Stainless steel weld metal designed to mitigate residual stresses

Abstract

There have been considerable efforts to create welding consumables which on solid state phase transformation partly compensate for the stresses which develop when a constrained weld cools to ambient temperatures. All of these efforts have focused on structural steels which are ferritic. In the present work, alloy design methods have been used to create a stainless steel welding consumable which solidifies as d ferrite, transforms almost entirely into austenite which then undergoes martensitic transformation at a low temperature of about 220uC. At the same time, the carbon concentration has been kept to a minimum to avoid phenomena such as sensitisation. The measured mechanical properties, especially toughness, seem to be significantly better than commercially available martensitic stainless steel welding consumables, and it has been demonstrated that the use of the new alloy reduces distortion in the final joint.

Contemporary approaches to reducing weld induced residual stress

“…It is generally taken that the transformation should occur at a temperature low enough to preclude subsequent build-up of stress, but should be complete by the time the metal cools to room temperature 10 [154,155]. Figure 16 shows schematically the effect of different phase transformations on the build-up of stress in uniaxially-constrained steel specimens as they are cooled from 1000°C.…”

Phase transformations contributing to the properties of modern steels

“…The stress may therefore favour the formation of certain crystallographic variants of the martensite over others whose deformations do not comply with the applied stress. [5] In recent years, this phenomenon of transformation plasticity has been exploited for one of the most pernicious problems in welding technology, that of the residual stresses [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. The aim is to design welding alloys which compensate for the effects of thermal contraction and stress whilst maintaining the overall mechanical performance [66,67].…”

“…• C. This has led to welding consumables which not only have been demonstrated to reduce residual stress and distortion, but also to consequently enhance the fatigue life by impressive amounts [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. This is an excellent example of how phase transformation theory has contributed to the alloy design for an essentially practical purpose.…”

Effect of variant transformations in fusion zones of gas metal arc welds

“…[3][4][5][6][7][8][9] It has been shown that weld fabrication using, for example, filler metal wires with a lowered  transformation temperature (so-called low transformation temperature or LTT wires) can result in lowered residual stresses and distortion. 8,[10][11][12] Text Click here to download Manuscript: Beres_Text. docx 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 Where the transformation is entirely reconstructive, one might initially believe that the transformation strain will simply be due to the volume change between the two unit cells.…”