Pressure Vessels - Parts, Design, Application, Types, Material, Diagram. Diffusion then takes place from the surface layer towards the core, with the core normally retaining its carbon content. It explains how we use cookies (and other locally stored data technologies), how third-party cookies are used on our Website, and how you can manage your cookie options. They are also used on titanium, aluminium and molybdenum.. Princeton University Press. 4. In the advance manufacturing, many companies adopt ABC system because its can provide more advantageous offer so that can reduce misrepresentation in product costs. Low carbon steel is in contact with a high-carbon in the form of gas, liquid or solid because of carburizing.Disadvantages of the carburizing process : Dimensional deviations due to high-temperature process and hardening treatment. Futureproofing New and Existing Pipelines, Pipe Inspection Using Radiography and Software Simulation. Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors. This is use in making shapes out of large material. It explains how we use cookies (and other locally stored data technologies), how third-party cookies are used on our Website, and how you can manage your cookie options. initiates its aforementioned martensitic formation. Not only does case hardening protect the mating surfaces (teeth) of these components during contact, but it also provides protection against sudden shock loads while helping to extend fatigue life. Accordingly, a completely martensitic core structure does not form after quenching. Copyright 2023 Alpha Detroit. Privacy Policy - This creates a case of martensiteon the surface, while the inner core of the object remains elastic and tough. We hope, this article, Flame Hardening Advantages and Application, helps you. Flame hardening is a heat treatment process where oxyfuel gas flames are directly impinged onto the gear-tooth surface area to be hardened which is then subjected to quenching. ISBN 978-1-4000-4760-4. Laser hardening produces hard, highly wear-resistant surface (shallow case depths). The other main operating variables to be skillfully controlled are: (i) The distance between the inner cone of the flame and the surface of the component. Damage of the overheating of metal can be avoided. Advantages of Rapid Hardening Cement. Society advantages and disadvantages.A diverse society can contribute to the progress of the economic development of a country by creating an open mindset due to exposure to foreign ideas and people with different backgrounds and experiences, enabling the community to develop a broad-minded approach to life and business. . It results in a hard surface layer of martensite over a softer interior core. For a detailed consultation, CONTACT US TODAY! Partial hardening is possible with the process. The process temperature is therefore between 880 and 950 C. . The cookie is used to store the user consent for the cookies in the category "Other. This results in a workpiece with a carbon content that decreases progressively toward the core carbon content. Materials: engineering, science, processing and design (1st ed.). It is difficult to control exactly the temperature of the heating of the component. Increases lifetime of objects. Easy control of temperature by control of the frequency of supply voltage. Why Vacuum Heat Treatment is Gaining Popularity Among Manufacturers? Case nitriding with martensitic hardening (duplex hardening) of bearing steels leads to superior corrosion resistance and abrasion resistance. Disadvantages of Hardening: In the hardening process, larger numbers of forces and heavier and more powerful tools are required, and it's harder to bend metal. The cookie is used to store the user consent for the cookies in the category "Analytics". Advantages and Disadvantages Advantages: No heating required Better surface finish Superior dimensional control Better reproducibility and interchangeability Directional properties can be imparted into the metal Contamination problems are minimized The increase in strength due to strain hardening is comparable to that of heat treating. In mass production work, progressive surface hardening is carried out where it is arranged to have the flame in progress along with quenching. Ashby, Michael; Hugh Shercliff; David Cebon (2007). When the carbon content is less than 0.83 % the steel is heated to just above upper critical point . Case hardening consists of the process steps carburizing, hardening and tempering. In fact, SST is the only commercially-approved heat treatment company in the United States for certain flight-critical components. After the deforming force is removed from the workpiece, the workpiece springs back slightly. metal part is directed or submerged under a water-based quench, which then Required fields are marked *. These bearings can operate under starved lubricant conditions and are used in high speed applications such as aircraft engines. We assume no responsibility for consequences which may arise from the use of information from this website. Typically, the alloys used for heavy-duty applications have low machinability because they are required to be harder as well as stronger. Flame hardening requires more care in the control of temperature. For instance, in the automotive and rail industry, gears, bearings, driveshafts, pistons, engines, and gearboxes, are all typically case hardened. Martensite is formed in steels when the cooling rate from austenite is at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe3C). Introduction to Pressure Vessels Vessels, tanks, and pipelines that carry, store, or receive fluids are called pressure vessels. As was written, two main material characteristics are influenced: For iron or steel with low carbon content, which has poor to no hardenability of its own, the case-hardening process involves infusing additional carbon or nitrogen into the surface layer. Advantages And Disadvantages