Water model study on inclusion removal from liquid steel by bubble flotation under turbulent conditions

Abstract

Inclusion removal from liquid steel by bubble flotation under turbulent conditions is analysed using a water model. Turbulence is realised by impeller stirring in a water containing vessel. First, the effects of variables such as filter pore size, gas flowrate, NaCl concentration, and stirring intensity on bubble size are investigated. Second, particle removal by bubble flotation is studied using the water containing vessel system. The results indicate that particle removal rate by bubble flotation is controlled by non-first order kinetics. The factors affecting the particle removal rate constant k ₁ are discussed and a final empirical equation is derived as follows: -dc/dt = k ₁ c^1·3665 and k ₁ = A(d _p/d _B)^2·65?0·104 Q _g^1·630, where c is particle number density, t is time, A is a constant parameter, d _p and d _B are the particle and bubble diameter respectively, ? is the turbulent energy dissipation rate, and Q _g is the gas flowrate.     

Mapping complex microstructures in powder metallurgy steels

Abstract

New methods of characterising multiple phase powder metallurgy steels have been investigated. Mapping of microhardness with a lateral resolution of as little as 5 μm and with up to 10⁴ indents can produce distributions of mechanical properties which are characteristic of different steel grades. Maps of these properties can be correlated with the different phases observed in etched microstructures, and quantification of size and interconnectivity of the regions with, for example, different hardness or stiffness is then possible. Electron backscatter diffraction can also produce simultaneously highly detailed maps of the different phases in a powder metallurgy steel with chemical composition information. Percentages of the different phases present can be determined from the crystallography and morphology of the grains observed, but the technique is limited by the speed with which maps can be acquired.     

Effect of MnS powder additions and vibratory ball peening on corrosion resistance of sintered 316LSC stainless steels

Abstract

As sintered parts are to be machined after sintering, the MnS powder is usually added to improve the machinability. Vibratory ball peening is used for deburring and improving the surface finish of sintered components in local PM industries. The effect of the MnS powder content and vibratory ball peening on the corrosion resistance of the sintered 316LSC alloys was investigated. Experimental results show that the addition of MnS powder slightly decreases the sintered density. The weight loss rate of the sintered specimens immersed in the 10%FeCl₃ corrosion test solution increases slightly with increas- ing MnS content, but decreases with increasing sintering temperature. Vibratory ball peening effec- tively decreases the weight loss rate of the sintered stainless steels. The chromium atoms actively migrate across the phase boundary and diffuse into the MnS particles during sintering. This intensive chromium diffusion affects the corrosion performance of the sintered alloys with MnS added. The surface morphology of the as sintered and the ball peened specimens before and after the corrosion test were studied with a SEM.     

Viscosity effect of titanium pickup by mould fluxes for stainless steel

Abstract

Mould flux samples from an operating continuous caster showed a steady state increase in titanium oxide content of 3–4% for a titanium stabilised ferritic stainless steel and about 6% for a titanium stabilised austenitic stainless steel. Owing to the reduction of silica the flux basicity increased from 0.8 to 0.9, and from 0.95 to 1.2, for the ferritic and austenitic steels, respectively. Similar changes in composition were found for mould shims, which had been recovered from the mould after casting the ferritic steel. The increased titanium oxide content caused a decrease in the flux viscosity, for the original basicity. However, when the flux basicity was increased from 0.95 to 1.2, the apparent viscosity of the mould flux of the austenitic steel increased markedly, for 10% TiO₂ and temperatures of 1250°C and below. Precipitation of perovskite was found to be responsible for the higher apparent viscosity.     

Ni-based superalloy as a potential tool material for thixoforming of steels

Abstract

Semisolid processing, already a well established manufacturing route for the production of intricate, thin walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for this near-net shape process to be attractive for steels on an industrial scale. The potential of a Ni-based superalloy, Inconel 617, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was investigated. The response to thermal cycling of this alloy at high temperatures was compared with that of X38CrMoV5 hot work tool steel widely used in the manufacture of conventional forging dies. The favourable thermophysical properties of the latter were completely negated by its limited temper resistance, while the Inconel 617 alloy responded to thermal cycling by the usual heat cracking mechanism.     

