Behaviour of Hydrogen in Industrial Scale Steel Melts

The behaviour of hydrogen during controlled industrial scale secondary steel making process has been examined in a variety of low alloy steels, sensitive to hydrogen flaking. The study examines the role played by the moisture in input raw materials such as the ferro-alloys, type of carbon additive and fluxes in enhancing the hydrogen content in the ladle furnace. Post alloying, the influence of vacuum degassing parameters such as the vacuum level, vacuum holding time, Ar flow rate, type of porous plug used, slag chemistry and the steel grade was examined. The vacuum degassing process was analysed using a kinetic model, which could justify the trends seen in the vacuum level, holding time and Ar gas flow rate. Finally, the hydrogen pick-up post vacuum degassing through slag cover and the casting tundish was found to be influenced by parameters such as the quality of the tundish spray mass, and casting sequence. The influence of steel grade in hydrogen removal was also examined.     

Removal of hydrogen in the vacuum treatment of steel

The degassing of 09Г2C steel produced in an arc furnace and treated in a ladle–furnace unit at AO Uralskaya Stal is analyzed. The vacuum-treatment parameters that determine the effectiveness of hydrogen removal from the steel are identified: the depth and duration of vacuum treatment; the argon flow rate; the steel temperature; the thickness of the slag layer; and the free board in the vacuum chamber. The hydrogen content changes most significantly when the degassing time is increased to 20 min. Longer treatment is not recommended. The greatest effect of the residual pressure in degassing is observed with simultaneous decrease in the minimum pressure to 2 mbar. Vacuum treatment of the steel is considerably impaired with increase in the residual pressure. Hydrogen removal is improved with increase in the steel temperature to 1600–1620°C, but slows considerably at higher temperatures. The influence of the vacuum-treatment parameters is established quantitatively, and a regression equation is derived for predicting the results of hydrogen removal and selecting the parameter values corresponding to specified hydrogen content in the steel. Vacuum-treatment parameters that permit the economical production of steel with 2.1 ppm are determined: steel heating before vacuum treatment by 100–110°C; vacuum treatment for 20 min at a pressure no higher than 1.5 mbar in the vacuum chamber; argon flow rate 0.05 m³/t. The temperature losses of the metal are determined by the total treatment time, consisting of the active degassing time and the auxiliary time (the preliminary evacuation time), which depends on the capabilities of the equipment and the organization of the process. The minimum residual hydrogen content in the steel for the given equipment (1.6 ppm) is ensured by vacuum treatment for 40 min at a pressure no higher than 1 mbar in the vacuum chamber, with preliminary heating of the steel by 120–125 °C and with an argon flow rate up to 0.072 m³/t.     

影响钢中氢含量的原因分析

分析影响经真空脱气处理后钢液中氢含量的因素，提出稳定控制钢中氢含量在较低水平的试验结果和措施。     

Change of Inclusion Characteristics during Vacuum Degassing of Tool Steel

The inclusion characteristics were studied during vacuum degassing by interrupting the operation at five different times after the start of operation. Slag and steel samples were collected and thereafter assessed with respect to steel and slag composition, total oxygen content, size distribution of inclusions and chemical composition of inclusions. The main conclusion is that the number of inclusions in the different size classes as well as the total oxygen content seem to reach a minimum value after around ten minutes of vacuum degassing. Furthermore, it seems to be a consistent trend that, during vacuum degassing, the top slag influences the inclusion composition.     

Current trends in the production of railroad wheels and the effect of out-of-furnace treatment of the steel on their properties

Current trends in the production of railroad wheels show the use of some promising techniques: a reduction in the carbon content of the finished steel; degassing the steel in a vacuum to decrease its hydrogen content; more efficient deoxidation and alloying of the steel. When used together, these measures are ensuring that the finished steel has the mechanical and service properties prescribed for wheel steel. Studies and factory testing of a new technology for making wheel steel have shown that the oxygen content of the steel can be reduced by its self-deoxidation during vacuum degassing. This approach also helps lower the steel’s hydrogen content while saving deoxidizers. Researchers have discovered certain laws that govern the relationship between the characteristics of wheel steel and its contents of sulfur and gases. The amount of sulfur and gases in this type of steel can be reduced by using efficient parameters for the treatment that is administered outside the steelmaking furnace. __________ Translated from Metallurg, No. 8, pp. 56–60, August, 2006.     

