Effect of heat input on the mechanical properties of high strength steel T-joints : Butt weld and fillet weld T-joints

Abstract

The Purpose of this Bachelor’sthesis was to discover, analyse and compare the differences in the behavior of different type and sizes of a t-joint welding of High strength steel (HSS). The joint sizes that were used in this thesis were ½ V-Butt weld T-joints of 8mm and 3 different sizes of Fillet weld T-joints (6mm, 10mm and 12mm). The use of this type of steel was introduced more than 30 years ago. However, sufficient data and information regarding welding parameters and behavior of this material are not presented in the EU Building codes and standards. The aim of this study was to provide information for future development and improvement in the better understanding of this product.

SSAB’s Strenx 700 (S700) steel plates, measuring, with nominal yield strength of 700 MPa were used in this study. While creating the specimens, the heat input parameters were varied depending on the size of the weld and the temperature in the Heat affected zone (HAZ) was measured in the process. In addition to that, the cooling time of the metal was recorded with a Thermographic camera (infrared camera), at different points during the welding. After this, the mechanical properties of the joint were tested through the Tensile strength and the Rock-hardness test. The results of this study show to a certain degree the effect that heat input and cooling time have on the mechanical properties of welded high strength steel. Also, we can observe the effect that welding errors have on tensile strength tests, creating discrepancies in the results. For future development regarding T-joints of high strength steel, this research can be used as a guideline.