Steel SUM31 CH-QT
Heat-treated state
JIS SUM31
CH-QT = carburized, quenched and low-temperature tempered
Use when the finished part needs a hard wear surface (pins, small gears, bushings) over a tough low-carbon core.
Values for the CH-QT condition
Other SUM31 tempers and conditions
SUM31 is listed in 6 conditions; see the grade overview at SUM31.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest state — pick for maximum cold formability, deep drilling or before carburizing. | 230 | 400 | 33 | 116 HB | — |
Hot rolled | Cheapest as-rolled bar for parts that will be fully machined or subsequently heat treated. | 250 | 430 | 28 | 126 HB | — |
Normalized | Uniform fine grain and predictable machining response; used to reset structure after forging. | 270 | 450 | 30 | 131 HB | — |
Cold drawn, stress relieved | Choose when asymmetric machining would otherwise cause the part to bow after cutting. | 370 | 490 | 18 | 143 HB | 10.5 % IACS |
CDDefault Cold drawn | The standard stocked condition: good size tolerance, straightness and free-cutting behaviour on automatic lathes. | 400 | 510 | 15 | 150 HB | — |
CH-QTThis page Carburized, quenched and low-temperature tempered | Use when the finished part needs a hard wear surface (pins, small gears, bushings) over a tough low-carbon core. | 480 | 700 | 12 | 60 HRC | 9.5 % IACS |
What is SUM31 CH-QT?
SUM31 CH-QT is SUM31 heat treated to CH-QT — use when the finished part needs a hard wear surface (pins, small gears, bushings) over a tough low-carbon core. SUM31 CH-QT has a yield strength of 480 MPa (69.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 59% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi). SUM31 CH-QT 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). CD is the default condition FabDigit quotes; CH-QT is available on request or by drawing note.
Advantages
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited formability — 5/100, worse than 99% of steel grades
- Hard to polish — 35/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
SUM31 CH-QT properties
Typical room-temperature values for SUM31 CH-QT; 21 are specific to this condition. Other listed values are SUM31 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUM31 CH-QT 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
SUM31 CH-QT has a yield strength of 480 MPa (69.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 59% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
SUM31 CH-QT is rated for continuous service to 180°C (356 °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
SUM31 CH-QT 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 SUM31 CH-QT takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
SUM31 CH-QT's machinability is poor (15/100, worse than 98% of steel grades); weldability not recommended (10/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUM31 CH-QT
Is SUM31 easy to machine?
Excellent free-cutting steel — MnS gives short chips at high feeds; run sharp positive tooling with good coolant, and expect ~90 % of AISI 1212 productivity.
Can SUM31 be welded?
Poor: 0.08–0.13 % S promotes hot/solidification cracking, so avoid structural welding or use low-heat-input, low-dilution processes with basic filler.
Can SUM31 be formed, bent or molded?
Only light bending or coining in the annealed state; sulfide stringers make transverse cold heading and deep drawing unreliable.
What surface finishes work on SUM31?
Not anodizable; protect by zinc/nickel plating, black oxide, phosphate + oil or paint — sulfide inclusions can cause pinholes in thin plating.
SUM31 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 | 0.14 – 0.2 | 0.17 |
| Mn | 1 – 1.3 | 1.15 |
| Pmax per JIS G4804 | ≤ 0.04 | 0.02 |
| Sfree-machining addition (MnS) | 0.08 – 0.13 | 0.1 |
| Sinot normally specified; rimmed/semi-killed practice | ≤ 0.1 | 0.05 |
| Fe | balance | — |
SUM31 CH-QT — frequently asked
What is SUM31 CH-QT used for?
SUM31 CH-QT is typically used for small shafts, pins and carburized components. In short: free-cutting carburizing grade; 82 machinability rating; not for welded assemblies.
What is the yield strength of SUM31 CH-QT?
SUM31 CH-QT has a typical yield strength of 480 MPa (69.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 59% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SUM31 CH-QT easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Excellent free-cutting steel — MnS gives short chips at high feeds; run sharp positive tooling with good coolant, and expect ~90 % of AISI 1212 productivity.
Can SUM31 CH-QT be welded?
Not readily — weldability is rated not recommended (10/100). Poor: 0.08–0.13 % S promotes hot/solidification cracking, so avoid structural welding or use low-heat-input, low-dilution processes with basic filler.
What surface finishes work on SUM31 CH-QT?
Not anodizable; protect by zinc/nickel plating, black oxide, phosphate + oil or paint — sulfide inclusions can cause pinholes in thin plating.
Can SUM31 CH-QT be formed, bent or molded?
Only light bending or coining in the annealed state; sulfide stringers make transverse cold heading and deep drawing unreliable.
What is the maximum service temperature of SUM31 CH-QT?
SUM31 CH-QT is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUM31-CD and SUM31-A?
CD is the default condition — the standard stocked condition: good size tolerance, straightness and free-cutting behaviour on automatic lathes. A: softest state — pick for maximum cold formability, deep drilling or before carburizing. Yield strength is 400 MPa in CD versus 230 MPa in A.
Sources
- JIS G 4804 — Sulfur and sulfur-compound free-cutting steels — JSA (2019)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.16 — Machining — 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.