Development Of 15CrMoR And 12Cr1MoVR For Medium-high Temperature Pressure Vessel Steel

With the rapid development of China's economy,the appliance of pressure vessels in various fields of national economy is increasing widespread.However,the pressure vessels belong to special equipment;there are a series of risk factors,including combustion,explosion,poisoning and so on.In order to ensure the use of pressure vessels equipment on a safe basis,reliable quality is ensured during the production of the vessel steel.In addition,taking into account the cost and complexity of the process,it is necessary to further optimize the process,improve production efficiency and reduce costs on the basis of the original process.Heat-resistant steel 15CrMoR and 12Cr1MoVR belong to medium-high temperature pressure vessel steel,and they widely used in petroleum,chemical and other fields.In this paper,the experiment steel is 15CrMoR and 12CrlMoVR.To study the production process of the medium-high temperature pressure vessel steel and realize the reduction production under ACC and ultra-fast cooling process conditions;To determine the influence of production process conditions on microstructure and microstructure transformation of medium-high temperature vessel steels;To research the effect of ultra-fast cooling condition on the subsequent heat treatment process.The main contents and research results are as follows:(1)The mechanism of every alloying element on the experimental steel was analyzed and the effect of interaction between alloying elements on microstructure and properties of heat-resistant steel.Taking into account mechanical properties,weld ability,cost and other factors of experimental steel,combined with national standards,to design a reasonable experimental steel composition.(2)When single-press experiment was carried out,the influences of different deformation temperature,deformation degree and deformation rate on the deformation resistance of the experimental steel were studied,and established the mathematical model of deformation resistance of experimental steel;the dynamic recrystallization behavior of austenite was investigated and analyzed the influence of work hardening and dynamic softening on high temperature deformation,the dynamic recrystallization activation energies of the two experimental steels were:356.4kJ/mol(15CrMoR)and 271.9 kJ/mol(12Cr1MoVR).(3)The static and dynamic CCT curves of the steel were drawn.Using thermal expansion method and lever principle,and combined with microstructure,the continuous cooling transformation curves of undercooled austenite under undeformed and deformed conditions are respectively plotted.The influence of deformation and cooling rate on the micro structure was investigated.The results show that the deformation makes CCT curve move leftward and upward,which promotes ferrite nucleation and increases the temperature at which the ferrite begins to change,meanwhile,the deformation expands ferrite and pearlite phase area.(4)Based on the thermal simulation experiments,designing hot rolling process reasonably,and controlling the parameters such as open cooling temperature,cooling rate and final cooling temperature.The microstructure and properties of the experimental steel under water cooling were analyzed,and compared with the conventional cooling method;the influence of water cooling on the experimental steel is summarized.(5)The heat treatment of the steel after hot rolling was carried out,the different heat treatment parameters and cooling methods were designed,the influence of different processes on the microstructure and properties of the steel was analyzed and the optimal production process was determined.The details as follows:Hot rolling and cooling processes for this two steels including heating at 1200?,rolling at 1100?,finishing rolling at 850-900?,the water cooling rate is 20?/s,the final cooling temperature is 600?;Heat treatment process as follows:15CrMoR steel normalized at 890?920? for 45 minute(3min/mm),then cooling slowly until room temperature,the second step is tempered at 700? for 75 minute(5min/mm),then cooling in air until room temperature;12Cr1MoVR steel normalized at 950? for 45 minute(3min/mm),then cooling slowly until room temperature,the second step is tempered at 690?750? for 75 minute(5min/mm),then cooling in air until room temperature.