Cause analysis of drilling cracks in free-cutting silver bright rod
1215 MS free-cutting steel has good machinability,and its surface quality can directly affect the production and processing of products.After drilling of 1215 MS free-cutting silver bright rod produced by one steel plant,the cracks were observed at the core of the parts.In order to find out the causes of drilling cracks,the corresponding area of the sample was studied by means of scanning electron microscope and en-ergy dispersive spectrometer(SEM/EDS).The results showed that the metallographic structure of 1215 MS free-cutting steel was mainly composed of ferrite+pearlite,which accounted for 92.0％and 4.4％,re-spectively.The coarse pearlite banded structure was found on the cracking side of the sample,and its equiv-alent diameter could be up to 15.0 μm,while the equivalent diameter of ordinary pearlite was only 6.2 μm.Compared with the ferrite structure,the average hardness of pearlite structure was higher,which was 243 HV0.01.The high hardness pearlite band led to uneven force of the drill bit during drilling,resulting in material cracking.
1215MSfree-cutting steelsilver bright rodsurface crackpearliteelement segregationscan-ning electron microscope(SEM)energy dispersive spectrometer(EDS)
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