Steel 15B41-AQ (As-quenched)
Heat-treated state
EN 15B41 · UNS G15411
Intermediate process condition only — maximum hardness but brittle; always temper before service.
Values for the AQ condition
Other 15B41 tempers and conditions
15B41 is listed in 9 conditions; see the grade overview at 15B41.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Standard condition for cold-heading and cold-extruding bolt blanks before quench and temper. | 320 | 550 | 30 | 155 HB | — |
Solution annealed | Softest ferrite/pearlite condition for machining or severe forming before hardening. | 350 | 600 | 25 | 170 HB | — |
Hot rolled | Mill-supply condition for bar and coil that will be re-heated, forged or heat treated by the customer. | 415 | 725 | 18 | 210 HB | — |
Normalized | Uniform fine grain and predictable response before hardening; used for forgings. | 480 | 780 | 18 | 225 HB | — |
Cold drawn | Sized, straight bar with raised yield strength for as-machined parts not requiring hardening. | 640 | 760 | 12 | 217 HB | — |
quenched and high-temper (Grade 5 class) | Choose for tough, moderately strong bolts and machine parts where impact matters more than peak strength. | 800 | 950 | 16 | 29 HRC | — |
QT-33-39HRCDefault quenched and tempered (Grade 8 class) | The workhorse fastener condition: full through-hardening plus ≥425 °C temper for 1040 MPa minimum tensile. | 1,030 | 1,160 | 13 | 36 HRC | — |
quenched and low-temper | Pick for wear-loaded parts, self-drilling/track bolts and shafts where strength and abrasion beat toughness. | 1,250 | 1,400 | 10 | 42 HRC | — |
AQThis page As-quenched | Intermediate process condition only — maximum hardness but brittle; always temper before service. | 1,550 | 2,000 | 2 | 55 HRC | 7 % IACS |
What is 15B41-AQ?
15B41-AQ is 15B41 heat treated to AQ — intermediate process condition only — maximum hardness but brittle; always temper before service. 15B41-AQ has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Elongation at break is 2% and the elastic modulus is 205 GPa (29.7 Msi). 15B41-AQ 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). QT-33-39HRC is the default condition FabDigit quotes; AQ is available on request or by drawing note.
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
Limitations
- Difficult to weld — 5/100, worse than 100% of steel grades
- Limited formability — 2/100, worse than 100% of steel grades
- Limited ductility — 2%, worse than 99% of steel grades
- Limited service temperature — 150°C (302 °F), worse than 99% of steel grades
- Difficult to machine — 10/100, worse than 99% of steel grades
15B41-AQ properties
Typical room-temperature values for 15B41-AQ; 22 are specific to this condition. Other listed values are 15B41 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
15B41-AQ 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).
Mechanical16
15B41-AQ has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Elongation at break is 2% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
15B41-AQ is rated for continuous service to 150°C (302 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
15B41-AQ conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 15B41-AQ takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability6
15B41-AQ's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (5/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 15B41-AQ
Is 15B41 easy to machine?
Machine in the annealed or spheroidized state (~55 % of 1212); in Q&T at 33–39 HRC use coated carbide, rigid setups and reduced speeds, and finish-grind after hardening for tight tolerances.
Can 15B41 be welded?
Poor — high carbon equivalent plus boron gives a hard, crack-prone HAZ; if welding is unavoidable use low-hydrogen consumables, 200–300 °C preheat and immediate stress-relief/temper, and expect loss of the Q&T properties.
Can 15B41 be formed, bent or molded?
Cold-head and cold-extrude in the spheroidize-annealed condition (excellent CHQ behaviour); hot forge 1100–1220 °C, then normalize before hardening. Austenitize ~840–860 °C, oil or polymer quench, temper 425–540 °C to the required hardness band.
What surface finishes work on 15B41?
No inherent corrosion resistance — zinc, zinc-nickel, phosphate-and-oil or zinc-flake (Dacromet/Geomet) coatings are standard; for parts above ~1000 MPa avoid or bake after electroplating (ASTM F1941/B850) to prevent hydrogen embrittlement.
15B41 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 |
|---|---|---|
| Csome listings quote 0.36–0.44 (as SAE 1541) | 0.35 – 0.45 | 0.4 |
| Mn | 1.35 – 1.65 | 1.5 |
| Sikilled-steel silicon range; may be restricted for CHQ wire | 0.15 – 0.35 | 0.22 |
| P | ≤ 0.03 | 0.02 |
| Smax, non-resulfurized | ≤ 0.05 | 0.02 |
| Beffective (soluble) boron; requires Ti/Al nitrogen control | 5×10⁻⁴ – 0 | 0 |
| Fe | balance | — |
15B41-AQ — frequently asked
What is 15B41-AQ used for?
15B41-AQ is typically used for grade 8 bolts, high-strength fasteners, threaded studs and rods, cold-extruded shafts, suspension and chassis fastenings and wheel studs. In short: grade 8 bolt boron steel; through-hardens to 45 HRC; not for welded assemblies.
What is the yield strength of 15B41-AQ?
15B41-AQ has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 2,000 MPa (290 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 15B41-AQ easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machine in the annealed or spheroidized state (~55 % of 1212); in Q&T at 33–39 HRC use coated carbide, rigid setups and reduced speeds, and finish-grind after hardening for tight tolerances.
Can 15B41-AQ be welded?
Not readily — weldability is rated not recommended (5/100). Poor — high carbon equivalent plus boron gives a hard, crack-prone HAZ; if welding is unavoidable use low-hydrogen consumables, 200–300 °C preheat and immediate stress-relief/temper, and expect loss of the Q&T properties.
What surface finishes work on 15B41-AQ?
No inherent corrosion resistance — zinc, zinc-nickel, phosphate-and-oil or zinc-flake (Dacromet/Geomet) coatings are standard; for parts above ~1000 MPa avoid or bake after electroplating (ASTM F1941/B850) to prevent hydrogen embrittlement.
Can 15B41-AQ be formed, bent or molded?
Cold-head and cold-extrude in the spheroidize-annealed condition (excellent CHQ behaviour); hot forge 1100–1220 °C, then normalize before hardening. Austenitize ~840–860 °C, oil or polymer quench, temper 425–540 °C to the required hardness band.
What is the maximum service temperature of 15B41-AQ?
15B41-AQ is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 15B41 QT-33-39HRC and 15B41-SA?
QT-33-39HRC is the default condition — the workhorse fastener condition: full through-hardening plus ≥425 °C temper for 1040 MPa minimum tensile. SA: standard condition for cold-heading and cold-extruding bolt blanks before quench and temper. Yield strength is 1,030 MPa in QT-33-39HRC versus 320 MPa in SA.
Sources
- SAE J403 — Chemical Compositions of SAE Carbon Steels (incl. boron grades) — SAE International (2014)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought, General Requirements — ASTM (2020)
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners — SAE International (2014)
- SAE J1268 — Hardenability Bands for Carbon and Alloy H Steels (15B41H) — SAE International (2019)
- 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 (boron hardenability) — ASM International (2013)
- GB/T 3077 — Alloy Structural Steels (40MnB comparison grade) — SAC (2015)
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.