Narrow Results

Grain boundary character distribution (GBCD) and triple junction character distribution (TJCD) in a 304 stainless steel cold rolled with the thickness reduction of 6% and then annealed at 1323K for 5 minutes(GBE process) were analyzed by electron back scatter diffraction (EBSD). The intergranular corrosion (IGC) resistance of various triple junctions and grain boundaries were evaluated after sensitization treatment at 1073K for 30 minutes. The results showed special TJ containing 2 or 3 CSL boundaries exhibit higher resistance to IGC than other TJs. In addition, the {411} and {221} symmetrical tilt grain boundaries (STGBs) are more resistant to intergranular corrosion for Σ9 boundaries.

To further clarify the effect of the polishing slurry dispersant on the chemical mechanical polishing (CMP) performance of 304 stainless steel, a series of tests were carried out. The correlation between the material removal rate (MRR), surface roughness of 304 stainless steel, dispersant composition, and their content was investigated under two kinds of polishing slurry (hydrogen peroxide oxidant and ferric chloride oxidant) conditions. The experimental results indicated that the MRR and surface roughness of 304 stainless steel arrived at the maximum when the content of sodium hexametaphosphate dispersant was 1.2% (wt) under the hydrogen peroxide–oxalic acid polishing slurry condition. The values of MRR and surface roughness were 146 nm/min and 10 nm, respectively. The MRR and surface roughness of 304 stainless also reached the maximum value as the content of the propanetriol dispersant was 1.2% (wt) under the ferric chloride–oxalic acid polishing slurry condition. However, the values of MRR and surface roughness were 457 nm/min and 22 nm, respectively. Therefore, sodium hexametaphosphate was recommended as the dispersant of hydrogen peroxide–oxalic acid polishing, and propanetriol was recommended as the dispersant of ferric chloride–oxalic acid polishing slurry condition, according to the above analysis. This study lays a theoretical foundation for the improvement of 304 stainless steel CMP performance.

Hybrid organic–inorganic coatings are deposited on 304 stainless steel substrates by the sol–gel technique to improve the corrosion resistance. A titania-based nanostructured hybrid sol–gel coating is impregnated with three different microencapsulated healing agents (inhibitors) including cerium, Benzotriazole (BTA), and 8-Hydroxyquinoline (8H). Field-emission scanning electron microscopy (FE-SEM) and electrochemical impedance spectroscopy (EIS) are performed to investigate the barrier performance properties. The optimum conditions to achieve corrosion protective coatings for 304 stainless steel were determined. The Nyquist plots demonstrate that the activation time of the coating containing 8H as an organic healing agent shows improved behavior when compared to other coatings including cerium and BTA. Cerium as an inorganic healing agent is second and BTA is third and minimum. An increase in the impedance parameters such as resistance and capacitance as a function of immersion time is achieved in a 3.5wt.% NaCl solution by using healing agents such as BTA. Actually, over the course of immersion, the barrier performance behavior of the coatings changes and reduction of the impedance observed from the coatings containing Ce and 8H discloses deterioration of the protection system after immersion for 96h of immersion in the 3.5% NaCl solution. However, after 96h of immersion time, the concentration of chloride ions is high and causes increase in defects, micro cracks, hole on the surface of hybrid titania nanostructured coating containing Ce and 8H by destruction of coating, and also hybrid titania nanostructured coating containing BTA; BTA is released from coating to improve the resistance of passive film, which is created on the surface.

Laser surface alloying was employed to enhance the wear resistance of 304 stainless steel with pure tungsten powder. The effect of laser fluence on phase constituents, microstructure, hardness and corrosion properties was investigated. It is found that the laser fluence has a direct correlation with the phases present in the coatings. Intermetallic Fe₇W₆ phase was found in the composite coating due to the metallurgical reaction of W with the Fe, Cr and Ni elements in the melting pool. Coatings with composite microstructure in nature were obtained resulting from the dilution of substrate and the laser-induced rapid cooling process. Intermetallic phase of Fe₇W₆ with solid solution of Ni and Cr shows dendrite or hallo structure depending on the laser fluence. Sintering and/or consolidation of W particles is observed for samples processed with lower laser fluences. It has been found that hardness of the coatings was improved significantly compared with the 304 stainless steel substrate. Coating processed with laser fluence of $2.5\times 10^7$ J/m² shows the best corrosion resistance.

In this paper, 0.6mm thick stainless steel plates were welded by YAG pulse laser machine. According to the performance parameters of 304 stainless steel and the preliminary experiments, welding parameters were determined. Laser scanning speed is 36mm/min. After welding, different heat treatment processes were carried out on 304 stainless steel samples. Experimental results show that by water cooling at 1000°C for 60min for welding samples, the microstructure of the weld center is fine and uniform equiaxed grains. The weld edge is columnar crystal that perpendicular to the fusion line and extends to the weld center. The hardness of the weld center is 216.39HV. The tensile strength of welded joint is 375MPa. It is much higher than that of the other heat treatment processes. By the heat treatment process, weld quality of the samples is nice, the interface of the joint achieve metallurgical bonding and has higher mechanical properties.