Microstructural Analysis and Microhardness Evaluation of Stainless Steel SS304 Joints Utilizing Microwave Hybrid Heating (MHH) and Cold/Heat Processing: A Fuzzy Logic Approach

Stainless steel SS304 is extensively used in dental applications for its high strength, hardness, and corrosion resistance. However, Conventional dental joining techniques such as soldering and fusion welding, reliant on elevated temperatures and toxic fluxes, present substantial oral health risks, leading to potential health deterioration due to toxic emissions. The study proposes the utilization of a microwave hybrid heating process (MHH) for joining stainless steel SS304 (15mm × 7.9mm × 0.2mm) and pure zinc metal powder (44 µm, 99% purity), citing its enhanced efficiency, speed, precision, and diminished environmental footprint as key characteristics without fume. It explores heat processing between 30°C to 60°C and cold temperature processing from 0°C to 10°C to analyze alterations in hardness properties and microstructures. The study identified a direct correlation between temperature and microhardness, observing an increase in microhardness with rising temperatures. Optimal microhardness of 208.6 HV was achieved at 60°C during a 3 min heat treatment. Cold temperatures induced slight deformation and grain transformation, while heat treatment enhanced grain density and hardness, particularly in the strongly bonded boundary layer, with experimental and predicted values using Fuzzy logic showing promising outcomes and errors below 10%. In conclusion, the study demonstrates that achieving a specific hardness value in stainless steel joints is highly desirable for dental applications, alongside the observation of favorable microstructures. These findings underscore the potential of MHH to propel dental technology forward and promote sustainable practices while addressing environmental concerns.