Ispitivanje zavarljivosti čelika TStE 420 nakon simulacije toplinskog ciklusa zavarivanja

The paper presents a short description and overview of the weld thermal cycle simulation methods. An experimental investigation on the weld cycle simulated specimens is predicted by a plan of experiment using single cycle simulation. The obtained hardness results are compared with double cycle simulated specimens results of individual points in the heat-affected zone. Beside that, the characteristic microstructures of points in the heat-affected zone after a single weld thermal cycle simulation are given. A thermal simulation method is suitable for different weldability examinations. In this paper, the authors would like to investigate the maximal hardness of individual points in the weld joint what is important when considering cold cracking sensitivity.U radu se daje kratak opis i pregled metoda simulacije toplinskog ciklusa zavarivanja. Planom eksperimenta je predviđeno eksperimentalno istraživanje na toplinski cikliranim uzorcima. Mjerenjem dobiveni rezultati tvrdoće nakon jednostruke simulacije toplinskog ciklusa u zoni utjecaja topline su uspoređeni s rezultatima nakon dvostruke simulacije toplinskog ciklusa. Pored toga, u radu su prikazane karakteristične mikrostrukture pojedinih točaka u zoni utjecaja topline nakon jednostruke simulacije toplinskog ciklusa zavarivanja. Simulacija toplinskog ciklusa je prikladna za različita ispitivanja zavarljivosti, a u ovom su radu autori željeli istražiti maksimalno očekivane tvrdoće pojedinih točaka u zoni utjecaja topline što je važno kod razmatranja osjetljivosti prema hladnim pukotinama

Ponašanje grubozrne zone utjecaja topline (ZUT) zavara tijekom cikličkog opterećenja

This paper presents results of a study on martensitic coarse grain heat affected zone that can appear in welded joints. Mechanical properties of martensitic coarse grain heat affected zone and its microstructure were investigated. Special attention was given to its behaviour during the cycle loading under stress concentration. Stress concentration was similar to the one in real welds. The S-N curve and the fatigue limit were determined. The Paris curve and the threshold for crack propagating were also determined.U radu se istražuje martenzitna grubozrnata zona utjecaja topline koja se može pojaviti pri zavarivanju. Istražena su mehanička svojstva i mikrostruktura ove zone. Posebna je pažnja posvećena njenom ponašanju tijekom cikličkog opterećenja kada je prisutna koncentracija naprezanja. Koncentracija naprezanja je slična onoj kod realnog zavarivanja. Određena je S-N krivulja i granica umaranja. Također je određena i Parisova krivulja i prag propagacije pukotine

Fitting curves and impact toughness transition temperature of quenched and tempered steel welds

Welded products of quenched and tempered (QT) structural steels are used from ambient to moderately low design/service temperatures. Therefore, besides base metal, a weld also must possess required minimal design impact toughness (KV) at temperatures lower than transition temperature (TT), where the transition from ductile to brittle fracture occurs. A common way to determine transition temperature is by use of appropriate fitting curves, in accordance with specified standardised criterion. From the point of welding procedure evaluation, it is important to analyse welds for its impact toughness and transition temperature, particularly for three main zones: weld metal, heat-affected zone (HAZ) and base metal. This paper covers welds of two QT steel grades, 690 and 890, which are interesting regarding their yield strength and characteristic weld zones. Basic details of gas metal arc welding (GMAW, process used in this experiment) are provided, while temperatures for impact toughness tests of weld zones were varied from +20 °C down to -60 °C. Based on acquired experimental results of impact toughness, fitting curves were developed by use of Oldfield model, e.g. hyperbolic tangent function. Acquired transition temperatures (TT) from fitting curves show mostly allowable values for all three weld zones. As expected, lower strength grade 690 possess higher impact toughness, in comparison to higher strength grade 890. The standardized criteria of minimal absorbed energy of 30 J (KV) and 50 % of shear fracture (SF) show different transition temperatures (TT-30J and TT-50%SF), while general dependence of impact toughness to shear fracture (KV vs. SF) shows a reasonable trend. Finally, used GMAW procedures may be considered as acceptable, since for both steel grades (690 and 890) all three weld zones show better TT-30J values than minimal required by standard (TT-30J=-40 °C) for QT structural steels

