Filler Metal Mixing Behaviour of 10 mm Thick Stainless Steel Butt-Joint Welds Produced with Laser-Arc Hybrid and Laser Cold-Wire Processes

Abstract

In thick section laser welding, filler metal addition is usually required to improve joint fit-up tolerances or to control the chemical composition of the weld metal. With deep and narrow welds produced using an over-alloyed filler metal, it may be challenging to ensure that the filler metal and its elements are homogeneously mixed and evenly distributed throughout the fusion zone. Inhomogeneous filler metal mixing can cause unfavourable changes to weld metal chemistry and microstructure. Filler metal mixing behaviour in laser-arc hybrid and laser cold-wire welding is studied in this work. Welding tests were conducted on 10 mm thick butt-welded joints of AISI 316L austenitic stainless steel. An overmatching type 2205 duplex stainless steel filler wire was used to obtain a composition contrast between the base metal and filler metal. Energy dispersive spectroscopy (EDS) with chromium as the trace element was used for element mapping and stepwise characterization of the weld cross-section samples. Optical metallography was used to observe possible inhomogeneous filler metal mixing behaviour like local acute changes in macro- and microstructural features. The results showed a clear difference in filler metal mixing between the weld surface part (upper half) of the weld and the weld root part (lower half) in 10 mm thick welded cross-sections for closed root gap of I-groove welds or when the gap was only 0.4 mm. In narrow I-groove preparations, inhomogeneous mixing phenomena were more pronounced in laser cold-wire welds than in laser-arc hybrid welds. In both welding processes, a combination of trailing wire feeding and the use of a wider groove enabled filler metal to be introduced deeper into the bottom of the groove and improved mixing in the root portion of the welds.

Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel

“…This provides a visible discoloration from the etching response [22,23]. Such technique has also been demonstrated by other studies [24][25][26]. However, welded specimens with such wires are not relevant for the assessment of mechanical properties.…”

Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels

“…A formation of an inward flow could be detected also at a laser leading process order, where this inward flow was formed when the fluid flowed from the rear end to the keyhole on the pool surface before flowing to the bottom, which also improved the filler wire mixing [10]. Another effective method to improve the filler wire mixing when thick-plate welding to set an air gap of 0.3 mm to 0.4 mm between the joining parts as reported in [7,11]. An air gap of 0.4 mm was recommended when laser hybrid welding of 45 mm thick steels in counter-layer technique with a laser power of 15 kW at welding speeds of < 1 m/min.…”

“…A further parameter influencing the filler wire mixing was the process order. A laser leading orientation was recommended when welding 10 mm thick steels with a laser power of 10 kW [7]. Differences in the flow pattern and temperature contours could be observed depending on the process order numerically.…”

Influence of Laser Beam Wobbling Parameters on Microstructure and Properties of 316L Stainless Steel Multi Passed Repaired Parts

“…However, the high cost of equipment and stringent requirements for the processed surfaces do not allow the use of these methods everywhere. Therefore, there are various combined methods such as hybrid laser-arc welding [16] and laser welding with cold filler wire [17][18][19][20].…”