摘要:

Die isotherme Reduktion von Eisenerzpellets mit Kohlenmonoxid, Wasserstoff und deren Gemischen bei Temperaturen zwischen 700 und 1000°C wird experimentell und theoretisch untersucht.Die Meßergebnisse folgen weitgehend einem Rechenmodell, das den topochemischen Verlauf einer oder mehrerer simultaner Reaktionen 1. Ordnung beschreibt und so eine detaillierte Analyse der experimentellen Befunde erlaubt. Die Reduktion mit reinem Wasserstoff ist um etwa eine Größenordnung schneller als die mit reinem Kohlenmonoxid. In Gemischen macht sich die beschleunigende Wirkung des Wasserstoffs besonders bei geringen Zusätzen bemerkbar. So sinkt die Reduktionsdauer auf weniger als die Hälfte, wenn dem Kohlenmonoxid 10% Wasserstoff zugesetzt werden. Die Reduktion durch Kohlenmonoxid ist bei der verwendeten Pelletgröße von 1,3 cm wesentlich diffusionsbestimmt, die durch Wasserstoff dagegen mehr reaktionsbestimmt.Der aus den Meßwerten ermittelte Porendiffusionskoeffizient wächst bei der Reduktion mit Kohlenmonoxid proportional zur fünften bis sechsten Potenz der Absoluttemperatur, was auf eine entsprechende Temperaturabhängigkeit der Porenstruktur schließen läßt. Demgegenüber zeigt jedoch der Porendiffusionskoeffizient bei der Reduktion mit Wasserstoff ein annähernd ideales Verhalten mit einem Temperaturexponenten um 1,5.Die ebenfalls aus den Meßwerten ermittelten Aktivierungsenergien und Häufigkeitsfaktoren der Phasengrenzreaktion liegen für die Reduktion mit Kohlenmonoxid bei 60 kJ/mol bzw. 1000 cm/s und für die Reduktion mit Wasserstoff bei 50 kJ/mol bzw. 700 cm/s. Einer engeren Eingrenzung der Werte steht hier jedoch ebenso wie bei den Porendiffusionskoeffizienten die relativ starke Streuung der aus den Messungen gewonnenen Punkte entgegen.

ISSN:0003-8962    

DOI:10.1002/srin.198700244

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

Initially, the paper gives a survey on known theoretical models of mixing in gas‐stirred melts. A new model that combines the concepts of the circulating concentration cloud and the two‐tank model is presented. In this model, the combined effect of recirculation flow and turbulent mixing is expressed by a number of ideally mixed tanks in series. The tanks in series are additionally connected with a dead volume according to the two‐tank model. In total, the model contains four characteristic parameters. The results of numerical calculations using the model are compared with experimental data of mixing in a water model and in a 40 t steel ladle both with centric gas‐stirring.

ISSN:0003-8962    

DOI:10.1002/srin.198700245

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

It is shown that with the aid of digital simulation methods complex multiphase interrelated systems, such as gas‐injection process can be analysed. Interdependencies can be revealed and quantitative evaluation of characteristic system quantities are provided. The method of digital system simulation is a very convenient tool for process analysis or system engineering. Results of the computer‐aided process simulations (Caps) yield a better understanding of complex phenomena and better aimed engineering of gas dispersion techniques in metallurgical processes.A particular interest of this investigation is to reveal the effect of mass‐transfer rate on the hydrodynamic behaviour of a gas‐injection process. The combined effects of total flow rate of injected gas and mass‐transfer rate on the system quantities such as mixing power, induced liquid flow rate, holdup, interfacial area and volumetric mass transfer coefficient are evaluated under steady state conditions of the investigated systems and illustrated in simulation plots.The liquid velocity has a minor effect on bubble size at some distance from the orifice but controls the location of bubble breakup. The frequency of bubble breakup and final bubble size depends on the intensity of mass transfer. Mixing power due to gas bubbles and circulation velocity of the steel bath increase appreaciably if there is a chance of bath reactions producing more gas. The integral mean values of mixing power, induced velocity of liquid and holdup in plume, specific interfacial area and volumetric mass‐transfer coefficient increase with increasing total flow rate of injected gas and intensity of mass transfer.

