Toughness of Tool Steel

University dissertation from Uppsala : Institutionen för teknikvetenskaper

Abstract: Toughness is the ability to resist tensile stresses in the presence of a notch or crack. Sometimes gross cracking of industrial tools, mould or dies, occurs due to insufficient toughness. As the economic consequences of the gross cracking are serious, the toughness of industrial tool material, generally tool steel, is of paramount importance. The aim of this work was to help to avoid gross cracking by collecting the most important facts about toughness of tool steel.There are different methods to test toughness. In this work fracture toughness testing and Charpy V-notch impact testing have been used. Characteristic for toughness testing is the considerable scattering in the result. It is therefore necessary to statistically analyse the result. This is done in this monograph and the result reveals that the outcome from toughness testing can be described by normal distributions. This fact facilitates statistical evaluation of toughness data.Tools are generally hardened and tempered. Investigations at Uddeholms AB revealed that the cooling rate during quenching has a strong effect on toughness of certain grades. Investigations confirmed that temperature has a strong influence on the toughness of many tool steel grades. The increase in toughness with increasing temperature was more pronounced with fracture toughness testing than with Charpy V-notch impact testing. The strong influence of temperature on hot-work tool steels means, preheating of dies is important for avoiding gross cracking.

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