27MnCrV is a new type of steel for the production of TP110T steel grade petroleum casing pipe. The conventionally produced TP110T steel grade petroleum casing pipe are 29CrMo44 and 26CrMo4. Compared with the latter two, 27MnCrV contains less Mo, which can greatly reduce production costs. However, there is obvious high temperature temper brittleness after the normal austenitizing quenching treatment process is used to produce 27MnCrV, which results in low and unstable impact toughness.
Two methods are usually used to solve such problems: one is to use rapid cooling after tempering to avoid high temperature brittleness and obtain toughness. Second, the sub-temperature quenching method effectively improves the harmful elements and impurities through the incomplete austenitization of the steel, and improves the toughness. The first method requires relatively strict heat treatment equipment and requires additional costs.
For 27MnCrV steel, AC1=736?, AC3=810?, the heating temperature during sub-temperature quenching is selected between 740-810?. For sub-temperature quenching, the heating temperature is 780°C, and the holding time of quenching heating is 15min; after quenching, the tempering temperature is 630°C, and the tempering heating holding time is 50min. As the sub-temperature quenching is heated in the a+? two-phase zone, the quenching is carried out in the state where part of the undissolved ferrite is retained, and the toughness is improved while maintaining high strength.
At the same time, the low temperature quenching is lower than the conventional temperature, which reduces the quenching stress, thereby reducing the quenching deformation, which ensures the smooth operation of the heat treatment production, and provides a good raw material for the subsequent wire processing.
The process has been applied in the processing plant. The quality assurance data shows that the yield strength Rt0.6 of the heat-treated steel pipe is 820-860MPa, the tensile strength Rm is 910-940MPa, the impact toughness Akv is between 65-85J, and the destruction performance is 100%. qualified. The data shows that the 27MnCrV steel pipe is already a very high-quality high-grade oil casing pipe. On the other hand, it also shows that the sub-temperature quenching process is a method to avoid high temperature brittleness in the production of steel products.