Materials.Business Weekly ⚙️
April 06, 2021
Quote of the week: "Learn from yesterday, live for today, and hope for tomorrow. The important thing is not to stop questioning.” — Albert Einstein.
From The Editor's Corner
CAST IRON. AN OLD MATERIAL FOR A BETTER FUTURE
More than two thousand years ago, the Chinese discovered cast iron production. Some of its properties like easy molding to get the desired shape of complex and large-size parts, harness, stiffness, high thermal conductivity, high compressive strength, and wear resistance were standing up. The Iron Age was starting. However, fairly limited the cast iron spread because of its properties as high brittleness and low malleability. Furthermore, other technological developments raced simultaneously, both in China and other regions. Only more than one millennium after, cast iron production started in the western culture when Europeans tried to a way of more robust cannon barrels production. And challenges related to a complicated technology of good quality cast iron production, e.g., high melting temperatures and malleabilization by graphite oxidation, were overcome. It was the right moment because cast iron became one of the First Industrial Revolution pillars during the last decades of the 18th Century. Cast iron was the material par excellence supporting the machinery's development for steam, cotton, and coal production. In the 19th Century, cast iron was the most used metallic engineering material. Some other advantages are a lower price and the option of an extremely low scalable production. For example, in Europe, there are around 4.500 metal casting firms, of which 70% are small businesses with less than 50 employees; an interesting situation facing the trends on international trade after the current pandemic. All of them are conditions for extensive usage of cast iron and technological development on issues like better-controlled composition, improved processing, and new characterization techniques, reached the last decades of the 20th Century. Nowadays, cast iron is used in traditional applications like mining, pipes & fittings, machinery bases, and cookware (a unique cooking material, even considered a source of human iron requirements). More specialized and recent applications include wind turbine housing, internal combustion engine blocks, oil well pumps, and agricultural labor machinery. Sand casting is the predominant process, and worldwide production is distributed as 63% gray iron, 35% nodular iron, and 2% malleable iron. The Asia Pacific is the biggest market, with about 60% of the global one. According to the firm Global Market Insights, the global iron & steel casting market size was estimated at USD $145.970 million in 2020 and is slated to surpass USD $210.000 million by 2027. According to its applications, automotive & transportation and industry are the main demanders. A segment of such global market in 2020, of about USD $2.600 million, belongs to the cookware market and is its projection to 2027 of USD $ 3.300 million. In the case of the USA, the total annual metal casting market reach about USD $20.000, shared between Al (45%), steel (25%), iron (20%), and others (10%). These last figures include USD $774 million of the USA cookware market.
Considering the iron alloys, in the case of cast iron alloys, we are talking about a group of Fe alloys containing 2 to 4% in weight of carbon, 1 to 3% of Si, and lower amounts of other elements like Mn, S, P, Mo, Ni, Cr, etc., as impurities or alloying elements. Basic members of the family are white and grey cast irons. Different colors associated with appearance when broken because of the nature of their microstructures. In white cast iron, characteristic compositions are 1.8 to 3.6% C, 0.5 to 1.9% Si, and 1.0 to 2.0% Mn. The resulting microstructure is essentially iron carbide, Fe₃C, or cementite, which gives its properties of hardness, brittleness, and color.
When the ferrous alloy contains 2.5 to 4.0% C and 1.0 to 3.0% Si, free graphite becomes stabilized as a constituent in the microstructure. Something like ceramic, fragile, soft, emollient, and black particles of graphite flakes embedded in a steel matrix. Consequently, physical, mechanical, and chemical properties are characteristic of such material, including a gray fracture. These are the gray cast irons. According to their minimum tensile strength, the ASTM standard A48M (2016) classifieds gray cast irons ranging from 150 to 400 MPa.
