Low Heat Joining – Manufacturing and Fatigue Strength of Brazed, Locally Hardened Structures

Abstract

Abstract. Low-heat brazing as a joining option for high strength steel sheets under cyclic load is still a challenge for manufacturing. For application arc brazing to locally hardened, high strength steel sheets a material specific manufacturing concept is needed to ensure a quality-related, reliable and reproducible processing. Thus the interaction of brazing parameters, metallurgical properties, types of brazed seams and different arc-processes under cyclic load were investigated. This should extinguish the base for an extended application of arc-brazed joints at cyclic loaded, high strength, property adjusted structures. IntroductionNowadays the interest in joining metal sheets by low-heat methods like adhesives, clinching and brazing remarkably increases. Especially the application of automated brazing processes and the development of new brazing fillers and process methods have resulted in an ongoing increase of the importance of brazing as a joining option [1][2][3]. Due to its flexibility hard-brazing has become an important alternative to common metal-arc-welding (MAW) processes in modern manufacturing. It can be regarded as a promising and cost-effective joining process for the fields of automotive and aerospace, energy, and logistics. The advantages of hard-brazing include corrosion resistance, low distortion, and over all local material properties are hardly influenced, due to the low heat input. As a result the brazing process is appropriate for joining heat-sensitive and locally hardened structures [4,5]. These materials pass through a complex manufacturing process to get their locally defined properties. They can be easily destroyed in case of heat exposure (e.g. martensite formation, local softening and others). As a consequence of the low heat process these complex characteristics are just limited affected. As a hard brazing process recently arc brazing is the most demanded for joining high strength and dynamical loaded structures [6][7][8][9].Deficits which have prevented the widespread use of brazed high-strength structures and nodes are associated especially with the reliability of the brazed joint. There is a lack of understanding the interaction of the brazing parameters, the geometry of the brazed seam, and the brazing filler regarding of reliability and reproducibility. Indeed these factors are not the only challenges for the use of brazed joints but there is also an immense divergence of the strength between locally hardened high strength steels, used in this project, and the applied copper-based filler. Mainly hardbrazed joints are qualified by static strength -tensile test -but normally not by fatigue testings. Fatigue strength is detected as add on at the end of investigations [4]. In particular, the behaviour of brazed structures of materials with locally altered properties under alternating stress cannot be appraised with conventional methods. Consequently, so far it has not been possible to predict the lifetime of brazed structures and nodes under alternating stress. To increase the...

Effects of Brazing Filler and Method on ITER Thermal Anchor Joint Crack

“…Moreover, the high heat input can remarkably reduce the excellent properties of 316L=316LN stainless steel. It is well known that brazing is a low heat-input welding method [4] which is generally considered to have little effect on the base metal; therefore, the breaking and deformation of thermal anchor can be avoided and controlled as much as possible [3,4]. In recent years, arc brazing was developed as an efficient and energy-saving brazing method.…”

“…In recent years, arc brazing was developed as an efficient and energy-saving brazing method. The arc brazing has the advantage of flexible adjustment of the heat input by controlling the process parameters (welding current, voltage, and speed), and easy realization of mechanization and automation compared with conventional brazing methods [4][5][6]. Therefore, arc brazing is a good choice for attaching ITER thermal anchor to magnet support basement.…”

Numerical Study of the Cold Metal Transfer (CMT) Welding of Thin Austenitic Steel Plates with an Equivalent Heat Source Approach

“…This process involves the assistance of a mechanical recoil of the wire to facilitate the detachment of the metal droplet. The welding operation is synchronized to ensure the detachment and deposition of the droplet that occurs when the current reaches almost zero (when the electrical resistance R is high) [2].…”

Numerical Study of the Cold Metal Transfer (CMT) Welding of Thin Austenitic Steel Plates with an Equivalent Heat Source Approach

“…This process involves the assistance of a mechanical recoil of the wire to facilitate the detachment of the metal droplet. The welding operation is synchronized to ensure the detachment and deposition of the droplet that occurs when the current reaches almost zero (when the electrical resistance R is high), [4].…”