55Si2Mn silicon and manganese spring steel to improve strength and yield ratio flexibility, improve hardenability, tempering stability and resistance to anti-relaxation stability, thermal sensitivity is also small, but decarburization tend to be larger, especially silicon and carbon content high, easily graphitized carbon, the steel brittle. 55Si2Mn spring steel used for cars, tractors and locomotive damping spring and coil springs, cylinder valve spring, can also be used with heat 250 ℃ the following spring.

   Chemical composition:


Carbon C: 0.52 ~ 0.60


Si Si: 1.50 ~ 2.00


Manganese Mn: 0.60 ~ 0.90


Sulfur S: ≤ 0.035


Phosphorus 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 (%): ≥ 6


Reduction of area ψ (%): ≥ 30


Hardness: hot, ≤ 302HB; 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.