The other two more distinguished members of the cast irons family are malleable and nodular ones. Here, again, a primary characteristic is free graphite in the microstructure. However, a certain level of spheroidization is achieved by chemical, thermal, or both treatments, and therefore the properties change as well. Malleabilization is an old antique process based on a slow annealing heat treatment of white cast iron. Thus, Fe₃C is transformed to spheroidal graphite in a metallic matrix. Consequently, malleability and ductility improve. The last member of the group is nodular or ductile cast iron. It is similar to the malleable one, but the graphite's nodules are usually more spherical due to Mg’s chemical treatments instead of the heat treatment for the malleable cast iron procurement. Characteristics of nodular iron as ductility and resilience are outstanding, and applications in severe conditions like vehicle brakes and housing of wind turbines prove its behavior. According to the ASTM standard A536-84 (2019), tensile strength ranged from 414 to 827 MPa, yield strength from 276 to 621 MPa, and elongation from 18 to 2%. Besides, modifications of the matrix, by thermal, chemical, or both kinds of treatments, let ferritic or pearlite malleable or nodular cast irons. Alloying with Cr, Ni, and other elements opens the possibilities of martensitic, austenitic, and other cast irons.
In principle, the cast iron's behavior in aqueous environments (water, soil, air, and chemical substances) is similar to steel. For example, little or no difference in the corrosion rate is found in natural waters. Under low aggressiveness conditions, uniform corrosion is the common mechanism of attack in all the cast-iron types. According to studies developed by us, in more aggressive environments, like strong acids, withe iron usually suffers a semi-generalized attack. Instead of that, with free graphite, behavior changes a lot. Gray iron suffers moderate to severe graphitic corrosion. Meanwhile, nodular iron behavior depends on the matrix constituents. Pearlitic nodular iron trends to be deeply dissolved, but ferritic nodular iron exhibits better behavior, and sometimes with a certain level of graphitization. As a result, simpler microstructures (e.g., ferritic nodular iron) perform better. Additionally, other variables affecting corrosion behavior in these environments include the size of graphite particles, the percentage of ferrite, the presence of cementite, the number of present phases, the relationship between the border length and the volume of the graphite particles, and the content of C, S, P, and Si. In other words, further than generalized corrosion, we can find a localized attack, both with and without other combined effects as mechanical or microbiological. For instance, we can discover crevice corrosion, pitting, cavitation-corrosion, galvanic pairs, etc. The most characteristic corrosion phenomena are associated with some of the more common applications. For example, in pipes and fittings as flanges and other joining areas, concentration cells are established, and crevice attack arises. It also happens with cavitation-corrosion and erosion-corrosion because there are many cast iron applications where both effects converge. Furthermore, cast iron is prone to stress corrosion cracking; consequently, in such cases, the more brittle white and austenitic gray cast irons are not recommended. In the same way, pitting is often related to microbiological activity usually occurring under rust tubercles, where conditions become highly acidic and aggressive as happens in the presence of sulfate-reducing bacteria, a common microorganism in many soils. Concerning galvanic attack, the starting point is the similarity with carbon steel at the beginning. But, depending on the environment, a shift in the noble direction of the cast iron potential with the time of exposure turns carbon steel anodic in front of cast iron. As a result, the established pair of mild steel/cast iron becomes a significant galvanic pair in many applications.
One of the sources of such cathodic shifting is graphitic corrosion. Here, we can remember that a basic rule of corrosive circumstances is heterogeneities. At the microstructural level, cast iron shows various constituents where micro galvanic effects are easy to establish. In aqueous environments, hydrogen evolution on particles like cementite and graphite happens, and meanwhile, metallic constituents like ferrite become anodic and points of preferential dissolution. It is a dealloying phenomenon when one or more constituents of an alloy are more anodic than the rest and are preferentially slowly dissolved. It also happens in brass and some other Cu and Al alloys, mainly. In the beginning, cast iron grains lost their properties due to weakening the bond’s strength and cohesion between matrix and “reinforcement,” segregation, micropores, intergranular cracking, etc. In addition, recently has been found that also takes place a significant reduction in the nano elastic and nano hardness of the grains of the cast iron due to the diffusion of hydrogen from the surrounding corrosive environments, directly related to pH and moisture content. The alloy loses some of the microstructural constituents, retaining the cathodic ones, in a porous “sponge” structure or graphite frame. Due to the network of graphite flakes, graphitization is common in gray iron. As a result, a graphite frame residue with its porous filled with rust holds its original shape, dimensions, and appearance unaffected. However, bulk mechanical properties become dramatically degraded. In such conditions, pipes and other stuff can serve for several decades if the effort level is low enough. But the risk of sudden and catastrophic failure remains latent.
