DTA‐Measurements to Determine the Thixoformability of Steels

Semi‐solid metallurgy (SSM), also known as “thixoforming” or “thixoprocessing”, is of special interest as a new potential manufacturing technology for components in the automobile, machine and electronic industries. The aim of this technology is to produce complex shapes which cannot be produced with conventional processing methods. An important process step of semi‐solid processing (SSP) is the reheating and isothermal holding of the billet within the solid‐liquid range in order to obtain the required fraction liquid content and the desired globular microstructure. Aside from the investigation of billet heating and the development of a suitable tool design, the development and evaluation of adequate microstructures over a wide temperature area is very important. The focus of this paper is to determine the semi‐solid area of different steels through Differential Thermal Analysis (DTA) measurements. To determine a process window for handling the alloys in the semi‐solid state, the DTA‐results can be combined with microstructure parameters. Subsequent quenching experiments show the development of the microstructure parameters (e.g. grain size, phase distribution, volume fraction, shape factor, matrix character, contiguity, and particle density of the primary solid and liquid phases). A comparison of the slopes of the determined solid‐liquid areas for different steels show the width of the melting or freezing intervals to evaluate the possible process windows. DTA‐experiments performed at different heating rates show the influence of faster heating and cooling rates on the solidus‐liquidus interval. To evaluate the suitability for the thixoforming processes, this paper describes, and then compares, the semi‐solid intervals of different steel grades, which have been investigated in the Department of Ferrous Metallurgy at the RWTH Aachen University. The tool steel HS 6‐5‐3 and the cold work tool steel X210CrW12 have a wide semi‐solid area, which can be explained due to the dissolution of different carbides. In contrast to this, the steels C45, 42CrMo4, 16MnCr5, 34CrNiMo4, 100Cr6, X220CrVMo13‐4 and the Alloy 33 show a much smaller semi‐solid area.     

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A 2D temperature model was proposed for heating rules and real-time calculation during heating process on billet reheating furnace, which included furnace temperature calculation along furnace length, billet surface fluxes calculation and conduction calculation inside billet. First, furnace temperature was accomplished according to thermocouple. Then fluxes on the above and below surfaces were calculated by total heat exchange factor method, as well as lateral fluxes. ADI and TDMA algorithms were adopted to calculate billet internal temperature distribution. Validation was carried out by thermocouple experiments and a model system was established in a hot rolling plant to provide appropriate heating rules and real-time temperature prediction. It shows precision and responsibility during reheating furnace production.     

Development of the steel AISI 4145HM for senior petroleum drill of BX Steel

The Steel AISI 4145HM for senior petroleum drill of BX Steel was produced by the follow sheet: hot metal pretreatment→converter→LF→RH→caster 350 mm×470 mm rectangular billet→hot delivery→reheating→800 mill rolling→insulation→straightening→anneal→grinding→inspection→packaging and pay into treasury→shipment.Selected BX Steel particular hor metal,adopted hot metal desulphurization pretreatment technology.The LF refining making the white slag,and keep a certain time.The RH treatment must make sure the vacuum degree and refining time,more importantly controlling argon blowing process.In addition,must design proper technology data continuous casting similar superheat,casting speed,and specific water flow rate.Depend on technological measures,the product been had series of the qualities:homogeneity of chemical composition,low content of harmful elements,high purity,compact organization.Adopted the process of casting billet hot delivery and hot charging,used stepping heating furnace,and designing reasonable thermal parameters.Two -high reversing mill rough rolls preparation square billet,short - stress - path rolling mill rolls round bar.Steel products bad holding and controlling soaking time and temperature. Steel products bad annealed,and annealing process must been controlled for ensuring steel hardness uniform. For avoiding residual stress,steel been straightened before anneal.The test results and using effect shows that the producing with uniform annealing hardness and nice processing properties,nice overall mechanical properties,were recognized by users.     

