Hot Ductility And Cooling Characteirstics Research On EQ47Offshore Platform Steel

EQ47offshore platform steel is quenched and tempered steel products with highstrength in structural classification rules, with good mechanical properties and welda--bility, and widely used in the construction of offshore platforms. Currently,It is timeto optimize continuous casting process、controlled rolling and controlled cooling andtempering process in order to make it more stable and mass.Therefore, thehigh-temperature plasticity plastic and cooling characteristics of EQ47offshoreplatform steel is studied and it provides a theoretical basis for optimizing EQ47offshore platform steel production process, and to achieve the new steel massproduction, which is important to the the development of offshore platforms.By single tensile test and thermal expansion test,the high temperature ductilityand cooling characteristics were studied,the high-temperature plastic curves and CCTcurves were established, Obtained the main following findings:（1）In this paper, The single tensile test of EQ47offshore platform steel isexperimented by Gleeble-1500D thermal simuiation machine.By measuring thetensile strength of steeland section shrinkage、observed microstructure and fracturesurface, we study the high-temperature ductility of steels. The results indicate thatthere was two brittle zones:the first brittle zones is between1270℃and1350℃、thethird brittle zones is between600℃and907℃，the good plastic zones is between907℃and1270℃. The fracture mode of the first brittle zones and the third brittlezones are intergranular fracture, the good plastic zones is transgranular fracture. TheZDT is1350℃，the ZST is1400℃, Crack sensitivity of EQ47offshore platform steelis weaker.（2）In this paper, the thermal expansion test of EQ47offshore platform steel isexperimented by Gleeble-1500D thermal simuiation machine. the CCT curve ofsteelis drawn out of by measuring the expansion curve, microstructure,hardness andStudied the cooling properties of steel. The results indicate that the criticaltemperature Ac1, Ac3, Ms were710℃,823℃,366℃successively;within range of0.05～1℃/s, the microstructure is ferrite、pearlite、 bainite, the hardness value is200～300N/mm2; within3～30℃/s range,the microstructure is pearlite、bainite、martensite, the hardness value of300～420N/mm2.