1. The heat treatment of spring generally requires quenching, fine grain and less retained austenite. The depth of decarburized layer on each side shall be in accordance with: < Φ 6mm steel wire or steel plate, Φ 6mm steel wire and steel plate, < 1.0% diameter or thickness
2. The large spring is processed in hot state and then quenched and tempered; the medium spring is processed in cold state (the raw material requires spheroidized structure or most spheroidization), and then quenched and tempered. The small spring is processed with cold rolled steel strip and cold drawn steel wire, and then tempered at low temperature
3. Shot peening after treatment
Using 40-50n / cm2 compressed air or 70m / s centrifugal machine, cast iron shot or hardened steel shot of Φ 0.3-0.5mm (for small parts, valve spring, gear, etc.) and Φ 0.6-0.8mm (for leaf spring, crankshaft, axle shaft, etc.) are sprayed onto the spring surface to strengthen the surface layer. The fatigue cycle times can be increased by 8-13 times and the service life can be increased by 2-2.5 times.