衡管40tVD精炼工艺实践

总结了衡阳钢管厂40tVD的精炼生产实践和精炼效果,从理论上分析了真空处理时间、氩气搅拌流量、钢中氧和硫的含量等对真空脱气、脱氮的影响.同时分析了真空精炼对钢液脱氧及夹杂物控制的影响.结果表明,衡管40tVD炉精炼具有良好的冶金效果.     

100t VD精炼脱气工艺实践

总结了安阳钢铁集团有限责任公司第一炼轧厂100tVD装置在热调试和试生产期间的精炼工艺实践及精炼效果,分析了真空处理时间、氩气搅拌流量、渣量、钢中硫和氧含量等对真空脱氢、脱氮的影响。同时分析了真空精炼对钢液脱氧及夹杂物控制的影响。     

Numerical Simulation of Dehydrogenation of Liquid Steel in the Vacuum Tank Degasser

Vacuum tank degassers are often utilized to remove hydrogen from liquid steel. A new comprehensive numerical model, which has been developed to simulate hydrogen removal in the vacuum degassers, is presented in this paper. The degassing model consists of two sub-models, which calculate the gas-steel flow field and the species transport of hydrogen. An extended k–ε turbulence model is adopted to consider the effect of gas injection on the turbulent properties and an interfacial area concentration model is introduced to compute the interfacial area density between liquid steel and the bubbles. The fluid dynamic sub-model is validated with a physical gas stirred tank, which is believed to have similar flow phenomena as the studied vacuum degasser based on the modified Froude number. Two fundamental expressions for mass transfer coefficient, which have been paid little attention by the researchers concentrating on vacuum degassing, are evaluated with a simulation case corresponding to practical operation. The effect of vacuum pressure on the dehydrogenation process is investigated and, moreover, the integrated model is verified with industrial measurements. The predicted final hydrogen contents in liquid steel show good agreement with the measured ones. The model and the main results are presented.     

天津钢管公司100t RH的设备功能和冶金效果

国内自行设计制造的100 t RH真空循环脱气设备的真空度可达67 Pa以下,真空处理能力为500kg/h以上。生产实践表明,氩气流量越大,钢水循环速度越大,高真空脱气时间越长,钢水脱气效果越明显,所处理的管线钢的氢、氧、碳含量可分别降至1×10^-6、20×10^-6和20×10^-6以下。     

降低重轨钢的氢含量

研究重轨钢中氢的来源及控制手段.分析表明,钢水增氢主要是外加材料,尤其是增碳剂带入的水分所引起的.通过控制各工序加入材料的水分,有利于减少重轨钢中的氢含量.通过VD真空脱气处理,能有效地脱去钢液中的氢.     

武钢重轨生产中取消缓冷工艺的探讨

介绍了武钢冶炼重轨钢经过真空脱气后氢含量控制以及钢轨热锯取样白点检验和性能对比情况，借鉴国外钢厂的经验提出了将武钢重轨除氢工艺从成品轨在缓冷坑除氢前移到低氢冶炼和钢水真空处理，并实行连铸坯热堆垛缓冷的工艺路线。     

Hydrogen pick-up after vacuum degassing

Abstract

The present work aimed at determining the major source for hydrogen pick-up of the steel after vacuum degassing but before casting. Samples of slag and metal were taken at different stages during ladle treatment at SSAB. Hydrogen increase after vacuum treatment was observed. Moisture contents of the industrial slags were analysed and their water capacities were calculated. It could be seen that the hydrogen increase was correlated to the amount of moisture in the slag and the water capacity. The study showed that the slag containing most water was also the heat having the largest hydrogen increase. The slag with most water had the highest water capacity. It could be concluded that the major source for hydrogen increase after degassing was due to the slag–metal reaction.     

Effect of Top Slag Composition on Inclusion Characteristics during Vacuum Degassing of Tool Steel

The focus of the study was to investigate the effect of the chemical composition of the top slag on the inclusion chemical composition during vacuum treatment of a plastic mould tool steel. Sampling was done before and after vacuum degassing. The chemical composition of the inclusions was determined by using SEM combined with EDX. The results showed that several inclusion compositions were found before vacuum degassing, while only one main composition of inclusions was present after vacuum degassing. Furthermore, the composition of the top slag was found to have a great influence on the composition of the inclusions found in samples taken after vacuum degassing. The present study also shows that the vacuum degassing effectively reduces the number of inclusions in steel. Finally, the thermodynamic calculations of the activities using Wagner's equation were found to predict a lower oxygen activity value than the calculations made using the Thermo‐Calc software.     

