Effect of Manganese Content and Cooling Rate on Transverse Crack in Low Carbon Steel

Abstract

Transverse crack which perpendicular to the direction of continuous casting is a main problem in straightening Although the problem of the transverse crack formation is suppressed by tailoring the microstructure on the slab surface the transverse cracks having the length of 2 to 15 mm are still found on the subsurface Thus this study was separated into two parts Firstly the transverse cracks were characterized in low carbon steel of SM570 in order to understand the transverse cracks Secondly three steels having Mn content of 0 67 1 39 and 1 98 wt% which had different chemical composition from SM570 were employed to know the effect of Mn addition on the formation of transverse cracks In addition the cooling rates of 0 01 0 05 0 09 and 3 ℃/s were investigated after heat treatment to understand the effect of the cooling rate on the formation of transverse cracks Then OM and SEM were used to analyze the morphology and microstructure Dilatometer and three-point bending together with digital image correlation (DIC) technique were applied to measure the Ar3 temperature and the mechanical property respectively In the first part it was observed that transverse cracks occur and grow along ferrite formed on the boundaries of austenite and the fracture mode was composed of brittle and ductile fracture In the second part increase in manganese content from 0 67 to 1 98 wt% leads to increasing the fraction of ferrite film forming on the boundaries of austenite from 6 4 to 24 3 % and to reducing the thickness of ferrite from 22 7 to 13 0 ?m at a cooling rate of 0 05 ℃/s At manganese content of 1 39wt% the increasing cooling rate from 0 01 to 3 ℃/s results in increasing the fraction of ferrite film forming on the boundaries of austenite from 14 4 to 36 1 % and to reducing the thickness of ferrite from 18 9 to 11 4 ?m

Date of Award	2019
Original language	English
Supervisor	Jui-Chao Kuo (Supervisor)