ISSN:0003-8962    

DOI:10.1002/srin.199605520

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

In this work the melting process of sponge iron particles in iron‐bath is mathematically modelled. Based on the fact that the heat conductivity of sponge iron is much smaller than that of dense iron, a simplified analytical solution for the system has been derived. This solution agrees very well with the exact one from numerical calculation. The melting time and melting course of sponge iron particles are calculated. The melting time depends mostly on the particle radius. The amount of un‐molten substance in the iron‐bath at continuous feeding of sponge iron is estimated. The results show that under smelting reduction conditions the melting runs fast and must not be the rate determining step of the whole process.

ISSN:0003-8962    

DOI:10.1002/srin.199605521

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

Since 1991, BGH Edelstahl, Siegen, operated a 0.4 MW tundish heater equipped with a DC metal plasma torch containing a tungsten electrode. Due to cost considerations, the metal torch has recently been replaced by a 100 mm diameter hollow graphite electrode. After 6 months of operational experience first results are now available on graphite wear rates, carbon pickup and running costs as compared to the metal torch system. The average wear rate was 0.46 kg/h or 0.03 kg/t steel. Carbon pickup under normal conditions was below 10 ppm for all steel grades investigated ranging from 0.015 to 0.455% C. The case of accidental direct contact between melt and graphite has also been investigated. The normal carbon pickup to be expected can be correlated to the tip wear rate of the graphite electrodes. From this correlation, carbon pickup would increase with power from 3 over 10 to 25 ppm for 0.3, 1 and 2 MW. The running costs proved to be lower than with metal torches due to less water cooling, less wear parts like nozzles and starting electrodes, and less personnel for maintenance.

ISSN:0003-8962    

DOI:10.1002/srin.199605522

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

Thermal analysis is a very powerful method for investigation and characterization of casting powders. The results depend on the measuring conditions to a high degree. That was the reason for the systematic optimization of the measuring conditions of differential thermal analysis and thermogravimetry (DTA/TG) which were used for this study. Especially the temperature program was developed carefully. The factor analysis of the results gives information about the variables which influence the thermal properties of the powders. Factor analysis was also used for cluster formation and identification of casting powders.

ISSN:0003-8962    

DOI:10.1002/srin.199605523

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

In the strip rolling process friction is needed at first to pull the strip into the roll gap, otherwise slipping occurs. After the neutral plane however, where the velocity of the work roll equals the velocity of the strip, the friction stress alters direction to the opposite. If the friction stress after the neutral plane then is lowered, the total roll force will decrease. This can be done by a properly applicated oil‐ and water dispersion close to the work roll gap and between the roll cooling wipers. The technique and the key to a successful lubrication is a work roll surface which is as dry as possible. If the roll surface is not dry, neither large changes in the oil concentration, nor changes in the oil composition can make the lubricant stick to the roll surface. The lubricate was partly washed away by the water and only a small roll force decrease could therefore be measured. Only when the roll cooling water on the entry side of the work roll was set off on purpose, the roll force decrease was significant. Due to this result, further test were performed in an upstream stand in the hot strip mill. Here, the work roll wipers were modified and the roll was substituted by one with a larger radius and lubricated. The result was very slight or no water leakage at all. The roll force decrease was then much greater than before and close to those measured for the same reduction in the case of no entry water for the later stand. The electrical current in main drives and the roll wear in the lubricated stand could also be lowered significantly. In addition, the strip surface was greatly improved, under conditions with a high possibility of oxide residual contamination from the roll surface.

ISSN:0003-8962    

DOI:10.1002/srin.199605524

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

Local elastic roll flattening in direction of the roll axis in flat rolling is one of the important displacement components related to the roll gap shape. Up to now some classical formulae to solve roll flattening have been proposed. These formulae were derived from the elastic half space theory or the 2‐dimensional contact theory. On calculating the flattening of the back‐up roll they may result in a great deviation. In the present effort a comparison was made between the flattening results obtained by a 3‐dimensional finite element method and by a classical formula. The relation between the deviation and the back‐up roll geometry was also examined and therefore the classical formula was modified. Calculated results indicate that the modified formula can more accurately predict the back‐up roll flattening.

