Nelson F. Garza-Montes-de-Oca

Development of accelerated wet–dry cycle corrosion test in marine environment for weathering steels

There is great interest in the steel industry of incorporating new products that go beyond the properties of existing ones. Among these properties, corrosion resistance is extremely important for countries that, like Chile, have an extensive ocean coastline. In costal zones, the chloride ions in air produce corrosion that reduces the service life of structures. For this reason, it is of utmost importance to study the influence of different alloying elements such as nickel, which lead to improve steels resistance to marine corrosion. In this context the development of new types of steel is hindered if the evaluation of their corrosion resistance takes very long times. This paper presents a methodology based on accelerated wet–dry cycle corrosion experiences to simulate the behaviour of steel over time in a marine environment. The results of the proposed methodology allow adequate prediction of corrosion thickness in ASTM A242 and A588 steels exposed for years to a specific marine environment.

High Temperature Oxidation of a Work Roll Grade High-Chromium White Cast Iron

High-chromium white cast iron is a common material for the manufacture of the work rolls used in the finishing stands in hot strip mills. The high temperature oxidation behaviour of as-cast and heat-treated high-chromium white cast iron was studied by gravimetric means at 650 °C in atmospheres that included dry air and a mixture of dry air and water vapour. For both environmental and material conditions, the oxidation rate of the alloys was represented by parabolic trends and the oxidation phenomenon was more obvious when the samples were oxidised in water vapour. Water vapour also influenced the chemical composition of the oxides formed in the alloy and under this condition, the oxide scale formed on the alloy contained the oxides FeCr2O4, (Fe,Cr)3O4 and (Fe,Cr)2O3. In contrast, the alloys exposed to dry air conditions only experienced the formation of FeCr2O4 and (Fe,Cr)2O3. It was found that the presence of water vapour and the chromium content of the alloys increased the oxidation rate by a mechanism that involved chromium depletion of the oxide as a result of hydroxide formation. The differences observed in the oxidation behaviour of the alloy are discussed in terms of the composition of the oxidant atmosphere and the metallurgical condition of the specimens.

High temperature oxidation of silicon and copper-silicon containing steels

Abstract The isothermal oxidation behaviour of silicon and copper containing steels was studied under laboratory dry air conditions at temperatures from 950 to 1180°C. The oxidation kinetics was determined by gravimetric means and followed by parabolic relationships at all temperatures for both steels. Characterisation of the oxide scales comprised X-ray diffraction, light optical microscopy and SEM including EDX analysis. It was found that the oxide microstructure depended on the silicon and copper contents in the alloys. For the copper containing steel oxidised at 950°C, enrichment of this element was not appreciated at the metal/oxide interface or across the oxide scale, a situation that changed at 1100°C where copper enrichment was localised next to the steel substrate. The specimens oxidised at 1180°C revealed that copper enrichment was located at the surface of the specimens. The effect of the alloying elements on the oxidation rate and the microstructure of the oxides formed on the steels are discussed.

Comportamiento a la corrosión atmosférica marina de aceros autopatinables con estructura ferrítico perlítica y ferrítico martensítica

La industria del acero se encuentra constantemente enfrentada al desafio del desarrollo de nuevos y mejores aceros para diversas necesidades, tales como la necesidad de aceros estructurales con mayor resistencia a la corrosion marina que los que existen en la actualidad, y que ademas posean una mayor resistencia mecanica. Por ello y en pos de lo anteriormente expuesto es evidente que, investigar en forma sistematica tanto la influencia de los elementos aleantes, como las variables del proceso de fabricacion de aceros estructurales resistentes a la corrosion marina es relevante para el desarrollo del mercado acerero nacional.El presente trabajo tendra por objetivo, la comparacion de comportamiento a la corrosion atmosferica marina (espesor corroido en el tiempo) entre aceros de composicion autopatinable (ASTM A242 y ASTM A588) con estructuras ferritico-perlitica y ferritico-martensitica. Para lo anterior se realizaron ciclos de humectacion salina y secado. La humectacion salina se realizo en camara de niebla salina, de acuerdo a los requerimientos presentados en la norma ASTM B177, y el secado, en una mufla a 40 °C. Tras el retiro de muestras, se realizaron decapados quimicos, segun lo requerido en ASTM G1, para la determinacion de espesor corroido.

