Steel 1078-BT
Finish state
AISI/SAE 1078 · UNS G10780
BT = hardened and blue tempered spring strip
Ready-to-use flat spring, shim and clip stock supplied hardened, tempered and blued.
Values for the BT condition
Other 1078 tempers and conditions
1078 is listed in 9 conditions; see the grade overview at 1078.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition; choose for cold forming, deep machining or before final hardening. | 370 | 615 | 22 | 174 HB | 49 W/m·K |
HRDefault Hot rolled | Standard mill condition for bar and coil that will be re-heat-treated by the user; cheapest form. | 385 | 690 | 12 | 200 HB | — |
Normalized | Fine pearlite for uniform structure and higher strength than hot rolled without quenching distortion. | 520 | 1,005 | 11 | 31 HRC | — |
Spheroidize annealed and cold drawn | Best combination of size accuracy, surface finish and machinability for screw-machine parts before hardening. | 570 | 655 | 10 | 192 HB | 9.6 % IACS |
Cold drawn | Standard cold-finished bar: higher strength and tight tolerance, but limited ductility and residual stress. | 700 | 830 | 8 | 22 HRC | — |
Q&T 42-47 HRC | Tough-hard condition for heavy springs, chisels and wear parts needing some shock resistance. | 1,280 | 1,450 | 8 | 45 HRC | 44 W/m·K |
BTThis page Hardened and blue tempered spring strip | Ready-to-use flat spring, shim and clip stock supplied hardened, tempered and blued. | 1,380 | 1,550 | 3 | 46 HRC | 8.5 % IACS |
Hard drawn spring wire | Heavily patented-and-drawn wire for coil springs used as-coiled with only a low-temperature stress relief. | 1,400 | 1,700 | 3 | 48 HRC | — |
Q&T 56-62 HRC | Maximum hardness and wear resistance for blades, punches and cutting edges; very brittle, avoid impact and notches. | 1,700 | 2,000 | 2 | 59 HRC | 42 W/m·K |
What is 1078-BT?
1078-BT is 1078 supplied in the BT condition — ready-to-use flat spring, shim and clip stock supplied hardened, tempered and blued. 1078-BT has a yield strength of 1,380 MPa (200 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Elongation at break is 3% and the elastic modulus is 205 GPa (29.7 Msi). 1078-BT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F). HR is the default condition FabDigit quotes; BT is available on request or by drawing note.
Advantages
- High strength — 1,380 MPa (200 ksi), better than 96% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 3%, worse than 99% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Low fracture toughness — 25 MPa·√m (22.8 ksi·√in), worse than 97% of steel grades
- Difficult to machine — 18/100, worse than 97% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
1078-BT properties
Typical room-temperature values for 1078-BT; 22 are specific to this condition. Other listed values are 1078 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
1078-BT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
1078-BT has a yield strength of 1,380 MPa (200 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Elongation at break is 3% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
1078-BT is rated for continuous service to 200°C (392 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.3 µm/m·K (6.28 µin/in·°F).
Electrical3
1078-BT conducts electricity at 8.5 % IACS, better than 63% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (8/100), worse than 99% of steel grades.
Sustainability4
Producing a kilogram of 1078-BT takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
1078-BT's machinability is poor (18/100, worse than 97% of steel grades); weldability not recommended (10/100); formability poor (18/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 1078-BT
Is 1078 easy to machine?
Machine in the spheroidize-annealed or SACD condition with sharp carbide tooling and generous coolant; hardened stock (>45 HRC) needs grinding or CBN.
Can 1078 be welded?
Poor weldability (CE ≈ 0.9): preheat 260–320 °C, use low-hydrogen consumables and temper immediately after welding; avoid welding on hardened springs.
Can 1078 be formed, bent or molded?
Cold form only when spheroidize annealed; hot work at 1050–1150 °C and never finish below ~800 °C, then slow cool to avoid quench cracks.
What surface finishes work on 1078?
Not anodizable — protect with oil, black oxide, zinc phosphate, zinc/nickel plating or paint; grind and polish easily to a fine finish when hardened.
1078 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/AISI 1078 carbon range | 0.72 – 0.85 | 0.78 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.05 | 0.03 |
| Sinot specified for rimmed/capped heats; typical for killed steel | 0.15 – 0.35 | 0.25 |
| Fe | balance | — |
1078-BT — frequently asked
What is 1078-BT used for?
1078-BT is typically used for music wire, leaf springs, coil springs and high-strength wire products. In short: heat-treatable spring steel; high strength, low weldability; wear resistance after hardening.
What is the yield strength of 1078-BT?
1078-BT has a typical yield strength of 1,380 MPa (200 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 1078-BT easy to machine?
Not especially — machinability is rated poor (18/100, worse than 97% of steel grades). Machine in the spheroidize-annealed or SACD condition with sharp carbide tooling and generous coolant; hardened stock (>45 HRC) needs grinding or CBN.
Can 1078-BT be welded?
Not readily — weldability is rated not recommended (10/100). Poor weldability (CE ≈ 0.9): preheat 260–320 °C, use low-hydrogen consumables and temper immediately after welding; avoid welding on hardened springs.
What surface finishes work on 1078-BT?
Not anodizable — protect with oil, black oxide, zinc phosphate, zinc/nickel plating or paint; grind and polish easily to a fine finish when hardened.
Can 1078-BT be formed, bent or molded?
Cold form only when spheroidize annealed; hot work at 1050–1150 °C and never finish below ~800 °C, then slow cool to avoid quench cracks.
What is the maximum service temperature of 1078-BT?
1078-BT is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 1078-HR and 1078 QT-58?
HR is the default condition — standard mill condition for bar and coil that will be re-heat-treated by the user; cheapest form. QT-58: maximum hardness and wear resistance for blades, punches and cutting edges; very brittle, avoid impact and notches. Yield strength is 385 MPa in HR versus 1,700 MPa in QT-58.
Sources
- SAE J403 — Chemical Compositions of SAE Carbon Steels — SAE International (2014)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought, General Requirements — ASTM (2020)
- ASTM A227 — Steel Wire, Cold-Drawn, for Mechanical Springs — ASTM (2017)
- ASTM A682/A684 — Hardened and Tempered / High-Carbon Steel Strip — ASTM (2018)
- 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)
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.