Study of Microestructure and Tempered Martensite Embrittlement in Aisi 15b41 Steel

In this paper we show that the evolution of the microstructure due to heat treatment for hardening and tempering of a commercial IRAM - IAS 15B41 boron steel, equivalent to AISI 15B41, is consistent with the mechanical behavior of materials and associated fracture mechanisms. The 15B41 steel alloy contains elements that influence the martensitic transformation. Such influence allows the formation of a needle shaped martensite whose thin slats and global shape close together. Such quenching microstructure leads to the precipitation of very fine carbides at low tempering conditions, which are very close together. On the other hand, at high tempering conditions the precipitated carbides are significantly larger and are not coherent with the iron matrix. These microstructures highlight the tensile strength of tempered steel, but also cause a noticeable loss of notch toughness when tempering around 350¡C, which weakens the steel's impact resistance.