In principle, measurements are similar to steel protection. Besides, it is possible and vital to keep in mind particularities like those mentioned earlier. A proper selection of the material and a good design of the specific part concerning the environment are the starting conditions. Heat treatment is a way of corrosion resistance improvement, looking for better microstructures. For example, austempering of nodular cast iron at 375 °C achieve a matrix of austempered ferrite or coarse grains of austenite in broad ferrite needles, and consequently, a better corrosion behavior. Alloying is another crucial option. Ni in austenitic cast iron avoids the graphitization attack when it is necessary. Cr alloying is often used, looking for the simultaneous improvement of the wear and corrosion resistance. Of course, the possibilities of alloying modification are infinite. Use a barrier between the material and the corrosive is also used. Several kinds of coatings and linings are used, depending on the engineering considerations. Plastic linings, paints, Portland cement coatings, metallic coatings like galvanizing, etc., are some of the more used protective barriers. Also, the modification of the corrosion cell by cathodic protection is a valuable method of anticorrosive protection, mainly for buried, submerged, or reinforced concrete structures. Some of the standards supporting engineering decisions concerning the management and protection of cast irons are:
● NACE TM0497-2018. “Measurement techniques related to criteria for cathodic protection on underground or submerged metallic piping systems.”
● ISO 1461:2009. “Hot-dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods.”
● A518/A518M-99(2018). “Standard specification for corrosion-resistant high-silicon iron castings.”
● A743/A743M-19. “Standard specification for castings, iron-chromium, iron-chromium-nickel, corrosion-resistant, for general application.”
● A744/A744M-20a. “Standard specification for castings, iron-chromium-nickel, corrosion-resistant, for severe service.”
● A890/A890M-18a. “Standard specification for castings, iron-chromium-nickel-molybdenum corrosion-resistant, duplex (austenitic/ferritic) for general application.”
In summary, the cast iron family is a group of valuable materials that have supported humanity's development throughout its history, which is critical even today, with great consolidation perspectives as an even more crucial material in the post-globalization era. Corrosion problems of cast iron are only partially studied, and better protection is necessary.
Remember: Protection of materials and equipment is a profitable business!
Prof. Carlos Arroyave, Ph.D. Editor.
Materials Biz News
A jump in inspection possibilities
DYNAMIC Infrastructure is an enterprise based in New York, aimed to apply artificial intelligence – AI -to inspect and maintain tunnels, dams, bridges, walls, and large structures. The company is currently offering service drones for image capture of bridges’ infrastructure and processing pictures by AI, achieving an automatic, quick, and accurate analysis according to AASHTO standards for maintenance decisions. Savings on time, required equipment, risks, traffic restrictions, and money are enormous.
Green steel as a fact
HYBRIT, the Hydrogen Breakthrough Ironmaking Technology, is a joint effort between the steel company SSAB, the mining and minerals group LKAB, and the energy producer and retailer Vattentfall in Sweden. The purpose of the agreement is to have a solution for the first fossil-free steel by 2035, reducing the CO₂ emissions and decarbonizing the iron and steel sector. As a result, a reduction of one-third of the country's industrial emissions and at least 10% of the national CO₂ emissions. In the meantime, a goal is to start the production of fossil-free sponge iron pellets in 2026, 1.3 million tons per year in the beginning, and 2.7 million tons in 2030.
Good opportunity to publish your research
Our colleague, Dr. Yujie Qiang from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, has been awarded as guest editor of a special issue on "Advances in Polymer-Based Materials for Corrosion Protection." This special issue belongs to the Polymers journal series published by MDPI. According to Dr. Quiang, interested authors must submit only original manuscripts. Subjects under consideration are conductive polymers, self-healing polymers, polyaniline, polypyrrole, corrosion, corrosion protection, anticorrosion coating, corrosion inhibitor, and nanocomposites. The Article Processing Charge (APC) for publication in this open-access journal is 2.200 CHF (Swiss Francs).
