In 2006, 32 special steel enterprises in China produced 509 1.5 million tons of special steel, accounting for 1.2% of the national crude steel output that year.
In 2007, 32 special steel enterprises in China produced 70.86 million tons of special steel, accounting for 14.5% of the national crude steel output that year. Although China's special steel industry has developed rapidly, compared with developed countries in the world, the intensification and scale of the industry are still insufficient. Lack of specialization and efficiency; Insufficient deep processing and extension of special steel products. Therefore, in order to obtain a healthy and sustainable development momentum, China special steel industry should improve the concentration of China special steel industry, eliminate backward production capacity and accelerate the pace of technological innovation of special steel industry.
During the Eleventh Five-Year Plan period, China's national economy will continue to maintain a rapid development trend, and the level of urbanization will increase to 47% in 20 10. The world economy will also maintain moderate growth, which will continue to form a strong pulling effect on the steel industry. As far as China's industrial structure is concerned, during the Eleventh Five-Year Plan period, China's major industries will be upgraded, and China will focus on improving the equipment manufacturing level, especially the localization level of major technical equipment, which provides a broad market prospect and rare development opportunities for China's special steel industry. Special steel refers to another component that works under special conditions and has special requirements for steel, such as physical, chemical and mechanical properties.
Special performance steel, also called special quality alloy steel, refers to steel with electromagnetic, optical, acoustic, thermal and electrochemical effects and functions. Commonly used are stainless steel, heat-resistant steel, electrical silicon steel, electronic pure iron and various precision alloys (soft magnetic alloy, magnetic alloy, elastic alloy, expansion alloy, thermal double alloy, resistance alloy, galvanic material, etc. ).
Stainless steel is named for its good corrosion resistance, and its main alloy components are chromium and nickel. Chromium has high chemical stability and can form a dense and tough purification film in oxidizing medium. In addition, when the chromium content exceeds 1 1.7%, the electrode potential of the alloy can be obviously improved, thus further oxidation of the alloy can be effectively prevented. Nickel is also a promoting element. Adding nickel to chromium steel can improve the corrosion resistance of the alloy in non-oxidizing medium. When the contents of chromium and nickel are constant, the lower the carbon content in steel, the better its corrosion resistance.
The corrosion resistance of stainless steel is also related to the uniformity of matrix structure. When uniform alloy solid solution is formed, the corrosion rate of steel in electrolyte can be effectively reduced.
Austenitic stainless steel belongs to Cr-Ni stainless steel and has a single austenite structure. It has good corrosion resistance, low temperature toughness, pressure working and welding manufacturability, and is non-magnetic. Widely used as low temperature steel and non-magnetic steel working in corrosive medium. Ferritic stainless steel mainly contains chromium, which changes phase during heating and cooling, and is a commonly used wear-resistant material in nitric acid and nitrogen fertilizer industries. Martensite stainless steel has high carbon content and good hardenability, and martensite structure can be obtained after quenching. This kind of steel has low carbon content and good toughness, and can be used to manufacture impact-resistant parts working in corrosive media. High carbon is used to make springs, bearings, surgical blades, etc. Stainless steel based on the mixed structure of austenite and ferrite is a kind of comparative stainless steel, which has the advantages of high strength, good toughness and intergranular corrosion resistance. Among them, DoCr 18Ni5Mo3Si2 steel is mainly used to manufacture heat exchangers and condensers in oil refining, chemical fertilizer, paper making, petroleum, chemical industry and other industries, and OCr26Ni5Mo2 is used to manufacture seawater corrosion equipment; Precipitation hardening stainless steel contains a large number of elements such as chromium, nickel, molybdenum, niobium, lead and copper which can precipitate precipitation hardening phases, so that it has high strength and toughness after quenching and aging treatment, and is mainly used to manufacture springs, washers and bellows.
Electrical steel, also known as silicon steel, is an iron-silicon binary alloy with carbon content less than 0.05%. It has the characteristics of small iron loss, small coercivity, high permeability and magnetic induction, and is one of the commonly used soft magnetic materials. The main factors affecting the properties of electrical steel are chemical composition and microstructure. Silicon has the greatest influence on the magnetic properties of electrical steel. When 3.0%Si is added to pure iron, the magnetic permeability is increased by 1.6-2 times, the hysteresis loss is reduced by 40%, the resistivity is increased by 4 times (eddy current loss can be reduced), the total iron loss is reduced by 1 times, but the hardness and strength are also obviously improved. Usually the silicon content does not exceed 4.5%, otherwise it is too difficult to process. The existence of harmful impurities (nitrogen, carbon, sulfur, oxygen, etc.). ) will cause lattice distortion of steel, increase stress and hinder the magnetization process, so the impurity content should be strictly controlled.
Silicon steel is mainly used in electric power industries such as motors, transformers, electrical appliances and electrical instruments. Most of them are rolled into 0.3, 0.35 and 0.5 sheets, including hot rolling and cold rolling. Cold-rolled silicon steel sheet has uniform shape, flat surface and no oxide film, which is beneficial to improve assembly quality and efficiency.
The brand of electrical silicon steel is represented by Chinese phonetic alphabet and two groups of numbers, in which "DR" means hot rolling, "DQ" means non-oriented cold rolling (the magnetic difference in all directions of steel is very small) and "DQ" means cold rolling orientation; The first set of figures represents the percentage of the maximum iron loss of silicon steel plate (unit watt/kg), and the second set represents one hundred times the rolling thickness of silicon steel plate.
Besides electrical silicon steel, electrical pure iron is also a widely used soft magnetic material.