【作者】 陈景浒；

【导师】 揭晓华； 毛新平；

【作者基本信息】 广东工业大学 ， 材料加工工程， 2011， 博士

【摘要】 本文研究CSP薄板坯连铸连轧工艺生产中高碳合金钢的物理冶金机理和工业生产技术。中高碳合金钢的应用十分广泛,使用的条件也很苛刻。因此要求要有高的淬硬性和淬透性、耐磨性和韧性,产品可以热轧直接退火应用或冷轧后应用；热轧状态使用的合金钢还要求保证板形优良、厚度精度高；微观组织要求有良好的等向性、高的洁净度及理想的金相组织,细小均布的碳化物形态。这些高的要求,除了在钢材化学成分上进行合理的配比优化外,相应在冶炼、浇注、热加工、热处理上还要采用一定的新的生产工艺技术。中高碳合金钢的碳含量都比较高,有资料显示,当碳的质量分数大于0.45%时,偏析会急剧增加,凝固过程的枝状晶充分生长,选分结晶也相当严重,铸坯中心的元素正偏析在加剧,同时枝状晶的搭桥现象还会阻碍钢液对凝固末端的补充,导致铸坯中心疏松就很严重。利用CSP生产工艺的铸坯的凝固速度快,薄板坯是由液态快冷形成,从γ-α无中间反复相变的技术特点。因此,通过合理的冶金成分设计,建立了全新的薄板坯连铸连轧工艺生产中高碳合金钢的冶金工艺控制技术,成功地开发出具有低脱碳层、产品均匀性好,高性能、高附加值低成本中高碳合金钢热轧薄板。本文对碳含量(Wt%)0.3～1.0%的中高碳合金钢成分波动规律进行了研究,提出了影响中高碳合金钢成分波动以及偏析的主要影响因素,并开发了保证成分均匀性以及减少偏析的炼钢、精炼和薄板坯连铸控制技术,实施后各类中高碳合金钢成分均匀性控制水平和偏析控制水平达到国外同类产品水平。通过对中高碳合金钢性能影响较大的Al2O3、SiO2、MnS等类型夹杂物的形貌、数量控制以及分布规律的研究。采用显微分析、扫描电镜分析以及电解分析等手段,对比分析不同工艺条件下夹杂物形貌、数量以及分布,研究电炉冶炼工艺、LF精炼工艺和中间包控制工艺的夹杂物控制技术,优选出合理的控制工艺。采用热膨胀以及金相法,测定出所试验的钢种在不同冷却速度下连续冷却时的膨胀曲线,绘制了30CrMo、50CrV4和SKS51的连续冷却转变(CCT)曲线；根据不同钢种的CCT曲线上特征点来确定各个相变点,从而确定了该钢种的连续冷却转变曲线；再利用电镜和光学显微镜观察试样的显微组织,分析不同的冷却速度对不同钢种的相变点的影响；另外,还分析讨论了不同的工艺参数对贝氏体转变、马氏体及珠光体转变和对CCT曲线的形状和位置的影响；研究了中高碳合金钢连续冷却过程中不同的钢种奥氏体转变的过程及转变产物的组织与性能,为实际生产工艺制度的优化提供了理论依据。为了控制热轧钢带的表面脱碳,对薄板坯连铸连轧流程生产的热轧中高碳合金钢的脱碳行为进行了研究；比较与分析了薄板坯连铸连轧流程与传统流程的脱碳规律,以及热轧中高碳合金钢带在不同的加工条件下所发生脱碳的程度以及影响因素。影响中高碳合金钢组织性能的重要因素是控制冷却工艺和合金元素的含量。钢的连续冷却转变曲线,即CCT曲线是研究和制定钢的控制冷却工艺的理论基础和前提。为此,根据测定的中高碳合金钢代表钢种的CCT曲线,研究了卷取温度对钢的组织性能的影响；研究了关键合金元素对钢的组织性能的影响。通过对薄板坯连铸连轧工艺生产中高碳合金钢的研究,使珠钢在国内第一次生产出高品质的中高碳合金钢系列热连轧钢板,产品质量与世界先进水平相当。这不仅提升了我国高强度热连轧钢板生产的技术水平,而且还改变了国内工程机械、高端合金工具制造等行业长期依赖进口的局面。更多还原

