Open Access Conference Proceedings

Using final machining, as a finishing technology, components with specific precise dimensions are obtained. Despite the precise type of machining, the integrity of the surface is significantly affected, and the material acquires some negative surface properties that cause a decrease in corrosion resistance. Such properties are increased hardness of the surface layers (and therefore reduced toughness), roughness or tensile residual stresses. The combination of these parameters leads in many cases to susceptibility to stress corrosion cracking or other corrosion degradation phenomena. In this work, final turning was used as the machining process using a tool with a positive cutting geometry and a sharp cutting edge, while the cutting parameters – cutting speed (100 and 250 m·min−1) and feed (0.12, 0.2 and 0.3 mm) were combined. The depth of cut remained the same in all cases (0.8 mm). The studied and compared materials were austenitic stainless steels AISI 304 and AISI 321. After turning their surface properties such as roughness or hardness were analysed. The susceptibility to stress corrosion cracking was monitored using the ASTM G36 test, where the samples were exposed to a boiling magnesium chloride solution for up to 96 hours. The samples were observed using SEM, where the areal density of cracks was monitored, as well as the depth and length of cracks on cross-sections. As part of the influence of cutting parameters, increased values of areal density were found with an increase in feed but also with an increase in cutting speed, while the surface of austenitic steel AISI 304 was significantly affected compared to AISI 321 under the same conditions. In addition to the exposure method, an electrochemical method was also used, specifically the electrochemical potentiokinetic reactivation analysis, the double loop method (DL-EPR), where it was observed whether the final turning in any way affects the sensitivity to intergranular corrosion, or how the resulting roughness affects the measurement itself.

Keywords: Stress corrosion cracking, austenitic stainless steel, machining, turning, corrosion

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