Impact of swiveling and intrusion effects on corrosion behavior of HSLA 420 steel formed by incremental forming

The effect of incremental forming parameters on corrosion characteristics of high-strength low-alloy (HSLA) 420 steel was studied in this work. Electrochemical impedance spectroscopy and potentio-dynamic polarization tests were performed on the as-received sample and formed samples, those with the lowest, moderate, and highest formability conditions. The largest average pit size (10 μm) was formed under the as-received condition because of tremendous elliptical pit groups. This results in a maximum corrosion rate (550 μm/year) and a very high oxygen (81.31%) in the corrosion layer. Narrow pits and severe stress corrosion cracking (SCC), with average pit size and crack width of SCC of 7 and 1.1 μm, respectively, were observed under the lowest formability condition. Shallow pits and minute SCC, with average pit size and crack width of SCC of 4 and 0.6 μm, respectively, were observed under the moderate formability condition. Pit susceptibility and intensity of SCC were reduced while forming with an increase in swiveling and a reduction in intrusion action, which improves the grain refinement. Micro pits without SCC were observed under the highest formability condition because of extreme grain refinement. This results in a minimum corrosion rate (114.7 μm/year) and a very less oxygen (38.46%) in the corrosion layer.