The Study Of Quenching Process And Fatigue Crack Growth Behavior On 75kg/m Heavy Rail

It is well known that the pearlite rail has a corresponding improvement in tensile strength and yield strength as the pitch of the pearlite sheet is reduced,and whether the fatigue life is increased,which needs further study.In order to make the rail have higher yield strength to improve the bearing capacity of the heavy rail,obtaining a small pearlite lamellar rail becomes one of the research and development points of each heattreated rail production enterprise,and how the increase of the yield strength of the heattreated rail affects its fatigue life.Be the key technical issue addressed in this article.In this paper,75kg/m BGRE heavy rail steel is studied.The effects of unheated state,heat treatment state and different quenching cooling rates on the fatigue crack growth of BGRE rail are studied.The fatigue crack propagation a-N curve in unheated state,heat treated state and different quenching conditions was measured.The material parameters C and m values of fatigue crack propagation in the Paris region（zone II）were linearly fitted.The unheated state of BGRE steel was determined.The crack growth rate of CT specimens under heat treatment state and different quenching conditions under the strength factors ΔK=10MPa? m^1/2and 13.5MPa? m^1/2.The experimental results show that the C is corresponding to the increase of different quenching cooling rates.The value increases and the value of m decreases.When ΔK=10MPa?m^1/2,the crack growth rate decreases with the increase of cooling rate,but the crack growth rate does not change significantly with the cooling rate when ΔK=13.5MPa?m^1/2.The effect of self-tempering of BGRE quenched steel rail at 450 °C on fatigue performance was studied under the condition of quenching final temperature of 450 °C.This paper passed the heating furnace to BGRE 3 °C/s cooling rate,5 °C/s cooling rate,8 The °C/s cold speed sample was heated to 450 °C for simulated self-tempering,and the fatigue crack propagation a-N curve was measured.The crack growth rate curve was drawn by a-N curve.The experimental results show that self-tempering at 450 °C quenches the fatigue of BGRE steel after quenching.The performance impact is large,as follows: As the crack growth rate curve I disappears,the crack propagation life decreases to a large extent.In this paper,the experimental steel containing microalloying element Cr-Nb was studied.The effect of microalloying element Cr-Nb on the fatigue properties of the test steel was studied by 8 °C/s quenching cooling rate and 450 °C self-tempering.The experimental results show that: At 8°C/s quenching cooling rate,the fatigue performance difference between test steel and BGRE steel is 1.07 million times and 1.06 million times respectively.After self-tempering at 450 °C,the fatigue properties of experimental steel and BGRE steel are different.1.07 million times and 880,000 times,indicating that the test steel has better self-tempering performance.Through the above experimental research,the influencing factors of the fatigue properties of BGRE rail and Cr-Nb microalloyed experimental steel under different quenching cooling rates are analyzed,which provides a scientific and reasonable theoretical basis for further improving the fatigue life of heat treated rails and ensuring the quality of rails has a very important guiding significance.