Wilian da Silva Labiapari

Strain Hardening: Can it Affect Abrasion Resistance?

It has been largely reported in the literature that previous strain hardening has none or negligible effect on abrasive wear resistance. Those results are mainly obtained using sand rubber wheel tests and pin-on-disk tests, and have been attributed to the large strain hardening promoted by the abrasion phenomena themselves. The stresses involved in those tests are very high and the stress distributions spread toward subsurface regions at large depths. This work investigates the effects of strain hardening on low-severity (low stress at low depth) abrasive wear resistance. Microabrasion tests, normally regarded as lower stress tests, were used in order to impose low severity. Two types of stainless steels were tested: an austenitic AISI 304 steel and a ferritic AISI 430 steel. Strain hardening was obtained via thickness reduction (20%) of stainless steel sheets in a laboratory cold rolling mill. The microabrasion wear tests were carried out in a fixed-ball microabrasion tester with a three-axis load cell to continuously and simultaneously monitor the forces involved in the tests. Contrary to many findings so far in the literature, previous strain hardening increased abrasion wear resistance (55 and 63%, respectively) for both materials. Hertz calculations, simulations using Finite Element Program with explicit solution, conventional mechanical tests, microhardness profiles, microstructural analysis, and X-ray diffraction analysis were used to explain this paradigm shift for the case of microabrasion tests.

Life of cutlery cutting tools: effects of surface finish

Purpose The progressive wear of cutting tools used in industrial cutlery production results in excessive burr formation and reduces tool service life. This paper aims to investigate the effects of the sheet surface finish on tool wear and service life during blanking. Design/methodology/approach Two alternative surface finish techniques were proposed and initially implemented under laboratorial conditions and compared with conventional acid pickling. Those surface finish techniques were then implemented on an industrial scale to improve the service life of cutting tools. Industrial blanking tests characterized the effect of sheet surface finish on tool life. Findings In the first technique, called skin pass, an additional mechanical pass under controlled conditions reduced the height of the surface peaks and resulted in partial embedding of the carbides into the surface. The second technique, called electrochemical pickling, removed solely the surface carbides, leaving behind a smoother surface without carbides. Real industrial blanking tests identified that the use of skin pass reduced burr formation and increased tool life by around 300 per cent when compared with conventional acid pickling. With electrochemical pickling, burr formation was further reduced and tool life increased further by 300 per cent when compared with skin pass. Research limitations/implications First, this work proposes an alternative surface finishing technique (electrochemical pickling) to be used after annealing of stainless steel. Second, the work clearly shows the presence of protruding surface carbides when conventional surface finishing techniques are used, which do not exist after acid pickling. Practical implications When electrochemical pickling is implemented on an industrial scale, the life of blanking tools is substantially improved. Originality/value Although the sheet surface finish is widely recognized to affect metalforming processes, the literature lacks studies on the effect of sheet surface finish on tool wear during blanking. First, this work proposes an alternative surface finishing technique (electrochemical pickling) to be used after annealing of stainless steel. Second, the work clearly shows the presence of protruding surface carbides when conventional surface finishing techniques are used, which do not exist after acid pickling. Third, when electrochemical pickling is implemented on an industrial scale, the life of blanking tools is substantially improved.

O Papel do Pó de Ferro no Mecanismo de Deposição de Eletrodos Revestidos

The main motivation for this work was a search for an answer to the dilemma of which higher deposition rates of metal powder based coating electrodes are due to either their capacity of working at higher currents or a higher fusion efficiency of the metal powder. This study was developed using three commercial coated electrodes, which main distinction was the iron powder content in their coatings. The electrodes were characterized in relation to their dimensions, coating densities and compositions (via MEV-EDS). Using two current levels, fusion and deposition rates and bead geometry from fillet carried out in flat position (T-joint) were assessed. From the results, fusion and deposition are greater when the iron concentration in the coating are higher, regardless the current level. It was demonstrated that the mechanism for reaching higher deposition rates is related to a lower required energy to melt the iron in powder than in solid state. A higher nominal carrying current capacity acquired by the electrode with iron powder is a secondary reason.