Steel 5145-QT315
Heat-treated state
AISI/SAE 5145 · UNS G51450
QT315 = oQ&T 315 °C
Very high strength with slightly better ductility than the 205 °C temper.
Values for the QT315 condition
Other 5145 tempers and conditions
5145 is listed in 14 conditions; see the grade overview at 5145.
Compare all 14 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for maximum machinability or cold heading/upsetting of this higher-carbon Cr grade. | 320 | 585 | 28 | 170 HB | 8 % IACS |
ADefault Solution annealed | Standard stock condition: softest, most machinable state before quench-and-temper. | 340 | 620 | 25 | 180 HB | — |
Hot rolled | Cheapest mill condition for parts that will be fully heat treated after rough machining. | 440 | 730 | 18 | 212 HB | — |
Normalized | Uniform fine pearlitic structure with medium strength; used as a pre-machining or as-supplied condition for lightly loaded parts. | 500 | 830 | 20 | 22 HRC | — |
Cold drawn | Pick for close-tolerance bright bar with raised yield strength when no further heat treatment is planned. | 660 | 760 | 12 | 225 HB | — |
quenched and tempered to hardness band | Common commercial purchase band for shafts and machined components needing good toughness and easy finishing. | 840 | 960 | 18 | 30 HRC | — |
OQ&T 650 °C | Toughest quench-and-temper condition; use where shock loading or later machining dominates. | 860 | 965 | 19 | 30 HRC | — |
Induction hardened | Use when a hard wear surface (55–60 HRC) is needed over a tough Q&T core, e.g. journals and gear teeth. | 870 | 1,000 | 14 | 57 HRC | 7.4 % IACS |
quenched and tempered to hardness band | Higher-strength commercial band for gears, cams and wear-loaded shafts still machinable with carbide tooling. | 1,030 | 1,140 | 15 | 36 HRC | — |
OQ&T 540 °C | Good general-purpose temper: high yield with usable impact toughness for machine components. | 1,050 | 1,140 | 16 | 36 HRC | — |
quenched and tempered to hardness band | Specify when wear resistance matters more than impact toughness; grind rather than mill to finish. | 1,260 | 1,390 | 13 | 42 HRC | — |
OQ&T 425 °C | Balanced high strength and wear resistance for gears, spindles and heavy-duty shafts. | 1,275 | 1,400 | 13 | 42 HRC | — |
QT315This page OQ&T 315 °C | Very high strength with slightly better ductility than the 205 °C temper. | 1,550 | 1,720 | 11 | 48 HRC | — |
OQ&T 205 °C | Maximum hardness and wear resistance for pins, wear plates and tooling where toughness is secondary. | 1,660 | 1,930 | 9 | 52 HRC | — |
What is 5145-QT315?
5145-QT315 is 5145 heat treated to QT315 — very high strength with slightly better ductility than the 205 °C temper. 5145-QT315 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi). 5145-QT315 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). A is the default condition FabDigit quotes; QT315 is available on request or by drawing note.
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Difficult to machine — 27/100, worse than 92% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Low fracture toughness — 48 MPa·√m (43.7 ksi·√in), worse than 88% of steel grades
- Limited service temperature — 260°C (500 °F), worse than 82% of steel grades
5145-QT315 properties
Typical room-temperature values for 5145-QT315; 13 are specific to this condition. Other listed values are 5145 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
5145-QT315 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).
Mechanical16
5145-QT315 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
5145-QT315 is rated for continuous service to 260°C (500 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
5145-QT315 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 5145-QT315 takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
5145-QT315's machinability is poor (27/100, worse than 92% of steel grades); weldability fair (35/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 5145-QT315
Is 5145 easy to machine?
Machine in the annealed or ≤32 HRC condition with carbide tooling and rigid setups; above 40 HRC switch to grinding or CBN turning.
Can 5145 be welded?
Poor weldability at 0.45 % C — preheat 250–350 °C, low-hydrogen consumables, and temper immediately after welding to avoid martensitic cracking.
Can 5145 be formed, bent or molded?
Cold form only when spheroidize annealed and in gentle bends; hot work at 1050–1180 °C and always cool slowly or normalize after forging.
What surface finishes work on 5145?
Not corrosion-resistant: use black oxide, phosphate + oil, zinc or hard-chrome plating; bake after plating to relieve hydrogen embrittlement at high hardness.
5145 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 |
|---|---|---|
| Cheat analysis per SAE J404 | 0.43 – 0.48 | 0.46 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.7 – 0.9 | 0.8 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
5145-QT315 — frequently asked
What is 5145-QT315 used for?
5145-QT315 is typically used for gears, shafts, bushings and hand tools. In short: deep-hardening chromium steel; lower-cost 4140 alternative; poor weldability above 0.4 %C.
What is the yield strength of 5145-QT315?
5145-QT315 has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,720 MPa (249 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 14 listed tempers.
Is 5145-QT315 easy to machine?
Not especially — machinability is rated poor (27/100, worse than 92% of steel grades). Machine in the annealed or ≤32 HRC condition with carbide tooling and rigid setups; above 40 HRC switch to grinding or CBN turning.
Can 5145-QT315 be welded?
With care — weldability is rated fair (35/100). Poor weldability at 0.45 % C — preheat 250–350 °C, low-hydrogen consumables, and temper immediately after welding to avoid martensitic cracking.
What surface finishes work on 5145-QT315?
Not corrosion-resistant: use black oxide, phosphate + oil, zinc or hard-chrome plating; bake after plating to relieve hydrogen embrittlement at high hardness.
Can 5145-QT315 be formed, bent or molded?
Cold form only when spheroidize annealed and in gentle bends; hot work at 1050–1180 °C and always cool slowly or normalize after forging.
What is the maximum service temperature of 5145-QT315?
5145-QT315 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 5145-A and 5145-QT205?
A is the default condition — standard stock condition: softest, most machinable state before quench-and-temper. QT205: maximum hardness and wear resistance for pins, wear plates and tooling where toughness is secondary. Yield strength is 340 MPa in A versus 1,660 MPa in QT205.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook, 31st ed. (machinability ratings) — Industrial Press (2020)
- GB/T 3077 — (45Cr equivalent) — SAC (2015)
- (alloy round bar) — Mysteel (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.