加热炉不同钢种板坯混装加热制度优化模型的研究与应用

优化大型加热炉混装板坯加热制度的关键在于应用模型计算与实际生产相结合的方法,直接根据钢种、初始温度、目标温度及均热时间确定钢坯入炉顺序、加热炉各段温度控制值、加热时间和钢坯加热过程温度变化情况.在保证加热炉钢坯加热温度的同时,采用合理的钢坯在炉加热时间,有利于降低加热炉燃料消耗和减少钢坯氧化烧损.模型在迁钢公司2 16...     

Numerical simulation of the induction heating of a magnesium-alloy round billet

A mathematical model of the transient electro-thermal coupling of the induction heating of a magnesiumalloy round billet is established herein. The heating curve and temperature distribution characteristics of a magnesium alloy were calculated during induction heating under different parameters. Factors such as the number of coil turns and the cooling conditions were analyzed. A method for optimizing the temperature control mode and coil length of the magnesium-alloy round billet is proposed. The length of the coil and corresponding heating mode are determined through the coil length ratio( CLR),which provides a theoretical basis for the optimization of the magnesium-alloy round billet's extrusion.     

基于可变容差法的步进梁式加热炉炉温设定优化

通过对钢坯在加热炉内的传热过程进行分析,建立钢坯的二维传热模型,并采用有限差分方法对钢坯温度场进行数值模拟。以钢坯出炉温度、出钢温差、加热过程中钢坯断面温差及表面温度等为约束条件,以能耗为目标函数,利用可变容差法求得加热炉各段的最优炉温设定值。运用该模型可方便地求得加热炉各段最优设定值,从而实现加热炉的最优工艺,提高加热炉效率,降低能源消耗,并提高产品质量。     

大方坯轴承钢的加热工艺探讨和优化

针对轴承钢坯料在加热炉加热中存在的问题,通过“黑匣子”（即在钢坯中植入热电偶装置,温度记录仪包在水冷装置内,随钢坯加热后炉外再提取数据）对钢坯实际加热工艺进行了测试,分析测试数据,讨论加热曲线变化趋势,结合现场加热炉实际炉长,对轴承钢的加热工艺进行了优化,改善了带状组织,使碳化物带状级别达到1.0级。     

脉冲式加热炉最优炉温控制

通过建立能量平衡和热传导方程,以板坯加热工艺为基础,针对以往优化算法需要进行全局搜索的不足,提出脉冲式燃烧加热炉最优炉温控制算法,使最优炉温控制可以通过使用有效集算法对目标函数进行求解,无需全局搜索,极大地提升了脉冲式燃烧加热炉炉温控制响应时间。实践表明,计算结果在综合考虑燃料消耗、板坯加热质量与氧化烧损的情况下,取得了理想的效果。     

带钢步进梁式加热炉节能技术的应用

莱风轧钢厂带钢国间采用步进梁式加热炉,在生产中应用了热送热装工艺,降低钢坯加热温度,对助燃空气进行预热,提高加热炉保温性能,采用高铲节能型燃烧器,实现计算机控制烧钢等节能技术,使煤气消耗平均降至１．１ＧＪ／ｔ。     

35CrMnSiA大规格连铸圆坯加热工艺的改进

莱钢特钢事业部新区轧钢系统冷装35CrMnSiA大规格连铸圆坯开坯轧制时出现鸟巢开裂现象,严重影响生产效率及产品质量。为解决该缺陷,进行了现场跟踪、原因分析、理论探讨和加热工艺调整,最终优化35CrMnSiA大规格连铸圆坯冷装加热工艺。降低铸坯的加热速度,延长铸坯在预热段停留时间,通过计算,500mm、650mm冷坯加热时间分别确定为7.5和9h以上,消除了冷装轧制时的鸟巢开裂缺陷。     

