| As the most widely used steel in anti-wear applications, austenitic high manganese steel demonstrated a very strong work hardening ability on the surfaces when they are employeed in the conditions of high impact abrasive wear and chipping wear, which leads to significant improvements in wear resistance of the components. This paper investigated the heating characteristics of the cast high manganese steel(Mn13) during heating process. The microstructure, mechanical properties, abrasion and wear behaviors of Mn13 and Mn18 treated ar various aging temperature have also been studied. Afterward, the cyclic heat treatment processes was desined with aims to refine the austenite grain.The heating transformation characteristics of the cast high manganese steel indicated that the microstructure of this steel was composed of austenite, carbide and pearlite. The morphology of carbides was bulk and dispersed in grain and grain boundary. Most of the pearlite was located in the grain boundary distributing in the fringe pattern. With the increase of heating temperature, the spacing of pearlite decreased, and the carbide particles became smaller. When the cast Mn13 steel was heated to 720°C, amount of austenite in the matrix were decomposed into pearlite. After an aging treatment in 720°C for 2h, the hardness of Mn13 steel reached the mamium of 36.0 HRC. On the other hand, when the heat treatment temperature increased to 1100°C, the impact toughness could reach the maximum of 112 J.When the water toughening treated Mn13 and Mn18 steels were further aged in 450°C for 6h, block particles appeared on the austenitic matrix. However, when the aging temperature increased to 500°C fine needle like carbides were precipitated from the austenite matrix. After the aging treated in 550°C, the precipitates of the needle like carbides became coarse. The carbide precipitates gradually increased when the aging temperature rose to 650°C. With the increase of aging temperature, the impact toughness decreased rapidly at first and then increased slowly while the hardness increased first and then decreased. The maximum impact toughness of Mn13 and Mn18 steels appeared at the aging temperature of 450°C, coresponding to 108.9J and 133.7J, respecively. The maximum hardnesses of Mn13 and Mn16 were 47.1 HRC and 34.1 HRC respectively, with the aging treatment temperature of 550°C. The wear mechanisms of Mn13 and Mn18 steels were both micro cutting and fatigue spalling under different impact loading conditions. When the impact loading was 1.0J, the wear mechanism was mainly micro cutting while the fatigue saplling was proominant when the impact loading was raised to 4.5J. With increasing the aging treatment temperature, the wear resistance of both the two kinds of steels became worse.In the first cycle of heat treatment, the particle size of carbides in Mn13 steel decreased at first and increased later with the prolongation of the holding time. The hardness decreased first and then increased while the impact toughness decreased with increasing the solution time.With respect to Mn18, the particles size decreased, the hardness decreased and then increased, and the impact toughness increased with the increase of solution time. After third time of cyclic heat treatment, the grain size of both austenite and carbides in Mn13 and Mn18 steels were obviously refined. Their hardness increased by about 5 HRC when compared to those in the firest cycle. In contrast to the results in the first cycle, the impact toughness of Mn13 and Mn18 steels increased by about 26.8J and about 71 J, respectively. The grain size of austenite in Mn13 steel was further refined after five cycles of heat treatment. It was found that the particle size of carbides decreased gradually after five cycles of heat treatment. The hardness of Mn13 steel was 25.5 HRC and the impact toughness was 149.7J. The hardness of Mn18 steel was 23.3 HRC and the impact toughness was 82.5J after the the five cycles of heat treatment. |
PDF Full Text Request