Irreversible temper embrittlement

Purpose: The new approach to the phenomenon of irreversible temper embrittlement was presented in hereby paper. Design/methodology/approach: Proposed in hereby paper, thesis trying to explain the undesirable known for a long time effect is based mainly on the ground of the authors research experience on the investigating of the fracture toughness as well as phase transformations during tempering. Findings: The carbon atoms redistribution to the grain boundaries and boundaries of the cellular structure in the martensitic matrix, during dissolving of the metastable carbides, mainly e carbide, was indicated as a main reason of the irreversible temper embrittlement. Research limitations/implications: Existing, old theories on irreversible temper brittleness such as preferential precipitations from martensite along grain boundaries, chemical and mechanical destabilization of the retained austenite, segregation of admixtures to grain boundaries etc. can be easily invalidated, using modern transmission and scanning electron microscopy. Originality/value: It was pointed out that the carbon atoms arranged in a privileged places along the grain boundaries and boundaries of the cellular structure, have incomparably stronger influence spread to temper embrittlement rather than existing in thousandths of a percent impurity atoms. The retained austenite (if it exists in the quenched matrix) increases fracture toughness, but it is only an accompanying effect, without any influence on intergranular (and rather intercellular) character of fractures characteristic for this type of brittleness.