Development of New 14 Cr ODS Steels by Using New Oxides Formers and B as an Inhibitor of the Grain Growth

In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y2O3 and Ti additions. Different alloying elements like boron (B), which is known as an inhibitor of grain growth obtained by pinning grain boundaries, and complex oxide compounds (Y-Ti-Zr-O) have been introduced to the 14Cr prealloyed powder by using mechanical alloying (MA) and were further consolidated by spark employing plasma sintering (SPS). Techniques such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to study the obtained microstructures. Micro-tensile tests and microhardness measurements were carried out at room temperature to analyze the mechanical properties of the differently developed microstructures, which was considered to result in a better strength in the ODS steels containing the complex oxide Y-Ti-Zr-O. In addition, small punch (SP) tests were performed to evaluate the response of the material under high temperatures conditions, under which promising mechanical properties were attained by the materials containing Y-Ti-Zr-O (14Al-X-ODS and 14Al-X-ODS-B) in comparison with the other commercial steel, GETMAT. The differences in mechanical strength can be attributed to the precipitate’s density, nature, size, and to the density of dislocations in each ODS steel.

The Technological Design of Geometrically Complex Ti-6Al-4V Parts by Metal Injection Molding

In this study, the metal injection molding (MIM) process is applied to produce Ti-6Al-4V parts using blended and prealloyed powders, respectively. The feedstocks are prepared from a polyformaldehyde-based binder system with a powder loading of 60 vol%, exhibiting a low viscosity. The decomposition behavior of the binders is investigated and the thermal debinding procedure is designed accordingly. The debound parts are subsequently sintered at 1200 and 1300 °C. The results show the mechanical properties of the sintered samples prepared from blended powder are comparable to those prepared from prealloyed powder, with yield strength of 810 MPa, ultimate tensile strength (UTS) of 927 MPa, and elongation of 4.6%. The density of the as-sintered samples can reach 4.26 g/cm3 while oxygen content is ~0.3%. Based on the results, watch cases with complex shapes are successfully produced from Ti-6Al-4V blended powder. The case gives a good example of applying metal injection molding to mass production of precise Ti-6Al-4V parts with complex shapes in a cost-effective way.

Processing and Properties of Distaloy Sa Sintered Alloys with Boron and Carbon

Prealloyed iron-based powders, manufactured in Höganäs Company, are used in the automotive parts industry. The properties and life time of such sintered parts depend, first of all, on their chemical composition, the production method of the prealloyed powder as well as on the technology of their consolidation and sintering. One of simpler and conventional methods aimed at increasing the density in sintered products is the process of activated sintering, performed, for example, by adding boron as elementary boron powder. Under this research project obtained were novel sintered materials, based on prealloyed and diffusion bonded powder, type: Distaloy SA, with the following chemical composition: Fe-1.75% Ni-1.5%Cu- 0.5%Mo with carbon (0.55%; 0.75%) and boron (0.2%, 0.4% and 0.6%). Distaloy SA samples alloyed with carbon and boron were manufactured by mixing powders in a Turbula mixer, then compressed using a hydraulic press under a pressure of 600 MPa and sintered in a tube furnace at 1473 K, for a 60 minute time, in the hydrogen atmosphere. After the sintering process, there were performed density and porosity measurements as well as hardness tests and mechanical properties were carried out, too. Eventually, analyzed was the effect of boron upon density, hardness and mechanical properties of novel sintered construction parts made from Distaloy SA powder.

Microstructure Development in Powder Metallurgy Steels: Effect of Alloying Elements and Process Variables

Microstructure of the powder metallurgy (PM) steels and especially mechanism of its formation differs significantly from the microstructure of the conventional steels even if composition will be exactly the same. The difference is not only connected to the presence of the pores, which are inalienable feature of the PM parts. Presence of the prior inter-particle boundaries, which can be contaminated by residual oxides, as well as microstructure heterogeneity are another characteristic features of the microstructure of PM steels. Microstructure heterogeneity is connected to the PM manufacturing process: powder mix, consisting of the base powder and additional alloying elements is compacted and then sintered. Fully prealloyed powder is not always possible to use in standard press & sintering route due to the solid solution strengthening of the ferrite resulting in bad powder compressibility. Hence, in order to provide good powder compressibility only pure iron or low-alloyed (typically <3 wt.%) powders are used. Required alloying elements and carbon (added as graphite) are further admixed in the powder form and are distributed during sintering by diffusion into iron particles at high temperatures. To assure satisfactory distribution of alloying elements, oxide layer, covering surface of the powder particles and hindering mass-transfer of the alloying elements, has to be removed first. This can be done by gaseous reducing agents as hydrogen and carbon monoxide. However, their cost and/or purity are of issue for modern alloyed PM steels. Admixed carbon, additionally to its function as alloying element, plays a role of effective reducing agent at higher temperatures. Paper summarizes the main features of microstructure formation during the whole sintering cycle (heating and isothermal sintering) and effect of alloying additives (different carbon sources, alloying elements) and processing parameters (sintering atmosphere composition, temperature profile) on the microstructure formation during conventional sintering process. Results indicate that for successful sintering of alloyed PM steels with homogeneous defect-free microstructure, hydrogen-rich atmospheres and high-temperature sintering are required.