Control of edge breaks during cold mill processing of commercial and drawing quality low-carbon steels

The effects of chemistry, reduction ratio and annealing cycle on edge breaks/Lüder lines during cold mill processing of commercial and drawing quality low-carbon steels have been investigated. It is possible to eliminate Lüder bands and associated yield-point elongation (YPE) by producing interstitial free steels that do not contain any free C or N. In low-carbon steel, however, it is necessary to develop other strategies for reducing Lüdering and YPE. Reduction ratios and annealing cycles that resulted in a uniform, completely recrystallised microstructure were ineffective at reducing YPE. It was determined that the most promising approach for reducing YPE in steels containing free interstitials is to develop a heterogeneous microstructure. This was achieved through abnormal grain-growth in the full-recrystallised material to create a bimodal grain-size distribution. The implications for the production of commercial and drawing quality low-carbon steels are discussed.