Steel SUM43 QT-255HB
Heat-treated state
JIS SUM43
QT-255HB = q&T ~248–302 HB
Use the general-purpose quenched and high-temperature tempered state at 248–302 HB for load-carrying shafts, bolts and pins that need 900 MPa tensile with balanced toughness.
Values for the QT-255HB condition
Other SUM43 tempers and conditions
SUM43 is listed in 8 conditions; see the grade overview at SUM43.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Pick the spheroidize or full anneal when maximum ductility and allowance for cold forming or heavy cutting matter; 167 HB and 20 % elongation come with the lowest strength of any state. | 345 | 585 | 20 | 167 HB | — |
Hot rolled | Use hot rolled bar for large diameters, heavy roughing allowances or parts to be quenched and tempered later; it is the economical supply form at 670 MPa tensile and 197 HB. | 360 | 670 | 15 | 197 HB | — |
Normalized | Normalize at about 870 °C with air cooling to refine the structure and remove banded segregation from forging or hot rolling, as preparation before quenching and tempering. | 400 | 715 | 15 | 15 HRC | 9.8 % IACS |
CDDefault Cold drawn | Choose the usual stock condition, cold drawn bright bar, for close size tolerance, good surface finish and 620 MPa yield with machinability suited to automatic screw machines. | 620 | 700 | 10 | 212 HB | — |
Induction hardened | Choose when journals, pins and guide faces need a 55 HRC wear surface over a tough cold-drawn core; the 0.45% C self-hardens under induction, but finish machining must precede hardening. | 640 | 760 | 10 | 55 HRC | 8.5 % IACS |
Cold Drawn + Stress Relieved (high-tensile bar) | Specify cold drawing followed by a 500–600 °C stress relief for slender shafts, lead screws and hydraulic rods that distort after machining; yield rises to 690 MPa at 229 HB. | 690 | 790 | 11 | 229 HB | — |
QT-255HBThis page Q&T ~248–302 HB | Use the general-purpose quenched and high-temperature tempered state at 248–302 HB for load-carrying shafts, bolts and pins that need 900 MPa tensile with balanced toughness. | 750 | 900 | 14 | 27 HRC | — |
Q&T 30–34 HRC | Choose quenching with an intermediate temper to 30–34 HRC for drive components needing 1030 MPa tensile and higher wear resistance, trading away toughness and machinability. | 860 | 1,030 | 12 | 32 HRC | — |
What is SUM43 QT-255HB?
SUM43 QT-255HB is SUM43 heat treated to QT-255HB — use the general-purpose quenched and high-temperature tempered state at 248–302 HB for load-carrying shafts, bolts and pins that need 900 MPa tensile with balanced toughness. SUM43 QT-255HB has a yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi). SUM43 QT-255HB 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; QT-255HB is available on request or by drawing note.
Advantages
- Easy to machine — 65/100, better than 93% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 750 MPa (109 ksi), better than 84% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Low fracture toughness — 50 MPa·√m (45.5 ksi·√in), worse than 86% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- Limited ductility — 14%, worse than 75% of steel grades
SUM43 QT-255HB properties
Typical room-temperature values for SUM43 QT-255HB; 13 are specific to this condition. Other listed values are SUM43 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SUM43 QT-255HB 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
SUM43 QT-255HB has a yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SUM43 QT-255HB is rated for continuous service to 400°C (752 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
SUM43 QT-255HB 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 SUM43 QT-255HB 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
SUM43 QT-255HB's machinability is good (65/100, better than 93% of steel grades); weldability poor (20/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SUM43 QT-255HB
Is SUM43 easy to machine?
First choice for automatic lathes: cutting speeds can run 30–50 % above 1045 with good chip breaking and long tool life, but the high sulfur gives low transverse toughness, so watch clamping distortion on deep-hole and thin-wall parts.
Can SUM43 be welded?
Not recommended (high S, 0.45 % C): hot cracking and a hard, brittle HAZ are likely; if welding is unavoidable, preheat 200–300 °C, use low-hydrogen consumables and temper after welding.
Can SUM43 be formed, bent or molded?
Cold forming — bending, knurling and cold heading — is poor because elongated MnS inclusions crack along the rolling direction; form in the annealed or hot condition.
What surface finishes work on SUM43?
No corrosion resistance, so specify black oxide, phosphate, zinc or hard chrome plating; acid can be retained at sulfide inclusions before plating, and inclusion streaks limit mirror polishing.
SUM43 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 |
|---|---|---|
| CJIS G 4804 SUM43 | 0.4 – 0.48 | 0.44 |
| Mn | 1.35 – 1.65 | 1.5 |
| Smanganese sulfide inclusions provide free-machining | 0.24 – 0.33 | 0.28 |
| P | ≤ 0.04 | 0.02 |
| Sinot specified by JIS for SUM4x; usually kept low in practice | ≤ 0.35 | 0.15 |
| Curesidual element limit, when specified by purchaser | ≤ 0.3 | — |
| Fe | balance | — |
SUM43 QT-255HB — frequently asked
What is SUM43 QT-255HB used for?
SUM43 QT-255HB is typically used for shafts, axles and high-strength fasteners. In short: strongest SUM free-cutting grade; induction-hardenable and free-cutting; poor cold formability.
What is the yield strength of SUM43 QT-255HB?
SUM43 QT-255HB has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SUM43 QT-255HB easy to machine?
Reasonably — machinability is rated good (65/100, better than 93% of steel grades). First choice for automatic lathes: cutting speeds can run 30–50 % above 1045 with good chip breaking and long tool life, but the high sulfur gives low transverse toughness, so watch clamping distortion on deep-hole and thin-wall parts.
Can SUM43 QT-255HB be welded?
Not readily — weldability is rated poor (20/100). Not recommended (high S, 0.45 % C): hot cracking and a hard, brittle HAZ are likely; if welding is unavoidable, preheat 200–300 °C, use low-hydrogen consumables and temper after welding.
What surface finishes work on SUM43 QT-255HB?
No corrosion resistance, so specify black oxide, phosphate, zinc or hard chrome plating; acid can be retained at sulfide inclusions before plating, and inclusion streaks limit mirror polishing.
Can SUM43 QT-255HB be formed, bent or molded?
Cold forming — bending, knurling and cold heading — is poor because elongated MnS inclusions crack along the rolling direction; form in the annealed or hot condition.
What is the maximum service temperature of SUM43 QT-255HB?
SUM43 QT-255HB is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUM43-CD and SUM43-A?
CD is the default condition — choose the usual stock condition, cold drawn bright bar, for close size tolerance, good surface finish and 620 MPa yield with machinability suited to automatic screw machines. A: pick the spheroidize or full anneal when maximum ductility and allowance for cold forming or heavy cutting matter; 167 HB and 20 % elongation come with the lowest strength of any state. Yield strength is 620 MPa in CD versus 345 MPa in A.
Sources
- JIS G 4804 — Sulfur and sulfur-composition free-cutting steels — JISC (2019)
- SAE J403 / ASTM A29 — Carbon and resulfurized carbon steel bars (1141/1144) — SAE / ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.16 — Machining (machinability ratings) — ASM International (1989)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
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.