Materials Science and Engineering A 472 (2008) 198–207 Thermal fatigue of materials for die-casting tooling D. Klobˇ car a,∗ , J. Tuˇ sek a , B. Taljat b a University of Ljubljana, Faculty of Mechanical Engineering, Materials Technology Department, Aˇ skerˇ ceva 6, 1000 Ljubljana, Slovenia b STEEL d.o.o, Litostrojska 40, 1000 Ljubljana, Slovenia Received 11 August 2006; received in revised form 6 March 2007; accepted 7 March 2007 Abstract This research is conducted to study the thermal fatigue resistance of different hot-work tool steels; AISI H11 and H13, special tool steel and 18% Ni maraging steel. The maraging steel is surface cladded by GTA welding to study the thermal fatigue resistance of surface layer. An influence of mechanical and microstructural properties on thermal fatigue resistance is evaluated. An innovative apparatus for thermal fatigue testing is developed to study the thermal fatigue resistance. The test specimens are subjected to cyclic heating in bath of molten Aluminum Alloy 226 and cooling in bath of water-based lubricant. They are continuously internally cooled with cold water. The specimens are periodically analyzed after completion of particular number of cycles. The microstructure, hardness profile and the surface cracks developed are analyzed. Temperature transients at different locations of test specimen are measured and used in computation of transient stresses performed by finite elements. The specimens of special geometry are developed using finite element modeling to improve testing efficiency. An optimal set of thermal fatigue testing parameters are developed to establish efficient testing. The influence of thermal loading on tempering of hot work tool steel and on aging of maraging steel claddings during testing is determined. The results showed significant differences in thermal fatigue resistance of tested materials and their heat treatments. The best thermal fatigue resistance achieved special tool steel due to its high thermal stability. The resistance of AISI H11 tool steel is slightly superior to that of maraging steel weld. © 2007 Elsevier B.V. All rights reserved. Keywords: High-pressure die-casting; Hot-work tool steel; Heat treatment; Thermal fatigue; Immersion test; Finite element modeling 1. Introduction Die-casting is a high volume production process, which produces geometrically complex parts of nonferrous materi- als. A production of 300,000 castings is a common series for die-casting industry. The production cost of die-castings is highly depended on the tool life, which is influenced by the tool design, material selection, its heat treatment, and cast- ing process parameters. During aluminium die-casting, molten aluminium at temperatures of about 700 ◦ C is injected into the mold at velocities of 30–100 m/s. The injection pressures are of the order 50–80 MPa [1]. The in-service tool life is affected by (a) thermal fatigue, which causes heat checks on the surface of the die, (b) corrosion and soldering of alu- minium to the die surface, (c) erosion due to melt flow, and (d) catastrophic failures [2–5]. In order to minimize these effects different approaches are applied to extend tool life. Applica- ∗ Corresponding author. Tel.: +386 1 4771 205; fax: +386 1 4771 225. E-mail address: damjan.klobcar@fs.uni-lj.si (D. Klobˇ car). tion of surface coatings minimizes corrosion, soldering and erosion. Surface coatings have good resistance to erosion and soldering, and a poor resistance to thermal fatigue [6], whereas, newly developed surface coatings achieve improved thermal fatigue resistance [7,8]. The second approach is to study ther- mal fatigue mechanisms and resistance of different materials and heat treatments [4,6,9,10] in order to extend the in-service tool life. This is established by development of a test appara- tus for simulation of thermal fatigue during die-casting. The main difference between the testing methods and the cast- ing process is in the specimen heating, which is achieved by immersion in molten alloy, induction heating or laser heating [2,4,6,11]. An innovative apparatus for thermal fatigue test- ing based on molten aluminium heating is developed for this study. In-service die life used for aluminium die-casting could be improved by proper material selection, its heat treatment or by development of repair welding technology. As part of this investigation four different hot-work tool steels are tested: (1) a generic AISI H11, (2) a premium H13, (3) a special tool steel (STS), and (4) a particular 18% Ni maraging steel 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.03.025