Liquid Metal Embrittlement during Hot Forming of Hot-Dip Galvanized Advanced High-Strength Unalloyed Steels (AHSS)

Abstract

Abstract Advanced High-Strength Steels (AHSS) are of interest as, owing to their increased strength, they are able to absorb more energy than conventional steels in a car crash. Thus, thinner metal sheets can be used for car design so that vehicle weight and fuel consumption are reduced. The elements Si, Mn, Al, and B are added in order to achieve the desired AHSS alloy properties. Corrosion protection for the automotive sheet metal is mainly ensured by hot-dip galvanizing. The sheets are further processed by hot forming. Hot-dip galvanized steel sheets made of 20MnB8 were examined after high temperature tensile tests. Metallographic examinations were performed on tensile test specimens which were tested at temperatures between 400 and 800 °C and strain rates between 0.05 and 5 s−1. Liquid metal embrittlement was observed at temperatures above 700 °C. Lower strain rates resulted in a smaller degree of liquid metal embrittlement. In order to avoid the occurrence of liquid metal embrittlement during hot forming of galvanized AHSS sheets, the relevant process parameters need to be further optimized.