The Study On Effect Of Plastic Deformation On Strength Character Index Of Pipeline Steel

Mostly high-end pipeline steel with heavy plate as a blank large diameter steel tube is LSAW manufactured by plastic forming method, which material is low alloy high-strength steel or micro-alloyed low carbon high-strength steel. The strength character index of the material changes with plastic deformation in the processing of the tube plastic forming and flattening test for tube mechanical properties. The study on the change rule of the strength character index change with plastic deformation of pipe steel and opening out the inner relationship in the processing of line pipe manufacture and using is a academic problem concerned by people. In this paper, aiming at several common pipeline steel and UOE forming process, we analyzed the effect of plastic deformation on strength character index of pipeline steel and established the mixed hardening model of X80 pipeline steel through the uniaxial positive loading test, uniaxial reverse loading test, bending and flattening test and other basic research.In this paper, two kinds of X80 pipeline steel plastic deformation were simulated in the UOE forming process by the methods of pre-tension once and pre-tension twice. In the condition of uniaxial positive loading, we also studied the change rule of yield strength and yield ratio of X80 pipeline steel with the pre-deformation changes, and the inner link with material organization.In this article, through uniaxial reverse loading test, we studied the change rule of yield strength of the X70 and X80 pipe steel under different strain in the process of uniaxial reverse loading. The results showed that the yield strength of the X70, X80 pipeline steel presented the trend of increasing firstly, then decreasing and smooth lastly with the increase of pre-strain. According to the test data of reverse loading, we determined the mixture strengthened coefficients and mixed hardening model parameters of X80 pipeline steel.Taking X60 pipeline steel for example, in this paper, bending deformation of features for different specifications during UOE processes was analyzed using FEM. Bending specimens with the same equivalent strain were made through four points bending. Mechanical properties change law of X60 pipeline steel plate after bending and flattening was investigated according to API standards regarding flattening test methods of mechanical properties for pipe body specimens, and reversal estimation model of yield strength for X60 pipeline steel plate in the equivalent strain range of 0.0104 ~0.0586 was presented.