Steel T12A-QT350
Heat-treated state
GB T12A
QT350 = water quenched + tempered 300–400 °C
Tough/spring-like condition for shock-loaded parts and light springs where full file hardness is not needed.
Values for the QT350 condition
Other T12A tempers and conditions
T12A is listed in 10 conditions; see the grade overview at T12A.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stock condition: globular carbides in ferrite, ≤207 HB, machine or cold-form now and harden afterwards. | 420 | 720 | 20 | 200 HB | — |
Cold rolled strip, annealed | Thin soft strip (0.1–3 mm) for blanking saw blades, springs, shims and small cutters that are hardened after forming. | 420 | 700 | 18 | 12 HRC | 9.5 % IACS |
Precision ground / silver steel, annealed | Ground round or flat stock held to h9/h11 tolerance in the soft state — for punches, gauge pins and reamer blanks finished by grinding after hardening. | 420 | 720 | 20 | 13 HRC | 9.5 % IACS |
Hot rolled | Cheapest mill condition for bar and plate that will be fully machined and heat treated by the user; hard, coarse pearlitic structure. | 480 | 850 | 10 | 25 HRC | 9.5 % IACS |
Cold drawn | Choose for close-tolerance small bar, wire and drill-rod blanks where some extra strength and a bright surface help before hardening. | 700 | 880 | 8 | 24 HRC | 9.5 % IACS |
QT350This page Water quenched + tempered 300–400 °C | Tough/spring-like condition for shock-loaded parts and light springs where full file hardness is not needed. | 1,450 | 1,700 | 4 | 52 HRC | 8.6 % IACS |
Water quenched + tempered 230–280 °C | Use where some impact is unavoidable — cold chisels, light punches, woodworking blades. | 1,650 | 1,900 | 2 | 58 HRC | 8.2 % IACS |
Water quenched, untempered | Maximum hardness reference state only; must be tempered promptly — untempered T12A cracks readily. | 1,750 | 2,100 | 0.5 | 65 HRC | 7.5 % IACS |
Water quenched + tempered 180–220 °C | Slight toughness gain for reamers, taps, gauges and small cutting tools with a little bending load. | 1,800 | 2,050 | 1 | 61 HRC | 7.8 % IACS |
Water quenched + tempered 150–180 °C | Standard file/scraper/hand-tool treatment: maximum wear resistance and edge holding, minimum toughness. | 1,900 | 2,200 | 1 | 64 HRC | — |
What is T12A-QT350?
T12A-QT350 is T12A heat treated to QT350 — tough/spring-like condition for shock-loaded parts and light springs where full file hardness is not needed. T12A-QT350 has a yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 97% of steel grades. Elongation at break is 4% and the elastic modulus is 210 GPa (30.5 Msi). T12A-QT350 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,300°C (2,372 °F). A is the default condition FabDigit quotes; QT350 is available on request or by drawing note.
Advantages
- High strength — 1,450 MPa (210 ksi), better than 97% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to weld — 4/100, worse than 100% of steel grades
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited formability — 5/100, worse than 99% of steel grades
- Limited ductility — 4%, worse than 98% of steel grades
- Low fracture toughness — 28 MPa·√m (25.5 ksi·√in), worse than 97% of steel grades
T12A-QT350 properties
Typical room-temperature values for T12A-QT350; 22 are specific to this condition. Other listed values are T12A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
T12A-QT350 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,300°C (2,372 °F).
Mechanical16
T12A-QT350 has a yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 97% of steel grades. Elongation at break is 4% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
T12A-QT350 is rated for continuous service to 300°C (572 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.8 µm/m·K (6.56 µin/in·°F).
Electrical3
T12A-QT350 conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (9/100), worse than 98% of steel grades.
Sustainability4
Producing a kilogram of T12A-QT350 takes about 28 MJ of energy and emits 2.1 kg of CO₂ — less than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
T12A-QT350's machinability is not recommended (12/100, worse than 99% of steel grades); weldability not recommended (4/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with T12A-QT350
Is T12A easy to machine?
