Fundamental Study On Wire And Arc Additive Manufacturing Technique For High Strength Steel Components

Wire and Arc Additive Manufacturing(WAAM)is a kind of rapid prototyping manufacturing technology for metal parts,which owns the advantages of high deposition efficiency and material utilization rate,low equipment cost and no restriction of depositing cavity,making it especially suitable for the fabrication of large metal parts.At present,the mainly research materials of WAAM are titanium alloy and aluminum alloy,and only few researches on processing,microstructure and properties of the WAAM high strength steel have been reported.In this paper,the effects of deposition parameters and heat treatment processes on the microstructure and properties of WAAM high strength steel parts were researched in detail by the Cold metal transfer(CMT)technology and the Atlantic CHW-95 C low alloy high strength steel welding wire.The effects of deposition path on the forming quality of parts were also studied according to the characteristic of WAAM.The main conclusions are listed as follows.Firstly,the effects of deposition parameters on the shape and size of single-layer singletrack and were studied.The results show that,the arc becomes unstable and the surface quality of the bead reduces when a traveling speed of more than 0.54 m/min is used.In addition,the effects of different parameters on the forming quality and size of multi-layer single-track deposition layer were studied systematically.By analyzing the effective area ratio,the optimal parameters of multi-layer single-track were obtained as wire feeding speed of 4.5 m/min,traveling speed of 0.36 m/min.Based on the above studies,the regression equation between deposition parameters and the size of bead was also obtained.Secondly,the effects of heat input on the microstructure and mechanical properties of WAAM high strength steel were studied systematically.The microstructure of the part is composed of granular bainite,acicular ferrite,carbon-free bainite and M-A constituent.With the increase of heat input,the content of granular bainite increases,whereas the content of acicular ferrite and carbon free bainite decreases.The variation in microstructure results in a increase trend of the tensile strength as well as a decrease trend of the elongation with the elevating heat input,whilst the yield strength first increases and then decreases.The difference between the horizontal and vertical tensile strength and yield strength are not obvious under different heat inputs.But the yield strength of as-deposited components is lower than the forgings.Thirdly,in order to improve the yield strength of the WAAM parts,the as-deposited components were heat-treated by normalizing,quenching and high temperature tempering,and the effects of tempering temperature on the microstructure and mechanical properties of the parts were studied systematically.It was found that the tensile strength and yield strength of the components decreases,the elongation increases gradually with the increase of tempering temperature.Meanwhile,the difference between the horizontal and vertical tensile properties increases with the increase of tempering temperature.Besides,tensile strength and yield strength of the horizontal and vertical samples are significantly improved compared with the non-heat treated components.A maximum increase in the yield strength of 199.6 MPa can be achieved when the tempering temperature is less than 565 °C.Fourthly,the effect of deposition path on the forming quality of the parts was studied.Through the research on the forming of the cruciform and the cylindrical part,it was found that the key of reducing the internal inclusion is to reduce the arc starting and the arc extinguishing point in the path planning.