Electric furnaces were gradually developed after the introduction of DC generators in the 1870s. Some commonly used electric furnaces, such as general resistance furnaces, steel-making electric arc furnaces, submerged arc furnaces, core induction melting furnaces, etc., had their prototypes in the 1880s and 1990s. In the 1920s and 1930s, due to the advent of nickel-chromium alloys, triode electron tubes, etc., especially the development of the power industry, the above-mentioned electric furnaces began to be popularized and applied in the industry, and medium and high-frequency induction melting furnaces were also developed. Infrared furnace, simple controlled atmosphere resistance furnace, etc. In the 1940s and 1950s, with the development of metallurgy, machinery, aviation, atomic energy and other industries, steelmaking electric arc furnaces began to develop in the direction of large-scale (capacity above 50t), and induction diathermy equipment and induction hardening equipment were popularized and applied.Vacuum Heat Treatment of Hand Hacksaw Blades