Steel T8A-QT400
Heat-treated state
GB T8A
QT400 = quenched and tempered ~400 °C
Impact-dominated tooling and heavy-duty springs where toughness outweighs edge hardness.
Values for the QT400 condition
Other T8A tempers and conditions
T8A is listed in 10 conditions; see the grade overview at T8A.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard delivery condition for bar, flat and forging stock; soft and machinable, ready for hardening. | 375 | 620 | 24 | 179 HB | — |
Hot rolled | Cheapest mill condition for stock that will be annealed or hardened by the user. | 450 | 830 | 12 | 22 HRC | 46 W/m·K |
Cold drawn | Bright drawn bar or soft cold-rolled strip where dimensional accuracy and surface finish matter before hardening. | 520 | 700 | 12 | 200 HB | 48 W/m·K |
Normalized | Used to refine grain and break up network carbide in forgings before spheroidize annealing. | 520 | 950 | 11 | 30 HRC | 45 W/m·K |
Cold rolled hard strip | Work-hardened thin strip for shims, saw and blade blanks and light springs used without further heat treatment. | 850 | 1,000 | 3 | 28 HRC | 9.3 % IACS |
Quenched and tempered ~500 °C | Rarely used soft-tempered condition for spring or structural parts needing maximum ductility from this grade. | 1,150 | 1,350 | 9 | 42 HRC | — |
QT400This page Quenched and tempered ~400 °C | Impact-dominated tooling and heavy-duty springs where toughness outweighs edge hardness. | 1,450 | 1,650 | 6 | 49 HRC | — |
Quenched and tempered ~300 °C | Tougher setting for punches, shear blades and cold chisels that take impact. | 1,650 | 1,950 | 3 | 56 HRC | — |
Water quenched from 780–800 °C, untempered | Intermediate as-quenched condition only — must be tempered immediately to avoid quench cracking. | 1,700 | 2,000 | 0.5 | 64 HRC | 7.5 % IACS |
Quenched and tempered 150–200 °C | Standard cutting-tool condition: maximum hardness and edge retention for wood chisels, files, razors and knives. | 1,900 | 2,200 | 1 | 61 HRC | — |
What is T8A-QT400?
T8A-QT400 is T8A heat treated to QT400 — impact-dominated tooling and heavy-duty springs where toughness outweighs edge hardness. T8A-QT400 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 210 GPa (30.5 Msi). T8A-QT400 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). A is the default condition FabDigit quotes; QT400 is available on request or by drawing note.
Advantages
- High strength — 1,450 MPa (210 ksi), better than 97% 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
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited ductility — 6%, worse than 97% of steel grades
- Difficult to weld — 18/100, worse than 87% of steel grades
T8A-QT400 properties
Typical room-temperature values for T8A-QT400; 11 are specific to this condition. Other listed values are T8A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
T8A-QT400 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).
Mechanical15
T8A-QT400 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 210 GPa (30.5 Msi).
Thermal6
T8A-QT400 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
T8A-QT400 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 T8A-QT400 takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability6
T8A-QT400's machinability is poor (15/100, worse than 98% of steel grades); weldability poor (18/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with T8A-QT400
Is T8A easy to machine?
Machine in the spheroidize-annealed state (≈65 % of AISI 1212); after hardening only grinding, EDM or superabrasive work is practical.
Can T8A be welded?
Poor weldability — high carbon gives hard, crack-prone martensite; if unavoidable preheat 250–300 °C, use low-hydrogen or high-nickel filler and temper immediately.
Can T8A be formed, bent or molded?
Cold form and bend only in the annealed/soft strip condition; hot forge 1050–850 °C followed by slow cooling and spheroidize anneal at 740–760 °C.
What surface finishes work on T8A?
Harden 780–800 °C water/brine quench then temper 150–200 °C; protect with oil, phosphate, black oxide or thin plating since the bare steel rusts quickly.
T8A 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 |
|---|---|---|
| Ceutectoid carbon level | 0.75 – 0.84 | 0.8 |
| Si | ≤ 0.35 | 0.2 |
| Mn | ≤ 0.4 | 0.25 |
| Ptighter than T8 (grade-A quality) | ≤ 0.03 | — |
| Stighter than T8 (grade-A quality) | ≤ 0.02 | — |
| Crresidual | ≤ 0.1 | — |
| Niresidual | ≤ 0.12 | — |
| Curesidual | ≤ 0.2 | — |
| Fe | balance | — |
T8A-QT400 — frequently asked
What is T8A-QT400 used for?
T8A-QT400 is typically used for woodworking tools, cutting blades and small dies. In short: harder edge than T7A; low-cost cutting tool steel; water-hardening, distortion-prone.
What is the yield strength of T8A-QT400?
T8A-QT400 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 10 listed tempers.
Is T8A-QT400 easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Machine in the spheroidize-annealed state (≈65 % of AISI 1212); after hardening only grinding, EDM or superabrasive work is practical.
Can T8A-QT400 be welded?
Not readily — weldability is rated poor (18/100). Poor weldability — high carbon gives hard, crack-prone martensite; if unavoidable preheat 250–300 °C, use low-hydrogen or high-nickel filler and temper immediately.
What surface finishes work on T8A-QT400?
Harden 780–800 °C water/brine quench then temper 150–200 °C; protect with oil, phosphate, black oxide or thin plating since the bare steel rusts quickly.
Can T8A-QT400 be formed, bent or molded?
Cold form and bend only in the annealed/soft strip condition; hot forge 1050–850 °C followed by slow cooling and spheroidize anneal at 740–760 °C.
What is the maximum service temperature of T8A-QT400?
T8A-QT400 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 T8A-A and T8A-QT180?
A is the default condition — standard delivery condition for bar, flat and forging stock; soft and machinable, ready for hardening. QT180: standard cutting-tool condition: maximum hardness and edge retention for wood chisels, files, razors and knives. Yield strength is 375 MPa in A versus 1,900 MPa in QT180.
Sources
- ASTM A686 Standard Specification for Carbon Tool Steel — ASTM International (2020)
- 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)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- JIS G 4401 Carbon tool steels (SK85/SK5 equivalent) — JSA (2009)
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.