Experimental study on Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the ferrite region

A Ti＋Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti＋Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.

Decarburization rate of RH refining for ultra low carbon steel

The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant （Kc） calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min^-1, and that of the stagnant period is 0.072 min^-1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14× 10^-6 after 10 min of decarburization.

Novel mechanism for the modification of Al_2O_3-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.

Structure Character of M-A Constituent in CGHAZ of New Ultra-Low Carbon Bainitic Steel under Laser Welding Conditions

800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.

Formation mechanism of spheroidal carbide in ultra-low carbon ductile cast iron

The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.

Correlation of Deactivation of Ni-Mo-W/Al2O3 during Ultra-Low-Sulfur Diesel Production with Surface Carbon Species

The deactivation of a Ni-Mo-W/Al_2O_3 catalyst during ultra-low-sulfur diesel production was investigated in a pilot plant. The reasons of catalyst deactivation were analyzed by the methods of elemental analysis, BET and TG-MS. The results showed that the catalyst deactivation rate was notable at the beginning of run, and then gradually reached a steady state after 448 h. In the initial period the catalyst deactivation may mainly be caused by the formation of the carbon deposits. The carbon deposits blocked the catalyst pores and the accessibility of active center decreased. The TG-MS analysis identified three types of carbon species deposited on the catalysts, viz.: the low temperature carbon deposit with high H/C atomic ratio, the medium temperature carbon deposit, and the high temperature carbon with low H/C atomic ratio. The amount of high temperature carbon deposits on the catalyst determined the overall activity and, therefore the high temperature carbon was a major contributor to the deactivation of Ni-Mo-W catalyst.

Mathematical Model of Decarburization of Ultra Low Carbon Steel during RH Treatment

According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring energy (ε) in the vacuum vessel on decarburization rate has been considered. The conclusion that the volumetric coefficients of the mass transfer of carbon is proportional to ε(1.5) is drawn. Industrical experiment proves this model is reliable. The influence of some factors on decarburization rate has been obtained. which can provide directions for RH treatment The decarburization behavior of steel with RH-OB treatment is also studied. The OB-or-not curve, the optimized OB time and OB amount are discussed.

Isothermal precipitation behavior of copper sulfide in ultra low carbon steel

Copper and sulfur are typical residual elements or impurity elements in steel.Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur.Utilization of copper and sulfur in steel, especially in steel scrap,has been an important issue for a long period for metallurgists.Copper and sulfur may combine to form copper sulfide,which may provide a prospect to avoid the detrimental effects of copper and sulfur in steel.Unfortunately the formation mechanism of copper sulfide in steel has not been completely clarified so far. In the present paper,solution treatment of samples containing copper and sulfur are firstly performed at 1623 K for 2.7×10~3 s followed by quenching into water.The samples are then isothermally heat-treated at 673 K,873 K, 1073 K,1273 K and 1373K for different time followed by quenching into water again.The size,morphology, constituent and crystallography of sulfide precipitates in these samples are investigated by scanning electron microscope(SEM) and TEM equipped with EDS.Fine copper sulfides(less than 100 nm) are observed to coexist with silicon oxide in samples even isothermally heat-treated at 1 373 K for 1.44×10~4 s;Film-like copper sulfides are generally observed to co-exist with iron sulfide in all samples;Plate-like copper sulfides are observed especially in sample isothermally heat-treated at 1 073 K for 1.44×10~4 s.The formation mechanisms of these copper sulfides have been discussed.

Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel

An induction levitation melting （ILM） refining process is performed to remove most microsized inclusions in ultra-low carbon steel （UCS）. Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nan remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthen- ing phase.

Deformation Behavior of Ultra-low Carbon Steel in Ferrite Region during Warm Processing

在铁酸盐范围的极端低的碳钢的热变丑实验在一个热模拟器被执行以便在低温度在铁酸盐范围研究极端低的碳钢的热变丑行为。结果证明流动应力上的变丑参数的影响对在奥氏体的变丑的那些不同。变丑特征参数在铁酸盐区域为极端低的碳钢被计算。为在在低温度的以铁酸盐为主要成的变丑的极端低的碳钢的流动压力方程被获得。

Prevention of burn-on defect on surface of hydroturbine blade casting of ultra-low-carbon refining stainless steel

The burn-on sand is common surface defect encountered in CO2 -cured silicate-bonded sand casting of hydroturbine blade of ultra-low-carbon martensitic stainless steel,its feature,causes and prevention measures are presented in this paper.Experiments showed that the burn-on defect is caused by oxidization of chromium in the molten steel at high temperature and can be effectively eliminated by using chromium-corundum coating.

Mechanical Method Determining Precipitation in an Ultra-Low Carbon Bainitic Steel

Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.

Advanced manufacturing technologies of large martensitic stainless steel castings with ultra low carbon and high cleanliness

The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.

