Explosive And Mechanism Of Explosion Hardening Of High Manganese Steel

High manganese steel is widely used in the railway frog and the related engineering mechinery because of the excellent work hardening performance and the high strength and toughness. In the initial stage of using the high manganese steel, the abrasion is larger and the severe crushing plastic deformation appears, so the service life of high manganese steel is decreased. In order to improve the service life of high manganese steel, the explosion hardening is proposed to improve the surface hardness of high manganese steel and ensure the high strength and toughness inside. At present, the high manganese steel frog explosion hardened has been widely used in some western countries. However, the high manganese steel frog explosion hardened has not been used in our country. At the same time, major differences on the mechanism of explosion hardening still exist. Therefore, it is of great social importance and economical to systematically study the mechanism of high manganese steel explosion hardening for using the high manganese steel frog explosion hardened as early as possible in our country.Based on homemade new explosive used for the explosion hardening, the relationship between the hardness increments after the explosion hardening of high manganese steel and the explosion hardening times, the influence of the detonation parameters of explosive on the effect of the explosion hardening of high manganese steel, the numerical simulation of the explosion hardening of high manganese steel, the mechanism of explosion hardening of high manganese steel, the variation of mechanical properties of high manganese steel after explosion hardening and the influence of explosion hardening on the service life of high manganese steel frog were studied systematically using experimental investigation, theoretical analysis and numerical method.Firstly, a new explosive formulation including RDX, rubber, desensitizing agent, plasticizer, antioxidant applied for the explosion hardening of high manganese steel was proposed according to the requirement of the explosion hardening of high manganese steel, which was initiated reliably using8#electric detonator. Its impact sensitivity and friction sensitivity were respectively28%and24%. Two different densities which were1.48g/cm3and1.38g/cm3were prepared on the basis of this formula and the detonation parameters were tested. The results show that:The detonation velocities are7200m/s and6470m/s respectively. The detonation pressures are19.18GPa and14.44GPa respectively. The specific volumes are0.51cm3/g and0.54cm3/g respectively. The particle velocities of detonation products are1800m/s and1617.5m/s.The quantitative relationships between the surface hardness increment and the detonation parameters, the thickness of explosive, the explosion hardening times were determined through the high manganese steel explosion hardening experiment under the premise that the surface hardness reached352HB and the compression amount was lesser than1.0mm. The results show that:The surface hardness increment of the high manganese steel increases as the thickness of explosive with the same density increases, and the surface hardness increment of the high manganese steel increases as the density of explosive with the same thickness increases under the first explosion hardening. The surface hardness increment of the high manganese steel always decreases with the explosion hardening times increases. The surface hardness increment of high manganese steel has exponent relation to the explosion hardening times. The surface hardness and the compression amount of high manganese steels for twice explosion with density of1.48g/cm3and triple explosion with density of1.38g/cm3meet for the requirements respectively.The computing models of initial parameters and impulse of the shock wave upon the high manganese steel were given considering the influence of detonation parameters on the effect of explosion hardening. The results of theoretical calculation show that:The normal impulse upon the high manganese steel increases as the density of explosive increases under the same thickness of explosive. As the thickness of explosive increases, the normal impulse upon the high manganese steel increases under the same density of explosive. The normal impulse of two different densities of explosive upon the high manganese steel keeps linear relation with the thickness of explosive, that is, the ratio of the corresponding normal impulse is a constant in the same thickness of explosive. The surface hardness increment of high manganese steel keeps linear relation with the normal impulse upon the high manganese steel. The surface hardness increment increases with the normal impulse increases.The standard model of high manganese steel explosion hardening was built by the AUTODYN-3D program and the appropriate material models and parameters of the explosive and the high manganese steel were selected. The high manganese steel explosion hardening was studied through numerical simulation using SPH solver. The results show that:The high manganese steel explosion hardening is an interaction between the sliding detonation and the high manganese steel, which transmits compression wave in high manganese steel and reflects rarefaction wave in the detonation products. The larger the density of explosive, the larger the impulse upon the high manganese steel for the same thickness of explosive. For the same density of explosive, as the thickness increases, the impulse upon the high manganese steel increases. The error between the theoretical calculating value and the numerical simulation value is less than5%, which shows the correctness of the theoretical and numerical model.The mechanism of explosion hardening and the variations of mechanical properties relating to the high manganese steel hardened were proposed through comparatively analyzing the microstructure, internal hardness, tensile strength, elongation rate and impact toughness of high manganese steel hardened free and under two conditions of explosion hardening. The results show that:Compared to the high manganese steel hardened free, a large number of slip lines are produced on the surface of the high manganese steel hardened and the plastic deformation happens. Through absorbing energy, a large amount of stacking faults and dislocations are generated in the material to make the high manganese steel hardened under the impact of the detonation wave. The high manganese steel explosion hardening can not only improve the surface hardness, but also improve the hardness in some depth. The hardness of the sample for triple explosion with density of1.38g/cm3is larger than which for twice explosion with density of1.48g/cm3at the same hardening depth. The tensile strength of high manganese steel hardened is increased. The tensile strength for triple explosion with density of1.38g/cm3is higher from the surface to15mm below the surface hardened but is lower from15mm down. The elongation rate and impact toughness of high manganese steel hardened are decreased. The elongation rate and impact toughness of the sample for triple explosion with density of1.38g/cm3is larger than which for twice explosion with density of1.48g/cm3at the same hardening depth. For the hardness, tensile strength, elongation rate and impact toughness hardened considered, the effect for the smaller single impulse is better.Based on the explosion hardening of high manganese steel specimen, the conditions of the explosion hardening of the whole frog were determined through the explosion hardening experiment of high manganese steel frog specimen. The explosion hardening of the whole frog was experimented. The results show:The hardness after explosion hardening on the steel plate, in air and on the sandy soil are raised by77%,70.1%and77.7%respectively using the explosive whose thickness is3mm and density is1.48g/cm3, while the hardness after explosion hardening are raised by85.1%,76.6%and82.6%respectively using the explosive whose thickness is3mm and density is1.38g/cm3. The deformations of the high manganese steel frog specimen hardened in air and on the sandy soil are smaller relative to that of the high manganese steel frog specimen hardened on the steel plate. The explosion hardening high manganese steel frog specimen on the sandy soil can ensure the hardness would be increased to350HB and the serious deformation would not take place. The service life of the whole frog hardened for twice explosion with density of1,48g/cm3is raised by40%, while which for triple explosion with density of1.38g/cm3is raised by53.3%.The research work can provide some theoretical guidance and engineering reference for the production of the high manganese steel explosion hardening.