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Rod mold material 8402 steel heat treatment process improvement 0 replies,461 views

8402 Steel is an excellent hardenability, hardened and good room and high temperature properties of die steel, widely used for hot and cold requirements of toughness and high fatigue resistance, high temperature hot die, its life away higher than the 5CrNiMo materials. However, after a period of use that tool life is not ideal, the conventional heat treatment, often appear early failure, the metallographic examination found that the state of their organization is not good, the uneven distribution of carbides, banded structure is not completely eliminated, it is necessary to The heat treatment process to improve it. The same batch of the material into the plant is divided into 2 groups, respectively, using two kinds of process methods for processing, and with the furnace with the tensile and impact test specimens. 2 process in Figure 1. The quenching furnace heating in the car, quenching conducted in the large ****. When cooled to below 200 ? tempering furnace installed directly. Of raw materials via the conventional annealed state of the organization for the annealed ferrite, carbide alloy. The conventional low temperature annealing, secondary cementite and special carbides can not be fully integrated into austenite, and therefore can not effectively change the distribution and size of carbide, carbide substrate so bad of globalization, and the grain boundary to retain the high density carbide segregation status, annealing organization is not ideal. 1040 ?and then quenched by the original process is still found after the organization of the existence of significant inequality, the two tempered martensite is tempered a small amount of undissolved carbide + retained austenite, there are still uneven banded structure is not completely eliminated. This uneven and annealing organizations related to heating at 1040 ?under the uneven concentration of high-temperature austenite, only carbon-rich region of Cr, Mo composite carbide part of the occurrence of dissolved carbon and alloy element diffusion is not sufficient, and thus be plate martensite and a small amount of lath martensite, twin-based sub-structure, large size carbide particles and uneven distribution of such organizations on the **** formation and expansion of benefit will result in material strength, Toughness is not ideal. The improved technology will increase the temperature to 1150 ?heat treatment temperature quenching, and the appropriate holding time, can make all the basic carbide solid solution, but also to the rapid spread of carbides, although this has been the austenite grain growth, but growth is not very obvious. This scheme eliminates the existing organization of the carbon-rich region, the organization's degree of uniformity than Annealing greatly improved. High-temperature quenching, so that the original organization dissolved in the matrix a large number of alloy carbides, thereby improving the degree of the alloy matrix, which is to improve the die strength, thermal stability and thermal fatigue beneficial. Improved Process through after quenching at 1150 ? the carbide dissolution speed, the matrix elements of carbon and alloy component concentration difference and the uneven size of the micro-area are relatively small, and uniformly dispersed carbides hinder Albright grains continue to grow, not only the carbide after quenching and thus did not significantly increase the size and dispersed, homogeneous austenite also helped increase the number of lath martensite and lath martensite and no significant increase in large. Tempered by two, in particular, is the second nitridation process, the equivalent of a long annealing, the stress was completely eliminated, while globalization has played the role of carbon diffusion and carbide carbides fully spheroidized, and mitigate the the rate of **** formation and expansion, is conducive to the improvement of toughness, and because of its dislocation from pinning effect and improve the plastic deformation resistance, and strengthen the matrix, increasing the dispersion strengthening effect of tempered martensite, the strength increased. Meanwhile, the surface hardness of nitrided improve and increase the surface resistance, thus improving the mold life. Looking at the results from the actual use of improved technology after testing the 10 sets of molds, die life has been greatly improved. 8402 steel treated by the improved technology Compared to the original process, the remaining more uniform carbide, carbide and basic elimination of enrichment conditions. Although the organization has increased the grain, but the mechanical properties, its plasticity, strength, impact toughness and hardness has improved significantly. Substantially increased die life, lower production costs, increased efficiency. (A cloud)
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