Caracterização Microestrutural Da Propagação De Trincas Em Aços Estruturais

Abstract

Two structural steels with different chemical compositions and similar mechanical properties were selected for the research, aiming to be alternatives for the manufacture of crankshaft (DIN 34CrNiMo6 steel) of Diesel and natural gas engines of thermoelectric plants. CT-type test specimens were machined in SAE 4140 and 4340 steels and subjected to fatigue crack propagation tests, in order to obtain the respective curves of d /dN versus ΔK. After the tests, the fatigue cracks were indicated on the specimens' surfaces by means of penetrating liquid. Samples from the crack propagation region, with emphasis on the threshold (∆Kth), were removed from the specimens and analyzed by optical microscopy, in an attempt to correlate ∆Kth and the crack propagation with microstructural characteristics and metallurgical heterogeneities of the materials, such as inclusions, voids and second phase particles.