Mikrostruktura i svojstva materijala uz crtu taljenja

In this paper, the formation of the HAZ that is caused by the thermal effects of welding is investigated from the theoretical and experimental points of view. Samples of the material found at the fusion line were prepared by simulating the thermal regimes that occur during welding. A number of CCT diagrams that are valid for the conditions during welding were designed, and the hardness and impact-toughness of the samples were measured. This information was then related to the results of metallographic examinations. The maximum temperature and the cooling rate of the applied thermal cycles were found to be decisive in terms of the properties of the HAZU ovom članku je sa teorijskog i eksperimentalnog motrišta istraživano ustrojstvo zone utjecaja topline (ZUT-a) koji je prouzrokovan termičkim utjecajima zavarivanja. Uzorci materijala, koji se nalazi uz crtu taljenja, bili su pripremljeni simulacijom termičkog postupka za vrijeme zavarivanja. Ustrojeno je više CCT dijagrama, koji važe za uvjete zavarivanja, a mjereni su takođe i tvrdoća te žilavost uzorka. Ti podaci su zatim uspoređeni sa rezultatima metalografskih ispitivanja. Obzirom na svojstva ZUT odlučujući su najviša temperatura primjenjenih termičkih ciklusa i brzina hlađenja

Nastanak zamorne pukotine iz mikrostrukturno malih vickersovih otisaka

The resistivity of a coarse grain steel against fatigue crack initiation in presence of micro-defects is discussed. Samples of material with martensitic microstructure were prepared by adequate thermal treatment. Microstructurally small Vickers indentations were used as artificial micro-defect. The compressive residual stresses are due to the irreversibility of plastic deformation. The moment of indenting enables to prepare samples with and without effects of residual stresses. The stress level for crack initiation depends on the actual indentation size. The location of initiated cracks is affected by the presence and character of residual stresses.Proučavana je otpornost grubozrnatog dijela zone utjecaja topline na nastanak zamorne pukotine u prisustvu mikro greški. Uzorci materijala s martenzitnom grubozrnatom mikrostrukturom pripremljeni su odgovarajućom toplinskom obradom. Kao umjetne mikro greške upotrijebljene su mikrostrukturno mali Vickers otisci. Tlačna zaostala naprezanja pojave se zbog nepovratnosti plastične deformacije. Moment kad se napravi otisak omogućava pripremu uzoraka s i bez efekata zaostalih naprezanja. Kritičkna razina naprezanja za nastanak pukotine zavisi od stvarne veličine otiska. Na lokaciju nastanka pukotine utječe i prisutnost te vrsta zaostalih naprezanja

Crack emanation from defects modelled by extremely small drilled holes in two conditions

Fatigue is the primary reason for the failure of structural components. Resistivity of a coarse grain heat affected zone against fatigue crack initiation in presence of micro-defects is discussed in the present article. Samples of material with a martensitic coarse grain heat affected zone microstructure were prepared by proper thermal treatments. Microstructurally small holes were used as artificial micro-defects. They were created by drilling. Compressive residual stresses appear in the material due to the irreversibility of plastic deformation. Moment of hole drilling enables to prepare samples with and without effects of residual stresses. Critical stress level for fatigue crack initiation depends on the actual size of the hole. The location and the way of crack initiation is affected by the presence and character of residual stresses

Charpy žilavost vibriranih mikrostruktura

The aim of this study was to investigate the influence of vibration on impact toughness of weld metal. Studies were carried out on two welds, of which one had been welded with applying vibration during welding. From test plates samples were made to simulate heat affect in combination with or without vibration after solidification. This way conditions at multi-pass welding were simulated. According to different conditions Charpy toughness on non standard specimens and fracture appearance were observed. Vibration during welding benefits impact energy of weld metal, especially if weld metal undergoes further heat treatment.Namjena ovog članka je istraživanje utjecaja vibriranja na udarnu žilavost zavara. S namjenom istraživanja zavarena su dva zavara s istim parametrima, s tim da je jedan od zavara tijekom procesa zavarivanja bio podvrgnut vibraciji. Iz probnih ploča uzeti su uzorci koji su bili dodatno grijani u peći. Neki uzorci su bili dodatno vibrirani u peći. Tim postupkom simulirano je višeprolazno zavarivanje. Mjerena je Charpy žilavost na nestandardnim uzorcima i analizirani prelomi obzirom na različite uvjete grijanja i vibriranja. Vibracije za vrijeme zavarivanja povećavaju udarnu žilavost zavara, posebno ako je zavar podvrgnut naknadnom toplinskom utjecaju

Utjecaj simuliranog termičkog ciklusa na stvaranje mikrostruktura višeprolaznog zavara

