Fatigue failure analysis of HSLA steel sheets holed by conventional and flow drilling processes

Abstract

Flow drilling process produces bushes for removable joints that can be threaded by forming tapping process, reducing stages in production of components of automobile industry and in construction sheds. High strength and low alloy steels (HSLA) are employed on several applications in the processing industry. Benefits provided by these materials make them an efficient solution, since their high cold resistance allows reducing weight on structures, as well as maintaining the required mechanical properties. The present study evaluated the conventional and friction drilling processes in HSLA steel sheets with a thickness of 4.25 mm. Specimens were subjected to cyclic loadings, with no rework after holemaking, so the resultant characteristics of each process were maintained. Fractured surfaces were analyzed with a scanning electron microscope (SEM) to identify the fracture mechanism in different drilling processes. Fractographies obtained on both processes indicated that the failure mechanism occurred due to ductile fracture resulting from the nucleation, growth and coalescence of micro cavities.

Image J Analysis of Six Different Annealed Temperatures of 0.17% C of HSLA Steels

“…It involves heating the material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling. [2] and [3] described annealing process as a thermal system applied to a material to transform or modify its internal structure from cold worked propagation; metallurgically, the effect of these changes in properties impacts on the performance characteristics and the expected application [4]. Annealing is the type of heat treatment most frequently applied in order to soften iron or steel materials and refines its grain due to ferrite-pearlite microstructure; it is used where elongations and appreciable level of tensile strength are required in engineering materials.…”