步进式加热炉内钢坯温度动态测试

利用“黑匣子”耐热温度数据记录仪，实测和记录了Q235钢在加热炉内加热过程中的温度分布，给出了钢坯加热过程中的上下炉温、钢坯上部、中部和下部的温度值，以及钢坯与水冷梁接触部位的温度值，并绘出了各测量值在钢坯整个加热过程中的变化曲线；分析了钢坯在加热炉内各段的温度分布特点。为数学模型控制、故障诊断、实际生产等方面提供了准确的参考资料。     

半固态A356合金重熔加热时初生相的组织演变

利用低过热度浇注技术制备了半固态A356铝合金坯料,研究了半固态温度区间重熔加热时半固态A356铝合金坯料的初生相形貌的转变过程.结果表明,在半固态两相区保温,半固态A356合金的初生相逐渐团球化,该过程随保温温度的升高而加快.半固态A356铝合金晶粒的圆度与保温温度和保温时间的关系不大,但晶粒的尺寸随着保温温度和保温时间的增加而增大.半固态A356合金试样重熔加热最佳工艺制度为583℃下保温30min,其晶粒平均等积圆直径为80μm,晶粒平均圆度为0.83.     

Phenomenological observations on mechanical and corrosion properties of thixoformed 357 alloys: A comparison with permanent mold cast 357 alloys

In the present study, the mechanical and corrosion properties of thixoformed 357 alloys were examined with different reheating temperatures, and the results were compared with those of permanent mold cast (PMC) 357 alloys. It was found that the thixoforming process significantly improved the mechanical properties (i.e., tensile elongation, impact energy, and resistance to fatigue crack propagation) and the corrosion resistance of 357 alloys. A 380 pct increase in tensile elongation and a 120 pct increase in impact energy were, for example, observed with the thixoforming process of 357 alloy in the T1-tempered condition, as compared to the PMC counterparts. The impact energy was extremely sensitive to reheating temperature due to the coarsening of eutectic Si particles. The resistance to fatigue crack propagation was also much higher for the thixoforming process than the PMC process in the T1-tempered condition. The resistance to both general corrosion and stress corrosion cracking was also greatly improved with thixoforming process. The present observations strongly suggest that the enhancement with thixoforming 357 alloy is largely associated with the size and shape of eutectic Si particles.     

Conversion of induction heating temperature from ANSYS to DEFORM

In the production of hot extrusion pipes,the billet will be heated in an induction furnace,before piercing or extrusion,to a certain temperature.The induction heating temperature field profile in the billet will exert an influence on the deformation processes.The study has developed an data conversion program to convert the temperature data from induction heating by ANSYS to deformation simulation software DEFORM; therefore,not only the relatively accurate temperature field can be made available,compared with the usually assumed uniform temperature field,but also the connection between induction heating and deformation can be established,which is essential to evaluate the processing parameters.Numerical simulation of the piercing processes of different temperature fields by induction heating was carried out,and the results have shown that the different initial temperature fields in the billet can lead to different deformation curves,which indicates that the conversion program is necessary to study the production process of hot extrusion pipes.     

连续加热炉数学模型控制中的炉温决策方法

根据连续加热炉炉温分段可控性和钢温的变化滞后于炉温的变化的特点，提出了一种新的炉温决策方法。该方法以控制段（加热段或均热段）内某处钢坯的平均温度和表面温度与设定值的偏差最小为控制目标，推导炉温决策的计算公式，因考虑了炉温对未来几个控制周期内的钢温的影响，很适合对加热炉动态热工过程的控制。模拟计算表明，该方法具有相当好的控制效果和收敛性。此外，还详细讨论了全炉钢温跟踪模型以及处理钢坯移动速度的两种途     

