Ján Viňáš

Analysis of Laser Welds on Automotive Steel Sheets

The paper presents results of quality analysis of the welded joints realized by CO2 laser (AF8P) using automotive body sheets and sheets for car chassis. There were used double-sided galvanized steel sheets of different grades and thicknesses. Welded joints were evaluated visually and then carrying capacity of the joints was established using tensile test. Welded joints were tested by following destructive tests: microhardness, macro and microstructure of the joints on metallographic sections using light microscopy. Results showed that the welding parameters were chosen appropriately.

Tribological properties of selected ceramic coatings

The paper presents the characteristics of some ceramic coatings obtained by a plasma spray method. The ceramic coatings Al2O3, Cr2O3 and Cr2O3 + 5% TiO2 were evaluated. Also the influence of the NiCr interlayer on the functional properties of sprayed coatings was studied. Other parameters studied included: thickness; microhardness; adhesion of the coatings; resistance to abrasive wear and thermal cyclic loading. The addition of TiO2 to the Cr2O3 material increased the coating density, but did not substantially reduce the hardness. On the other hand, the lowest loss of material thickness was seen for Cr2O3; while the Al2O3 and the Cr2O3 + 5 wt.% TiO2 material showed a higher loss. The loss in the case of the latter two was about the same. Relatively, higher values of abrasive wear resistance were observed in the Cr2O3 coatings, as compared to the reference material (Al2O3 coating), and the highest microhardness values were measured in the Cr2O3 coating. Finally, the metal interlayers in all coatings increased their resistance to thermal shock. All the coatings, using the interlayer to reduce differences in coefficients of thermal expansion, were suitable for the purpose of the thermal loading up to 1000 °C.

Degradation of renovation layers deposited on continuous steel casting rollers by submerged arc welding

The factors that affect the life of continuous steel casting rollers were investigated. Rollers that were removed from a manufacturing line because they had failed were renovated by submerged arc welding and subjected to working conditions until they again failed. The welding parameters (welding current, welding voltage, welding speed, current polarity, preheating temperature, interpass, postheating, and cooling conditions of clad) and chemical reactions and compositions had important effects on roller lifetime. Chromium has a dominant influence on the abrasion resistance of hard martensitic structures of the roller. Cr produces several types of precipitates (M3C, M23C6, M7C3, and M3C2). Alloying elements Mo and V in welding wire form fine carbides Mo2C and VC in weld layers. In low-carbon welding wires, precipitation hardening by N2 is used, by formation of chromium nitrides CrN and Cr2N. This article analyzes the process of failure of the functional surfaces of the repaired roller, in order to identify the origin and propagation of the cracks and share of corrosive environment on the tribo-degradation processes.

Optimization of resistance spot welding parameters for microalloyed steel sheets

Abstract The paper presents the results of resistance spot welding of hot-dip galvanized microalloyed steel sheets used in car body production. The spot welds were made with various welding currents and welding time values, but with a constant pressing force of welding electrodes. The welding current and welding time are the dominant characteristics in spot welding that affect the quality of spot welds, as well as their dimensions and load-bearing capacity. The load-bearing capacity of welded joints was evaluated by tensile test according to STN 05 1122 standard and dimensions and inner defects were evaluated by metallographic analysis by light optical microscope. Thewelding parameters of investigated microalloyed steel sheets were optimized for resistance spot welding on the pneumatic welding machine BPK 20.

Evaluation of the quality of cladding deposited on continuous steel casting rolls

Abstract This paper presents the quality analysis of cladding layers deposited on continuous steel casting rolls made of 41CrMo4 (EN 10083-1-91). The effect of filler used on the tribological properties of claddings was analyzed. There was minimal mixing between the base material and interlayer observed in the process of hard surfacing. The microstructure of the interlayer and the coatings is martensite–ferrite. Dispersed carbides MC, M7C3, and Cr23C6 were observed in the interlayer. Small amounts of carbides were also observed in the cover layer along with Cr2N and CrN, which was confirmed by energy dispersive X-ray analysis. The highest average hardness, 410 HV30, was measured in the cover layer at a distance of 1 mm from the surface. The lowest hardness was found in the base material, 239 to 243 HV30. The hardness of the interlayer metal is affected by mixing of cladding and cover layer metal. The cladding metal showed a martensite–ferrite structure and fine precipitates in the interlayer, and diffraction spectra of the carbides had the characteristics of MC, M7C3, and Cr23C6 carbides. Lower abrasive wear has been reported in the reference material (a roll with a surface-hardened layer), which is in line with the contact surface hardness of test samples.

