Steel 10B21
EN 10B21 · UNS G10211
10B21 (G10211) is a low-carbon boron-treated steel in which a small boron addition raises hardenability, so cold-headed parts can be quenched and tempered to fastener strength classes at lower cost than plain-carbon or low-alloy grades.
Values for the HR condition
10B21 tempers and conditions
10B21 is supplied in 9 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/subcritical anneal (softest condition) | Choose for maximum ductility before severe cold forming or for stress-free machining of preforms. | 250 | 400 | 34 | 111 HB | — |
Spheroidize annealed, cold-heading quality | The condition wire is actually shipped in for multi-station cold heading of bolts and screws — lowest work-hardening, best die life. | 260 | 420 | 36 | 110 HB | 11 % IACS |
HRDefault Hot rolled | Standard mill supply form for wire rod and bar destined for drawing, cold heading or heat treatment. | 290 | 430 | 30 | 126 HB | — |
austenitize ~900 °C, air cool | Use to refine grain and homogenize after hot working, giving uniform strength and good toughness prior to hardening. | 320 | 470 | 30 | 135 HB | — |
Cold rolled | Pick for close size tolerance, bright finish and higher as-supplied strength when no further heat treatment is planned. | 470 | 550 | 15 | 163 HB | — |
case hardened surface, tough core | Used for self-drilling/self-tapping screws and case-hardened bolts needing a hard thread-forming surface over a ductile core. | 620 | 800 | 10 | 57 HRC | — |
Q&T 25–34 HRC | Standard fastener condition for class 8.8 / SAE Grade 5 bolts up to about M16 where boron gives full through-hardening. | 760 | 900 | 16 | 30 HRC | — |
Q&T 28–32 HRC | Narrow-band Q&T ordered when a tight hardness window is specified for threaded parts or self-tapping screw cores. | 810 | 950 | 15 | 30 HRC | — |
Q&T 32–39 HRC | Highest common strength level for 10B21 fasteners; mind hydrogen embrittlement and delayed fracture risk above ~ 34 HRC when electroplated. | 990 | 1,100 | 12 | 35 HRC | — |
What is 10B21?
10B21 (G10211) is a low-carbon boron-treated steel in which a small boron addition raises hardenability, so cold-headed parts can be quenched and tempered to fastener strength classes at lower cost than plain-carbon or low-alloy grades. It is supplied as hot- and cold-rolled coil, CHQ wire and bar, with annealed, spheroidize-annealed, normalized, carburized and Q&T conditions (roughly 25–39 HRC bands) on file. The default annealed condition gives 290 MPa yield, 430 MPa tensile, 30 % elongation and 126 HB. It has no corrosion resistance, service is limited to about 400 °C, and welding after heat treatment removes local strength. 10B21 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). 10B21 has a yield strength of 290 MPa (42.1 ksi) and a tensile strength of 430 MPa (62.4 ksi) — weaker than 88% of steel grades. Elongation at break is 30% and the elastic modulus is 205 GPa (29.7 Msi).
What is 10B21 used for?
- Fasteners
- Bolts
- Studs
Advantages
- 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
- Forms and bends easily — 82/100, better than 94% of steel grades
- Ductile — tolerates forming and impact — 30%, better than 93% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Low strength — 290 MPa (42.1 ksi), worse than 88% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
10B21 properties
Typical room-temperature values for 10B21-HR; bars are the position among steel grades.
Physical3
10B21 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 has a yield strength of 290 MPa (42.1 ksi) and a tensile strength of 430 MPa (62.4 ksi) — weaker than 88% of steel grades. Elongation at break is 30% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
10B21 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 conducts electricity at 10.8 % IACS, better than 94% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 10B21 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's machinability is good (62/100, better than 89% of steel grades); weldability excellent (85/100); formability very good (82/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 10B21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 10B21
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.
Manufacturability
The process limits FabDigit applies to 10B21. Every 10B21 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair62 / 100 |
|---|---|
| ISO material group | P.1 |
| Cutting speed (rough / finish) | 220 / 260 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair82 / 100 |
|---|---|
| Weldability | Fair85 / 100 |
| Bendable | Yes |
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 10B21 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G10211
How much does 10B21 cost?
10B21 is a budget-cost steel ($), cheaper than about 100% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
10B21 — frequently asked
What is 10B21 used for?
10B21 is typically used for fasteners, bolts and studs. In short: hot-stamping boron steel.
What is the yield strength of 10B21?
10B21 has a typical yield strength of 290 MPa (42.1 ksi) and a tensile strength of 430 MPa (62.4 ksi) — weaker than 88% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 10B21 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% 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 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?
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 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?
10B21 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.
How much does 10B21 cost?
10B21 is a budget-cost steel ($), cheaper than about 100% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 10B21?
Yes — 10B21 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.