Vacuum Oxy-nitro carburizing of tool steels: structure and mechanical reliability

5-18AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using “phase diagram” module of FactSageto predict the steels’ phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe3O4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance

Sulfide capacities of lead oxide containing silicate and alumina silicate slags

Bu çalışmada PbO-SiO2 ve PbO-AlO1.5-SiO2 curuf sistemlerinin kükürt kapasiteleri gaz-curuf dengeleme yöntemi kullanılarak araştırılmıştır. Bu amaçla, 1 atm. basıncında saf SO2 gazının 1373 K sıcaklıkta oluşturduğu 2.07x10-8 atm. PO2 ve 2.94x10-5 atm. PS2 kısmi basınçları altında platin ve/veya alumina pota içerisindeki curuf numuneleri 8 saat süreyle dengelenmiştir. Her iki sistem için de bazikliğin artışıyla curuf içerisindeki kükürt miktarında artış meydana geldiği belirlenmiştir. Elde edilen kükürt kapasiteleri sonuçları (Cs), oksitlerin ve sülfürlerin kimyasal ve çözelti özelliklerini kullanarak curufların kükürt kapasitesini hesaplayan Reddy-Blander modeliyle (RB) kıyaslanmıştır. Deney ve modelleme ile belirlenen kükürt kapasitesi sonuçları birbirleriyle uyumlu bulunmuştur.Anahtar Kelimeler: Curuf, kurşun oksit, kükürt kapasitesi, Reddy-Blander modeli.  PbO-SiO2 subsystem is one of the important parts of the lead/zinc smelting slag system. PbO-AlO1.5-SiO2 subsystem is also important, since the alumina is introduced into the system as an impurity from ore feed stocks, coke ash and refractory lining of the smelting furnace. In order to understand the sulfide capacity behavior of the complex smelting slag system, first it is necessary to investigate these subsystems. In this study, the sulfide capacities of PbO-SiO2 and PbO-AlO1.5-SiO2 slags were studied using gas-slag equilibrium technique. The experiments were conducted in platinum and alumina crucibles using 1 atm. SO2 gas which created 2.07x10-8 atm. PO2 and 2.94x10-5 atm. PS2 at 1373 K for 8 hours. It was found that for both slag systems, sulfide solubility increased with an increase of basicity. The experimental sulfide capacity (Cs) results were also compared with the Reddy-Blander model based on a simple solution model and on knowledge of the chemical and solution properties of sulfides and oxides. The Reddy-Blander model (RB) for calculating Cs in the binary PbO-SiO2 and ternary PbO-AlO1.5-SiO2 slags ?a priori? is shown to be in good agreement with the experimental data. It can be concluded that the sulfide capacities of slags are directly proportional (i) to the equilibrium constant KM, and (ii) to values of aMO, which are related to the solution properties.Keywords: Slag, lead oxide, sulfide capacity, Reddy-Blander model

Vacuum Oxy-nitro carburizing of tool steels: structure and mechanical reliability

AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using “phase diagram” module of FactSageto predict the steels’ phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe3O4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance

Exploring Hydride Formation in Stainless Steel Revisits Theory of Hydrogen Embrittlement

Various mechanisms have been proposed for hydrogen embrittlement, but the causation of hydrogen-induced material degradation has remained unclear. This work shows hydrogen embrittlement due to phase instability (decomposition). In-situ diffraction measurements revealed metastable hydrides formed in stainless steel, typically declared as a non-hydride forming material. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen-induced material degradation can only be understood if measured in situ and in real-time during the embrittlement process.Comment: 31 Pages, 18 Figures, Preprin

Enrichment of W2B5 from WO3 and B2O3 by Double SHS Method

A second self-propagating high-temperature synthesis (SHS) was carried out to enrich the W2B5 content in the SHS product containing a mixture of various tungsten boride compounds. In the experiment, the process called Double-SHS (D-SHS) was conducted in two steps. In the first SHS reaction, an initial molar composition ratio of WO3:B2O3:Mg mixture was selected as 1:3:8. The product was then hot-leached with hydrochloric acid to eliminate MgO and Mg3B2O6 phases. The leached product, consisting of 72.6 wt.% W2B5, 16.1 wt.% WB, 8.4 wt.% W2B, and 2.9 wt.% W, was again reacted with the Mg and B2O3 mixture by second SHS. After another acid leaching step, W2B5 content in the D-SHS product was found to be 98.2 wt.%. The study showed that D-SHS is an effective method for boron enrichment in the tungsten compounds.DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17834</p

Sulphide Capacity Prediction of Molten Slags by Using a Neural Network Approach

In the present study, the neural network approach was applied for the estimation of sulfide capacities (Cs) in binary and multi-component melts at different temperatures. The calculated results obtained using neural network computation were plotted against the experimental values for comparison comparative purposes. Besides, iso-sulfide capacity contours on liquid regions of some ternary melt phase diagrams were generated and plotted by using neural network model results. It was found that calculated results obtained through neural network computation agree very well with the experimental results and more precise than those of some models