Steel Forging Damage Mn18cr18n Theoretical And Experimental Research

Cracking is understood here as the crack formation inside or on the surface of the plastic-deformation body. It is the focus of analysis and optimization to solve the problem in metal forming process and the essential factors of affect product quality. It is an important long-term academic research topics that reveal the causes of crack formation and development processes of crack in metal forming process and find ways to prevent crack formation, thus guide the design and optimization in forming process. As China's economic development, we are increasing demand for energy. However, as a crucial component of power plant, a large generator retaining ring for more than 300MW power plant is still unable to stabilize the production in our country. Mn18Cr18N steel is the major material used in large generator retaining ring of more than 300MW. This steel is easy to crack in forming process. It became a key issue that restrict the production of large generator retaining ring.In this paper, based on the key impact factors of crack initiation and crack growth, research on the forming of 300MW retaining ring of Mn18CR18N steel. The role of law of deformation temperature, stress state, strain rate and microstructure on the hot ductility, crack formation and crack growth of Mn18Cr18N of high-nitrogen austenitic stainless steels was studied by thermal simulated test of tension, quantitative metallography testing technology and numerical simulation. The results show that the hot ductility of Mn18Cr18N of high-nitrogen austenitic stainless steels is increased with the increase of test temperature when the deformation temperature is between 800℃and 1100℃.The steel exhibits a peak plasticity at 1200℃, and then the hot ductility is reduced with the increase of test temperature . The effects of strain rate on the cracking tendency of Mn18Cr18N steel is by through the role of recrystallization . The hot ductility of Mn18Cr18N steel with fine grained is better than with coarse grained at temperature below 1100℃. Above 1100℃, however , the hot ductility with moderate grained is the best . The conditions that each variable should be conform were given in forming of retaining ring. Strain rate should take a large value at high temperatures. on the contrary, low strain rate should be obtained at low temperatures.A comprehensive overview of various ductile fracture criteria are widely used in the current and their view on the crack initiation and crack propagation process. Ductile fracture testing and numerical simulation of Mn18Cr18N steel has been completed. The strain when necking taken place in uniaxial test was seen as cavity initiation strain, and the fracture strain was seen as the strain when cavity coalescence taken place in uniaxial test.The threshold of damage factor has been calculated corresponding to the ductile fracture criterion and its variation with temperature has been given. Applicability and accuracy of various ductile fracture criteria were tested in order to find the most accurate ductile fracture criteria. The results shows that C+L gave moderately good (quantitative) correlation between the forging and uniaxial tension behaviors. The ductile fracture criteria was implemented into the finite element code Deform in order to evaluation and forecast the key forming process of retaining ring such as punching and mandral drawing. The result show that, the forecast results conform with the actual production. Based on the simulated results of punching-exmmion process of retaining ring, the most optimal forming process has been given.