Cooling curves of 28CrMoVNiRE steel oil well tube under different water mists,water pressures and nozzle height cooling conditions were measured by establishing a physical simulation platform of ultra-high pressure jet ultra-fast cooling heat transfer.The heat flux density and heat transfer coefficient of the specimen surface were calculated by inverse heat transfer method.The heat transfer mechanism of ultra-high pressure jet ultra-fast cooling of seamless steel tube was studied,and the accuracy of inverse heat transfer calculation was verified by finite element simulation.In order to explore the effect of ultra-high pressure jet ultra-fast cooling on the microstructure and properties of seamless steel tubes,the microstructure analysis and mechanical properties tests of the steel tube under original hot-rolling state and different ultra-fast cooling conditions were carried out respectively.The results show that when the nozzle height is 100 mm,the water pressure increases from 6 MPa to 7 MPa,the average heat transfer coefficient increases from 386.0 W/(m2·℃)to 859.1 W/(m2·℃),and the average heat flux density increases from 0.15 MW/m2 to 0.35 MW/m2.When the water pressure is 7 MPa and the nozzle height increases from 100 mm to 160 mm,the average cooling rate increases by 6.2％.The heat transfer coefficient with the decrease of temperature difference △T goes through two stages:high temperature,medium temperature near linear rapid growth stage and low temperature rapid decline stage.It is found that the martensite lath width of the tested steel can be refined to 0.35 μm on average under the cooling conditions of spray water pressure of 7 MPa and nozzle height of 160 mm.Compared with the original hot-rolled steel,the hardness and the impact absorbed energy increase,which verifies the feasibility of ultra-high pressure jet ultra-fast cooling technology.
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