Steel 81B45
EN 81B45 · UNS G81451
A boron-modified Ni-Cr-Mo alloy steel where trace boron additions boost hardenability economically, allowing lower alloy content while still achieving good through-hardening for medium-strength parts.
Reference datasheet — 81B45 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the A condition
81B45 tempers and conditions
81B45 is supplied in 9 conditions, soft to hard. A 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 | Best condition for cold heading, cold extrusion and deep boring of this 0.45 %C grade. | 370 | 600 | 26 | 8 HRC | 7.9 % IACS |
ADefault Solution annealed | Softest supplied condition; choose for heavy machining or cold forming before quench-and-temper. | 400 | 640 | 22 | 187 HB | — |
Hot rolled | Lowest-cost mill condition for parts that will be fully heat treated after rough machining. | 450 | 760 | 18 | 217 HB | — |
Normalized | Uniform fine-grained structure with higher strength than annealed; common pre-treatment before hardening or for medium-duty parts. | 530 | 830 | 17 | 24 HRC | — |
Cold drawn | Tight-tolerance bright bar with raised yield strength; pick for as-supplied dimensional accuracy and light machining. | 635 | 745 | 12 | 217 HB | — |
Q&T 28–32 HRC | Tough, machinable prehardened condition for shafts and general machine parts. | 860 | 1,000 | 18 | 30 HRC | — |
Q&T 34–38 HRC | Balanced strength/toughness level for gears, spindles and heavy-duty fasteners. | 1,060 | 1,170 | 15 | 36 HRC | — |
Q&T 40–45 HRC | High-strength wear-resistant level for pins, links, sprockets and ground-engaging parts. | 1,280 | 1,400 | 12 | 42 HRC | — |
Q&T 48–52 HRC | Maximum hardness/wear level for tips, blades and abrasion parts where toughness can be traded away. | 1,520 | 1,720 | 9 | 50 HRC | — |
What is 81B45?
A boron-modified Ni-Cr-Mo alloy steel where trace boron additions boost hardenability economically, allowing lower alloy content while still achieving good through-hardening for medium-strength parts. 81B45 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). 81B45 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
What is 81B45 used for?
- fasteners
- shafts
- structural forgings
- heat-treated machine parts
81B45 properties
Typical room-temperature values for 81B45-A; bars are the position among steel grades.
Physical3
81B45 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
81B45 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
81B45 is rated for continuous service to 400°C (752 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
81B45 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 81B45 takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
81B45's machinability is good (58/100, better than 75% of steel grades); weldability fair (45/100); formability fair (50/100).
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. 81B45 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 81B45
Is 81B45 easy to machine?
Machine in the annealed or spheroidized condition (≈65 % of AISI 1212); use rigid setups, carbide tooling and flood coolant, and finish-machine before final tempering above 40 HRC.
Can 81B45 be welded?
Weldable only with care — CE ≈ 0.7–0.8, so preheat 200–300 °C, low-hydrogen consumables and immediate post-weld tempering are needed to avoid HAZ martensite cracking.
Can 81B45 be formed, bent or molded?
Cold forming and cold heading are practical only in the spheroidize-annealed state; hot forge at 1050–1200 °C and never below ~870 °C, then normalize before hardening.
81B45 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 J404 81B45 | 0.43 – 0.48 | 0.45 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.2 – 0.4 | 0.3 |
| Cr | 0.35 – 0.55 | 0.45 |
| Mo | 0.08 – 0.15 | 0.12 |
| B0.0005 % min per SAE; boron treatment for hardenability | 5×10⁻⁴ – 0 | 0 |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 81B45?
No natural corrosion resistance — protect with zinc/manganese phosphate + oil, black oxide, zinc or hard-chrome plating; nitriding and induction hardening also work well on the tempered structure.
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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 81B45 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G81451
How much does 81B45 cost?
81B45 is a budget-cost steel ($), cheaper than about 90% 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.
81B45 — frequently asked
What is 81B45 used for?
81B45 is typically used for fasteners, shafts, structural forgings and heat-treated machine parts. In short: boron-economy alloy steel; deep hardening at low alloy cost; poor weldability.
What is the yield strength of 81B45?
81B45 has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 81B45 easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machine in the annealed or spheroidized condition (≈65 % of AISI 1212); use rigid setups, carbide tooling and flood coolant, and finish-machine before final tempering above 40 HRC.
Can 81B45 be welded?
With care — weldability is rated fair (45/100). Weldable only with care — CE ≈ 0.7–0.8, so preheat 200–300 °C, low-hydrogen consumables and immediate post-weld tempering are needed to avoid HAZ martensite cracking.
What surface finishes work on 81B45?
No natural corrosion resistance — protect with zinc/manganese phosphate + oil, black oxide, zinc or hard-chrome plating; nitriding and induction hardening also work well on the tempered structure.
Can 81B45 be formed, bent or molded?
Cold forming and cold heading are practical only in the spheroidize-annealed state; hot forge at 1050–1200 °C and never below ~870 °C, then normalize before hardening.
What is the maximum service temperature of 81B45?
81B45 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 81B45-A and 81B45 QT48-52?
A is the default condition — softest supplied condition; choose for heavy machining or cold forming before quench-and-temper. QT48-52: maximum hardness/wear level for tips, blades and abrasion parts where toughness can be traded away. Yield strength is 400 MPa in A versus 1,520 MPa in QT48-52.
How much does 81B45 cost?
81B45 is a budget-cost steel ($), cheaper than about 90% 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.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 — Hardenability Bands for Carbon and Alloy H Steels — SAE International (2019)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought, General Requirements — ASTM International (2020)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4 — Heat Treating — ASM International (1991)
- ASM Handbook Vol. 16 — Machining — ASM International (1989)
- MatWeb / UNS G81451 alloy steel typical property listings — MatWeb LLC (2024)
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.