JOURNAL OF MATERIALS SCIENCE LETTERS 21, 2 0 0 2, 1631 – 1634 Effects of the grain size on the corrosion behavior of refined AISI 304 austenitic stainless steels A. DI SCHINO, J. M. KENNY ∗ Materials Engineering Center, University of Perugia, Loc. Pentima Bassa 21, 05100 Terni, Italy E-mail: kenny@unipg.it Although there have been many studies on fine grained ferritic steels, only a few research reports are available on refined austenitic stainless steels and, in particular, on the influence of the grain size on the corrosion resis- tance of this class of material [1, 2]. The grain size of ferritic steels can be easily induced by phase transfor- mation, but in austenitic alloys, following the absence of a phase transformation, the grain diameter is usually controlled by recrystallization after cold working [3]. This method is mainly affected by the working tem- perature, amount of deformation and recrystallization temperature. Recrystallization after hot rolling is re- ported to have the effect of grain refining [4] but this method seems to be limited. In a previous paper [5] we examined the effect of subzero working on the grain refining of austenitic stainless steels. In particular, ul- trafine grained AISI 304 stainless steel of ca. 1 μm av- erage grain size was obtained by applying the reverse transformation of martensite to austenite on subzero- worked steel annealed at low temperatures. Up to now, the corrosion behavior of such ultrafine- grained austenitic stainless steels has not been reported. This paper deals with the corrosion behavior, espe- cially general corrosion (GC), intergranular corrosion (IGC) and pitting corrosion (PC) of ultrafine-grained AISI 304 stainless steel. Results are compared with those of similar measurements on standard AISI 304 steel. The chemical composition of the AISI 304 stainless steel, obtained from a commercial batch, is shown in Table I. After subzero working down to 90% thickness reduction, the material was subjected to the following four heat treatments in order to obtain different mi- crostructures: annealing at 800 ◦ C for 160 s and 900 s (specimens A and B respectively) and at 1000 ◦ C for 10 s and 600 s (specimens C and D respectively). The grain sizes corresponding to the above specimens, as measured by automatic image analyzer, are shown in Table II. The typical microstructures of the 1 μm and 50 μm specimens are shown in Fig. 1. Tensile properties of the specimens are shown in Fig. 2. Ultimate tensile stress and 0.2% yield stress increase with decreasing grain size, according to the Hall Petch relation [6]. Steel materials were machined into corrosion test specimens of 15 × 15 × 1 mm. The specimen surface was polished by using increasingly finer abrasive pa- pers, starting with a 300 grit paper and finishing up with ∗ Author to whom all correspondence should be addressed. T A B L E I Chemical compositions of the material (wt%) C Mn Ni Cr Mo N Si AISI 304 0.06 1.50 8.6 18.4 0.06 0.024 0.61 T A B L E I I Grain sizes corresponding to the four analyzed specimens Sample Grain size (μm) A 1.1 B 3.0 C 10.2 D 50.0 Figure 1 Typical microstructures of AISI 304 steel with 1 μm and 50 μm average grain diameter. 0261–8028 C  2002 Kluwer Academic Publishers 1631