Steels for Automotive Coil Springs With Improved Resistance to Relaxation

Electron microscopy studies showed that automobile coil springs made of 9260 steel have greater resistance to relaxation than coil springs made of 5160 and 15B62 steels, because the carbides in the 9260 steel are smaller and more closely spaced than the carbides in the other two steels. Further research work established that steels containing nominally 1.0 and 1.25 percent silicon have satisfactory resistance to relaxation. Because of its good resistance to relaxation, and because of its hardenability and cost effectiveness, a 0.6 OC-0.90Mn-1.0Si steel containing 0.45 to 0.65 percent chromium has been used for coil springs in several models of General Motors cars since 1977.