The development of free-cutting steel is inseparable from the development of environmentally friendly alloy elements and the control of inclusions shape. Alloying elements can affect the composition, morphology, size, and distribution of inclusion, which are the main factors affecting the machinability of free-cutting steel. This study selected sulfur free-cutting steel with different chemical compositions as the research object to examine the effects of bismuth and bismuth tellurium on sulfur-containing free-cutting steel through electrolytic corrosion experiments, metallographic microscopy, scanning electron microscopy, energy spectrum, and electron backscattering analyzer. The results showed that the microstructures of free-cutting-steel containing sulfur, free-cutting steel containing sulfur bismuth, and free-cutting steel containing sulfur bismuth tellurium are composed of ferrite, pearlite, and inclusions. The inclusions in sulfur-containing free-cutting steel are chain, cluster, and a few dotted MnS. The inclusions in sulfur-bismuth free-cutting steel are point and a few dotted MnS. After the addition of Te, the number of dotted inclusions is reduced, while the number of chain and cluster inclusions is increased. Most of the inclusions in bismuth-containing free-cutting steel are flake inclusions, and the class II MnS change into class III MnS, which is beneficial for improving the free-cutting property of steel and to reduce anisotropy. With the addition of Te, MnS of other shapes, such as heart, water drop, butterfly, etc. of a length–width ratio of less than 4 also appeared as MnS and MnTe complex inclusions, and the fusiform manganese sulfide accounted for most of the steel. Both Bi and Te had modification effects on MnS.

In this study, WC-Co-TiC/304 stainless steel composites were successfully prepared by compression at room temperature and vacuum sintering in a special mold. Through analysis and comparison of the microstructure, density, and particle size of WC-Co-TiC/304 stainless steel composite, the effects of different WC contents on the structure and properties of WC-Co-TiC were studied. The results show that among different WC contents when the WC content is 60%, the distribution of each structure is relatively uniform and fine, and the agglomeration of each structure is not obvious. The bonding effect of WC-Co-TiC cemented carbide and 304 stainless steel composite interface is the best. With the increase of WC content, the side defects of WC-Co-TiC cemented carbide increase gradually. When WC content is 60%, the best ratio is 1:1 of Co/TiC, as the density is 94.45%, the particle size of 0.2–0.3 μm is 38.9%, and the highest hardness of WC-Co-TiC cemented carbide side is 1370 HV0.1, but it is better when the ratio of Co/TiC is 3:2 at the composite interface, as the hardness value is 852 HV0.1 and the diffusion of Cr element is more uniform, while other elements have little difference.

In this paper, an ultra-thin Cu/Al composite sheet with a thickness of 0.08 mm was obtained via the cold-rolling composite method using a four-high micro-rolling mill in the laboratory. The rolling reduction of a single pass was 65%. After the annealing of the ultra-thin Cu/Al composite sheets at temperatures ranging from 350 °C to 500 °C, the interface bonding mode of the Cu/Al composite sheets changed from mechanical bonding to metallurgical bonding, and the bonding strength was significantly improved. The microhardness value at the bonding interface of the ultra-thin Cu/Al composite sheets increases with the increase in annealing temperature. When the annealing temperature is 500 °C, the maximum microhardness value at the bonding interface reached 2.0 GPa. With the increase in annealing temperature, the tensile strength and elongation of the ultra-thin Cu/Al composite sheets decreases significantly. The peel strength of the extremely thin Cu/Al composite sheets increases at first and then decreases with the increase in annealing temperature, and reached the maximum value at an annealing temperature of 400 °C. When the annealing temperature was 400 °C, the tensile and peel properties of the ultra-thin Cu/Al composite sheet reached the best state.