Estudo do efeito trip produzido pela laminação a frio do aço inoxidável austenítico aisi 316l e avaliação de seu uso como biomaterial

Abstract

Austenitic stainless steel AISI 316L grade ASTM F138:2019 is used as a metallic biomaterial in prostheses and surgical equipment. Its mechanical properties, especially its high corrosion resistance, associated with a competitive cost, facilitate its use as a biomaterial. However, the mentioned characteristics can be altered with the emergence of the magnetic phase induced in mechanical forming processes by the effect of plasticity induced by phase transformation (TRIP effect). These changes are undesirable for its use as a biomaterial according to ISO5832:2016. Therefore, this study aimed to evaluate the implications of the TRIP effect in the normative specification (ISO 5832: 2016) for the use of cold-rolled AISI 316L steel as a biomaterial. Soon, AISI 316L stainless steel under the conditions as received and formed by cold rolling, with percentages of thickness reduction (deformation) of 10%, 20% and 30%, was studied through mechanical, electrochemical, morphological, magnetic analyses, crystallographic, biological and thermal. The increase in the percentage of applied deformation increased the mechanical tensile strength and hardness on the Vickers scale of the samples. Potentiodynamic polarization curves showed that pitting corrosion resistance and corrosion resistance decreased with increasing cold rolling thickness reduction. The MO and SEM micrographs of the AISI 316L steel samples showed the predominance of grains characteristic of the austenitic phase, also indicating an increase in the average grain diameter with the increase in thickness reduction by cold rolling. In the ferritoscopy test, the sample with 10% thickness reduction showed a percentage of magnetic volumetric fraction equal to 0.8%, while the sample with 30% thickness reduction showed the highest magnetic percentage, 2.2%. X-ray diffraction analysis indicated the presence of the α' martensite crystalline phase for samples with 20% and 30% thickness reduction. The results obtained from the ferritoscopy and XRD tests showed evidence of the emergence of the α' martensite phase. Cytotoxicity analysis, using the disk-diffusion method, indicated that there was no formation of inhibition halos for the thickness reduction percentages evaluated. Tests carried out after the thermal treatment of reversion of the induced martensite indicated the reduction of the microhardness of all the samples, and also the reduction of the magnetic percentage of the samples to the maximum value of 0.3%. These results point to the reversion of the induced martensite phase to the austenite phase, a microstructure specified for the use of AISI 316L stainless steel for applications as a metallic biomaterial according to ISO 5832:2016.