Steel SUM31
JIS SUM31
SUM31 is a low-carbon resulfurized free-machining steel from the JIS free-cutting family, equivalent to AISI 1108, in which 0.08–0.13 % sulfur forms manganese sulfide inclusions that break chips.
Reference datasheet — SUM31 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the CD condition
SUM31 tempers and conditions
SUM31 is supplied in 6 conditions, soft to hard. CD is the default FabDigit quotes; the values on this page are for it.
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 | — |
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 |
Supply forms, finishes and certifications
Ways SUM31 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
TGP | Turned, ground and polished bar | Surface finish |
What is SUM31?
SUM31 is a low-carbon resulfurized free-machining steel from the JIS free-cutting family, equivalent to AISI 1108, in which 0.08–0.13 % sulfur forms manganese sulfide inclusions that break chips. It is chosen for lightly loaded turned and carburized parts and is stocked hot-rolled, annealed, normalized, cold-drawn, stress-relieved, as TGP bar and quenched and tempered. Cold-drawn bar gives about 400 MPa yield, 510 MPa tensile, 15 % elongation and 150 HB, with a machinability rating of 82. The same sulfur rules out structural welding and lowers transverse ductility; step up to SUM32 (1117) when a deeper case and more strength are needed. SUM31 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). SUM31 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Elongation at break is 15% and the elastic modulus is 200 GPa (29 Msi).
What is SUM31 used for?
- Small shafts
- Pins
- Carburized components
Advantages
- Easy to machine — 82/100, better than 98% of steel grades
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
- High electrical conductivity — 10.5 % IACS, better than 89% of steel grades
Limitations
- Hard to polish — 35/100, worse than 99% of steel grades
SUM31 properties
Typical room-temperature values for SUM31-CD; bars are the position among steel grades.
Physical3
SUM31 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 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Elongation at break is 15% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
SUM31 is rated for continuous service to 350°C (662 °F). It conducts heat at 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
SUM31 conducts electricity at 10.5 % IACS, better than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of SUM31 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's machinability is very good (82/100, better than 98% of steel grades); weldability poor (30/100); formability fair (35/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SUM31 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUM31
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SUM31 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 1108
How much does SUM31 cost?
SUM31 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SUM31 — frequently asked
What is SUM31 used for?
SUM31 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?
SUM31 has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SUM31 easy to machine?
Yes — machinability is rated very good (82/100, better 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 be welded?
Not readily — weldability is rated poor (30/100). 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?
Not anodizable; protect by zinc/nickel plating, black oxide, phosphate + oil or paint — sulfide inclusions can cause pinholes in thin plating.
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 is the maximum service temperature of SUM31?
SUM31 is rated for continuous use to about 350°C (662 °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.
How much does SUM31 cost?
SUM31 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.