4.2.2. Performance Testing for the Weld Beads

To comprehensively obtain the performances of the weld beads of L1–L9, key performance tests can also be conducted in this work, in this part, tensile and hardness testing were carried out.

The first was the tensile testing, which was employed to test the axial toughness of the weld bead at room temperature (20 ◦C). The instrument used the WA-600 hydraulic universal testing machine (Yangzhou Jiangdu Open Source Test Machinery Factory, Yangzhou, China) to explore the toughness of the weld beads. Two terminals of each weld bead were seriously processed in order to conveniently hold, and then each specimen can be stretched to completely fracture. The species and experimental results are shown in Figure 5.

It can be noticed that the species of L1–L8 were fractured at the base plate which located in terminals of the weld beads, only for the weld bead of L9, the fracture occurred in the middle of the weld bead, and this bead had the longest elongation. The elongation of each specimen is recorded in Table 6.

Combining the observation and analysis results about microstructure of the weld beads in preceding part, the results in Table 6 showed that the weld beads which had larger grain sizes had stronger toughness, and as the grain sizes decreased, the toughness was weaker and weaker.

**Figure 5.** (**a**) Geometry of your tensile samples, (**b**) Tensile tests of the weld beads.

**Table 6.** Elongation of each specimen (mm).


Apart from the tensile testing, the hardness testing was also conducted. The measuring instrument used the SCTMC HR-150DT electric Rockwell hardness tester (Shanghai Shangcai Testermachine CO., LTD, Shanghai, China) to test the harness for the weld bead. To accurately reflect the performance of the weld bead, five testing points were selected from the cross-section of each weld bead to conduct the hardness testing. The first testing point was in the center of the cross-section, and other four testing points were evenly distributed. A Cartesian axis was used, the origin was the center, and the horizontal axis was a line which went through the origin and parallel the surface of the base plate, while the vertical axis was a line which also went through the origin and vertical to the horizontal axis. Then, the four testing points were distributed in the four quadrants and the distance between the point and the edge the bead was 1.5 mm, as shown in Figure 6, and the applied external force on each point was 980.7 N.

**Figure 6.** Testing points in the weld bead during hardness testing.

Where the dotted lines were axes. Then both maximum and minimum values in the five output values were rejected, and the final result was the mean value of the other three values for each specimen, corresponding results for nine weld beads are shown in Table 7.

**Table 7.** Hardness test of weld beads.


Where HRB is the abbreviation of Hardness Rockwell B, which is a commonly used criterion to describe the hardness of the weld bead using stainless steel. According to the testing results, it can be observed that each three tests formed one array, and there were three arrays in the experiments: the first array was from L1 to L3, the second array corresponded to L4 to L6, while the last array referred to L7 to L9. The overall hardness was increasing from the first to the third array. The harness values from L1 to L3 were very small and the values were so approaching. The average value of the second array was about 78.5, which was a little bigger than that of the first array. The third array had the biggest HRB values, whose average value was about 80. The HRB of the base plate was 73, which denoted that the hardness of these weld beads was higher than that of base plate. It can be concluded that the variation characteristic of the hardness was approximately the same as that of grain size.
