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Abstract
The influence of tempering on the mechanical properties of an En 56C steel has been studied. The plane-strain fracture toughness was found to be sensitive to tempered-martensite embrittlement; under these conditions, the embrittlement was associated with the replacement of micro-void coalescence either by quasi-cleavage (450–500°C temper), or in the most brittle condition (540°C temper), by intergranular fracture. It is proposed that the apparent degree of embrittlement in plane-strain, and the related fracture mode, depends on the plastic-zone size at the crack tip and on the grain-boundary microstructure. These factors could account for the inconsistencies to be found between previous studies of tempered-martensite embrittlement.