Research On Fatigue Properties Of Low-Alloy Duplex-Phase Wear-Resisting Steel

low-alloy duplex-phase wear-resisting steel were extensively studied as a new wear-resistant materials at home and abroad. It can acquire different contents of martensite (M)-bainite (B) to meet different wear situations of material strength and wear-resisting performance through adjust chemical composition, heat treatment process and casting factors. It also overcomes the shortcomings for concrete application of high manganese steel.The conclusions from preliminary tests were that the new development of low-alloy duplex-phase wear-resisting cast steel was significantly higher strength, hardness and wear resistance than normal high manganese steel (Mnl3), but the elongation far below high manganese steel. Tanks and armored vehicles’s crawler board, require high strength and hardness and good abrasion resistance, on the other hand the safe use of crawler board without fractured also be ensured. In the course of driving, the crawler slabs effected by alternating cyclical loading such as tension-compression, and bending stress repeatedly. The crawler board easily fatigue crack by this kind of circumstance which many load stress coactions. Therefore, the study of fatigue behavior and its influencing factors for low-alloy duplex-phase wear-resisting steel and compare that with high manganese steel were of great significance. According to the theory of experience, the higher strength were, the more likely to brittleness and cause fatigue crack, on the contrary, plastic good materials less tendency to produce fatigue fracture. This topic were on the basis of researching mechanical properties and wears abrasion resistance of low-alloy duplex-phase wear-resisting steel, in the further research on fatigue properties. In the test process, with traditional wear-resistant materials of high manganese steel as a contrast material, mainly research on the following:1. Use rotation bending fatigue test method for determining fatigue life (S-N) curve of duplex-phase steel and high manganese steel within which range from104to107cyclic times. Use scanning electron microscopy to study fatigue fracture mechanism of duplex-phase steel and high manganese steel under different stress cycle conditions.2. Through determination the fatigue life (S-N) curve of duplex-phase steel and ordinary high manganese steel’s gap samples within which range from104to107cyclic times, the effect of stress concentration of the gap on material fatigue properties was discussed.3.3-Point bending fatigue crack propagation test method was used for determining relation curve between fatigue crack growth rate and the stress intensity factor range. The reference formulas for Paris and fatigue crack propagation threshold of duplex-phase steel and chromium-molybdenum alloying of high manganese steel were discussed. Secondly, according to the sample fracture morphology, the macroscopic fracture mechanism and fatigue feature of duplex-phase steel and ordinary manganese steel were analyzed. On the other hand, the effect of the chromium-molybdenum alloying on fatigue properties of high manganese steel was studied.Comprehensive analysis of experimental results, some conclusions are drawn below:1. Casting duplex-phase steel’s limit fatigue strength was300MPa, genral high manganese steel’s fatigue strength was250MPa, alloying high manganese steel (add Gr、 Mo)’s fatigue strength was240MPa. Duplex-phase steel’s ultimate fatigue strength was higher than that of ordinary high manganese steel and chromium molybdenum alloying high manganese steel.There was no obvious fatigue striation with high and low stress for duplex-phase steel in fatigue crack growth areas. There were no obvious plastic changes in finally fracture zone and with plastic cleavage brittle fracture. There were many torn mark accompany with ductile nest in chromium molybdenum alloying high manganese steel which defined toughness fracture. There were many obviously fatigue striations in where fatigue crack propagation areas in high manganese steel and final fracture zone with prospective cleavage brittle fracture which in the same level of stress to the duplex-phase steel..2. Duplex-phase steel gaps-specimen’s ultimate fatigue strength was280MPa; genral high manganese steel gaps-specimen’s ultimate fatigue strength was180Mpa. Duplex-phase steel’s fatigue gap stress concentration factor was1.071and gap sensitivity was0.08. Genral high manganese steel’s fatigue gap stress concentration factor was139and gap sensitivity was0.486. Duplex-phase steel’s fatigue gap stress concentrating coefficients and gap sensitivity were lower than high manganese steel’s.3. The fatigue crack growth rate of high manganese steel was slower than duplex-phase steel. With the crack front stress intensity increases, high manganese steel’s crack propagation speed is faster. Duplex-phase steel and alloying high manganese steel(add Cr、Mo)’s Paris reference equation were and Duplex-phase steel’s fatigue crack propagation threshold△Kth=1.3kgfmm-3/2when stress ratio R is equal to0.1. High manganese steel’s fatigue crack propagation threshold△Kth=4kgfmm-3/2when stress ratio R is equal to0.1.