Optimum process of RH-MFB refining for ultra-low carbon steel

A mathematical model was established and applied to simulate thedecarburization of RH-MFB process in Pansteel Company. Study of theeffects of w_[C]0, w_[O]0, Ar flowrate, evaluation rate the MFB lanceblowing parameters on the decarburization process was car- Ried out.The results showed that this model could give the quantitativeunderstanding of the process, especially the behavior of MFB Lanceblowing. This model has realized the optimum process of RH-MFBrefining for ultra-low carbon steels in Pansteel.

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.

考虑超碳需求响应的综合能源系统低碳优化调度

西北地区新能源发展迅速,充分利用当地独有的光热资源优势,同时结合火电低碳化改造与新能源协同运行,有利于推动当地能源系统绿色低碳转型。为尽最大限度地提升系统的减碳能力,提出一种基于源荷协同降碳的超碳需求响应模型,将动态碳排放因子作为分时电价的惩罚因子,从而将源侧碳信号传递至荷侧,驱使用户侧进行低碳性状态转移。首先,在日前调度阶段,构建预调度-再调度两阶段调度运行机制,再调度根据预调度的系统状态信息进行超碳需求响应,来深度降低系统碳排量。其次,将光热电站引入综合能源系统,与风电场、碳捕集电厂协同运行,从而构建高比例新能源场景,来验证超碳需求响应在此场景下的减碳效益。最后,建立了基于超碳需求响应的预调度-再调度两阶段低碳调度模型。经算例仿真分析表明,所提源荷协同降碳的新思路能有效提高系统的减碳能力,深入挖掘系统的降碳空间,提升系统的经济效益。

镍/木棉纤维衍生碳复合材料的制备及吸波性能研究

近年来,生物质碳因成本低廉、易制备、理化性能优异和具有多孔结构被广泛应用于吸波领域。然而,其吸波性能仍然受较高电导率引发的不良阻抗限制。在此,使用镍(Ni)改性木棉纤维,并使用不同的碳化温度获得镍/木棉纤维衍生碳(Ni/C)复合材料。扫描电镜结果表明,随着碳化温度的升高,Ni颗粒的尺寸增加,且木棉纤维表面出现更多的缺陷结构。XRD和XPS结果证明了Ni和木棉纤维衍生碳的成功复合。Raman结果表明碳化温度的升高导致碳组分石墨化程度增加,提高了复合材料的传导损耗能力。最后,我们将复合材料与石蜡以5∶95的超低填充比例混合,Ni/C-800展现出-52.6 dB的反射损耗值和8.32 GHz的有效吸收带宽。复合材料优异的吸波性能取决于衰减能力和阻抗匹配的协同、介电损耗和磁损耗的共同作用以及大比表面积和中空多孔结构造成的多重散射能力的增强。

钢铁行业大气污染治理科技发展分析与展望

钢铁行业是我国工业领域重要的大气污染排放源之一,钢铁行业的大气污染治理是降低重点行业污染排放、打好污染防治攻坚战的重中之重。近年来,我国在钢铁行业大气污染治理方面取得了显著成果。总结了我国“十一五”以来钢铁行业污染防治科技工作的部署,并梳理分析了钢铁行业大气污染治理技术发展的阶段。基于末端治理、源头减排和过程控制、全过程耦合控制三个方面技术发展现状,剖析了当前我国钢铁行业在多污染物协同深度减排和实现超低排放面临的形势和问题。最后,面向“十四五”时期,聚焦碳达峰碳中和目标,提出了相关建议,旨在深化大气污染防治科技工作,为建设“美丽中国”和实现“双碳”目标提供关键科技支撑。在未来的发展中,我们有理由相信,在全社会的共同努力下,钢铁行业将迎来更加清洁、高效和可持续的发展。

既有超高层建筑的绿色低碳改造研究

既有超高层建筑的碳排放是建筑领域碳排放的重要组成部分,但其绿色低碳改造的关键技术集成与创新还不充分,实现碳达峰、碳中和的技术路径还不清晰。本文分析了既有超高层建筑的碳排放核算标准、核算关注点、核算边界和核算方法,从而提出基于能效水平提升、用能结构优化、资源循环利用和ESG体系搭建的既有超高层建筑绿色低碳改造路径。

钢铁企业减污降碳协同增效技术实践及启示

我国当前正处于深入打好污染防治攻坚战阶段,同时也处于积极部署“双碳”战略目标的开局阶段。钢铁行业是国民经济的支柱产业,推动减污降碳协同增效发展是促进行业绿色可持续发展的关键。本文系统回顾了钢铁生产中烧结、高炉等主要工序在减污降碳协同增效方面的技术发展,并结合企业生产案例分析了超低排放改造在实现减污降碳协同增效方面的成效,以期为我国钢铁行业绿色低碳高质量发展提供参考。