Research On Wire And Arc Additive Manufacturing Of Bainite Steel Crossing

Wire and Arc Additive Manufacturing(WAAM)is a technique with high efficiency, low cost, rapid response to market for mass popularity. Whereas, the lack of deposition accuracy and microstructure performances are still restricting the going on of its rapid development. This paper focus on the deposition characteristics, heat treatment, and micro-rolling of Bainite steel crossing, with the aim of enhancing the engineering application process of WAAM.A multi-objective optimization process with the controlling of acceleration and interpass temperature have been used for improving the surface appearance of deposition. The results show that the optimized sample surface appearance is smooth which has little spatters and no visible defects. Moreover, the machining allowance of optimized sample is less than 1.5mm which is satisfied.In order to improve the strength and toughness of deposition, the heat treatment has been further studied. The results show: with the increase of isothermal quenching temperature, bainite morphology changes from lower bainite to granular bainite then to carbide-free bainite, the matensite contents, tensile strength, elongation and impact toughness decrease generally; however, the tensile strength appears change suddenly because of the dispersion strengthening M/A islands when isothermal quenching temperature at 370?. With the extension of isothermal time, the contents of bainite and residual austenite increase, the contents of matensite decrease, the elongation and impact toughness increase, and the tensile strength reduces; with the further increase of isothermal time, a large number of bainites separete and refine the austenite grains result in the increase in tensile strength, elongation and impact toughness. With increasing tempering temperature, carbon atoms show a certain law like segregation, precipitation, aggregation and growth; When temper temperature at 280?, the bainite steel shows good tempering stability with higher yield strengh; When temper temperature at 350?, the strength and toughness decrease with the precipitating of carbides and the decreasing of bainite and austenite contents; When temper temperature at 420 ?, each mechanical properties reduce dramatically and brittleness appear.A crossing of bainite steel has been prepared by using the aforementioned deposition and heat treatment progress, the result shows that progress has good stability and reproducibility.Hybrid arc-based deposition and micro-rolling(HADMR) process has been used to eliminate the anisotropy of WAAM. For the problems of deficient deformation and larger remelting area due to deeper penetration and higher temperature gradient, a optimizedly initial micro-rolling morphology with shallower penetration and larger ratio of width to reinforcement has been proposed. Moreover, the motivated TMCP technique has been usded to refine grains. The results show: the tensile strength of three directions are 1275MPa?1256MPa?1309MPa respectively; The elongation of three directions are 17.4%?16.6% ? 17.7% respectively; The impact toughness is 99J/cm2; According to the GBT6394-2002, the average grain sizes of banite steel have been decided to grade 11~12.Compared with traditionally heavy rolling equipment, the micro roller this paper used has transformative cost advantage to achieve overall grain refining strengthening. The HADMR process has provided a novel way to online control morphology and performance of metal additive manufacturing.