Reason Analysis on the Inner Wall Cracks of AISI 13300 Seamless Pipe
AISI 13300 seamless pipes with the chemical contents of 0.29-0.34C,0.17-0.35Si,1.50-1.65Mn,P≤0.020 and S≤0.02 are manufactured by the process including BOF steel making,LF refining,continuous casting bloom,hot rolling,quenching and tempering.NDT (Non-destructive-testing) unqualification of the pipes occurred in April 2014.Some research work has been carried to solve the problem.At first,the etch test for macrostructure and defects was performed on the specimens cut from the NDT unqualified part of pipe.Then,the microstructures of both the transverse and longitude specimens have been examined with OM and FEI 650 type SEM.The non-metallic inclusions have also been determined by the SEM-EDS analysis.The research results are obtained as follow: There are a large number of cracks along the axle of pipes (rolling direction) on the inner wall of the macrostructure specimen.The cracks extend into the steel matrix along the radius direction in the zig-zag way which shows the obvious crack extension along the primary austenite grain boundary.No oxides have been observed beside the cracks.There exist calcium aluminate inclusions in some cracks but does not in others,so the crack formation has little relationship with the inclusions.The microstructure show that there are a lot of wedge micro-cracks extending along the primary austenite grain boundary in the steel matrix less than 3mm deep from the inner wall,which coincides the morphology of grain boundary crack during the quenching process.Therefore,the inner wall cracks of the pipe originate from grain boundaries of crude primary austenite during quenching process.The appearance of crude primary austenite grains may be due to the excessive high heating temperature or final rolling temperature.It is important for good internal quality to obtain the microstructure with fine primary austenite grains.Apart from this,it is good to prolong the interval time from the water spraying on the outside to that on the inner wall under the condition of qualified mechanical properties.
inner wall crack primary austenite grain seamless steel pipe
FAN Jianwen YU Xianghui FENG Guanghong ZHANG Hongliang YU Guiling
Central Iron & Steel Institute, Beijing 100081, China Qinghai Province Hydrogeology and Engineering Geology and Environmental Geology Survey Institute, Xi
国际会议
成都
英文
768-770
2016-11-16（万方平台首次上网日期，不代表论文的发表时间）