Position: Scientific Project Manager for KALDERA Project Office
Seeker: German Electron Synchrotron - DESY
Location: Hamburg, Germany
The basic profile of the candidate:
● Education: Ph.D., preferably in physics, chemistry, or a related field.
● Experience: Planning and performing scientific experiments at different large-scale infrastructure photon science facilities or ultrafast laser systems. Dealing with software like LaTeX, python, confluence, and Matlab.
● Skills: Excellent communication skills in German and English.
Job description: General managing of the internal and external duties concerning the research project.
Position: Senior Software Engineer
Location: Cambridge, UK.
The basic profile of the candidate:
● Experience: Strong and demonstrable experience working on full-stack technology products and expertise using agile and lean development practices.
● Skills: In-depth knowledge of software engineering principles, interest in IoT and writing resilient software (cloud and desktop), understanding of strongly typed languages (Go, Java, JS, C/C++, C#, Scala
Etc.), and knowledge of databases (SQL and others).
● Bonus: Entrepreneurial edge.
Job description: Developing and maintaining CR’s cloud-based Industrial IOT software platform, developing and maintaining CR’s IoT platform and internal automation tools, developing custom software solutions or tools to meet and achieve clients specifications (e.g., visualization, data processing), and building strong relationships, communicating and collaborating with clients and colleagues.
Position: Senior Industrial Development Officer
Seeker: African Development Bank (AfDB)
Location: Abidjan, Côte d'Ivoire
The basic profile of the candidate:
● Education: Master's degree in Economics, Public Policy, Industrial Policy, International Trade, Business Administration or related fields or related discipline.
● Experience: A minimum of five (5) years of relevant experience in a similar institution or solid industrial development experience and a strong understanding of Africa's industrial structure.
● Skills: Competence in using Bank standard software (Word, Excel, Access, and PowerPoint). Negotiations and consensus-building skills.
● Bonus: Experience with multilateral development institutions in developing countries. Experience/ good knowledge of one of the following sectors: textile, building materials, mining, consumer goods, pharmaceuticals, automotive, machinery and equipment, consumer durables, metal manufacturing, chemicals, agro-industries, tourism, and blue economy. Knowledge of SAP. Experience conducting cost-benefit analyses/ economic analyses of projects financed by development finance institutions.
Job description: The incumbent is responsible for developing and implementing programs, projects, and initiatives of the Bank, including lending operations and non-lending activities to Regional Member Countries, about the Bank's Industrialization Strategy. The incumbent is responsible for providing advice, developing technical assistance, and lending operations to governments, institutions, and regulatory bodies in the private sector and industrial development, concerning the Bank's Industrialization Strategy. The incumbent is expected to help countries identify the most promising products, sectors, and commercial opportunities and forge strategic partnerships with relevant international organizations and development financiers.
Networking & Knowledge Exchange
Another gain for the corrosionists’ community, boosted by the pandemic, has to be the initiative launched by James (Jim) Kunkle, current Manager of Business Development for AMPP Contractor Accreditation and Professional Certifications. As an outstanding evangelist, Jim presents a YouTube channel devoted to sharing information and knowledge from the corrosion and protective coatings industries. The channel features interviews, “two-minute lessons,” live streaming, and more.
Hannover Messe (Hannover trade fair) has become a more attractive meeting point for people focused on technological development in the Fourth Industrial Revolution. In this opportunity, the event will be in a digital form. As always, organizers promise an ideal space for innovation, inspiration, and interaction. The motto is “Industrial Transformation,” and most of the subjects emphasize factories, energy systems, and the future supply chains. Main activities are an exposition of products and services (live streaming), interactive conferences about trends and future topics of the industry, and a space for networking with exhibitors and other participants (personal dashboard and matchmaking).
Date: Monday to Friday, April 12th – 16th, 2021.
Time: 09:00 - 18:00 ECT (GMT + 2).
One more webinar of the Spring Program 2021, organized by the European MIC Network, will be presented by Jo Philips from the Aarhus University. The title of her presentation is “Acetogenic bacteria and their role in microbial induced corrosion.”
Date: Tuesday, April 13th, 2021.
Time: 14:30 CET (GMT + 2).
Contact: [email protected]