Study On Mechanism Of Edge Cracking Of SS400Boron-bearing Steel

Because of SS400boron-bearing steel having fine comprehensive properties andusability, which shows as high strength, good ductility and quick industrial productionspeed, it is widely used in production and living field. Boron element plays an importantrole in improving comprehensive performance of SS400boron-bearing steel. However,in the actual production of SS400boron-bearing steel, the slab edge cracking problemtends to exist with the addition of boron. In order to mitigate edge cracking of SS400boron-bearing steel, this paper systematically studies on the mechanism of edgecracking of SS400boron-bearing steel, and finds that the main reasons for the edgecracking of SS400boron-bearing steel are the precipitation of BN particles and theremleting property of steel. The main contents of this paper are summarized as follows:(1)The significance of studying on the mechanism of edge cracking of SS400boron-bearing steel was clarified by introducing the research background, and theresearch status in related fields at home and abroad was also summarized.(2)Based on analysis of edge cracking morphology of SS400boron-bearing steel,the high temperature mechanical properties of steel was investigated through theGleeble-1500thermal simulator. In general, the high-temperature strength of SS400boron-bearing steel decreases with the temperature increasing. Morever, there existthree brittle zones respectively named theⅠbrittle zone (1300℃to the melting point),theⅡbrittle zone (1150℃to1250℃), and the Ⅲ brittle zone (700℃to950℃).(3)The precipitation temperature of BN particles and the precipitation amount atvarious temperatures was calculated by thermodynamic method under the condition ofSS400boron-bearing steel chemical composition. The results show that theprecipitation temperature of BN is much higher than AlN, and the nitrogen fixation oftitanium in steel can reduce the amount of BN precipitation. Meanwhile, BN inclusionswere detected on SS400boron-bearing steel edge cracking area by electron probetechnology (EMPA), which means that the cause of ductility reducing in the Ⅲ brittlezone is the precipitation of BN in SS400boron-bearing steel.(4)Micro-segregation models analysis, Original position statistic distributionanalysis and Secondary ion mass spectrometry indicate the boron segregation behavioron SS400boron-bearing steel, and the remelting phenomenon are observed during the solidification of SS400boron-bearing steel by high-temperature laser scanning confocalmicroscope (CLSM). The segregation of boron on SS400boron-bearing steel is thecause of remelting phenomenon at high temperature and the ductility reducing in the Ⅱbrittle zone.(5)The precipitation of BN causes the Ⅲ brittle zone of SS400boron-bearingsteel, and the brittle zone has a narrow temperature region and a high temperaturelimit.The segregation of boron on SS400boron-bearing steel leads to the remeltingproperty of the steel and the existence of the Ⅲ brittle zone. Both of them significantlyreduce the thermoplastic, which are also the main reasons of edge cracking formation ofSS400boron-bearing steel slab.