Indian Welding Journal

K. Bhanu Sankara Rao ¹, M. Valsan ¹, S. L. Mannan ¹

Affiliations
1 Indira Gandhi Centre for Atomic Research, Kalpakkam, IN

Abstract

The emergence of liquid metal fast breeder reactor (LMFBR) technology made it necessary to use austenitic stainless steels at elevated temperatures where the mechanical properties are significantly influenced by time and cycle dependent phenomenon such as creep and low cycle fatigue (LCF).

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S. L. Mannan ¹, V. Shankar ¹

Affiliations
1 Materials Development Group, IGCAR, Kalpakkam-603 102, IN

Abstract

Hot cracking is an important problem encountered during the welding of austenitic stainless steels. It is known that hot cracking occurs by the formation of low melting eutectic phases in the solidifying weld metal and in the heat-affected zone(HAZ), under the action of shrinkage stresses and restraint imposed on the joint (ref. 1-3). In the HAZ, cracking occurs by liquation of grain boundaries in the partially melted zone adjacent to the fusion line and in previously deposited weld metal in a multipass weld (ref.4).

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S. L. Mannan ¹, S. Venugopal ¹, A. Veeramani ¹

Affiliations
1 Indira Gandhi Centre for Atomic Research, KALPAKKAM, IN

Abstract

Structural components such as in bridges, cranes, engines, pressure vessels and offshore structures are often subjected to cyclic loading Fatigue failures generally occur at stress concentration sites in the components The geometrical and metallurgical states of welds make them prone to fatigue failures owing to stress concentrations caused by weld shape and discontinuities. Moreover, welding introduces unfavourable tensile residual stresses, often of yield magnitude, which increases the severity of the applied fatigue loading. As a result, both applied compressive and tensile stresses can be equally damaging. In addition, the existence of defects in weld eliminates the fatigue crack initiation stage, and hence, the life IS predominantly governed by fatigue crack propagation.

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S. K. Albert ¹, T. P. S. Gill ¹, P. Rodriguez ¹, S. L. Mannan ¹, S. D. Kulkarni ²

Affiliations
1 Indira Gandhi Centre for Atomic Research, Kalpakkam, IN
2 Indian Institute of Technology, Powai, Mumbai, IN

Abstract

Hardness variation in the Cr-Mo steel weld metal as a function of Cr content and weld cooling rate was studied Chromium in the weld metal was varied by adding known amount of high purity Cr into the weld pool produced by a stationary arc. The cooling rate of the weld was measured by plunging W-Rh thermocouple in to the weld pool just at the time of extinguishing the arc and measuring the variation in temperature as a function of time using a X-t recorder. The microstructural studies revealed that in the low Cr steels the structure varied from fully martensitic to a mixture of bainite and martensite as the weld cooling rate decreased while for weld metal with Cr content higher than 5 wt% the structure remained fully martensitic irrespective of the cooling rate. The measured hardness of the weld metal for different Cr contents and cooling rates was compared with that predicted by Yurioka's and Hart's formulae. It was found that Yurioka’s formula can be used to predict the hardness of the weld metal with reasonable accuracy. It was further noticed that there is a reduction in the maximum hardness at Cr content above 5wt% and it is attributed to the presence of delta ferrite in the weld metal.

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K. Lahas ¹, K. S. Chandravathi ¹, K. B. S. Rao ¹, S. L. Mannan ¹

Affiliations
1 Materials Development Division Indira Gandhi Centre for Atomic Research Kalpakkam - 603102, IN

Abstract

Creep rupture behaviour of 2.25Cr-1Mo and 9Cr-1Mo base metals and weld joints has been studied at 823 K over a stress range of 100 - 250 MPa. In the stress range examined, 2.25Cr-1Mo showed better creep rupture strength than that of 9Cr-1Mo steel. Both the weld joints displayed inferior creep rupture strength than their respective base metals. Failures occurred in ths intercritical region of heat affected zobe (HAZ) for both the weld joints. At a given applied stress, the difference in rupture life of base and weld joint was more pronounced for 2.25Cr-1Mo than for 9Cr-1Mo steel and this difference increased with decrease in applied stress. As presence of MOj,C precipitates imparts creep resistance to 2.25 Cr-1 Mo steel, its absence in intercritical region of joints is responsible for poor creep life. On the other hand, 9Cr-1Mo, which is strengthened by solid solution hardening and dislocation substructure, is less prone to degradation due to heating in intercritical region. Also presence of 5-ferrite in the coarse-grained region of HAZ of 9Cr-1Mo reduces its grain growth tendency and also its susceptibility to intergranular creep cavitation compared to 2.25Cr-1Mo steel.

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