Control method of the hottest grain refinement

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Control method of grain refinement

by using the process method to control the space, it can meet the pressure test of all materials, and the grain of metal materials can be refined, uniform and impact test; Free fall test, etc., so as to improve the strength, toughness and plasticity of materials and better meet the requirements of engineering projects for materials. By adopting process control, the grain of metal materials can be refined and uniform, so as to improve the strength, toughness and plasticity of materials and better meet the requirements of engineering projects for materials. For grain refinement, the current control methods are:

1. Oxide metallurgy technology

rapid release of NH3

the basic principle is to use the early formation and uniform distribution of oxides in steel as the heterogeneous nucleation core of sulfide, nitride, carbide and other precipitates in steel, and complete the control of grain growth by controlling the location and distribution of these precipitates, Then the composite inclusions in steel are used to induce intragranular acicular ferrite nucleation to refine the structure of the material

the key of this method is how to obtain fine inclusions in steel. First of all, the purity of molten steel must be improved, and all kinds of large particles of non-metallic inclusions generated in molten steel must be removed; Secondly, in order to obtain fine second phase particles and ensure that the second phase particles can precipitate in the solid state, the concentration product of various inclusion generating elements should be controlled below the equilibrium concentration product of the solid phase line. The methods of obtaining second phase ions include internal precipitation method and external addition method. The former uses the precipitates in steel as the heterogeneous nucleation core, which can automatically obtain the original of experimental parameters such as Reh, rel, Rp0.2, FM, Rt0.5, rt0.6, rt0.65, rt0.7, RM, e to refine the structure, while the latter refines the structure by adding second phase particles outside the material

2. TMCP process

tmcp process includes two stages: controlled rolling process and controlled cooling process after rolling. It mainly controls the microstructure and phase transformation process of high-temperature austenite by controlling the rolling temperature and cooling rate after rolling, as well as the start temperature and end temperature of cooling. The purpose is to refine the austenite grain structure, increase the dislocation density of austenite, and improve the nucleation rate of ferrite to refine the microstructure after phase transformation, So as to refine the structure and improve the mechanical properties

3. HIP process and relaxation technology

1) hip process is developed on the basis of conventional TMCP process, which mainly increases the content of Nb in steel. In addition to preventing austenite recrystallization and refining ferrite grains, Nb also significantly improves the recrystallization and refining ferrite grains of steel. In addition, it also significantly improves the recrystallization termination temperature of steel and reduces the phase transformation temperature. Therefore, through hip technology, the final rolling temperature of pipeline steel can be significantly increased, and then coupled with a faster cooling rate, so as to obtain fine acicular ferrite structure, So as to refine the grain

2) in order to meet the development trend of high-grade materials with high strength and toughness and high plasticity, relaxation technology has been developed. The key of this technology is to air cool the steel plate after final rolling for a period of time, so that the temperature of the steel plate before entering the water is reduced to below Ar3 ℃, and a certain amount of proeutectoid ferrite is generated. Finally, through water cooling at a certain cooling rate, the dual phase structure of proeutectoid ferrite and bainite/ma is obtained, which greatly improves the strength, plasticity and toughness of pipeline steel

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