CARBIDES

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler

The effect of the addition of Cr on tensile properties in high Co–Ni secondary hardening steels containing W has been seen in as-quenched and aged conditions. Two kinds of Co–Ni steels, containing only W (W steel), and W and Cr (WCr steel), were severely multipass-rolled in the unrecrystallized region, followed by direct quenching. Both steels showed secondary hardening peaks with precipitation of fine M2C carbides during aging. The secondary hardening reaction was promoted by the Cr addition although there was some decrease in tensile strength. In terms of tensile behavior, it is pointed out that both yield strength and yield ratio (YS/UTS) were considerably decreased by the Cr addition. In addition, the tensile strength to hardness ratio is larger in the as-quenched condition compared with the aged condition.

The effect of austempering on the microstructure and toughness of nodular cast iron (designated as CuNiMoSG) alloyed with molybdenum, copper, nickel, and manganese has been studied. Light microscopy (LM), scanning electron microscopy (SEM), and X-ray diffraction technique were performed for microstructural characterization, whereas impact energy test was applied for toughness measurement. Specimens were austenitised at 860 °C, then austempered for various times at 320 and 400 °C, followed by ice-water quenching. Austempering at 320 °C produces a microstructure consisting of a mixture of acicular bainitic ferrite and the stable carbon-enriched austenite. In this microstructure ε-carbides are also identified after austempering up to 5 h. Fracture mode is changed from ductile to brittle with the prolonged time of austempering at 320 °C. The highest impact energy (115 kJ) corresponds not only to ductile fracture, but also to the maximum value of the volume fraction of retained austenite. Only martensitic structure was observed during austempering at 400 °C, inducing brittle fracture and significantly low-impact energy (10–12 kJ).

V4AlC3, a new MAX phase, was synthesized by reactive hot pressing of a V, Al, and C powder mixture at 1700°C. Using a combination of Rietveld refinement with X-ray diffraction data and ab initio calculations, the crystal structure was determinated. It was found that V4AlC3 has a Ti4AlN3-type crystal structure. The lattice constants are a=0.29310 nm and c=2.27192 nm. And the atomic positions are V1 at (4f) (1/3, 2/3, 0.0544), V2 at (4e) (0, 0, 0.1548), Al at (2c) (1/3, 2/3, 1/4), C1 at (2a) (0, 0, 0), and C2 at (4f) (2/3, 1/3, 0.1080).

Ball indentation technique (BIT) has been used to explore its usefulness in revealing the effect of high temperature exposure on mechanical properties of a gas turbine (GT) blade of Ni base super alloy. The dependence of yield strength (YS), ultimate tensile strength (UTS ...

High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills (HSM). Good wear resistance and hardness at high temperatures, are defining features of HSS. Previous experience has shown that HSS rolls containing mainly hard MC carbides have a high friction coefficient, which is detrimental for the rolling power consumption and for the strip surface quality. On the other hand, HSS rolls containing eutectic rod shaped carbides are brittle and more susceptible to spalling. To overcome these problems, a suitable grade, called HSS7, that gives the best compromise between a low friction coefficient and a high crack propagation and wear resistance was developed. That alloy contains well-dispersed hard VC carbides improving wear, and non-interconnected eutectic carbides of the M2C and M7C3 type, hindering crack propagation. All the metallurgical factors affecting the performance and damage of under rolling condition in front finishing stands are reviewed: wear resis...

Pressureless sintering of ZrC–Mo cermets was investigated in a He/H2 atmosphere and under vacuum. A large density increase was observed for specimens with >20 vol% Mo after heating at 2150°C for 60 min in a He/H2 atmosphere. The increase in density was attributed to the formation of Mo2C during heating and its subsequent eutectic reaction with Mo, which produced rounded ZrC grains in a Mo–Mo2C matrix. Sintering in vacuum did not produce the same increase in density, due to the lack of Mo2C formation and subsequent lack of liquid formation, which resulted in a microstructure with irregular ZrC grains with isolated areas of Mo. Mechanical properties testing showed a decrease in Young's modulus with increasing Mo content that was consistent with the models presented. Flexure strength of ZrC–Mo cermets sintered in He/H2 atmosphere materials increased with increasing Mo content from 320 MPa at 20 vol% Mo to 410 MPa at 40 vol% Mo. Strength was predicted by adapting theories developed previously for WC–Co cermets.

A new concept for very high specific impulse (>~2000 seconds) direct nuclear propulsion is described. The concept, termed LARS (Liquid Annular Reactor System) uses liquid nuclear fuel elements to heat hydrogen propellant to very high temperatures (~6000 K). Operating pressure is moderate (~10 atm), with the result that the outlet hydrogen is virtually 100% dissociated to monatomic H. The molten fuel is contained in a solid container of its own material, which is rotated to stabilize the liquid layer by centripetal force. LARS reactor designs are described, together with neutronic and thermal-hydraulic analyses. Power levels are on the order of 200 megawatts. Typically, LARS designs use 7 rotating fuel elements, are beryllium moderated and have critical radii of ~100 cm (core L/D~=1.5).

Information is summarized which is the result of investigations of phase ; equilibria in the binary systems C- Zr, Ta- C, and B- C. A completed phase ; diagram, which encompasses experimental results and considerations heretofore ; unreported in the literature, is presented for the Zr- C system. A tentative ; phase diagram for the Ta- C system is included, which, in general, resembles the ; version released by Ellinger in 1943. Preliminary results for the B- C system, ; depicting maximum solubility in the graphite lattice below the eutectic ; temperature of approximately 2390 un. Concent 85% C, are also included. (auth);