The bogie made of Grade B＋ steel is one of the most important parts of heavy haul trains. Some accidents were found to be the result of fracture failure of the bogies. It is very important to find the reason why the fracture failure occurred. Because AI was added for the final deoxidation during the smelting process of the Grade B＋Steel, residual AI existed to some extent in the castings. High residual AI content in the bogie casting was presumed to be the reason for the fracture. In this work, the influence of residual AI content in the range of 0.015wt.% to 0.3wt.% on the microstructure and mechanical properties of the Grade B＋ Steel was studied. The experimental results showed that when the residual AI content is between 0.02wt.% and 0.20wt.%, the mechanical properties of the steel meet the requirements of technical specification for heavy haul train parts, and the fracture is typical plastic fractures. If the residual AI content is less than 0.02wt.%, the microstructures are coarse, and the mechanical properties can not meet the demand of bogie steel castings. When the residual AI content is more than 0.2wt.%, the elongation, reduction of area, and low-temperature impact energy markedly deteriorate. The fracture mode then changes from plastic fracture to cleavage brittle fracture. Therefore, the amount of AI addition for the final deoxidation during the smelting process must be strictly controlled. The optimum addition amount needs to be controlled within the range of 0.02wt.% to 0.20wt.% for the Grade B＋Steel.
Wang KaifengGuo ErjunCao GuojianWang LipingFeng YichengJiang WenyongTao Chunguo
The multi-axial forging （MAF） process was introduced into the strain induced metal activation （SIMA） process to replace conventional forging. Microstructure evolution of MAF formed AZ80 magnesium alloy during partial remelting was investigated. Furthermore, the tensile mechanical properties for AZ80 magnesium alloy thixoextruded from the starting materials treated by MAF were determined. For comparison, as-cast AZ80 magnesium alloy was also thixoextruded. The results show that the SIMA route produced ideal, fine semi-solid microstructure, in which almost completely spheroidal primary solid grains had a little amount of entrapped liquid. The microstructure of the as-cast alloy in the semi-solid state is less spheroidized compared with the MAF alloy under the similar isothermal holding conditions. With prolonged holding time, the size of the solid grain increases and the degree of spheroidization is improved in the MAF formed alloys. However, the solid grain size of the as-cast alloys decreases initially, and then increases with further increasing temperature. The tensile mechanical properties for AZ80 magnesium alloy thixoextruded from the starting material produced by MAF are better than those of AZ80 magnesium alloy thixoextruded from the starting material produced by casting. The ultimate tensile strength, yield strength and elongation of the alloy thixoextruded from the starting material produced by MAF are 314 MPa, 238 MPa and 14%, respectively.
（TiB2＋TiC）/Ni3Al composites were prepared by mechanical alloying of elemental powders and subsequently spark plasma sintering.Microstructure of（TiB2＋TiC）/Ni3Al composite sintered at 950°C was finer than that of composite sintered at 1050°C.The influence of grain size on cyclic oxidation behavior was investigated.Cyclic oxidation results showed that the composite sintered at 950°C had smaller mass gains than the composite sintered at 1050°C.XRD and EDS results indicate that finer grain size is beneficial for increasing the oxidation resistance by improving the formation of a continuous TiO2 outer layer and a continuous Al2O3 inner layer on the surface of the composites sintered at 950°C.
As a brazing foil, 4004 A1 alloy has good welding performance. However, the high Si content decreases the plasticity of the alloy. In order to improve the plasticity of 4004 A1 alloy and subsequently improve the productivity of 4004 AI foil, 4004 A1 alloy was modified by RE-Ba-Sb. As a comparison, the 4004 A1 alloy was also modified by RE with different addition. The tensile properties of the alloy reach the best when the addition of RE was 0.2%, in which the tensile strength and elongation were 194 MPa and 5%, respectively. For RE-Ba-Sb modification, the addition of three elements was optimized by orthogonal analysis. The results showed that the greatest impact parameter of RE-Ba-Sb modification was RE addition, followed by addition of Ba and Sb. The optimum addition amounts of RE, Ba and Sb obtained by orthogonal analyses were 0.01%, 0.3%, and 0.05%, respectively. The tensile strength and the elongation of 4004 A1 alloy modified by the optimal modification process were 224 MPa and 6%, respectively. The amount of RE addition in RE-Ba-Sb modification is lower than that in RE modification.
The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.
