Dissimilar welded joints operating in sub-zero temperature environment

Abstract

The vast expanses of the Arctic have for some decades been the subject of considerable scientific interest as regards potential industrial exploitation. However, the cold climatic conditions of the area pose major challenges, particularly with respect to the metals used, infrastructure design, and manufacturing techniques required for cold-resistant structures. Dissimilar welding of metals can supply added value (lightness, thermal difference) in the construction of Arctic structures, but the behavior of dissimilar high-strength metal welds in very cold environments remains under-investigated and improved understanding is required before such metals can be adopted for Arctic applications. The objective of this research is to identify possible difficulties arising from the use of dissimilar metal welds in Arctic structures, in particular the causes of potential defects and failures, and to propose means to remedy or prevent such failures through the adoption of suitable procedures and the choice of suitable metals. This study covers steels used for structural design of work in cold environments such as low-carbon content steels with tensile strength from 379 to above 586 MPa along with alloyed steels containing nickel (Ni) up to 4.5 % or chrome (Cr) and molybdenum (Mo) and stainless steels like austenitic stainless steels which keep their ductile properties even in sub-zero temperature. These steels are known for their better weldability and toughness. The methodology consists of a review of scientific articles and research experiments on the microstructures and physical and mechanical properties of dissimilar welded structures for low-temperature environments. In-service behavior is analyzed on the basis of literature data and the relationship between the types of structure failures and weld defects investigated. Finally, appropriate joints and applicable methods are proposed. The analysis shows that a microstructure with very large grains and a large HAZ are features that increase the size and prevalence of cracks. An acicular ferrite microstructure is required in the weld metal. Migration of carbon is a further aggravating factor for cracking. With nonferrous metals, the risk of undesired intermetallic compound hardness and brittleness increases, and processes that minimize the temperature of the HAZ are recommended. Heat treatment is recommended to refine the grains. The major implication of the work is that significant care is required in the selection of the base metal, electrodes and welding parameters, and appropriate heat treatments. Effective control of such factors can lead to improvement in the quality, reliability, and service life of Arctic welded structures.