Steel 15B21
EN 15B21 · UNS G15211
15B21 is a low-carbon manganese steel micro-alloyed with 0.0005–0.003 % boron, which sharply raises hardenability without adding carbon or costly alloying elements.
Values for the HR condition
15B21 tempers and conditions
15B21 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 |
|---|---|---|---|---|---|---|
Spheroidize annealed, cold heading quality (CHQ) wire | Standard supply state for fastener wire: spheroidized carbides give the best cold-heading and thread-rolling behaviour. | 240 | 390 | 35 | 110 HB | 11 % IACS |
full/subcritical anneal | Softest condition; pick for maximum ductility before heavy cold work or machining of large sections. | 250 | 400 | 33 | 115 HB | — |
HRDefault Hot rolled | Default mill condition for wire rod and bar destined for spheroidizing, cold heading or subsequent quench and temper. | 280 | 450 | 28 | 131 HB | — |
austenitize ~900 °C, air cool | Use to homogenize grain structure and restore uniform properties after hot working or forging. | 310 | 470 | 30 | 137 HB | 10 % IACS |
Cold rolled | Choose for close size tolerance, bright finish and higher as-supplied strength where only limited forming is needed. | 440 | 520 | 14 | 155 HB | — |
Quenched and tempered, SAE J429 Grade 5 / class 8.8 level | Standard heat treatment for medium-strength boron-steel bolts and screws up to ~M16/5/8 in. | 720 | 880 | 16 | 29 HRC | — |
Case hardened / carbonitrided (case 55–62 HRC, tough core) | Pick for tapping screws, pins and light gears needing a hard wear surface over a tough boron-hardened core. | 900 | 1,100 | 9 | 58 HRC | 8 % IACS |
Quenched and tempered, SAE J429 Grade 8 / class 10.9 level | High-strength fastener condition; watch hydrogen embrittlement risk when electroplating and avoid notches. | 930 | 1,060 | 13 | 36 HRC | — |
Low-temper quench and temper | Used for self-drilling/tapping screws, chain links and wear parts where hardness matters more than toughness. | 1,150 | 1,300 | 10 | 42 HRC | — |
What is 15B21?
15B21 is a low-carbon manganese steel micro-alloyed with 0.0005–0.003 % boron, which sharply raises hardenability without adding carbon or costly alloying elements. It is supplied mainly as cold-heading-quality wire and bar for quenched-and-tempered fasteners (SAE J429 Grade 5/8, property class 8.8/10.9) and stampings, where excellent cold formability in the annealed state is combined with good response to quench and temper. Limits are poor corrosion resistance (needs plating or coating), reduced hardenability effect if the steel is not properly Ti/Al-treated to protect the boron from nitrogen, and susceptibility to hydrogen embrittlement after acid pickling/electroplating at high strength levels. 15B21 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). 15B21 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).
What is 15B21 used for?
- Bolts
- Threaded fasteners
- Inserts
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 89% of steel grades
- High electrical conductivity — 10 % IACS, better than 83% of steel grades
- Readily welded — 85/100, better than 83% of steel grades
Limitations
- Low strength — 280 MPa (40.6 ksi), worse than 90% of steel grades
15B21 properties
Typical room-temperature values for 15B21-HR; bars are the position among steel grades.
Physical3
15B21 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 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 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 conducts electricity at 10 % IACS, better than 83% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 15B21 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'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.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 15B21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 15B21
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.
Manufacturability
The process limits FabDigit applies to 15B21. Every 15B21 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair55 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 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 | Better78 / 100 |
|---|---|
| Weldability | Better85 / 100 |
| Bendable | Yes |
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 |
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.
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 15B21 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G15211
How much does 15B21 cost?
15B21 is a standard-cost steel ($$), cheaper than about 71% 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.
15B21 — frequently asked
What is 15B21 used for?
15B21 is typically used for bolts, threaded fasteners and inserts. In short: hot-stamping boron steel.
What is the yield strength of 15B21?
15B21 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 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 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?
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 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?
15B21 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.
How much does 15B21 cost?
15B21 is a standard-cost steel ($$), cheaper than about 71% 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 15B21?
Yes — 15B21 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 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; 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.