Balázs Verő

A Simplified Semi-Empirical Method to Select the Processing Parameters for Laser Clad Coatings

A semi-empirical method for selecting the processing parameter s of laser cladding is proposed. This phenomenological approach uses simple mathematical formulae, derived from a statistical analysis of measured data, to relate the laser cladding parameters with the geometric features of the clad track. Given the prescribed clad height and avai lable laser beam power, the proposed method allows to calculate values of the scanning speed and powder feed rate which are required to obtain low dilution, pore free coatings, fusion bonded to the substra te. To illustrate the application of this method, variable powder feed rate laser cladding e xperiments were carried out with Stellite 6 powder on mild steel substrates. In this technique t he laser beam power and radius and the processing speed are kept constant, while the powder feed rate is varied along a single track length according to a specified linear function. The expressions derive d from the model allowed to plot the experimental data in a coherent manner, revealing the combine d role of the different processing parameters.

Material Structural Aspects of Micro-Scale Chip Removal

In these days one of the most important field of interest lies i n the manufacturing of miniaturized parts. The economical and flexible alternative for produc tion in small and medium lot sizes is machining with miniature, fine-grained carbide end mill. The experimental research and analytical observations of the authors in connection with material st ructural aspects of micro scaled chip removal and the effects of the very thin micro milling tool are described in this pa per.

Theoretical analysis of entrapment kinetics in hydrogen permeation experiments

A simulation program has been developed to analyze hydrogen entrapment during hydrogen permeation experiments where the input side hydrogen concentration is constant and the exit side hydrogen concentration is zero. The simulations performed focused on the effect of traps on the exit side hydrogen flux and that on the capture and release of hydrogen by traps as a function of the distance from the entry surface. The number of dimensionless parameters to be defined in the presence of traps was much higher than in the absence of traps. It was found that in several cases the first breakthrough time of hydrogen is a linear function of the trap concentration. However, when the capture of hydrogen by traps is slow, the permeation curve may have a very unusual shape, and the trap saturation profile changes substantially during the permeation experiment. The impact of the hydrogen entrapment kinetics on the result of permeation experiments in connection with the industrial test of enamel-grade steel plates is also discussed.

Laser Surface Treatment of Steels

To reveal the possible use of laser technology in the ferrous meta llurgy we started an M.E.(Ministry of Education) project in 1998. Based on the laser equipment of BAYATI and the experience of its collaborators and operated by DUNAFERR Researc h Institute we examined the following four fields: • laser cutting, • laser surface heat-treatment (quenching), • laser surface alloying, • laser cladding. In this paper the authors evaluated the most important results of the work done, the applicati on are s of each method and the odds of the further steps.

The Combined Application of Nanoindentation and Scanning Probe Microscopy to Materials Sciences

Nanoindentation, as all depth sensing hardness measurement techniques has different sources of error compared to conventional hardness and microhardness test methods. Surface effects, as roughness of the polished sample, and pile-up and sinking-in ef fects during the indentation process greatly affect the measured hardness value. Combi nation of the nanoindentation equipment with atomic force microscopy facilitates the study of t hese effects, and offers a key procedure also for methodological development in this field.

Macrosegregation in CC Slabs

In continuously cast semi-finished products, fluid flow results in macrosegregation patterns. There are two reasons for fluid flow during solidification: density differences in the liquid phase and outer forces or constraints, which mix, suck or squeeze the liquid inside. The calculation method described in this paper can be used to analyze the effects of fluid flow caused by outer constraints and to estimate the expected macrosegregation level.

Advanced Structural Steels in the Hungarian Steel Industry

At the beginning of the third millennium, the world’s annual steel production reached 900 million tons. Flat products account for the majority of the production. It is also known that around three times the amount used today would be needed if the mechanical properties of the steels produced would have stagnated on the level characteristic of the 1930s and 40s. The history of the development and production of HSLA steel in Hungary dates back to the beginning of the 1960s. For the construction of the new Erzsébet Bridge, research workers at Danube Steelworks and at Steel Industry Research Institute developed the Ti micro-alloyed steel MTA50. In the study, we will summarise the history of the development of steels of the 700MPa strength category, thereafter we will introduce the main features of the project running within the scope of the National Research and Development Programme aimed at the development of DP- and TRIP-steels, and we will finally report on the results of the first year of the three-year project.

Effect of the Enamel Firing Thermal Cycle on the Microstructure and the Hydrogen Permeability of Enamel-Grade Steels

The tendency for fish-scale formation of steel sheets is charac terized by the t o value directly related to the microstructure of the sheet. During the f iring thermal cycle the microstructure undergoes several changes. Changes of the t o value and the microstructure were examined for three steel grades. A new conception for the development of steel sheet for vitre us enamelling has also been formulated.

Hot Ductility Variations of ST52-3 Continuously Cast Steel within the Cast Strand

Along the metallurgical length at continuous casting, the temperature within the strand ranges from above melt temperature (>1500) to about 900 oC. In this range, mechanical properties drastically drop at above the zero deformation temperature (ZDT) and the zero strength temperature (ZST), therefore crack susceptibility increases. These temperatures depend on (local) chemical and microstructural properties. We investigated the change in ZDT and ZST for ST52-3 steel grade by taking samples from the as-cast strand from positions of the columnar grains and from the centreline segregated zone. We found more than 100 oC drop in ZDT due to segregations in the centreline compared to the columnar zone within the strand.

The Effect of Alloying Elements on the Stability of Centerline Segregation

The paper deals with the stability of centerline inhomogenity of continuously cast slabs and hot rolled products. The centerline segregation is a disadvantageous failure of slabs which can affect the quality properties of the final products. During hot rolling of slabs the centerline segregation pattern will become thin and stretch and it can also be detected in the middle part of heavy plates and coils. It is a common experience that the centerline segregation of heavy plates can not be easily decreased by post heat treatment. The pattern of the centerline segregation was modeled physically by preparing a sandwich structure of steel plates with different levels of carbon and alloying elements. Homogenization experiments were performed and the samples were examined metallographically. Diffusional calculations proved the governing role of carbon activity which is influenced by the distribution of alloying elements.