In the context of automobile lightweighting, integrated die-casting technology has become a universal model to better realize automobile lightweighting. The die-casting molds required for integrated die-casting technology are large and complex. Therefore, higher requirements are put forward for the comprehensive performance of mold steel. Although progress with traditional strengthening methods has stalled, improving the performance of die steels is becoming increasingly challenging. In fact, new mold steels need to be explored and heat treatment and strengthening techniques optimized. The development status of mold steel and the corresponding heat treatment, structure control and strengthening methods were summarized and analyzed, and an excellent nano-strengthening technology was elaborated. In addition, this review will help researchers gain a comprehensive understanding of the development status of die steel and its strengthening processes. It will also assist them in developing mold steel with higher comprehensive performance to meet the high demand for mold steel in the new era of integrated die-casting technology.

1. Introduction

In order to slow global warming and achieve sustainable development, the automotive industry has faced many challenges in recent years. Those challenges include steady increases in carbon emissions standards in different countries, with residents facing additional concerns such as rising gasoline prices and manufacturers grappling with the rising production costs of new energy vehicles. Driven by these factors, the automotive industry urgently needs new technological directions to reduce consumption and save energy. Therefore, the lightweight concept was introduced into the automotive field, thus proposing integrated die-casting technology. The production of light vehicles in various countries is increasing year by year. Automobile lightweighting is the development trend of the world’s automobiles, and its purpose is to achieve energy conservation and emission reduction.

2. Direction

At present, automobile lightweighting mainly faces three directions: lightweight materials, lightweight structures, and lightweight manufacturing processes. The expression of lightweight materials is to use lightweight materials to replace materials with higher specific gravity. As a result, the curb weight of the car is reduced. Aluminum alloy is currently the most widely used lightweight material. Structural lightweighting optimizes the structure, size, shape and morphology of parts to obtain the best design parameters, thereby reducing the amount of material used. The lightweight goal of the manufacturing process is to improve material performance, shape, and form through process optimization; integrated die-casting technology is an extremely important component of lightweight manufacturing. Integrated die casting realizes the integral casting of aluminum alloy parts, replacing many scattered parts with large integral parts, reducing the number of parts and equipment. The preparation of lightweight, complex, and large-scale aluminum alloy parts is conducive to promoting the lightweight process. It turns out that the use of lightweight and integrated die-casting technology in automobile manufacturing can solve the above challenges very effectively, thus becoming a key technology to solve this problem.

3. Development

“Aluminum and Automobiles” is closely related to the progress and development of the automobile industry. In addition, today, when energy conservation has become a primary requirement, manufacturers are forced to actively pursue weight reduction and compactness in the design of future cars. Therefore, lightweight alloys, especially aluminum and magnesium, are increasingly used as materials for automotive components.
The International Conference on Aluminum and Automobiles held in West Germany in 1976 is a good example of the widespread use of lightweight alloys in automobiles. On display were aluminum bumpers, truck cabs, door panels, hoods, steering columns and many other parts, illustrating the rapid trend toward weight reduction through expanded use of aluminum. However, despite great strides in weight reduction through design, full market acceptance cannot be achieved unless a product of consistent quality and low manufacturing cost can be provided.