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The production of high-strength (8.8) fasteners steel, due to the requirements of the ultimate strength quenched and tempered carbon steel or low alloy steel. Metallurgical manufacturers of fasteners steel because of its microstructure is far from ideal, generally are difficult to direct the cold heading deformation. Therefore, the spheroidizing annealing necessary is an indispensable part of the fastener prior to production, however, not only increase the cost of this processing step. But also pollute the environment. Especially for a large number of small and medium enterprises do not have the protective atmosphere heat treatment furnaces, often cause surface oxidation and decarbonization, seriously affecting the surface quality of the standard parts. Therefore, the standard parts manufacturing industry eager metallurgical plant can supply craft materials or direct drawing free annealing of cold forging heading steel wire. By controlled rolling and cooling process combined with the TRIP effect, can significantly improve the strength and ductility of the steel. Controlled rolling and cooling can improve the overall performance of the hot-rolled steel, such as strength and toughness, and ultimately achieving free heat treatment, can save the alloy, simplify processes, reduce energy consumption, improve labor productivity, and increase the economic efficiency of enterprises. In this paper, set Heading steel chemical composition of the steel on Gleeble-1500 thermal simulation machine simulation experiment, through the dynamic CCT curve determination, as well as the microstructure observed under an optical microscope to determine rolling in cooling speed of phase change products, select reasonable control rolling and cooling process provides a theoretical basis for the subsequent hot rolling experiment. Northeastern University, Key Laboratory the the Φ450 hot rolled experiment unit carried out the experiment of controlled rolling and cooling process hot-rolled, rolling sample tensile test results by analyzing mechanical properties, microstructure, scanning electron microscopy, tissue and transmission electron microscopy organization. study different TMCP parameters (finishing temperature, the end of the cold temperatures, cooling method) heading steel microstructure and properties. Experiments show that low temperature after rolling control cold heading steel mechanical properties than conventional controlled cooling after rolling heading steel, low temperature secondary cooling after rolling and controlled cooling, ferrite, bainite and residual austenite three-phase tissue. Controlled rolling and controlled cooling technology, the steel tensile strength up to 800MPa, an extension of up to 16% more than the national standards can meet the performance requirements of 8.8 strength bolts, riveting Lo to achieve a low-carbon instead of carbon the actual production of steel to provide a theoretical basis.
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