Study on the Hot Cracking Law of Inconel 690/52M Welding Material on F304LN Base Metal by Multi-Layer Cladding

During the welding of 690 nickel-based alloy, solidification cracking (SFC) and ductility-dip cracking (DDC) easily forms, which has a negative effect on the quality of welded joints and service life. The present study examined the effects of welding heat input and cladding layers on the SFC and DDC, as well as their formation mechanism. The microstructure observation, elemental distribution, and Varestraint test were carried out. The results show that SFC and DDC were formed for the Inconel filler metal 52M, and SFC is more prone to form than DDC. The alloy elements such as Fe, Si, C, and P from base metal can expand the solidification temperature range, such that the SFC sensitivity increases. With the increase of welding heat input, the grain size of cladding metal is increased with a great SFC sensitivity. The increasing welding heat input also makes DDC possible due to the formation of a large angle grain boundary.

Swarm intelligence based selection of optimal end-milling parameters under minimum quantity nano-green lubricating environment

With the development of ideas such as green and sustainable processing, recently evolved lubrication methods are commonly used to resolve the disadvantages of the flood lubrication approach. In the minimum quantity lubrication (MQL) technology, a small lubricant mist is inserted into the tool-workpiece interface to achieve better lubrication. The present study, therefore, explored the viability of alumina-reinforced palm oil as a lubricant in the MQL environment. A diverse volume fraction of aluminium (0-1.4%) was mixed with palm oil, and the optimal concentration of nanoparticles (0.8%) was chosen through spectroscopic analysis. Subsequently, twenty-seven milling operations were carried out on Inconel 690 material under the best lubricating medium. Statistical analysis of the machining values was conducted using the main effect plot (MEP), empiric cumulative distribution (ECD), and analysis of variance (ANOVA). Besides, Response surface methodology (RSM) was used to create a mathematical equation between input and machining responses. Finally, the Particle Swarm Optimization (PSO) approach was applied to achieve an optimal machining environment: cutting speed = 88.348 m/min, feed rate = 0.108 mm/tooth, and depth of cut = 1 mm. The optimal machining conditions were confirmed by functional experimentation, which has shown that the mean error between the experimental and the predictive outputs is minimal (less than 2%).

Deployment of Laser Peening to Prevent CISCC of Nuclear Fuel Dry Storage Canisters

By generating very deep levels of compressive stress, laser peening can eliminate stress corrosion cracking of materials of use in the nuclear industry; tested materials include Alloys N06600 (Inconel 600), N06690 (Inconel 690), N06022 (Alloy C22) and stainless steels K44220 (300M), S30400 (304) and S31600 (316L). In this work we take a further step in direct application to the welds of multi-purpose canisters (MPCs) employed for dry storage of spent fuel at nuclear plants. This storage is a temporary approach awaiting interim or permanent storage.. For storage in coastal, lakeside and even humid environments, air-entrained chlorides can make the canister welds susceptible to pitting and chloride induced stress corrosion cracking (CISCC). Using ASTM G36 (2013) accelerated corrosive testing we evaluated CISCC lifetimes of welded 316L stainless steel canister plates configured to MPC geometry showing in excess of 19 times lifetime increase of laser peened panel sections vs. those left as-welded. Specifically cracks never developed within and were arrested when propagating into the laser peened area. We measured residual stress in test plates and related it to calculations of stress intensity and depth expected in the full canister geometry. We discuss the relevance of stress depth to pitting depth and crack growth rates. Our two-dimensional stress mapping shows that high energy laser peening provides deep (> 5 mm) plastic compression in the canister material and geometry. In parallel, as we gained customer and NRC approvals, we developed and deployed the hardware and control technology that enabled a transportable system to peen canisters welds during the fabrication process. The canisters are now loaded or in process of being loaded at the San Onofre Nuclear Power Plant.