27MnCrV is a new type of steel used in the production of TP110T steel grade oil pipe sleeves. The steel types used in conventional production of TP110T steel grade oil pipe sleeves are 29CrMo44 and 26CrMo4. Compared with the latter two, 27MnCrV contains less Mo element, which can greatly reduce the production cost. However, after the 27MnCrV is produced by the normal austenitizing quenching process, there is obvious high temperature tempering brittleness, resulting in low impact toughness and instability.
Two methods are usually used to solve such problems: First, the method of rapid cooling after tempering is used to avoid high temperature brittleness and obtain toughness. Second, the sub-temperature quenching method effectively improves harmful elements and impurities and improves toughness through the incomplete austenitization of steel types. The first method has relatively strict requirements on heat treatment equipment and requires additional costs.
The 27MnCrV steel has AC1 = 736 ℃ and AC3 = 810 ℃, and the heating temperature during sub-temperature quenching is selected between 740-810 ℃. The sub-temperature quenching selects a heating temperature of 780 ° C, and the holding time of the quenching and heating is 15 minutes; after the quenching, the tempering selects a temperature of 630 ° C, and the heating and holding time is 50 minutes. Since the sub-temperature quenching is heated in the α + γ two-phase region, the quenching is performed in a state where the ferrite is left undissolved, 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. This ensures the smooth operation of heat treatment production, and provides a good raw material for subsequent wire processing.