Steel T12-QT300
Heat-treated state
AISI/SAE T12 · GB T12A
QT300 = water quenched + 300–350 °C temper, 52–56 HRC
Tougher medium-hardness setting for springs, chisels and impact tools; wear resistance drops noticeably.
Values for the QT300 condition
Other T12 tempers and conditions
T12 is listed in 9 conditions; see the grade overview at T12.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
High-grade quality | Same carbon level with tightened phosphorus and sulphur limits and cleaner steel — choose for fine cutting edges and gauges where quench cracking must be minimised. | 420 | 740 | 24 | 13 HRC | 9.5 % IACS |
ADefault Solution annealed | Standard stock condition for bar, plate and drill rod — machine or form now, harden later. | 430 | 750 | 22 | 200 HB | — |
Hot rolled | Mill as-rolled condition; buy only if you will spheroidize-anneal or harden it yourself. | 500 | 900 | 12 | 25 HRC | 9.5 % IACS |
Normalized | Used to break up carbide networks in forgings before spheroidizing; not a delivery condition for finished tools. | 550 | 1,000 | 10 | 30 HRC | 9.3 % IACS |
Cold drawn | Bright cold-drawn rod or hard cold-rolled strip for close tolerance and better finish before hardening. | 700 | 880 | 8 | 25 HRC | 9.5 % IACS |
QT300This page Water quenched + 300–350 °C temper, 52–56 HRC | Tougher medium-hardness setting for springs, chisels and impact tools; wear resistance drops noticeably. | 1,500 | 1,750 | 5 | 54 HRC | — |
Water quenched + 240–260 °C temper, 57–59 HRC | Trades a little hardness for chipping resistance in punches, shear blades and hand tools with impact loading. | 1,600 | 1,900 | 3 | 58 HRC | — |
Water quenched + 200 °C temper, 60–62 HRC | The usual working condition for taps, reamers, drills and small cutters — near-peak hardness with slightly relieved stresses. | 1,750 | 2,050 | 2 | 61 HRC | — |
Water quenched + 150–180 °C temper, 62–64 HRC | Maximum hardness and wear resistance for files, scrapers, engraving tools and gauges where toughness is secondary. | 1,900 | 2,200 | 1 | 63 HRC | 42 W/m·K |
What is T12-QT300?
T12-QT300 is T12 heat treated to QT300 — tougher medium-hardness setting for springs, chisels and impact tools; wear resistance drops noticeably. T12-QT300 has a yield strength of 1,500 MPa (218 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 5% and the elastic modulus is 210 GPa (30.5 Msi). T12-QT300 has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,370°C (2,498 °F). A is the default condition FabDigit quotes; QT300 is available on request or by drawing note.
Advantages
- High strength — 1,500 MPa (218 ksi), better than 97% of steel grades
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Limited ductility — 5%, worse than 98% of steel grades
- Difficult to machine — 16/100, worse than 98% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited service temperature — 280°C (536 °F), worse than 82% of steel grades
T12-QT300 properties
Typical room-temperature values for T12-QT300; 11 are specific to this condition. Other listed values are T12 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
T12-QT300 has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,370°C (2,498 °F).
Mechanical15
T12-QT300 has a yield strength of 1,500 MPa (218 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 5% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
T12-QT300 is rated for continuous service to 280°C (536 °F). It conducts heat at 47 W/m·K (27.2 BTU/hr·ft·°F), better than 75% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
T12-QT300 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 T12-QT300 takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability7
T12-QT300's machinability is poor (16/100, worse than 98% of steel grades); weldability not recommended (12/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with T12-QT300
Is T12 easy to machine?
Machine only in the spheroidize-annealed state (~200 HB) with sharp HSS or coated carbide and generous coolant; once hardened above 60 HRC it is a grinding/EDM-only material.
Can T12 be welded?
Effectively unweldable for structural joints — very high carbon equivalent; if repair is unavoidable, preheat 300–400 °C, use a low-hydrogen or nickel-based filler and immediately re-temper.
Can T12 be formed, bent or molded?
Cold form only thin annealed strip with generous bend radii; hot work between 1050 °C and 850 °C, then slow-cool and spheroidize to avoid carbide networks and cracking.
What surface finishes work on T12?
Takes a very fine ground and lapped finish; protect with oil, black oxide, phosphate or hard chrome because bare surfaces flash-rust — no anodizing (ferrous).
T12 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 | 1.15 – 1.24 | 1.2 |
| Si | ≤ 0.35 | 0.25 |
| Mn | ≤ 0.4 | 0.3 |
| PT12A ≤0.030 | ≤ 0.04 | — |
| ST12A ≤0.020 | ≤ 0.03 | — |
| Crresidual | ≤ 0.1 | — |
| Niresidual | ≤ 0.12 | — |
| Curesidual (T12A ≤0.15) | ≤ 0.2 | — |
| Fe | balance | — |
T12-QT300 — frequently asked
What is T12-QT300 used for?
T12-QT300 is typically used for files, reamers, razor blades and precision cutting tools. In short: hardest carbon tool steel; file and reamer grade; grinding-only when hardened.
What is the yield strength of T12-QT300?
T12-QT300 has a typical yield strength of 1,500 MPa (218 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is T12-QT300 easy to machine?
Not especially — machinability is rated poor (16/100, worse than 98% of steel grades). Machine only in the spheroidize-annealed state (~200 HB) with sharp HSS or coated carbide and generous coolant; once hardened above 60 HRC it is a grinding/EDM-only material.
Can T12-QT300 be welded?
Not readily — weldability is rated not recommended (12/100). Effectively unweldable for structural joints — very high carbon equivalent; if repair is unavoidable, preheat 300–400 °C, use a low-hydrogen or nickel-based filler and immediately re-temper.
What surface finishes work on T12-QT300?
Takes a very fine ground and lapped finish; protect with oil, black oxide, phosphate or hard chrome because bare surfaces flash-rust — no anodizing (ferrous).
Can T12-QT300 be formed, bent or molded?
Cold form only thin annealed strip with generous bend radii; hot work between 1050 °C and 850 °C, then slow-cool and spheroidize to avoid carbide networks and cracking.
What is the maximum service temperature of T12-QT300?
T12-QT300 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 T12-A and T12-QT150?
A is the default condition — standard stock condition for bar, plate and drill rod — machine or form now, harden later. QT150: maximum hardness and wear resistance for files, scrapers, engraving tools and gauges where toughness is secondary. Yield strength is 430 MPa in A versus 1,900 MPa in QT150.
Sources
- GB/T 1298 Carbon Tool Steel Bars — SAC (China) (2008)
- GB/T 1299 / JIS G 4401 SK120 (SK2) carbon tool steel — SAC / JISC (2009)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (W1 water-hardening tool steel) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
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.