| Processing of quenching and tempering (QT), quenching and intercritical quenching then tempering (QLT) was studied in this paper to research the effect of aging treatment on micro structure and properties of Copper-bearing high strength steel, which was redsigned on the alloy composition of 10Ni5CrMo. Meanwhile, the mechannism of Cu and C on microstructure and properties of steels was also researched.The results indicated that alloying elements has a significant impact on the microstructure and properties of Copper-bearing high strength steel. Adding Cu element in 10Ni5CrMo steel can obviously improve the strength of steel and in the range of 1.0% to 1.5%, the tested steel within 1.20% Cu had the best mechanical properties, which can ensure the strength level and significantly improving the ductility and toughness of the tested steel. The adding of Cu content can improve the strength and low temperature toughness of steel owing to the increase of Cu content which promoted the precipitation of the second phase and refined grain.With the reduction of C content from 0.04% to 0.02%, the low temperature toughness of steel was improved while the strength was reduced. The reduction of C content hindered the precipitation of the second phase and increased the width of lath which reduced the intensity of tested steel. Therefore, the tested steel containing 0.04%C and 1.20% Cu can obtain excellent strength, ductility and low temperature toughness, which was the best design system components.Aging treatment can also significantly affect the microstructure of Copper-bearing high strength steel and precipitation of Cu, leading to the changes of mechanical properties of steel. While aging at 640℃ for 2h, the tested steel can get the optimum match of strength and toughness. During the aging process, Competition between the softening of matrix and the strengthening by second phase determines the microstructure and properties of steel. The strength of steel decrease with the rising of the temperature between 600℃ and 660℃, because the softening of matrix having the major contribution in strength. The characteristic of the aging temperature above 660℃ is associate with a secondary increase in tensile strength but a decrease in yield srength as a great numble of M-A island formed in the steel, which decrease the yield ratio at the same time. Meanwhile, the block size of steel which is named as "effective grain size" also decrease with the rising of the temperature and this is the reason that improve the low temperature toughness.The aging temperature and aging time play an important role in Cu precipitation. Under the higher aging temperature, the size of Cu particles happen to be coarsen obviously, which is greater than 30nm, and it grows to become into rod-like from spheral in the particle shape, and finally its precipitation strengthening is weakened. The aging time also had a great effect on Cu precipitation, whose size increased gradually as prolongation of aging time at 640℃. The length and width reached 100nm and 50nm respectively when aging last for 100h. Therefore, it is benefit to the good combination of strength and thoughness by controlling the aging time in 2 hours.Processing of QLT has the greatly effect of increasing low temperature toughness of Copper-bearing high strength steel.The increment of-84℃ impact energy at that aging temperature are more than 80J after QLT. It caused the fluctuation of component during intercritical quenching, in the subsequent tempering process, the Aci temperature of these areas that the alloying elements were concentrated is dropped, and lower than the aging temperature, therefore, It formed reversed austenite and stabilized at room temperature which improved the low temperature of Cu-bearing steel effectively. |
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