Study On The Strength-toughness And Effect Factors Of Deformation Fe-base Alloys

In this paper, the deformation features and the change regularities of the synthetic mechanical properties with the annealing temperatures are investigated into the Fe-C alloys, for example 35#, 15MnB, 35CrMo etc. Recrystallization temperatures of the various deformation alloys are determined by means of the methods of metallograph and hardness. Microstructures of the various alloys under various treatment conditions are observed by means of transmission electronic microscope (TEM), and the evolution regularities of structures during annealing and mechanism of the recovery recrystallization are investigated.Results show that the crystallography relationship between the -Fe matrix and the eutectoid cementite lamellae in 35CrMo alloy are kept asfollows:The recrystalline temperatures of the deformation alloys, 35#, ISMnB and 35CrMo, are determined as 525 ,550 and 640 , respectively. The synthetic mechanical properties obtained by the deformation strengthening and recovery recrystallization treatment are almost the same as the ones obtained by quenching and high temperature tempering. Therefore, the process of quenching and high temperature tempering treatment may be replaced by the process of deformation strengthening and recrystallization treatment for manufacturing high strength bolt. During cool drawing deformation, when the directions of the eutectoid cementite lamellae and the one of the shearing stress applied are at an angle of 45 or 90 , the cementite lamellae may be contorted or sheared, respectively. For the alloys with the particle cementite, the dislocations produced during the deformation may detour though the secondary phase by Orowan mechanism, therefore, thematerial displays a better toughness. After annealed at different temperatures, the alloys display the various values of the maximum strength and increasing strength in the curves -T of different materials. The maximum strength of 15MnB alloy appear at 300 , of 35CrMo alloy appear at 400 . That results from the role of subgrain strengthening within the ferrite matrix, the subgrains may be formed from the clustering of the dislocation tangles. The size of subgrains is increased and the quantities of the grain boundary are decreased with the increase of annealing temperature, which results in the reduction of the yield strength and the improvement of the toughness. The cementite phase in alloys displays a hindering role for the recrystallization and grain growing up in alloys. The temperature of recrystallization is enhanced with the increase of C content. Compared with the particle cementite phase, the cementite lamellae phase possesses a stronger role for hindering the recrystallization and grain growth in alloys. Therefore, the alloys with structure of the cementite lamellae phase display a smaller rate and higher temperature of recrystallization. Under the test condition, two mechanism for forming subgrains are found as follows: firstly, the subgrains may be formed by the clustering of dislocation tangles into the structure like-Y typed. Secondly, the subgrains may be formed within the strip-ferrite grains in the high strain regions in which dislocation tangles are clustered into the cell walls that are at angle of 90?with the original boundary. The dislocation cells are changed into the sub-grain structure by diffusing and migrating of the grain boundary.