Impact forging of sintered steel preforms

Abstract

The results of a fifteen year research and development programme on the application of forge hammers to the impact powder forging of 46xx steel preforms are reviewed and assessed. The main topics are suitability of forge hammers to powder forging; effects of forging strain and forging pressure on core residual porosity; importance of pressure dwell or contact time in determining residual porosity near the surfaces and corners of powder forgings; dependence of tensile ductility, toughness, and fatigue strength on high strength, impact powder forged 46xx steel on lateral strain, residual porosity, oxygen, and sulphur contents; and inclusion volume fraction and spacing. It is shown that impact forged steels can achieve mechanical property parity at very high strength levels with high quality wrought steels. State of the art forge hammers have significant technical and economic advantages over presses in powder forging applications and are best suited to powder forging processes for which the forging strains and energy requirements are small.     

Magnetically graded materials fabricated by inhomogeneous heat treatment of deformed stainless steel

Abstract

The present work was undertaken with the objective of developing a magnetically graded material by a reverse martensitic transformation (RMT) technique in a controlled manner. Tensile deformed SUS type 304 stainless steel was annealed within a temperature gradient to introduce the reverse martensitic transformation inhomogeneously. The magnetisation distributions within specimens were evaluated using a vibrating sample magnetometer. It was found that the desired saturation magnetisation gradient was formed in the magnetically graded material fabricated by the RMT technique. Therefore, by controlling the thermal gradient in the furnace very carefully, it is possible to obtain a magnetically graded material with a suitable gradient of magnetisation using the α′ –γ reverse transformation in SUS 304 stainless steel.     

Microstructural and mechanical characterisation of some sinter hardening alloys and comparisons with heat treated PM steels

Abstract

Four grades of sinter hardening materials have been compared, using industrial equipment. Three powder types were completely prealloyed; the last one was a hybrid, combining prealloying and diffusion bonding. Different amounts of Cu have been added by mixing. The lubricated mixes, containing 0.6% graphite, have been compacted at different pressures, to form gears at green densities ≥7.0 g cm^?3 ; the compacts have been sintered at 1120°C, under endogas from methane and fast cooled (at least 7 K s^?1 within the range 850–400°C). The final step has been stress relieving, at 180°C, for 1 h. Material properties have been investigated, focusing on porosity, pore shape, hardness, microhardness, microstructure, local chemical composition and mechanical properties. For comparison, other gears, compacted in the same tool and at the same density level, but manufactured according to a more conventional cycle, i.e. starting from less alloyed powders and adding carbonitriding, quenching and stress relieving, have been used. The analysis of the different experimental results enabled the authors to find out and outline some criteria suitable for selecting sinter hardening materials and for choosing more reliable manufacturing conditions to fulfill specific application requirements.     

Next-generation structural steels for nuclear and thermonuclear power engineering

The creation of a new direction of research in radiation materials science, i.e., the designing of low-activated materials exhibiting a rapid decrease in the induced radioactivity and intended for nuclear power, is described. This direction was developed according to the plan of building an international magnetic confined fusion reactor. The problems of decreasing the induced radioactivity in structural austenitic steels are considered. Theoretical models for designing such steels and experimental data obtained at the Baikov Institute of Metallurgy and Materials Science, the Vernadsky Institute of Geochemistry and Analytical Chemistry, and other Russian and foreign scientific centers are presented.     

Novel high performance,dimensionally controlled PM steels for sinter-hardening

Abstract

Recent trends in the technology, production and applications of diamond tooling are reviewed. The continuing fall in the price of synthetic diamond as production volumes increase provides a strong incentive for tooling companies to reduce the cost of matrix materials and of their manufacturing processes, with an accompanying need for research in these areas. Diamond wires for the cutting of granite and other rock continues to grow in application and provides another focus for materials and technology advances.     