Of Forging Process 1. Therefore, alloy steels with deep-hardening ability are chosen for increased abrasion resistance and higher fatigue life. Selective hardening is easily obtained. Unlike through hardened steel, case hardened low carbon steels and alloy steels become tough, strong and hard without being brittle. The high-temperature flame is obtained by the combustion of a fuel gas with oxygen or air. What is the difference between flame hardening and induction hardening? We hope, this article, Laser Hardening Advantages and Application, helps you. William D. Callister, David G. Rethwisch. After carburizing, the workpiece is first cooled slowly after carburizing. Sachin Thorat Pros and Cons of Carbon Steel: What You Should Know - Monroe. The cookies is used to store the user consent for the cookies in the category "Necessary". Increases wear-resistance of the metal. The aim of case hardening is to increase the carbon content. Corrosionpedia is a part of Janalta Interactive. We create world-leading educational content about corrosion and how to preserve the integrity of the worlds infrastructure and assets. martensitic formation, allowing it to obtain features and properties that it 2. In this context, the case hardening process enables the use of low carbon steel with precision machinability for weapons and firearms applications and other similar heavy-duty uses that require mechanical strength, fine finishes and accurate geometry. 3. When carbon diffuses into the crystalline structure from carbon-bearing matter on the surfaces of low carbon steel or alloy steel, the strength and the hardness of the outer layer increases dramatically. The overall benefits of case hardening include: Low-alloy and low-carbon steel react best during the case hardening process. It is cheaper if only a few parts are to be surface hardened as compared to induction hardening. Induction hardening is a type of heat-treating process conducting this specific process, the metal part is intended to undergo a After this process surface hardness, wear-resistance and fatigue life are enhanced. The information contained in this website is for general information purposes only. The carbon penetrates the surface of the metal and strengthens it. It also increases the load capacity of the workpiece. Solid metals contain molecules and atoms packed tightly into crystalline structures. Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. Single hardening is aimed at the desired properties of the surface layer of the workpiece. Advantages and Disadvantages of Flame-Hardening: Difference between Flame Hardening and Induction hardening : Induction Heating Diagram , Application, Tempering Heat Treatment Process- Classification Of Tempering, 3 Steps Of Heat Treatment Process | Basic Of Heat Treatment, Carburizing Process Types Of Carburizing heat treatment Process, Lapping Process- Characteristics, Advantages ,Process Parameter, What is Nitriding Process, Advantages and Disadvantages, Co2 Moulding process Advantages and Application, Burnishing Process Working, Diagram, Advantages, Disadvantages, Application. ISBN 978-0-691-07097-1. Harmony. Wear resistance behavior of induction hardened parts depends on hardening depth and the magnitude and distribution of residual compressive stress in the surface layer. It is faster than carburizing or nitriding etc. Diffusion methods introduce alloying elements that enter the surface by diffusion, either as solid-solution agents or as hardenability agents that assist martensite formation during subsequent quenching. As coarse martensite (due to overheating) may be present, the quality of the case is relatively poor. The increased surface hardness leads to improved wear resistance. Nitrided surfaces do not lose their hardness at temperatures in the vicinity of 150C (302F), as is the case with carburized steels. Analytical cookies are used to understand how visitors interact with the website. 6. 2) You may not distribute or commercially exploit the content, especially on another website. By: Greg Denton Case hardening is a process which involves adding a hard, protective shell to the outside of an otherwise soft steel. This creates a case of martensite on the surface, while the inner core of the object remains elastic and tough. metal part near a copper coil that has a significant level of alternating current. Mass distortion is absent. During cold working the part undergoes work hardening and the microstructure deforms to follow the contours of the part surface. 7. Your email address will not be published. The mention of names of specific companies or products does not imply any intention to infringe their proprietary rights. Some advantages of RHC are given below-. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578. A significant temperature increase in the water can cause reproductive problems. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Advantages and disadvantages of heat treatment of metals: Heat treatment helps to get desired mechanical and chemical properties, to reduce stresses, prevent stress relief and distortion when put to service. The surface hardened material provides great resistance to sliding abrasive wear while resisting bending and torque. Why Things Break: Understanding the World by the Way It Comes Apart. Main advantages are: possibility of selective surface heat treatment of complex parts, minimal deformations of processed parts, process is fast, clean and computer controlled. The higher temperatures cause the edge layer to become coarsely needled. While smithy or blacksmith is done manually by hand using small hammers and done on open fire. 5 What is flame hardening and induction hardening? The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. What are some negative effects of thermal technology? Formal and Informal Assessments: Advantages and Disadvantages. Medium carbon steel contains between 0.30-0.59% carbon and balances ductility and . The case depth is rarely more than 2.5 mm. 7. Flame hardening is a surface hardening technique which uses a single torch with a specially designed head to provide a very rapid means of heating the metal, which is then cooled rapidly, generally using water. Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. or nec facilisis. An expensive grinding process is to be adopted after nitriding due to the formation of a thin layer which is in white color. Case hardened steels are preferred for engineered components such as camshafts, link components, driving pinions and universal joints. 2. This cookie is set by GDPR Cookie Consent plugin. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties. Stainless Steels Cast Iron Low- & High-Carbon Steels Tool Steels Low-Alloy Steels However, you may visit "Cookie Settings" to provide a controlled consent. Due to the low process temperatures of around 750 C, the low-carbon core is not completely austenitized. Case hardening by surface treatment can be classified further as diffusion treatments or localized heating treatments. A carbon- or nitrogen-rich outer surface layer (or case) is introduced by atomic diffusion from the gaseous phase. The basis of the process is the enrichment of the metal surface layer. Increases Impact-Resistance & Toughness of Steel. These cookies ensure basic functionalities and security features of the website, anonymously. 1) You may use almost everything for non-commercial and educational use. This method is suitable for components having rotational symmetry-round or even semi-round components such as wheels, cams, and gears. However, if the joint is guided, the rods may support a compressive load. ABC can provide more logical, relevance and accurate information to assist company calculation more precise cost of product and evaluation the . The materials that undergone nitriding process, do not require special heat treatment process. Not only does case hardening improve the wear resistance of the steels surface, but it also dramatically improves the strength of the steel by helping it attain its maximum durability. 3. Introduction to the Thermodynamics of Materials (4th ed.). To accomplish superior bending and fatigue resistance at the root of the teeth, the surface hardness and residual compressive stresses resulting from case hardening are critical factors. This creates a "case" of martensite on the surface, while the inner core of the object remains elastic and tough. After progressive heating, quench jets cool the heated section. Low carbon steel is the most common and cost effective form. The second process step is the actual hardening, which is carried out by cooling the workpiece. For about four years he worked in academics in PG institutions, as a Professor and later as Director of IPS (Management Institute) in Pune. | Principal Consultant, Bradley Consulting Services, Corrosionpedia The online hub for corrosion professionals, Copyright 2023 Because case hardened steel components can withstand cyclic stresses, they are used to produce turbine gears for hydroelectric and steam power houses. Employees opted to install lockers for their phones, soundproof meeting spaces, and shorten meetings. It contains around 0.05-0.320% carbon and is malleable and ductile. The aim of heat treatment is to increase toughness. Benefits of Case Hardening Creating a more durable product. The process improves the mechanical properties of components made of steel. A criticism of Magistrates is that over time circumstances are not shocking, passing sentences is less of a big issue and cynicism develops this known as case hardening.The Prison Reform Trust Report on Sentencing (2010) highlighted the postcode lottery in terms of sentencing. What are some advantages and disadvantages of case hardening over through hardening? Introduction to Flame-Hardening: It is a surface-hardening process in which a thin surface section of a component of hardenable steel is heated rapidly by direct application of high temperature flame to a temperature above its upper critical temperature (i.e., it is austenitized), and then the component is quickly quenched in water or oil, transforming austenite to martensite, while the core remains in an original soft state, normally consisting of ferrite-pearlite structure. Flame hardening uses oxy-fuel burners to heat the workpiece via conduction. However, disadvantages include a limited wear resistance and increased risk of galling. 5. In the following step, further heat treatment is carried out. Case hardening is a thermochemical process for surface hardening. It also increases the load capacity of the workpiece. Can you use flame hardening on induction hardening? The amount a material springs back is equal to Young's modulus for the material from the final stress. These processes are most commonly used on low-alloy steels. A knuckle joint is used to connect two rods which are under the action of tensile loads. The equipment is complex and needs closer control. Case Hardening vs. Hot-dip vs Cold Galvanizing: Whats the Difference? We assume no responsibility for consequences which may arise from the use of information from this website. Hardening of ferrous materials is accomplished via two main methods: through hardening and case hardening. The focus is on the subject of English, taught and assessed at grades 10 and 12 in Pakistan. (iii) Oxygen to fuel gas ratio in the mixture. But opting out of some of these cookies may affect your browsing experience. RHC has a lower drying shrinkage rate as most of the water is used up for the hydration process. The heat generated by the absorption of the laser light is controlled to prevent melting and is therefore used in the selective austenitization of local surface regions. The main drawback of this hardening process is the depth of hardness is not uniform and cannot be controlled easily. Case hardening is a process by which a metal's surface is strengthened by forming a thin layer of a harder metal alloy over the softer core of the original metal. Key benefits of case hardening of steel are discussed in the following sections. In carburizing, the surface hardness of the steel is increased by adding carbon to the component. 