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In order to investigate the effect of shot distance and impact sequence on the residual stress distribution of 42CrMo steel in shot peening (SP) finite element (FE) simulation, 3D dynamic models with order dimple pattern and stochastic dimple pattern were established via ABAQUS/Explicit 6.14, and the simulation results were compared with experiments. The results show that shot overlap has a significant effect on the residual stress distribution of peened parts. Meanwhile, there is a threshold (related to SP parameter) for shot distance in the vertical and horizontal directions. When the shot distance is greater than the threshold in this direction, the residual stress distribution after SP tends to be stable. The impact sequence has almost no effect on the impact of a small number of shots, but this effect will appear when the number of shots increases. It is necessary to avoid shot overlap and continuous impact of adjacent dimples when the FE model is established; on this basis, the distance between shots and the number of layers of the shots can be reduced as much as possible without affecting the residual stress distribution. In addition, the comparison of simulation and experimental results shows that the residual stress evaluation area consistent with the experimental measurement is essential to obtain accurate residual stress distribution in the FE simulation process.

Two types of steels which are different in Ni content were tested in three groups of different quenching temperatures and same tempering temperature respectively under the same conditions, and then tested the mechanical properties and observated the microstructure, comparing with the effects of different Ni content on the microstructure and properties. When 1Ni-steel is under the different quenching temperature, its tensile strength range is 1269-1290MPa and changes subtlely. The yield strength and impact energy reach the highest at 910°C, and the mircostructure is fine and uniform. With the quenching temperature increasing, the strength of 3Ni-steel decreases ,but the toughness increases comparing with both kinds of the steels, the microstructure of 3Ni-steel has much more hard phases in its tempered martensite microstructure. Its tensile strength, yield strength and toughness are higher than 1Ni-steel at the lower quenching temperature. The inclusions of 3 Ni-steel are characterized by spheroidization and refinement. In the NACE-A test, the SSC resistance of 3Ni-steel is better than that of 1Ni-steel, which indicates that the high Ni steel has better comprehensive properties.

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The35kg ingot was refined with vacuum induction furnace by means of three various deoxidationprocesses in laboratory. From the steel-making point of view, effect of deoxidationprocess on inclusions and was analyzed. The fraction, size and distribution ofinclusions were studied with scanning electron microscope (SEM)and energy dispersive spectrometer (EDS) in three various deoxidation processessteel . The results showed that the volume fraction of inclusions was thelargest in Ti/Zr deoxidation process and the inclusions distributed uniformly. Itwas found that the amount of fine inclusions size in the range of 0.5~1.5 μmwas the largest atTi/Zr deoxidation process. The fraction of inclusions decreased with holdingtime increasing during alloying in present study.