Technology Optimization Of Tempering And Straightening For Hot Rolling Large Section 13Cr Supermartensitic Stainless Steel Pipe Blanks

Hot rolling large section 13Cr supermartensitic stainless steel Pipe blanks,are finished by several processes,manufactured into pipes in seamless tubing plants,and then used in oil extracting industries.Due to high level requests of end products' surface qualities,pipe blanks usually are tempered and straightened and peeled in order to eliminate the micro cracks on the surfaces of the pipe blanks.However,the bending of pipe blanks,which appeared in tempering,is rather harmful to several subsequent processes,such as peeling,grinding,pipe-inserting etc.Even thorough pipe blanks are straightened,the bending can not be totally eliminated due to the large section and high level alloy ingredients,which lead to rather high strength.Secondly,high level surface hardness of the pipe blanks after being tempered lead to high level wastage of cutter blades and groove shape defects on the pipe blanks in the peeling process.Using skills such as industrial tests,production practice tracking,comparative analysis,hardness testing,metallography theory analysis,this paper had studied the influence of straightening parameters to the straightness of 13Cr SMSS Pipe blanks,the influence of tempering temperature and tempering finishing temperature to the surface hardness of 13Cr SMSS Pipe blanks,the influence mechanism is also discussed Based on the research conclusions,technological measures were settled down,which increase the straightness and decrease the surface hardness of 13Cr SMSS Pipe blanks effectually?The conclusions were obtained as follows(1)Because of the high strength of large section 13Cr SMSS pipe blanks,straightening at normal temperature,will bring about strong impact on equipment and the straightness is unqualified after straightening.Straightening at certain temperature will bring about overall bending which appeared in the cooling period,because of the difference of cooling speed?(2)Technology of thermal straightening-uniform cooling was settled down.Straightening at the temperature of 150?-300?,the strength of pipe blank was decreased,and equipment load was decreased,straightness of pipe blank was also ensured.Uniform cooling after thermal straightening technology can avoid overall bending meting the requirements of peeling processes.(3)Tempered above 665?,higher tempering temperature will bring about higher surface hardness of the pipe blanks and more difficulties in peeling process.And when the drawing out temperature after tempering is above 400?,higher drawing out temperature will bring about higher surface hardness rapidly,and more difficulties in peeling process.The drawing out temperature after tempering is decreased below 400? to take advantage of the slow cooling effect in furnace.Cooling speed between 640? and 400? were decreased,the amount of residual austenite were increased,the surface hardness of the pipe blanks and the peeling difficulties were decreased efficiently.