Material Name: 70 spring steel

Standard: GB / T 1222-1984
● Features and Scope:
Similar performance and 65 gauge steel, higher elasticity and strength, for the manufacture of small cross-section, less demanding strength to withstand vibration machines on the circle in general, square coil springs, such as automobiles, tractors and other machinery flat or train circular coil spring and a leaf spring.
● Chemical Composition:
Carbon C: 0.65 ~ 0.75
Si Si: 0.17 ~ 0.37
Mn Mn: 0.50 ~ 0.80
Sulfur S: ≤0.035
Phosphorus P: ≤0.035
Chromium Cr: ≤0.25
Ni Ni: ≤0.25
Copper Cu: ≤0.25
● Mechanical Properties:
Tensile strength σb (MPa): ≥1029 (105)
Yield strength σs (MPa): ≥833 (85)
Elongation δ10 (%): ≥8
Reduction of ψ (%): ≥30
Hardness: hot, ≤285HB; Cold Drawn + heat, ≤321HB
● Heat treatment and microstructure specifications:
Heat treatment specifications: quenching 830 ℃ ± 20 ℃, oil cooling; tempering 480 ℃ ± 50 (when special needs, ± 30 ℃).
Microstructure: a small amount of fine pearlite eutectoid ferrite.
● Delivery status: hot-rolled steel to heat treatment or heat treatment delivery, cold drawn steel to heat treatment delivery.