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This study was done to evaluate precipitation annealing of 18 % Ni maraging steel repair welds during aluminium alloy die casting and to predict the prolonged in-service tool life. The emphasis of this study was the influence of post-weld precipitation annealing heat treatment and aluminium die casting thermal cycling on metallurgical and mechanical properties. A series of specimens of 1.2344 tool steel was prepared to which 1.6356 maraging steel was gas tungsten arc weld clad. Analysis of weld microstructure and hardness was made in order to understand the metallurgical processes during heat treatment at elevated temperatures and at prolonged time. The Response Surface model for prediction of hardness after heat treatment was developed. The edges of immersion test specimens are gas tungsten arc weld clad with 1.6356 maraging steel and machined to the final edge geometry. Two specimens were tested in as-welded condition and two in optimally aged condition. Testing was performed on specially developed immersion test apparatus, which enables the simulation of thermal fatigue during aluminium alloy die casting. After completion of a particular number of thermal fatigue cycles the weld microstructure and hardness were evaluated. A hypothetical model for prediction of precipitation annealing time during aluminium alloy die casting was proposed. The results showed that tool heating lasts 30 % of molten metal injection time, preparing conditions for precipitation annealing at 10 % of injection time, and precipitation annealing at 60 % of injection time. These results, together with a finite element model for prediction of tool temperature and response surface model for prediction of hardness after precipitation annealing, enable accurate prediction of maraging steel tool hardness after any particular number of die casting cycles and consequently in-service tool life. The thermal fatigue resistance of maraging steel welds was compared to AISI H13 tool steel. The results showed superior thermal fatique resistance for AISI H13.

international journal of materials research

Suitability of maraging steel weld cladding for repair of die casting tooling: Part II: Influence of ageing during aluminium alloy die casting on maraging steel weld microstructure, mechanical properties and crack growth