Abstract
The isothermal transformation diagrams have been determined for the case and core campositions of a series of four carburising steels,and the physical properties resulting from various alternative heat-treatment procedures Suggested by the diagrams determined. The dimensional changes occurring during all stages of isothermal heat-treatment have been determined, and the effects of these dimensional changes on the stress developed between the case and core of carburised specimens demonstrated. The most suitable heat-treatment procedures for optimum core properties with adequate case hardness and minimum case/core stress are given. It was noticed that during isothermal transformation of certain of the cose compositions, changes in as-quenched hardness occurred before the commencement of transformation. This behaviour appeared to be associated with the presence of carbon and carbide forming elements. The investigations were therefore extended to include a series of chroma molybdenum hot-work steels having varying tungsten and vanadium contents. By plotting the hardness values obtained on the isothermal transformation specimens on a perspective summary diagram for each steel composition, three types of behaviour were shown, and an explanation is proposed for these alternative behaviour patterns.