铁素体轧制关键技术与机制研究现状

摘要：铁素体轧制是控制精轧过程在铁素体范围内的板带热轧工艺,与传统的“热轧-冷轧-退火”工艺相比,可以实现“以热代冷”,显著节约成本。然而对于一些短流程生产工序,粗轧和精轧之间的高冷速会影响产品的尺寸和组织均匀性,尤其是两相区较宽的低碳钢,更难实现全铁素体区精轧。总结了板带铁素体轧制的相关研究工作,结合各企业铁素体轧制工艺的特点,提出了铁素体轧制工艺参数及组织性能控制目标。围绕铁素体轧制技术应用的几个关键问题展开分析讨论,重点讨论了两相区变形的软化机制及对织构的影响机制,为今后铁素体轧制关键技术的开发提供理论指导。     

Hot direct rolling in ferrite region in extra low-carbon steel

For the first time, hot direct rolling was applied in ferrite region in the mill and the resulting quality of the cold rolled and annealed sheet steel was as good as that hot direct rolled in austenite region with respect to microstructure and mechanical properties. In case of ferrite phase rolling, microstructure of the hot strip reveals abnormal grains and deformation bands in the grains, and elongation and r value are not so good as those rolled in the austenite phase. However, these abnormal grains left no traces and appeared to be equiaxed grains like the austenite phase rolled microstructure after 75 % cold rolling and continuous annealing at 830°C. This is attributed to the deformation bands which provide nucleation sites for recrystallization during annealing so that recrystallization occurs uniformly in the matrix. (111) texture was well developed and r value thus appeared high.     

Effect of Lubrication during Hot Rolling on the Evolution of Through‐Thickness Textures in 18%Cr Ferritic Stainless Steel Sheet

Samples of a ferritic stainless steel sheet were hot‐rolled with and without application of lubrication. The effect of the different hot rolling processes on the evolution of texture and microstructure after hot rolling, cold rolling and subsequent recrystallization annealing was studied by means of macro and micro‐texture analysis and microstructure observations. After hot rolling, the sample rolled with lubrication displayed uniform rolling textures through the sheet thickness, while the sample rolled without lubrication showed shear textures in the outer layers of the sheet. The finite element method was employed to reveal the strain states during hot rolling with and without lubrication. The texture of the hot rolled sheet strongly influenced the formation of texture after cold rolling and final recrystallization and, therewith, planar anisotropy as well as the severity of ridging of the final gauge sheet. Hot rolling with lubrication was beneficial to the formation of strong recrystallization textures through the whole thickness layers leading to an enhanced planar anisotropy of the sheet. The recrystallized sheet hot‐rolled without lubrication displayed less severe ridging, however, which was attributed to a less frequent formation of orientation colonies in the outer thickness layers of the sheet.     

铁素体轧制工艺热轧板显微组织研究与分析

为进一步摸清Ti- IF钢在铁素体轧制工艺下热轧板的金相组织分布规律,以及铁素体轧制工艺和常规轧制工艺下热轧板的金相组织差异性,结合某热轧厂半连轧生产线新开发的铁素体区轧制工艺技术,利用透射电镜试验对Ti- IF钢铁素体区轧制工艺的热轧板金相组织和析出物的控制情况作了初步研究,并分析了铁素体轧制工艺和常规轧制工艺热轧板金相组织以及析出物类别、晶粒尺寸的差异。研究可知,铁素体轧制工艺能得到细小均匀的再结晶晶粒,且比奥氏体晶粒尺寸小6~10 μm,其组织整体的均匀性理想。析出物方面,铁素体轧制工艺整体比奥氏体工艺大30~50 nm,不过TiN析出物尺寸相差不大。     

低温加热取向硅钢组织与织构演变研究

采用OM、EBSD、XRD分析研究了含Cu低温加热取向硅钢组织、织构的演变特征,研究结果表明：热轧板中存在铁素体层和珠光体层彼此交替的带状组织,且显微组织在厚度方向上分布不均匀,热轧板中{001}〈110〉、{112}〈110〉织构以及{110}〈001〉织构在板厚方向上分布不均匀;经过冷轧后,铁素体晶粒被严重拉长,形成了沿轧向伸长的纤维状组织,冷轧板织构类型主要是α织构和γ织构;脱碳时基体发生回复再结晶,显微组织为单一的铁素体等轴晶粒,织构主要为γ织构;二次冷轧板经渗氮后织构仅从强度上有所降低,其织构类型变化不明显。成品二次再结晶组织发展比较完善,晶粒尺寸约为10~20 mm。织构类型为锋锐的Goss织构。成品磁感B800达到了1.926 T,铁损P1.7/50为1.047 W/kg。     