Machine only in the spheroidize-annealed state (≤207 HB) with sharp HSS/carbide and generous coolant; after hardening it is a grinding-only material.
Can T12A be welded?
Essentially unweldable for tool duty — if repair is unavoidable, preheat 300–350 °C, use a matching or low-hydrogen filler, and re-temper immediately to avoid quench cracks.
Can T12A be formed, bent or molded?
Cold bending and blanking only from fully spheroidized strip with generous radii; hot work at 1050–850 °C, cool slowly, then anneal. Harden 760–780 °C in water/brine, temper at once 150–200 °C; hardened depth is only a few mm, so keep sections thin and avoid sharp corners.
What surface finishes work on T12A?
No native corrosion resistance — protect with oiling, black oxide, phosphating, or hard chrome; polishes to a fine finish in the hardened state thanks to the low S/P A-grade cleanliness.
T12A 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 |
|---|---|---|
| Chypereutectoid — free cementite gives max hardness | 1.15 – 1.24 | 1.2 |
| Si | ≤ 0.35 | 0.2 |
| Mn | ≤ 0.4 | 0.25 |
| PA-grade (high-quality) restriction | ≤ 0.03 | — |
| SA-grade (high-quality) restriction | ≤ 0.02 | — |
| Crresidual | ≤ 0.1 | — |
| Niresidual | ≤ 0.12 | — |
| Curesidual | ≤ 0.2 | — |
| Fe | balance | — |
T12A-QT350 — frequently asked
What is T12A-QT350 used for?
T12A-QT350 is typically used for files, scrapers, reamers and razor-type blades. In short: hardest carbon tool steel; file and scraper grade; brittle — light cutting only.
What is the yield strength of T12A-QT350?
T12A-QT350 has a typical yield strength of 1,450 MPa (210 ksi) and a tensile strength of 1,700 MPa (247 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is T12A-QT350 easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machine only in the spheroidize-annealed state (≤207 HB) with sharp HSS/carbide and generous coolant; after hardening it is a grinding-only material.
Can T12A-QT350 be welded?
Not readily — weldability is rated not recommended (4/100). Essentially unweldable for tool duty — if repair is unavoidable, preheat 300–350 °C, use a matching or low-hydrogen filler, and re-temper immediately to avoid quench cracks.
What surface finishes work on T12A-QT350?
No native corrosion resistance — protect with oiling, black oxide, phosphating, or hard chrome; polishes to a fine finish in the hardened state thanks to the low S/P A-grade cleanliness.
Can T12A-QT350 be formed, bent or molded?
Cold bending and blanking only from fully spheroidized strip with generous radii; hot work at 1050–850 °C, cool slowly, then anneal. Harden 760–780 °C in water/brine, temper at once 150–200 °C; hardened depth is only a few mm, so keep sections thin and avoid sharp corners.
What is the maximum service temperature of T12A-QT350?
T12A-QT350 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between T12A-A and T12A-QT150?
A is the default condition — standard stock condition: globular carbides in ferrite, ≤207 HB, machine or cold-form now and harden afterwards. QT150: standard file/scraper/hand-tool treatment: maximum wear resistance and edge holding, minimum toughness. Yield strength is 420 MPa in A versus 1,900 MPa in QT150.
Sources
- GB/T 1298 (Carbon tool steels) (2008)
- ASTM A686 Standard Specification for Tool Steel, Carbon (W1 grades) — ASTM (2021)
- JIS G 4401 Carbon tool steels (SK120/SK2) — JSA (2009)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Water-hardening tool steels) — ASM International (1990)
- ASM Handbook Vol. 4 — Heat Treating (Tool steel heat treatment) — ASM International (1991)
- ASM Handbook Vol. 16 — Machining (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.