【作者】 李贞顺；

【导师】 李胜利；

【作者基本信息】 山东大学 ， 材料学， 2010， 硕士

【摘要】 高强度船板钢大量应用于造船工业,对于360MPa级船板钢,国内多家钢厂已探索出较为成熟的生产工艺,如何进一步优化生产工艺和合金设计是这类钢目前比较突出的问题。本文通过测定360MPa级船板钢的再结晶曲线、CCT曲线,试轧了Nb微合金化360MPa级船板钢,并用价格相对低廉的V元素取代Nb元素,采用不同轧制工艺轧制了V微合金化360MPa级船板钢。通过拉伸试验、夏比冲击试验、显微硬度试验测定轧制钢的力学性能,采用光学显微镜、扫描电镜、透射电镜观察钢的组织,研究了不同微合金元素与轧制工艺对360MPa级船板钢组织、强度性能的影响。经过系统研究得出以下结果：(1)根据测定的再结晶曲线及CCT曲线结合钢厂其他级别船板钢的试制经验,优化出360MPa级Nb微合金化船板钢轧制方案：控制轧制时的开轧温度为880℃左右,终轧温度为850℃左右,未再结晶区总的压下率控制在70%,轧后控冷,开冷温度810℃,终冷温度740℃,冷速为5℃／s,控冷后钢板直接空冷至室温。(2)钢的组织受粗轧末阶段奥氏体晶粒形态影响明显,该过程中的奥氏体晶粒形态取决于微合金元素的特性及粗轧道次压下量。添加Nb微合金元素时,铁素体晶粒尺寸不均匀,带状组织严重；添加V微合金元素时,若粗轧阶段压下量过小,则铁素体晶粒较为粗大,带状组织严重,而采用大的压下量时,铁素体晶粒细小均匀。(3)Nb、V、Ti在微合金钢中有不同的析出温度,Ti元素在铸坯冷却过程中析出,其在微合金钢中的主要作用是抑制奥氏体化过程及粗轧再结晶后的晶粒长大；V元素在相变后冷却过程中于铁素体内均匀共格析出,V在微合金钢中主要起沉淀强化作用；Nb元素在粗轧末阶段及精轧阶段析出,析出的Nb(C,N)将对再结晶产生强烈的抑制作用。(4)强度计算结果显示,V微合金钢中,粗轧阶段增大压下量细化相变铁素体晶粒后,可以使钢的强度提高约60MPa,而添加的0.03～0.05%的V元素,能够使基体产生50～70MPa的沉淀强化增量,因此,生产V微合金化360MPa级船板钢,粗轧阶段应采用相对大的压下量,轧后空冷。更多还原

【Abstract】 High-strength ship plate steels have been widely used in shipbuilding industry, The mature process of 360MPa grade ship plate steel has been well explored by severel domestic steel factories and the major problem with this steel is to optimize further the process and designation of alloys.The Nb-microalloyed 360MPa grade ship plate steel was rolled experimentally by measuring the recrystallization curve and the continuous cooling transformation curve. The V-microalloyed 360MPa grade ship plate steel was rolled with different rolling process by substituting Nb with cheaperⅤ. Mechanical properties of these steels were measured by using tensile test, Charpy V-notch impact test, microhardness test and the microstructures were observed by OEM, SEM and TEM. The microstructures and itensities were studied which were influnced by different microalloying elements and rolling process. Conclusions by means of systerm study are as follows:(1) The rolling process was optimized according to the recrystallization curve, continuous cooling tranformation curve measured and the experience of manufacturing other grade of steel:the starting temperature of finish rolling is about 880℃,the final temperature is about 850℃,the total reduction of non-recrystallization zone rolling is 70%, controlled cooling technology should be applied after rolling with a cooling velocity of 5℃/s and a final cooling temperature of 450℃.The plates can be cooled naturely after controlled cooling.(2) The ferrite structures are influenced evidently by the shape of austenite grain after rough rolling and the latter is depend on the characteristic of microalloy element and ruduction in pass.When the steels are microalloyed by Nb, the sizes of ferrite grains are not uniform. Microalloyed by V, if the pass ruduction of rough rolling is not large enough the ferrite grains are coarse and the banded structure is dramatic, then if the pass ruduction is large enough the ferrite grains are small and uniform.(3) The precipitation temperature of TiN, V(C,N), Nb(C,N) varis from each other, TiN precipitates at high temperature when the continuous casting is cooled, Its main function is to suppress the coarsening of grains during austenitizing and intervals of rolling passes. V(C,N) precipitates with a dispersive distribution in ferrite grain and keeps a coherency with the matrix. It’s main function is to strengthen the ferrite. Nb(C,N) precipitates at the end of rough rolling and during finish rolling, it will suppress the recrystallisation effectively.(4) Strength calculation results show that, in V-microalloyed steel, the intensity can gain an increment of 60MPa with fine ferrite grains caused by large pass reduction of rough rolling.The added 0.03～0.05% V can bring a precipitation strengthening of 50-70MPa. Therefore, relative large pass reduction should be applied when the V-microalloyed ship plate steels is produced, the steel can be cooled naturely after rolling.更多还原