Effect of recycled raw materials on microstructure and mechanical properties of smoke turbine blades made of K213 alloy

Abstract K213 alloy has excellent casting properties, outstanding comprehensive properties, and microstructure stability below 750°C. The alloy mainly produces turbocharger turbine blades, gas turbine blades, and smoke turbine blades working below 750°C. However, due to the complex structure of the blade, the casting molding is difficult, the yield is low, and many waste blades appear, forming many return materials. The smoke turbine blades made of K213 alloy are studied in the paper. The microstructure and mechanical properties at room temperature and high temperature of K213 alloy blades prepared by new raw materials and recycled raw materials were studied by OA, XRD, SEM, EDS, and quasi-static tensile equipment. Results show that the chemical composition of K213 alloy leaves prepared by new raw materials and recycled raw materials meets the requirements of GB/T 14992 standard, but the content of C and B elements in the leaves prepared from return raw materials is slightly higher than that of the leaves prepared from new raw materials. Secondly, the microstructure, dendrite morphology, and precipitated phase types of the leaves prepared from the above two raw materials are similar in the as-cast and the standard heat treatment states. However, the alloy’s microstructure prepared from recycled raw materials contains a massive TIN phase, namely MN, and many Ti and N elements. The yield strength, ultimate tensile strength, and elongation of the blades prepared with new raw materials at 750°C are higher than those prepared with recycled raw materials under the casting and standard heat treatment conditions. Under the standard heat treatment condition, the mechanical properties of the alloy blades prepared by the two raw materials meet the casting technical indexes of smoke turbine blades at 750°C (tensile strength ≥ 588 MPa at 750°C, elongation after fracture ≥ 4.0%). In addition, carbides and borides in the microstructure are the main causes of cracks in the tensile process of the alloy at room temperature and high temperature.