Heterogeneous Grain Microstructure Reducing/Eliminating Edge Breaks in Low Carbon Steels

Edge breaks initiating at both edges of steel strip are strain lines/Lüders lines which are unacceptable for surface critical and semi-critical applications. Some steel manufacturers are using de-gassing technology by producing interstitial-free steel to reduce or eliminate Edge breaks and associated Yield point elongation (YPE). Nonetheless, in low carbon steel with free interstitials (C, N), it is necessary to develop other approaches to reduce Edge breaks and YPE. This paper proposed that heterogeneous grain microstructures can reduce Yield point elongation in steels containing free interstitials. Heterogeneous grain microstructures can be obtained in two ways during cold mill processing low carbon steels: (1) through partially recrystallized microstructure using a low AnnealingTemperature, and (2) creating a bi-modal grain size distribution in a full-recrystallized material. The mechanisms of heterogeneous grain microstructure on the formation of Edge breaks/Lüders lines, as well as the effects of chemical composition, reduction ratio, AnnealingTemperature, and Mechanical properties are discussed.