Steel S4-HT50
Hardness band
AISI/SAE S4 · UNS T41904
HT50 = hardened & tempered ~425 °C
Maximum-toughness condition for heavy shock work such as jackhammer and chipping tools.
Values for the HT50 condition
Other S4 tempers and conditions
S4 is listed in 7 conditions; see the grade overview at S4.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault spheroidize annealed bar/plate, machinable condition | Stock condition for machining, forming and drilling before hardening. | 430 | 720 | 25 | 210 HB | — |
Hot rolled | Mill-supplied stock for forging shops that will anneal or heat treat in-house. | 620 | 950 | 15 | 29 HRC | — |
Normalized | Used to refine forged structure prior to spheroidize annealing; not a finished tool condition. | 700 | 1,100 | 12 | 34 HRC | 3 % IACS |
HT50This page Hardened & tempered ~425 °C | Maximum-toughness condition for heavy shock work such as jackhammer and chipping tools. | 1,420 | 1,700 | 10 | 50 HRC | — |
Hardened & tempered ~315 °C | Balanced hardness/toughness for rivet sets, shear blades and pneumatic tool bits. | 1,550 | 1,900 | 7 | 55 HRC | — |
Hardened & tempered ~205 °C | Maximum hardness/wear condition for chisels and punch tips where edge retention outweighs toughness. | 1,750 | 2,100 | 4 | 58 HRC | — |
As-quenched | Untempered martensite; must be tempered immediately — brittle and crack-prone in this state. | 1,900 | 2,200 | 1 | 62 HRC | 2.7 % IACS |
What is S4-HT50?
S4-HT50 is S4 heat treated to HT50 — maximum-toughness condition for heavy shock work such as jackhammer and chipping tools. S4-HT50 has a yield strength of 1,420 MPa (206 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 96% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi). S4-HT50 has a density of 7.79 g/cm³ (0.281 lb/in³), lighter than 90% of steel grades. It melts at 1,420°C (2,588 °F). Annealed is the default condition FabDigit quotes; HT50 is available on request or by drawing note.
Advantages
- High strength — 1,420 MPa (206 ksi), better than 96% of steel grades
Limitations
- Difficult to machine — 16/100, worse than 98% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
- Low electrical conductivity — 3.1 % IACS, worse than 89% of steel grades
- Poor heat conductor — 25 W/m·K (14.4 BTU/hr·ft·°F), worse than 88% of steel grades
- Difficult to weld — 22/100, worse than 81% of steel grades
S4-HT50 properties
Typical room-temperature values for S4-HT50; 14 are specific to this condition. Other listed values are S4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
S4-HT50 has a density of 7.79 g/cm³ (0.281 lb/in³), lighter than 90% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical13
S4-HT50 has a yield strength of 1,420 MPa (206 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 96% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
S4-HT50 is rated for continuous service to 380°C (716 °F). It conducts heat at 25 W/m·K (14.4 BTU/hr·ft·°F), worse than 88% of steel grades. Thermal expansion is 12.4 µm/m·K (6.89 µin/in·°F).
Electrical3
S4-HT50 conducts electricity at 3.1 % IACS, worse than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of S4-HT50 takes about 33 MJ of energy and emits 2.4 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 35%.
Manufacturability7
S4-HT50's machinability is poor (16/100, worse than 98% of steel grades); weldability poor (22/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with S4-HT50
Is S4 easy to machine?
Machine only in the annealed (≤235 HB) condition with sharp carbide or cobalt HSS; the ~2 % Si is abrasive, so use rigid setups, generous coolant and finish-grind after hardening.
Can S4 be welded?
Poor weldability — preheat 260–320 °C, use matched or low-hydrogen filler, weld with minimum heat input and temper immediately at the tool's tempering temperature to avoid quench cracks.
Can S4 be formed, bent or molded?
Forge 1040–1150 °C, stop above 900 °C and cool slowly, then spheroidize anneal at ~790 °C; cold forming is limited to mild bending of annealed stock.
What surface finishes work on S4?
Protect against decarburization during austenitizing (neutral salt, vacuum or stop-off paint), then finish by grinding and apply oil, black oxide, phosphate or nitriding for corrosion and galling resistance.
S4 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 | 0.5 – 0.65 | 0.57 |
| Sihigh Si gives temper resistance and hardenability | 1.75 – 2.25 | 2 |
| Mn | 0.6 – 0.95 | 0.8 |
| Crresidual/optional in ASTM A681 | ≤ 0.35 | 0.2 |
| Voptional grain refiner | ≤ 0.35 | 0.2 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
S4-HT50 — frequently asked
What is S4-HT50 used for?
S4-HT50 is typically used for shear blades, rivet sets, punches and chisels. In short: high-toughness impact steel; high-silicon S grade; not a wear grade.
What is the yield strength of S4-HT50?
S4-HT50 has a typical yield strength of 1,420 MPa (206 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is S4-HT50 easy to machine?
Not especially — machinability is rated poor (16/100, worse than 98% of steel grades). Machine only in the annealed (≤235 HB) condition with sharp carbide or cobalt HSS; the ~2 % Si is abrasive, so use rigid setups, generous coolant and finish-grind after hardening.
Can S4-HT50 be welded?
Not readily — weldability is rated poor (22/100). Poor weldability — preheat 260–320 °C, use matched or low-hydrogen filler, weld with minimum heat input and temper immediately at the tool's tempering temperature to avoid quench cracks.
What surface finishes work on S4-HT50?
Protect against decarburization during austenitizing (neutral salt, vacuum or stop-off paint), then finish by grinding and apply oil, black oxide, phosphate or nitriding for corrosion and galling resistance.
Can S4-HT50 be formed, bent or molded?
Forge 1040–1150 °C, stop above 900 °C and cool slowly, then spheroidize anneal at ~790 °C; cold forming is limited to mild bending of annealed stock.
What is the maximum service temperature of S4-HT50?
S4-HT50 is rated for continuous use to about 380°C (716 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between S4 Annealed and S4-AQ?
Annealed is the default condition — stock condition for machining, forming and drilling before hardening. AQ: untempered martensite; must be tempered immediately — brittle and crack-prone in this state. Yield strength is 430 MPa in Annealed versus 1,900 MPa in AQ.
Sources
- ASTM A681 Standard Specification for Tool Steels Alloy — ASTM International (2022)
- SAE J437/J438 Tool and Die Steels — SAE International (2007)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys (Tool Steels) — ASM International (1990)
- ASM Specialty Handbook: Tool Materials — ASM International (1995)
- ASM Handbook Vol.16: Machining (tool steel machinability ratings) — 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.