Study On High-nitrogen Stainless Steel Wire And Its CMT Arc Additive Manufacture

High nitrogen austenitic stainless steel with good mechanical properties and corrosion resistance has become one of the hot spots in the research of iron and steel materials.CMT?cold metal transition welding technology?additive manufacturing is a new wire arc additive manufacturing technology that has the characteristics of a one-time forming of complex parts and can achieve the goal of the free manufacturing of parts.High nitrogen steel is prepared into wire,and study the CMT arc additive manufacturing of high nitrogen steel,so as to make it is possible to achieve a wider range of practical application of high nitrogen steel.In this paper,the composition of various high nitrogen steel wire used for CMT additive was designed.Its CMT process properties were studied.The solidification microstructure and mechanical properties of high nitrogen steel prepared by CMT additive were analyzed,And the effect of heat treatment on microstructure and properties was studied.The results show that:1)the addition of Nb?Mo?element can improve the surface smoothness,refine the grain and improve the mechanical properties of high nitrogen steel alloy ingot after melting and solidification;High nitrogen steel wire with various components was designed and prepared by combining nitrogen balance theory and schaeffler phase diagram.The evaluation of welding technology shows that Nb microalloying can reduce the surface roughness of wire and the amount of splash and smoke,improve the formability and maintain better stability of melting pool.2)CMT additive manufacturing of high nitrogen steel take a staggered stacked approach?i.e.first print a layer in x-y plane,and then print the second layer along the Z direction staggered 90 degrees,and so on?.The thickness of each layer of is about 2.6 mm,and each layer can be divided into remelting area?the thickness of 0.1 mm?,dendrite area?the thickness of 2.1 mm?,heat affected zone?the thickness of 0.4 mm?.There is an austenitic phase and a small amount of delta-ferrite phase in the CMT additive high-nitrogen steel,and the microstructure is small Cr-rich dendrites and the secondary dendritic arm spacing is less than 8.5?m.the dendrites growth direction is mainly along the Z direction.But the principal axis of local dendrites tilt about 45°in the Z direction because of the influence of heat loss that results from the printed part of the same layer.3)Grains of the additive show?200?optimal orientation growth along the Z direction.Mechanical properties of the additive in the Z direction are lower than those in the X?Y?direction:tensile strength in the X?Y?direction is 872 MPa,elongation is 13%,impact toughness is 258 J/cm²;The Z direction tensile strength is 745 MPa,elongation is 12%,impact toughness is 228 J/cm².4)Heat treatment of the additive of high nitrogen steel in 500?⁹00?is an aging precipitation process in essence,and the main precipitated phase is?and Cr₂N.With the increase of heat treatment temperature or time,there are three stages of under-aging,peak aging and over-aging.Under the condition of heat preservation for 3 hours,500?⁷00?is in the under-aging stage.700?is in the peak aging,the yield strength?tensile strength?of X?Y?and Z direction direction is respectively 774 MPa?951 MPa?and 725 MPa?778 MPa?,hardness is respectively 373 HV0.5 and 369 HV0.5;700?⁹00?is in the over-aging stage.Under the condition of 600?,0⁵0 h is in the under-aging stage.50 h is in the peak aging.50 h¹00 h is in the over-aging stage.In the peak aging,the yield strength?tensile strength?of the X?Y?direction and Z direction is respectively 856 MPa?991 MPa?and 789 MPa?872MPa?.The dendrites in the additive of high-nitrogen steel are completely decomposed in the peak aging and a large number of second-phase particles are precipitated in the chrome-rich zone of the original dendrite,and the precipitated zone and the non-precipitated zone form a network-like interweaving feature in space.