Optimization Of Low Alloy High Strength Steel E7015

Through changing the addition of different content of ferrotitanium, zirconium ferrosilicon, rareearth ferrosilicon and composite alloy in electrode E7015used for10CrNi3MoV high strength structuralsteel, we achieved four different kind of base electrodes with almost the same depositedmetal. The oxygen content of the deposited metal are respectively420ppm、400ppm、360ppm and300ppm. And the four deposited metal are respectively added in Ti-B、Ti-Zrand Ti-Zr-Ce.Via the mechanical property test and the microstructure analysis, weinvestigated the influence of oxygen and microelement on microstructure and mechanicalproperty of the deposited metal.Then the cause of difference in properties andmicrostructures are analyzed from the following several parts: the influence of inclusionson the formation of acicular ferrite, the fracture surface of tensile and impact specimen andaverage grain size, the second phase, et al.The results showed that the microstructure content of the deposited metal change withthe oxygen content and microelement content. oxygen and microelement have little effecton strength of the deposited metal but performed great impact on toughness of thedeposited metal.（I）By adding a certain amount of microelement,the size of the inclusion can berefined, and the number of inclusion which contributes to form acicular ferrite will beincreased. Most of the inclusion are spherical oxide.There is no sulfide nor nitride.（II）Inclusions are complex-oxide which composed by several elements,differencesexit in inclusion composition and structure because of the different alloy-elements. The0#in which Ti added,owing to the formation of Al、Mn complex-oxide,but Al2O3cannotefficiently form acicular ferrite, acicular ferrite was not the main phase in themicrostructure of the weld metal. The57#in which Ti-Zr-Ce added, contained a largeamount of dispersed fine Al、Si、Mn、Ti、Ce complex-oxide which can efficiently formacicular ferrite in the weld metal.（III）The number of inclusion and the size of inclusion have a tendency of decreasingaccording to the decrease of oxygen content. The decrease of dimple nucleation particlemake the material should go across more distance to get connection to other dimples, so itcosts more energy when materials fracture. The impact toughness of the deposited metal improves with the decrease of oxygen content.（IV）The second phase in deposited metal is another important factor on impacttoughness.When there is a small amount of cementite in deposited metal, dislocations blockin front of cementite while the material is deformed, dislocation loops will bypasscementite. Residual austenite in deposited metal deviates the patulous cracks and benefitsto release the crack tip stress.Above all, through changing the oxygen content and microelement content of highstrength steel deposited metal,the size of the inclusion can be refined, and the number ofinclusion which contributes to form acicular ferrite will be increased. It showed that bycontrolling of the alloy composition, cooling rate, oxygen content and microelements, wecan obtain the microstructure which was mainly acicular ferrite and get good jointtoughness.