Study On Loading Rate Sensitivity And Microstructure Evolution Of Casing Drilling Steel

In this paper,using C64-305 static hydraulic universal testing machine,muffle furnace and JSM-6390 SEM and other instruments,the influence of different heat treatment methods on the evolution of casing drilling steel structure is studied,and the loading rate on the tensile properties of different heat treated steels is studied.And the influence of structure evolution,and its hardness is analyzed at the same time,which provides a basis for improving the performance of casing drilling steel and improving the process.The main test results show that the casing drilling steel obtained after water quenching +tempering at different temperatures,as the tempering temperature increases,the structure changes from tempered martensite to tempered troostite and finally to tempered sorbite,and the hardness also varies with It is lowered.The casing drilling steel obtained after water mist quenching + tempering at different temperatures,the structure changes from tempered martensite + bainite to tempered troostite + bainite and finally to tempered sorbite + bainite Body,the hardness also decreases.The casing drilling steel obtained after normalizing at different temperatures has a microstructure composed of pearlite + ferrite and a small amount of bainite.As the normalizing temperature increases,the hardness first increases and then decreases,at 870℃ Maximum hardness.Comparing the casing drilling steels obtained by three different heat treatment methods,the casing drilling steel obtained after water quenching + tempering has the highest tensile strength and yield strength,but the elongation after fracture is the lowest;after water mist quenching+tempering The casing drilling steel obtained after the fire has high tensile strength and yield strength,and the elongation after fracture is low;the casing drilling steel obtained after normalizing has the lowest tensile strength and yield strength,and the elongation after fracture highest.The casing drilling steel obtained after normalizing gradually changes from brittle fracture to ductile fracture with more dimples as the loading rate increases.After water spray quenching + tempering and water quenching + tempering,the yield strength and tensile strength of casing drilling steel obtained after water spray quenching+tempering and water quenching + tempering increase slightly,and the toughness increases slightly.Many large dimples are transformed into small and evenly distributed dimples.Different heat treatment processes result in different microstructures,resulting in a significantly different loading rate sensitivity of casing drilling steel.The strain sensitivity coefficient of normalized steel is 0.006;the strain sensitivity coefficient of water spray quenching+tempered steel is 0.004,and water quenching+The strain sensitivity coefficient of tempered steel is 0.003.The strain sensitivity coefficients of water mist quenching+tempered steel and water quenching+tempered steel are relatively close and relatively small,indicating that these two heat treatment processes are less sensitive to the loading rate and adapt to the environment It is stronger and safer.It also shows that the hardenability of the material is better,the quenching medium has little effect,and the performance of the material is more stable.