The Influence of Microstructure on the Corrosion Rate of Carbon Steels

Abstract

This paper presents the influence of carbon steel microstructure on the corrosion rates. Four types of microstructures have obtained by quenching and tempering and iso-thermal annealing. These microstructures are: banded ferrite/pearlite microstructure, fine ferrite/pearlite microstructure, coarse ferrite/pearlite microstructure and tempered martensite microstructure. General corrosion and localized corrosion (penetration rates) were determined via mass loss and optical microscopy. The different microstructures of steels investigated in this paper revealed corrosion rate variations of 0.8-3.2 mm y-1 and 3.3-6.4-mm y-1 for the general and localized forms, respectively. The corrosion stability of the various microstructures may arise from variations of phases within the steel. A banded ferrite/pearlite microstructures have worse general corrosion properties, while tempered martensite worse microstructures have localized pitting corrosion properties. Coarse ferrite/pearlite microstructures have better localized pitting corrosion resistances compared to others investigated microstructures This paper has demonstrated that, microstructure is an important consideration when selecting carbon steel for an industrial corrosion resistance application. ‫اﻟﻜﺮﺑﻮﻧﻲ‬ ‫اﻟﻔﻮﻻذ‬ ‫ﺗﺄﻛﻞ‬ ‫ﻣﻌﺪﻻت‬ ‫ﻋﻠﻰ‬ ‫اﻟﻤﺠﮭﺮﯾﺔ‬ ‫اﻟﺒﻨﯿﺔ‬ ‫ﺗﺄﺛﯿﺮ‬ ‫اﻟﺨﻼﺻﺔ‬ ‫اﻟﺤﺎﻟﻲ‬ ‫اﻟﺒﺤﺚ‬ ‫ﯾﮭﺪف‬ ‫إﻟﻰ‬ ‫دراﺳﺔ‬ ‫ﺗﺄﺛﯿﺮ‬ ‫اﻟﻔﻮﻻذ‬ ‫ﺑﻨﯿﺔ‬ ‫اﻟﻜﺮﺑﻮﻧﻲ‬ ‫ﻣﻌﺪﻻت‬ ‫ﻋﻠﻰ‬ ‫اﻟﺘﺂﻛﻞ‬. ‫ﺑﻨﻰ‬ ‫دراﺳﺔ‬ ‫ﺗﻤﺖ‬ ‫ﻣﺨﺘﻠﻔﺔ‬ ‫ﻣﺠﮭﺮﯾﺔ‬ , ‫ﻗﺴﻤﺖ‬ ‫إﻟﻰ‬ ‫أرﺑﻌﺔ‬ ‫ھﻲ‬ ‫ﻣﺠﺎﻣﯿﻊ‬ : ‫اﻟﻔﺮاﯾﺖ‬ ‫ﻣﻦ‬ ‫ﺣﺰم‬ / ‫اﻟﺒﯿﺮﻻﯾﺖ‬ , ‫اﻟﺜﺎﻧﯿﺔ‬ ‫اﻟﻤﺠﻤﻮﻋﺔ‬ : ‫اﻟﻔﺮاﯾﺖ‬ / ‫اﻟﺒﯿﺮ‬ ‫اﻟﻨﺎﻋﻢ‬ ‫ﻻﯾﺖ‬ , ‫اﻟﻔﺮاﯾﺖ‬ / ‫اﻟﺨﺸﻦ‬ ‫اﻟﺒﯿﺮﻻﯾﺖ‬ , ‫اﻟﻤﺮاﺟﻊ‬ ‫اﻟﻤﺎرﺗﻨﺰاﯾﺖ‬. ‫ﻛﺸﻒ‬ ‫ﺗﻢ‬ ‫اﻟﺘﺂﻛﻞ‬ ‫اﻟﻀﻮﺋﻲ‬ ‫واﻟﻤﺠﮭﺮ‬ ‫ﺑﺎﻟﻮزن‬ ‫اﻟﻔﻘﺪان‬ ‫ﺑﻮاﺳﻄﺔ‬ ‫ﻣﻌﺪﻻﺗﮫ‬ ‫وﺣﺴﺎب‬. ‫ان‬ ‫اﻟﻨﺘﺎﺋﺞ‬ ‫ﺑﯿﻨﺖ‬ ‫ﯾﺆدي‬ ‫اﻟﻤﺠﮭﺮﯾﺔ‬ ‫اﻟﺒﻨﻰ‬ ‫اﺧﺘﻼف‬ ‫إﻟﻰ‬ ‫ﻣﻌﺪﻻت‬ ‫ﻓﻲ‬ ‫ﺗﻐﯿﺮ‬ ‫اﻟﺘﺂﻛﻞ‬ ‫ﻣﻦ‬ 0.8-3.2 ‫ﻣﻢ‬ / ‫وﻣﻦ‬ ‫ﺳﻨﺔ‬ 3.2-6.4 ‫ﻣﻢ‬ / ‫ﻟﻜﻞ‬ ‫ﺳﻨﺔ‬ ‫ﻣﻦ‬ ‫اﻟﺘﺂﻛﻞ‬ ‫اﻟﻌﺎم‬ ‫واﻟﺘﺂﻛﻞ‬ ‫اﻟﺘﻮاﻟﻲ‬ ‫ﻋﻠﻰ‬ ‫اﻟﻤﻮﺿﻌﻲ‬. ‫إن‬ ‫اﺳﺘﻘﺮارﯾﺔ‬ ‫اﻟﺘﺂﻛﻞ‬ ‫ﺗﺄﺗﻲ‬ ‫اﺧﺘﻼف‬ ‫ﻣﻦ‬ ‫اﻟﻤﺠﮭﺮﯾﺔ‬ ‫اﻟﺒﻨﻰ‬. ‫اﻟﻔﺮاﯾﺖ‬ ‫ﺣﺰم‬ ‫ﺗﻤﺘﻠﻚ‬ / ‫ﻣﻘﺎوﻣﺔ‬ ‫ﻋﻠﻰ‬ ‫ﺑﯿﺮﻻﯾﺖ‬ ‫ﺗﺄﻛﻞ‬ ‫ﻗﻠﯿﻠﺔ‬ ‫ﻋﺎم‬ , ‫ﺑﻨﯿﺔ‬ ‫ﺗﻤﺘﻠﻚ‬ ‫ﺑﯿﻨﻤﺎ‬ PDF created with pdfFactory Pro trial version www.pdffactory.com 1826 ‫ﻣﻘﺎوﻣﺔ‬ ‫اﻟﻤﺮاﺟﻊ‬ ‫اﻟﻤﺎرﺗﻨﺰاﯾﺖ‬ ‫ﺗﺄﻛﻞ‬ ‫اﻟﻔﺮاﯾﺖ‬ ‫ﺑﻨﯿﺔ‬ ‫ﺗﻤﺘﻠﻚ‬ ‫ﻗﯿﻤﺎ‬ ‫ﻗﻠﯿﻠﺔ‬ ‫ﻣﻮﺿﻌﻲ‬ / ‫اﻟ‬ ‫اﻟﺒﯿﺮﻻﯾﺖ‬ ‫ﻋﻠﻰ‬ ‫ﺨﺸﻦ‬ ‫أﻓﻀﻞ‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫ﺗﺄﻛﻞ‬ ‫ﻣﻘﺎرﻧﺔ‬ ‫ﻣﻮﺿﻌﻲ‬ ‫ﺑﺎﻟﺒﻨﻲ‬ ‫اﻟﻤﻔﺤﻮﺻﺔ‬ ‫اﻟﻤﺠﮭﺮﯾﺔ‬ ‫اﻷﺧﺮى‬. ‫اﻟﺒﺤﺚ‬ ‫ﻧﺘﺎﺋﺞ‬ ‫أﻛﺪت‬ ‫إن‬ ‫اﻟﻔﻮﻻذ‬ ‫اﺧﺘﯿﺎر‬ ‫ﻓﻲ‬ ‫ﻣﮭﻢ‬ ‫ﻋﺎﻣﻞ‬ ‫اﻟﻤﺠﮭﺮﯾﺔ‬ ‫اﻟﺒﻨﯿﺔ‬ ‫اﻟﻜﺮﺑﻮﻧﻲ‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫ﺗﺘﻄﻠﺐ‬ ‫اﻟﺘﻲ‬ ‫اﻟﺼﻨﺎﻋﯿﺔ‬ ‫اﻟﺘﻄﺒﯿﻘﺎت‬ ‫ﻓﻲ‬ ‫ﺗﺄﻛﻞ‬ ‫ﻋﺎﻟﯿﺔ‬. INTRODUCTION he importance of microstructure on corrosion of carbon and low alloy steels has been widely recognized, but different aspects are still uncertain and contradictory results can be found in the literature. This is mainly due to the complexity of the problem and the difficulty to describe the involved