Improving the sensitivity of automotive spring steel

In order to improve the strength of automobile suspension spring steel, the sensitivity of delayed fracture caused by hydrogen in corrosive environment must be reduced. In Japan, spring steels with different pitting corrosion resistance, namely ordinary spring steel jissup12 and high strength spring steel hds13, and high strength spring steel hds13m series with high pitting corrosion resistance were tested by SSRT in 5mass% NaCl solution. According to the penetration behavior of hydrogen produced by corrosion reaction in steel and SSRT test characteristics, the resistance point was studied The results are as follows.

The hds13m series high strength spring steel added with Ni, Cr, Cu, Mo and B elements which can improve the pitting corrosion resistance is better than that of hds13 spring steel with higher Ni and Mo contents.
The radius and depth of pitting corrosion of spring steel with good pitting corrosion resistance represented by v’cq100 are small, and the deviation is also small.

According to the SSRT test results before and after repeated dry wet corrosion, the higher the v’cq100, the lower the normalized maximum load and fracture time.
According to the results of hydrogen thermal analysis after repeated dry wet corrosion test, abnormal hydrogen peak can be seen in the temperature range of 673 ~ 773k. The results show that the peak value corresponds to the release of hydrogen enriched at the interface between rust layer and steel after corrosion reaction.

With the increase of the amount of hydrogen enriched at the interface, the normalized fracture time will be shortened and the delayed fracture sensitivity will be increased.
By reheating the hydrogen enriched at the interface to more than 673k and releasing it, the increased delayed fracture sensitivity due to repeated dry wet corrosion can be restored.
The addition of alloy elements which can improve the pitting corrosion resistance can reduce the hydrogen generated by repeated dry and wet corrosion and improve the delayed fracture resistance of spring steel.