热轧深冲钢板的分析和应用

在对比冷轧深冲钢的基础上,分析了工业试制的热轧深冲钢板的组织和性能。研究结果表明：该钢的碳含量较低,相应的金相组织和晶粒度合适;厚度大于２ｍｍ的钢板未经冷轧和退火处理可达到与冷轧深冲钢弧相当的成型性能,是代替冷轧深冲钢板冲压汽车零件的理想材料。该钢生产工艺简单,质量稳定,具有明显的经济效益和社会效益。     

国内外铁素体轧制的研究和应用

超薄热轧带钢(<1.2mm)的铁素体轧制(低温轧制)能显著节约能源和降低生产成本。当前迅速发展的薄板坯连铸连轧技术为铁素体轧制的发展与应用创造了良好的条件。已采用铁素体温轧工艺的钢板为低碳钢薄板和微合金化钢薄板。总结了铁素体轧制时流动应力,再结晶,轧后产品组织和性能的研究现状和铁素体轧制的应用情况。     

5083 H321铝合金板材制备组织性能研究

基于“1+4”热连轧生产线、2800mm冷轧生产线,采用不同工艺线路制备了5083 H321铝合金板材,研究了不同制备工艺对板材组织性能的影响。结果表明,不同工艺路线成品板材力学性能、耐腐蚀性能及微观组织均存在明显差异。采用“1+4”热连轧生产线短流程工艺制备的5083 H321铝合金板材性能:抗拉强度358MPa、屈服强度257MPa、延伸率17%、剥落腐蚀等级PA、晶间质量损失3.22mg/cm2。     

高强镀锌板表面发麻缺陷产生机理

针对高强镀锌板表面发麻缺陷问题，从全流程分析角度，探讨引起此缺陷的根本原因。利用扫描电镜分析发现，发麻原因在于锌层表面厚度不均匀、粗糙度差异明显以及镀锌板表面存在较多的表层裂纹。跟踪分析发现该表层裂纹主要产生在冷轧工序，结合钢种的热轧微观组织特点，提出形成表层裂纹的机理在于热轧钢板在轧制过程中抗开裂能力较弱，导致冷轧过程中钢板表面形成 10 μm 的表层裂纹。结合 CCT 曲线的模拟分析发现，控制热轧钢板表层微观组织状态可以明显抑制高强镀锌板表面发麻缺陷的产生。     

Effects of Process Parameters prior to Annealing on the Formability of Two Cold Rolled Dual Phase Steels

This study concerns the effects of coiling temperature after hot rolling and the degree of reduction during cold rolling on formability‐related properties of high strength cold rolled dual phase (DP) steels. The effect of coiling temperature on the final structure and properties of two cold rolled and annealed DP‐steels is investigated. Further, the effect of cold rolling reduction and its impact on the final properties of the material is studied. Aspects of the impact of the different process parameters on the ferrite to austenite and austenite to martensite transformation are discussed based on results from production scale experiments, tensile testing and metallographic examinations of the materials.     

冷轧高强集装箱板轧制稳定性控制技术

 冷轧高强集装箱板由于其屈服强度、成形性能及尺寸精度的要求,对冷轧轧制稳定性和板形控制提出极大挑战。针对某钢厂薄规格冷轧高强集装箱板生产过程存在的肋浪和边裂情况进行分析,采用试验方法研究了热轧带钢库区冷却过程对钢卷温度及性能均匀性的影响,利用数值模拟的方法研究了该钢种在UCM机型冷轧轧制过程中带材变形特征,揭示了带材浪形和边裂的并发机理,同时分析了不同工艺对带钢变形均匀性的影响规律。结合理论及仿真分析,提出了针对热卷性能均匀性及酸轧轧制稳定性的优化方案,改进后冷轧板形质量明显提高,带材边裂缺陷完全消除,冷轧高强集装箱板的轧制稳定性及产品质量均得到大幅提升。     

冷轧带肋钢筋专用母材的开发

针对各冷轧带肋钢筋厂家所用原料存在的问题,通过化学成分的确定,高线轧制冷却工艺的研究,开发了冷轧带肋钢筋专用母材系列产品,提高了冷轧带肋钢筋的轧制合格率;研究了[C]、[Si]、[Mn]、[N]含量以及铁素体含量和晶粒度对冷轧带肋钢筋专用母材系列产品性能的影响,提出了提高冷扎带肋钢筋母材性能的措施.     

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Effect of double cold rolling on magnetic properties and microstructure of 3.98%Si-0.71%Al non-oriented silicon Steel Sheets cast by twin-roll thin strip casting process were investigated. The results show that the structure of the thin strip is equiaxed crystal, the recrystallization is complete and normalizing has lesser effect on microstructure. Using both cold rolled and double cold rolled process, the microstructure is equiaxed grain after final annealing. The average grain size of annealed sheet in double cold rolled specimen was smaller than single stage cold rolled sheet. Double cold rolling process is helpful for iron loss and magnetic flux density.     

