strain-hardening capacity and characterization method of X70 high strain line pipe were investigated by metallographic analysis
electron backscatter diffraction
quasistatic tension and finite element method. It is concluded that X70 high strain line pipe steel does not follow the Hollimon formula in the entire deforming process
and the strain-hardening exponent of the steel is not constant. At the beginning of plastic deformation
the strain-hardening exponent of the steel gets higher
but the value decreases rapidly with stain increasing
and then becomes stable after 2.0% of total strain. The stress ratios of R
t1.5
/R
t0.5
R
t2.0
/R
t1.0
and R
t5.0
/R
t1.0
are verified to perfectly characterize the strain-hardening capacity of X70 high strain line pipe steel in engineering. As R
t1.5
/R
t0.5
≥1.070
R
t2.0
/R
t1.0
≥1.025
and R
t5.0
/R
t1.0
≥1.050
the average strain over the gauge length of 2 times of outer diameter centered at the wrinkle on intrados peak is above 1.3%.
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