Macrographs & Micrographs

Transcription

1 OVERVIEW Keyhole gas tungsten arc welding is applicable to a wide range of materials. However, it is true to say its attractiveness is strongly correlated to the cost of the material being welded. This is a direct reflection on the high quality of the welds, the reduced risk of contamination associated with the elimination of multiple weld passes, and the overall saving in filler materials. As a result there has been a continual market-driven emphasis on applications across the range of stainless steels, and also the more exotic materials such as nickel, titanium and cobalt alloys. This wide range of process applications has resulted in the specific evaluation of the weld properties (eg microstructure, mechanical and corrosion) of many individual alloys and this list is continuing to grow. Ultratig is well equipped to undertake such assessments if required. The macrographs and micrographs presented on the following pages are provided courtesy of the CSIRO. They indicate typical microstructures and some of the materials that have been studied in detail.

2 1. MACROGRAPH OF 10.5 MM THICK AISI 304 STAINLESS STEEL Figure 1. Macrograph of a keyhole GTA weld in 10.5 mm thick AISI 304 stainless steel plate (as welded).

3 2. MICROGRAPH OF THE ROOT REGION IN AISI 304 Figure 2. Low magnification micrograph of the root region of the keyhole GTA weld in AISI 304 stainless steel shown in Figure 2.1 showing absence of defects such as porosity. Etchant: Beraha s tint etchant (potassium metabisulphite + HCl).

4 3. MACROGRAPH OF 6.5 MM THICK 3CR12 Figure 3. Macrograph of a keyhole GTA weld in 6.5 mm thick 3Cr12 (12% chromium) steel plate (as welded).

5 5. KEYHOLE AND CONVENTIONAL WELDS IN CP TITANIUM Figure 5. Macrographs of keyhole GTA weld (top) and conventional GTA weld (bottom) in 13 mm thick ASTM B265 Grade 2-95a (CP titanium) plate. The conventional GTA weld was made using matching filler material, a double-v edge preparation and 6 welding passes.

6 6. MICROGRAPH OF THE ROOT REGION IN CP TITANIUM Figure 6. Low magnification micrograph of the root region of the keyhole GTA weld in ASTM B 265-Grade 2 (CP titanium) plates shown in Figure 2.5, showing that defects such as porosity are not present. Tint etchant (ammonium bifluoride + water).

7 7. MACROGRAPHS OF 13 MM THICK Ti-6Al-4V PLATE Figure 7. Macrographs of keyhole GTA welds in 13 mm thick ASTM B265 Grade 5-95a (Ti-6Al-4V) plate. The upper photo shows a single pass keyhole GTA weld while the lower has an additional dressing pass for improved bead profile.

8 8. MICROGRAPHS OF Ti-6Al-4V PLATE Figure 8. Low magnification micrographs of the root region (upper) and heat affected zone of a keyhole GTA weld in 13 mm thick ASTM B265 Grade 5-95a (Ti-6Al-4V) plate. The micrographs confirm absence of defects such as porosity and lack of fusion. Etchant: Kroll s Reagent. (Note: The row of dots in the upper photo is a row of microhardness indentations).

9 9. MICROGRAPHS OF FUSION ZONE IN 13 MM Ti-6Al-4V Figure 9. Micrographs of the as-welded fusion zone of a keyhole GTA weld in 13 mm thick ASTM B265 Grade 5-95a (Ti-6Al-4V) plate. (a) shows a region near the top of the weld; (b) and (c) show the root regions of the weld. Etchant: Kroll s Reagent.

10 10. MACROGRAPH OF 10 MM THICK INCONEL 718 PLATE Figure 10. Macrograph of a keyhole GTA weld in 10 mm thick Inconel 718 plate (as-welded). Beraha s tint etchant.

11 11. LOW MAGNIFICATION MICROGRAPHS OF INCONEL 718 Figure 11. (a) and (b) Low magnification micrographs of the fusion zone and HAZ of the Inconel 718 keyhole GTA weld in Figure (c) and (d) Higher magnification micrographs showing absence of cracks in weld centreline and the HAZ, respectively.

12 12. MICROGRAPH OF 6.35 MM CP ZIRCONIUM Figure 12. Macrograph of a keyhole GTA weld in 6.35 mm thick commercially pure zirconium, ZR 702 plate (as-welded). An additional dressing pass has been laid for improved bead profile. The sample was etched during the final stage of polishing using a mixture of 75 ml water, 4 ml of HNO3 and 10 drops of HF.