Oxidation of low carbon steel in multicomponent gases: Part I. Reaction mechanisms during isothermal oxidation

The article describes rates of oxidation of low carbon steel in various nitrogen-based atmospheres of O₂, CO₂, and H₂O in the temperature range 800 °C to 1150 °C. In characterizing the oxidation process, the weight gains of the samples per unit surface area vs time data were analyzed. Reaction rates during oxidation in the binary atmospheres of CO₂-N₂ and H₂O-N₂ followed a linear rate law and were found to be proportional to the partial pressures of CO₂ or H₂O. These rates were controlled by rate of reactions at the oxide surface and were highly dependent on oxidation temperature. The activation energies of the phase boundary reactions obtained were approximately 274 and 264 kJ/mole, for oxidation in CO₂ and H₂O atmospheres, respectively. Oxidation in gases containing free oxygen showed that the main oxidizing agent was the free oxygen and that additions of CO₂ and H₂O had little effect on the magnitude of the initial oxidation rates. Experiments for oxidation in multicomponent gases showed that the overall oxidation rates were the additions of rates resulting from oxidation with the individual gaseous species O₂, CO₂, and H₂O. Oxidation in these atmospheres exhibited an initial linear rate law which gradually transformed into a parabolic. Examination of scale microstructure after 1 hour of oxidation showed that, for oxidation in carbon dioxide and water vapor atmospheres, only wustite was present, while in atmospheres containing free oxygen, all three iron oxides, wustite, magnetite, and hematite, were present.     

A study on oxide scale formation of low carbon steel using thermo gravimetric technique

Abstract

The aim of this paper was to investigate the effect of oxygen content and temperature on the formation of oxide scales of four different steel grades. Thermo gravimetric experiments were carried out. Small samples of low carbon steels with different compositions were exposed to a gas containing a certain amount of oxygen and at temperatures in the range of 1373–1623 K. The mass gain of the steel sample was recorded. On the basis of the oxidation curves, the parabolic rate constants were reported. Post-experimental investigation of the samples was performed using scanning electron microscope and light optical microscope techniques. The results were compared with the scanning electron microscopy graphs of the steel samples taken from the real industrial reheating furnace.     

Kinetic studies on surface segregation of manganese during annealing of low-carbon steel

Surface segregation of manganese, an example of a selective oxidation process, occurs at annealing temperatures when low-carbon steel is in contact with typical commercial protective atmospheres. Laboratory kinetic studies show that the enrichment process follows a parabolic rate law, that the rate constant in the low range of oxygen potential for the annealing atmosphere increases linearly with oxygen potential, and that although higher rates apply for relatively high-manganese steels than for relatively low-manganese steels, the same surface-reaction mechanism applies. A rate expression was developed that implicitly includes oxygen potential and free manganese (uncombined, in solid solution) content in the steel.     

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。     

高效蓄热式烧嘴在二段式轧钢加热炉上应用的可行性研究

介绍了高效蓄热室技术的特点及技术关键。通过对大型厂现有二段式加热炉的分析,论述了高效蓄热式烧嘴在二段式加热炉上应用的可行性,并分析了其经济效益和社会效益。     

The Influence of Oxide Scale on Heat Transfer during Reheating of Steel

The present work presents methodology and development of a mathematical model for prediction of the influence of oxide scale on heat transfer during reheating of steel in an industrial furnace. In this developed model, temperatures inside the steel billet were measured and with thermocouples at selected places and were collected by a water cooled computer that was traveling inside the slab. CFD is used to calculate the flow field inside of a furnace. The mass‐transfer coefficient of the scale formation is obtained by solving the convection mass‐diffusion equation across a boundary layer to the surface of a flat plate. A model for inverse heat conduction is employed to calculate the local surface temperature and heat flux on top of the growing oxide scale layer on a slab moving through a walking beam reheating furnace. By using the inverse method, the transient temperature and heat flux was firstly determined on the surface of the steel. During subsequent computations, the growth of the scale was calculated and the surface temperature of the oxide scale was extracted by using the Cauchy data from the previous calculations. The sensibility of the model on steel physical parameters is studied, and suitable parameters were obtained for heating a low carbon steel plate in the reheating furnace. Results show that the oxide scale layer should not be neglected in reheating models.     

Nonintrusive Uncertainty Quantification in the Simulation of Steel Reheating Using Polynomial Chaos Expansion

Uncertainty quantification (UQ) is deemed critical in steel reheating simulations due to the significant input uncertainties arising when defining steel surface properties and atmospheric furnace conditions. In order to conduct UQ, the study utilizes polynomial chaos expansion, which has been found to significantly curtail the computational effort needed to obtain reliable convergent statistics for the model of interest. Results from a comprehensive UQ analysis of a walking-beam reheat furnace simulated using Tata Steel's reheat furnace control model, online slab temperature calculation, are presented. Slab temperature evolution and oxide scale growth are chosen as the study's QoIs. The analysis reveals that at the earlier stages of reheating, the majority of the output variance in slab temperature can be traced back exclusively to the emissivity of the slab surface, and the majority of the output variance in oxide scale growth is traced back to the combination of slab's surface emissivity and the initial scale thickness found on steel products prior to reheating. However, as the steel product advances toward the furnace's discharge end, inputs related to oxide scale growth become increasingly important, ultimately becoming the most influential input parameters, although the dynamics of this transition differ between the QoIs.     