宽厚板坯双炉加热生产工艺的优化

对宽厚板坯加热过程中,坯料出炉温度波动较大的现象,进行了较详细的分析,找到了解决这一问题的有效途径。通过优化加热炉生产工艺,提高了板坯加热质量,效果显著。     

高碳钢连铸坯加热脱碳的有限元模拟

进行了0.72%C-1.30%MnU71Mn高碳钢250 mm×280 mm×6000 mm连铸坯加热时的传热有限元模拟和通过非线性回归分析,得出钢坯在加热后钢坯脱碳深度d (mm)与加热前脱碳深度d₀ (mm)、钢坯表面温度 T(K)和加热时间 t (min)之间关系的数学模型: d=d₀+(2.132×10^-7T²-0.0002T+0.0163)·(0.208 t^0.5-d₀)。实测结果表明,模型的相对预报误差≤3.2%。根据模型计算得出铸坯的优化工艺为预热段1150℃ 86min,加热段1250℃ 131min,均热段1230℃ 68min。检验结果表明,采用优化工艺,成品脱碳深度可降低20%左右。     

链轮电磁感应加热过程中的优化设计

 电磁感应加热技术有效地节约了钢铁制造成本,积极推动了钢铁行业绿色制造。优化重载链轮电磁感应加热过程是生产高品质链轮的一个重要分支。在对链轮进行热处理强化时,普通圆形感应线圈在单一电流频率下难以实现齿廓的均匀加热,容易导致淬火层的硬度分布不均,造成工件开裂。仿形感应线圈比普通圆形感应线圈具有更好的加热效果,但是仿形感应线圈研发周期长,成本昂贵,不利于大规模推广应用。考虑到实际加工成本及生产需求,在完全仿形感应线圈的基础上,提出了一种齿顶位置为V形角的仿齿廓感应线圈,该感应线圈到齿顶和齿根的间隙不等。进一步建立了双排链轮电-磁-热耦合温度场模型,并进行试验验证。研究发现这种带V形角的感应线圈与圆形感应线圈相比,能够改善磁通量在空间的分布方式,强化感应线圈和齿根之间的临近效应,同时减弱感应线圈和齿顶间的临近效应,提高了链轮沿齿廓温度的均匀性。量化分析了不同电磁参数(电流频率和电流密度)和感应线圈的结构(V形角,感应线圈到齿轮的距离)对提升加热速率和改善温度均匀性的作用规律。感应线圈的V形角结构有利于提高齿轮的电磁加热质量,对推动实际加工应用和提升企业效益具有重要生产价值,有利于促进精品钢生产。     

连铸过程铸坯皮下裂纹的产生及控制

摘要：通过数值模拟的方法研究了典型大方坯（325mm×280mm）连铸过程中温度场和应力场分布,分析了铸坯皮下裂纹产生的原因和主要影响因素,制定了控制铸坯皮下裂纹的具体措施。结果表明：在连铸过程中铸坯的最大回温为121℃,二冷一区最高回热速率达到217.48℃/m,二冷二区最高回热速率达到131.95℃/m,其他各区回热速率都较低。温度回升后铸坯横断面距铸坯表面15~30mm处的最大应力应变值已经超过了钢的极限应力应变值,因此,二冷一区和二区温度回升是铸坯产生皮下裂纹的主要原因。增加二冷一区水量,将此水量在二冷三区和四区相应地减小,可以降低二冷一区回热速率,降低最大回热温度到88℃,控制铸坯皮下裂纹的产生。     

基于目标钢温的加热炉在线动态优化控制

由于鄂城钢铁有限责任公司宽厚板厂步进式加热炉无法很好地适应钢种和实际生产条件的变化,因此造成钢坯出炉温度无法精确满足轧线的要求。针对该问题,本文建立了步进式板坯加热炉数学模型,通过优化计算得到钢坯的理想升温曲线和相应的炉温制度,提出了基于各段目标钢温的在线炉温动态优化控制策略,建立了带有钢温负反馈的在线优化控制系统,实现了对出炉钢温的精准控制,同时达到了一定的节能效果。在实际应用中使开轧温度的命中率提高了12个百分点,吨钢燃料消耗降低了10 m3。