Fatigue life improvement of AISI 304L cruciform welded joints by cryogenic treatment
Introduction
Fillet welded cruciform joints of stainless steel are the most common in various structures including offshore and nuclear applications. The fatigue strength of welded structures is inferior to those of the base metal partly due to high tensile welding residual stress of yield strength magnitude [1] in the weld metal. The high tensile residual stresses are induced in weld metal as it contracts during cooling [2]. The important variables in determining the fatigue life of a flawed weldment would seem to be the nature of internal flaws contained within the weld and the manner in which these flaws interact within the stress field in and around the weld during its fatigue life [3]. Many of the fatigue failures that occur in welded joints involve fatigue cracking from severe imperfections, which are actually an inheritance of the joint [4].
There are two types of fatigue cracking in cruciform joints: (a) root cracking and (b) toe cracking. In welded cruciform joints, the lack of penetration (LOP) occurs in the joint due to the lack of access to the root. The structures in which such joints are used are often subjected to fatigue loading. This may result in the initiation of fatigue cracks at the LOP tip as well as from the toe region which depends on the LOP size, fillet geometry, leg length and the cyclic stress applied. This investigation has been carried out to study the influence of cryogenic treatment on the fatigue life of cruciform joints failing from root LOP.
Cryogenics is the treatment of materials at extremely low temperatures. For ferritic steels, sub-zero treatment at temperatures of approximately −80 °C transforms retained austenite left by the heat treatment process to martensite [5] enhances the material properties.
Cryogenic processing uses temperatures around −185 °C because this is a temperature easily obtainable with liquid nitrogen. Liquid nitrogen is a relatively inexpensive means of cooling. There is some evidence to indicate that some of the desirable changes are happening very near this temperature, because these changes do not happen when higher temperatures are used. There is also some evidence to indicate that some of the changes happen as the component is within certain temperature ranges on the way down to low temperature and some on the way back to room temperature. This makes the ramp up and ramp down parts of the cryogenic process important.
Section snippets
Sample preparation
Load-carrying cruciform joints with LOP were prepared using 6-mm thickness AISI 304L austenitic stainless steel cold rolled plate. The initial joint configuration in the case of the cruciform joint was obtained by securing the long plates (300×100 mm2) and stem plate (300×50 mm2) in a cruciform position by tack welding in a fixture. Subsequently, fillets were made between the long plate and stem plate using semiautomatic gas metal-arc welding process, argon shielding gas and 308L electrode.
Crack initiation analysis
The crack initiation life ‘NI’ was evaluated experimentally using the crack initiation criteria [6], [7], [8], [9] used in welded joints. Here, in our investigations the initiation criterion is the number of cycles required to grow 0.5 mm length of crack in excess of its original LOP length under a particular stress range.
From Fig. 3, it can be seen that the initiation cycles of treated joints are almost double those of non-treated ones. It is well known that austenitic stainless steels are
Conclusions
This work presents the findings of a study of the axial fatigue performance of AISI 304L load-carrying cruciform joints which failed in the weld metal with and without cryogenic treatment. The fatigue properties of cryogenically treated samples have shown improvement. The strain-induced martensites formed during the cryogenic treatment and the associated generation of compressive stresses in the weld metal are considered to be effective in fatigue life extension of welded joints in the high
Acknowledgements
This work was done at I.I.T., Madras as part of the first author's Ph.D. programme financed by Avesta Sheffield Research Foundation, Sweden. The authors are indebted to Avesta AB and in particular Prof. Hans Nordberg for provision of the Stainless steels and the welding materials.
References (15)
A further study on fatigue crack initiation life-mechanical model for fatigue crack initiation
Int. J. Fatigue
(1986)- et al.
Prediction of fatigue crack initiation lives for welded plate T-joints based on the local stress-strain approach
Int. J. Fatigue
(1989) - et al.
Acta. Metall.
(1964) - Frank KH. The fatigue strength of fillet welded connections. PhD thesis, Lehigh University, October...
Thermal stresses developed in high-strength steels subjected to thermal cycles simulating weld heat affected zone
Trans. JWS
(1973)- et al.
Fatigue crack initiation and propagation in high yield strength steel weld metal
Weld. Res.
(1970) Resent advances in the fatigue assessment of weld imperfections
Weld. J.
(1993)
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