| As an important branch of roller manufacturing, composite manufacturing bysurfacing welding and remanufacturing technology of metallurgical rollers have beenrapidly developed. However, fatigue cracks generated during surfacing welding andinferior mechanical performance of the deposited metal at high temperature haveprevented the wide application of composite manufacturing and remanufacturing inthe production of high-performance rollers. How to improve the strength anddurability of surfacing welding material, the uniformity of microstructures and grainrefinement level of the deposited material have become an important direction ofcurrent research on high-performance deposited material.In this dissertation, submerged-arc surfacing welding with flux-cored wire isstudied. By optimizing the ingredients of Cr5series alloy and the ways of addingalloy into the fluxed-wire, the performances of the deposited metal inhigh-temperature stretch, thermal fatigue, and wear and tear are studied. Moreover,the solidified structures in molten droplets and weld pool, evolution of microstructurein as-welded and heat-treated states, and the factors and rules affecting the mechanicalperformance of deposited surfacing metal are also analyzed.First, the failure route cause of roller surfacing material is analyzed for surfacingwelding composite manufacturing of pinch rolls. The poor strength and plasticity ofthe deposited surfacing metal, and its coarse columnar crystals, high content ofinclusions, and high content of residual austenite in microstructure are considered tobe the main causes. Based on Cr5series surfacing alloy, the method of single variableis used to study how the content of V and Mo affect the performance of depositedmetal in high-temperature stretch, thermal fatigue, and wear and tear, and also impactdurability and hardness at normal atmospheric temperature. Through analysis of themicrostructure of deposited surfacing metal, the relation between the variation ofmicrostructure and mechanical performance is discussed. The optimized depositedsurfacing metal has superior general mechanical performance when the V and Mocontent are0.5%and2.4%，respectively. Moreover, proper amount of strong carbideforming elements such as Ti and RE are added into the flux-cored wire of surfacingwelding to deoxidize and control the S and P content in the wire, so that the plasticityof deposited surfacing metal is improved. This is also critical in preventing thegeneration of surfacing cracks.Given the condition of keeping the same alloy composition in the deposited surfacing metal, the manner of adding Cr, C, and V into the flux-cored welding wireis changed. Chromium carbide and vanadium carbide are added in the1#and11#wire formula，respectively, and graphite and extra-low-carbon ferrochromium orgraphite and ferrovanadium are added in the2#and22#wire formula. OA, SEM,EDS, XRD, TEM, and SAD analysis show that the deposited surfacing metal iscomposed of lath martensite and residual austenite. Complex alloy inclusions andcomplex deoxidized inclusions are also found in the deposited surfacing metal. Highcontent of alloy in and near to complex alloy inclusion grains help to stabilizeaustenite, and residual austenite tends to form in the as-welded state and does notdecompose after tempering. The deposited surfacing metal obtained with theflux-cored wire added with chromium carbide contains more complex alloy inclusions,with more lath martensite twin structures and coarser original austenite grains. In thedeposited surfacing metal obtained with the flux-cored wire added with graphite andextra-low-carbon ferrochromium, the distributions of alloy ingredients andmicrostructure are more uniform, and the original austenite grains are finer.The complex alloy inclusions formed in as-welded deposited surfacing metal arestudied with5methods: changing the manner of adding alloy in the flux-cored wire,size of alloy grain, filling factor of flux-cored wire, welding heat input, the proportionof alloy with high melting point in the flux-cored wire. These inclusions may resultfrom incompletely melted and decomposed beads at later stage of weld pool or in situprecipitated beads in cooling because of local segregation of alloy elements. Largeamount of complex alloy inclusions may seriously damage the high-temperatureplasticity and ductility of deposited surfacing metal. The surfacing metal depositedwith the flux-cored wire added with chromium carbide has inferior thermal fatigueperformance and high-temperature wear and tear performance than that with theflux-cored wire added with graphite and extra-low-carbon ferrochromium powder.Proper manner of adding alloy into the flux-cored wire may be considered as a newapproach to improving the strength and durability, thermal fatigue performance andhigh-temperature wear and tear performance of deposited surfacing metal. Thisapproach breaks through the limitation of concentrating on the adjustment of alloyingredients and provides theoretical and practical basis for high-performancedeposited surfacing metal with fine grains, uniform structure and improved thermalfatigue performance.The developed flux-cored wire competed with the same series of foreign wiresand has passed the comparison test conducted by Dalian Huarui Special Spare PartsManufacturing Co., Ltd. It is now widely used in multiple well-known domesticmetallurgical and machinery manufacturing enterprises, and has repaired about3000high-performance rollers for Shougang, Wuhan Iron and Steel Corp., and Baosteel and achieved stable and excellent quality with larger economic benefit. Additionally,we compiled the―YB/T4326-2013technical code for composite manufacturingcasting roller welding‖of the Ministry of Industry and Information Technology. In themeanwhile, we have been compiling a standard of the Ministry of Industry andInformation Technology named―Pinch, wrapper code for composite manufacturingtechnology of roller surfacing‖. Implementation of the two standards would end thecurrent situation of roller surfacing without domestic composite manufacturingstandard and regulate domestic roller surfacing composite remanufacturing industry. |
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