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Thursday, June 5, 2008 - 10:25 AM

Restraint Conditions and Welding Residual Stresses in Self-Restrained Cold Cracking Tests

C. Schwenk, T. Kannengiesser, M. Rethmeier, Federal Institute for Materials Research and Testing, Berlin, Germany

In the last decade, high-strength fine grained steels and welding consumables have gained a strong raise of application ranging from mobile cranes to bridge constructions. However, the cracking susceptibility of these steels increases significantly in correspondence with the achieved improvements in yield strength and the loss in plastic deformation reserves.

In order to determine this behavior a series of different standardized cold cracking tests has been developed. One remaining major problem of these tests is the uncertainty about the quantitative intensity of the restraint conditions as well as the corresponding welding residual stresses. Consequently, the comparison of different tests and welding conditions as well as the transferability of the results onto real parts is difficult at best.

The main topic of this paper is the analysis of the restraint conditions and their link with the welding induced residual stresses. The importance of the given standardized self-restrained tests and first results about the transferability of results onto real parts are discussed. The influence of the test specimen geometry on the restraint conditions of the test is investigated for a selected test with numerical simulation using commercial FEA software. Additionally, the residual stresses caused by the welding process are measured and linked with the restraint conditions which are defined mainly by the geometry parameters.

Finally the transferability of the selected cold cracking test results is validated experimentally. The test results of a multilayer weld on high-strength fine grained steel are compared with the data of real size weldments. For these experiments a 16 MN large scale testing facility is used which is capable of applying the high reaction forces and clamping conditions found at large scale demonstrator parts.

The results show the importance of the quantitative knowledge of the restraint conditions and the welding residual stresses on the cold cracking resistance.


Summary: The quantitative restraint conditions of cold cracking tests for high-strength fine grained steels and their link with the welding residual stresses are investigated. The influence of the specimen geometry on the restraint conditions is shown using numerical simulation. The Transferability is evaluated by experiments using a large scale testing facility. The results show the importance of the restraint conditions and the residual stresses on the cracking resistance.