Effect by Tempering Temperature on Strength and Toughness Matching of V150 Steel for Drill Pipe Service

Systematic tempering temperature optimization experiments are conducted to the V150 steel for drill pipe service. As a result, the impact toughness of the steel is enhanced significantly. Based on the statistics of morphology and fraction of the second phase particles, the strength and toughness matching law of the steel is explained from the point of view of micromechanisms. It is finally identified that the impact toughness of drill pipe-purpose steel can be increased by about 50% within the range of the turning-point tempering temperature, while the steel is still in possession of the nature of the 150 grade steel; and that as the tempering temperature increases, the volume fraction of second phase particles first increases, and then decreases, which provides an enough room for optimization of the steel so as to get it remaining as a hi-strength grade steel. It is also revealed that the spheroidization of the second phase particles from their original bar shape together with gradual softening of the substrate greatly contribute to improvement of the steel's impact toughness.