Vlatko Marušić

Characteristics of modified martensitic stainless steel surfaces under tribocorrosion conditions

Abstract Stainless steel samples were tested in the laboratory and under real conditions of tribocorrosion wear. Electrochemical tests were also carried out to verify the corrosion resistance of modified steel surfaces. Metallographic analysis and hardness testing were conducted on stainless steel samples X20Cr13 and X17CrNi16 2. The possibilities of applications of modified surfaces of the selected steels were investigated by testing the samples under real wear conditions. The results have shown that the induction hardened and subsequently nitrided martensitic steels achieved an average wear resistance of up to three orders of magnitude higher as compared to the delivered condition.

Multi-objective optimization of cut quality characteristic in CO2 laser cutting stainless steel

Original scientific paper In this paper, multi-objective optimization of the cut quality characteristics in CO2 laser cutting of AISI 304 stainless steel was discussed. Three mathematical models for the prediction of cut quality characteristics such as surface roughness, kerf width and heat affected zone were developed using the artificial neural networks (ANNs). The laser cutting experiment was planned and conducted according to the Taguchi’s L27 orthogonal array and the experimental data were used to train single hidden layer ANNs using the Levenberg-Marquardt algorithm. The ANN mathematical models were developed considering laser power, cutting speed, assist gas pressure, and focus position as the input parameters. Multi-objective optimization problem was formulated using the weighting sum method in which the weighting factors that are used to combine cut quality characteristics into the single objective function were determined using the analytic hierarchy process method.

Pipes Life Prolonging Possibility in Boilers Fired up by Municipal Waste

This paper describes the specifics of the waste incineration boiler with natural circulation fueled with municipal waste. During operation, certain parts of the boiler are exposed to corrosion and erosion due to effect of particles from the flue gas stream at high temperature. Tests have been performed which include sediment and pipe damage after one year of boiler work. Chemical analysis of sediment samples was taken from the tubes was determined presence of NaCl and Fe compounds and share from 18 % organic substances in the presence of SO3.

Resistance of Thin Layers in Abrasion Under High Pressures

Abstract Testing of wear resistance of the layers in contact with abrasive SiO2 was done by two procedures: I – in a laboratory according to ASTM G 65-94, and II – in practice on knives of screw (worm) presses used for oil extraction from sunflower seeds. By comparing of mass loss it was estimated that there is poor correlation between results by dry sand/rubber wheel method compared with results obtained from knives. Carburised layers are compared with thin and harder than SiO2 vanadium created by duplex procedure, and boron treated layers, as well as with CrN and multilayer SiC + DLC protective layers applied by PVD procedures. Based on wear marks analysis of all protective layers and based on mass loss between the samples after testing according to both methods, it has been concluded that there is highly emphasised influence of hardness change from the beginning of under layer towards the core. The influence of hardness change from the beginning of the sub-layer towards the core is very important. That is indicated by greater resistance of vanadium, SiC + DLC and carburised knives as compared to CrN and boron treated ones which have a sub-layer with much smaller hardness.