Steel L3 QT-55
Hardness band
AISI/SAE L3 · UNS T61203
QT-55 = hardened & tempered 315–370 °C
Tougher setting for shock-loaded punches, chisels and shafts where some wear resistance is traded for impact life.
Values for the QT-55 condition
Other L3 tempers and conditions
L3 is listed in 5 conditions; see the grade overview at L3.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard as-supplied bar/flat condition for machining and forming before hardening. | 430 | 730 | 25 | 197 HB | — |
Cold drawn / ground annealed bar | Precision-ground annealed bar and drill rod for direct machining to size before hardening. | 550 | 780 | 15 | 17 HRC | 8 % IACS |
QT-55This page Hardened & tempered 315–370 °C | Tougher setting for shock-loaded punches, chisels and shafts where some wear resistance is traded for impact life. | 1,650 | 1,900 | 4 | 55 HRC | — |
Hardened & tempered 205–260 °C | Balanced wear/toughness condition for punches, forming rolls and arbors. | 1,850 | 2,100 | 2 | 59 HRC | — |
Hardened & tempered 150–175 °C | Maximum hardness/wear condition for gauges, ball races and cutting-edge tools with light shock. | 2,050 | 2,350 | 1 | 63 HRC | 34 W/m·K |
What is L3 QT-55?
L3 QT-55 is L3 heat treated to QT-55 — tougher setting for shock-loaded punches, chisels and shafts where some wear resistance is traded for impact life. L3 QT-55 has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Elongation at break is 4% and the elastic modulus is 207 GPa (30 Msi). L3 QT-55 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). ANN is the default condition FabDigit quotes; QT-55 is available on request or by drawing note.
Advantages
- High strength — 1,650 MPa (239 ksi), better than 99% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- Limited ductility — 4%, worse than 98% of steel grades
- Difficult to machine — 14/100, worse than 98% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited service temperature — 260°C (500 °F), worse than 82% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
L3 QT-55 properties
Typical room-temperature values for L3 QT-55; 12 are specific to this condition. Other listed values are L3 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
L3 QT-55 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
L3 QT-55 has a yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Elongation at break is 4% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
L3 QT-55 is rated for continuous service to 260°C (500 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
L3 QT-55 conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of L3 QT-55 takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
L3 QT-55's machinability is not recommended (14/100, worse than 98% of steel grades); weldability poor (15/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with L3 QT-55
Is L3 easy to machine?
Machine only in the spheroidize-annealed condition (~200 HB) with sharp carbide or cobalt HSS at moderate speeds; after hardening above 58 HRC only grinding, EDM or CBN turning is practical.
Can L3 be welded?
Essentially not weldable in service condition — high carbon causes quench cracking; repair only with preheat 300–350 °C, matching/tool-steel electrode and immediate stress relief or re-temper.
Can L3 be formed, bent or molded?
Hot work 900–1050 °C with slow cooling and full spheroidize anneal (760–790 °C, slow cool to ~590 °C); cold forming is limited to mild bending of annealed stock.
What surface finishes work on L3?
Hardened parts polish to a fine mirror finish thanks to the fine carbide dispersion; protect with oil, black oxide, phosphate or thin hard chrome since the steel has no corrosion resistance.
L3 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 |
|---|---|---|
| C | 0.95 – 1.1 | 1 |
| Mn | 0.25 – 0.8 | 0.45 |
| Si | 0.1 – 0.5 | 0.25 |
| Cr | 1.3 – 1.7 | 1.5 |
| Vgrain refinement + hard MC carbides | 0.1 – 0.3 | 0.2 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
L3 QT-55 — frequently asked
What is L3 QT-55 used for?
L3 QT-55 is typically used for gauges, precision tools, mandrels and wear-resistant machine parts. In short: higher wear than L2; dimensionally stable gauge steel; polishes to mirror finish.
What is the yield strength of L3 QT-55?
L3 QT-55 has a typical yield strength of 1,650 MPa (239 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is L3 QT-55 easy to machine?
Not especially — machinability is rated not recommended (14/100, worse than 98% of steel grades). Machine only in the spheroidize-annealed condition (~200 HB) with sharp carbide or cobalt HSS at moderate speeds; after hardening above 58 HRC only grinding, EDM or CBN turning is practical.
Can L3 QT-55 be welded?
Not readily — weldability is rated poor (15/100). Essentially not weldable in service condition — high carbon causes quench cracking; repair only with preheat 300–350 °C, matching/tool-steel electrode and immediate stress relief or re-temper.
What surface finishes work on L3 QT-55?
Hardened parts polish to a fine mirror finish thanks to the fine carbide dispersion; protect with oil, black oxide, phosphate or thin hard chrome since the steel has no corrosion resistance.
Can L3 QT-55 be formed, bent or molded?
Hot work 900–1050 °C with slow cooling and full spheroidize anneal (760–790 °C, slow cool to ~590 °C); cold forming is limited to mild bending of annealed stock.
What is the maximum service temperature of L3 QT-55?
L3 QT-55 is rated for continuous use to about 260°C (500 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between L3-ANN and L3 QT-62?
ANN is the default condition — standard as-supplied bar/flat condition for machining and forming before hardening. QT-62: maximum hardness/wear condition for gauges, ball races and cutting-edge tools with light shock. Yield strength is 430 MPa in ANN versus 2,050 MPa in QT-62.
Sources
- ASTM A681 — Standard Specification for Tool Steels, Alloy — ASTM International (2015)
- SAE J437/J438 — Tool and Die Steels — SAE International (2015)
- ASM Handbook Vol. 1: Properties and Selection: Irons, Steels and High-Performance Alloys (Tool Steels) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- ASM Handbook Vol. 16: Machining — ASM International (1989)
- UNS T61203 alloy record — SAE/ASTM Unified Numbering System (2019)
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.