Structure Formation Control of Microalloyed Pipe Steels During TMCP for Enhanced Low Temperature Toughness

A continuous demand for plates for X60-X120 pipes with high toughness and cold resistance requires the development of new methods of additional grain refinement at all stages of thermo-mechanical control processing (TMCP). An effect of structure formation during slab reheating was studied. Physical models of secondary recrystallization during reheating and austenite recrystallization at roughing rolling of Nb-microalloyed pipeline steels were developed. Grain refinement in the course of hot deformation was studied through physical modeling. Using the recrystallization model, new rolling schedules were introduced. Industrial trials were conducted; the effect of reheating and deformation parameters on cold resistance of steel was investigated. Implementation of the results of given study into production practice made it possible to produce plates with excellent properties, including strength, toughness, and cold resistance.