MICROSTRUCTURAL EVOLUTION DURING SIMULATED OLAC PROCESSING OF A LOW-CARBON MICROALLOYED STEEL

The microstructural evolution during simulated on-line accelerated coo ling (OLAC) of a commercial Grade: 80 pipe steel was studied using a q uench deformation diIatometer, The transformed matrix microstructure c ontains various amounts of polygonal ferrite, granular bainite and aci cuIar ferrite, depending mainly on the accelerated-cooling interrupt t emperature. The final microstructure is predicted well by drawing the OLAC schedule on the appropriate CCT diagram. Three distinct groups of precipitates are found in the finaI microstructure, which form during reheat, austenite deformation, and cooling, respectively. The distrib ution and composition of the precipitates varies widely with steel com position and processing schedule. The microstructure of industrially p rocessed plate agrees well with that of corresponding laboratory simul ations.