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Molds for plastic automotive components such as bumpers and dashboards are usuallymachined from large pre-hardened steel blocks. Due to their dimensions, quenching andtempering yield continuously varying mixed microstructures as the distance from the surfaceincreases. As a consequence, fracture toughness as well as fatigue properties are not welldefined and, in any case, lower than those of a fully quenched and tempered steel. Moreover,the final machining of the bloom may expose the heart microstructure in some parts of themold surface, giving rise to not easily predictable toughness and fatigue behaviour.An investigation of the mechanical properties of a few commercial blooms of 1.2738 steel wascarried out, including tensile, Charpy V-notched, fracture toughness. The samples wereobtained from different depths of the blooms. Some of them were tested in their originalcondition, while others were re-heat-treated by air quench and tempering.Moreover some da/dN tests were carried out at different depths and both the threshold and theParis zones were investigated. All the tests were carried out according to the compliancemethod for the determination of the crack length.The relationship between mechanical properties, fracture surfaces, sampling position andmicrostructure was also investigated.