Mechanical Properties of High Density Low Alloyed PM Steels: Effect of Sintering and Secondary Heat Treatments

Nowadays sintered components are widely used for different applications. One of the biggest end user is the automotive industry. The growth of the PM Industry in recent years can to a very large extent be explained by the shaping ability of PM processes.
In this work the mechanical properties of two main low alloyed PM steel groups were studied as a function of density, sintering temperature and microstructure (modified by carbon content and either heat or thermochemical treatment). The former group is based on the Fe-Mo-(Ni) system, widely used in the industry today and the latter is based on Astaloy CrL prealloyed powder based on the Fe-Cr system. Astaloy CrL was designed as complement or replacement to powders based on common Fe-Mo-Ni-Cu systems used for medium-to-high strength applications.
The purpose of this study was to check how the mechanical properties (tensile, impact and fatigue resistance) of materials are influenced by the processing conditions investigated, through their effect on density, porosity and microstructure.
Different methods to obtain high density, such as warm compaction and high velocity compaction were used, the results in any case were compared to convectional (cold) compacted materials.
Generally, the sintering during this project was carried out in 90%N2/10%H2 atmosphere at 1120 (belt furnace) and 1250ºC (batch furnace) for 30 min. Some additional high temperature sintering tests were carried out in an industrial vacuum furnace, with different cooling rate.
Experiments with different secondary heat treatments, such as through hardening, steam oxidation and carburizing, subjected to improve the material’s performance were carried out.