Steel 70
AISI/SAE 1070
70 (AISI 1070 equivalent) is a plain high-carbon spring steel at about 0.7 % C, taking its elastic limit from carbon content alone rather than from alloy additions.
Reference datasheet — 70 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 QT45-50 condition
70 tempers and conditions
70 is supplied in 10 conditions, soft to hard. QT45-50 is the default FabDigit quotes; the values on this page are for it.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Pick for blanking, deep drawing, machining or cold coiling before hardening. | 360 | 640 | 20 | 190 HB | — |
Hot rolled | Cheapest mill condition for bars and coil that will be re-heat-treated by the fabricator. | 440 | 780 | 12 | 230 HB | — |
Normalized | Uniform pearlitic structure for bar stock before machining and final hardening. | 480 | 830 | 11 | 23 HRC | 9.8 % IACS |
Cold drawn | Bright, dimensionally accurate bar for lightly stressed clips and pins; strength from drawing only. | 800 | 950 | 8 | 29 HRC | 9.6 % IACS |
Cold rolled hard strip | Thin strip for stamped flat springs, shims and clips that are only low-temperature stress relieved after forming. | 1,150 | 1,250 | 2 | 41 HRC | 10 % IACS |
Stress relieved | Low-temperature bake applied to cold-formed hard strip or wire springs to raise the elastic limit and stabilise set. | 1,250 | 1,350 | 3 | 43 HRC | 9.6 % IACS |
Q&T 40–45 HRC | Tougher spring temper for thicker leaf springs and parts with impact or bending after hardening. | 1,300 | 1,450 | 8 | 43 HRC | — |
Oil quenched and tempered spring wire | Uniform through-hardened wire for coil springs needing consistent properties in larger diameters and better relaxation resistance than cold-drawn wire. | 1,450 | 1,650 | 6 | 46 HRC | 9.6 % IACS |
QT45-50Default Q&T 45–50 HRC | Standard spring service condition: best balance of elastic limit, fatigue life and residual toughness. | 1,550 | 1,750 | 6 | 47 HRC | — |
Q&T 50–55 HRC | High-hardness condition for saw blades, scrapers, wear strips and thin clips where wear beats toughness. | 1,700 | 1,950 | 4 | 52 HRC | — |
Supply forms, finishes and certifications
Ways 70 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
PW | Patented cold-drawn spring wire | Supply option |
What is 70?
70 (AISI 1070 equivalent) is a plain high-carbon spring steel at about 0.7 % C, taking its elastic limit from carbon content alone rather than from alloy additions. Quenched and tempered it gives roughly 1550 MPa yield, 1750 MPa tensile, 450 HB / 47 HRC and 6 % elongation, and is available as hot-rolled and cold-rolled strip, cold-drawn and oil-tempered wire, and in pre-hardened CR-H and QT conditions for flat springs, clips and light coil springs. Hardenability is shallow, so sections stay thin, corrosion resistance is nil and service is capped near 250 °C. For deeper hardening or better relaxation resistance, move to 65Mn or 61SiCrV6. 70 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,410°C (2,570 °F). 70 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi).
What is 70 used for?
- Flat springs
- Clips
- Light coil springs
Advantages
- High strength — 1,550 MPa (225 ksi), better than 97% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- High electrical conductivity — 9.6 % IACS, better than 78% of steel grades
Limitations
- Limited ductility — 6%, worse than 97% of steel grades
- Limited formability — 10/100, worse than 95% of steel grades
- Low fracture toughness — 35 MPa·√m (31.9 ksi·√in), worse than 94% of steel grades
- Difficult to machine — 25/100, worse than 93% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
70 properties
Typical room-temperature values for 70-QT45-50; bars are the position among steel grades.
Physical3
70 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,410°C (2,570 °F).
Mechanical16
70 has a yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Elongation at break is 6% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
70 is rated for continuous service to 250°C (482 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.3 µm/m·K (6.28 µin/in·°F).
Electrical3
70 conducts electricity at 9.6 % IACS, better than 78% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (8/100), worse than 99% of steel grades.
Sustainability4
Producing a kilogram of 70 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability6
70's machinability is poor (25/100, worse than 93% of steel grades); weldability poor (15/100); formability not recommended (10/100).
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. 70 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 70
Is 70 easy to machine?
Machine in the annealed/spheroidized state (≈45–55 % of 1212) with sharp carbide or HSS tooling; above 45 HRC use grinding, EDM or CBN turning.
Can 70 be welded?
Effectively unweldable for structural joints — 0.7 %C gives brittle martensite; if unavoidable use 200–300 °C preheat, low-hydrogen consumables and immediate temper, and expect loss of spring temper in the HAZ.
Can 70 be formed, bent or molded?
Blank, bend and coil in the annealed or cold-rolled-hard state with generous bend radii along the grain; harden by oil quench from 800–830 °C then temper 380–480 °C, or stress relieve 200–300 °C for formed hard strip.
70 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 |
|---|---|---|
| CGB/T 699 / GB/T 1222; SAE 1070 is 0.65–0.75 | 0.67 – 0.75 | 0.71 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 0.5 – 0.8 | 0.65 |
| Crresidual | ≤ 0.25 | |
| Niresidual | ≤ 0.3 | |
| Curesidual | ≤ 0.25 | |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 70?
No corrosion resistance: specify oiling, phosphate + oil, black oxide, zinc or Zn-Ni plating (with 190–220 °C bake to avoid hydrogen embrittlement), or e-coat; shot peening markedly improves spring fatigue life.
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 70 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- 1070
How much does 70 cost?
70 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.
70 — frequently asked
What is 70 used for?
70 is typically used for flat springs, clips and light coil springs. In short: low-cost carbon spring steel; good strip formability; shallow hardening only.
What is the yield strength of 70?
70 has a typical yield strength of 1,550 MPa (225 ksi) and a tensile strength of 1,750 MPa (254 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 70 easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine in the annealed/spheroidized state (≈45–55 % of 1212) with sharp carbide or HSS tooling; above 45 HRC use grinding, EDM or CBN turning.
Can 70 be welded?
Not readily — weldability is rated poor (15/100). Effectively unweldable for structural joints — 0.7 %C gives brittle martensite; if unavoidable use 200–300 °C preheat, low-hydrogen consumables and immediate temper, and expect loss of spring temper in the HAZ.
What surface finishes work on 70?
No corrosion resistance: specify oiling, phosphate + oil, black oxide, zinc or Zn-Ni plating (with 190–220 °C bake to avoid hydrogen embrittlement), or e-coat; shot peening markedly improves spring fatigue life.
Can 70 be formed, bent or molded?
Blank, bend and coil in the annealed or cold-rolled-hard state with generous bend radii along the grain; harden by oil quench from 800–830 °C then temper 380–480 °C, or stress relieve 200–300 °C for formed hard strip.
What is the maximum service temperature of 70?
70 is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 70 QT45-50 and 70-A?
QT45-50 is the default condition — standard spring service condition: best balance of elastic limit, fatigue life and residual toughness. A: pick for blanking, deep drawing, machining or cold coiling before hardening. Yield strength is 1,550 MPa in QT45-50 versus 360 MPa in A.
How much does 70 cost?
70 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
- GB/T 1222 — SAC / (2016)
- SAE J403 Chemical Compositions of SAE Carbon Steels (1070) — SAE International (2014)
- ASTM A684/A684M High-Carbon Cold-Rolled Strip — ASTM (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Machinery's Handbook (spring materials, machinability ratings) — Industrial Press (2020)
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.