轧钢加热炉燃烧智能控制技术实践及节能减排分析

针对缺少煤气热值和废气氧含量在线检测,加热炉燃烧控制系统不能投入全自动的状况,采用模糊控制与专家系统结合对加热炉燃控系统智能化改造,使得加热炉燃烧控制得以优化,实现加热炉加热过程全自动控制,提高钢坯加热质量、降低氧化烧损、节约能源、减少碳排放。     

Present development of rolling reheating furnace technology in Shougang

By analyzing recent development of reheating furnace in Shougang,the direction of rolling reheating furnace is large type,high efficiency,lower pollution and automation etc.Many advanced technologies are integrated in new rolling reheating furnace such as working beam,regenerative combustion,evaporation cooling and hot loading and hot feeding etc.It shows that reheating furnace technology is upgraded.During the process of product structure adjustment in Shougang,because product heating quality is improved,energy-saving of reheating furnace should pay attention to aspects such as energy-saving of heating variety steel,equality of heating steel,heating system,oxidation loss and so on.This will offer reference for energy-saving of domestic and overseas reheating furnace technology.     

Estimation of the Transient Surface Temperature,Heat Flux and Effective Heat Transfer Coefficient of a Slab in an Industrial Reheating Furnace by using an Inverse Method

In the steel industry it is of great importance to be able to control the surface temperature and heating or cooling rates during heat treatment processes. In this paper, a steel slab is heated up to 1300°C in an industrial reheating furnace and the temperature data are recorded during the reheating process. The transient local surface temperature, heat flux and effective heat transfer coefficient of the steel slab ares calculated using a model for inverse heat conduction. The calculated surface temperatures are compared with the temperatures achieved by using a model of the heating process with the help of the software STEELTEMP® 2D. The results obtained show very good agreement and suggest that the inverse method can be applied to similar high temperature applications with very good accuracy.     

送装工艺对板坯再加热过程奥氏体晶粒细化的影响

连铸坯下线至加热炉的温度制度及其表层组织演变与热送或粗轧裂纹密切相关.基于热模拟实验分析了送装工艺对奥氏体转变特征和再加热晶粒尺寸的影响.高温共聚焦激光扫描显微镜原位观察表明，含Nb J55钢在双相区700℃热装时，组织为晶界膜状先共析铁素体、魏氏体和大量残留奥氏体，再加热至1200℃，奥氏体晶粒大小、位置都不变；单相区600℃温装时，组织为大量铁素体+珠光体，再加热至1200℃时，奥氏体晶粒明显细化.马弗炉模拟SS400钢双相区不同热装温度发现，铁素体转变量至少达70%时才可细化再加热后的奥氏体晶粒.在临界转变量以上，基体中铁素体转变量越多晶粒细化程度越明显.      

The oxidation resistance of fine-grained sputter-deposited 304 stainless steel

The air oxidation of free standing 0.1 cm thick sputter-deposited and wrought 304 stainless steel specimens was studied and the long term oxidation weight gains of the sputterdeposited material were much less than weight gains for the wrought material at 800, 900, and 1000°C. The amount of scaling was also much less on the sputtered material and a thin, adherent oxide formed. The oxide on the sputtered material was more uniform in composition and was higher in chromium and manganese compared to oxide on wrought stainless and eventually formed MnCr₂O₄ after long periods of exposure. No stratified oxide layers, as typically observed in wrought stainless steel, formed on the fine-grained sputtered material. The improved scaling resistance of the sputter-deposited steel was attributed to a combination of grain boundary enhancement of chromium diffusion, reduced stresses in the oxide and mechanical keying of the oxide to closely spaced grain boundaries. The stability of grain size for the sputtered material (grain size ≤ 6 μm) also contributed to the better oxide adherence.     

Tempering of Martensite in Dual-Phase Steels and Its Effects on Softening Behavior

The isothermal and nonisothermal tempering of martensite in dual-phase (DP) steels was investigated mainly by analytical transmission electron microscopy, and the effect on softening behavior was studied. The isothermal tempering resulted in coarsening and spheroidization of cementite and complete recovery of laths. However, nonisothermal tempering manifested fine quasi-spherical intralath and platelike interlath cementite, decomposition of retained austenite, and partial recovery of laths. The distinct characteristic of nonisothermal tempering was primarily attributed to the synergistic effect of delay in cementite precipitation and insufficient time for diffusion of carbon due to rapid heating that delays the third stage of tempering. The finer size and platelike morphology of cementite coupled with partial recovery of lath resulted in reduced softening in nonisothermal tempering compared to severe softening in isothermal tempering due to large spheroidized cementite and complete recovery of lath substructure. The substitutional content of precipitated cementite in nonisothermal tempering was correlated to the richness of particular steel chemistry. Softening resistance during nonisothermal tempering was related to DP steel chemistry, i.e., Cr and Mn content. Fine cementite and less decomposed martensite in rich chemistry confer high resistance to softening compared to leaner chemistries, which indicated severe decomposition of martensite with coarser cementite.     

