| With high acid oil and gas have emerged,the traditional anti-corrosion technology has difficult to meet the current needs of the natural gas pipeline construction,nickel based alloy-carbon steel double metal composite pipe with excellent mechanical properties and corrosion resistance shows a good application prospect in oil and gas pipeline construction.Overlaying welding is widely used in the production and processing of bimetal composite pipes,at the same time,dissimilar metal surfacing is a complicated metallurgical process,which leads to a series of problems such as inhomogeneous structure,coarse structure and element segregation affect mechanical properties and corrosion resistance of the surfacing layer,which has an adverse effect on the safe service of the pipe and pipe fittings.In this paper,in order to eliminate welding defects and improve performance of surfacing layer,surfacing Inconel625 nickel based alloy on X90 pipeline steel surface,prepared Inconel625/X90 surfacing layer,study the solution temperature,cooling mode and effect of solid solution aging heat treatment on the Microstructure,composition distribution,mechanical properties and corrosion resistance of surfacing layer,In order to provide a theoretical and technological reference for the establishment of mature heat treatment process of Inconel625/X90 surfacing layer,lay the foundation for the successful application of the subsequent Welding bimetal composite pipe in corrosive gas and other industrial fields.After heat treatment of deposited metal tissue types did not change significantly,the grain size was decreased with increasing temperature,from the fusion line to the top of the deposited metal,the crystalline area,the crystalline region,the dendritic crystal region,the equiaxed crystal region and partial top lateral organization are successively arranged.Before the heat treatment,the growth of the surfacing layer is disordered,the corrosion of the coating is uneven,and the grain boundary erosion is more serious,which leads to larger grain gap.After heat treatment,the organization becomes uniform,the etching effect is weakened,among them,850 ? air cooling,980 ? air cooling,and 850? water cooled surfacing layer are the most obvious;The effect of heat treatment on the substrate structure of surfacing layer is remarkable,bead weld makes loud superheating ferritic structure-Widmannstatten structure at the fusion line of base material,base organization is not uniform,after the heat treatment,the coarse overheated ferrite structure at the weld line disappears,substrate tissue becomes uniform;Before and after heat treatment,the distribution of elements in the bonding layer of the surfacing material and the coating material is three steps,but with the increase of temperature,the fluctuation range of each element content curve is decreasing gradually,the distribution of elements in the surfacing layer tends to be uniform by thermal action.After heat treatment,the content of Ni and Fe in the side diffusion zone of the treated material changed greatly,but the content of Cr,Mo and Nb changed little.At the distance of 1000 ?m from the fusion line,the content of alloying elements in the surfacing layer has been little changed before and after heat treatment,and it is very close to that of the welding wire,and the diffusion phenomenon becomes less obvious in this area.The hardness of untreated sample is decreased and then increased from the applied material to the base material.The hardness falls to the minimum near the fusion line,and the minimum value is 169.3 HV,which appears on the base material side.After heat treatment,the hardness of the substrate changed obviously,the hardness value of the heat affected zone of the base material is obviously higher than that of the untreated sample,except for the 910?air cooling sample,the 850? water temperature sample has the largest lifting range,the highest hardness value was 258.2 HV,the maximum lifting range is 77 HV,overall hardness better than the untreated sample;Tensile strength of 850? water sample and 910? water sample increased to some extent compared with untreated sample,tensile strength was 742.5 MPa and 730 MPa,respectively,lifting ranges were 6.07%and 4.29%,respectively,but the ductility decreased obviously;The impact absorption energy of untreated sample is 180.30 J,the impact toughness of 850 ? air cooling,980 ? air cooling and 850 water cooling samples increased obviously,the impact toughness of water cooled sample at 850 ? was the best,and the impact absorption energy reached 189.58 J.The minimum impact absorption energy of solid solution aging treatment is 148.56 J.In the electrochemical tests,in the AC impedance test time,there exists only one reflection mode in the 7 sets of specimens,after heat treatment,the corrosion resistance of the surfacing layer is improved to some extent,of which the 850 ? water-cooled surfacing layer has the best corrosion resistance,solid solution and aging treatment to enhance the corrosion resistance of the surfacing layer is not obvious,with the untreated surfacing layer little difference;surfacing layer polarization curve test results with AC impedance test results are basically consistent,very good to confirm the accuracy of AC impedance test. |
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