Influencia de Ni y Ti en la respuesta a la corrosión marina simulada de un acero autopatinable A242

Existe un gran interes en la industria siderurgica por incorporar nuevos productos que superen las propiedades de los ya existentes. Dentro de estas propiedades, la resistencia a la corrosion es de gran importancia para los paises que, al igual que Chile, tienen abundante litoral marino. En las zonas costeras los iones cloruro presentes en el aire producen deterioro por corrosion lo que disminuye la vida util de las estructuras. Por esta razon es que es de vital importancia investigar la influencia de los distintos elementos aleantes y tratamientos que lleven a mejorar la resistencia de los aceros frente a la corrosion marina. Este trabajo apunta al estudio de aceros autopatinables ASTM A242 de baja aleacion, especificamente con adicion de Niquel a la aleacion, y a la adicion de Titanio como afinador de la microestructura, y su influencia sobre la resistencia a la corrosion atmosferica utilizando ensayos de corrosion acelerada producida en camara de niebla salina con ciclos de humectacion y secado. En las aleaciones estudiadas se determino el espesor corroido de las muestras y la velocidad de corrosion. Los diferentes productos de corrosion, oxidos y oxihidroxidos de hierro se identificaron por rayos X. Los resultados muestran claramente que luego de 40 ciclos (960 horas) de tratamiento, en comparacion con un acero ASTM A242, la velocidad de corrosion disminuye en forma significativa en el mismo acero con aleacion de Niquel, y mas aun con adicion de Titanio como afinador de grano. Este resultado se ve tambien reflejado en una disminucion del espesor corroido de los cupones, observandose el menor espesor corroido en el acero ASTM A242 con Ni y Ti.

Oxidation behaviour of amorphous steel: impact on electromagnetic properties

Purpose High silicon amorphous steels are gaining preference as the material of choice for the fabrication of the core of low and medium power electrical transformers because they present a better electromagnetic behaviour compared to that offered by common grain-oriented and non-oriented high silicon steels. This study aims to investigate the effects that the environmental conditions present during the high temperature annealing of cores exert on the surface oxidation and electromagnetic changes experienced by a commercial amorphous steel alloy. Design/methodology/approach The effect of environmental impact on the correct development of annealing practices during the manufacture process of amorphous steel cores used in distribution transformers was studied by the development of an oxidation reactor. With this installation, it was possible to simulate environmental conditions that could affect the surface of magnetic cores made from amorphous steel. Findings It was found that: the surface oxidation of amorphous steels affects their electromagnetic behaviour, environmentally induced surface degradation can be modelled at laboratory scale and oxide formation does not affect the amorphous condition of the alloy. Originality/value The effect of surface oxidation induced by the existence of water vapour in the annealing process of cores made from amorphous steels and its impact on the electromagnetic behavior of these alloys has been barely studied.

High-temperature Oxidation of a Nickel Base Superalloy at Different Oxygen Partial Pressures

A series of oxidation tests were conducted for a nickel base superalloy, as these materials are used at high temperature in aggressive conditions, thus the influence of oxygen on their degradation mechanisms must be known. The material was treated for up to 150 h at 900 and 1000°C in a furnace able to control and maintain atmospheres with different partial oxygen pressures. The oxidation rate of the material was determined by gravimetric means. In all cases, the rate of oxidation followed parabolic regimes that depended on the value of oxygen partial pressure. The oxide scale formed was characterised by X-ray diffraction and scanning electron microscopy; these analyses revealed that the oxide scale consisted of an outer TiO2 layer and inner Cr2O3 layer under all experimental conditions. Cross-section analyses indicated the development of internal oxidation and the presence of gamma-prime free zones.

Mechanical stability of boron-based coatings grown on Incoloy 909 superalloy by thermochemical diffusion

ABSTRACT Incoloy 909 superalloy was treated at 950°C to form coatings of different chemical composition by thermochemical diffusion. Packing of the samples in reactive powders lead to the formation of iron borides (Fe2B and FeB) together with nickel boride, NiB, and nickel silicide, Ni2Si, on the surface of the alloy depending on the exposure time. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses suggest that growth of the coatings is controlled by diffusion of reactive species into the metal structure. Microabrasion wear resistance of the coated specimens was studied at 1 N load for a fixed sliding speed of 0.11 m s−1 and it was compared against uncoated samples of the alloy. It was found that coating the alloy for 12 and 20 h increased the hardness of the alloy and therefore its wear resistance.

Gravimetric and electrochemical methods to evaluate the performance of corrosion inhibitors for galvanized steel strips

Abstract Corrosion inhibitors with Cr+6 and Cr+3 are applied on the surface of metals to increase their chemical resistance when they are exposed to severe degradation conditions. For galvanized low-carbon steel strip, these compounds are applied to reduce corrosion mainly during transport operations of this metal. The performance of corrosion inhibitors deposited on the surface of galvanized steel strip was evaluated through combined physical and electrochemical modeling. The physical model takes into account direct exposure of specimens to different conditions including simulated marine, industrial and rain environments for periods up to 8 weeks. The efficacy of the experimental method was also evaluated using polarization resistance and gravimetric means. A good correlation between the evolution of the degradation phenomenon obtained directly from the physical model and the electrochemical and gravimetric data was found. The results showed that this method is an effective tool that allows the comparison of the performance of different corrosion inhibitors that could be used to prevent surface degradation of galvanized steel strip.