Steel 15B21 · supply condition · default condition
Steel 15B21-HR
Properties of the HR condition, compared with the other 15B21 tempers.
Default mill condition for wire rod and bar destined for spheroidizing, cold heading or subsequent quench and temper.
What is 15B21-HR?
15B21-HR is 15B21 supplied in the HR condition — default mill condition for wire rod and bar destined for spheroidizing, cold heading or subsequent quench and temper. 15B21-HR has a yield strength of 280 MPa (40.6 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 90% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi). 15B21-HR 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).
Advantages
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
- Forms and bends easily — 78/100, better than 91% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 88% of steel grades
- Readily welded — 85/100, better than 83% of steel grades
- High electrical conductivity — 10 % IACS, better than 82% of steel grades
Limitations
- Low strength — 280 MPa (40.6 ksi), worse than 90% of steel grades
15B21-HR properties
Typical room-temperature values for 15B21-HR — 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-HR 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-HR has a yield strength of 280 MPa (40.6 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 90% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
15B21-HR 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-HR 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-HR 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-HR's machinability is good (55/100, better than 62% of steel grades); weldability excellent (85/100); formability very good (78/100).
Common Calculations5
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-HR
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-HR — frequently asked
What is 15B21-HR used for?
15B21-HR is typically used for bolts, threaded fasteners and inserts. In short: hot-stamping boron steel.
What is the yield strength of 15B21-HR?
15B21-HR has a typical yield strength of 280 MPa (40.6 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 90% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 15B21-HR 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-HR be welded?
Yes — weldability is rated excellent (85/100). 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-HR?
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-HR 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-HR?
15B21-HR 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-HR?
Yes — 15B21-HR 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.