Optimisation of hot workability and control of microstructure during deofrmation processing of AISI type 304L stainless steels

摘要

The deformation behaior of 304L stainless steel was evaluated, under compression in the temperature range of 600degC to 1200degC and strain-rae range of 0.001 s~-1 to 100 s~-1 with the view to establishing processing-microstructure relationships during hot working. Ferrite forms at temperatures above 1150degC during deformation. The material exhibits a dynamic recrystallisation domain (DRX) in the temperature range of 1000degC to 1200degC and strain-rate ragne of 0.01 s~-1 to 5 s~-1, which is the optimum one for hot working. The development of microstructure in 304L stainless steel during industrial hot-forming operations such as press forging, rilling, extrusion, and hammer forging at different temperatures in the range 600degC to 1200degC, was studied and compared with the results of the laboratory tests for assessing the applicability of simulative tests in the optimisation of processing parameters. In order to cotnrol the final microstructure of the product, an anlytical model for the evolution of microstructure during hot working (in DRX domain) was obtained. Using the above model, the optimum strain, strain-rate, and temperature trajectories were arrived at for obtaining a grain size of 35 mum in an extruded product. Process control parameters, such as ram velocity, die profiles and billet temperature, which achive the optimal trajectories were calculated using a process model. Extrusion trials were conducted at optimal conditions and a good agreement with those predicted in the design stage has been achieved.