Metallographic Study on 1Cr18Ni9 Weld Joint
Introduction
Welding is a very important manufacturing process which is widely used in fabricating structural components and machine components. To evaluate the quality and capability of welded components, metallographic analysis is one of the most frequently used methods which could provide useful informaiton in regard with the microstructrue, grain structure, defects and etc. The 1Cr18Ni9 weld joint is one of the frequently used welding metals which is made of low carbon martensitic stainless steel. The metallographic analysis is conducted to examine the microstructure and defect formation of 1Cr18Ni9 weld joint. The scanning electron microscopy (SEM) is adopted in this research to provide detailed informaiton about the microstucture morphology, grain structures, defect and etc.
Experimental Procedure
The specimen which was welded by gas tungsten arc welding (GTAW) was used for the metallographic analysis and the examination area of specimen was 18 mm thick with a dimension of 30 mm × 15 mm shown in Figure 1. The optical microscope with a magnification of 150x was adopted to take images of specimens and Magnaflux ZY-3 was used to test them with surface magnetic particle inspection. The Metallographic specimens were fabricated according to industrial acceptably practice. The specimens were cut and ground in proper manner and then were yield loaded by 4.8 kg to enhance the accuracy of cross sectioning. Post the passing of micrographic specimens surface preparation, the specimens were etched employing α- Picric acid etch solution. Corrosion susceptibility was assessed with an electrochemical corrosion test.
Figure 1 The welding area
An SEM whose accelerating voltage and collection angle were 8kV, 85deg.was used to examine the microstructure and nonmetallic zone in specimen. Rockwell B hardness test was adopted to measure the hardness of welded joints and the hardness value represented the base metal hardness.
Result and Discussions
The examination of surface topography acquired by SEM was presented in Figure 2 and Figure 3. Figure 2 suggested the lack of fusion defect and black smelting on the welded surface. The excrusion of black layer suggested the existence of brazing. The SEM micrograph of fillet weld toe which is located within the welding side was presented in Figure 3 and it revealed that there were some small cracks and low heat affected zones.
Figure 2 The welded surface
Figure 3 The fillet weld toe
The etching result of 1Cr18Ni were showed in Figure 4 and the microstructure of the welded property exhibits a distinct lamination structure, indicating presence of joint segment belonging to complete weldment. The nonmetallic zone beneath the weld is clearly visible. The nonmetallic zone indicated presence of alpha phase and chromium concentration as proven by ferrite content measuring device.
Figure 4 Microstructure of the welded joint
The Rockwell B hardness results for the base metal, weld metal and the nonmetallic zone were 63.4, 65.7 andZ 61.2, respectively. It could be observed that the hardness of the weld metal was higher than the base metal, attributed to the solid solution hardening. Also the the nonmetallic zone hardness was lower than the weld and base metal, considering the fact that its hardness was affected by higher concentration of chromium.
Conclusion
In this study, a metallographic examination of 1Cr18Ni9 weld joint was performed by optical microscope and SEM. The examination result reveals obvious lamination formation and lack of fusion defect. The Rockwell B hardness test suggested that the weld metal hardness was higher than the base metal with a value of 63.4 and 65.7 respectively. The hardness of nonmetallic zone was lower than the weld and base metal, attributed to its chromium concentration. Based on the result from the metallographic analysis, the welded joint could meet the designated requirements and its quality could be deemed as good.