【Abstract】 This paper makes a study of physical metallurgical mechanism and manufacture techniques of thin slab continuous casting and rolling process of medium and high carbon alloyed steels.As is well known, medium and high carbon alloyed steels are widely applied nowadays while its operating conditions are very harsh as followings. First, it demands high grinding, harden ability, wear resistance and ductility; Secondly, they can be applied only after hot rolling annealing or cold rolling; Thirdly, the hot-rolled alloyed steels should be of fine-shape and high-precision thickness; Last but not the least, the microstructure should have good isotropy, high cleanliness, ideal metallurgical microstructure and evenly distributed carbide shape. To meet all these high demands, some new production technologies must be applied on metallurgical、casting、thermo-mechanical process besides the optimal ratio of the steels chemical composition.When the carbon content is high, with the content of lactose higher than 0.45%, its segregation will increase shapely and the columnar grain crystal will grow sufficiently during the solidification processing. What’s more, select crystallization will be severe, and the positive segregation of the centerline will intensify. At the same time, the bridging will hinder the supplement to the solidification end from the molten steel. Thus,.center porosity comes into being. Considering some technical characteristics that the slabs produced by CSP solidify quickly, the slabs come into being by liquid cooling and there is no repeated transformation from, thin slab continuous casting and continuous rolling (CSP) process is adopted. After the rational composition design, the totally new metallurgical control technique is used and hot-rolled steel plates of the medium and high carbon alloyed steels with low decarburized layer, good product homogeneity, high-performance, high additional-value and low cost are successfully developed.This paper did research on oscillating regulation of the components of the medium and high carbon alloyed steels with the carbon content (Wt%) from 0.3% to 1.0%, put forward the main factors which affected the oscillation and segregation and developed the access control to guarantee the composition uniformity and decrease the segregation during steelmaking, LF, and continuous casting and hot rolling process. The access control over the composition uniformity and segregation all has reached the international advanced level after the enforcement. The paper did research on morphology, quantity control and distributive characteristics of the inclusions such as Al2O3、SiO2、MnS and so on, which has much effects on the performance of the medium and high carbon alloyed steels. By The microscopic analysis, scanning electron microscopy analysis and electrolytic analysis, the author took inclusion morphology、quantity and distribution in different process conditions as well as furnace smelting process, and inclusion control of tundish into consideration, choosing the rational control process.By using thermal expansion and metallographic method, the author measured the thermal curve when the samples went through continuous cooling at different rate and drew the CCT curve of 30CrMo、50CrV4 and SKS51. Also the author determined the transformation temperatures of Austenite and its continuous cooling transformation curve. Through optical microscope and electron microscope, the author observed the samples’microstructure and analysed the effects on transformation temperature at different cooling rate. The author also analysed the effects on deformation parameters, Bainite transformation, pearlite transformation, CCT curve shape and location and the formation discipline of CCT curve under different processing. And at the same time, Austenite transformation process and the products microstructure and properties were researched during the continous cooling process, which laid a theoretical basis for establishing practical process systems.In order to control decarburization, the author did research on decarburization when the strip was hot-rolled during the thin slab casting and rolling process, compared the different decarburization between the thin slab casting and rolling process and traditional process and investigated the decarburization degree and influencing factors when the medium and high Carbon alloyed steels were hot-rolled under different processing condition.Controlled cooling processing (cooling rate and cooling temperature) and alloying element content are the main factors affecting the microstructure and properties. Continuous cooling transformation (CCT) is the theoretical basis on considering and determining the cooling technology. So according to the CCT of the characteristic steels, the author investigated how the coiling temperature and the key alloying elements affected the microstructure and properties.With the research on.high carbon alloy steel in the thin slab casting and rolling processing, Guangzhou Zhujiang Steel Co.,ltd. has produced high-quality continuous hot rolling plates for the medium and high carbon alloyed steels, with the quality up to the advanced level in the world, which not only upgrades our production technology on high-strength continuous hot rolling plates, but also changes the current situation that some industries such as construction machinery, advanced alloy tool manufacture and so on relies on import over a long period of time.更多还原