Analysis of Internal Surface Defects of Seamless Steel Tubes
There are defects in the inner surface of the seamless steel pipe processed by the round billet through piercing and rolling.Four defects with different appearances can be seen in the palm-sized area.The surface samples and transverse and longitudinal cross-section samples of the defect site were observed by using a metallurgical microscope,a scanning electron microscope and an energy spectrum analyzer.High-temperature iron oxide and high-temperature oxidation origin were observed at the four defects.It can be determined that the internal surface defects of the steel pipe are generated during continuous casting.Through the observation and analysis of the surface morphology and the measurement of the depth of the longitudinal section defects,the causes of defect formation are the central crack,central shrinkage hole and shrinkage porosity,which are caused by rolling deformation.There are Na,Mg,Al,Si,P,K,Ca and other elements in the four defects,which are the residues of the sodium phosphate lubricant used in the perforation process.
central crackshrinkage hole and porositycentral segregationhigh temperature iron oxide
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