Steel 38Si7 +S
Heat-treated state
EN 38Si7
+S = treated for high shearability
Hardness deliberately held in a narrow mid band so bar can be cold-sheared to blanks without cracking or excessive burr.
Values for the +S condition
Other 38Si7 tempers and conditions
38Si7 is listed in 8 conditions; see the grade overview at 38Si7.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Softest, most ductile delivery state — choose for heavy cold upsetting, cold extrusion or deep machining before hardening. | 350 | 590 | 22 | 195 HB | — |
Annealed | Standard soft delivery condition for bar and flat that will be machined, cold formed or coiled before hardening. | 390 | 640 | 18 | 215 HB | — |
Restricted (narrow) hardenability band | Tighter Jominy scatter than +H for heat-treaters needing repeatable core hardness and distortion in mass-produced springs. | 395 | 650 | 17 | 17 HRC | 7.5 % IACS |
Supplied to a specified hardenability (Jominy) band | Order option when the quench response must be guaranteed; bar ships soft (annealed/hot rolled) and quench-hardens to about 52–57 HRC before tempering. | 400 | 660 | 17 | 18 HRC | 7.8 % IACS |
+SThis page Treated for high shearability | Hardness deliberately held in a narrow mid band so bar can be cold-sheared to blanks without cracking or excessive burr. | 430 | 700 | 16 | 225 HB | — |
Hot rolled | Cheapest mill condition for stock that will be fully re-heat-treated after forming; surface decarburization must be machined or ground off. | 470 | 780 | 14 | 22 HRC | 7.5 % IACS |
Cold drawn | Bright, close-tolerance bar for machined spring pins and clips where only moderate strength is needed without heat treatment. | 660 | 820 | 9 | 23 HRC | 7.2 % IACS |
+QTDefault Quenched and tempered | Standard in-service condition for leaf/coil springs and torsion bars: oil-quench from ~870 °C, temper 400–500 °C. | 1,150 | 1,300 | 9 | 42 HRC | — |
What is 38Si7 +S?
38Si7 +S is 38Si7 heat treated to +S — hardness deliberately held in a narrow mid band so bar can be cold-sheared to blanks without cracking or excessive burr. 38Si7 +S has a yield strength of 430 MPa (62.4 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 51% of steel grades. Elongation at break is 16% and the elastic modulus is 206 GPa (29.9 Msi). 38Si7 +S has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F). +QT is the default condition FabDigit quotes; +S is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Difficult to weld — 15/100, worse than 91% of steel grades
- Low fracture toughness — 50 MPa·√m (45.5 ksi·√in), worse than 86% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
38Si7 +S properties
Typical room-temperature values for 38Si7 +S; 10 are specific to this condition. Other listed values are 38Si7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
38Si7 +S has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
38Si7 +S has a yield strength of 430 MPa (62.4 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 51% of steel grades. Elongation at break is 16% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
38Si7 +S 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
38Si7 +S conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 38Si7 +S takes about 24 MJ of energy and emits 1.9 kg of CO₂ — less than 97% of steel grades. Typical recycled content is 30%.
Manufacturability6
38Si7 +S's machinability is fair (48/100, worse than 57% of steel grades); weldability poor (15/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 38Si7 +S
Is 38Si7 easy to machine?
Machine in +A/+AC condition with sharp carbide tooling; the high Si makes chips gummy and abrasive, and above ~40 HRC only grinding or ceramic/CBN turning is practical.
Can 38Si7 be welded?
Essentially not recommended for loaded springs — high carbon equivalent and Si cause hard, crack-prone HAZ; if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and temper immediately after.
Can 38Si7 be formed, bent or molded?
Cold coil or bend only in the spheroidized/annealed state; hot form at 900–1050 °C, then austenitize ~860–880 °C, oil quench and temper 400–500 °C to the target 40–45 HRC.
What surface finishes work on 38Si7?
Shot-peen springs after tempering for fatigue life; protect with phosphate + oil, zinc-rich or epoxy paint — avoid acid pickling and electroplating on hardened parts unless baked to relieve hydrogen.
38Si7 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 | 0.35 – 0.42 | 0.38 |
| Simain alloying element; raises elastic limit and relaxation resistance | 1.5 – 1.8 | 1.65 |
| Mn | 0.5 – 0.8 | 0.65 |
| Crresidual limit | ≤ 0.4 | 0.15 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Fe | balance | — |
38Si7 +S — frequently asked
What is 38Si7 +S used for?
38Si7 +S is typically used for leaf springs, coil springs and stabilizer bars. In short: entry-level silicon spring steel; 1300 MPa at 42 HRC; not weldable when hardened.
What is the yield strength of 38Si7 +S?
38Si7 +S has a typical yield strength of 430 MPa (62.4 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 51% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 38Si7 +S easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machine in +A/+AC condition with sharp carbide tooling; the high Si makes chips gummy and abrasive, and above ~40 HRC only grinding or ceramic/CBN turning is practical.
Can 38Si7 +S be welded?
Not readily — weldability is rated poor (15/100). Essentially not recommended for loaded springs — high carbon equivalent and Si cause hard, crack-prone HAZ; if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and temper immediately after.
What surface finishes work on 38Si7 +S?
Shot-peen springs after tempering for fatigue life; protect with phosphate + oil, zinc-rich or epoxy paint — avoid acid pickling and electroplating on hardened parts unless baked to relieve hydrogen.
Can 38Si7 +S be formed, bent or molded?
Cold coil or bend only in the spheroidized/annealed state; hot form at 900–1050 °C, then austenitize ~860–880 °C, oil quench and temper 400–500 °C to the target 40–45 HRC.
What is the maximum service temperature of 38Si7 +S?
38Si7 +S 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/-2 — Steels for quenching and tempering, general and technical delivery conditions — CEN (2006)
- EN 10084 — Case hardening steels (delivery-condition symbols +A, +AC, +S, +H, +HH, +HL) — CEN (2008)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Stahlschlüssel (Key to Steel) — Verlag Stahlschlüssel Wegst (2019)
- EN 13906-1 — Cylindrical helical springs, design and calculation — CEN (2013)
- Mysteel / 1688 (2026)
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.