DEVELOPMENT OF TECHNOLOGICAL METHODS OF ADDITIONAL GRAIN REFINEMENT FOR PRODUCTION OF COLD RESISTANT Nb-BEARING PLATE STEEL WITH SMYS 450-485 MPA AND THICKNESS UP TO 40 MM

摘要

A continuous demand for thick plates for structural applications with yield strength of 450-485 MPa, high toughness and cold resistance requires the development of new methods of additional grain refinement at all stages of thermo-mechanical control process (TMCP). The effect of Ti-Nb precipitates morphology on grain growth during reheating was investigated. It has been shown that Nb is a key element for grain growth control. Submicron Nb carbonitrides suppress austenite grain growth at lower slab reheating temperatures. The effect of Ti additions on suppression of grain growth during low-temperature reheating is negligible. Parameters of reheating such as duration and temperature were adjusted in order to maximize the effect of Nb microalloying and to receive finer austenite grain before hot rolling. 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 set of properties, including strength, toughness, and cold resistance.