HEAT AFFECTED ZONE MICROSTRUCTURE OF WELD JOINT PREPARATION IN ARTIFICIAL MANNER

This paper presents two possibilities of martensitic (fine grain and coarse grain) microstructure preparation. These microstructures are present as sub-zones in the heat-affected zone of welded joints, but due to the narrow region of HAZ in a real weld, only a few tests are possible to perform such as micro-hardness. Welding simulator and laboratory furnace were used as methods for the preparation of the specimens. The material used in this study was a Nickel Molybdenum alloy steel (18CrNiMo7-6). Investigation of the mechanical properties of sub-zones of the HAZ of this particular alloy steel, were done by applying proper thermal cycles. Hardness and diameter of grain size were measured, tensile strength is calculated and Charpy instrumented test of both microstructures were performed in room temperature. The difference in Impact toughness was remarkable due to the difference in microstructure, energy for initiation and propagation were calculated by comparing (F-t and E-t) diagrams for both microstructures. The study revealed that the preparation of specimens with microstructure as at welded condition is possible, and it could lead to prepare samples for investigation of other mechanical properties such as fatigue crack growth and fracture toughness test

Analiza absorbera kinetičke energije željezničkih vozila metodom konačnih elemenata

The paper describes the Finite Element Method (FEM) analysis of elastic plastic deformation of steel tube impact absorbers for railway vehicles. Experiment investigation is used as a base for FEM modelling and simulation. The developed FEM model includes material nonlinearity (plasticity), nonlinear contact and large deformation of finite elements. All of aspects used in the absorber FEM model are detailed explained. The Finite Element Analysis results for a chosen absorber are presented and discussed. Developed model opens the possibilities for next investigations in similar problems.Rad daje opis analize elastoplastičnih deformacija čeličnog cevnog apsorbera kinetičke energije sudara željezničkih vozila metodom konačnih elemenata (MKE). Eksperimentalna istraživanja korišćena su kao osnova za modeliranje i simuliranje MKE modela. Razvijeni model konačnih elemenata uključuju nelinearne karakteristike materijala (plastičnost), nelinearni kontakt i velike deformacije konačnih elemenata. Svi aspekti korišćeni u MKE modelu apsorbera detaljno su opisani. Rezultati MKE analize za izabrani apsorber prikazani su i diskutovani. Razvijeni model otvara nove mogućnosti za buduća istraživanja u sličnim problemima

Coupled nonlinear problems in finite element analysis: A case study

Rad daje opis analize elastoplastičnih deformacija čeličnog cevnog apsorbera kinetičke energije sudara železničkih vozila metodom konačnih elemenata (FEM). Eksperimentalna istraživanja korišćena su kao osnova za modeliranje i simulaciju FEM modela. Razvijeni model konačnih elemenata uključuje nelinearne karakteristike materijala (plastičnost), nelinearni kontakt i velike deformacije konačnih elemenata. Svi aspekti korišćeni u FEM modelu apsorbera detaljno su opisani. Rezultati FEM analize za izabrani apsorber prikazani su i analizirani. Razvijeni model otvara nove mogućnosti za buduća istraživanja u sličnim problemima.The paper describes the Finite Element Method (FEM) analysis of elastic plastic deformation of steel tube impact absorbers for railway vehicles. Experiment investigation is used as a basis for FEM modelling and simulation. The developed FEM model includes material nonlinearity (plasticity), nonlinear contact and large deformation of finite elements. All aspects used in the absorber FEM model are explained in detail. The finite element analysis results for a chosen absorber are presented and discussed. The developed model opens the possibilities for future investigations of similar problems

Acceptability of Residual Stresses Measurement Methods of Butt Weldments and Repairs

The joints made by fusion of materials are exposed to the influence of residual stresses induced by welding thermal cycles. Residual stresses were measured on butt welded plates made of NIOMOL 490K, before and after reparation. The objective of this paper is to compare three methods of residual stress measurement (hole-drilling method, x-ray diffraction and directional effective permeability) induced by two welding processes (Submerge Arc Welding and Transferred Ionized Molten Energy) of V-butt welded plates. The residual stresses values are higher after reparation than before reparation of welded joints

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Acceptability of Residual Stresses Measurement Methods of Butt Weldments and Repairs

The joints made by fusion of materials are exposed to the influence of residual stresses induced by welding thermal cycles. Residual stresses were measured on butt welded plates made of NIOMOL 490K, before and after reparation. The objective of this paper is to compare three methods of residual stress measurement (hole-drilling method, x-ray diffraction and directional effective permeability) induced by two welding processes (Submerge Arc Welding and Transferred Ionized Molten Energy) of V-butt welded plates. The residual stresses values are higher after reparation than before reparation of welded joints