Search

The replica technique was applied to evaluate crack initiation and crack propagation behavior of welded joints on high strength structural steel with a minimum yield strength of 690MPa. Wöhler tests (cyclic loading tests) on these high strength welded joints, supported by the replica technique, show, that at a given particular stress amplitude, crack initiation occurs in several areas of the heat affected zone. At high stress amplitudes, the failure occurs in the intercritical zone, whereas stress amplitudes near the endurance limit lead to a failure within the coarse grained zone. This can be attributed to the crack initiation and propagation behavior within these individual zones. Evidence for this can very well be provided by means of the microstructure replica technique described in this article.

Welded structures made of high-strength steel offer benefits in fatigue strength for finite life applications. The high-cycle fatigue limit, however, depends mostly on the geometry, and the metallurgy of the notch is of little account. Therefore, an optimised weld process is required to achieve an improvement in the fatigue strength. This paper contributes to the field of fatigue behaviour of thin-walled, high-strength steel butt joints, with regard to an optimisation of the gas metal arc weld process. An existing methodology was extended to manufacture welded specimens with minimised production scatter. The majority of the butt joint samples were dynamically tested, with the root surface ground flush to plate, to study the effect of the weld process on fatigue. The investigated specimen were carefully analysed by metallographic studies along with hardness, distortion, and weld toe topography measurements. This facilitated in finding a relation between experimental fatigue life and the weld parameters. The nominal stress approach, including a benign, nonconservative thinness correction, and the recommended notch stress concept, were applied to assess the fatigue behaviour of the thin-walled, high-strength steel butt joints. The experimental results showed that in case of high-quality welds with negligable geometric notch factor, a small, but distinct influence of the filler metal on fatigue is observable. The highest fatigue strength for the investigated butt joint design was obtained with a high-strength metal-cored wire filler in combination with a three-component shielding gas.

The present study describes the methods for the characterization of the microstructure of welded joints from test welds. This comprises the analysis of the solidification microstructure (primary and secondary dendrite arm spacing) as well as the former austenite grain size and the final phase distribution. The main focus is the characterization of nonmetallic inclusions by means of SEM/EDX and light microscopy. Based on already-developed prototypes with a weld yield strength of more than 800 MPa, different kinds of inclusions and precipitates have been assessed with respect to grain refinement and the resulting impact on strength and ductility. The effect of aluminum, in the range 90 to 800 ppm, on the microstructure and the mechanical properties of high-strength steel weld metals has been studied and it has been found that at low aluminum contents good values for the tensile strength and the toughness could be obtained. The results of metallographic investigations of test welds with different alloy compositions are presented. The results indicate a significant change of the size distribution, the morphology, and the composition of the inclusions. These results are finally compared with results from literature and discussed with respect to the expected influence on the mechanical properties of the welded joint.

Laser-gas metal arc (GMA)-hybrid welding enables a high deposition rate and a stable welding process. Process stability was found to be profoundly dependent on the type of the applied filler wire (solid or tubular cored). Whereas solid wires are deposited in pulsed arc mode, tubular cored wire electrodes are weldable by a stable spray-arc process within a wide operating range. This fact applies above all to a high alloyed metal cored wire electrode, of which the achievable deposition rates exceed the upper limits recommended by the manufacturer. A further interesting aspect is the application of a rutile tubular cored wire for positional laser-GMA-hybrid welding. A modern 20 kW-fibre laser source was available for the experiments. This study is concerned with the weldability of high alloyed tubular cored electrodes for high power laser-GMA-hybrid welding. Results obtained from comparative investigations between tubular cored and solid wire electrodes relating to process stability are summarised.

Bauteilkomponenten im chemischen Anlagenbau kommen oft in Berührung mit korrosiven Medien. Um diesen korrosiven Belastungen stand zu halten, werden im Falle von oxidierenden Medien häufig austenitische rostfreie Stähle erfolgreich eingesetzt. Diese Stähle haben allerdings verglichen mit un- und niedriglegierten Stählen zwei wesentliche Nachteile: neben dem höheren Preis ist auch die Werkstoffkenngröße für die Auslegung der Bauteile, die Streckgrenze, niedriger. Dadurch werden größere Querschnitte benötigt und damit verbunden wieder mehr Stahl. Als wirtschaftlicher Kompromiss bietet sich ein Verbund von un- bzw. niedriglegiertem Stahl als Trägerwerkstoff und einer dünnen Schicht aus hochlegiertem Stahl, einer sogenannten Plattierung an. Der ferritische Stahl gewährleistet dabei die hohen Festigkeiten, die austenitische Plattierung die notwendige Korrosionsbeständigkeit. Die Herstellung von plattierten Stählen geschieht dabei hauptsächlich durch Aufwalzen von hochlegiertem Blech auf dem unlegierten Trägerwerkstoff oder auch durch Aufschweißprozesse.

A new test method called “Bead Bend Test” for evaluation of the hydrogen-assisted cold cracking — (HAC) susceptibility of multi-layer welds will be presented. The main advantage of this test is the possibility of evaluation of weldments that are established by using real welding procedures. Also, different on-site stress conditions can be taken into account by variation of the clamping system. The test results can be used for theoretical investigations, but also for practical recommendations regarding the necessary minimum interpass temperatures to prevent HAC under consideration of the plate thickness, the materials strength level, and the diffusible hydrogen content of the weld metal. As an example, the HAC behaviour of high strength cellulosic pipeline weldments are discussed. An additional feature of this test procedure is the HAC evaluation of joints built up by a combination of different electrode types; e.g., cellulosic and basic types which are shown in a second example.

As already described earlier, stainless steels can form on their surface a protective, passive film on exposure to a service environment. This passive film, especially its stability and homogeneity, is responsible for the corrosion resistance of these materials. Welding can have a strong impact due to the typical segregated, multiphase weld metal structures and the additional influence of the weld heat cycle. This may result in a lower corrosion resistance of the weld metal compared to the base metal in case of a similar chemical composition. To describe the corrosion behaviour, many different tests have been developed, using different environments, different test temperatures and different test specimen preparation. But due to the variety of parameter settings and test conditions, the corrosion test results are often not comparable. To overcome this problem, standardized corrosion tests were established. Specimen preparation, test solution composition, test duration and temperature setting are defined to allow a “world wide” comparison. This paper gives an overview of which standardized tests are applied in practical use for typical types of material. Additionally some results of weld metal and joint testing are shown from which the influence of different thermal cycles, alloying concepts, surface conditions and shielding gases on the corrosion behaviour can be derived.

The innovative technological solutions by VAI (VOEST-ALPINE Industrieanlagenbau, Austria), which are presented, allow to obtain substantially improved results for profile and flatness of hot rolled strip. These solutions concern, on the one hand, the design of rolling stands and rolls and, on the other hand, highly modern numerical models for the control of the important parameters.