Influences Of Cold Rolling And Fusion Welding On The Microstructure And High-temperature Oxidation Resistance Of Fe-Al Alloyed Layer

Fe-Al based alloys are regarded as promising materials for industrial applications because of their excellent corrosion and oxidation resistance. However, it is difficult to fabricate components using massive Fe-Al based materials due to its inherent brittleness at room temperature. Recently, surface coating technologies have attracted researchers to produce Fe-Al intermetallic anti-corrosion coatings on the surface of components, which provides a feasible approach to the applications of Fe-Al intermetallic compound.In this paper, Fe-Al alloyed layers were prepared on the Q235 steel by using hot dip aluminized technology and double glow plasma surface alloying (DPSA) technology, respectively. The microstructure, elements distribution, phase identification and micro-hardness were analyzed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and nano-indentation. Then the Fe-Al alloyed layers were processed under different deformation rates of cold rolling and conducted using gas arc tungsten welding process, respectively. The influences of cold rolling and fusion welding on the microstructure and high-temperature oxidation resistance of Fe-Al alloyed layer were investigated.All the results indicate that a dense Fe-Al alloyed layer had been synthesized on the surface of Q235 steel by hot dip aluminized technique, the average thickness of the alloyed layer is about 170μm and the main phase compositions of the alloyed layer is FeAl phase; The thickness of the alloyed layer prepared by DPSA is about 70μm and the alloyed layer is composed of FeAl and Fe3Al compound phases. The hot dip aluminized layers were processed different cold rolling reductions (20.5%, 34.1% and 40.9%), while the DPSA aluminized layers were conducted 15.9%, 31.8%, 45.5% cold rolling reductions, respectively. The interface between the Fe-Al alloyed layers and the substrate using hot dip aluminized technology, as well as the DPSA technology, characterizes by metallurgical adhere and no fracture and delamination has been found after cold rolling process. The long range order has been destroyed during the cold rolling process and the microstrain slowly increases as the cold rolling reduction rises for both alloyed layers. The Fe-Al alloyed layers still possess excellent high-temperature oxidation resistance at 800°C temperature after cold rolling process. For the hot dip aluminized layer, the weight gain increases by 2.3%, 6.8% and 8.4% subjected 20.5%, 34.1% and 40.9% cold rolling reductions, respectively. While the weight gain increases by 3.6%, 9.0% and 14.2% subjected 15.9%, 31.8% and 45.5% cold rolling reductions for the DPSA layer. Welding Q235 aluminized steel was conducted using gas arc tungsten welding process. The results show that the elements of Cr, Ni and Al vary gradiently near fusion line and the main phase compositions of the fusion area are Al2Cr, AlCrFe2 and (Fe,Cr) solid solution. The oxidation curve at the temperature of 800°C follows parabolic law similarly within oxidation time. The oxidation films of the fusion area are consist of Al2O3, Cr2O3 and Fe2O3. The Fe-Al alloyed layers using hot dip aluminized technology and DPSA technology still possess excellent high-temperature oxidation resistance after welding process and the weight gain increase by 1.3% and 8.5%, respectively, compared with the unwelded sample.