Stainless Steel Production Research Articles

Mortality of iron and steel workers in Korea

The mortality experience of iron and steel workers from modern plants in developing countries has not been extensively described. Mortality at two Korean iron and steel manufacturing complexes was analyzed using Poisson regression methods with both direct and indirect standardization. Work histories were linked with a national mortality registry. Workers (44,974) hired beginning in 1968 were followed from 1992 to 2001. The 806 deaths observed during 10 years of follow-up comprised 2% of the population at risk and represented a large healthy worker effect (HWE) for all causes (SMR = 0.59, 95% CI = 0.55-0.63) and for cancer (SMR = 0.79, 95% CI = 0.70-0.90). Mortality at subsidiaries was considerably higher than at the parent plants (SRR = 1.71, 95% CI = 1.47-1.99). Relative mortality rates declined with employment duration: > 20 years had significantly reduced mortality (SRR = 0.59, 95% CI = 0.43-0.82) compared to duration < 1 year (test for trend: P = 0.0006). Fatal injury deaths in the first year were highly elevated (SMR = 3.10, 95% CI = 2.17-4.26) declining to less than that expected after 5 years. Cancer mortality was elevated in stainless steel production (SRR = 3.26, 95% CI = 1.37-6.49) and overall mortality was elevated for work in plant maintenance departments (SRR = 1.17, 95% CI = 1.00-1.37), particularly for fatal injuries (SRR = 1.67, 95% CI = 1.29-2.14). All-cause mortality increased with employment duration in the steel-production departments, as did fatal injuries in material handling/construction. This steelworker cohort exhibits excess mortality in some process areas. More detailed retrospective exposure assessment and future follow-up of this cohort will better define health risks in the modern iron and steel manufacturing.

開発裏話〜窒素吸収処理を利用したＮｉフリーステンレス鋼製品の製造技術の開発〜

開発裏話〜窒素吸収処理を利用したＮｉフリーステンレス鋼製品の製造技術の開発〜

Utilização de um aparato em escala de laboratório para o estudo da recuperação do cromo contido em resíduos gerados na produção de aço inoxidável

Os resíduos gerados no processo de fabricação de aço inoxidável representam um problema para as siderúrgicas devido ao teor de metais pesados e à forma hexavalente do cromo. Visando a contribuir para o desenvolvimento de um processo que possa tratar esses tipos de resíduos, foi realizado o presente estudo. Quatro diferentes tipos de resíduos, sendo uma poeira e três lamas, foram caracterizados utilizando várias técnicas. Depois, os resíduos foram aglomerados na forma de briquetes juntamente com a liga FeSi75, utilizada como redutor. Além da liga FeSi75, a cal ou a sílica (dependendo da composição química do resíduo) foi adicionada à composição do briquete para o ajuste da basicidade binária da escória que seria formada no experimento. Foram fabricados três briquetes com cada tipo de resíduo para a realização dos experimentos de fusão - introdução de briquetes em aço líquido a 1570, 1600 e 1635ºC e retirada periódica de amostras de aço do banho. Para a fusão do aço e do briquete, foi utilizado um aparato experimental em escala de laboratório. Verificou-se que o cromo que se encontrava no resíduo foi completamente incorporado ao aço para determinadas condições experimentais. O tempo necessário para se atingir esse percentual de incorporação foi de cerca de 15 minutos na temperatura de 1635ºC.

