Steel T7A QT42-48
Hardness band
GB T7A
QT42-48 = q&T 42–48 HRC
Toughest hardened condition, used for heavily loaded striking tools and spring-like tool sections.
Values for the QT42-48 condition
Other T7A tempers and conditions
T7A is listed in 9 conditions; see the grade overview at T7A.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard mill-supplied soft condition for machining and forming before hardening. | 380 | 660 | 22 | 180 HB | 48 W/m·K |
Hot rolled | Cheapest mill form for forging stock; harder and less uniform than annealed, normally annealed before machining. | 430 | 780 | 15 | 19 HRC | 9.3 % IACS |
Normalized | Grain refinement of forgings before final anneal or hardening. | 450 | 830 | 14 | 22 HRC | 9.2 % IACS |
Cold drawn | Choose for close-tolerance bright bar going straight into automatic machining before hardening. | 570 | 750 | 10 | 16 HRC | 9.4 % IACS |
QT42-48This page Q&T 42–48 HRC | Toughest hardened condition, used for heavily loaded striking tools and spring-like tool sections. | 1,250 | 1,450 | 8 | 45 HRC | — |
Q&T 50–54 HRC | The classic impact-tool condition for hammers, riveting sets and rock drills where shock beats wear. | 1,450 | 1,750 | 5 | 52 HRC | — |
Q&T 54–57 HRC | Balanced hardness/toughness for cold chisels, punches and shear blades. | 1,650 | 1,950 | 2 | 56 HRC | 8 % IACS |
As-Quenched | Untempered reference condition proving hardenability; must be tempered immediately to avoid cracking. | 1,800 | 2,200 | 0.5 | 63 HRC | 7.8 % IACS |
Q&T 57–60 HRC | Maximum wear resistance condition for wood chisels, files and light punches on thin sections. | — | 2,100 | — | 58 HRC | — |
What is T7A QT42-48?
T7A QT42-48 is T7A heat treated to QT42-48 — toughest hardened condition, used for heavily loaded striking tools and spring-like tool sections. T7A QT42-48 has a yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Elongation at break is 8% and the elastic modulus is 207 GPa (30 Msi). T7A QT42-48 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; QT42-48 is available on request or by drawing note.
Advantages
- High strength — 1,250 MPa (181 ksi), better than 95% of steel grades
- Easy to machine — 62/100, better than 89% 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 — 8%, worse than 95% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
T7A QT42-48 properties
Typical room-temperature values for T7A QT42-48; 11 are specific to this condition. Other listed values are T7A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
T7A QT42-48 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
T7A QT42-48 has a yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Elongation at break is 8% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
T7A QT42-48 is rated for continuous service to 350°C (662 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
T7A QT42-48 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 T7A QT42-48 takes about 26 MJ of energy and emits 2.1 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability8
T7A QT42-48's machinability is good (62/100, better than 89% of steel grades); weldability poor (20/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with T7A QT42-48
Is T7A easy to machine?
Machine in the spheroidize-annealed condition (~180 HB, ~65 % of 1212); HSS works fine but carbide and rigid setups improve finish — grinding is the only practical route above 55 HRC.
Can T7A be welded?
Poor weldability at 0.7 % C: preheat 250–350 °C, use low-hydrogen or matching filler, and temper immediately after welding; avoid welding on finished tool edges.
Can T7A be formed, bent or molded?
Hot forge 1050–850 °C then slow cool and spheroidize anneal at 730–750 °C; cold bending only in the annealed state with generous radii.
What surface finishes work on T7A?
No corrosion resistance — protect with oil, black oxide, phosphate, or hard chrome; hardened surfaces polish well but must be kept below the tempering temperature during grinding.
T7A 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 T7/T7A | 0.65 – 0.74 | 0.7 |
| Si | ≤ 0.35 | 0.2 |
| Mn | ≤ 0.4 | 0.25 |
| Pgrade A high-quality, tighter than T7 (0.035) | ≤ 0.03 | — |
| Sgrade A high-quality, tighter than T7 (0.030) | ≤ 0.02 | — |
| Crresidual | ≤ 0.25 | — |
| Niresidual | ≤ 0.2 | — |
| Curesidual | ≤ 0.3 | — |
| Fe | balance | — |
T7A QT42-48 — frequently asked
What is T7A QT42-48 used for?
T7A QT42-48 is typically used for chisels, hammers, punches and hand tools. In short: toughest carbon tool steel; impact tools over cutting edges; shallow hardening only.
What is the yield strength of T7A QT42-48?
T7A QT42-48 has a typical yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is T7A QT42-48 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machine in the spheroidize-annealed condition (~180 HB, ~65 % of 1212); HSS works fine but carbide and rigid setups improve finish — grinding is the only practical route above 55 HRC.
Can T7A QT42-48 be welded?
Not readily — weldability is rated poor (20/100). Poor weldability at 0.7 % C: preheat 250–350 °C, use low-hydrogen or matching filler, and temper immediately after welding; avoid welding on finished tool edges.
What surface finishes work on T7A QT42-48?
No corrosion resistance — protect with oil, black oxide, phosphate, or hard chrome; hardened surfaces polish well but must be kept below the tempering temperature during grinding.
Can T7A QT42-48 be formed, bent or molded?
Hot forge 1050–850 °C then slow cool and spheroidize anneal at 730–750 °C; cold bending only in the annealed state with generous radii.
What is the maximum service temperature of T7A QT42-48?
T7A QT42-48 is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between T7A-A and T7A-AQ?
A is the default condition — standard mill-supplied soft condition for machining and forming before hardening. AQ: untempered reference condition proving hardenability; must be tempered immediately to avoid cracking. Yield strength is 380 MPa in A versus 1,800 MPa in AQ.
Sources
- JIS G 4401 Carbon Tool Steels (SK7) — JIS (2009)
- ASM Handbook Vol.1: Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4: Heat Treating (Water-hardening tool steels) — ASM International (1991)
- T7A/T8A/T10A — Mysteel / 1688 (2025)
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.