双相钢DP600热轧工艺的优化

介绍了高强度双相钢DP600热轧工艺的优化过程。通过热模拟测定了热轧DP600动态CCT曲线,制定了生产工艺参数并进行3.4 mm厚度DP600的工业试制。在分析首次试制的热轧DP600微观组织构成和力学性能基础上,对终轧温度和空冷时间进行优化,获得了合理配比的微观组织。试制结果表明:采用优化后的热轧工艺,DP600主要由铁素体+马氏体组成,马氏体的比例在15%左右,铁素体晶粒较细小,为11.5级,产品组织均匀;横向屈服强度387 MPa,抗拉强度642 MPa,延伸率(A_(80))27%,各项性能指标均优于首次试制,完全满足双相钢的基本要求。     

700 MPa级热轧双相钢的组织和性能

 采用热模拟并借助光学显微镜、SEM技术研究了双相钢的相变规律及不同工艺参数下的组织演变规律。根据热模拟结果在实验室试制出700 MPa级热轧双相钢,优化了轧制和冷却工艺参数。实验结果表明：热轧双相钢组织为多边形铁素体+马氏体岛,抗拉强度730 MPa,屈强比062,伸长率236%,达到了DP700级双相钢的性能要求,并讨论了热轧卷取温度对双相钢最终力学性能的影响。     

含钼双相钢DP600相变研究和工艺实践

采用热模拟试验研究了含钼双相钢DP600在不同冷却模式、转变温度和冷却速率时的显微组织转变,分析了相变后的马氏体比例和晶粒度级别,根据热模拟结果设计了DP600钢的生产工艺,并探讨了钼元素对双相钢的影响。结果表明,DP600钢在热轧组织转变时,两段式冷却工艺比一段式工艺形成的马氏体细小,且晶粒度提升1级。奥氏体向铁素体转变过程中,存在最佳相变温度平衡点;590 ℃以上减缓DP600钢铁素体＋珠光体的过冷转变速率,可以细化晶粒、增加马氏体比例。生产的DP600钢金相显微组织为铁素体＋马氏体,马氏体比例为17%,晶粒度为11级;纵向、横向抗拉强度分别为592和620 MPa,伸长率分别为28.5%和26.5%。钼元素可以强烈抑制C- Si- Mn- Cr- Mo系DP600钢的铁素体转变,缩小铁素体转变区。     

冷却模式对CSP线生产热轧双相钢DP600的影响

针对酒钢CSP线,设计了600 MPa级热轧双相钢的化学成分,测定了其动态CCT曲线。根据动态CCT曲线,分别采用三段式与两段式冷却模式进行了现场试制,对试制热轧板进行了显微组织观察与力学性能检测。结果表明:通过化学成分的合理设计及关键工艺参数的合理控制,热轧板的显微组织为铁素体+马氏体,屈服强度均达到325 MPa以上,抗拉强度均达到600 MPa以上,屈强比为0.53～0.58,伸长率均达到26.9%以上,并且其应力-应变曲线为连续屈服。两段式与三段式冷却模式都可使热轧板的综合性能达到了DP600热轧双相钢的性能指标。虽然两段式冷却模式在工艺上控制简单、更易于实现,但二段式冷却模式得到的屈服强度偏低;采用三段式冷却模式,并将一段快冷结束温度控制在700℃左右,可得到相对较高的屈服强度,使热轧板的综合性能更佳。     

DP600级热轧双相钢的开发

分析双相钢的组织特点和生产工艺,介绍本钢DP600级热轧双相钢的开发,具体阐述了工艺条件对C-Si-Mn-Cr-Mo系双相钢组织性能的影响及工艺参数的确定.     

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。     

冷却工艺对DP590热轧双相钢组织及性能的影响

通过实验室轧制DP590热轧双相钢,研究了卷取温度、快冷温度对热轧双相钢显微组织和力学性能的影响。结果显示,快冷温度提高,马氏体含量显著增加,同时抗拉强度升高,延伸率下降;试验钢在550℃、600℃卷取时,随着卷取温度的升高热轧双相钢中马氏体含量下降,抗拉强度下降明显,延伸率提高。在600℃时得到的铁素体和马氏体比例合适,实现了抗拉强度600 MPa,屈强比0.5左右,延伸率22%以上的热轧双相钢,综合性能满足DP590热轧双相钢的要求。     

轧后冷却对DP590热轧双相钢组织及性能的影响

针对DP590热轧双相钢,通过实验室热轧试验,研究了卷取温度、快冷温度对热轧双相钢显微组织和力学性能的影响,对比分析了显微组织中马氏体的数量及形貌。结果显示,快冷温度提高,马氏体含量显著增加,同时抗拉强度升高,延伸率下降;试验钢在550℃、600℃卷取时,随着卷取温度的升高,热轧双相钢中马氏体含量下降,抗拉强度下降明显,伸长率提高。在600℃时得到的铁素体和马氏体比例合适,热轧双相钢抗拉强度600 MPa,屈强比0.5左右,伸长率22%以上,综合性能满足要求。     

