| About this Abstract |
| Meeting |
2023 AWS Professional Program
|
| Symposium
|
2023 AWS Professional Program
|
| Presentation Title |
Reduction of Cold Cracking in Welded Overlays via Reduced Martensite Start Temperature |
| Author(s) |
Carter David Trautmann, Patricio F Mendez |
| On-Site Speaker (Planned) |
Carter David Trautmann |
| Abstract Scope |
Introduction
The surface cladding industry continues to expand and find great success in extending the lifetime of components in heavy-wear environments. In applications involving the repair and manufacture of existing parts, hard facing via plasma and directed energy welding allows many high-wear components to have dramatically improved lifetimes. The production time and success rate of these hard-facing techniques is often limited by the initiation of cold cracking after deposition, in particular when depositing onto very large base materials. At the same time, the weld filler-metal industry is seeing great innovation with the introduction of Low Transition Temperature (LTT) Alloys. These materials undergo their martensitic transitions at much lower temperatures; creating the potential for dramatic reductions in the tensional residual stress after welding. Improving performance and potentially reducing cold cracking during deposition.
The confluence of these two technologies creates an opportunity for a new approach to surface cladding optimization and the extension of the lifetime of components in unique high-wear applications. Rail transport industry wheels presented an excellent testing ground. Traditional hard-facing techniques see limited success in this application as the high heat capacity of these large steel wheels means the cooling rate of the weld is very high. This introduces a higher-than-typical level of residual stress generation during cooling. The use of LTT alloys as a surfacing material could provide a solution by reducing the tensional residual stress. Via the introduction of compressive surface residual stresses without increasing hardness.
Experimental procedures
A set of alloys of varying compositions were developed to be a representative cross-section of materials of potential use for application onto rail wheel rims. A low alloy material of very similar composition to the base wheel material, a high-alloy material designed to maximize the potential for LTT without exceeding hardness constraints, and an intermediate composition. These alloys are deposited via Plasma Transferred Arc Welding (PTAW) onto the rim of a prepped 36” train wheel
Welds were deposited into a slot in 3 passes. After application, welds were allowed to fully cool and were then checked for crack formation with liquid penetrant testing. Subsequent welds were then deposited to fill the prep slot and crack testing was repeated. Micrographs were used to assess the microstructure and quality of the fusion layer after sectioning the wheel. Materials were assessed for hardness and their impact on base material hardness using the Vickers hardness test. The potential exists for through-section or hole-drill residual stress testing as well.
Results and Discussion
Early research results suggested that these LTT alloys could improve the overlay quality. This is attributed to what literature has determined to be a potential inversion of residual stresses from tensional stress to compressive inside the weld material. This compressive stress is derived from the volumetric expansion associated with the transformation to martensite by the filler material. When this expansion occurs at low temperatures the remaining thermal contraction is too small to absorb the expansion resulting in a final stress state of compression. The application of such materials via PTA has shown promising early results with limited or no cold cracking in plate welds in the LTT welds, but audible cracking and even delamination in the plain filler materials. and microstructures suggesting effective martensitic transitions as well as a successful fusion to the dissimilar base material. Further work is to be explored in the functional gradation of the material to ease dilution issues or allow more variety of deposition compositions.
Conclusion
As an assessment of the use of PTA and LTT alloys for the application of materials to rail wheels for repair and fabrication. A series of alloys were applied to the surface of the locomotive wheel with varying compositions; in an attempt to create a wear-resistant overlay with good fusion to the base material without the formation of cold cracks. The selected alloys were designed to exhibit some LTT properties to explore the viability of these materials for rail-industry applications. Preliminary results suggest this system provides a promising option for future applications as a cladding process. with further development to refine the process and materials required to reach an industrially viable result. There is substantial opportunity for future research to explore optimizing both alloy composition and application processes. Further mechanical testing will be required to establish viability for in-service applications. |
| Proceedings Inclusion? |
Undecided |