| The rail joint bar(abbreviated as fishplate)is important section that is connectingthe rail joint and its quality will influence the security of railway transportation directly.The fishplate was made with B6 and B7 steel originally, but with the development ofmodern railway to a high speed, heavy load and high density transport, these two kindsof materials can't already satisfy the current situation . Materials Bureau of Ministry ofRailways and the offices of industrial and mining in 1988 proposed and the researchinstitute of Anshan Iron and Steel Plant and medium-sized factory are responsible fordeveloping the 56Nb fishplate (refined in Martin furnace).The former Ministry ofMetallurgical Industry appraised the fishplate in 1991 after trial-produces for three yearsand , confirmed 56Nb steel fish plate had reached the advanced level of the formerSoviet Union and Japan in the world.After summarizing the developing history of microalloy steel of niobium, thisthesis tells us about controlled rolling and controlled cooling technology, the domesticfishplate material and chemical composition , organization and performance etc.. Then,structural design , work condition , stress state and invalid reason of the fish plate ,etc.is analysed.From 1997, the railway of our country successively raises speed greatly five times,railway transportation is strenuous day by day too with the fast development of nationaleconomy, having put forward higher demand to the highway section of the railway,certainly, no exception to the fish plate. For fishplate produced by Railway machinefactory of Chongqing Railway Bureau of Chengdu can satisfiy the need of southwestclimatic change heavily, humidity , many bridges and caves etc.. coordinated by them,the technology of school side is participated in, we make the 56Nb fishplate craftprinciple (get rid of the structural design factor ) after consulting now with Hualongsteel factory.1. Smelt the 56Nb steel with eight tons of three-phase electric arc furnace;2. After blooming basing on equipment of Hualong steel factory , as much as possible to realize CR and AcC on 56Nb steel fishplate.Obviously, the purpose of this thesis is to make the quality of the 56Nb steelfishplate material improved, satify the need of transport fast-develop badly in therailway of southwest of our country in the new century.In the course of development of the 56Nb steel fishplate , utilizing three-phaseelectric arc furnace smelting this steel can guarantee high pureness degree than openhearth steel, this has laid a very good foundation for result of the microalloy. But thekey in this thesis is that the rolling equipment is comparatively outmoded, and werealize fine CR very difficult ( AcC is easier). Because of this, we analyse, compare anddiscuss and we fix the primary rolling temperature of 56Nb at 1050-1150℃, andfinishing rolling temperature ≥900 ℃;as ratio of decrease section is equivalent to Φ180mm toΦ70mm round steel; The whole rolling time ≤180s, shorten intervaltime of each as much as possible; Cool to about 550-600℃with 70℃hot water afterfinishing rolling , take out from the hot water , and then put it in bell-type temperfurnace at 560℃for 2 hours, then make the size for manufacturer. Examine the craft of 56Nb steel fishplate based on existing equipment (600 rollingmill and 350 rolling mill ) of Hualong steel rolling mill how CR craft is appropriate,how degree CR is, how the result is. We have been to know about, analyse and solverelevant problems live frequently since the past three years, has also made a series oftest, such as the mechanics performance , cold formed test, metallographyanalyse(microstructure,grain size) , shock test(AKU), hardness test, fracture SEM analysisand TEM analysis etc.. Thus guiding and improving the rolling process of Hualong steelfactory, and make 56Nb steel fishplate quality becoming more improving and steady. Now, because steel ingot quality is steady, the 56Nb steel fishplate made by CRand AcC craft not merely reach TB/T2345-93 totally << the specification requirementof 43-75Kg/m fishplate >>,and performance is improved more than 56Nb steel fishplateproduced by Anshan Iron and Steel Plant at the time of reseach (σb improvesd by100MPa, σs improvesd by 200MPa , AKU improvesd by 10J/cm2, δand ψimprovednotably too). At present, 56Nb steel fishplate quality that Railway machine factory ofChongqing Railway Bureau of Chengdu produce has been generally approved forsystems of southwest district railway.
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