Method for manufacturing high-strength steel sheet parts subject in use to fatigue stresses

Abstract

The manufacturing method comprises the steps of: carrying out one or more forming operations so as to give the desired geometry to the part; and subjecting the part thus formed to a single heat treatment having only a stress relieving treatment, which is preferably carried out at a temperature in the range from 530° C. to 580° C. for a time in the interval from 45 to 60 minutes and is followed by cooling of the part in air. By virtue of the formed part being subjected to a stress relieving heat treatment, the residual stress state due to the initial forming process and to the bead welding, if any, is eliminated or at least significantly reduced.

1 . Method for manufacturing sheet metal parts of high-strength steel which are subject in use to fatigue, the method comprising in the order the steps of:
 a) carrying out one or more forming operations on a sheet of high-strength steel so as to provide the part with the desired geometry; and   b) subjecting the part thus formed to a single heat treatment having only a stress relieving treatment, which is carried out keeping the formed part at a temperature in the range from 530° C. to 580° C. for a time in the range from 45 to 60 minutes and then leaving the part to cool in air.   
     
     
         2 . Method according to  claim 1 , wherein the forming step a) is carried out using a sheet of high-strength low-alloy steel. 
     
     
         3 . Method according to  claim 1 , wherein the forming of the part carried out at step a) comprises at least one of the following operations: tube making, shaping, cold-forming and hydro-forming. 
     
     
         4 . Method according to  claim 1 , further comprising the step of carrying out at least one bead welding on the part, wherein such a welding step is carried out before the stress relieving step b).