mechanisms. The chemical composition and the microstructure are not independent variables; the same microstructure can be obtained with different chemical compositions and vice versa. Some authors [1] report the effect of one of these parameters without taking into account that the other has been also modified. The corrosion rate of carbon steel is not only governed by the electrolyte conditions, but can also be influenced by its chemical composition and microstructure. Furthermore, the driving force for corrosion in aqueous media is the difference in potential of small areas due to heterogeneities in the material [2]. It is important to note that these heterogeneities range from atomic to several hundred microns in scale, and can arise from various factors such as defects in the crystal structure of the metal, different phases, segregation of elements or phases, non-metallic inclusions, etc. [3]. It is reported that many of these heterogeneities are controlled by the elemental composition, thermal and mechanical history of the material [3]. In work [4] has found that, pitting was initiated almost exclusively at non-metallic inclusions. From the results of thermodynamic considerations, the sulfides themselves are not thermodynamically stable and tend to dissolve making a microcrevice at the periphery along the inclusion/metal interface. Furthermore, the compositional and microstructural properties can vary significantly between steels of the same grade from different manufacturers, and these variations may lead to substantial differences in the corrosion resistance. In study[5] revealed, that microstructure and chemical composition of carbon and low alloy steels are important factors and they have a significant influence on CO2 corrosion performance. If a low chromium alloy steel is to be selected, it is worth noting that even when the influence of steel microstructure seems of less importance than for carbon steels, it is recommended not to have a ferritic-perlitic microstructure[6]. The steel microstructure plays a significant role in terms of the corrosion rate and mechanism. Studies[4-6] undertaken recently revealed that the corrosion behaviour like mechanical properties is related to the alloy microstructure which is determined by heat treatment parameters (like austempering temperature, austempering time, austenitizing temperature and austenitizing time). The study[7] shows an increase in the corrosion resistance of the material due mainly to spheroidal annealing process. The effect of temperature and time of annealing on hardness indicates that, the best time and temperature for spheroidal annealing is 740 °C over 60 min for hardness and 45 min for corrosion resistance for the same temperature[7]. In work [1] had been shown the change in the Icorr value as a function of the annealing temperature for specimens quenched in the different media. The lowest Icorr value was for the steel cooled in icy water, whereas the highest corrosion rate was for specimen cooled in hot water.