Strain-hardening Capacity and Microstructure Analysis of X70 High Strain Line Pipe

摘要

Strain-hardening capacity is the most effective way to improve the deformability of line pipe.In this paper,four kinds of new X70 high strain line pipe have been produced by four manufactures respectively.Microstructure,strain-hardening capacity,and characterization of the X70 high strain line pipe have been analyzed.It is concluded that X70 high strain line pipe steel does not fit to the Hollimon formula in the entire deforming process,and a stable strain-hardening exponent is not available.At the beginning of plastic deformation,the strain-hardening capacity of X70 high strain line pipe steel is excellent.It decreases rapidly as the stain increases then becomes stable after 2.0％ total strain.The stress ratios of Rt1.5/Rt0.5 、Rt2.0/Rt1.0 and Rt5.0/Rt1.0 are proved to characterize the strain-hardening capacity of X70 high strain line pipe steel.When Rt1.5/Rt0.5≥1.070,Rt2.0/Rt1.0≥1.025,and Rt5.0/Rt1.0≥1.050,the average strain over the gauge length of 2 times the outer diameter,centered at the wrinkle on intrados peak,is above 1.3％.