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Laser welding of DP steel - characterization of microstructure of steel and welded joint

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Increasing demands on weight reduction, safety and cost have led to a rapid development in car body engineering. A number of new materials are being investigated, especially steels of greater strength. Advanced High Strength Steels (AHSS) are being intensively explored by the automotive industry [1]. The combination of excellent structural properties and good formability makes AHSS such as DP (Dual Phase) steel attractive candidates for light-weight vehicles. Dual Phase steels, so called because they consist essentially of a dispersion of martensite in a ferrite matrix, are produced by intercritically annealing and cooling with rate appropriate to achieve the desired structure [2]. Apart from the chemical composition, the microstructure and mechanical properties from the practical point of view the most important property is weldability of automotive steels [3]. Traditionally, resistance welding and fusion welding have been used in the automotive industry. However, the most prospective welding process in this branch of industry is laser welding. The main advantages of laser welding are small distortions of the sheets caused by a small width of HAZ, high welding speed and flexibility of this process [3]. Kang et al. [4] have shown results of laser welding of DP 600 steel 1.4 mm in thickness. They have performed hardness measurements, microstructure examination, mechanical properties and formability tests. The results have shown that the maximum hardness in the heat affected zone (HAZ) exceeds 350 HV. The maximum hardness was mainly the result of bainite, ferrite and small amounts of martensite phase. In another studies [5], High Strength Low Alloy (HSLA) and DP980 (980 MPa) sheet steels, 1.2 mm in thickness, were welded with a 4 kW diode laser. For the DP steel weld formability was much lower than that of corresponding base metal, due to the formation of soft zones in the outer region of the HAZ of the welds. Results of DP 600 [...]

Symulacje numeryczne i badania doświadczalne deformacji spawanego laserowo połączenia teowego typu I-core DOI:


  Praca dotyczy prognozowania numerycznego i pomiarów rzeczywistych odkształceń spawalniczych w spawanych laserowo innowacyjnych połączeniach teowych typu I-core, wykonanych ze stali S355. Analizę numeryczną zjawisk cieplnych i mechanicznych przeprowadzono za pomocą pakietu oprogramowania inżynierskiego Abaqus FEA. W algorytmie numerycznym zastosowano dodatkowe, autorskie procedury numeryczne służące do modelowania złożonych zjawisk cieplno-mechanicznych procesu spawania, takich jak: ruch źródła ciepła spawającego, rozkład mocy źródła ciepła wiązki laserowej oraz kinetyki przemian fazowych stali w stanie stałym. W obliczeniach numerycznych uwzględniono zmienne z temperaturą własności termomechaniczne spawanej stali. Wykonano badania doświadczalne struktury złącza i deformacji złączy spawanych. Przedstawiono porównanie obliczonych rozkładów temperatury i deformacji spawalniczych z wynikami eksperymentu. This paper contains numerical prediction and measurements of real welding deformations in laser welded innovative T-joints I-core type, made of 355 steel. Numerical analysis of thermal and mechanical phenomena is performed in Abaqus FEA engineering software. In the numerical algorithm additional author’s numerical procedures are used for modelling of coupled thermomechanical phenomena in welding process, such as: the motion of welding source, the distribution of laser beam heat source power and the kinetics of phase transformation in solid state. Changing with temperature thermomechanical properties of welded steel are taken into account in numerical calculations. Experimental measurements of welded joints structure composition and welding deformations are performed in this study. Presented results include calculated temperature distribution and welding deformations compared with experimental results. Słowa klucze: Spawanie laserowe, połączenie teowe, modelowanie numeryczne, zjawiska cieplne, przemiany fazowe, odkształcenia spawalnicze Ke[...]

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