13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- place in the API 5L X70 steel during fracture process from the fracture toughness testing. Evaluation of microtexture and Taylor factor mapping were performed from the EBSD technique in the perpendicular region to the propagation fracture direction where delamination occurred. 2. Experimental Procedure The material used in the investigation was obtained from an API X60 steel plate grade of 5/8 inch thickness. Table 1 shows the chemical composition of API X60 steel and the requirement of the API standard. Table 1. Chemical Composition obtained for API X60 steel and maximum specification through API standard (in wt. %) [1]. Element C Mn P S Ni +V+T Cr Cu Co Si Composition 0,15 1,45 0,014 0,005 0,011 0,032 0,037 0,02 0,3 API Specification 0,26 1,40 0,030 0,030 0,015 To obtain the tensile properties, three specimens from the rolling direction (RD) and transverse direction (TD) were extracted in each direction. The specimens were tested in tensile testing SHIMADZU machine at room temperature according to ASTM E8M [16]. The single edge tension SE(T) specimens were used to obtain J-R curves. All specimens crack planes were oriented in the LT orientation according to ASTM E1820 [17]. The SE(T) specimen has following dimensions: length of reduction section of 156 mm, radius of fillet of 10 mm, overall length of 276 mm, width, W, of 32 mm and thickness of 12.5 mm. This specimen was loaded with a centered pin at center distance of 214 mm. Crack length to width ratios of 0.21 and 0.52 were investigated, corresponding shallow and deep cracks respectively. The specimens were loaded in three-point bending with a span of 128 mm, after precracking by fatigue according to the procedure in ASTM E1820. The specimens were side grooved using a Charpy cutter to a total thickness reduction of 20%, in an attempt to develop plane strains conditions along crack front. The fracture toughness tests were performed in MTS Flex Test GT servo hydraulic machine according to ASTM E1820 [17]. All specimens were tested at room temperature. The J-R curves were obtained from unloading compliance technique using clip gage to measure the crack mouth opening displacement (CMOD). Procedure to calculate the J-R resistance such as, k, η, γ factors were obtained from the results of Cravero [18]. Microstructure analysis were performed from the rolling direction (RD), transverse (TD) and normal direction (ND) which were grinding, polished and chemically etched with Nital 2%. The microtexture was carried out by EBSD technique. The sample was obtained from perpendicular fracture surface in the delamination region, as can be seen in Figs. 1.a e 1.b. Samples were polished in the solution of OP-S (colloidal silica), and then etched with Nital 2%. For EBSD data collection was used software TSL 5 IOM Data collection and for data processing was used software OIM Analysis 5. The scanning electron microscope used for performing of such measures was the EDAX TSL EVO MA 10.
RkJQdWJsaXNoZXIy MjM0NDE=