Steel 81B45 QT34-38
Heat-treated state
EN 81B45 · UNS G81451
QT34-38 = q&T 34–38 HRC
Balanced strength/toughness level for gears, spindles and heavy-duty fasteners.
Values for the QT34-38 condition
Other 81B45 tempers and conditions
81B45 is listed in 9 conditions; see the grade overview at 81B45.
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 | — |
QT34-38This page 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 QT34-38?
81B45 QT34-38 is 81B45 heat treated to QT34-38 — balanced strength/toughness level for gears, spindles and heavy-duty fasteners. 81B45 QT34-38 has a yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi). 81B45 QT34-38 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). A is the default condition FabDigit quotes; QT34-38 is available on request or by drawing note.
Advantages
- High strength — 1,060 MPa (154 ksi), better than 93% of steel grades
Limitations
- Difficult to machine — 38/100, worse than 80% of steel grades
81B45 QT34-38 properties
Typical room-temperature values for 81B45 QT34-38; 14 are specific to this condition. Other listed values are 81B45 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
81B45 QT34-38 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 QT34-38 has a yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
81B45 QT34-38 is rated for continuous service to 420°C (788 °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 QT34-38 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 QT34-38 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 QT34-38's machinability is fair (38/100, worse than 80% of steel grades); weldability fair (45/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 81B45 QT34-38
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.
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.
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 | — |
81B45 QT34-38 — frequently asked
What is 81B45 QT34-38 used for?
81B45 QT34-38 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 QT34-38?
81B45 QT34-38 has a typical yield strength of 1,060 MPa (154 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 81B45 QT34-38 easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% 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 QT34-38 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 QT34-38?
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 QT34-38 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 QT34-38?
81B45 QT34-38 is rated for continuous use to about 420°C (788 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.