| With the heavy consumption and gradual shortage of onshore oil as well as gas resources,the exploitation of oil and gas resources has begun to transfer to the harsh areas,such as marine,polar region,which has abundant hydrocarbon storage.Because of the special conditions of the polar region,the H-beam used in the polar region must have good low temperature toughness besides the high strength.In accordance with the special performance requirements of the polar oil-gas exploitation on hot rolled H-shaped steel,the paper adopts the TMCP process to make the material meet the performance requirements of the cold area in C and Mn,which are based on the addition of NB and V microalloyed elements.In this paper,three different compositions of test steels were designed,and the microstructure transformation regularity of test steels were studied.Moreover,the author also has studied the relationship between microstructure change and performance and process parameters,and the relationship between deformation quantity,deformation temperature and alloy composition and dynamic recrystallization of materials.It provides a basis for the determination of TMCP process of hot rolled H-beam.Through thermal expansion test and microstructure observation,the constant transformation regularity of three kinds of test steels was studied and CCT curves of three test steels were plotted.The results suggested that three kinds of test steels consist of four basic organizations,Ferrite,Bainite,Pearlite and Martensite,and have a wider bainite transformation region,which can produce bainite microstructure at 1℃/s cold speed.In the cooling process the 1# Test steel obtains small ferrite + bainite range of 3℃/s~7℃/s,and the 2# test Steel obtains small ferrite + bainite with the range of 3℃/s~10℃/s.3 # Test Steel get small ferrite + bainite with the range of 3℃/s~7℃/s.Through the thermal simulation test,the relationship between the microstructure transformation and the performance and process parameters of three kinds of test steels was investigated.The results suggested that when the cold speed is 1℃/s,the microstructure of 1 # and 3 # test steels is ferrite + pearlite,2 # test steel has a small amount of carbide,and the cold speed is 5℃/s.Three test steel microstructure are ferrite + pearlite + small number of bainite.When the cold speed is 10℃/s,the microstructure of the three test steels is a small number of Pearlite + ferrite + bainite.The deformation temperature of the test steels should be controlled in the 800 range,the optimum cold speed should be controlled in 3~5℃/s,and the composite tissues of fine quasi polygon ferrite and bainite with good toughness can be obtained.The relationship between the dynamic recrystallization and deformation temperature as well as deformation quantity of two kinds of test steels containing V and NB were studied,and the recrystallization diagram was plotted.The recrystallization study suggested that the degree of recrystallization of test steels is increasing with the increase of deformation,and the increasing trend of deformation temperature is also increasing,in deformation 50% and 60% when the basic completion of recrystallization.1 # test steel occurred recrystallization in deformation 10%,and the temperature reaches more than 800 ℃,2 # test steel occurred recrystallization in 20% of the deformation and the temperature reaches more than 900℃.Moreover,adding Nb can enlarge the experimental steel non-recrystallization area,which is conducive to the test steel in the non-recrystallization area to achieve high temperature rolling.Meanwhile,it can reduce the partial recrystallization region.Based on the above study,the deformation process was designed and the pilot rolling test was carried out.The results suggested that the fine ferrite + bainite microstructure can be obtained by formulating a reasonable process,so that the material has excellent comprehensive mechanical properties,especially the high low temperature impact toughness,and meets the needs of polar steel. |
PDF Full Text Request