电渣重熔工艺对GH4169脱硫的影响

为进一步降低GH4169中的硫含量,进行了大气下、氩气氛保护及氩气氛保护下向渣池加钙精炼3种工艺条件对脱硫效果影响的电渣重熔试验。结果表明,大气下重熔时脱硫效果明显,硫含量（质量分数,下同）由18×10-6降低到6×10-6,渣中的硫通过气化反应脱除;氩气氛保护不利于电渣重熔工艺的脱硫,硫含量降低到7×10-6后提高到9×10-6,熔渣中的硫不断富集;硫分配比的计算值与实测值的对比研究表明,电渣重熔脱硫热力学条件优越,动力学条件是限制实际脱硫效率进一步提高的主要因素;氩气氛保护下通过向渣池加钙后,熔渣中钙元素能够对合金进行脱硫且脱硫率有较大幅度的提升,合金中硫含量随钙含量的增加而减少,重熔结束时硫含量降至3×10-6。     

Electroslag Remelting Withdrawing Technology for Offshore Jack-up Platform Rack Steel Manufacturing Process

Offshore jack-up platform rack steel must exhibit high strength and toughness as well as excellent welding properties.A high-quality large ingot is a prerequisite for obtaining a high-performance rough part.The electroslag remelting withdrawing(ESRW)technology using a T-shaped mold and bifilar mode was introduced to replace casting technology.Numerical simulation of the ESRW process was performed to determine the distribution of the temperature and velocity fields and to determine the optimum process for producing rack steels.Several A514 Qslab ingots with dimensions of 0.32m×1.40m×4.00 m were produced using ESRW technology in an industrial plant.The industrial test indicated that slab ingots produced by the ESRW method exhibited uniform chemical compositions and compact macrostructures.A 115.4mm thick plate was produced from the rough ingot after 11 rolling passes.Samples were obtained from different positions in the steel plate to test the mechanical performance and examine the microstructure,and the results revealed that the properties of the steel plate satisfied ASTM standards.The ESRW process improved the tensile strength and toughness of the slab ingot,enabling significant improvements in the anisotropy and low temperature toughness,which are critical for the development of rack steel for offshore platforms.     

The Cellular Automata Model of Electroslag Remelting Ingot Structure

Electroslag remelting (ESR) is an advanced process for the production of high quality steels. The microstructure of remelted steel which affect the mechanical properties and the performance of the ingot was determined by the technological parameters. A two-dimensional axisymmetric geometry which was established in this paper was divided into macro-grid finite element in order to compute temperature field; then the grid was divided into more detailed and uniform cells, and at last the continuous nucleation model based on the Gaussian distribution and KGT growth model was established for nucleation and growth calculations using cellular automaton method (CA) on the solidification of molten steel. The results show that: a vertical columnar grain zone and a inverted V-shaped columnar crystal zone appeared in the ESR ingot. In addition, the temperature field with different electrode melting rate and slag pool temperature parameters and the microstructure with different average nucleation under cooling and maximum grain density were studied in this paper. The simulation results agree well with the experimental results, so it is proved that the model and calculation method is reliable. To produce ideal solidified ingot and achieve the purpose of optimizing the production process, the production process was adjusted according to the simulation results.     

电渣重熔高氮钢技术的进展

 高氮钢,尤其是高氮不锈钢,由于其优异的性能和诱人的应用前景受到国内外钢铁材料界的广泛关注。在理论计算分析氮在钢中溶解行为的基础上,指出了高氮钢制备的主要技术难点;概述了目前高氮钢的主要制备方法,重点讨论了常压和高压电渣重熔高氮钢的特点和存在的问题;分析了用电弧渣重熔(ASR)法生产高氮钢的技术优势,认为用ASR法生产高氮钢是目前比较可行的方案。     

Segregation of Niobium During Electroslag Remelting Process

 Experiment was carried out after the process parameters were calculated by the model previously established. The relationship between interdendritic spacing and local solidification time (LST) mainly determined by process parameters was exposed. Furthermore, the extent of segregation was studied. The results indicate that LST and interdendritic spacing are the largest and the amount of Laves phase as a result of the niobium segregation is the highest in the center of the ingot, whereas the opposite results are obtained at the edge of ingot. The extent of element segregation and the amount of Laves phase can be reduced when appropriate parameters are used. Therefore, the duration of subsequent homogenization treatments for 718 is shortened and the alloy quality is improved.     

