Steel 10B21 · heat-treated state
Steel 10B21-SA
Properties of the SA condition, compared with the other 10B21 tempers.
The condition wire is actually shipped in for multi-station cold heading of bolts and screws — lowest work-hardening, best die life.
What is 10B21-SA?
10B21-SA is 10B21 heat treated to SA — the condition wire is actually shipped in for multi-station cold heading of bolts and screws — lowest work-hardening, best die life. 10B21-SA has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 420 MPa (60.9 ksi) — weaker than 92% of steel grades. Elongation at break is 36% and the elastic modulus is 205 GPa (29.7 Msi). 10B21-SA has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,465°C (2,669 °F). HR is the default condition FabDigit quotes; SA is available on request or by drawing note.
Advantages
- Forms and bends easily — 95/100, better than 99% of steel grades
- Ductile — tolerates forming and impact — 36%, better than 97% of steel grades
- Conducts heat well — 51.9 W/m·K (30 BTU/hr·ft·°F), better than 96% of steel grades
- High electrical conductivity — 10.8 % IACS, better than 94% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Low strength — 260 MPa (37.7 ksi), worse than 92% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
10B21-SA properties
Typical room-temperature values for 10B21-SA — 9 properties are specific to this condition; the rest are grade-level values shared by every 10B21 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
10B21-SA has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,465°C (2,669 °F).
Mechanical14
10B21-SA has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 420 MPa (60.9 ksi) — weaker than 92% of steel grades. Elongation at break is 36% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
10B21-SA is rated for continuous service to 400°C (752 °F). It conducts heat at 51.9 W/m·K (30 BTU/hr·ft·°F), better than 96% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
10B21-SA conducts electricity at 10.8 % IACS, better than 94% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 87% of steel grades.
Sustainability4
Producing a kilogram of 10B21-SA 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
10B21-SA's machinability is fair (52/100, better than 52% of steel grades); weldability excellent (85/100); formability excellent (95/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 10B21 tempers and conditions
10B21 is also supplied in 8 other conditions. The full side-by-side table is on the 10B21 overview.
- HRDefaultStandard mill supply form for wire rod and bar destined for drawing, cold heading or heat treatment.290 MPa yield · 126 HB
- QT-3239Highest common strength level for 10B21 fasteners; mind hydrogen embrittlement and delayed fracture risk above ~ 34 HRC when electroplated.990 MPa yield · 35 HRC
- QT-2832Narrow-band Q&T ordered when a tight hardness window is specified for threaded parts or self-tapping screw cores.810 MPa yield · 30 HRC
- QT-2534Standard fastener condition for class 8.8 / SAE Grade 5 bolts up to about M16 where boron gives full through-hardening.760 MPa yield · 30 HRC
- CarburizedUsed for self-drilling/self-tapping screws and case-hardened bolts needing a hard thread-forming surface over a ductile core.620 MPa yield · 57 HRC
- CRPick for close size tolerance, bright finish and higher as-supplied strength when no further heat treatment is planned.470 MPa yield · 163 HB
- NormalizedUse to refine grain and homogenize after hot working, giving uniform strength and good toughness prior to hardening.320 MPa yield · 135 HB
- SAThe condition wire is actually shipped in for multi-station cold heading of bolts and screws — lowest work-hardening, best die life.260 MPa yield · 110 HB
- AnnealedChoose for maximum ductility before severe cold forming or for stress-free machining of preforms.250 MPa yield · 111 HB
Working with 10B21-SA
Is 10B21 easy to machine?
Machines like plain 1020 — soft and gummy, so use sharp positive-rake tools, high speed and generous coolant; hardened Q&T 32–39 HRC states cut best with coated carbide at reduced feed.
Can 10B21 be welded?
Readily weldable by MIG/TIG/resistance (CE ≈ 0.35); no preheat needed below ~25 mm, but welding after quench-and-temper destroys the fastener strength locally.
Can 10B21 be formed, bent or molded?
Excellent cold headability in the spheroidize-annealed CHQ condition — designed for multi-station bolt heading and thread rolling; hot forge 1100–1200 °C.
What surface finishes work on 10B21?
Not anodizable; standard finishes are zinc or zinc-nickel electroplating, hot-dip galvanizing, zinc-flake (Dacromet/Geomet) and phosphate + oil — bake plated parts above 32 HRC to prevent hydrogen embrittlement.
10B21 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 |
|---|---|---|
| CSAE J403 boron steel | 0.18 – 0.23 | 0.2 |
| Mn | 0.6 – 0.9 | 0.75 |
| Sinot specified in J403 for bar; typical for killed CHQ wire | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.02 |
| Smax; fastener quality often ≤0.035 | ≤ 0.05 | 0.02 |
| Bhardenability agent; requires Ti/Al to fix N | 5×10⁻⁴ – 0 | 0 |
| Tiproducer addition to protect boron from nitrogen | ≤ 0.05 | 0.03 |
| Fe | balance | — |
10B21-SA — frequently asked
What is 10B21-SA used for?
10B21-SA is typically used for fasteners, bolts and studs. In short: hot-stamping boron steel.
What is the yield strength of 10B21-SA?
10B21-SA has a typical yield strength of 260 MPa (37.7 ksi) and a tensile strength of 420 MPa (60.9 ksi) — weaker than 92% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 10B21-SA easy to machine?
Reasonably — machinability is rated fair (52/100, better than 52% of steel grades). Machines like plain 1020 — soft and gummy, so use sharp positive-rake tools, high speed and generous coolant; hardened Q&T 32–39 HRC states cut best with coated carbide at reduced feed.
Can 10B21-SA be welded?
Yes — weldability is rated excellent (85/100). Readily weldable by MIG/TIG/resistance (CE ≈ 0.35); no preheat needed below ~25 mm, but welding after quench-and-temper destroys the fastener strength locally.
What surface finishes work on 10B21-SA?
Not anodizable; standard finishes are zinc or zinc-nickel electroplating, hot-dip galvanizing, zinc-flake (Dacromet/Geomet) and phosphate + oil — bake plated parts above 32 HRC to prevent hydrogen embrittlement.
Can 10B21-SA be formed, bent or molded?
Excellent cold headability in the spheroidize-annealed CHQ condition — designed for multi-station bolt heading and thread rolling; hot forge 1100–1200 °C.
What is the maximum service temperature of 10B21-SA?
10B21-SA 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 10B21-HR and 10B21 QT-3239?
HR is the default condition — standard mill supply form for wire rod and bar destined for drawing, cold heading or heat treatment. QT-3239: highest common strength level for 10B21 fasteners; mind hydrogen embrittlement and delayed fracture risk above ~ 34 HRC when electroplated. Yield strength is 290 MPa in HR versus 990 MPa in QT-3239.
Can FabDigit make parts in 10B21-SA?
Yes — 10B21-SA 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 J1268 — Hardenability Bands for Carbon and Alloy H Steels — SAE International (2019)
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners — SAE International (2014)
- ISO 898-1 — Mechanical properties of fasteners, carbon and alloy steel bolts, screws and studs — ISO (2013)
- ASTM A510 / A29 — General requirements for wire rods and carbon steel bars — ASTM (2018)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4A — Steel Heat Treating Fundamentals (boron hardenability) — ASM International (2013)
- GB/T 6478 / GB/T 5953 — (10B21 equivalent grades) — 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.