Reciclagem da poeira e lama geradas na fabricação de aço inoxidável

Foi realizado, em escala de laboratório, um estudo da recuperação dos metais cromo e níquel, contidos em resíduos gerados no processo de fabricação de aço inoxidável, utilizando-se altas temperaturas (1570, 1600 e 1635ºC). A maioria desses tipos de resíduos, principalmente a lama, ainda é disposta em aterros ou estocada. Nesse trabalho foram utilizados dois tipos de resíduo com alto teor de cromo, uma poeira (RESA) e o uma lama (RESB). A primeira etapa do estudo, fundamental para o estudo visando à reciclagem dos resíduos, foi a caracterização utilizando as seguintes técnicas: análise química, distribuição granulométrica (MALVERN), difração de raios X, microscopia eletrônica de varredura (MEV) e análise de micro-regiões (EDS). A segunda etapa envolveu a aglomeração dos resíduos caracterizados e outros reagentes, antes de serem introduzidos no aço líquido, utilizando-se uma briquetadora manual. Foram fabricados três briquetes com cada um dos resíduos. A terceira etapa da pesquisa foi a adição dos briquetes de resíduos no aço líquido e retirada periódica de amostras do banho para avaliação da incorporação do cromo contido nos resíduos no aço. O tipo de aço utilizado foi o aço carbono ASTM 1020. Os experimentos foram realizados em um equipamento em escala laboratorial, composto de um forno vertical que pode atingir até 1700ºC e seu controlador. O forno possui uma região de temperatura uniforme de cerca de 13 cm e, nessa região, o cadinho de alumina contendo aço é colocado. Esse equipamento foi construído para o estudo das reações envolvidas quando se adicionam resíduos em aço líquido. A atmosfera interna do aparato pode ser controlada. Após a introdução do briquete no aço líquido e sua fusão foram retiradas, periodicamente, amostras do banho em intervalos de tempo de três em três minutos para análise dos teores de vários elementos, principalmente o cromo, o níquel e o silício, principalmente. Cada experimento durou até 30 minutos. Os resultados mostraram que é possível, recuperar os metais contidos nos resíduos através desse processo, produzindo uma liga à base de ferro, cromo e níquel. O novo resíduo gerado (escória) contém uma menor quantidade de metais, em relação ao resíduo inicial. Altos valores de recuperação de metais dos resíduos foram atingidos. Para o níquel, a recuperação foi total, tanto para a poeira, quanto para a lama e para o cromo, os teores atingidos foram próximos a 100%.

Large area mapping of non-metallic inclusions in stainless steel by an automated system based on laser ablation

Large area compositional mapping (>6 mm 2) using a fast and automated system based on laser-induced plasma spectrometry is presented. The second harmonic of a flat top Nd:YAG laser beam was used to generate a microline plasma on the sample surface. The emitted light from the microline plasma was imaged onto the entrance slit of an imaging spectrograph and was detected by an intensified charge-coupled device to generate a spatially and spectrally resolved data set. Individual LIPS images, each measuring roughly 2500×2500 μm with spatial resolution of 50 μm between adjacent craters and 4.8 μm along the microline are presented. These large area maps were acquired in less than 1 min. Steel samples containing MnS and TiN inclusions were chosen as the most adequate for this study. The results are presented for the characterization of inclusionary material in stainless steel products in terms of morphology, distribution and abundance.

Application of oxygen-injection technology using the RCB system, especially for the production of stainless steel in an EAF

For the production of steel with an EAF (especially, also, for stainless steel, as shown at CORUS Engineering Steels in Stocksbridge), the RCB system of VAI FUCHS (Refining Combined Burner) represents an important step forward, in many respects, for the injection of oxygen. The constitution of the system, its working mode and its advantages are described. This innovative solution is already applied in the case of quite a number of furnaces.

Extension of the Ugine & ALZ steel plant at Genk: project review after one year of operation

This paper describes the equipments and systems, designed and supplied by VOEST-ALPINE Industrieanlagenbau (VAI), for the extension of the stainless steel production plant of Ugine & ALZ at Genk. The main results obtained during the first year of full operation of this modernized plant are presented.

Influence of atmospheric humidity and grain size on the friction and wear of high nitrogen austenitic stainless steel

Research on steels is still active and is motivated by the need to make further improvements in their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a relatively low yield strength. One method of increasing the yield strength is by alloying the steel with nitrogen. Such nitrogen-alloyed austenitic stainless steels exhibit attractive properties such as high strength and ductility, good corrosion resistance and reduced tendency to grain boundary sensitation [1]. The high austenitic potential of nitrogen allows the reduction of nickel content in steel. This offers additional advantages such as cost savings and makes the steel more suitable for stainless steel applications involving contact with human skin for people with nickel allergies. Due to the above-mentioned properties, in recent years significant efforts have been devoted to the production of high nitrogen austenitic stainless steels, and metallurgists have been very active in research concerning this class of steels. Particularly, considerable attention has been paid to solidification mechanisms and recrystallization processes [2–4]. Nitrogen in solid solution produces, in the austenitic stainless steel, many desirable properties: it stabilizes the austenite γ phase and increases the resistance to intercrystalline and pitting corrosion, but the most important property is the increase of the yield strength (RP0.2) without a corresponding decrease in ductility. There is another way of increasing the yield strength without severely affecting the ductility. This can be achieved by grain refining. Since austenitic stainless steels do not undergo phase transformation at typical annealing temperatures, the only way to refine the grain size is by recrystallization after cold rolling. An alternative way to obtain fine grains is by applying an austenite-martensite-austenite transformation. In previous publications [5, 6], we examined the influence of grain size and chemical composition on the mechanical properties and corrosion resistance of this family of steels.

