Change search
ReferencesLink to record
Permanent link

Direct link
Undermatching butt welds in high strength steel
2007 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The last years improvements in steel making technologies have resulted in steel grades with higher tensile strength, hardness, weldability etc. compared to conventional construction steel. This category steel gives lighter and smaller sized structures and cost reductions. Since the weld metal is still only a cast alloy whose strength mainly depends on its chemical composition, the differences in mechanical properties between the base plate and the consumable are increasing. The question is how to choose the undermatching level between the base plate and weld metal without compromising the global strength of the joint. In this master’s thesis, the effects of different weld geometries on the mechanical properties of undermatched welds in high strength quenched and tempered steel, are studied. Different undermatching levels have been accomplished by combining two different steels: Weldox 960 and Weldox 1100 together with two consumables: Filarc PZ6145 and Filarc PZ6149. Two methods have been used to gather information: 30 test specimens have been manufactured and tested at SSAB’s plant in Oxelösund and previous studies in this field have been analyzed in a literature review. Three different parameters were chosen to be studied in the laboratory tests, only one parameter was changed at a time: • Width- to thickness relation • Undermatching • Relative thickness The hypothesis was that if the weld metal is softer than the adjacent steel, it will yield before the base metal does. When the weld starts to deform, this deformation is constrained by the non-yielded surrounding metal. Tension is developed in both the width- and thickness directions, in addition to tension in the longitudinal direction due to the applied load. When the weld experiences tension in two or three material directions, the mean stress or hydrostatic stress in the weld is increased. As the hydrostatic stress is increased, by constraint, the magnitudes of the deviatoric stresses, which govern yielding, are reduced. This results in a stronger weld where increases in the applied load can be achieved. When the width- to thickness relation was studied, five different specimen widths, from 6 mm to 96 mm, were created out of the same plate. All specimens were taken from the same coupon which means that the welding parameters were identical for all specimens. In this case the effect of the width was obvious: the ultimate strength of the joint increased from 1070 MPa (6 mm) to 1192 MPa (96 mm). The ultimate strength of the weld metal was, in this case, 1015 MPa. When it comes to undermatching, all test specimens in Weldox 960 steel, welded with the stronger electrode, fractured in the base metal. This in spite of that the ratio between the weld metal’s and base metal’s yield strengths was as low as 0,77. In other literature only 15 % undermatching is recommended to achieve the full base metal strength in a joint. Only two different relative thicknesses could be accomplished. It was still obvious that the joint with a large weld volume had a lower strength than the one with a smaller volume.

Place, publisher, year, edition, pages
Keyword [en]
Technology, undermatchning, svets, höghållfast stål, stumsvets
Keyword [sv]
URN: urn:nbn:se:ltu:diva-51834ISRN: LTU-EX--07/220--SELocal ID: 9038c96e-1781-413a-ba7a-0369ae5cec24OAI: diva2:1025198
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

Open Access in DiVA

fulltext(3264 kB)0 downloads
File information
File name FULLTEXT01.pdfFile size 3264 kBChecksum SHA-512
Type fulltextMimetype application/pdf

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

ReferencesLink to record
Permanent link

Direct link