Kamil Kolařík

Effect of Boriding Time on Microstructure and Residual Stresses in Borided Highly Alloyed X210CR12 Steel

Boriding of highly alloyed steels done with the aim of increasing their wear resistance faces several issues connected with the microstructure of the base material and restraints during the diffusion of boron. The aim of the performed analyses was to ascertain whether significant increase of boriding time can enhance the surface hardness, contribute to creation of more compact microstructure and even lead to beneficial state of residual stresses in the borided layer. Using combination of X-ray diffraction and electro-chemical polishing, residual stress depth distributions in few tens of micrometres thick borided layers were obtained.

Study of Residual Stress Surface Distribution on Laser Welded Steel Sheets

Advent of high power diode laser has substantially contributed to the popularity of laser welding in industry where its virtues such as low heat input and good weld strength are highly appreciated. However, one of the drawbacks of the laser welding is distortion of the welded bodies that is closely linked with the generation and/or redistribution of residual stresses in the vicinity of the weld. In this contribution, mapping of surface macroscopic residual stresses in two directions, i.e. parallel and perpendicular to the welds, were performed for two bodies. The first contained a weld created with the high power diode laser beam speed of 2 m/min and the second with the speed of 15 m/min. Our aim was to compare not only resulting fields of residual stresses, but also to perform qualitative assessment of the possible presence of crystallographic texture and gain a qualitative apprehension about the grain sizes in the vicinity of a laser weld joining two steel sheets. Larger distortion of the body with a laser weld is exhibited by the sample manufactured with approximately 8 times bigger speed of laser beam. This sample is in the immediate vicinity characterized by substantial compressive residual stresses in the direction perpendicular to the weld.

REAL STRUCTURE AND RESIDUAL STRESSES IN ADVANCED WELDS DETERMINED BY X-RAY AND NEUTRON DIFFRACTION

The paper outlines the capability of X-ray diffraction (XRD) for evaluation of real structure changes and residual stresses (RS) on cross-section of advanced thick welds due to the welding of ferromagnetic plates. The results of neutron diffraction describe a three-dimensional state of RS and also verify previous assumptions of RS redistribution as a result of the surface preparation for determination 2D maps measured by XRD.

COMPARISON OF PARAMETERS OF SURFACE INTEGRITY OF MACHINED DUPLEX AND AUSTENITE STAINLESS STEELS IN RELATION TO TOOL GEOMETRY

The goal of this contribution was to describe parameters of surface integrity of two machined materials; austenite and duplex stainless steel. Residual stresses and presence of straininduced martensite were studied as a function of the side rake angle. Residual stresses of surface and sub-surface layers were determined using X-ray diffraction techniques and hole-drilling method. By using X-ray diffraction, it is possible to determine residual stresses in each phase separately, in comparison with hole-drilling method. The presence of strain-induced martensite was investigated using Barkhausen noise and optical microscope.

INFLUENCE OF MACHINING TECHNOLOGIES ON VALUES OF RESIDUAL STRESSES OF OXIDE CUTTING CERAMICS

Currently, the intensive development of engineering ceramic and effort to replace sintered carbides as cutting materials are in progress. With the development of the sintering technology it is now possible to produce compact ceramic cutting samples with very good mechanical properties. The advantage of these materials is their easy accessibility and low purchase price. In this work, the influence of the finishing machine technology on the values of surface residual stresses of cutting ceramic samples Al2O3+TiC were studying. The samples were supplied by Moscow State University of Technology STANKIN. Measurements made in the X-ray diffraction laboratory at the Department of solid state engineering were performed for both the phases. The influence of the parameters of machining to residual stresses was studied and the resulting values were compared with each other.

X-Ray Diffraction Analysis of Steel with Oxidised Surface Layer

The basic principle of the X-ray diffraction analysis is based on the determination of components of residual stresses. They are determined on the basis of the change in the distance between atomic planes. The method is limited by a relatively small depth in which the X-ray beam penetrates into the analysed materials. For determination of residual stresses in the surface layer the X-ray diffraction and electrolytic polishing has to be combined. The article is deals with the determination of residual stress and real material structure of a laser-welded steel sample with an oxide surface layer. This surface layer is created during the rolling and it prevents the material from its corrosion. Before the X-ray diffraction analysis can be performed, this surface layer has to be removed. This surface layer cannot be removed with the help of electrolytic polishing and, therefore, it has to be removed mechanically. This mechanical procedure creates “technological” residual stress in the surface layer. This additional residual stress is removed by the electrolytic polishing in the depth between 20 and 80 μm. Finally, the real structure and residual stresses can be determined by using the X-ray diffraction techniques.

X-Ray Diffraction and Barkhausen Noise Diagnostics of Thick Welds Prepared by Metal Active Gas and Laser Welding

Non-destructive methods for detection and measurement of residual stresses (RS) have been increasingly used in the last few years. The paper outlines the capability of Barkhausen noise analysis (BNA) for evaluation of real structure changes and RS on cross-section of welds due to welding of ferromagnetic plates compared with X-ray diffraction (XRD). The purpose of this study is to evaluate the RS distribution of specimens joined using by high power diode laser and metal active gas (MAG) welding that can be used for quantitative analysis of macro and micro level RS separately. The principal advantages of BNA over XRD as a tool for RS analysis and real structure characterisation are that it is mobile, faster with more facile carrying out and hence BNA is frequently used for continuous monitoring of RS in industrial processes.

Behaviour of domex S355 laser welds under stress

The stresses in welds are the result of phase transformations and thermal expansion. Both mechanisms are connected with the heat input which is less in laser welding than arc welding methods. The paper describes laser welding of high-strength steel with the yield strength of 355 MPa without and with filler material. As expected, laser welds show a lower level and lower concentrations of internal stresses at critical points. The result is a higher level of mechanical properties and a tensile strength close to that of the base material. Cracks in parts laser welded with filler material propagate in the base metal, while cracks in parts welded without filler material occur in the heat affected zone. The filler material also leads to improved impact strengths when compared to plain laser welds.The stresses in welds are the result of phase transformations and thermal expansion. Both mechanisms are connected with the heat input which is less in laser welding than arc welding methods. The paper describes laser welding of high-strength steel with the yield strength of 355 MPa without and with filler material. As expected, laser welds show a lower level and lower concentrations of internal stresses at critical points. The result is a higher level of mechanical properties and a tensile strength close to that of the base material. Cracks in parts laser welded with filler material propagate in the base metal, while cracks in parts welded without filler material occur in the heat affected zone. The filler material also leads to improved impact strengths when compared to plain laser welds.