电渣重熔H13钢中一次碳化物形成机制

 H13热作模具钢在电渣重熔过程中会在凝固末端形成粗大的碳化物及氮化物,由于生成温度高,热稳定性好,会保留到最终热处理状态,对钢材的性能产生严重影响。应用偏析模型计算并说明了凝固过程生成粗大的共晶碳化物和氮化物的可能,当固相率达到0.82时由残余液相生成TiN,随着温度进一步下降在接近凝固终点时生成VC0.88,由于碳化物中固溶了其他合金元素,认为生成的VC0.88的活度不为1,试验检测的碳化物合金元素含量与理论假设基本吻合。对粗大的碳氮化物的特点及细化减少碳化物进行简单讨论。     

Assessment of Oxygen Control and Its Effect on Inclusion Characteristics during Electroslag Remelting of Die Steel

Deoxidation during electroslag remelting of S136 die steel was experimentally studied. The characteristics of inclusions in the electrode and ESR ingots were determined by image analyzer and SEM‐EDS. The results show that the oxygen content can be reduced from 89 ppm in the electrode to the lowest (12 ppm) in the ingot only when protective Ar gas remelting in combination with specially designed slag deoxidation treatment were employed simultaneously. The proportion of the oxygen combined as oxide inclusions increases with decreasing the total oxygen content in ESR ingot. The original inclusions in the electrode are mainly large (Mn,Cr)S and the large inclusions in the form of Al₂O₃ core surrounded by an outer sulfide layer, besides a few pure Al₂O₃ inclusions. After ESR process, while only pure Al₂O₃ inclusions with the size of about 1 µm were observed in ESR ingots. The large inclusions in the electrode were removed during ESR process. With higher oxygen content in the ingot, the contents of inclusions and large inclusions would be relatively higher. The results from industrial experiments have confirmed the availability of the present oxygen control technique. The mechanisms of oxygen behavior and control as well as inclusion evolution during ESR process were proposed based on experimental results along with thermodynamic analysis.     

Effect of Low-Frequency AC Power Supply During Electroslag Remelting on Qualities of Alloy Steel

The effect of frequencies of AC power supply on the quality of the electroslag-melted ingot is studied. The results show that with a decrease in the frequency, electromagnetic force becomes more violent, and the temperature in the slag bath becomes more homogeneous, and therefore, the depth of molten metal pool is decreased; electrochemical reactions occur with the decrease in the frequency, and the atomic oxygen electrolyzed dissolves in the molten metal pool; the nonmetallic inclusions, which are distributed dispersively in the ingot, have an increased content,and their size is approximately in the range of 2-3 μm.     

Modeling of Microstructure Evolution in 22MnB5 Steel during Hot Stamping简

Automobile manufacturers have been inereasingl~r adopting hot-stamped parts for use in newly designed ve- hicles to improve crash worthiness and fuel efficiency. However, the simulation of hot stamping is rather complex and challenging, and further research still needs to be done on hot stamping hardening mechanism. The microstruc- ture evolution and hardening mechanisms during hot stamping of 22MnB5 steel were thoroughly investigated, using information provided in the literatures as well as experimental results. New models were developed to predict the grain growth during heating and the flow stress of a manganese boron steel （22MnB5） with high hardenability by the Gleeble simulation experimental results. The deformed austenite decomposition during stamping and quenching was emphatically quantified based on the transformation thermodynamic and kinetic theories, and the relationship of mi- crostructure to properties was analyzed. The results showed that the optimal process to obtain homogeneous and small lath martensite is heating at 900--950 ℃ for 5 min and then auenching at 50 ℃/s with a Dressing time about 8 s.     

