Abstract
The fracture toughness of two acicular ferrite, high strength low alloy (HSLA) pipeline steels was investigated utilizing a linear elastic fracture mechanics analysis (KIC testing according to ASTM E399-74) as well as an elastic plastic fracture mechanics analysis (J-Integral and crack opening displacement COD methods). The tests were conducted at a strain rate of 10-4/s, K= 10 Ksi√in/s (11 MPa√m/s) using 0.5 in. (12.7 mm) thick compact tension specimens. A resistance curve test technique developed by Landes & Begley was employed to obtain the JIC fracture toughness, whereas, the British Standard for COD testing was followed for measuring the δc fracture toughness. It was observed that the semi-killed AF-1 steel possesses anisotropic fracture toughness properties whereas, the AF-2 steel which is rare earth treated steel for sulfide shape control exhibits isotropic fracture toughness properties. The temperature dependence of the fracture toughness was determined to assess the usefulness of these steels for arctic applications. An attempt was made to correlate the linear elastic fracture toughness KIC or KQ values with the elastic-plastic fracture toughness, JIC and COD data for both steels tested in three notch orientations. The data shows that JIC and δQ fracture toughness parameters can be used for specifying the fracture toughness of these steels for service temperatures extending down to −130 °C.
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