Reliability and performance evaluation of stainless and mild steel products in methanolic and aqueous media

Reliability and performance of stainless and mild steel products in methanolic and aqueous sodium chloride media have been investigated. Weight-loss and pre-exposure methods were used. There was a higher rate of weight-loss of mild steels and stainless steels in 1% HCl methanolic solution than in aqueous NaCl solution. Solutions containing traces of sodium nitrite were found to enhance the reliability and performance of these steels. Mercuric and stannous chlorides were observed to reduce performance and reliability. Reliability and performance of these specimens decreased with continued exposure. Keywords: Reliability, performance, stainless steels, mild steels. [Global Jnl Engineering Res. Vol.2(1&2) 2003: 69-76]

Ageing of chromium(III)-bearing slag and its relation to the atmospheric oxidation of solid chromium(III)-oxide in the presence of calcium oxide

Slag arising in ferrochromium and stainless steel production is known to contain residual levels of trivalent chromium. As the chromium is normally bound in the slag matrix in various silicate or spinel phases, and hence not easily mobilised, utilisation or controlled disposal of such slag is generally considered unproblematic. Experimental test work with a number of slag materials indicates, however, that very gradual oxidation of trivalent to hexavalent chromium does occur when the slag is exposed to atmospheric oxygen, rendering a quantifiable but small portion of chromium in this much more mobile and toxic form. Mechanisms and rates of the oxidation reaction were investigated in a number of long-term studies using both original slag materials and artificial mixes of chromium and calcium oxides. Powders of these materials, some of them rolled into balls, were left to age under different conditions for periods of up to 12 months. In the slag samples, which contained between 1 and 3 wt.% chromium, 1000–10 000 μg Cr(VI) were found per gram of chromium within 6–9 months of exposure to an ambient atmosphere. The rate of the oxidation reaction decreased exponentially, and the reaction could generally be said to have ceased within 12 months. In mixtures of calcium and chromium oxides the oxidation reaction is presumed to occur at the boundaries between chromium oxide and calcium oxide phases through diffusion of oxygen along the grain boundaries and of Cr 3+ across the boundaries, resulting in the formation of calcium chromate. In the slags, where calcium and chromium oxide can form a solid solution, the oxidation is likely to occur at the exposed surface of grains containing this solution.

Stainless steel production technology - Trends, developments and new projects

Against the background of the several years lasting slump in the real price of stainless steels, different ways to reduce the production costs of these steels are analyzed. They consist in innovative technologies, some of which are already applied and others are still waiting for confirmation at the industrial scale. The emphasis is put on developments made by Voest-Alpine Industrieanlagenbau (VAI).

Characterisation of dusts and sludges generated during stainless steel production in Brazilian industries

During the stainless steel production process, wastes are generated at the electric arc furnace (EAF) and at the converters. These wastes are a problem for stainless steel industries, for they must be disposed of in controlled landfills. Finding areas to make more landfills is becoming difficult, and new landfills are being placed far from the industries. This leads to an increase in disposal prices and, furthermore, in production prices. Recycling of these wastes, besides solving the disposal and environmental problems, makes it possible to recover valuable metals such as iron, chromium, and nickel. These three metals are needed in stainless steel manufacture and could be returned to the production procedure, hence bringing profit to the industry. It is important, therefore, to develop a recycling process. Waste characterisation is an essential step in the definition of such a process. Four kinds of dust and two kinds of sludge, generated in stainless steel production, were characterised in the present work. The techniques used to characterise the waste were chemical analysis, size separation, density measurement, X-ray diffraction analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) microanalysis. The largest proportion of the dust and sludge particles was of spherical shape. This kind of particle was composed mainly of iron and chromium in the form of a spinel, or of oxides. Precipitation of a secondary phase was identified in some particles.