热轧薄规格DP600双相钢组织演变

采用MMS- 200热模拟试验机对DP600双相钢进行双道次压缩，研究带有中间坯补热工序的无头轧制工艺和常规轧制工艺对试验钢奥氏体组织和变形抗力的影响，并在实验室进行了2种工艺条件下的热轧试验。结果表明，具有中间坯补热工序的无头轧制工艺有利于精轧前奥氏体组织的均匀化，降低钢材的变形抗力，试验钢更易于变形；轧制薄规格双相钢时，中间坯补热工序可以抑制马氏体带状组织的生成，试验钢具有较高的断后伸长率，马氏体含量的增加提高了试验钢的抗拉强度，力学性能满足DP600的标准要求。该研究结果为无头轧制工艺开发薄规格DP600双相钢奠定了理论基础。     

高强度热轧双相钢的低周疲劳性能

从热轧双相钢的实际应用需求出发,研究了高强度热轧双相钢DP600的低周疲劳性能。采用轴向应变控制方法对DP600钢进行了低周疲劳试验,并对试验数据进行拟合计算,得到DP600钢的循环应力-应变曲线、应变-寿命曲线和过渡疲劳寿命。通过扫描电镜观察疲劳断口,结果显示低周疲劳条件下,DP600钢断裂裂纹起源于试样表面,裂纹扩展前期呈现部分脆性断裂特征,后期则以明显的韧性断裂为主。     

Rolling and Coiling Technology for the Production of Thin Strip on a Casting Rolling Line

One aim of the casting rolling plant is the production of hot strip with low thicknesses [1]. Results form an ECSC project [2], dealing with the introduction and optimisation of the new rolling and coiling technology for thin strip production at ThyssenKrupp Stahl are presented. Several series of hot rolling with different mild steels were performed. The strips were produced by two‐step (ferritic) rolling, as well as by austenitic rolling. In both cases direct application and hot‐dip galvanising of the strips were tested. The thinnest strip thickness achievable was 0.8 mm. Industrial trials were also carried out successfully with HSLA and dual phase steels.     

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.     

Ti-IF钢热轧时第二相粒子析出行为研究的最新进展

介绍了有关Ｔｉ－ＩＦ钢热轧时第二相粒子析出行为的一些最新研究成果,内容包括：第二相粒子的种类;第二相粒子在热轧时的析出过程,化学成分和热轧工艺参数对第二相粒子析出行为的影响,今后应着重研究溶度积和析出动力学、尤其是各种析出物之间的相互作用,并寻找定量分析第二相粒子的方法。     

退火温度和平整对冷轧热镀锌双相钢组织和性能的影响

本文在实验室试制了高强度冷轧热镀锌用双相钢,探讨了不同的退火温度和平整工艺对双相钢力学性能和组织的影响规律.研究表明:退火温度在800℃以上时,试制的低硅C-Mn-Cr系双相钢才能得到由铁素体和马氏体组成的性能优良的双相钢.平整工艺显著提高双相钢的屈服强度和屈强比,降低双相钢的延伸率,平整率小于1%时,有利于工业上得到综合性能良好的双相钢.     

Nb对C Si Mn Cr双相钢相变规律、组织和性能的影响

  根据C Si Mn Cr和C Si Mn Cr Nb实验钢的相变规律,在实验室进行了控轧控冷实验研究,分析了微合金元素Nb对高强度热轧双相钢相变规律、组织和性能的影响。实验结果表明,Nb可显著推迟铁素体和珠光体转变,并显著降低铁素体开始转变温度,但对铁素体终止转变温度和贝氏体转变温度区间基本没有影响。经Nb微合金化后,实验钢的屈服强度和抗拉强度增幅均在100 MPa以上,屈服强度的增幅高于抗拉强度,且在强度大幅度升高的同时,伸长率下降并不明显,表明Nb的细晶强化作用对提高中温卷取热轧双相钢强度级别的效果明显。     

Rheological Model for Simulation of Hot rolling of New Generation Steel Strips for Automotive Applications

The main objective of this paper is the development of a rheological model for automotive steels for the conditions of hot strip rolling and implementation of this model in a finite element program is. Three types of steels were investigated, IF, dual phase and TRIP steel. Plastometric tests were performed on a Gleeble 3800 simulator for the temperature range 850‐1200°C and strain rates 3‐150 s^?1. Inverse analysis was applied to eliminate the influence of disturbances occurring in the plastometric tests and to determine the real flow stress of the material. The coefficients in the flow stress equation were evaluated and this equation was implemented in the FEM code as the constitutive law. The model was validated by comparison of measured and calculated loads in the compression tests and by strip rolling experiments conducted in the laboratory mill. Validation confirmed a good predictive capability of the rheological model.     

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.