Microstructure Evolution and Microhardness of Ultrafine-grained High Carbon Steel during Multiple Laser Shock Processing

Surface microstructure and microhardness of(ferrite+cementite)microduplex structure of the ultrafinegrained high carbon steel after laser shock processing(LSP)with different impact times were investigated by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and microhardness measurements.Equiaxed ferrite grains were refined from 400 to 150nm,and the cementite lamellae were fully spheroidized,with a decrease of the particle diameter from 150 to 100nm as the impact times increased.The cementite dissolution was enhanced significantly.Correspondingly,the lattice parameter ofα-Fe and microhardness increased with the impact times.     

Microstructure Evolution and Mechanical Properties of HR3C Steel during Long-term Aging at High Temperature

Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase and a trace amount of Nb(C,N).The M23C6 carbides were distributed mainly at the grain boundary,while Z-phase was mainly inside the grains.Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature.Coarsening of M23C6 carbides was influenced significantly by aging time and temperature,while the size of the Z-phase was relatively less affected by the aging time and temperature,which had a steady strengthening effect.Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750℃.The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.     

Effect of Slab Subsurface Microstructure Evolution on Transverse Cracking of Microalloyed Steel during Continuous Casting

As to the continuous casting process of low carbon microalloyed steel, subsurface microstructure evolution plays an important role in the slab surface cracking. In order to study the effect of the slab subsurface microstructure evolution on the transverse cracking, three different secondary cooling patterns （i. e. , mild cooling, strong cooling and controlled cooling） were performed in the corresponding slab curved continuous caster. Based on the metallo- graphic results, three transformation regions were found to be formed with the evolution of microstructures at different depths in the slab subsurface. The three regions are strong cooling transformation （SCT） region, double phase transformation （DPT） region and mild cooling transformation （MCT） region, respectively. Meanwhile, it was also found that the crack index used for evaluating slab surface cracking susceptibility was decreased when the range of the DPT region was increased. This can be explained by the fact that the double phase transformation （austenite-ferrite-austenite） occurred resulting from thermal cycling in DPT region, which resulted in promoting the refinement of prior austenite grains and inhibiting the precipitation of film-like ferrite and chain-like precipitates. Under the con- trolled cooling pattern, the widely-distributed DPT region was formed in the range of 3.5--8.0 mm to the slab surface. And compared with other cooling patterns, the cracking susceptibility is lowest with a crack index of 0.4.     

Improvement of Impact Toughness and Creep Properties in Reduced Activation Ferritic Steels by Consumable Electrode Remelting

 The effect of smelting processes on mechanical properties and microstructure of reduced activation ferritic steels was studied. Creep properties and impact toughness of reduced activation ferritic steels were obviously improved by vacuum induction melting followed by consumable electrode remelting process in comparison with the conventional vacuum induction melting process. The difference of impact toughness and creep properties between both steels mainly depended on the aspect ratio and mean size of precipitates. Decreasing the aspect ratio of carbides makes development of a shear band more difficult, which could increase impact energy and creep resistance.     

气体保护电渣重熔过程氧传递的动力学研究

基于渗透理论建立了气体保护电渣重熔过程渣-钢间氧传递的动力学模型,并在50 kg电渣炉进行模具钢S136(/%:0.39C、0.26Si、0.43Mn、0.020P、0.018S、13.37Cr、0.21Mo、0.34V)的重熔实验,得出渣中FeO含量-0～2.0%(FeO),电极端部钢液中原始氧含量-0～0.010 0%[O],自耗电极半径-40～300 mm和重熔速率-(0.5～5.0)×10^-6 m³/s对熔渣和钢液间传氧速率的影响。结果表明,熔渣中FeO含量-(FeO)存在一个临界值,(FeO)小于此临界值时,氧的传递过程为电极端部钢液向渣中传递;反之,氧的传递过程为渣中FeO向电极端部钢液内传递。随自耗电极半径的增加,钢-渣间传氧速率减小;随着重熔速率和钢液中原始氧含量增加,钢-渣间传氧速率增加。