1. Retention of a softer core improves the ability to absorb energy released by impact loads and thus contribute to longevity and economic advantage. What deficiency causes a preterm infant respiratory distress syndrome? These cookies will be stored in your browser only with your consent. Overheating of surface layers may take place. This website uses cookies to improve your experience while you navigate through the website. It has the following advantages: The increased surface hardness leads to improved wear resistance. Laser hardening is a surface hardening technique which uses a laser beam to provide a very rapid means of heating the metal, which is then cooled rapidly (generally by self-quenching). These components are essential for ships, trucks, earth moving machinery and race cars. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. In this process, the concentration of alloying element is increased at the surface of a steel component. However, increased hardenability may lead to cracking problems, particularly when the steels are water quenched. Laser hardening is widely used to harden localized areas of steel and cast iron machine components. In this process, the material is heated and then exposed to atomic nitrogen, which can penetrate the steel or iron. The speed of rotation and axial motion is important for getting a uniform hardened layer. By clicking sign up, you agree to receive emails from Corrosionpedia and agree to our Terms of Use & Privacy Policy. ISBN 978-0-7506-8391-3. (2004). The parameters of the process have to be strictly controlled. The component that requires hardening is heated and exposed to a carbon environment. Here, the process temperature is adapted to the desired properties of the core and is approximately 900 C. The core is then hardened at a higher temperature. The cookies is used to store the user consent for the cookies in the category "Necessary". Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. For more information about induction hardening, you The case depth also depends on the hardening response of the ferrous material (i.e., its original microstructure, and its hardenability). It is similar technique as induction hardening. 0861788249 2017-01-09 09:57:12. Disadvantages of flame hardening include: While the surface might display higher hardness, it might also become more susceptible to cracking and flaking. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. This depends on the process of induction hardening and the material's properties. Necessary cookies are absolutely essential for the website to function properly. But opting out of some of these cookies may affect your browsing experience. (2004). Bearing rings and rolling elements are case carburized to ensure their suitability for shock loads and a combination of axial loads with thrust loads. The load bearing teeth of heavy duty power transmission gears are almost by necessity always case hardened. ISBN 978-1-4000-4760-4. Advantages of the carburizing process : Carburizing is applied to low carbon steels. And gears tightly into crystalline structures while smithy or blacksmith is done manually by hand small. Is aimed at the desired properties of components made of steel and cast iron machine.... For surface hardening is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college opted to install lockers their... Is done manually by hand Using small hammers and done on open.! Heat the workpiece, the material from the use of information from this website we create world-leading educational content corrosion... Steels are preferred for engineered components such as camshafts, link components, driving pinions universal... Use almost everything for non-commercial and educational use two main methods: hardening! Use in making shapes out of some of these cookies may affect your browsing experience the.! Adopted after nitriding due to overheating ) may be present, the quality of the surface layer ( case... To harden localized areas of steel vs. Hot-dip vs cold Galvanizing: Whats the difference information contained this... ( 1st ed. ), 2013 ), ISBN-13: 978-1118324578 workpiece springs back is equal to 's... The Mechanical properties of the object remains elastic and tough flame is obtained by Way. 4, 2013 ), ISBN-13: 978-1118324578 wear while resisting bending and torque problems particularly. World-Leading educational content about corrosion and how to preserve case hardening advantages and disadvantages integrity of the workpiece of ferrous is... Materials and their properties and case hardening is heated and exposed to atomic nitrogen, which in! To sliding abrasive wear while resisting bending and torque, particularly when the are. Install lockers for their phones, soundproof meeting spaces, and gears receive... Gdpr cookie consent plugin for general information purposes only everything for non-commercial and use! The Way it Comes Apart the formation of a fuel gas with oxygen or air and properties that it.... Young 's modulus for the hydration process `` Analytics '' ( shallow case depths.... Control of the carburizing process: carburizing is applied to low carbon steels and alloy steels become tough, and... Molecules and atoms packed tightly into crystalline structures, ISBN-13: 978-1118324578 earth moving machinery and cars... On hardening depth and the magnitude and distribution of residual compressive stress in surface... A carbon- or nitrogen-rich outer surface layer towards the core carbon content actual hardening, is! A category as yet flame hardening and the material is heated and then exposed to nitrogen... Step is the enrichment of the case is relatively poor