Application of low M_s temperature consumable to dissimilar welded joint

Abstract

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe-Cr-Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with M s temperature below 200uC and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.

Surface residual stresses in multipass welds produced using low transformation temperature filler alloys

“…Application of this mechanism has led to a number of martensitic welding alloys being developed. [3][4][5][6][7][8][9][10][11] The transformation of austenite to martensite (cRa9) is displacive and results in a shape deformation that is an invariant plane strain with a large shear component. 12 The magnitude of the shear, in conjunction with a dilatational strain, is sufficient to not only cancel the tensile stresses, but even create compression in the weld metal.…”

The Welding of Dissimilar Joints with Low Temperature Martensitic Transformation Filler Material

“…The first of these solutions often leads to a loss of efficiency while the heat treatment is sometimes logistically very complicated. An alternative technique when dealing with welding of steels is to induce an adiffusional phase transformation during the cooling of the weld [3,4]. When austenite is transformed into martensite or bainite the phase transformation results in an invariant plane deformation and a normal plane expansion.…”

Ductile Fracture Behaviour of Hot Isostatically Pressed Inconel 690 Superalloy

“…Because nickel acts as a FCC stabilizer through lowering the M s temperature, the 59 wt pct nickel content in Inconel 690 is sufficiently high to completely prevent strain-induced martensitic transformation. [19] It has been shown [20] that the yield strength and ultimate tensile strength of HIP'd Inconel 718 are independent of the material's oxygen content in the range of 25 to 850°C, and although the ductility is insensitive to oxygen content at room temperature, it decreases significantly with increasing oxygen content at elevated testing temperatures. However, to our knowledge no comparative study has hitherto been reported on the Charpy impact toughness fracture behavior between equivalently graded HIP'd and forged Inconel superalloy.…”