Precipitation Characterization and Creep Strength at 600°C for Creep Resistant Cr–Mo Steel

Abstract

The creep strength of 5Cr-0.5Mo steel was determined at 600°C and 78-170 MPa, as well as its relation to the microstructural changes during the creep tests. The microstructural characterization showed that the creep tests were conducted under the presence of a mixture of both intergranular and intragranular M 7 C 3 and M 23 C 6 carbides dispersed in the ferrite matrix. The n exponent of Norton-Bailey law suggested that the creep deformation process occurred through the ferrite grains, which conducted to a transgranular ductile-fracture mode after creep testing. The creep strength of this steel is directly related to the average radius and number density of carbides present during the test. The ferrite grain size of 5 μm seemed to cause an enhancement of the creep strength for this steel in comparison to that of other similar steels reported in the literature.

The Analysis of the Microstructure of Welded Joints in Steel P5 after Service

“…Precipitates of various morphology were observed within and on the boundaries of bainite laths as well as on the boundaries of former austenite grains. Depending on the chemical composition and the parameters of heat treatment, the microstructure of the Cr-Mo low-alloy steels in the as-received state contained M₃C, M₇C₃, M₂₃C₆ and M₂C precipitates [11,12]. The M₇C₃ and M₂₃C₆ precipitates were rich in chromium, the M₂C carbide was a precipitate rich in molybdenum, whereas the M₃C precipitates were alloy cementite [14].…”

“…5). The coagulation of the precipitates in the area primarily concerned the M23C6 carbides [11,15], which was probably related to the faster diffusion of substitutive elements along the grain boundaries. According to information contained in publication [16,17], in the welded joint of steel Cr-Mo, because of its fine-grained microstructure, the normalised/partially normalised area could develop creep damage (triggered by the IV type mechanism) during operation [18].…”

Weld Repair Technique for Petroleum Product Pipeline in Extreme Conditions of Prolonged Thermal Cycling

“…This change in the structure of the fusion zone leads to an abrupt change in properties in a very short section. The decarburized layer is weakened, and the carburized zone is characterized by increased brittleness [1][2][3][4][5][6][7][8].…”