Potential of grain boundary engineering to suppress welding degradations of austenitic stainless steels

Abstract

Grain boundary phenomena strongly depend on grain boundary structure and characteristics, i.e. coincidence site lattice (CSL) boundaries, as contrasted with random boundaries, are highly resistant to intergranular degradation. Grain boundary engineering (GBE) primarily intends to prevent the initiation and propagation of intergranular degradation along random boundaries by frequent introduction of CSL boundaries into the grain boundary networks in materials. A high frequency of CSL boundaries by GBE processing leads to high resistance to grain boundary degradations. Annealing twins bring CSL boundaries into austenitic stainless steels. By twin induced GBE utilising optimised single step thermomechanical processing consisting of a slight strain followed by annealing, a very high frequency of CSL boundaries was introduced into austenitic stainless steels. The resulting steels indicated remarkably high resistance to intergranular corrosion even to weld decay and knife line attack during welding. Grain boundary engineering could have a high potential to suppress a variety of grain boundary related degradations of welded austenitic stainless steels.

Effect of post-GBE strain on weld decay resistance of grain boundary engineered 304 austenitic stainless steel

“…Recent literature suggests different types of criteria 7 and definitions to identify the 'special' boundary. 22 In this study, the grain boundaries with low S value (S<29) were classified as CSL boundaries and Brandon's criterion 23 was adopted to define the critical deviation from the exact CSL orientation relationship, because CSL boundaries defined by these criteria could explain experimental results in our previous GBE studies, to significant extent, such as weld decay resistance, 13 percolation probabilities 29 and effects of strain sensitisation. 20 The frequency of CSL boundaries was quoted as a percentage by length.…”

“…11 Grain boundary engineered (GBEed) materials were reported to have higher resistance to weld decay than conventional, non-GBEed, materials. 12,13 Other studies have shown that GBE is also effective to prevent various forms of grain boundary degradation in many polycrystalline materials, 14 such as segregation induced embrittlement in ultrafine grained nickel, 15 grain boundary sliding in nickel, 16 liquation cracking in weld HAZ of nickel based superalloys, 17 corrosion-erosion in 316 austenitic stainless steel 18 and intergranular corrosion due to sensitisation subsequent to carbon redissolution in stabilised 321 austenitic stainless steel. 19 In the practical use of GBEed materials as structural materials, they would be deformed and welded during manufacturing following the GBE process.…”

Study on The Effect of Cold-Rolling and Subsequence Welding on the Corrosion Rate of 304L

“…It can be seen that microstructure is a typical microstructure with austenite phase stainless steel. After the rolling and subsequent annealing, the microstructure will change and contains a twin-boundary which is a part of the crystal that changes orientation to form a symmetrical twin to the original lattice [11,16]. The twinning crystal part is an inverted image of the parent crystal due to the shear stress that acts.…”

“…The cold rolling process and annealing treatment afterward change the grain's structures. These grain boundary changes have been known can be controlled to reduce the corrosion rate of austenitic stainless steel [11][12][13].…”

1000 gems: Celebration of STWJ

“…In the next issue, there will be a paper by Palmer and co-workers 22 describing the use of synchrotron X-radiation to study austenite formation during continuous heating, and the discovery is made that the last austenite to form grows as nearly pure iron because the higher carbon regions of the original microstructure are consumed first. The paper by Kokawa on the control of crystal orientations to enhance the resistance of austenitic stainless to corrosive attack also relies on detailed characterisation and follows a long history of grain orientation engineering research from Japan 23 .…”