SUP7 is widely used silicon-manganese spring steel, strength, flexibility and higher hardenability than 55Si2Mn. For railway vehicles, automobile and tractor industry to bear a greater load on the production of flat spring 30mm or less in diameter coil spring, is also suitable for production of the following operating temperature of 250 ℃ heat-resistant non-corrosive medium under alternating load spring and and work under high stress the important roll the large spring. ● Chemical Composition: C: 0.56 ~ 0.64 Si Si: 1.50 ~ 2.00 Mn Mn: 0.60 ~ 0.90 Sulfur S: ≤ 0.035 P P: ≤ 0.035 Chromium Cr: ≤ 0.35 Ni Ni: ≤ 0.35 Copper Cu: ≤ 0.25 ● Mechanical Properties : tensile strength σb (MPa): ≥ 1274 (130) yield strength σs (MPa): ≥ 1176 (120) elongation δ10 (%): ≥ 5 shrinkage section ψ (%): ≥ 25 hardness: hot , ≤ 321HB; cold-drawn + heat treatment, ≤ 321HB ● heat treatment and microstructure specifications: standard heat treatment: quenching 870 ℃ ± 20 ℃, oil cooling; tempering 480 ℃ ± 50 ℃ (special needs, ± 30 ℃). Microstructure: Tempered troostite.