2Cr13 Steel (Qualified Fracture Critical Assessments) Fracture Analysis
Introduction
Fracture analysis is the procedure by which a fracture is studied to determine its nature and cause. The principal objectives of fracture analysis are to identify design or fabrication errors, operator misuse, improper maintenance, wear, or other potentially hazardous or unsafe conditions. This paper will assess the fracture analysis of 2Cr13 steel, a martensitic stainless steel containing 13% chromium. As the steel contains a relatively high proportion of chromium, known to be the primary element of corrosion resistance in stainless steel, this type of material is generally used in applications that require superior corrosion resistant properties. It is usually used in the production of knives, surgical instruments, medical implants, and even food-processing equipment as it is considered to be safe for food use.
Descriptions of the Fracture
The fracture in the 2Cr13 steel specimen is characterized as a type of brittle fracture. This means that the fracture appears to have been caused by a lack of sufficient plastic deformation that would have normally occurred if there had been sufficient ductility in the material. The fracture appears to be finely serrated and the fracture surface appears to have evidence of microvoid coalescence. The presence of fine serrations is a classic sign of a brittle fracture in which the presence of small voids, or microvoids, is observed on the fracture surface. These microvoids grow in size over time and eventually coalesce leading to the brittle fracture of the specimen.
The fracture surface also exhibits a directional preference. This is an indicator of the type of loading the specimen was subject to during failure. The directional preference observed can be assumed to be consistent with the loading direction (i.e. tension or compression) as the fracture surface appears to have a plane-strain orientation. Additionally, there is evidence of a deformation band adjacent to the fracture surface. This is an indication that plastic deformation had occurred prior to fracture and that the fracture was the result of a classic ductile-to-brittle fracture transition.
Mechanism of Fracture
Due to the small amount of plastic deformation observed in the specimen, it is likely that the mechanism of fracture in the 2Cr13 steel was initiated by a sudden release of strain energy. This sudden release of strain energy is commonly referred to as a brittle fracture and is largely associated with the presence of microvoids in the material. These microvoids can expand over time, resulting in the formation of larger voids, which coalesce and ultimately result in the brittle fracture of the specimen.
It is also possible that the fracture may have been caused by a low-level fatigue loading. The presence of fine deformation bands on the fracture surface may be indicative of a classic fatigue crack initiation and propagation mechanism, which can lead to a brittle fracture of the specimen. However, this is relatively unlikely as the stress concentration at the notch location is likely to have contributed significantly to the fracture. Moreover, no evidence of cyclic loading was observed in the fracture surface, which may indicate that the fracture was caused by a sudden release of strain energy rather than a classic fatigue crack formation.
Conclusion
Fracture analysis of the 2Cr13 steel is considered to be a brittle fracture type, in which the fracture was caused by a sudden release of strain energy. The lack of evidence of a fatigue crack formation indicates that the fracture was likely caused by a single-event. The directional preference of the fracture surface and the presence of deformation bands near the fracture region indicate that a low-level of plastic deformation had occurred prior to fracture, indicating a classic ductile-to-brittle fracture transition.
