The Research On Process Microstructure And Performance Of Cladding Sulfuric Acid Corrosion Resistant Alloy By Variety Of Heat Source

There is enormous demand for valves of concentrated sulfuric acid which are resistant to high temperatures in the field of sulfuric acid manufacturing and chemical industry.Those traditional valves are usually forged from corrosion-resisting alloy and because of the sulfuric acid with stronger corrosion resistance,it is necessary to add lots of chemical elements with higher price,such as Ni,Cr and the like in the alloy materials resistant to sulfuric acid corrosion,which leads to high manufacturing cost of the valves.In order to get the valve products which not only can meet the technical requirements,but also have a lower price,this thesis group at the request of relative enterprises uses TIG,laser and laser-TIC to clad anti-corrosion alloy powders on the metals with lower price,thus reducing the cost of the corrosion-resisting valves while maintaining the original properties.The technical requirements of equipment resistant to sulfuric acid of relative enterprises are as follows: hardness > HRC40,corrosion rate < 0.1a/mm,the corrosion resistance reaches level 5.Firstly,a test platform of heat source system is established.Based on the composition prescription of XDB-6 anti-corrosion casting alloys of Zhejiang Xuanda Special Alloy Process and Equipment AG,anti-corrosion alloy powders suitable for cladding are developed.As the basis material,304 stainless steel is clad with anti-corrosion alloy by using TIG,laser and laser-TIC respectively.Then this thesis group analyses the forming characteristic effect of different technological parameters on single-layer-single-channel cladding layers and the forming effect of overlap distance on single-layer-multi-channel layers.Secondly,micro-structure and phase composition of the TIG cladding layer,the laser cladding layer and the laser-TIC cladding layer are analyzed by scanning electron microscope,EDS,XRD.This thesis group also analyzes the effect of different micro-structural compositions and phases on the performance of cladding layers.Finally,the micro-hardness and the Rockwell hardness of the cladding layers are tested by a micro-hardness tester and a Rockwell hardness tester.The corrosion rate of the cladding layers in high-temperature concentrated sulfuric acid is tested by means of uniform corrosion method.The morphology and elementary composition of cladding layers corroded are examined and the corrosion mechanism of which is also analyzed by scanning electron microscope,EDS,etc.The electrochemical corrosion of cladding layers is tested by electrochemical workstation.Results of the trial indicates that in the single-layer-single-channel welding,the three heat sources and the basis material realize nice metallurgical bo nding.The laser cladding layer shows the best macro morphology and the lowest dilution rate.The laser-TIC cladding layer takes second place.The TIG cladding layer possesses worse morphology and the highest dilution rate.The laser-TIG can realize the similar macro morphology of the laser cladding layer by using lower laser power and the dilution rate is also lower at the same time.The phases of cladding layers are mainly consist of Ni2.9Cr0.7Fe0.36,Fe Ni3,Fe0.64Ni0.35,?-(Fe,Ni)and so on,which are largely different from XDB-6 casting alloys.The micro-structure of the laser cladding layer is smaller,while that of the TIG cladding layer is bigger.The micro-structure of the laser-TIC falls in between.The micro-hardness of the TIG cladding layer is about HV0.2500~HV0.2700.The micro-hardness of the laser cladding layer is about HV0.2600 ~ HV0.21000.The micro-hardness of the laser-TIC cladding layer is about HV0.2500~HV0.2900.The micro-hardness of the XDB casting alloy is HV0.2550.The Rockwell hardness of the TIG cladding layer is HRC52;the laser cladding layer is HRC63;the laser-TIG cladding layer is HRC60 and the XDB-6 alloy is HRC53.In 98% concentrated sulfuric acid with 120 degrees,the corrosion rate of the TIG cladding layer is 0.0298 mm/a.The corrosion rate of the laser cladding layer is 0.0205 mm/a.The corrosion rate of the laser-TIC cladding layer is 0.0224 mm/a.The corrosion rate of the XDB-6 casting alloy is 0.02mm/a.The corrosion levels of cladding layers and XDB-6 alloy are all level 4.Although the corrosion resistance of the cladding layers dose not reach that of XDB-6 casting alloys,there is little difference between them.Above research result indicates that the micro-structure and the phase composition of the cladding layer are much different from those of XDB-6 casting alloy.The Rockwell hardness and the corrosion resistance of the cladding layer can all meet the requirement of enterprises.Therefore,by means of the cladding method,valves with cladding layers which are resistant to high temperature and concentrated sulfuric acid on cheap basis materials can take the place of the full cast and anti-corrosion valves,thus achieving the objective of the cost reduction.