INFLUENCE OF THICKNESS AND HOT ROLLING ON DWTT OF HOT ROLLED PIPELINE STEEL X70M
Pipeline steel grade of X70M or more than X70M is mainly used for oil and natural gas transportation because of larger strength and better low temperature toughness.The drop weight tear test,which adopts full wall thickness samples,can reflect the fracture of steel pipe better than Charpy impact test,and is widely used to evaluate the brittle-fracture resistance of pipeline steel.This paper introduces test methods of DWTT,and analysis the effect of thickness and hot rolling on DWTT.Under the same process conditions,DWTT shear area ratio decreases with the increase of hot rolling thickness,and the tough-brittle transition temperature increases.For critical temperatures with shear area ratio ≥ 85％,the 10.8 mm thickness specification is about-38 ℃.The X70M structure is mainly composed of acicular ferrite,a small amount of polygonal ferrite and bainite,which can effectively prevent crack propagation and is conducive to the tear toughness of the drop hammer.The grain size is generally above grade 11.Under the condition of the same composition system,reducing the coiling temperature can refine the grain and improve the toughness.For 15.5 mm thickness specifications,different hot rolling comparative process comparative tests were carried out.Under-10 ℃ test conditions,the DWTT shear area ratio of low temperature cooling(480～510 ℃)was 97％on average,which was better than that of high temperature cooling(540～570 ℃)DWTT shear area of 80.5％.
DWTTpipeline steeltoughnesscoiling temperatureshear area ratio
NETL
NSTL
万方数据
