PSI - Issue 5

Lars Sieber et al. / Procedia Structural Integrity 5 (2017) 1011–1018 Sieber et al. / Structural Integrity Procedia 00 (2017) 000 – 000

1017

7

3.6. Transverse tensile tests

The strengths of the base material as well as of the welded joints were determined by flat tensile specimens. Previously, excess weld metal was removed. At several specimens the additional influence of different material thicknesses was excluded by face milling (Figure 6). In order to ensure an accurate test run, specimens with angular deflection were also directed. This was done exclusively in the area of the clamping, in order not to influence the result by cold hardening.

Fig. 6. Exemplary tensile specimens of sample AV

All tensile specimens of all welding samples exclusively failed within the base metal of this steel (similar to Figure 6). Speculations that inclusions and impurities impair the strength of HAZ or weld significantly and incite a local failure where not fulfilled. However, based on the results of the metallographic analysis in Section 3.5 this behavior is plausible, as hardness and grain structure are actually enhancing the strength in the usually critical HAZ and weld for these steels. The higher strength of the weld metal in conjunction with the X-shape of the weld seam impairs the contraction at fracture in the vicinity of the weld seam. It has to be investigated whether another seam shape (V- or K shaped seam) has a similar effect on the bearing capacity of the joint. In order to evaluate the ductility of the welded joint, the toughness was analyzed in Charpy impact tests. The toughness of the unaffected base material was determined as the reference value. Since only six notch impact specimens could be produced from the available sample material, a complete impact energy vs. temperature curve could not be determined. Based on the investigations by Sieber (2016) it is known, the transition temperature T 27J of old mild steels is approximately in the range of 0 to 40 °C. Accordingly, three notch impact tests were carried out at room temperature (about 20 °C). If the mean value of the impact energy of these three tests was higher than 27 J, three other samples were analyzed below 20 °C (see Figure 7), otherwise above. The transition temperature T 27J was determined by interpolation from the results. Subsequently, at this temperature the notch impact specimens from the heat affected zones were analyzed. The initial results from sample AV confirm the findings from the metallographic studies. The thermal impact of the base material in the heat affected zone does not lead to any significant deterioration of the toughness. The impact strength in the HAZ of all investigated materials is equal to or higher than that of the base material. Similar to the tensile tests, the high strength of the weld metal and the X-shape of the weld seem to support the fracture zone of the samples and impair the contraction. Due to the very high toughness of the filler material (see Section 3.2), the impact energy of the samples from the weld seams exceeded 200 J (upper shelf). 3.7. Material toughness influenced by the welding