The U.S. patent U.S. Pat.No. US5482675 relates to a high-strength, fine-grained medium-low carbon alloy steel. The cast steel consists of carbon 0. 15-0.2 1%, silicon 0.35-0.65%, manganese 0.90- 1.30%, sulfur? 0? 50.025%，P？ 0? 50.025%, 0.25-0.60% of chromium, 0. 10-0.30% of molybdenum and the balance of iron and impurities. At suitable quenching and tempering temperatures, the strength, plasticity and low temperature toughness of steel can meet the requirements of AAR-M-20 1 standard for C-grade steel. European patent EP 1306458 discloses a turbine rotor steel with corrosion resistance, stress corrosion cracking resistance and a proper balance between strength and toughness, which contains (wt %) C: 0.0 1-0. 10%, and si: 0.01-0.50. Nickel: 2-7%, molybdenum: 0.3-3%, nitrogen: 0.0 1-0. 10%, boron: 0.0005-0.005%, calcium: 0.001-0.009. The heat treatment of alloy steel adopts quenching and tempering at 500-700℃ for more than two times. The tensile strength, yield point and elongation at break of the steel can meet the requirements of AAR for C-grade steel by selecting appropriate composition ratio.
The development history of low-alloy high-strength cast steel materials in China is not long. At present, there are three kinds of C-grade steels: ZG24SiMnVTi, ZG25MnCrNiMo and ZG32MnMoNiCu. Among them, ZG24SiMnVTi cast steel adopts normalizing and tempering heat treatment, and its mechanical properties are σb 688.8MPa, σS 472.3MPa, δ4 24.3%, ψ 54%, Akv (normal temperature) 7 1.8J/cm2. The strength and plasticity of this steel meet the requirements of AAR for grade C steel. The ZG25MnCrNiMo C grade steel developed by Qishuyan Locomotive and Rolling Stock Technology Research Institute contains 0.25% C, 0.36% Si, 0.36% Mn/Kloc-0, 0.031%S, 0.028% P, 0.42% Cr, 0.43% Ni and 0.2/Kloc-. Mechanical properties σb 640MPa, σS 470MPa, ψ 56 The ZG32MnMoNiCu steel coupler material developed by Inner Mongolia No.1 Machinery Factory contains molybdenum, nickel, copper and other alloy elements. It belongs to quenched and tempered grade C steel, and its mechanical properties are σb 623MPa, σS 4 17MPa, δ4 22%, ψ 45%, and Akv (-40℃) 27 J.
Lack of toughness and poor low temperature brittleness resistance are the main defects of railway freight car couplers in China. A comprehensive study on the causes of coupler damage in the 1970s in the United States shows that C-grade steel has tempered martensite and lower bainite structure after quenching and tempering, which is beneficial to improve the low-temperature toughness of steel and is more suitable for manufacturing couplers. Therefore, producing quenched and tempered C-grade steel and improving the comprehensive mechanical properties of steel is the direction of research and development of railway coupler materials in China in the future.