Restoration of Worn Movable Bridge Props with Use of Bronze Claddings

This article examined the possibility of using CuSn6P claddings in sliding bearing renovation of movable pontoon bridge props. The bronze layer was welded on cylinders of the high-strength steel S355J0WP EN 10155-93, in an inert atmosphere using an automated welding method (gas tungsten arc welding). Pulsed arc welding was used to minimize the effects of heat on the cladding area, while also accounting for the differences in the physical properties of the joined metals. The sliding bearing was created in two layers. The quality of the cladding layer was evaluated by nondestructive and/or destructive tests. The quality of the surface was assessed by visual inspection (visual testing) in accordance with the EN ISO 17637 standard. The quality of the claddings was evaluated by metallographic analysis, performed using light microscopy. The microhardness values of a few weld areas were determined by Vickers tests, performed according to the EN ISO 9015–2 standard. The analyses confirmed that the welding parameters and filler material used resulted in high-quality weld joints with no internal (subsurface) or metallurgical defects.

Cladding of Wear-Resistant Layers in Metallurgy and Engineering

The paper presents the application of weld layers used in renovations of functional surfaces of components that are exposed to several tribodegradation factors in operation of metallurgical and engineering industries. Surfaces of selected components are renovated using arc welding processes, namely: (MMAW) Manual Metal Arc Welding, (SAW) Submerged Arc Welding methods, (GMAW) Gas metal arc welding and (FCAW) Flux cored wire metal arc welding without gas shield. Claddings were made always three-layered directly on the surfaces of renovated components using dedicated cladding machines in operations and laboratory conditions respectively. Their quality was assessed using non-destructive tests, namely (VT) visual testing by STN EN ISO 17637 and (UT) Ultrasonic testing STN EN ISO 11666. Within the destructive tests the quality of claddings was evaluated using the metallographic analysis conducted on a light microscope Olympus BX and electron microscope Jeol where the impact of mixing the weld metal as well as heat treatment after cladding on the final structure of claddings was observed. Using the Shimadzu HMV 2 device the microhardness of cladding layers was evaluated on metallographic samples by STN EN ISO 9015-2. In laboratory conditions the resistance of cladding layers to abrasive wear was verified on the device Di-1. Experimental testing of the claddings confirmed that the selected additives and cladding parameters witting individual technology were chosen correctly as in cladding layers no presence of internal defects was observed.

Resistance of Cladding Layers Made by FCAW Method to Erosive Wear

The paper deals with the tribological properties of investigated types of hard-faced materials at erosive wear process. Influence of inclination angle of elements on friction resistance and microhardness changes of hard-faced layer were investigated too. From quantitative aspect were hard-faced layers evaluated on the base of weight loses. From achieved results follow that inclination angle is one from determining factors on to material’s wear measure.

Quality Analysis of Welding Joints on Helically Welded Pipes

This material presents the results of the quality evaluation of the weld joints on helically welded pipes, diameter DN 800 mm, made of HSLA steel X 70 (L 485 MB EN 10208-2) with a wall thickness of 11mm. The pipes designed for transportation of natural gas were submerged arc welded by method 121 EN ISO 4063. The filler material used was welding wire OK Autrod 12.24, and the basic flux S A AB 1 67 AC H5 EN ISO 14 174 in two grain-size ranges (0.2-0.8 mm) and (0.8-1.6 mm). The quality of the weld joints was evaluated using a visual inspection, radiation inspection, static tensile test, impact strength tests, macroscopic and microscopic analysis of the weld joints using the light microscopy. The analysis confirmed only minimal differences in the quality of weld joints in favor of the joints welded by the filler with 0.8-1.6 mm grain-size.

Analysis of Welds Made by Delta Spot Method

Resistance spot welding has been widely used in sheet fabrication for several decades. Development of new materials leads to innovation of welding processes. The paper describes the principle of innovative welding method known as Delta Spot and evaluates the properties of Delta Spot joints made by combination of galvanized steel sheets H220PD (a0 = 0.9 mm) and TRIP 40/70+Z100MBO (a0 = 0.77 mm). The quality of welded joints was evaluated by tensile test and metallographic analysis. The influence of the welding parameters on the structure of welded joint was observed too. The properties of Delta Spot joint were compared to the properties of standard resistance spot welds.