Production And Application Technologies Of 12Cr2Mo1R Heavy Plate For Equipment Under Critical Hydrogen Atmosphere

Due to the requirement to high performance in critical environment and the complicacy of producing and processing, the 12Cr2Mo1R heavy plates for equipment under critical hydrogen atmosphere were not able to be produced in China and had been depended on import for a long time. The set up of Baosteel heavy plate mill made it possible to domestically produce the steel by supplying the production facilities, while the production technologies were still absent and had to be developed. Therefore, the application environment, chemical composition system, requirement on the properties and micro structure and its physical metallurgical mechanism, and performances of the plate imported are analyzed in detail for the steel, the basic production approach is also summarized, and the design of composition and key production processes are proposed accordingly. The feasibility of production of the steel through processing route including 5 meters heavy plate mill in Baosteel is investigated, and a series of deep experiments and simulations are carried out to determine the key process parameters. Finally, the production technologies of 12Cr2Mo1R heavy plate for equipment under critical hydrogen atmosphere has been developed and put into practice on this production line, and the plates have been successfully produced with the performance passing authority evaluation. In order to make the plate easy to use, detail analysis of mechanical properties and research on the key application technologies, such as welding and flame cut, are made on the 12Cr2Mo1R heavy plate with thickness of 95mm. Consequently, some conclusions are drawn with several breakthrough achievements as follows.(1)The results of analyzing the feasibility of three key processes, i.e., steelmaking, rolling and heat treatment, in 5 meters heavy plate production line in Baosteel branch, for the manufacture of 12Cr2Mo1R heavy plate for equipment under critical hydrogen atmosphere show that the steelmaking process can assure the temper embrittlement factors J less than 96, the rolling machine of 5 meters heavy plate mill has the capacity to achieve that the forming shape coefficient larger than 0.23 and assuring the enough deformation in the center of special heavy plate, and the air or accelerated cooling after normalization can ensure the realization of required microstructure. As a result, the required composition and microstructure are achievable in Baosteel production line.(2) Under the precondition of safety of equipment, the 12Cr2Mo1R heavy plate with the thickness of less than 100mm can be manufactured by simulating the cooling processes of different thickness plates and measuring the effecting of hot plates on the equipment and instruments in quench machine.(3) In order to ensure the microstructure in all thickness is mainly of Bainite, the critical thickness of 12Cr2Mo1R heavy plate for equipment under critical hydrogen atmosphere, which is normalized after air cooling, is 50mm through numerical simulating and industrial production validating by referring to the microstructure features in the static CCT diagram of 12Cr2Mo1R steel under constant cooling rate. When the 12Cr2Mo1R heavy plate with not less than the thickness of 50mm is manufactured, the accelerated cooling measure should be adopted after normalization. This conclusion gives a guideline to select the cooling pattern for the heat treatment.(4) It is suggested for the first time in China to realize the accelerated cooling of 12Cr2Mo1R heavy plate by using quench machine. The 12Cr2Mo1R heavy plate with thickness of 95mm with good flatness and the microstructure of Bainite in across thickness section is manufactured by utilizing the cooling in the low-pressure zone of quench machine through reasonable technological parameters. And the required mechanical properties of this plate are achieved after tempering with suitable parameters.(5) The 12Cr2Mo1R heavy plates with thickness of 50mm and 95mm produced have been successfully produced in this production line by using the developed production technologies. After the 95mm12Cr2Mo1R heavy plate is heated by minimum post weld heat treatment and step cooling, its value of vTr55 +2.5ΔvTr55 is-97℃.(6) The results of examining mechanical properties of 12Cr2Mo1R heavy plate with thickness of 95mm with delivery condition of normalized with accelerated cooling and tempered show that the tensile properties and impact properties at half of thickness are homogeneous and the ductile and brittle transition temperature is low. After the plate is treated by different simulated post weld heat treatment, its tensile properties are stable and its ductile and brittle transition temperature keeps almost the same. The high toughness mechanism of this plate is researched by using optical microscope and transmission electron microscope, and it is concluded that the microstructure of 12Cr2Mo1R heavy plate with thickness of 95mm is kept as Banite after different simulated heat treatments and the amount of precipitation phases vary with the condition of simulated conditions. It is revealed by observation that the basis of the plate is consisted of many sub-grains with size of 1～2μm. It is suggested for the first time that the carbides existed in delivery 12Cr2MolR heavy plate and formed under different simulated heat treatments does not display the obvious effect on impact toughness, as well as the sub-grains with size of 1～2μm lead to the high low temperature impact absorb energy and lower ductile and brittle transition temperature.(7) The cutting surfaces which are formed by different cutting processes and the features of microstructure and hardness near the surface are firstly researched comprehensively through flame cutting and thermal simulation tests of the finished 12Cr2MolR heavy plate with thickness of 95mm. Following tested results are achieved, the flame cut surface before normalization of 12Cr2MolR heavy plate with thickness of 95mm is treated by normalizing with accelerated cooling and tempering, the microstructures on the original cutting surface and neighboring zone are changed and hardening zone is weakening. The flame cutting surface of finished plate which is normalized and tempered has no obvious effect on the bend property of the plate. The hardening zone should be existed near the cutting surface no matter the finished plate is cut at room temperature or after preheating. But the thickness and width of hardening zone are different when the plate is cut at room temperature or preheating. In order to reduce the effect of the hardening zone on bend forming, the flame cutting after preheating is recommended.(8) The 12Cr2Mo1R heavy plate with thickness of 95mm and its welding procedure qualification are evaluated. The results show that the plate meets the requirement of manufacturing of the head and drum of the equipment under critical hydrogen atmosphere and completely suitable to the welding processes and welding consumables used in the manufacturing of equipment for equipment under critical hydrogen atmosphere. The heavy plates produced by Baosteel were evaluated by National Boiler & Pressure Vessel Standardization Committee, and concluded that the 12Cr2Mo1R heavy plate with thickness of 95mm can be used to manufacture the equipment for equipment under critical hydrogen atmosphere.