Steel 5120 · heat-treated state
Steel 5120 Q&T
Properties of the Q&T condition, compared with the other 5120 tempers.
Through-hardened low-carbon martensite for small tough parts where full case hardening is not required.
What is 5120 Q&T?
5120 Q&T is 5120 heat treated to Q&T — through-hardened low-carbon martensite for small tough parts where full case hardening is not required. 5120 Q&T has a yield strength of 640 MPa (92.8 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 79% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi). 5120 Q&T 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). HR is the default condition FabDigit quotes; Q&T is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
- High strength — 640 MPa (92.8 ksi), better than 79% of steel grades
Limitations
- Limited service temperature — 300°C (572 °F), worse than 77% of steel grades
5120 Q&T properties
Typical room-temperature values for 5120 Q&T — 11 properties are specific to this condition; the rest are grade-level values shared by every 5120 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
5120 Q&T 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).
Mechanical14
5120 Q&T has a yield strength of 640 MPa (92.8 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 79% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
5120 Q&T is rated for continuous service to 300°C (572 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
5120 Q&T conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 5120 Q&T takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
5120 Q&T's machinability is good (62/100, better than 89% of steel grades); weldability good (60/100); formability good (58/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 5120 tempers and conditions
5120 is also supplied in 6 other conditions. The full side-by-side table is on the 5120 overview.
- HRDefaultStandard stock form for bar and billet destined for forging, machining and subsequent carburizing.295 MPa yield · 145 HB
- CarburizedThe intended service condition: hard wear- and pitting-resistant case over a tough low-carbon core for gears, splines and pins.700 MPa yield · 60 HRC
- Q&TThrough-hardened low-carbon martensite for small tough parts where full case hardening is not required.640 MPa yield · 23 HRC
- CDChoose for close-tolerance, bright-finish bar with higher yield strength and better surface for turned parts.480 MPa yield · 170 HB
- NormalizedUniform fine-grain structure and stable machining response prior to carburizing; standard pre-treatment for forgings.330 MPa yield · 155 HB
- AnnealedSoftest and most machinable/formable state; use before heavy cold forming or deep drilling.280 MPa yield · 131 HB
Working with 5120 Q&T
Is 5120 easy to machine?
Machines well in annealed/normalized state (~65% of 1212); rough-machine before carburizing and leave grinding stock for post-hardening finishing.
Can 5120 be welded?
Weldable with low-hydrogen consumables at ~150–250 °C preheat; avoid welding carburized surfaces and stress-relieve afterwards.
Can 5120 be formed, bent or molded?
Good cold formability when annealed — used for cold-headed and stamped blanks; hot forge 1150–850 °C then normalize.
What surface finishes work on 5120?
No anodizing; protect with oil, phosphate, black oxide or zinc/nickel plating — bake after plating to avoid hydrogen embrittlement in hardened parts.
5120 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 | 0.17 – 0.22 | 0.2 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.7 – 0.9 | 0.8 |
| P | ≤ 0.04 | — |
| Smax; 5120H/resulfurized variants differ | ≤ 0.04 | — |
| Fe | balance | — |
5120 Q&T — frequently asked
What is 5120 Q&T used for?
5120 Q&T is typically used for gears, pins and shafts. In short: carburizing Cr-Mn bar.
What is the yield strength of 5120 Q&T?
5120 Q&T has a typical yield strength of 640 MPa (92.8 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 79% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 5120 Q&T easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines well in annealed/normalized state (~65% of 1212); rough-machine before carburizing and leave grinding stock for post-hardening finishing.
Can 5120 Q&T be welded?
Yes — weldability is rated good (60/100). Weldable with low-hydrogen consumables at ~150–250 °C preheat; avoid welding carburized surfaces and stress-relieve afterwards.
What surface finishes work on 5120 Q&T?
No anodizing; protect with oil, phosphate, black oxide or zinc/nickel plating — bake after plating to avoid hydrogen embrittlement in hardened parts.
Can 5120 Q&T be formed, bent or molded?
Good cold formability when annealed — used for cold-headed and stamped blanks; hot forge 1150–850 °C then normalize.
What is the maximum service temperature of 5120 Q&T?
5120 Q&T 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 5120-HR and 5120-CD?
HR is the default condition — standard stock form for bar and billet destined for forging, machining and subsequent carburizing. CD: choose for close-tolerance, bright-finish bar with higher yield strength and better surface for turned parts. Yield strength is 295 MPa in HR versus 480 MPa in CD.
Can FabDigit make parts in 5120 Q&T?
Yes — 5120 Q&T is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- GB/T 3077 (20Cr) — SAC (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals and Processes — ASM International (2013)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
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.