R & D and Microstructure Characterization of Ultra-high Strength-toughness Casing for Ultra-deep Well Service

According to the requirements of ultra-deep well development，the alloying technology and the manufact- uring process for developing the high strength-toughness casing are investiagted. As a result the ultra high strengthtoughness BG160V casing with excellent toughness and resistance against delayed fracture is developed，and the strength and micro- structure of the said casing under different service temperatures are analyzed. The results of the performance tests to the pipes as massively produced show that the yield strength of the pipe is over 1 100 MPa，and its transverse Charpy impact energy at 0 ℃ is more than 10% of the nominal yield strength，which meets the requirements of the exploitation of the ultra-deep well oil and gas；and the grain size of the casing is up to Level 11，and the average effective grain diameter is 2.45 μm，and such fine grain size is responsible for high toughness and delay fracture resistance of the material.