Research on Processes of Solid Solution Treatment and Cold-hardening of N08028 Alloy Steel Oil Well Pipe

Analyzed in the paper are the effects on the microstructure morphology of the N08028 alloy steel oil well pipe by the pipe blank’s initial microstructure morphology，hot-extrusion and the subsequent solid solution treatment. Also studied is the cold-hardening process of the N08028 alloy. Relevant test results show that the original precipitation phase of the pipe blank can be dissolved during the hot-extrusion process，while the hot-extrusion process itself can develop the new precipitation phase which needs to be eliminated by the solid solution process；and the N08028 alloy oil well pipe as solid solution treated has to be subjected to cold-hardening process to get its mechanical properties up to applicable specification. The cold-hardening process in general leads to the linear relationship between yield strength and tensile strength of the N08028 alloy steel oil well pipe and its sectional shrinkage ratio，and accordingly the stress-strain equation thereof is established.