Part 1: Use of Low Carbon 1 1¼ Cr-½ Mo Weld Metal for Fabrication and Repair of Cr-Mo Components: Efficacy of Low Carbon 1 ¼ Cr--½ Mo Weld Metal for Repair Welding of Elevated Temperature Service Exposed Cr-Mo Components
The creep service suitability of low carbon (~0.030%) weld metal intended for controlled deposition repair welding of 1 ¼ Cr--½ Mo steel was studied. Results indicate weld metal stress rupture properties in excess of the virgin base metal ASTM data base minimum. The tensile behavior of the weld metal in the as-welded and PWHT condition is in accordance with ASTM A387 Grade 11 Class 1. The toughness of the low carbon weld metal in the as-welded and PWHT condition is greater than that normally industrially specified. Following determination of the suitability of stress rupture properties of the low carbon weld metal, weld repair of service exposed full-scale components was carried out using controlled deposition procedures. Full thickness cross-weld specimen stress rupture testing revealed that the repaired weldment behavior is equivalent to, or better than, the service exposed weldment and rupture life exceeds the ASTM base metal minimums in the as-welded condition and the life is greater than the ASTM mean in the PWHT condition. Thus, it is evident that repair weld behavior using low carbon consumables and controlled deposition procedures is suitable for elevated temperature applications
Part 2: Use of Low Carbon 1¼ Cr--½ Mo Weld Metal for Fabrication and Repair of Cr-Mo Components: Development of W-Nb-V Modified Low Carbon Filler Metals for Fabrication and Repair of 1¼ Cr--½ Mo Steel Weldments
Modified Cr-Mo filler metals were developed with elemental combinations of W-Nb-V, Nb-V and W only. A standard low carbon Cr-Mo weld metal was used for comparison. Creep stress rupture tests show that the combination of W-Nb-V alloy elements provides the optimum contributions for improvement in creep properties. The enhanced properties of the W-Nb-V modified weld metals are far superior to standard 1 ¼Cr--½Mo weld metal and base metal. A creep strengthening mechanism for the W-Nb-V modified weld metal is proposed based on the creep results, carbide evolution sequence, and carbide morphology corresponding to the postweld heat treatment (PWHT) condition. In addition, tensile strength and ductility of the modified low carbon weld metals in the as-welded and PWHT condition are in accordance with ASME A387 Grade 11 Class 2 requirements. Charpy impact tests show that the addition of W-Nb-V or W only modified weld metal is detrimental to weld metal toughness. However, PWHT significantly improved the toughness of the weld metals. The addition of Nb-V in the low carbon weld metal results in higher toughness than the standard low carbon weld metal in the as-welded condition and similar to the standard low carbon weld metal in the PWHT condition. Continuous cooling transformation (CCT) diagrams were determined for the modified and standard low carbon weld metals at heat inputs ranging from 12 to 120 KJ/in using Gleeble thermal simulation techniques accompanied by high speed dilatometry.
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| Number of Pages : | 109 |
| Published : | 1999 |
