Avalia??o da sensitiza??o em a?os inoxid?veis ferr?ticos estabilizados e n?o estabilizados usando-se a t?cnica reativa??o eletroqu?mica potenciocin?tica em meio sulf?rico.

A principal causa da corros?o inter granular de a?os inoxid?veis ferriticos ? a sensitiza??o que ? causada por tr atamentos t?rmicos inadequados onde ocorr e a precipita??o de fases ricas em cromo nos contornos de gr ?o, gerando regi?es empobreidas deste elemento em suas vizinhan?as. A resist?ncia ? corros?o intergranular dos a?os inoxid?veis ferr?ticos ( AIF) ? normalmente avaliada por ensaios de imers?o. Neste trabalho, avaliou - se o estado de sensitiza??o d os a?os do tipo AISI 444, AISI 439 e AISI 430 e , P430 (AISI 430 modificado) que foram submetidos a aquecimentos, varando - se as condi??es de temperatura, 900?C e 950? C, e tempo de perman?ncia em um forno, 10 e 20 minutos, sendo resfriados no pr?prio forno, ao ar, em ?gua, ?leo e nitrog?nio l?quido. Par a caracterizar o grau de corros?o intergranular nos a?os inoxid?veis ferr?ticos foi realizado o ensaio em ?cido ox?lico (Pr?tica W) da norma ASTM A763 - 93. Os resultados obtidos foram cor relacionados com o m?todo da reativa??o eletroqu?mica potenciocin?tica na vers?o Double Loop (DL - EPR) , t?cnica n?o destrutiva e quantitativa. O ensaio DL - EPR f oi realizado em solu??o 0,5M H 2 SO 4 a uma taxa de var redura de 1,67mV/s. Os re sultados indicaram que o a?o AISI 430 e P430 apr esentar am dif erentes gr aus de sensitiza??o. No entanto, esse compor tamento n?o foi observado par a os a?os AISI 444 e AISI 439The main cause of the inter gr anular corr osion of f erritic stainless steel is the sensitization that is caused by inadequate heat treatments due pr ecipitates phases rich in chromium in the gr ain boundar y that gener ate depleted r egions in this element of its neighborhoods. The r esistance to the inter gr anular corr os ion of the fer ritic stainless steel normally is evaluated by immer sion assays. In this wor k, the state of sensitization of f erritic stainless steel , AISI: 430; 439; 444 and P430 ( AISI 430 modif ied) was evaluated These steels were heated, var ying the condi tions of temper atur e, 900?C and 950? C, and holding time in an oven, 10 and 20 minu tes, being cooled in the oven, in air, in water, oil and liquid nitrogen. To characterize the degree of inter gr anular cor rosion in f er ritic stainless steel, the test in acid oxalic (Pr actical W) of Norm ASTM A763 - 93 was car ried through. The gotten r esults had been cor related with the method of the potentiocinetic electrochemical r eactivation in the version Double Loop ( DL - EPR), not destructive and quantitative technique. The DLEPR test was carried out in solutions containing 0 . 5M H 2 SO 4 and a scan r ate was of 1 . 67mV/s. The r esults indicated that the AISI 430 and P430 steels pr esented dif f er ent degr ees of sensitiza tion . However , sensitization was n o t obser ved for AISI 444 and 439 steel