| Recently, well comprehensive mechanical properties, excellent casting properties and weldability, espcially the abrasion resistance, super martensite stainless steels of 00Cr13Ni5 Mo and 00Cr13Ni4 Mo were introduced to take the traditional low carbon martensitic steel’s place which can be used to fabricate new turbine runner blades.The paper experimentally studied the 00Cr13Ni4 Mo and 00Cr13Ni5 Mo steels under eight different heat treatments respectively. It is theoretically designed the threatments which are totallyfixed normalized at 1050℃,then five groups of the specimen were chosen to take first tempered at 500℃, 550℃, 600℃, 650℃, 700℃, and the other three were applied to take the first tempered at 500℃, 600℃, 650℃ and then treated second tempered at 480℃, 580℃, 630℃, individually. Meanwhile, the microstructure, mechanical properties and abrasion properties of all the treated specimen were deeply investigated.The study had analyzed the microstructure of two super martensitic stainless steels at diffierent heat treatments by optical microscopy and SEM(scanning electron microscopy). Moreover, the TEM(transmission electron microscopy) and X-ray diffraction were introduced to investigate the reverse austenite among the steels. The results indicatedthat: the 00Cr13Ni5 Mo and 00Cr13Ni4 Mo steels normalized at 1050℃ and temperd at 500℃ can get lath martensite, and reverse austenite precipitated in lath martensite and austenite grain boundaries when tempered at 550℃~650℃.The tensile test, hardness test and impact test were also applied to study properties of the 00Cr13Ni5 Mo and 00Cr13Ni4 Mo steels under different heat treatments. The results displayed that: Tensile strength and hardness of the matierials decreased when first tempered at range of 500℃~600℃. Tensile strength and hardness of the steels increased when tempered above 600℃. The tensile strength and hardness of the steelssencond temperedbelow 600℃ got the similar tender with the one treated at the first tempered. Tensile strength and hardness of steels continuously decreased whensecond tempered at the range of 600℃~650℃. The values of KV2(room temperature) and KV2(0℃) of two super martensitic stainless steels were large when first tempered at 550℃, 600℃ and 650℃, while that of the specimen first tempered at 500℃ and 700℃ were small. The second tempering method had less effect on the KV2(room temperature) and KV2(0℃) of two steels.Erosion wear tests of two steels showed that the cumulative weight loss of two steels increased quickly at the first range of time and then the curves seems to increased smoothly accompany with the time while the cumulative rate of weight loss continuously decreased. The minimum cumulative weight loss of twosteels were the one tempered at 550℃ which got the best abrasion resistance. It was accepted that the abrasion resistance of two steels were mainly related with its hardness, while the impact absorption energy also affected their abrasion resistance. The surface morphology of them after erosion wear test were plowing grooves as the main feature, and the surface topography changed slightly in the process of erosion wear, and plowing grooves depth becomed smaller after long time. The composition and hardness of two super martensitic stainless steels are almost the same, so the abrasion resistance difference between two matierials is very small.Investigation on the results of microstructure, mechanical properties tests and Erosion wear tests of the 00Cr13Ni4 Mo and 00Cr13Ni5 Mo steels indicated that two steels had high hardness and well toughness when tempered at 550℃, so it can achieve the best abrasion resistance if were normalized at 1050℃ and first tempered at 550℃. The hardness toughness had decreased at second tempering to it at first tempering, and abrasion resistance also was not the best at second tempering. Comprehensively considering the properties and economy, the normalized at 1050℃ and first tempered at 550℃ of two steels is the best heat treatment process. |
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