The present work is part of a research programme to study the effect of variation of the coating composition of covered rutile manual electrodes on both operational and deposited weld metal properties. According to previous results obtained for rutile electrodes, an increase of slag basicity, achieved through modifications in the coating, produces an improvement of the impact properties of the deposited weld metal, as well as a decrease in the diffusible hydrogen, along with beneficial changes in the operational properties of the electrode. The aim of the present work is to study the influence of the replacement of titanium oxide with oxides of alkali metals (sodium and potassium), alkaline earth metals (calcium and magnesium), and iron and manganese oxides in the coating of an ANSI/AWS A5.1–91 E6013 type electrode on the operational characteristics of the electrode and the microstructure, mechanical properties, and diffusible hydrogen content of the electrode weld metal. Tensile strength and Charpy V notch impact properties were measured in the all weld metal samples produced using each of the seven electrodes designed for the present study. A cross-section from each coupon was used to determine the chemical composition of the deposit and to carry out a metallographic study using a light microscope. As a result of the addition of different oxides, changes in the operational properties were observed using both direct and alternating current, as well as a decrease in the diffusible hydrogen content in the weld metal. Also, electrodes in which rutile was substituted by sodium oxide in the coating showed an improvement in the impact properties of the deposit.
Analysis of the relationship between variables involved in the wear of mandrels used for seamless tube making was carried out. Laboratory-scale mandrels were pierced in sequences with different process parameters. Process data were acquired during piercing events and digital photographs of the mandrels’ silhouette were taken to study their profile evolution. Direct variables were registered and others were created. Data were first analysed in ranges of furnace temperature and cooling water flow. A self-organizing map (a kind of artificial neural network) was trained with experimental data for further multi-variable analysis. Results were analysed from the data clusters found and conclusions were extracted. Furnace temperature and cooling water flow were important for their influence on wear but a definite relationship could not be established. Results showed that the mandrel shape and wear condition could be inferred through the study of the axial force curve. A first equation for mandrel wear prediction is introduced, taking into account the relations found between the most important variables involved in the process. Nevertheless, additional research must be done considering the billet material stress fields and friction contact conditions.
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