Effects of warm extrusion temperatures on corrosion performance of 40Cr steel

Abstract

A 40Cr steel was formed into a chain-wheel using a warm extrusion technique. The salt spray corrosion of the obtained chain-wheel, which was formed at extrusion temperatures of 550, 650, and 750°C, was investigated with a 3.5% NaCl solution. The corrosion morphologies of the chain-wheel were analysed using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction, respectively. The results show that corrosion of the chain-wheel formed at different extrusion temperatures starts with pitting corrosion, in which the oxides on the sample surfaces decrease obviously with the increase in extrusion temperatures. The primary corrosion products in the corrosion test are composed of Fe–Cr and Fe(OH)₂ compounds. In the presence of the 3.5% NaCl solution, with the increase in extrusion temperatures, the potential of the steel becomes negative before becoming positive again. The corrosion resistance of the chain-wheel at the warm extrusion temperature of 750°C is the worst.