The stress intensities for slow crack growth in steels containing hydrogen

A test technique has been developed to determine the stress intensity for slow crack growth in hydrogen precharged steels. Measurements on several grades of maraging steel and a 300M steel show that hydrogen contents on the order of 2 ppm reduce the stress intensity for slow crack growth by 50 pct or more of theK _Ic values. At equivalent hydrogen contents the 300M steel was more severely embrittled than the mar aging steels. Comparison of the present results with aqueousK _Iscc data indicates that the amount of hydrogen “picked up by the steels in stress corrosion increases with increasing yield strength. Formerly with International Nickel Co.     

风力发电主轴轴承用锻棒材的国产化

采用"DC炉+LF+VD+浇注3.7t钢锭+快锻"的工艺技术,试制了风力发电主轴轴承用高品质的高碳铬轴承钢锻棒,规格为250～380mm。检测结果表明,通过控制钢中的有害元素钛和氧的含量、采用LF精炼加VD真空脱气和软吹氩技术、选用合理的锻造比,提高了钢水的纯净度、改善了碳化物不均匀性和低倍组织,生产出品质较好的超大规格锻棒,满足了风力发电主轴轴承用钢的性能要求。     

Properties of ultra-low carbon,cold-rolled sheet steels containing titanium or boron for use in enameling

Ultra-low carbon(ULC),cold-rolled sheet steels for porcelain enameling containing alloys of titanium and boron are studied. The microstructure,mechanical properties,inclusions,and precipitates of the sheet steels are analyzed. The hydrogen permeation time of the sheet steels as-annealed and after skin-passed or cold-rolled at different reductions are measured. It is show n that the sheet steels possess different features of enameling properties in hydrogen permeability,fishscale resistance,and pinhole resistance.     

Manufacture of centrifugal cast high speed steel rolls for wire rod mills

Abstract

By means of a centrifugal casting method, high speed steel (HSS) rolls with excellent wear resistance have been manufactured. The hardness of the HSS rolls was 65–67 HRC, the range of hardness variation was smaller than 2 HRC and the impact toughness exceeded 15 J. The wear rate of the rolls was 2.5 × 10^?4 mm t^?1 of steel passing through the prefinishing stands of the high speed hot wire rod rolling mill. Casting cracking of the HSS rolls was definitely decreased and the rejection rate owing to the presence of cracks was less than 3%, as a result of the use of a two layer paint and varying the rotation rate. In addition, the segregation of alloying elements could be decreased by adding a suitable amount of niobium (0.6–2.0%).     

Molybdenum steels for pipelines

Abstract

Stringent property requirements are specified for steels to be used for oil and gas pipelines, especially for application in extremely cold climates. The effect of controlled plate mill processing (including water spray cooling between hot rolling passes), and of simulated strip mill processing on the mechanical properties and microstructure of pipe skelp of varying thickness has been studied in a family of Mn-Mo-Cb steels developed to meet these specifications. By virtue of chemistry and process control, desired minimum levels of yield strength in the range of 60 to 90 ksi (415 to 620 N/mm²) have been achieved, with excellent corresponding toughness values, in strip and plate gauges up to 0.75 in (19 mm). The microstructure of these steels varies, according to chemistry, from ferrite plus pearlite to acicular ferrite.

Résumé

Des propriétés mécaniques particulièrement strictes son t exigées des aciers pour pipe-lines (gaz ou pétrole) situés spécialement dans des régions très froides. Pour une série d'aciers au Mn-Mo-Cb développés pour de telles applications, les auteurs ont étudié la variation des propriétés mécaniques et de la microstructure de tôles a tube d' épaisseur variable en fonction de la procédure de laminage contrôlé des tôles fortes (incluant un refroidissement par aspersion d'eau entre les passes) ou d'une procédure simulée de laminage des feuillards. Du fait de la composition chimique et du contrôlé du laminage, des limites d' élasticité de l'ordre de 60 à 90 ksi (415 à 620 N/mm²) ont été atteintes et sont associées a d'excellen tes valeurs de la résilience des feuillards et des tôles jusqu'à 0.75 in. (19 mm) d' épaisseur. Selon la composition, la microstructure de ces aciers varie de ferritico-perlitique à une ferrite aciculaire.     

