Alloy steel has a history of over a hundred years. Its widespread industrial use began around the latter half of the 19th century. At that time, due to the increasing production and consumption of steel, the machinery manufacturing industry needed to solve the problem of steel machining. In 1868, the Englishman R.F. Mushet invented self-hardening steel with a composition of 2.5% Mn-7% W, increasing the cutting speed to 5 meters per minute. With the development of commerce and transportation, in 1870, a 158.5-meter span bridge was built on the Mississippi River in the United States using chromium steel (1.5-2.0% Cr). Due to difficulties in machining components, some industrialized countries later switched to nickel steel (3.5% Ni) to build long-span bridges. Simultaneously, some countries also used nickel steel in the construction of warships. With the development of engineering technology, there was a demand for faster machine rotation speeds, and high-carbon chromium rolling bearing steel appeared in Western Europe in 1901. In 1910, the 18W-4Cr-1V type high-speed tool steel was developed, further increasing cutting speeds to 30 meters per minute. It is evident that the emergence and development of alloy steel was in line with the demands of social productivity development, particularly the needs of machinery manufacturing, transportation, and the military industry.
After the 1920s, the widespread use of electric arc furnace steelmaking created favorable conditions for the mass production of alloy steel. The development of the chemical and power industries further promoted the expansion of alloy steel varieties, leading to the emergence of stainless steel and heat-resistant steel during this period. In 1920, the German E. Maurer invented the 18-8 type stainless acid-resistant steel; in 1929, Fe-Cr-Al resistance wire appeared in the United States; and by 1939, Germany began using austenitic heat-resistant steel in its power industry. From the end of World War II until the 1960s, the development of high-strength and ultra-high-strength steels was primarily driven by the needs of the aerospace industry and rocket technology. Many new high-strength and ultra-high-strength steel grades emerged, such as precipitation-hardening high-strength stainless steel and various low-alloy high-strength steels. After the 1960s, many new metallurgical technologies, especially ladle refining, were widely adopted. Alloy steels began to develop towards higher purity, higher precision, and ultra-low carbon, leading to the emergence of new steel grades such as maraging steel and ultra-pure ferritic stainless steel. Internationally, there are thousands of alloy steel grades and tens of thousands of specifications. Alloy steel production accounts for approximately 10% of total steel production and is a crucial metallic material used extensively in national economic construction and defense.
The main alloying elements in alloy steel include silicon, manganese, chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, aluminum, copper, boron, and rare earth elements. Vanadium, titanium, niobium, and zirconium are strong carbide-forming elements in steel. Given sufficient carbon and appropriate conditions, they can form their respective carbides. When carbon is deficient or under high-temperature conditions, they enter the solid solution in an atomic state. Manganese, chromium, tungsten, and molybdenum are carbide-forming elements; some enter the solid solution in an atomic state, while others form substitutional alloy cementite. Aluminum, copper, nickel, cobalt, and silicon are non-carbide-forming elements and generally exist in the solid solution in an atomic state. Alloy Steel Classification: Alloy steels come in many types, typically classified by alloy element content as low-alloy steel (10%); by quality as high-quality alloy steel and special alloy steel; and by properties and applications as alloy structural steel, stainless steel, acid-resistant steel, wear-resistant steel, heat-resistant steel, alloy tool steel, rolling bearing steel, alloy spring steel, and special performance steel (such as soft magnetic steel, permanent magnet steel, and non-magnetic steel).
Besides iron, carbon, and unavoidable traces of silicon, manganese, phosphorus, and sulfur, steel also contains a certain amount of alloying elements. These alloying elements include one or more of silicon, manganese, molybdenum, nickel, chromium, vanadium, titanium, niobium, boron, lead, and rare earth elements. This type of steel is called alloy steel. The alloy steel systems vary from country to country depending on their resource conditions, production, and usage. Previously, nickel- and chromium-based steel systems were developed abroad, while my country has discovered alloy steel systems primarily composed of silicon, manganese, vanadium, titanium, niobium, boron, lead, and rare earth elements. Alloy steel accounts for about ten percent of total steel production and is generally smelted in electric furnaces. Based on their applications, alloy steel can be divided into eight major categories: alloy structural steel, spring steel, bearing steel, alloy tool steel, high-speed tool steel, stainless steel, heat-resistant and non-scaling steel, and electrical silicon steel.