Thermodynamic Assessment to Chromium Oxidation in the Production of Stainless Steel

A solution model called ε approach is applied to predict the thermodynamic solution behaviour of Cr in steel melts. The calculated results are supported by the available experimental results. Further predictions on chromium scorification are achieved in view of melting and refining processes for Cr‐containing steels. Chromium reduction from slags after meltdown during EAF melting and AOD or VOD refining treatment is important for the production of Cr‐containing steels. It is thermodynamically predicted that chromium is inevitably oxidized during decarburization process which coincides with the industrial and experimental results. Minimum oxidation of chromium can be reached by lowering the partial pressure of CO gas at high temperatures.

Reduction of steel‐making slags for recovery of valuable metals and oxide materials

Extensive researches on slag reduction for recovery of valuable metals and oxide materials from metallurgical slags and other wastes using a DC furnace with a hollow electrode have been conducted in 2 major EU projects with close cooperation between MEFOS, FEhS and CRM. Steel slags and other residues were introduced into the reactor through the hollow electrode to the hot plasma. The materials were melted, reduced and mixed. The final products were a metal product, a slag product with targeted chemical composition and a dust fraction with a high content of ZnO. Different steel‐making slags and residues including BOF slag with low and high V‐content as well as EAF and AOD slags from stainless steel production, EAF dust, oily millscale, hydroxide sludge, BOF and BF dust have been treated. The slag products include a metallurgical powder for desulfurization of steel, hydraulic binder and slag stones for construction applications. The metals obtained are rich in Fe, Mn, V and Cr depending on the treated slag and residues. The environmental compatibility and mechanical properties of the slags have been improved after slag reduction.

Observation on foaming of EAF slags in the production of stainless steel

This study focused on slag‐foaming phenomena, the main emphasis being on slags used in the electric arc furnace (EAF) practice in the manufacture of stainless steel. Plant trials were carried out at Sandvik Steel for slags of high and low chromium content. The viscosity of the slags was predicted using a mathematical model for multi‐component slags developed at KTH, Stockholm. Next, the foaming characteristics were predicted using different relationships suggested in the literature. The predicted foaming behavior was then compared to estimations of foaming determined visually and acoustically by operators. Sound measurements were also carried out during the trials. In comparing foaming characteristics determined from sound measurements with the operator estimations, a relationship was found to exist between the two.

Nasal cell micronuclei, cytology and clinical symptoms in stainless steel production workers exposed to chromium.

The objective of the present study was to determine whether workers in stainless steel production with low exposure to various forms of chromium show an increase in micronucleated nasal cells or an excess of nasal symptoms or disease. Altogether, 48 workers employed in a stainless steel production chain were studied, 29 of them in the steel melting shop with exposure to hexavalent chromium (Cr(6+)), 14 in the sintering and crushing departments of the ferrochromium plant with exposure to trivalent chromium (Cr(3+)) and five in the mine with exposure to chromite ore (Cr(3+)). Thirty-nine workers from the cold rolling mill, with very low exposure to chromium, served as referents. All the subjects were never smokers with a minimum of 14 years employment in the same department. There were no significant differences between the exposure groups and the referents regarding the mean frequency of centromere-negative or centromere-positive micronuclei (studied by pancentromeric fluorescence in situ hybridization), nasal diseases and symptoms or mucociliary clearance of the nasal cavity. No statistically significant differences in the incidence of cell atypia or inflammatory cells were detected between the exposed workers and the reference group, except for an increase in lymphocytes among the chromite ore workers. Anterior rhinoscopy indicated slight inflammatory changes in nasal mucosa and secretion more often in the Cr(6+) and Cr(3+) groups than in the referents, the Cr(6+)-exposed workers showing more livid or oedemic epithelium. In conclusion, the stainless steel production workers, with low exposure to dusts or fumes containing hexavalent or trivalent chromium, did not show clinical changes in the nasal mucosa or an increase in nasal cell micronuclei or symptoms of nasal diseases, except for slight changes in the nasal epithelium and secretion.

Respiratory health effects of long-term exposure to different chromium species in stainless steel production.

