Study On Microstructure-Properties Control And Corrosion Resistant Mechanism Of High Strength Weathering Steel

In this thesis,taking Cr-Ni-Cu,Cr-Cu and Ni-Cu steels as the research object,the continuous cooling transformation behavior as well as the room temperature microstructure and mechanical properties under different coiling temperatures were discussed systematically.In addition,corrosion resistance mechanism were studied and analyzed,in order to provide experimental data for industrial production.The main contents and results are as follows:(1)Through dynamic continuous cooling transformation experiments,it was found that the microstructure of Cr-Ni-Cu and Cr-Cu steel are made of ferrite and pearlite at the cooling rate of 0.2?/s,the percentage of ferrite being respectively 98.8%and 97.1%.The microstructure of Ni-Cu steel is made of ferrite and pearlite when the cooling rate is between 0.2?/s to 0.5?/s,and the percentage of ferrite was increased from 96.7%and 98.8%with increasing of the cooling rate from 0.2?/s to 0.5?/s.(2)The coiling temperatures experiment showed that the yield strength,tensile strength and impact energy at-40? of Cr-Ni-Cu steel were respectively 698MPa,744MPa and 115J at the coiling temperature of 640?.For the Cr-Cu steel,when the coiling temperature was at 640?,the yield strength and tensile strength were 642MPa and 698MPa respectively,the impact energy was 77J at-40?.For the Ni-Cu steel,when the coiling temperature was at 600?,the yield strength and tensile strength were 665MPa and 710MPa respectively,the impact energy was 81J at-40?.(3)The different coiling temperatures experiment showed that,when the Cr-Ni-Cu steel was at different coiling temperature,the nanometer sized particles and interphase precipitation can be observed.With the coiling temperature dropping from 730?to 640?,the sheet spacings of interphase precipitation can be reduced from?37.6nm to?20.5nm,the size of precipitated particles decreased from?7.6nm to?5.5nm,and the calculated value of precipitation hardening increased from 78.1MPa to 239.2MPa.(4)The corrosion experimental results show that the weight loss rate sequence of the experimental steel is as follows:Q345B steel>Cr-Cu steel>Ni-Cu steel>Cr-Ni-Cu steel.The atmospheric corrosion resistance of banded pearlite is the worst on ferrite,the atmospheric corrosion resistance of fine bainite is slightly better on ferrite,and the atmospheric corrosion resistance of diffused pearlite is better on ferrite.