Steel 15B35 QT-AC
Heat-treated state
EN 15B35 · UNS G15351
QT-AC = q&T
Salt-bath bainitic treatment for thin sections needing 40–45 HRC with less distortion and better toughness than martensitic Q&T.
Values for the QT-AC condition
Other 15B35 tempers and conditions
15B35 is listed in 9 conditions; see the grade overview at 15B35.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition; choose for severe cold heading, cold extrusion or deep machining before hardening. | 330 | 560 | 28 | 160 HB | — |
Hot rolled | Mill-supplied stock for forging, hot heading and subsequent heat treatment. | 400 | 655 | 20 | 190 HB | — |
Normalized | Uniform fine-grained structure for forgings prior to machining or as a moderate-strength delivery condition. | 450 | 720 | 18 | 14 HRC | 9.7 % IACS |
CDDefault Cold drawn | Standard stocked fastener and shaft stock: good size tolerance and straightness, ready for cold heading or machining then quench-and-temper. | 620 | 730 | 13 | 217 HB | — |
quenched and tempered (high tempering temperature) | Tough, machinable strength level for shafts, links and forged parts where impact matters more than hardness. | 780 | 900 | 18 | 28 HRC | 44 W/m·K |
quenched and tempered, SAE J429 Grade 8 / ASTM A325 fastener level | The classic 15B35 fastener condition: ≥1040 MPa proof-load capability with acceptable ductility for bolts and screws. | 1,070 | 1,200 | 13 | 36 HRC | — |
QT-ACThis page Q&T | Salt-bath bainitic treatment for thin sections needing 40–45 HRC with less distortion and better toughness than martensitic Q&T. | 1,150 | 1,350 | 12 | 42 HRC | 8.6 % IACS |
quenched and tempered, high strength | For high-strength links, chain parts and wear-moderate components; ductility and notch tolerance start to drop. | 1,270 | 1,400 | 10 | 43 HRC | — |
quenched and low-temperature tempered (tillage / wear parts) | Hardness-driven condition for plow shares, sweeps, cutting edges and mower blades where abrasion beats toughness. | 1,450 | 1,650 | 8 | 49 HRC | — |
What is 15B35 QT-AC?
15B35 QT-AC is 15B35 heat treated to QT-AC — salt-bath bainitic treatment for thin sections needing 40–45 HRC with less distortion and better toughness than martensitic Q&T. 15B35 QT-AC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 15B35 QT-AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). CD is the default condition FabDigit quotes; QT-AC is available on request or by drawing note.
Advantages
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Limited formability — 12/100, worse than 92% of steel grades
- Difficult to machine — 32/100, worse than 87% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
15B35 QT-AC properties
Typical room-temperature values for 15B35 QT-AC; 22 are specific to this condition. Other listed values are 15B35 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
15B35 QT-AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical14
15B35 QT-AC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
15B35 QT-AC is rated for continuous service to 300°C (572 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
15B35 QT-AC conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 15B35 QT-AC 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
15B35 QT-AC's machinability is poor (32/100, worse than 87% of steel grades); weldability poor (20/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 15B35 QT-AC
Is 15B35 easy to machine?
Best machined in the spheroidize-annealed or cold-drawn state (~60–65 % of 1212); above 35 HRC use carbide/CBN, rigid setups and reduced feeds.
Can 15B35 be welded?
Boron raises hardenability sharply — preheat 150–250 °C, low-hydrogen consumables and post-weld temper; avoid welding parts already Q&T above 35 HRC.
Can 15B35 be formed, bent or molded?
Excellent hot forging (1050–1200 °C) and good cold heading/extrusion after spheroidize annealing plus phosphate-soap lubrication.
What surface finishes work on 15B35?
Zinc, zinc-nickel or phosphate-and-oil are standard; bake at 200 °C within 4 h of electroplating parts above ~1040 MPa to avoid hydrogen embrittlement.
15B35 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 | 0.32 – 0.38 | 0.35 |
| Mn | 0.8 – 1.05 | 0.92 |
| Sibar/forging ranges; may differ for wire rod | 0.15 – 0.35 | 0.25 |
| B0.0005 % min; Ti/Al used to fix N so B stays effective | 5×10⁻⁴ – 0 | 0 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
15B35 QT-AC — frequently asked
What is 15B35 QT-AC used for?
15B35 QT-AC is typically used for high-strength bolts, studs and structural fasteners. In short: alloy-grade hardenability, carbon-steel cost; forgeable and cold-headable; mid-range boron fastener steel.
What is the yield strength of 15B35 QT-AC?
15B35 QT-AC has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 15B35 QT-AC easy to machine?
Not especially — machinability is rated poor (32/100, worse than 87% of steel grades). Best machined in the spheroidize-annealed or cold-drawn state (~60–65 % of 1212); above 35 HRC use carbide/CBN, rigid setups and reduced feeds.
Can 15B35 QT-AC be welded?
Not readily — weldability is rated poor (20/100). Boron raises hardenability sharply — preheat 150–250 °C, low-hydrogen consumables and post-weld temper; avoid welding parts already Q&T above 35 HRC.
What surface finishes work on 15B35 QT-AC?
Zinc, zinc-nickel or phosphate-and-oil are standard; bake at 200 °C within 4 h of electroplating parts above ~1040 MPa to avoid hydrogen embrittlement.
Can 15B35 QT-AC be formed, bent or molded?
Excellent hot forging (1050–1200 °C) and good cold heading/extrusion after spheroidize annealing plus phosphate-soap lubrication.
What is the maximum service temperature of 15B35 QT-AC?
15B35 QT-AC 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 15B35-CD and 15B35 QT-AC?
CD is the default condition — standard stocked fastener and shaft stock: good size tolerance and straightness, ready for cold heading or machining then quench-and-temper. QT-AC: salt-bath bainitic treatment for thin sections needing 40–45 HRC with less distortion and better toughness than martensitic Q&T. Yield strength is 620 MPa in CD versus 1,150 MPa in QT-AC.
Sources
- SAE J403 — Chemical Compositions of SAE Carbon Steels — SAE International (2014)
- SAE J404 / J1268 — Alloy & Boron Steel Chemical Compositions and Hardenability Bands — SAE International (2015)
- ASTM A29/A29M — General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners — SAE International (2014)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (boron hardenability) — ASM International (1991)
- 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.