Steel T7-QT50
Hardness band
AISI/SAE T7 · GB T7A
QT50 = water quenched + 300–400 °C temper
Toughest hardened setting — for heavy-impact chisels, pneumatic tool bits and spring-like sections.
Values for the QT50 condition
Other T7 tempers and conditions
T7 is listed in 8 conditions; see the grade overview at T7.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard delivery condition for bar and flat stock; softest, best machinability, ready for machining then hardening. | 400 | 660 | 22 | 183 HB | 48 W/m·K |
High-grade quality | Same carbon range with tighter sulphur/phosphorus limits and cleaner steel — choose for tools that must survive repeated heavy impact. | 405 | 670 | 24 | 11 HRC | 9.5 % IACS |
Hot rolled | As-rolled bar with mill scale; cheapest form, normally annealed before machining. | 430 | 780 | 14 | 20 HRC | 9.5 % IACS |
Normalized | Used to refine grain and break up network carbide before spheroidizing or hardening. | 450 | 800 | 15 | 22 HRC | 9.5 % IACS |
Cold drawn | Bright drawn bar with close tolerance and good surface for direct machining of small tools. | 640 | 820 | 9 | 23 HRC | 9.5 % IACS |
QT50This page Water quenched + 300–400 °C temper | Toughest hardened setting — for heavy-impact chisels, pneumatic tool bits and spring-like sections. | 1,400 | 1,600 | 6 | 48 HRC | — |
Water quenched + 200–250 °C temper | Balanced hardness/toughness setting for cold chisels, punches and riveting tools. | 1,650 | 1,950 | 2 | 57 HRC | 8.5 % IACS |
Water quenched + 150–180 °C temper | Maximum hardness condition for cutting edges on chisels and punches where wear matters more than shock. | — | 2,100 | — | 61 HRC | 44 W/m·K |
What is T7-QT50?
T7-QT50 is T7 heat treated to QT50 — toughest hardened setting — for heavy-impact chisels, pneumatic tool bits and spring-like sections. T7-QT50 has a yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,600 MPa (232 ksi) — stronger than 96% of steel grades. Elongation at break is 6% and the elastic modulus is 207 GPa (30 Msi). T7-QT50 has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F). A is the default condition FabDigit quotes; QT50 is available on request or by drawing note.
Advantages
- High strength — 1,400 MPa (203 ksi), better than 96% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Limited ductility — 6%, worse than 97% of steel grades
- Difficult to machine — 18/100, worse than 97% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited service temperature — 280°C (536 °F), worse than 82% of steel grades
T7-QT50 properties
Typical room-temperature values for T7-QT50; 10 are specific to this condition. Other listed values are T7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
T7-QT50 has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
T7-QT50 has a yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,600 MPa (232 ksi) — stronger than 96% of steel grades. Elongation at break is 6% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
T7-QT50 is rated for continuous service to 280°C (536 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 11.6 µm/m·K (6.44 µin/in·°F).
Electrical3
T7-QT50 conducts electricity at 9.5 % IACS, better than 75% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of T7-QT50 takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability7
T7-QT50's machinability is poor (18/100, worse than 97% 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 T7-QT50
Is T7 easy to machine?
Machine in the spheroidize-annealed condition (~62 % of AISI 1212) with HSS or coated carbide; once hardened above 55 HRC only grinding or EDM is practical.
Can T7 be welded?
Poor weldability — high carbon promotes martensite and quench cracking; if unavoidable, preheat 300–400 °C, use low-hydrogen or Ni-base filler and temper immediately after.
Can T7 be formed, bent or molded?
Forge 1050–1150 °C and stop above 800 °C, then slow cool; cold bending only in the annealed state with generous radii.
What surface finishes work on T7?
Grind and polish after hardening, then protect with black oxide, phosphating, oiling or hard chrome — the steel has no intrinsic corrosion resistance.
T7 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 |
|---|---|---|
| CGB/T 1298 | 0.65 – 0.74 | 0.7 |
| Si | ≤ 0.35 | 0.22 |
| Mn | ≤ 0.4 | 0.25 |
| PT7A ≤0.030 | ≤ 0.04 | — |
| ST7A ≤0.020 | ≤ 0.03 | — |
| Crresidual; ≤0.10 for some deliveries | ≤ 0.25 | — |
| Niresidual | ≤ 0.2 | — |
| Curesidual; ≤0.25 for T7A | ≤ 0.3 | — |
| Fe | balance | — |
T7-QT50 — frequently asked
What is T7-QT50 used for?
T7-QT50 is typically used for chisels, hammers, punches and hand tools. In short: toughest carbon tool steel; impact-tool carbon grade; lowest carbon of T-series.
What is the yield strength of T7-QT50?
T7-QT50 has a typical yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,600 MPa (232 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is T7-QT50 easy to machine?
Not especially — machinability is rated poor (18/100, worse than 97% of steel grades). Machine in the spheroidize-annealed condition (~62 % of AISI 1212) with HSS or coated carbide; once hardened above 55 HRC only grinding or EDM is practical.
Can T7-QT50 be welded?
Not readily — weldability is rated poor (15/100). Poor weldability — high carbon promotes martensite and quench cracking; if unavoidable, preheat 300–400 °C, use low-hydrogen or Ni-base filler and temper immediately after.
What surface finishes work on T7-QT50?
Grind and polish after hardening, then protect with black oxide, phosphating, oiling or hard chrome — the steel has no intrinsic corrosion resistance.
Can T7-QT50 be formed, bent or molded?
Forge 1050–1150 °C and stop above 800 °C, then slow cool; cold bending only in the annealed state with generous radii.
What is the maximum service temperature of T7-QT50?
T7-QT50 is rated for continuous use to about 280°C (536 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between T7-A and T7-QT57?
A is the default condition — standard delivery condition for bar and flat stock; softest, best machinability, ready for machining then hardening. QT57: balanced hardness/toughness setting for cold chisels, punches and riveting tools. Yield strength is 400 MPa in A versus 1,650 MPa in QT57.
Sources
- GB/T 1299 (heat treatment and hardness requirements) — SAC (2014)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (W-type water-hardening tool steels) — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
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.