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The technique of hot isostatic pressing (HIP) is used to simultaneously heat up and apply high isostatic pressure to a metallic or ceramic entity in order to reach compaction. The integration of heat treatment into the compaction process generates much curiosity in the HIP community. This paper resumes the different methods for accelerated cooling and gives an overview of the research done with integrated heat treatment. Results in the field of steels, lightweight alloys and superalloys are resumed.The market for HIP treatments is divided into the post-densification of castings, which covers about 54%, powder metallurgy has about 43%, and the remaining 3% are firm bonds. The powder metallurgy sector itself is again divided into pure powder metallurgy and powder cladding, each with an equal share. Cladding entails that a layer of PM steel, typically high performance material, is applied via HIP (diffusion bonding) onto a solid material, which is typically a material of lower cost.The two biggest product sectors for PM + HIP are tool steel and stainless steel. Within the tool steels sector, high speed steels constitute the by far biggest division. For stainless steel, there are three markets of highest interest: oil/gas, offshore, and the food industry. All these markets demand large, custom-made items of stainless steel that are of high quality. Small yet growing markets include medical products such as implants and post-densification of additively manufactured parts.In general, customers decide upon HIP processing because forms are possible that cannot be manufactured with other methods, such as casting or forging, because of short production times, homogeneous material properties and the greater freedom in design it offers.As of yet, the large majority of the worldwide used HIP units are not equipped with mechanisms for accelerated cooling. Several benefits, such as drastically reduced cycle times, fewer post processing steps, and lastly, better and more homogeneous material properties lead to increasing interest at new acquisitions. The temperature-time profile of a standard HIP treatment with separate densification and heat treatment steps is displayed in Fig. 1. Efforts and breakthroughs in saving cooling timeNatural cooling, which comprises of switching off the heating elements, leads to cooling rates below 1 K/min. When furnace diameters are large, HIP cycles can require up to 30 h without active cooling. HIP manufacturers have strived to meet the customer needs for faster cooling for many years. Several approaches have been made to increase the cooling speed in comparison to natural cooling.The first possibility is to install more than one heating zone to support the natural convection. This method does somewhat speed the process. The next measure realized by HIP producers was the installation of a blower or fan inside the pressure vessel. The fan is utilized to maintain forced convection, which enhances the cooling. Through this method, the cooling reaches roughly some Kelvin per minute, which still resul...

Hot isostatic pressing (HIP) units are worldwide used for the compaction of metal alloy powders. The cooling rate in a HIP unit is usually comparatively low. This lengthens cycle times and requires an additionally heat treatment for quenched and tempered steels. Novel cooling HIP concepts in HIP units feature high quenching rates. In this study, tool steels were investigated with respect to their time-temperature-transformation behaviour for different cooling parameters. The paper shows that encapsuled powdered tool steels can be compacted and hardened in the HIP unit. The examined steels exhibit a comparable or even a higher hardness and a finer microstructure. HIP units with high-quenching rates enable to compact and heat treat materials in one step.

Ni-free austenitic steels alloyed with Cr and Mn are an alternative to conventional Ni-containing steels. Nitrogen alloying of these steel grades is beneficial for several reasons such as increased strength and corrosion resistance. Low solubility in liquid and d-ferrite restricts the maximal N-content that can be achieved via conventional metallurgy. Higher contents can be alloyed by powder-metallurgical (PM) production via gas-solid interaction. The performance of sintered parts is determined by appropriate sintering parameters. Three major PM-processing routes, hot isostatic pressing, supersolidus liquid phase sintering (SLPS), and solid-state sintering, were performed to study the influence of PM-processing route and N-content on densification, fracture, and mechanical properties. Sintering routes are designed with the assistance of thermodynamic calculations, differential thermal analysis, and residual gas analysis. Fracture surfaces were studied by X-ray photoelectron spectroscopy, secondary electron microscopy, and energy dispersive X-ray spectroscopy. Tensile tests and X-ray diffraction were performed to study mechanical properties and austenite stability. This study demonstrates that SLPS process reaches high densification of the high-Mn-containing powder material while the desired N-contents were successfully alloyed via gas-solid interaction. Produced specimens show tensile strengths >1000 MPa combined with strain to fracture of 60 pct and thus overcome the other tested production routes as well as conventional stainless austenitic or martensitic grades.

In austenitic stainless steel nitrogen stabilizes the austenitic phase, improves the mechanical properties and increases the corrosion resistance. Nitrogen alloying enables to produce austenitic steels without the element nickel which is high priced and classified as allergy inducing. A novel production route is nitrogen alloying of CrMn‐prealloyed steel powder via the gas phase. This is beneficial as the nitrogen content can be adjusted above the amount that is reached during conventional casting. A problem which has to be overcome is the oxide layer present on the powder surface which impedes both the sintering process and the uptake of nitrogen. This study focuses on whether heat treatment under pure nitrogen is an appropriate procedure to enable sintering and nitrogen uptake by reduction of surface oxides. X‐ray photoelectron spectroscopy (XPS) in combination with scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS) are used to investigate the surface of powdered FeMn19Cr17C0.4N heat treated under nitrogen atmosphere. The analyses showed reduction of iron oxides already at 500 °C leading to oxide‐free metallic surface zones. Mn and Cr oxides are reduced at higher temperatures. Distinct nitrogen uptake was registered, and successful subsequent sintering was reached. Copyright © 2014 John Wiley & Sons, Ltd.