Numerical simulation technology of large ingots and castings

1.Current situation

Large castings refer to large-scale casting products in major technical equipment, with high performance requirements, mainly steel castings. Large ingot usually refers to the metal mold ingot which needs further large hydraulic press to be finally formed. Its quality has a direct impact on the overall level and operation reliability of major equipment. It is the basis for the development of power, ship, metallurgy, petrochemical, heavy machinery, national defense and other industries, the premise for the development of advanced equipment manufacturing industry, and one of the important indicators to measure the development level and comprehensive national strength of a country’s heavy industry.

The application of digital, intelligent and network technology in the research of large ingots and castings in China is still in the initial stage, and there is still a big gap with the advanced level of foreign countries. At present, most of the research is only aimed at a certain link in the production process of large ingots and castings, such as the formation of shrinkage porosity and other defects in the solidification process of large ingots / castings, The microstructure evolution of large ingot / casting after heat treatment was studied. With the rapid development of computer technology, the idea of multi-scale, whole process numerical simulation technology has been adopted by relevant scholars and research institutions.

Tsinghua University integrated the casting process and solidification process, coupled the heat and mass transfer phenomena on the macro scale and the grain nucleation and growth on the micro scale, and studied the influence of multi ladle casting process on the formation process of macro segregation of ingot, thus realizing the integration of macro and micro coupling model [7]. For a steel casting, Huazhong University of science and technology simulated the filling process and subsequent solidification process of casting, predicted the distribution of shrinkage cavity and porosity in the final solidification process, compared and analyzed different riser feeding process schemes, designed the riser optimization scheme of the steel casting, and realized the integration of process flow [8]. In view of the transformation of structure in the process of casting and heat treatment of martensitic stainless steel castings, Tsinghua University established a thermal stress analysis system for the whole process of casting and heat treatment of hydraulic turbine castings, studied the stress and deformation of the actual production of hydraulic turbine castings, and realized the integration of casting and heat treatment.

2. Challenges

As the country continues to increase investment in energy and national defense industry, as well as the demand of high-end equipment in the development of emerging industries for large ingots and castings, especially the domestic demand for high-end short of large ingots and castings, the production technology level of large ingots and castings in China needs a major breakthrough. However, most of the large castings are produced by single piece, the production process is complex, the cycle is long, the cost is high, and the shape is huge, the manufacturing is difficult, and the service conditions are severe. In addition, the production process of large castings consumes a lot of energy and materials, which is not suitable for the research of real objects.

For large castings of different purposes, from material selection to material optimization design, smelting and refining control to process design, and using more accurate models to simulate the casting process and subsequent heat treatment process in macro and micro scale, and then develop process integration tools to integrate the processes in various production stages, and finally achieve the performance and life prediction of the engineering system.

3. Objectives

(1) Target to be achieved by 2020:

Realize the numerical simulation of large-scale casting and ingot casting process as well as the prediction of defects, such as shrinkage cavity, porosity, macro segregation and cracks; realize the macro micro coupling in the model, model the physical phenomena in different scales, and establish the chain relationship between different scale models.

(2) Target to be achieved by 2025:

To realize the technological evaluation of the casting process and the prediction of the organizational structure, such as the pouring process, the model design, the equiaxed columnar crystal transformation, etc.; to realize the model coupling of the material and smelting process and the casting process, to give the input parameters of the model for different materials or components, and to establish the initial conditions of the model under different processes.

(3) Target to be achieved by 2030:

The performance prediction and life evaluation of large-scale castings are realized, and the engineering life under specific service environment is given. In order to realize the coupling of numerical simulation of casting and heat treatment process, the parameters of heat treatment process are initialized according to different casting processes, and the relationship between microstructure evolution and structure defect genetic evolution is established.