ISSN:0003-8962    

DOI:10.1002/srin.199605525

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The influence of strain rate on the stress‐strain curve of materials showing yield point phenomenon are determined in the range of small strains and high strain rates by means of the indirect impact tension test. With increasing deformation velocity, the Lüders strain is found to increase considerably. The stress reduction after reaching the upper yield point, is not abrupt and takes place gradually with increasing strain. These phenomena are investigated on Armco iron, on the tempered steel 42 CrV 6, on pure tantalum and tungsten alloys.A simple mechanical model is introduced which shows that the Lüders front velocity increases with strain rate approaching asymptotically the value of the plastic wave velocity as an upper limit. With this restriction, the local strain within the Lüders band must increase by increasing the rate of elongation of the tensile specimen. The Lüders strain could be estimated quantitatively as a function of strain rate. The model describes also the stress‐strain function after reaching the upper yield point considering the limited stiffness of the test arrangement.

ISSN:0003-8962    

DOI:10.1002/srin.199605526

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

In this study, the internal and residual stress states in quenched C60 steel cylinders are analyzed both numerically and experimentally in order to investigate the effects of boundary conditions (such as quench severity and temperature of quench bath) and specimen geometry. Specimen geometry has been analyzed by introducing a hole in a cylinder and varying hole diameter and its eccentricity. In the numerical analysis, the finite element method is applied and both temperature gradients and phase transformations are considered. Experiments include microstructural examination and X‐ray measurements of residual stresses of the first kind. It has been found that the value of the convective heat transfer coefficient is very critical to obtain simulation results close to real ones. For instance, when a constant value obtained as the mean of a temperature dependent distribution is used for this parameter, residual stresses are seriously underestimated (up to 40%). The temperature of the quench bath affects directly the convective heat transfer coefficient. The lower the bath temperature, the higher are the resulting residual stresses. Under the same quenching conditions, if the diameter of the hole is greater than a critical value, a transition occurs from the shallow hardening case to the through hardening case, i.e., the residual stress distribution is reversed. On the other hand, for a constant hole diameter, if the eccentricity ratio reaches a critial value, a complex residual stress state results, i.e., compressive/tensile stress transition regions along the circumference are observed.

ISSN:0003-8962    

DOI:10.1002/srin.199605527

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The formation of carbides during the aging of a quenched steel with mass contents of 0.04% carbon was investigated by means of internal friction by measuring the carbon Snoek peak height. The aging was carried out at different temperatures ranging from 40 to 350°C so that different types of carbides were formed. Low‐temperature carbides develop after aging below 100°C. The Johnson‐Mehl equation is applied to evaluate the kinetics of precipitation and re‐dissolution of the different carbides. The solubility of carbon in ferrite is influenced by the pre‐existing carbides, which is, in part, the reason for the variation of thermodynamic data in previous work.

ISSN:0003-8962    

DOI:10.1002/srin.199605528

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

A model for the stability of dispersed austenite in low alloy triple‐phase steels has been developed. The model was based on the dislocation dissociation model for classical heterogeneous martensitic nucleation by considering stress effects on the nucleation site potency distribution. The driving force for martensitic transformation has been calculated with the aid of computational thermodynamics. The model allows for the effects of chemical composition of austenite, mean austenite particle size, yield strength of the steel and stress state on austenite stability. Chemical enrichment in C and Mn, as well as size refinement of the austenite particles lead to stabilization. On the contrary, the increase in the yield strength of the steel and triaxiality of the stress state lead to destabilization. The model can be used to determine the microstructural characteristics of the austenite dispersion, i.e. chemical composition and size, for optimum transformation plasticity interactions at the particular stress state of interest and can then be useful in the design of low‐alloy triple‐phase steels.

ISSN:0003-8962    

DOI:10.1002/srin.199605529

出版商:Wiley    

年代:2016

数据来源: WILEY