钢铁厂屋顶光伏发电效率分析及优化设计

结合某钢铁厂屋顶光伏发电项目实测数据,对光伏电站发电效率进行了计算,并辅助试验分析,对组件朝向倾角、低照度、阴影灰尘遮挡几个影响因素进行了深入研究,给出了钢铁厂屋顶光伏发电项目优化设计的建议:优先选择接近最佳朝向和最佳倾角方式安装组件。低光照时逆变器跟踪效率较低,设计时要考虑MPPT电压匹配;组件布置应充分考虑周围烟囱等构筑物的遮挡情况,表面积灰对组件发电量的影响较大,从设计源头上应尽量避免组件行遮挡。     

莱钢400m~2烧结机提高余热发电量的改造

通过对400 m2烧结机进行台车栏板改造,圆辊出料口整体更换,安装压料辊,平料器加装置陶瓷衬板,同时在环冷机上重新安装平料器等一系列措施,保证了烧结机机尾断面红火层厚度均匀,环冷机布料平整,为提高烧结余热发电量打下了坚实基础。     

Development of ultrasonic sensor for non-intrusive measurement of temparture in powder materials

Abstract

Fine and ultrafine powders are often used as starting materials for fabrication of advanced materials; they are first formed into desired shapes and then consolidated into high density parts by application of pressure and heat. Electroconsolidation is a densification method for rapid pressure assisted densification of complex shaped parts made from powder preforms. The part to be densified is immersed in a bed of free flowing, electrically conducting, graphite powder medium within a cylindrical die chamber. Pressure is applied externally and heat is generated internally by resistively heating the graphite powder. Because of rapid heating and the attendant wide temperature fluctuations possible with resistive heating, it is of paramount importance to measure and control the temperature in the die to achieve reproducible densification properties. This paper describes an ultrasonic pitch-catch sensor that can be used to non-intrusively measure the temperature of a graphite powder bed. Results of ultrasonic data for heating trials conducted at up to ≈3000°C indicate that the average temperature in a graphite powder bed can be predicted to within 2-3%. The ultrasonic sensor can be used to precisely control the heating trajectory and densification of parts with reproducible properties.     

A theoretical model for the flow behavior of commercial dual-phase steels containing metastable retained austenite: Part II. calculation of flow curves

The role of metastable retained austenite(γ _R), its volume fraction, and mechanical stability on the flow characteristics of a dual phase steel containing 20 vol pct of ‘as quenched’ martensite in a ferrite matrix has been examined in this paper employing the flow curve expressions derived in Part I of this paper. It has been found that for a given volume fraction ofγ _R, its mechanical stability plays a crucial role in enhancing the ductility. Whereas highly stableγ _R does not contribute either to strength or ductility of the steel, highly unstableγ _R which causes an increase in the strength is detrimental to ductility. Aγ _R which is moderately stable and undergoesγ _R → α′ transformation over a larger strain range is beneficial to enhanced ductility. Increasing amounts of moderately stableγ _R significantly increase both the strength and the ductility of dual-phase steels through a sustained work-hardening due toγ _R → α′ transformation. Load transfer which is determined by a parameterq has a significant contribution to work-hardening. A value of ∣|q∣|= 4500 MPa has been found to partition realistically the stress and strain in these steels.     

Determination of optimum process conditions for the extraction and separation of zirconium and hafnium by solvent extraction

Taguchi's method was used to determine the optimum conditions for separation of zirconium from hafnium by solvent extraction. The experimental conditions were studied in the range of 0.1 to 2.0 M for three different acids and TBP, D2EHPA or Cyanex 272 as extractant. The optimum extraction of zirconium was 71% when 2.0 M nitric acid and Cyanex 272 were used. The optimum zirconium/hafnium separation was also achieved using this combination.