Features and application: silicon and manganese 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 higher carbon content, carbon graphite easy to make steel brittle. For cars, tractors and locomotive damping spring and coil springs, cylinder valve spring, can also be used with heat 250 ℃ the following spring.
Similar performance and 55Si2Mn steel, but higher hardenability, quenching in oil critical diameter of about 90 ~ 180mm, fatigue strength was also significantly increased. Application: Suitable for manufacturing, small cross-section of the leaf spring, such as car leaf springs front and rear vice.
Chemical composition
Carbon C: 0.52 ~ 0.60 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 55Si2MnB
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 process
Standard heat treatment: quenching 870 ℃ ± 20 ℃, oil cooling;
Tempering 480 ℃ ± 50 ℃ (special needs, ± 30 ℃).
Microstructure: Tempered troostite.
Delivery status: hot-rolled steel to heat treatment or heat treatment delivery, cold-drawn steel with heat treatment delivery.