The aim of this study was to determine whether occupational exposure to chromite, trivalent chromium (Cr(3+)) or hexavalent chromium (Cr(6+)) causes respiratory diseases, an excess of respiratory symptoms, a decrease in pulmonary function or signs of pneumoconiosis among workers in stainless steel production. Altogether, 203 exposed workers and 81 referents with an average employment of 23 years were investigated for indicators of respiratory health on two occasions, in 1993 and in 1998. Data collection with a self-administered questionnaire, flow volume spirometry, measurement of diffusing capacity, chest radiography and laboratory tests were carried out by a mobile research unit. Exposure to different chromium species and other metals was monitored regularly and studied separately. No adverse respiratory health effects were observed in the group exposed to Cr(6+), either in comparison with the control group in the first cross-sectional study or during the additional 5 year follow-up. Among the Cr (3+) exposed people, the production of phlegm, shortness of breath and breathlessness on exertion were significantly more frequent than in the control group, but the frequency of the symptoms did not increase during the follow-up; no differences were observed in the lung function tests and the radiographic findings did not progress. In the chromite group, the prevalence of breathlessness on exertion was higher than in the control group. However, in the follow-up, the occurrence of symptoms did not differ from 1993 to 1998. In the first study, most parameters of lung function were lower among the smokers in the chromite group than among the smoking controls, but in 1998 the difference was less marked. An average exposure time of 23 years in modern ferrochromium and stainless steel production and low exposure to dusts and fumes containing Cr(6+), Cr(3+), nickel and molybdenum do not lead to respiratory changes detectable by lung function tests or radiography. The workers exposed to Cr(3+) had more respiratory symptoms than those in the control group. The workers in the chromite mine had lower lung function test results than the control group due to earlier exposure to higher dust concentrations.

Metallurgical Process DesignA Tribute to Douglas' Conceptual Design Approach

This case study illuminates a practical design problem for cleaner metallurgical manufacturing. The task consists of assessing the feasibility of a novel low-waste process capable of eliminating unwanted, hazardous waste streams in stainless steel production. The novel flowsheet evolves gradually as prescribed by the decision hierarchy of Douglas (Douglas, J. M. AIChE J. 1985, 31, 353−362). Successively refined economic potential estimators discriminate inferior options and discard process configurations with marginal economic performance early in the design cycle. The complex liquid metal reaction network is optimized via a multiphase total Gibbs free energy model. A bilevel mathematical program for the simultaneous optimization of economic performance at equilibrium within specified operational bounds is presented. The article uses the case study to elucidate methodological aspects in systematic decision making for metallurgical process synthesis. Examples for the beneficial use of mathematical modeling...

コールドクルーシブル浮揚溶解による極低リンステンレス鋼の溶製

コールドクルーシブル浮揚溶解による極低リンステンレス鋼の溶製

Phase Equilibria between SiO2 and Iron-Chromite Spinel Structure Solid Solution, and Deoxidation of Liquid Fe-Cr Alloy with Silicon.

Oxygen control in liquid stainless steel production is extremely important for the removal of impurities and improvement of Cr yield. Precise information on the thermodynamics of oxygen in liquid Fe-Cr alloy is necessary for this purpose. The equilibrium relation between dissolved Cr and O in liquid iron saturated with pure solid Cr 2 O 3 or FeO.Cr 2 O 3 solid solution and thermodynamic behavior of FeO.Cr 2 O 3 solid solution had been established in our previous works. Following these studies, the deoxidation equilibrium of Si in liquid Fe-Cr alloy was thermodynamically discussed in this paper. Mutual solubility between SiO 2 and (Fe,Mg)O. (Cr,Al) 2 O 3 solid solution was observed at 1 573 and 1 873 K, in order to know the activity of SiO 2 coexisted with Cr 2 O 3 based oxide solid solution after Si deoxidation of liquid Fe-Cr alloy. It was found that Si deoxidation equilibrium of liquid Fe-Cr alloy could be thermodynamically evaluated based on unit activity of SiO 2 due to negligibly small mutual solubility between SiO 2 and Fe t O-Cr 2 O 3 based solid solution. As the result, the deoxidation power of Si would not enough high to produce low oxygen high Cr steel because of the attraction between Cr and Si in liquid iron.