Z. Brytan

Surface Layer Properties of Sintered Ferritic Stainless Steel Remelted and Alloyed with FeNi and Ni by HPDL Laser

Laser surface remelting and alloying of sintered stainless steel type 410L with FeNi and Ni have been studied for improvement of corrosion resistance and hardness increase. The influences of high power diode laser (HPDL) processing conditions, laser power in range 0.7-2.1 kW on the microstructure and properties of alloyed surface layer have been evaluated. The FeNi alloyed layer shows microstructure composed of austenite and martensite formed, due to high cooling rate in laser remelting process, with average Ni content in range of 39 to 8% depending on laser processing conditions. The Ni alloyed layer was composed of austenitic microstructure with Ni content from 65% to 33%. The improvement in microhardness was achieved by laser surface alloying and remelting. Excellent corrosion properties were observed for such remelted and alloyed layers in salt spray test.

Stainless Steels Sintered Form the Mixture of Prealloyed Stainless Steel and Alloying Element Powders

The aim of the presented paper is to describe the sintered duplex stainless steels manufactured in sinter-hardening process and their structural and mechanical properties. Duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed base powders by controlled addition of alloying elements powder. Prepared mixes were compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at temperature of 1240°C for 1h. After sintering different cooling cycles were applied: rapid cooling (6°C/s) using nitrogen under pressure and slow cooling (0.1°C/s) with furnace in argon atmosphere. Produced sintered duplex stainless steels were studied by scanning and optical microscopy and EDS chemical analysis of microstructure components as well as X-ray analysis. Mechanical properties were studied through tensile and three-point bending tests and Charpy impact test. It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Produced sintered duplex steels show good mechanical properties which depend on austenite/ferrite ratio in the microstructure and elements partitioning (Cr/Ni) between phases. The optimal mechanical properties were obtained for compositions based on ferritic 410L powder where the balanced distribution of α and γ is present and the tensile strength can reach value about 500MPa with 16% of elongation and impact energy about 120J. The precipitations of hard intermetallic σ-FeCr phase take place when sintering with slow cooling cycle what cause substantial decrease of plastic properties, including reduce of elongation to 7% and in particular decrease of impact energy to 68 J.

Effect of Different Vacuum Heat Treatments on the Microstructure of a Low Alloyed Sintered Steel

The main aim of the present contribution is to show how different heat treatment conditions influence the microstructure of a Fe - [1.5Cr - 0.2Mo] - 0.6C powder system. In vacuum furnaces, the cooling rate is generally determined by the pressure of the gas (basically N2) introduced into the chamber. Different gas pressures have been applied, from 0 to 6 bars. The average cooling rates were calculated in the range of 1180 °C to 400 °C and were varying from 0.1 to 6 °C/s, according to the gas pressure. Considering the cooling rates, increasing the nitrogen pressure resulted in an increased amount of bainite/martensite microstructure. The microstructure constituents ranged from 97% pearlite + 3% ferrite in the system treated at 0 bar to 82 % martensite + 18 % bainite (with small amount of tempered martensite) in the system cooled applying N2 at 6 bars. Mechanical properties have been evaluated in terms of toughness, TRS and hardness for all processing conditions; the analysis of the properties allowed to plot graphs correlating the different properties as function of the characteristic microstructures.

Sintered Duplex Stainless Steels Corrosion Properties

This work presents mechanical properties and corrosion resistance of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo17-12-2 (AISI 316L), martensitic X6Cr13 (AISI 410L) powders by controlled addition of alloying elements in the proper quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler’s diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen. Produced duplex stainless steels have been studied by SEM with EDS and light optical microscopy (LOM) and X-rays analysis to determine obtained structures. Corrosion properties have been studied through electrochemical methods in 1M NaCl.

Application of the Finite Element Method for Modelling of the Spatial Distribution of Residual Stresses in Hybrid Surface Layers

The presented investigations concern PVD/CVD surface treatment performed on samples of heat treated cast magnesium and aluminium alloys and properties modelling of obtained coatings using the finite element method (FEM). In order to identify the structure and fractures of the analysed surface coatings, investigations using the scanning electron microscope Zeiss Supra 35 were performed. Evaluation of the adhesion of the PVD/CVD coatings was carried out using a scratch test. The obtained coatings—Ti/Ti(C,N)-gradient/CrN; Ti/Ti(C,N)-gradient/(Ti,Al)N; Ti/(Ti,Si)N-gradient/(Ti,Si)N as well coatings: Cr/CrN-gradient/CrN; Cr/CrN-gradient/TiN and Ti/DLC-gradient/DLC are characterized by a clear heterogeneity of the surface associated with the presence of microparticles in the structure in form of droplets broken out of the target during the deposition process, as well immersions occurring in the surface due to the loss of some droplets during solidification. It was also found that the applied coatings are characterized with a mono-, di-, or multi-layer structure according to the applied layer system; the individual layers are applied uniformly and tightly adhere to the substrate and to each other. The obtained results of the numerical FEM analysis, have enabled a full integration of the material engineering knowledge and informatics tools, confirming compliance of the simulation model with the obtained experimental results.