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Heat treatment of a hot-work die steel

Qamar S. Z., Sheikh A. K., Arif A. F. M., Pervez T., Siddiqui R. A.

Archives of Materials Science and Engineering

2007

Vol. 28, nr 8

503-507

Purpose: This paper reports results of in-house experimentation and an exhaustive literature search on heat treatment of H13 tool steel. Heat treatment strategy practiced by the industry is described in detail. Effect of various types of heat treatment on fracture toughness and hardness is also analyzed. Design/methodology/approach: Because of its versatility and wide applications, aluminum has been dubbed as the metal of the millennium. Commercial extrusion of aluminum alloys is a cyclic hot-working process. The magnitude of the thermal and mechanical stresses generated in the die and relevant tooling is therefore a major factor in extrusion. The die and mandrel (used for hollow profiles) are the most important tools subject to wear and are, at the same time, the most highly stressed tools in extrusion. For reliability and durability of an extrusion die, the load carrying capacity of the tool steel, its high-temperature fatigue properties, and its wear resistance become critically important. To withstand large stresses, the steel should have high strength and toughness, and to resist wear it should have high hardness and surface integrity. This combination of high toughness and high hardness is usually achieved through specific heat treatment and surface hardening sequences. Findings: Toughness (expressed in terms of plane-strain fracture toughness KIC or Charpy impact energy CVN) and hardness (HRC) of H13 steel vary in a nonlinear manner against tempering temperature. Toughness shows a decreasing-increasing trend, while hardness exhibits an opposite increasing-decreasing pattern with increasing tempering temperature. Research limitations/implications: Optimum heat treatment strategy for commercial aluminum estrusion dies (H13 steel) appears to be tempering in the 525-550 °C temperature range, to get the best combination of high toughness and high hardness Originality/value: Experimental data from closely monitored heat treatment and mechanical testing has been added to the available published data. Careful and judicious extrapolatiopn-intrapolatioon has also been carried out to complete the data matrices. Analysis of the resulting variation pattersns provideds a good scientific foundation for devising an optimal heat treatment strategy.