Cause and control of surface crack on M100 large-scale electroslag remelting slab
M100 steel is a high strength ship structure steel produced by electroslag process,and the surface cracks generated during the electroslag remelting process can have adverse effects on the yield and surface quality of the product.In order to solve the surface cracking problem of M100 large-scale electroslag remelting slab,the charac-teristics and formation mechanism of surface cracks on electroslag slab were investigated using the methods of resid-ual stress,macrostructure,crack morphology,microstructure and hardness analysis.The results show that most of the surface cracks on electroslag slab distribute along the coarse columnar crystal grain boundaries,their fracture ex-hibit the typical feature of intergranular fracture.And there is obvious oxidation phenomenon at the cracks,indica-ting that the cracks are mainly generated in the solidification and cooling stage of electroslag slab.The formation mechanism of surface crack on electroslag slab is analyzed,the intergranular bonding force of coarse martensite co-lumnar crystals which is formed under a rather large cooling intensity by crystallizer is weak,it caused cracks along grain boundaries under the instantaneous tensile stress produced by martensitic transformation,and it is the main reason for surface intergranular cracks on the experimental electroslag slab.Based on the formation mechanism of surface cracks,the process optimization measure of reducing the crystallizer cooling water flow rate from 130 m3/h to 80 m3/h was proposed and tested industrially.It is verified that the microstructure of electroslag slab is mainly composed of mixed martensite and bainite,whose average hardness is reduced by about 40HV10 compared with the pre-optimization electroslag slab.And no crack is found on the surface,which indicates that the adopted optimiza-tion measure for the cooling rate of crystallizer is reasonable and effective.The research results can provide reference for the control of surface quality in the electroslag production of large martensitic alloy steel slabs.
M100 steelelectroslag slabsurface crackcooling intensity of crystallizertissue stress
NETL
NSTL
万方数据
