Carbonitrides corrosion

In the polyacrylic synthetic fibre industry, carbonitrided molybdenum guides have been used in place of chromium plated steel because of their resistance to corrosion and erosion. Chemicals that attack molybdenum are listed in Table 5.9. 

The best results were obtained with compound 21 that exhibited high vapor pressure and low decomposition temperature (<523 K). Various CVD conditions were applied and gave in all cases shiny, dark-brown deposits.43 XRD and XPS analyses of the deposits indicated the presence of a vanadium carbonitride phase with little contamination from oxygen and free carbon. The films were less adherent on steel substrates than on silicon ones. The steel substrates seemed to suffer corrosion due to the presence of Cl-containing species. We had noticed the same feature in the case of Cl-containing precursors to vanadium carbide. Therefore, in order to increase the volatility of compound 23 and to reduce the Cl content of the molecule, we prepared compounds 24 and 25. Unfortunately, the yields obtained in their syntheses were much too low to permit TG and CVD experiments. 

The few investigations available for the new precursor-derived silico-carbonitrides do not permit their corrosion behavior to be assessed in detail. Most studies of interest here deal with thermal stability only. 

In recent years silicon-based polymers were investigated as precursors for SiC and Si3N4 ceramics, as well as for crystalline or amorphous Si/C/N and SiC/Si3N4 composite materials [1, 2]. This is due to the very interesting chemical and thermomechanical properties of silicon carbonitrides, such as high hardness, toughness and corrosion resistance. In most of these studies polycarbosilanes, polysilazanes and polycarbosilazanes were applied [3]. 

Niobium is used to combine with carbon and nitrogen, thus reducing the formation of chromium carbonitrides. This reduces the possibility of intergranular corrosion when stainless is welded or heat-treated. Niobium also contributes to age hardening in some precipitation-hardening stainless grades. 

Corrosion Performance and Tribological Properties of Carbonitrided 304 Stainless Steel... 

In this paper we present the effect of N2 to C2H2 gas pressure ratio on the corrosion performance and tribological properties of AISI 304 austenitic stainless steel after rf plasma carbonitriding at a relatively low pressure. 

Under applied anodic potential the corrosion of stainless steels in molten chlorides is electrochemical in nature. At the initial period the exchange reaction between steel components and alkali metal cations takes place in parallel with the electrochemical process. It was found that titanium in steels forms stable carbonitride species that do not dissolve during anodic oxidation. Preliminary thermal treatment of austenite steels has an effect on anodic dissolution processes. 

Alloy 800 series are derived from Incoloy 800, originally developed in the 1950s by the International Nickel Company [18]. AUoy 800 series have high nickel and chromium contents which give them superior resistance to corrosion in many kinds of environments (Table 17.2). Titanium and aluminum additions lead to the precipitation of different carbonitrides which enhance the material properties. But this Ti + A1 content also leads to the precipitation of hard y Ni3(Ti,Al) phase which enhances creep resistance but decreases the material ductility at high temperature. This is why the Ti + A1 content has been limited in some specifications (800 HT, 800 SPH). On the other hand, annealed material was historically differentiated from solution annealed material, with the terms grade 1 annealed at approximately 980°C, and grade 2 solution annealed at approximately 1150°C [19]. 

Polymer derived ceramics have been known for the last four decades and are prepared via solid-state thermolysis of preceramic polymers. They exhibit a unique combination of remarkable properties due to their covalent bonding and amorphous nature. Thus, silicon oxycarbide (SiOC) and silicon carbonitride (SiCN) based ternary PDCs have been shown to possess outstanding high-temperature properties such as stability with respect to crystallization and decomposition, oxidation and corrosion resistance as well as excellent thermomechanical properties (e.g., near zero steady state creep resistance up to temperatures far beyond 1000 °C). Their properties are directly influenced by the chemistry and the architecture of the preceramic precursors, thus there is an enormous potential in tuning the microstructure and properties of the PDCs by using tailored polymers. Furthermore, suitable chemical modification of the preceramic precursors leads to quaternary and multinary ceramics, as it has been shown for instance for silicon boron carbonitride ceramics in the last 25 years, which in some cases exhibit improved properties as compared to those of the ternary materials. 

---