Study on corrosion resistance of high-strength medium-carbon spring steel and its hydrogen-induced delayed fracture

The disadvantages of poor corrosion resistance and delayed fracture resistance of high-strength medium-carbon spring steel have significantly limited its application in the construction industry. Therefore, there is a need to improve these characteristics of spring steel. In this paper, the effects of Ti, Cu, and Ni on the microstructure, mechanical properties, corrosion resistance, and hydrogen-induced delayed fracture behaviour of spring steel were investigated by scanning electron microscopy, transmission electron microscopy, electrochemical workstation analysis, neutral salt spray test and hydrogen permeation testing methods. The results showed that the tensile strength of the experimental steel reached 2000 MPa and the yield strength reached 1800 MPa. These values were observed when the quenching and tempering temperatures were 900 degrees C and 350 degrees C. respectively; further, the experimental steel had a tempered martensite microstructure at these temperatures. Ti increased the self-corrosion potential of the experimental steel and reduced the self-corrosion current. With an increase in the content of alloying elements (Ti, Cu, and Ni), the depth of the corrosion pits in the experimental steel became shallower and the degree of surface damage was reduced. Moreover, Ti could refine the crystal grains, TiC had high a trap activation energy of hydrogen, and Ti-containing steel had better hydrogen-induced fracture resistance. (C) 2019 Elsevier Ltd. All rights reserved.