Metallurgical Model of Diffusible Hydrogen and Non-Metallic Slag Inclusions in Underwater Wet Welding of High-Strength Steel

High susceptibility to cold cracking induced by diffusible hydrogen and hydrogen embrittlement are major obstacles to greater utilization of underwater wet welding for high-strength steels. The aim of the research was to develop gas–slag systems for flux-cored wires that have high metallurgical activity in removal of hydrogen and hydroxyl groups. Thermodynamic modeling and experimental research confirmed that a decrease in the concentration of diffusible hydrogen can be achieved by reducing the partial pressure of hydrogen and water vapor in the vapor–gas bubble and by increasing the hydroxyl capacity of the slag system in metallurgical reactions leading to hydrogen fluoride formation and ionic dissolution of hydroxyl groups in the basic fluorine-containing slag of a TiO2–CaF2–Na3AlF6 system.

Sintering of Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni Cermets Investigated by CO and N2 Outgassing

Cermets of the type Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni with changing [Mo]/([Mo] + [W]) ratio were subjected to an investigation of outgassing of CO and N2 upon sintering. Quantification of CO and N2 was performed by gas calibration, measurement of masses 12 (12C), 14 (14N) and 28 (28CO and 28N2), as well as C, N, O analysis of the samples before and after sintering. The formation of CO occurs at lower temperatures than that of N2, both gases being completely evolved already at solid-state sintering conditions. If pre-alloyed powders are employed in the starting formulation, the amount of evolved gases is substantially reduced, because part of the formation of mixed hard phases is anticipated. Changing binder composition from Co:Ni = 1:1 to 2:1 and 3:1 does not change the outgassing characteristics, while different batches of nominally the same Ti(C,N) powder can have significant influence. Mass spectrometry is a most valuable in situ tool for getting insight into the metallurgical reactions occurring upon sintering. These reactions result in the typical microstructure and influence the properties of cermets.

Tubes’ Rupture at Faulty Fusion of Welding Seam

In the straight-seam tubes, the appearance of defects in the area of the welding seam welded under the flux layer and the seam geometry are closely related to the technology and metallurgy of welding process. Possible defects are the pores, incisions, slag inclusions and cracks. The pores can appear in different shapes, with different distribution and in different amounts during the solidification of welding seam. When molten metal solidifies, the gas bubbles can come to the surface or remain inside the metal. The incisions may occur due to the fact that the juncture is not completely filled. Such incisions, passing most often along the edge of welding seam, are explained by the discrepancy between the amount of metal deposited per unit of time and the volume of the juncture. The occurrence of the slag inclusions is determined by the metallurgical reactions between the slag and the drop, separating from the end of the electrode, as well as the bath of molten metal. The cracks differ depending on the size, the nature of location and the causes. There are the macro-cracks and micro-cracks, the hot and cold cracks. In this paper the critical in-tube pressure, at which the destruction of tube occurs at the partial faulty fusion of the tube’s welding seam, is obtained. The results can be used in the diagnosis of the causes of the destruction of the steel large-diameter tubes of the main gas-oil tube-lines.

Preparation of Neodymium Metal by Pyro-Metallurgical Process Using Fluoride Salt

The neodymium fluoride was reduced to metal by thermal reduction or pyro-metallurgical process using calcium as reducing agent. Thermal reduction was carried out in a sealed reactions chamber in inert atmosphere with a nickel crucible having dry calcium fluoride lining. The stoichiometric mixture of neodymium fluoride and calcium metal chips were used in the form of pallets for pyro-metallurgical reactions. Small iodine was also added to increase heat available during ignition and to yield a lower melting and more fluid slag. The contents were heated electrically at a predetermined rate until ignition took place. The reaction was self-supporting and neodymium metal was obtained with fairly good efficiency.