Machine only in the +A/+AC/+S soft states with rigid setups and carbide tooling — the high silicon is abrasive and the Q&T condition (≈48 HRC) needs grinding or CBN.
Can 56Si7 be welded?
Effectively non-weldable for load-bearing joints; if unavoidable, preheat 250–350 °C, low-hydrogen filler and immediate post-weld temper, and never weld a finished spring.
Can 56Si7 be formed, bent or molded?
Hot coil/roll at 850–1000 °C, or cold form only from spheroidize-annealed stock followed by austenitize 850–870 °C, oil quench and temper 400–480 °C; guard against surface decarburization.
What surface finishes work on 56Si7?
No corrosion resistance — shot peen, then phosphate + epoxy paint, powder coat or zinc-flake; avoid acid pickling and electrolytic zinc plating without baking due to hydrogen embrittlement.
56Si7 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 |
|---|---|---|
| CAISI 9255 range 0.51–0.59 | 0.52 – 0.6 | 0.56 |
| SiAISI 9255 range 1.80–2.20 | 1.6 – 2 | 1.8 |
| Mn | 0.6 – 1 | 0.8 |
| Crresidual limit | ≤ 0.4 | 0.15 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Fe | balance | — |
56Si7 +QT+SP — frequently asked
What is 56Si7 +QT+SP used for?
56Si7 +QT+SP is typically used for heavy-duty coil springs, leaf springs and clutch springs. In short: highest strength of the Si7 springs; 1650 MPa at 48 HRC; shot-peened stock available.
What is the yield strength of 56Si7 +QT+SP?
56Si7 +QT+SP has a typical yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 56Si7 +QT+SP easy to machine?
Not especially — machinability is rated poor (18/100, worse than 97% of steel grades). Machine only in the +A/+AC/+S soft states with rigid setups and carbide tooling — the high silicon is abrasive and the Q&T condition (≈48 HRC) needs grinding or CBN.
Can 56Si7 +QT+SP be welded?
Not readily — weldability is rated not recommended (10/100). Effectively non-weldable for load-bearing joints; if unavoidable, preheat 250–350 °C, low-hydrogen filler and immediate post-weld temper, and never weld a finished spring.
What surface finishes work on 56Si7 +QT+SP?
No corrosion resistance — shot peen, then phosphate + epoxy paint, powder coat or zinc-flake; avoid acid pickling and electrolytic zinc plating without baking due to hydrogen embrittlement.
Can 56Si7 +QT+SP be formed, bent or molded?
Hot coil/roll at 850–1000 °C, or cold form only from spheroidize-annealed stock followed by austenitize 850–870 °C, oil quench and temper 400–480 °C; guard against surface decarburization.
What is the maximum service temperature of 56Si7 +QT+SP?
56Si7 +QT+SP 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.
Sources
- EN 10089 — Hot-rolled steels for quenched and tempered springs — CEN (2002)
- EN 10083-1 — Steels for quenching and tempering: delivery conditions (+A, +AC, +S, +QT, +H) — CEN (2006)
- DIN 17221 — Hot-rolled steels for quenched and tempered springs (56Si7 / 1.5026) — DIN (1988)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (spring steels) — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture (spring steel fatigue data) — ASM International (1996)
- SAE J404 / GB/T 1222 — spring steel chemical compositions (9255, 60Si2Mn analogues) — SAE / SAC (2016)
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.