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Effect of charpy impact test on microstructure properties of AISI4140 steel

Chaouch D., Sadok A., Bendaoudi S.-E., Chaouch A.

Mechanics and Mechanical Engineering

2018

Vol. 22, nr 4

1463--1469

In this paper, the mechanical properties and microstructures of AISI4140 low alloy steel under different tempering conditions are investigated. The samples are quenched, tempered to a martensite structure and loaded to fracture by means of Charpy machine according to standard test. Fractography analysis showed that the morphology fracture surface was changed by increasing tempering temperature. The variation of energy of Charpy impact fracture as a function of tempering temperature exhibits minimum values at 300 ◦C, which suggests the occurrence of temper embrittlement.

Irreversible temper embrittlement

Pacyna J., Kokosza A., Dziurka R.

Archives of Materials Science and Engineering

2013

Vol. 62, nr 2

67--72

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 ε 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.