China's steel production and development of cold heading Analysis

2016/1/25 Hits:599

"The development of cold heading steel production has achieved initial results, but the quality should be further improved, understanding and knowledge of domestic and cold heading steel production technology, improve the quality of cold heading steel is necessary. Fastener and steel cartel market requirements will be able to produce high-quality performance of cold heading steel. "
According to reports, the "Eleventh Five-Year" period, China's automobile industry, machinery processing and manufacturing, construction and other rapid development of these industries on the fasteners, standard parts of the growing demand. Thus cold heading steel wire rod, wire rod demand is also growing. According to the data show that the cold heading steel market in 2006 reached 600 million tons of national demand, is expected to increase to 800-850 million tons in 2007, in which high-grade automotive fasteners cold heading steel will be more than 1.2 million tons.
Cold heading steel wire rod, wire rod of steel is generally low, high carbon and low alloy carbon steel. Cold heading steel with good performance due to cold forming, drawing in the mechanical processing industry instead of hot-rolled sheet by cutting machining, the advantages of this technology to save a lot of work in the same time, the metal consumption can be reduced by 10% -30%, in line with cleaner production , large-scale production enterprises based on resources conservation, and product dimensional accuracy, surface finish, high production efficiency, is focused on the promotion of advanced machining technology.
Domestic cold heading steel wire rod, wire rod development despite the late start, but has developed rapidly, especially in the 20th century, after the mid-80s, high-speed wire production line, wire rod rolling line after another operation, for the cold heading steel wire rod, wire rod provide the equipment on the production guarantee.
State-owned enterprises in the Maanshan Iron and Steel, Baotou Steel, Bao Steel, Anshan Steel, Xiangtan Steel, Wuhan Iron and Steel, Shougang, Taiyuan, Tangshan Iron and Steel, stone steel, Changcheng Special Steel Dengjun the successful development of cold heading steel wire rod, plate amended and made good economic and social benefits. In the 21st century, China has developed varieties of cold heading steel increased production in the growth, quality improvement, Hangzhou Iron and Steel, Xingtai Iron and Steel, Jiangsu Sha Steel, Jiangyin Xingcheng, heavy steel, Chengdu Iron & Steel, Anyang Iron and Steel, the Great Wall Special Steel, etc. more than 40 companies into the field of cold heading steel, obviously, the development of cold heading steel production has formed a certain volume and scale.
As cold heading steel metallurgy ask for a higher quality, so not only during the design of chemical composition of the steel in the strict control of the content of chemical elements, especially for cold heading is not conducive to the performance of the chemical elements Si, residual elements Cu, Ni , As and N content in the control of steel, and to be on the inclusions and segregation to become useful after the cold heading directly affect the factors that strict control of processing performance to ensure high purity and composition of steel with high uniformity.
Cold heading steel wire rod, wire rod is mainly used for manufacture of bolts, nuts, screws, rivets, screws and other fasteners and cold heading shape of the parts. Therefore, the national standard GB/T6478 its surface quality, internal quality, composition uniformity, cold working properties and dimensional accuracy requirements are high, we must have sufficient strength, but also has good toughness and ductility. Obviously, because of cold upsetting of cold heading steel with high cleanliness requirements, the control of steel in the Si, Al content, the use of controlled rolling and controlled cooling technology to avoid martensite, bainite and Wilcoxon tissue, the steel with fine grain and carbide ball of tissue, in order to improve the plasticity of steel and cold-forging performance. Throughout the overseas production of wire rod, such as the Kobe, Japan, Russia, Taiwan, China Steel, South Korea, Pohang, their composition and the production of wire rod made of 35 # carbon steel similar, but very fine and homogeneous microstructure, grain size is only 1 - 2μm, is about one-tenth of China-made products, has good strength and plasticity, shown in the drawing process of drawing a good performance, cold heading deformation of 80% -85% or more do not crack, while the domestic cold heading steel evident lack of quality, especially in high-grade steel such as SCM435, SCM440, SWRCH35K, SWRCH45K, ML35, ML45 steel, can only meet the stability of chemical composition, and organization for the big gap between low-ploidy, some specifications there are a lot of non- metallic inclusions, with folding, scratches and other surface defects, thickness of the mixed-level grain size is not conducive to cold forming of steel.
Such as motor vehicles on the use of standard parts, special fasteners, non-standard shaped pieces, with the car power, speed continuously improve their working conditions even worse, work stress was significantly increased.
Lightweight automotive components, bolt type parts that reduce the size, weight, requiring higher strength steel fasteners. The strength of steel cold heading level is more commonly used 400-1000MPa level has to increase to 1100-1300MPa level, and even increased to 1400MPa above requirements. In addition to strength, but on the cold heading steel made in other performance requirements such as resistance to delay destruction of properties, corrosion resistance and processing properties. Use of low carbon dual phase (ferrite + pearlite deformation) of steel and non-quenched and tempered steel bolts and other standard parts manufacture cold heading steel in recent years also focuses on the development of cold heading steel, one of the topics.