The 12CrNi2 alloy steel powder studied in the present paper is mainly used to manufacture camshafts for nuclear power emergency diesel engines. Laser cladding deposition is of great significance for the manufacture of nuclear power emergency diesel camshafts, which has the advantages of reducing material cost and shortening the manufacturing cycle. However, due to the extremely uneven heating of the components during the deposition process, a complex residual stress field occurs, resulting in crack defects and residual deformation of the components. In the present paper, 12CrNi2 bulk specimens were prepared on the Q460E high-strength structural steel substrate at different preheating temperatures by laser cladding deposition technique, and a finite element residual stress analysis model was established to investigate the effects of different preheating temperatures on the microstructure, properties, and residual stress of the specimens. The results of the experiments and finite element simulations show that with the increase of preheating temperature, the content of martensite/bainite in the deposited layer decreases, and the ferrite content increases. The proper preheating temperature (150 °C) has good mechanical properties. The residual stress on the surface of each specimen decreases with the increase of the preheating temperature. The longitudinal stress is greater at the rear-end deposition part, and the lateral residual stress is greater on both sides along the scanning direction.

No abstract

No abstract

No abstract

In view of the difficulty of fully-mechanized mining in steeply inclined coal seam with thickness of 4 to 8 m, the horizontal section short wall fully-mechanized caving mining method is innovatively proposed. In the No. 3-3c steeply inclined coal seam of a Coal Mine, the single roadway integrated with excavation and recovery is arranged as working face, the pillar on sides of roadway is recovered ahead by spiral drilling machine, and the top coal is recovered by the vertical and horizontal self-moving supports. The Z-type ventilation is formed by constructing a ventilation roadway along the side of gob. Through theoretical analysis, numerical calculation and physical similarity simulation, the main mining parameters, including sectional height and ratio of mining height to caving height, were determined, and the characteristics of roof movement evolution, floor failure and sliding and the generalization of surrounding rock bearing structure were revealed. The results show that the effect of coal caving is better when the section height is 10 m and the ratio of mining height to caving height is 2.85. The cross-layer multi-ladder voussoir structure is formed by transformation and migration of the critical layer, and the failure and slip modes of floor are extruding-translation, extruding-underdraught and extruding-upthrust in different areas of horizontal sublevel caving stope. Roof, pillar and floor are interrelated to form the Roof-Pillar-Floor (R-P-F) chain structure. When the height of section with three sublevels is 30 to 45 m, the mutual conversion of strong and weak chains between structural units can be cut effectively in mining process, and the impact disaster caused by the roof falling over great extent and the instability of pillar can be prevented. The new mining method proposed and studied above provides the technological and theoretical basis for the safe and efficient production of such coal seams, and is of great significance to the sustainable development of coal in Xinjiang province and even western China.