ISSN:0003-8962    

DOI:10.1002/srin.198700246

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The metal flow in a rod extrusion is theoretically discussed in relation to a frictional condition, strain hardening and strain rate hardening. An existing rigid plastic FEM‐program was modified in order to take a rate sensitivity of a material into consideration through a constitutive equation of the form. An interfatial friction was incorporated by a constant Coulomb‐frictional coefficient. When the frictional coefficient is smaller than 0.1, a large effect of the friction does not appear. The larger then‐value is, the stronger the distortion of the grid in a billet becomes even under small frictional resistance. The effect of them‐value is similar qualitatively to that of then‐value. When the rate sensitive material is extruded at very low punch speed under large frictional resistance, the material is strained very irregularly all over the billet at an early stage.

ISSN:0003-8962    

DOI:10.1002/srin.198700247

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

A study was made of the influence of hot deformation on the transformation behaviour, the structure and the mechanical properties of a pearlitic steel containing 0.65% C. The production parameters of a modern hot strip mill were taken as a basis for the deformation schedule and cooling performed with the aid of a hot deformation simulator (Wumsi). Parameters to be pointed out as significantly influencing the transformation behaviour are, in particular, the finishing temperature and the cooling rate after hot deformation. By exploiting the possibility of raising the cooling rate after deformation in the same measure as is attainable on a hot strip mill, a yield strength increase of at least 150 MPa is achievable.

ISSN:0003-8962    

DOI:10.1002/srin.198700248

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

In the present investigation experiments were carried out to find strain history effects on deformation‐induced austenite transformation in a metastable stainless steel sheet. The aim of this work was to obtain information on a final amount of martensite formed during γ → α’ transformation under various strain paths. All tests were performed at room temperature and at 0°C. Relationships of volume fraction α’ martensite vs true plastic strainXM=f(ε) are presented and analysed.

ISSN:0003-8962    

DOI:10.1002/srin.198700249

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

In steels produced and utilized in the Fed. Rep. of Germany the elements P and Sn may occur as impurities. Both these elements tend to enrich (segregate) at grain boundaries. The equilibria of grain boundary segregation in iron and the effects of alloying elements have been studied for P and Sn by Auger‐electron‐spectroscopy and were thermodynamically described. For a 3.5% NiCrMoV‐turbine steel the grain boundary segregation of P and its effect on ductility have been studied in detail, with the results that the long‐term embrittlement of this steel during application at temperatures around 400°C can be predicted and the maximum bulk concentration of P can be given.The effect of Sn on the creep of a 1% CrMoNiV steel at 550°C has been investigated, Sn favours cavity nucleation and growth, therefore tertiary creep starts earlier and premature failure occurs with increasing Sn content. Therefore, the Sn content should be kept as low as possible in heat resistant steels. Since carbon also segregates to grain boundaries and can displace P and Sn if there is enough free C in a steel, plain carbon steels are not subjected to embrittlement by P and Sn. The susceptibility to intergranular stress corrosion cracking in nitrates and other electrolytes is somewhat enhanced by P, however, only in a restricted range of potentials. In the range of maximum susceptibility the impurities have no effect, all carbon steels are susceptible to IGSCC, independently of their purity. So stress corrosion cracking cannot be suppressed by diminishing the content of phosphorus – only by avoiding the critical corrosion conditions concerning electrolyte and potential.

ISSN:0003-8962    

DOI:10.1002/srin.198700250

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

Under the sponsorship of the President of the Bulgarian Academy of Science organized by the Institute of Metallography and Metals Technology the first international conference of COMECON Countries on Rapid Quenching of Metallic Alloys (RQMA‐1) was held from 11.‐16. May, 1987 in Varna.

ISSN:0003-8962    

DOI:10.1002/srin.198700251

出版商:Wiley    

年代:2016

数据来源: WILEY

ISSN:0003-8962    

DOI:10.1002/srin.198700252

出版商:Wiley    

年代:2016

数据来源: WILEY