In the present work was analysed the influence of weld thermal cycle on the microstructural changes in weld metal by use of the simulated microstructures. We examined the kinetics of the formation of austenite from the starting microstructure. The simulated microstructures were prepared by the application of simulated thermal cycles with different peak temperatures on a sample of real single-pass weld metal. The reproduction of thermal cycles were carried out by the SMITWELD simulator. Special attention was dedicated to the influence of thermal cycle on the formation of microstructures, which can be potential triggers of brittle fracture (local brittle zones).U ovom radu je eksperimentalno analiziran utjecaj termičkog ciklusa kod zavarivanja na mikrostrukturne promjene u zavaru. Simulirane mikrostrukture bile su pripremljene pri termičkim ciklusima različitih maksimalnih temperatura na uzorcima realnog jedno prolaznog zavara. Simulirani termički ciklusi bili su izvedeni na SMITWELD simulatoru termičkog ciklusa. Posebna pažnja bila je usmjerena utjecaju termičkog ciklusa na stvaranje mikrostruktura, koje bi mogle biti potencijalna mjesta za krti lom (lokalno krte zone)

Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slag

The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT

Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slag

The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT

Втомна міцність зварних з’єднань за наявності дефектів створених пірамідою вікерса

The fatigue strength of polycrystalline metals is hardness and defect size dependent. The fatigue strength of welds depends upon the size of grains and actual local mean stress, too. Local mean stress is influenced by the global R-ratio and static preloading. The welds in the as-welded condition are pre-stressed due to the existence of welding residual stresses. The sign and magnitude of residual stresses depend upon the welding conditions. Changes of residual stresses, hardness and defect size were experimentally determined in the present work. Samples of studied metals were prepared by using either thermal cycle simulator or laboratory furnace and water quenching. The methods of microstructure preparation and type of loading result in actual local R-ratio at the used weld toe models. Specimens were cyclic loaded in the similar way like steel at the weld toe. The bottom of the notch was either defects-free or defected by Vickers indentation. Final results show that coarser grain and higher local R-ratios lower the fatigue strength of welds.Втомна міцність полікристалів залежить від розміру дефекту та твердості матеріалів Проте, втомна міцність зварних з’єднань залежить також від розміру зерна та локальних напружень матеріалу. Локальні передні напруження визначаються величиною залишкових напружень та параметрами попереднього статичного навантаження. Після формування зварного шва у ньому формуються залишкові напруження знак та величина яких залежать від режиму зварювання. В цій роботі досліджено зміну остаточних напружень твердості та розмірів дефектів у зразках з модельованим термоциклом та після нагрівання в термокамері та наступного гартування. Методи фізичного моделювання структури матеріалу дозволяють відтворити матеріал зони зварного шва. За результатами відтворення експлуатаційного циклічного навантаження виявлено, що збільшення розміру зерна та залишкових напружень в матеріалі знижують втомну міцність зварних швів

Mikrostruktura i svojstva materijala uz crtu taljenja

In this paper, the formation of the HAZ that is caused by the thermal effects of welding is investigated from the theoretical and experimental points of view. Samples of the material found at the fusion line were prepared by simulating the thermal regimes that occur during welding. A number of CCT diagrams that are valid for the conditions during welding were designed, and the hardness and impact-toughness of the samples were measured. This information was then related to the results of metallographic examinations. The maximum temperature and the cooling rate of the applied thermal cycles were found to be decisive in terms of the properties of the HAZU ovom članku je sa teorijskog i eksperimentalnog motrišta istraživano ustrojstvo zone utjecaja topline (ZUT-a) koji je prouzrokovan termičkim utjecajima zavarivanja. Uzorci materijala, koji se nalazi uz crtu taljenja, bili su pripremljeni simulacijom termičkog postupka za vrijeme zavarivanja. Ustrojeno je više CCT dijagrama, koji važe za uvjete zavarivanja, a mjereni su takođe i tvrdoća te žilavost uzorka. Ti podaci su zatim uspoređeni sa rezultatima metalografskih ispitivanja. Obzirom na svojstva ZUT odlučujući su najviša temperatura primjenjenih termičkih ciklusa i brzina hlađenja

Charpy žilavost vibriranih mikrostruktura

The aim of this study was to investigate the influence of vibration on impact toughness of weld metal. Studies were carried out on two welds, of which one had been welded with applying vibration during welding. From test plates samples were made to simulate heat affect in combination with or without vibration after solidification. This way conditions at multi-pass welding were simulated. According to different conditions Charpy toughness on non standard specimens and fracture appearance were observed. Vibration during welding benefits impact energy of weld metal, especially if weld metal undergoes further heat treatment.Namjena ovog članka je istraživanje utjecaja vibriranja na udarnu žilavost zavara. S namjenom istraživanja zavarena su dva zavara s istim parametrima, s tim da je jedan od zavara tijekom procesa zavarivanja bio podvrgnut vibraciji. Iz probnih ploča uzeti su uzorci koji su bili dodatno grijani u peći. Neki uzorci su bili dodatno vibrirani u peći. Tim postupkom simulirano je višeprolazno zavarivanje. Mjerena je Charpy žilavost na nestandardnim uzorcima i analizirani prelomi obzirom na različite uvjete grijanja i vibriranja. Vibracije za vrijeme zavarivanja povećavaju udarnu žilavost zavara, posebno ako je zavar podvrgnut naknadnom toplinskom utjecaju