Steel 15B21 · hardness band
Steel 15B21 Q&T 40-45 HRC
Properties of the Q&T 40-45 HRC condition, compared with the other 15B21 tempers.
Used for self-drilling/tapping screws, chain links and wear parts where hardness matters more than toughness.
What is 15B21 Q&T 40-45 HRC?
15B21 Q&T 40-45 HRC is 15B21 heat treated to Q&T 40-45 HRC — used for self-drilling/tapping screws, chain links and wear parts where hardness matters more than toughness. 15B21 Q&T 40-45 HRC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi). 15B21 Q&T 40-45 HRC 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). HR is the default condition FabDigit quotes; Q&T 40-45 HRC is available on request or by drawing note.
Advantages
- High strength — 1,150 MPa (167 ksi), better than 94% 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 % IACS, better than 82% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
- Limited formability — 12/100, worse than 91% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
15B21 Q&T 40-45 HRC properties
Typical room-temperature values for 15B21 Q&T 40-45 HRC — 11 properties are specific to this condition; the rest are grade-level values shared by every 15B21 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
15B21 Q&T 40-45 HRC 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).
Mechanical13
15B21 Q&T 40-45 HRC has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
15B21 Q&T 40-45 HRC is rated for continuous service to 400°C (752 °F). It conducts heat at 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
15B21 Q&T 40-45 HRC conducts electricity at 10 % IACS, better than 82% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 87% of steel grades.
Sustainability4
Producing a kilogram of 15B21 Q&T 40-45 HRC takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
15B21 Q&T 40-45 HRC's machinability is good (55/100, better than 62% of steel grades); weldability poor (25/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 15B21 tempers and conditions
15B21 is also supplied in 8 other conditions. The full side-by-side table is on the 15B21 overview.
- HRDefaultDefault mill condition for wire rod and bar destined for spheroidizing, cold heading or subsequent quench and temper.280 MPa yield · 131 HB
- Q&T 40-45 HRCUsed for self-drilling/tapping screws, chain links and wear parts where hardness matters more than toughness.1,150 MPa yield · 42 HRC
- Q&T 33-39 HRCHigh-strength fastener condition; watch hydrogen embrittlement risk when electroplating and avoid notches.930 MPa yield · 36 HRC
- CH-CarburizedPick for tapping screws, pins and light gears needing a hard wear surface over a tough boron-hardened core.900 MPa yield · 58 HRC
- Q&T 25-32 HRCStandard heat treatment for medium-strength boron-steel bolts and screws up to ~M16/5/8 in.720 MPa yield · 29 HRC
- CRChoose for close size tolerance, bright finish and higher as-supplied strength where only limited forming is needed.440 MPa yield · 155 HB
- NormalizedUse to homogenize grain structure and restore uniform properties after hot working or forging.310 MPa yield · 137 HB
- AnnealedSoftest condition; pick for maximum ductility before heavy cold work or machining of large sections.250 MPa yield · 115 HB
- SAStandard supply state for fastener wire: spheroidized carbides give the best cold-heading and thread-rolling behaviour.240 MPa yield · 110 HB
Working with 15B21 Q&T 40-45 HRC
Is 15B21 easy to machine?
Machines like 1021 but slightly gummier — boron reduces the AISI rating a few points; use sharp positive tools, good chip lubrication, or specify a resulfurized/leaded variant for screw-machine work.
Can 15B21 be welded?
Readily weldable in the annealed/hot-rolled condition (low carbon equivalent); avoid welding after quench and temper, or re-temper, since the boron hardenability produces hard HAZ martensite.
Can 15B21 be formed, bent or molded?
Excellent cold heading, upsetting and thread rolling in spheroidize-annealed CHQ wire; hot forge 1100–1250 °C and normalize afterwards.
What surface finishes work on 15B21?
Not anodizable — protect with zinc or zinc-nickel electroplate (bake to relieve hydrogen at ≥32 HRC), zinc-flake coatings, phosphate + oil, or black oxide.
15B21 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 | 0.17 – 0.24 | 0.2 |
| Mn | 0.7 – 1 | 0.85 |
| Si0.15–0.30 in some mill practices | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.05 | 0.02 |
| Bboron addition for hardenability; Ti/Al treatment protects it from N | 5×10⁻⁴ – 0 | 0 |
| Fe | balance | — |
15B21 Q&T 40-45 HRC — frequently asked
What is 15B21 Q&T 40-45 HRC used for?
15B21 Q&T 40-45 HRC is typically used for bolts, threaded fasteners and inserts. In short: hot-stamping boron steel.
What is the yield strength of 15B21 Q&T 40-45 HRC?
15B21 Q&T 40-45 HRC has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 15B21 Q&T 40-45 HRC easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like 1021 but slightly gummier — boron reduces the AISI rating a few points; use sharp positive tools, good chip lubrication, or specify a resulfurized/leaded variant for screw-machine work.
Can 15B21 Q&T 40-45 HRC be welded?
Not readily — weldability is rated poor (25/100). Readily weldable in the annealed/hot-rolled condition (low carbon equivalent); avoid welding after quench and temper, or re-temper, since the boron hardenability produces hard HAZ martensite.
What surface finishes work on 15B21 Q&T 40-45 HRC?
Not anodizable — protect with zinc or zinc-nickel electroplate (bake to relieve hydrogen at ≥32 HRC), zinc-flake coatings, phosphate + oil, or black oxide.
Can 15B21 Q&T 40-45 HRC be formed, bent or molded?
Excellent cold heading, upsetting and thread rolling in spheroidize-annealed CHQ wire; hot forge 1100–1250 °C and normalize afterwards.
What is the maximum service temperature of 15B21 Q&T 40-45 HRC?
15B21 Q&T 40-45 HRC 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 15B21-HR and 15B21-CR?
HR is the default condition — default mill condition for wire rod and bar destined for spheroidizing, cold heading or subsequent quench and temper. CR: choose for close size tolerance, bright finish and higher as-supplied strength where only limited forming is needed. Yield strength is 280 MPa in HR versus 440 MPa in CR.
Can FabDigit make parts in 15B21 Q&T 40-45 HRC?
Yes — 15B21 Q&T 40-45 HRC is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J403 — Chemical Compositions of SAE Carbon Steels — SAE International (2014)
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners — SAE International (2014)
- ASTM A29/A29M — General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ISO 898-1 — Mechanical properties of fasteners, bolts, screws and studs — ISO (2013)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (boron steels, 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.