Study On The Thermal Fatigue Properties Of H13Steel Welded Joints

It is easy to produce cracks when hot work die steel works in the status of alternatecooling and heating cycle, which even leads to invalidation of the mould. Hot work diesteel has high cost and complicated production technology, once being disused becauseof partial failure will results in a huge waste, therefore, there will be a wide applicationprospect to utilize welding technique to repair for hot work die steel. Work of thermalcycle and thermal stress when mould repaired makes microstructure and properties ofrepairing region disproportionation, which results in thermal fatigue property decrease,thus, improving thermal fatigue property of repaired joints is of significance forrepairing hot work die steel.The research object in this text is H13steel and gas tungsten arc welding isadopted to H13steel; H13steel welded joints are treated by quenched and temperedtreatment and electrical pulsed treatment respectively, the characteristics ofmicrostructure and morphology which H13steel welded joints are treated are analyzed.Thermal fatigue tests are conducted to H13steel,H13TIG welded joints,H13weldedjoints after heating treatment and H13welded joints after electrical pulsing treatment,the rule which the initiation and propagation of thermal fatigue crack on H13steelwelded joints influenced by heating treatment and electrical pulsing treatment isacquired, the mechanism which heating treatment and electrical pulsing treatment makethermal fatigue property of H13steel welded joints enhance is acquired, measures ofimproving their thermal fatigue property are proposed.Study results indicate: the microscopic structure of as welded H13steel joints aremartensite,carbide and a little tempered sorbite, the microscopic structure of quenchedand tempered H13welded joints is mainly tempered martensite, the microscopicstructure of electrical pulsed treatment H13welded joints are tempered martensite andfine spheroidized carbide.The thermal fatigue property of H13steel welded joints with TIG repaired is belowthe base material, at the same time, the crack growth rate of welded joints is faster thanthe base mental; the number and depth of cracks in specimens with quenched andtempered treatment are less than as welded ones; the specimens with electrical pulsingtreatment have no obvious crack growth until cycle index for thermal fatigue tests reach to2000. Electrical pulsing treatment and quenched and tempered treatment can improvethe thermal fatigue property of H13welding bead obviously, but the result underquenched and tempered treatment is not so well as under electrical pulsing treatment. Inthe crack growth stage, the resistance value of H13steel welded joints is totality on therise with the number of times for thermal fatigue tests increasing, which indicates thenumber of defects in the specimens is increasing with the number of times for thermalfatigue tests increasing.Quenched and tempered treatment improve the thermal fatigueproperty by grain refinement, electrical pulsed treatment improve the thermal fatigueproperty by refining grains and reducing defects.