[en] To improve the mechanic characteristics, especially hardness and strength, the literature of specialty recommend the use of Cr₃C₂ carbides more than 0,5 %. In this paper the research made emphasis that also at contents of maximum 0,5 % Cr₃C₂ can be obtain certain performance for hard alloys from WC-Co system with Cr₃C₂ addition. (author)

No abstract available

[en] The coatings deposited on the surface of a substrate of a material in powder form, by injection in a laser beam, they could have important advantages opposite coatings deposited with other technical. These advantages are a very important decrease of the porosity, an interval of thickness of wide covering, a higher coating hardness, treatment in located areas, etc. In this paper our investigation group presents the problems found utilising this technique: inadequate speed of the particles, unstableness of the powder flow rate, effect of the angle of injection and alterations on the powder flow caused by the protective gas of the laser focusing head. We also present the adopted solutions and the improvements that these solutions have supposed for the properties of the coatings. The influence of the laser processing parameters in the dilution and in the characteristics of the coating is also studied (height of the track, penetration, etc). Our final objective is to contribute to the knowledge of this technique. (Author) 7 refs

[en] Detonation gun coatings in the standard thickness range of 0.05 to 0.20 mm are currently specified used and under evaluation for many applications in different nuclear reactor systems. Deposition of tungsten and chromium carbides on structural components in nuclear reactor is studied to prevent wear, high friction and self-welding. Chosen material combinations have to show long term stability and have to withstand high temperatures, thermal shocks and irradiation stress

[en] A mechanism for modelling the growth of faceted primary M₇C₃ needles during solidification of chromium carbide overlays is presented for the first time. In contrast with existing models that consider diffusion-controlled growth over the length of the needle, this work disaggregates the flow of solute at the tip (diffusion-controlled) and the faceted sides (interface-controlled). The proposed solution predicts an initial transient followed by a steady state longitudinal growth. The outward growth of the needle prism faces is linear and slow, consistent with interface-dominated kinetics. Abrupt decreases in longitudinal growth rate was observed when the tip of the carbides approached other carbides, consistent a soft-impingement effect when the diffusion field of two carbides a overlap. The model was compared to in-situ visualisation of the solidification of an alloy with primary chromium carbide needles, and was found to match closely to observations.

[en] The roles of Ti-carbonitrides, chromium carbides and chromium depleted zone in the early stage of pitting corrosion of Alloy 600 were investigated in deaerated 10,000 ppm chloride solution at 90.deg.C. Open circuit potentials and polarization curves of TiC, Cr₇C₃ and Cr₂₃C₆ were also measured to determine their roles on pit initiation in the same test condition. It was observed that fast dissolution of the matrix around Ti-carbonitrides occurred during anodic polarization and immersion test, leading to pit initiation. Corrosion rates of chromium carbides and chromium depleted zone were higher than that of grain of Alloy 600TT, which was attributed to the decrease in the pitting potential and the increase in current density of Alloy 600TT, compared with those of Alloy 600MA. The results obtained were discussed with respect to microchemistry, microstructure and electrochemical behaviors of the precipitates

[en] This investigation highlights the creep deformation and rupture behaviour of Nb and Cu added 18Cr-8Ni austenitic stainless steel and compared with those of commercial 18Cr-8Ni steel. Uni-axial creep tests were performed at (288–320) MPa/600 °C and (80–110) MPa/750 °C on Nb and Cu added 18Cr-8Ni austenitic stainless steel. Accelerated creep tests predicted that creep characteristic of the alloy was insignificant or anelastic type below the stress level of ∼166 MPa at 600 °C and ∼57 MPa at 750 °C. True creep exponent value of 8 at (288–320) MPa/600 °C and 4 at (80–110) MPa/750 °C, exhibited that the alloy followed high temperature climb controlled power law creep in the specified creep test condition. The alloy was more creep brittle in nature than that of commercial 18Cr-8Ni austenitic stainless steel. The brittleness was attributed to the presence of Nb(C, N), nano-sized Cu precipitation along the transgranular region and occurrence of Cr₂₃C₆ secondary carbides along the grain boundaries. Fractographic features revealed that the alloy was prone to intergranular fracture due to creep cavitation and their linkages. (paper)

No abstract available

[en] In thermodynamic modelling of phase diagrams it is often necessary to deal with the properties of metastable compounds, which are not known from experiments. As an illustrative example, the Cr₃C(oP16) carbide is chosen, which is involved in the modelling of the Me₃C(oP16) ('cementite') structure of the Fe-Cr-C system, but is metastable in the Cr-C system. The estimation of its thermodynamic properties, relying on regularities in bonding properties of 3d-transition metal carbides and an account of the vibrational entropy through the so-called 'entropy Debye temperature', are discussed in detail. The predictions are compared with values derived in thermodynamic modelling of the Fe-Cr-C phase diagram. Relying on the present results, calculations of metastable phase-equilibria in the Cr-C system are calculated and these were used in analysing information about Cr₃C from splat-quenching experiments. (Author)

[en] When austenitic stainless steels are heat treated in the range of 500∼850 .deg. C, the alloys are sensitized due to the formation of chromium carbide at grain boundaries and then intergranular corrosion occurs. This paper aims to evaluate the intergranular corrosion rate and microstructural change of forged 316L stainless steel. To analyze the microstructure by forging conditions, ferrite phase, sigma phase, intergranular precipitation were observed. In order to evaluate the intergranular corrosion rate. Huey test was performed by ASTM A262. On the base of microstructural observation, ferrite and sigma phases were not detected, and also intergranular precipitation was not revealed in optical microscopic observation. By ASTM A262 Practice A, step structure was shown in all forging conditions. Intergranular corrosion rate gradually increased by Huey test periods but average corrosion rate was under 0.03 mm/month