FRACTURE TOUGHNESS ASSESSMENT X80 PIPELINES STEELS WITH DIFFERENT CHEMICAL AND MICROSTRUCTURAL FEATURES

Ano: 2019

Instituições de ensino: Universidade de São Paulo, Universidade de São Paulo, Universidade Estadual Paulista "Júlio de Mesquita Filho"

Idioma: Ingles

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Resumo

X80 steels are broadly used in the gas and oil industry as pipelines, which are usually fabricated by thermomechanical controlled process, have low carbon content and some alloy elements. This pipeline grade steel presents high strength-to-toughness ratio, such as yield strength above 555 MPa and ductile-brittle transition temperature around -100ºC. However, differences in chemical composition and plates processing result in different microstructures and mechanical properties. Microstructure features and mechanical properties of two low alloy rolled steels produced by different routes were compared in this study. One steel presented a homogenous bainite matrix and the other presented banded microstructure composed of elongated ferrite grains. Microstructure and toughness were correlated analyzing the crack tip opening displacement tests results and samples. Light optical and scanning electron microscopy were used to perform the microstructural characterization. The steel with bainite matrix presented better fracture toughness behavior than the ferrite matrix steel due to less anisotropy and microstructural homogeneity.

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