| Elastic bar is an important engineering accessory in the field of rail transportation,which mainly plays the role of fixing the steel rail and reducing vibration and noise.The spring steel60Si2 Mn and 60Si2 Cr are generally used in the production of elastic bars in China,and oil cooling is often used in the production process for quenching,which will cause serious environmental pollution in the subsequent process of medium temperature tempering and surface anti-corrosion treatment.In addition,the fatigue life of elastic bars in China generally requires 5 million fatigue tests without fracture,relatively short service life,frequent replacement and high maintenance cost.Therefore,it is urgent to develop a production process of green and long-life elastic bar preparation technology.In order to solve the problems of environmental pollution and short fatigue life in the production of elastic bar,55Si2 MnV is used as the research material in this paper.During the preparation of elastic bar,oil and water are used as the cooling medium respectively,and the quenching process and medium temperature tempering process are studied.Combined with the analysis and test results of microstructure,mechanical properties and fatigue properties,a kind of water-cooling quenching technology in the production process of elastic bar was obtained.On this basis,the effect of austempering process on the microstructure,mechanical properties and fatigue properties of 55Si2 MnV spring steel was further discussed.The feasibility of the application of austempering process in the production of elastic bar was theoretically analyzed.The results show that the best heat treatment process is 880 ?× 30 min oil cooling +500 ?× 60 min tempering(oil cooling).The mechanical properties of the samples prepared on the basis of this technology are better than those of spring steel used for elastic bar.The elastic bar processed by this technology has passed 20 million fatigue tests,which is four times of the current railway elastic bar fatigue test standard(5 million times).When water is used as cooling medium,the best heat treatment process is 880 ?× 30 min water cooling + 500 ?× 60 min tempering(water cooling).The mechanical properties of the samples prepared on this basis are similar to those of oil quenching,and the fatigue life of the railway elastic bar can reach 20 million times without fracture.This shows that it is feasible to use water as cooling medium in the production of elastic bar.Through the isothermal quenching of 55Si2 MnV spring steel sample,the best process is880 ?× 30 min + 275 ?× 30 min isothermal quenching + water cooling to room temperature.The yield strength,tensile strength,elongation,reduction of area and impact toughness of Vnotch spring steel are 1885 MPa,2232MPa,7.09%,36.26% and 13.50J/cm2 respectively.By studying the fatigue properties of 55Si2 MnV spring steel after isothermal quenching,the fatigue strength of spring steel after isothermal quenching at 275 ? for 30 min is 950 ± 32 MPa.The results of the above comprehensive analysis show that the isothermal quenching process has very great potential in the application of ultra-high strength railway elastic bar. |
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