Abstract In sheet metal forming (SMF), deformation is caused by the relative movement between the sheet and tool, which generates friction forces. However, materials behave differently during plastic deformation. In this study, a tribo-simulator was designed to investigate the effect of different contact conditions or formability tests on the tribological behavior of AISI 304 and AISI 430 stainless-steel sheets. The effects of the texture and microstructure of the sheets on the measured coefficients of friction (COFs) and changes that occurred on the tribosurfaces also were investigated. Roughness and microhardness measurements, optical and scanning electron microscopy, and X-ray diffraction were used in the analyses. The tribo-simulator was successfully manufactured, and the repeatability of the measured COFs was satisfactory (standard deviation of ~0.02). A comparative analysis of the formability tests revealed differences in the COFs. In the bending under tension test, the COF for ferritic steel was 33% higher, while in the strip-tension test, the COF for austenitic steel was 44% higher. Friction was strongly influenced by the texture and microstructural characteristics of the steel sheets. The samples exhibited galling due to severe adhesive wear.

RESUMO Na conformação de chapas metálicas, as propriedades mecânicas do material e os aspectos relacionados ao atrito têm sido uma das principais preocupações, pois têm grande influência na produtividade, qualidade do produto e custos de produção. Nesse contexto, é de extrema importância compreender e ser capaz de controlar os diferentes fatores que afetam o atrito durante o processo de deformação plástica. O objetivo deste trabalho foi investigar a influência da variação da velocidade de estampagem e da anisotropia no comportamento tribológico e na fratura de uma tira de aço inoxidável ferrítico AISI 430 estabilizado com Nb deslizando sobre um pino de metal duro (WC-12% Co). Para isso, foi utilizado um teste de conformabilidade que simula o atrito entre a chapa e a ferramenta. O coeficiente de atrito, ductilidade e dureza na fratura foram medidos para investigar o efeito da velocidade de ensaio e da anisotropia da chapa de aço nos resultados experimentais. Uma análise comparativa dos resultados revelou que o coeficiente de atrito diminuiu com o aumento da velocidade de teste. Além disso, a orientação da tira metálica influenciou sintomaticamente no atrito, sendo maior no sentido de laminação, cuja rugosidade superficial foi maior que no sentido transversal. Como resultado da deformação plástica, a dureza e resistência da chapa de aço aumentaram, mas a ductilidade diminuiu, porém, o aumento da velocidade de ensaio também influenciou os valores desses parâmetros causando uma diminuição, muito provavelmente, devido ao aumento da temperatura na interface de contato.

ABSTRACT In sheet metal forming, mechanical properties of the material and aspects related to friction have been one of the main concerns, as they have a great influence on productivity, product quality and production costs. In this context, it is extremely important to understand and to be able to control the different factors that affect friction during the plastic deformation process. This study aims to investigate the influence of drawing speed and anisotropy on the tribological behavior and fracture of an AISI 430 ferritic stainless-steel strip stabilized with Nb sliding over a hard metal pin (WC-12%Co). A formability test that simulates the friction between the sheet and tool was used. The coefficient of friction, ductility and hardness in the fracture were measured to investigate the effect of drawing speed and anisotropy of the steel for the experimental results. A comparative analysis of the results revealed that the coefficient of friction due to increases surface roughness by roping effect. Furthermore, the orientation of the metallic strip influenced symptomatically on the friction, being higher in the rolling direction, which surface roughness was higher than the transverse direction. As a result of plastic deformation, the hardness and strength of the steel sheet increased, but the ductility decreased; however, the increase in drawing speed also influenced the values of these parameters causing a decrease, most probably, due to the increase temperature at the contact interface.