Study On Microstructure And Properties Of Heat Affected Zone Of T4003Ferritic Stainless Steel

With the development of economy and technology, the application ofeconomical material is becoming more and more widely. Ferritic stainless steel(FSS), containing little or no Nickle, has the advantages of resource save andhighly cost-effective considering the situation that Nickle resource is very scarcein our country. With the continuously improvement of the componentpurification and smelting technology, especially the development of12Crferritic stainless steel, its welding structures not only can be applied to a varietyof conditions, but also greatly reduce the production cost conbiningpracticability and economy. In the process of welding, the heat affected zone(HAZ) exists serious problem of grain growth, which is decided bycharacteristics of alloy composition and phase change. Therefore, the HAZproperty is the key factor of the safe use of welding structures.In this work, microstructural characteristics and properties of the HAZ ofT4003FSS welded joint were investigated, and microstructure transformation,grain growth and precipitating phases of the HAZ for MIG were investigatedcombining experimental measurement with finite element simulation of weldingtemperature field. On this basis, three kinds of different welding heatsources-CMT, EBW, PAW were applied to analyze the microstructuraldistribution of the HAZ, respectively. Mechanical properties andelectrochemical corrosion of the four kinds of welding methods were analyzedto provide a theoretical basis for its practical application.Microstructural characteristics and development within the HAZ of T4003FSS welded joint were investigated combining experimental measurement with finite element simulation of welding temperature field. The results indicate thatthe HAZ was characterized with heterogeneous microstructure due to theextensive peak temperature range which could be divided into three sub-zonesnamed as HAZ1, HAZ2and HAZ3. The HAZ1(the region next to weld zoneboundary) experienced peak temperatures of1300~1500°C during weldingprocess. This region presented almost fully ferrite microstructure withirregular grain, which was attributed to the high element diffusion rate and theabsence of elevated-temperature austenite. The HAZ2(center region of HAZ)suffered the peak temperatures of1150~1300°C. It presented martensite+ferrite dual microstructure with limited grain growth due to the formation of γphase at grain boundaries. The HAZ3(the region closed to the base meta l) wasundergone the peak temperatures of830~1150°C and was characterized withboth martensite and ferrite structure. Grain size in the HAZ1(D=50.69μm) iscalculated using the equation of grain growth with the computed thermal cycle.Meanwhile, the effect of particles [TiN,(Nb, Ti)C] on grain growth mechanismwas analyzed.Micostructure distributions of the HAZ for different welding methods CMT,EBW, PAW were analyzed. The width of HAZ and coarse grain zone,microstructure evolution of different temperatures were analyzed, respectively.The mechanical test showed that the hardness of the HAZ is relativelyheterogeneous. With the increasing of welding heat input, the width of the HAZincreased significantly. The change trends of these different hardness curveswere similar. The impact properties of the HAZ were greatly influenced bywelding heat sources. The specific performance was reflected in the differencesof impact energy and ductile-brittle transition temperature. With the decreasingof the test temperature, the impact energy of the HAZ showed a decline trend. Inthe fatigue test, the fatigue limit and fatigue life of PAW specimen weredecreased comparing with base metal specimen, and the decreases in the fatiguelimit and fatigue life were27%,31.81%, respectively.Polarization curves and metallographs were analyzed by electrochemicalcorrosion test in3.5wt%NaCl solution. The results showed that corrosion resistant ability from strong to weak, in order: MIG> CMT> PAW> EBW.The weldability of T4003ferritic stainless steel can be obtained by a seriesof tests, and the steel can be applied to a variety of working environment.Comparing welding processes with each other, the results show that themechanical properties and corrosion resistance of the HAZ for MIG arerelatively superior to meet the requirement.