超纯轴承钢的精炼工艺

通过控制电炉(供氧强度、渣中氧化铁比例、出钢挡渣率、出钢钢液的氧活度)、钢包炉(精炼渣系、脱氧剂、钢液温度、精炼时间、底吹氩压力、精炼钢包耐火材料的选择、铁合金种类的选择)、真空脱气(真空度、真空时间、底吹氩压力)的工艺参数以及真空后的软吹氩搅拌、并采用IPAS系统和控制钢液浇铸速度,使超纯轴承钢(SFGCr15)的w(S)、w(Ti)、w(O)分别达到0.003%、0.001 2%和0.000 7%以下,钢中非金属夹杂物也处于较好水平,满足了国际顶尖轴承厂家对轴承钢的超纯要求.     

RH真空精炼过程的动态模拟

建立了描述RH真空精炼装置内钢液动态脱碳（脱气）模型。对RH真空精炼时的脱碳、脱氧、脱氮和脱氢过程进行了动态模拟研究，考察了浸渍管直径、循环流量、吹氩量、氧含量和真空度对脱碳和脱气过程的影响。动态脱碳（脱气）模型考虑了反应机理，认为脱碳是通过上升管中Ar气泡表面、真空室中钢液的自由表面和真空室钢液内部脱碳反应生成的CO气泡表面进行的，并且考虑了精炼处理时的抽真空制度。该模型能全面描述RH精炼过程中不同时刻钢液中碳、氧、氮和氢的含量，能较好预测实际过程，可用于RH真空精炼过程的优化和新工艺开发。     

钢水脱气用机械真空泵的最新发展

 对比了钢水脱气工艺使用的干式机械真空泵和蒸汽喷射泵的特点,结果表明,干式机械真空泵在脱气的质量以及泵和配套的除尘系统、气体冷却系统的可靠性方面有明显优势;标准化真空泵可以使制造成本相对更低,标准化的预组装模块式系统不仅在安装和调试方面降低了成本,而且结构更为紧凑,更加节能、节水。     

Technology for out-of-furnace treatment of steel with the use of a new deoxidizer

A technology has been proposed for obtaining rolled plates with the use of calcium carbide instead of vacuum degassing. The technology makes it possible to obtain steel that is equivalent to vacuum-degassed steel with respect to the composition and quantity of nonmetallic inclusions and the quality of the finished plates. It is shown that the use of calcium carbide reduces the content of nonmetallic inclusions by a factor of roughly 1.5 compared to use of the standard technology without vacuum degassing. The percentage of hot-rolled plates rejected for defects detected in ultrasonic tests is also decreased.     

Degassing of pipe steels under the conditions of KKTs OAO MMK

The relations for the determination of the required hydrogen content under various conditions are determined. The required parameters of steel degassing are found to achieve the optimum hydrogen content.     

气泡搅拌和炉渣成分对低碳钢水洁净度的影响

在80t氧气转炉、钢包吹氩和RH真空处理工序进行净化钢水的试验,考察反应器内氩气流量、真空脱气操作和顶渣成分对低碳钢水全氧含量的影响以及夹杂物的尺寸分布和全氧的排除速率,改进操作的结果表明,二次精炼后低碳钢水全氧w[T.O]降低到0.001%。     

Behaviors of Denitrogenation in RH-MFB

 According to the analysis related to kinetic mechanism of vacuum denitrogenation and combining with the actual production of RH-MFB (a combination of Ruhstahl-Hausen vacuum degassing process with a multifunctional oxygen lance) at Liansteel, the limit step and model equation of vacuum denitrogenation are determined. Meanwhile, the influencing factors of nitrogen removal from liquid steel in vacuum of RH-MFB are analyzed. The results show that the limit step of vacuum denitrogenation in RH-MFB is the mass transfer of nitrogen in liquid boundary layer and the reaction follows first order kinetics. Keeping the necessary circulation time under the working pressure (67 Pa) is helpful to nitrogen removal from steel. The oxygen content in molten steel has little influence on the removal of nitrogen after deep deoxidation, while the sulphur content in liquid steel is always relatively low and has little effect on denitrogenation. The sharp decrease of carbon content in steel drives the process of denitrogenation reaction so as to exhibit a faster denitrogenation rate. The interfacial chemical reaction and argon blowing play a major role in the nitrogen removal when the carbon content in liquid steel is stable.