Investigation of the Effect of Deformation on γ‐α Phase Transformation Kinetics in Hot‐Rolled Dual Phase Steel by Phase Field Approach

Dual phase steels, consisting of hard martensite particles in a ductile ferritic matrix, offer high strength and deformability at the same time. Additionally, they are cost effective by a dilute alloying concept. In industrial production, two manufacturing concepts have been implemented: intercritical annealing of cold rolled sheet, or hot rolling. The current work has investigated the effect of deformation on the γ‐α phase transformation kinetics in the dual phase steel production using the hot rolling scheme. The pancaked austenite grains containing denser nucleation sites have a strong influence on the ferrite transformation kinetics. In addition, the multiplication of dislocations which results in the increase in elastic strain energy and dislocation core energy contributes to some acceleration in ferrite growth kinetics. A modelling approach for the γ‐α phase transformation kinetics in dual phase steels has been developed employing the phase field theory. The nucleation behaviour, i.e. the number and size of nuclei developed after an elapsed time as well as their nucleation sites which were evaluated from microstructure analysis, and the increase in the driving force of grain growth were integrated into this model.     

应用铁素体区轧制工艺生产ELC钢

通过铁素体区热轧工艺生产ELC钢的工业试验,研究了一种ELC钢的热轧组织、织构及性能。结果表明,铁素体区热轧后,ELC钢大部分为变形带组织,放大1 000倍可以看到鱼骨状的晶内剪切带;热轧后,织构沿板厚方向均匀分布,织构的遗传性使得冷轧和退火后的织构沿板厚方向也均匀分布,但是退火织构中仍有{001}<110>织构存在;退火后钢板的r值在1.3左右,达到普通冲压级钢板的要求。     

冷轧退火板DP钢成材率低原因分析

摘要：以冷轧退火板DP980为研究对象,结合生产过程中的工艺过程参数,利用金相显微镜、电子显微镜、显微硬度计、室温拉伸试验机对热轧卷、冷硬卷、退火卷试样的显微组织、硬度、强度、伸长率等进行了分析。结果表明,热轧卷生产过程中,为了控制带尾抛钢稳定性而降低卷取速度,导致带尾卷取温度较低,力学性能不均,遗传到冷轧工序转变为厚度波动。目前,冷轧各工序通过切头尾的方法,对于此问题进行控制,也就导致了DP钢成材率较低。     

Textures and Properties of Hot Rolled High Strength Ti-IF Steels

The texture evolution in a high strength Ti-IF steel during the processing of hot rolling, cold rolling, and annealing is studied. For comparison, both ferrite rolling and austenite rolling are employed. It is found that the texture type is the. same after ferrite rolling and austenite rolling, but the texture intensity is much higher in the ferrite rolled sample. Furthermore, texture characteristics at the surface are absolutely different from those at the mid sec tion in both ferrite rolled and austenite rolled samples, as well as under the cold rolled and annealed conditions. The shear texture { 110 } 〈001 〉 disappears and orientation rotates along { 110 } 〈001 〉→ { 554 } 〈 225 〉→ { 111 } 〈 112 〉→{111}〈110〉→{223}〈110〉 during cold rolling. Compared to the austenite rolled sample, the properties of the cold rolled and annealed sheet which is subjected to ferrite rolling are higher.     

冷轧板常见表面缺陷特征及成因分析

通过生产实践和检验,分析认为冷轧板常见表面缺陷包括原料缺陷和冷轧缺陷两大类,原料缺陷源于炼钢和热轧。原料缺陷如果控制不当,会遗传到冷轧成品板上,冷轧缺陷宏观易于辨识。提高冷轧板表面质量需要冶炼、连铸、热轧、冷轧各工序协调配合。     

热轧双相钢DP600关键工艺技术

在热轧双相钢中,终轧温度、卷曲温度、控冷时间和控冷温度对铁素体晶粒的大小和马氏体的形态、分布和含量都有重要影响,直接影响双相钢力学性能。通过对双相钢动态CCT曲线的模拟,制定出了合理的工艺制度,系统分析了热轧双相钢DP600热轧生产过程中终轧温度、卷取温度、控冷时间和控冷温度对双相钢的影响,对热轧双相钢的关键技术参数进行了研究,最终确定了合适的双相钢热轧生产工艺。     

含铌冷轧DP780钢的连退工艺对组织及性能的影响

 通过成分工艺优化,在传统冷轧铁素体和马氏体双相钢DP780的显微组织上引入了一定体积分数的残余奥氏体,研究了冷轧退火工艺参数对双相钢DP780的显微组织和力学性能的影响。通过调整连续退火工艺来控制显微组织中一次铁素体、二次铁素体、马氏体、残余奥氏体的比例、尺寸、形貌、分布,同时获得了连退工艺参数-显微组织-力学性能的本质关系。结果表明,通过在传统冷轧铁素体和马氏体双相钢的组织上引入了体积分数为5%～7%的残余奥氏体,不仅可以获得[ReL/Rm≤0.5]的超低屈强比型冷轧DP780,也改善了成型性能。