加热炉工作性能研究与优化

从不同角度对加热工作性能进行了描述，对实验的数据，结果进行了理论分析，提出了减少氧化烧损，降低炉子单耗，提高加热质量的一系列具体措施。     

Study on the surface cracking in hot-rolled plates of Fe-23Mn-2Al-V austenitic steel

The study introduces the chemical composition,mechanical properties,physical properties and production processes of the Fe-23Mn-2Al-V austenitic steel.Investigations were made into the formation of cracks in the hot-rolled Fe-23Mn-2Al-V steel plates,with optical microscopy(OM),scanning electron microscopy(SEM)and energy dispersive spectrum(EDS).The results have shown that intergranular oxidation in the reheating fumace is the main cause of the cracks on the surface of the hot-rolled steel plates.The surface cracking can be largely avoided by controlling the remaining oxygen content in the reheating furnace and improving continuous casting(CC)processes to increase the thickness of fine equiaxed grain layer of the steel slabs.     

加热炉内钢坯非稳态温度场模拟及“黑匣子”实验研究

采用数值模拟方法,以能量平衡和热传导方程为基础,通过分析加热炉内的传热过程,按照加热工艺要求,采用总括热吸收率法,建立了加热炉热工过程数学模型。并以普碳钢为实验钢种,合理设置测试点,完成了＂黑匣子＂实验,模拟结果与实验结果吻合较好。钢坯柱坐标下非稳态温度场的模拟是准确合理的,所建立的数学模型可以作为加热炉在线控制中钢坯温度场的动态实时跟踪计算和SCC决策的基础。     

轧钢加热炉上应用富氧燃烧的试验研究与技术分析

通过工业试验研究表明,富氧燃烧对加热炉生产有提高产量,节约能源,降低成本的作用,特别是加热炉加热能力不够又有丰富的氧气资源的企业,可以取得较好的效果.     

DC06 IF钢精炼渣成分优化及钢 渣中氧的控制

摘要：无间隙原子钢（IF钢）对含铝夹杂物要求极为严格。为冶炼洁净IF钢,采用热力学软件FactSage 7.0对IF钢精炼渣系做了优化计算,并采取6组工业实验做验证,根据结果提出改进措施。实验中采取氧传感器、碳硫分析仪及ICP AES对钢和渣成分进行检测,并通过ASPEX自动扫描电子显微镜检测钢中夹杂物成分与数量。热力学计算及实验研究发现,转炉脱碳结束时钢液中碳质量分数宜控制在0.04%,转炉渣中FeO质量分数控制在149%以内,降低钢中［O］质量分数到470×10-6。精炼时控制补吹氧炉次比在64%以下,补吹量在17m3内,精炼渣中SiO2、MgO及TFe质量分数分别控制在6%~8%、6%和5%~10%,钙铝比控制在1.4~1.6时,钢中［O］质量分数可控制在10×10-6,且该精炼渣系对Al2O3有较好的吸附性。在确保精炼脱氧的同时,降低钢液二次氧化,达到IF钢洁净冶炼目的。     

Formation of Edge Crack in 1.4%Si Non-oriented Electrical Steel during Hot Rolling简

Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 1.4 % Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were found to be coarse as-cast microstructure, grain boundary oxidation in reheating furnace, lack of dynamic recrystallization during hot rolling and increase of temperature, resulting in reduced hot ductility in strip edge region. Countermeas- ures against the edge crack are proposed accordingly. Lowering reheating temperature and reducing holding time re- duced oxidation and decarburization. Hot charging temperature was increased to decrease reheating temperature. And using an edger can refine microstructure in strip edge region. Finally, edge heater can be added to increase edge re- gion formability by inducing dynamic reerystallization and ductility by increasing temperature.     

莱钢钢坯防氧化的研究与应用

在实验室内研究钢坯高温防氧化机制和高温下腐蚀防护原理。把喷涂的小试样和正常的热送钢坯一起放进加热炉,通过系统分析钢坯从连铸到加热炉过程中的温度变化、钢坯表面变化,特别是氧化情况调查分析,研究莱钢钢坯防氧化配方以及在钢坯上实施喷涂的方法,以减少钢坯在加热炉中烧损,提高钢坯的成材率。确定了防氧化涂料的配方并进行试验,试验中喷涂钢坯未对轧制制度产生影响,减少了钢坯的表面氧化,提高了钢材的表面质量。