Abstract
Herein, it was conducted a study in order to examine the main fracture characteristics in the transverse rupture strength test (TRS) of a high speed steel (HSS) AISI M2 produced by powder metallurgy (PM) and with boriding treatment. Four conditions have been studied: as-sintered, borided, normalized and borided + TiN. The TRS tests were conducted in accordance with ASTM B528-12 standard. Density, Vickers hardness and transverse rupture strength properties were evaluated. Fractography was observed by scanning electron microscope (SEM). TRS test in the as-sintered condition had the best performance. The fractography of samples showed very irregular appearance, with interconnected porosity for the matrix of the samples and the boride layer had a smooth surface with low porosity. It was observed on the boride layer, the growth of boride layers inside the pores, filling them, which is a positive factor on the TRS. However, cracks were observed in the FeB/Fe2B interface of boride layer, which embrittle the material and reduce the TRS. In fractography of borided samples, it is observed that two fracture modes occur, mode I and mode II. This should be explained owing to the difference between the elasticity modulus of FeB and Fe2B interface.
Highlights
The wear resistance, high mechanical strength and the possibility of near net shape manufacturing led to the increasing relevance of powder metallurgy steels in the tool manufacturing or automotive sector[1,2]
The material involved in the research, is the AISI M2 high speed steel produced by powder metallurgy
This study was conducted in order to examine the main fracture characteristics in the transverse rupture strength test (TRS) of a high speed steel (HSS) AISI M2 produced by powder metallurgy (PM) and with treatment of boriding
Summary
The wear resistance, high mechanical strength and the possibility of near net shape manufacturing led to the increasing relevance of powder metallurgy steels in the tool manufacturing or automotive sector[1,2]. PM properties are affected by several parameters such as the shape, size and the composition of the powder particles, lubricant type, compacting pressure, sintering temperature and time, and finishing operations[5]. The boriding is a thermochemical treatment technique used in many areas of engineering processes of metals, where the boron atoms are diffused in the surface to form borides with the base metal[8,9,10]. The boron atoms owing to its relatively small size and high mobility can diffuse into the substrate. The composite layer (FeB and Fe2B) the diffusion zone hardly
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