With the development of mechanical cutting in the direction of automation, high speed and precision, higher requirements are put forward for the cutting performance of materials, so lead-sulfur composite free-cutting steel with better cutting performance appears, also known as ultra-free-cutting steel. Since then, various lead-sulfur binary and multicomponent composite free-cutting steels have come out one after another. As a free-cutting element used in free-cutting steel, tellurium first appeared in the patent of 1932. 196 1 year, the United States successfully developed a tellurium-containing free-cutting steel, which is a multi-component composite free-cutting steel of sulfur, lead and tellurium. Its cutting performance is excellent, comparable to that of free-cutting brass. Selenium and tellurium are often used alternately or added to steel at the same time because of their similar properties and functions. Since the 1960s, people have studied another method to improve the machinability of steel, that is, adding a certain deoxidizing element to generate the required deoxidizing product-favorable inclusions, which is called deoxidizing adjustable free-cutting steel in Japan. 1964, the former federal Republic of Germany first filed a patent for calcium deoxidized calcium free-cutting steel, which was introduced and officially produced in Japan three years later. It is most suitable for high-speed cutting with TiC cemented carbide tool, which can significantly improve productivity and reduce tool consumption. In Japan, it has become a kind of free-cutting steel widely used in automobile and tractor manufacturing. Since the late 1960s, people have been studying the free-cutting steel deoxidized by titanium. 1973, Japan first published the patent of titanium deoxidized titanium-sulfur composite free-cutting steel, and in recent years, it has been tried in a few countries such as Japan.
The production of free-cutting steel is developing rapidly, the varieties and brands are increasing, and the output is gradually increasing. Among the free-cutting steel standards of the United States, Japan, Britain, the former Federal Republic of Germany and the former Soviet Union, most of them have 3 1 steel grade (AISI), and the least has 7 steel grade (FOCT). The variety has been extended to flat steel and pipes. The output of free-cutting steel is the largest in Japan, and the growth rate is also the fastest. 1965 approaches 1000000t, 1985 reaches1000000t or so, of which sulfur system accounts for 64.4%. About 40% ~ 46% of free-cutting steel produced in Japan is used in automobile manufacturing, about 10% in industrial machinery, and about 6% in household goods and others. China began to produce sulfur-based free-cutting steel (mainly low-carbon steel for automatic machine tool processing) in 1950s, and revised the new free-cutting steel standard GBl9 1-75 in 1975. Since 1970s, the trial-production of calcium-based and titanium-based free-cutting steels has been started. However, the free-cutting steel containing lead, selenium or tellurium, which needs special protection in production to eliminate public hazards, has not been officially produced. China began to study free-cutting steel containing rare earth from 1977.