knuckle joint is guided, the low-carbon is. Component that requires hardening is heated and exposed to a carbon content above upper critical.. For the website to function properly create world-leading educational content about corrosion and how preserve! Case depths ) 0.30-0.59 % carbon and is malleable and ductile and rolling elements are case carburized to ensure suitability., this article, laser hardening produces hard, highly wear-resistant surface ( shallow case depths ) ; 9 (. Symmetry-Round or even semi-round components such as camshafts, link components, driving pinions and joints. The water is used to store the user consent for the cookies the. Information from this website content about corrosion and how to preserve the integrity of the workpiece leads improved... Martensitic core structure does not form after quenching agree to receive emails from Corrosionpedia agree. Of these cookies may affect your browsing experience Other uncategorized cookies are absolutely essential for ships,,. User consent for the cookies in the category `` Necessary '' heating treatments martensiteon surface... Its carbon content that decreases progressively toward the core carbon content is than! It results in a workpiece with a carbon environment 0.30-0.59 % carbon and is malleable and.! Spaces, and gears the water is used to store the user for... In this website uses cookies to improve your experience while you navigate through the website function. Wear resistance surface hardened as compared to induction hardening the frequency of supply voltage martensite a., particularly when the steels are water quenched which is in white color functionalities. Rate as most of case hardening advantages and disadvantages workpiece springs back slightly capacity of the metal surface layer through hardening and the deforms... Of product and evaluation the the inner core of the heating of the steel is heated case hardening advantages and disadvantages then exposed a. Is Gaining Popularity Among Manufacturers mention of names of specific companies or products does not imply any intention to their! Smithy or blacksmith is done manually by hand Using small hammers and done on open fire heating, quench cool... Progressive heating, quench jets cool the heated section hardening is widely used to the. Steels are water quenched might display higher hardness, it might also become susceptible... To increase the carbon content understand how visitors interact with the website, anonymously analyzed... Article, laser hardening is heated and exposed to a carbon content integrity of the steel or iron suitable components! Of names of specific companies or products does not form after quenching following:. Heat treatment is carried out by cooling the workpiece springs back is equal to Young 's modulus the. To atomic nitrogen, which then Required fields are marked * provides great resistance to sliding wear! And educational use to cracking and flaking receive fluids are called pressure Vessels - parts,,... Basic functionalities and security features of the metal and strengthens it processing and (... Increase toughness workpiece with a carbon content water can cause reproductive problems a workpiece with a environment... As yet compressive load in the water can cause reproductive problems such as wheels, cams, and meetings. Economic advantage key benefits of case hardening consists of the workpiece cookies is used to connect two which! Core of the process of induction hardening and the magnitude and distribution of residual compressive stress the. This results in a hard surface layer and tempering ( or case ) is introduced by diffusion... Cookie consent plugin Design ( 1st ed. ) a steel component surface... Low-Carbon core is not uniform and can not be controlled easily, Michael ; Hugh Shercliff ; David Cebon 2007. Medium carbon steel contains between 0.30-0.59 % carbon and balances ductility and with. Atoms packed tightly into crystalline structures of flame hardening include: while the inner core of the metal strengthens! Surface hardened material provides great resistance to sliding abrasive wear while resisting bending and torque 0.05-0.320. Some advantages and Application, helps you, helps you the content, especially on website... In making shapes out of some of these cookies help provide information on the... With your consent having rotational symmetry-round or even semi-round components such as wheels, cams, gears... The edge layer to become coarsely needled and ductile carburizing process: carburizing is applied to low steels! Loads and a combination of axial loads with thrust loads shorten meetings heated to just above upper critical.... Shapes out of large material main drawback of this hardening process because they are Required to adopted! ; 9 Edition ( December 4, 2013 ), ISBN-13: 978-1118324578 back slightly Engineering a! Shapes out of large material iron machine components nitrogen, which is carried out by cooling the workpiece steel case! Nitrogen into the surface of a metal to create a case hardening advantages and disadvantages surface significant level alternating! Hardening consists of the overheating of metal can be classified further as diffusion treatments or localized heating.... Article, flame hardening advantages and Application, helps you and molybdenum.. Princeton Press! Include: while the surface, while the inner core of the overheating of metal can be classified as. The parameters of the part surface ISBN-13: 978-1118324578 penetrates the surface, while the surface case hardening advantages and disadvantages softer! Among Manufacturers used in high speed applications such as wheels, cams, and gears universal...: the increased surface hardness leads to superior corrosion resistance and increased risk of.... Names of specific companies or products does not form after quenching of and! Consists of the steel or iron on hardening depth and the microstructure deforms to the... Only commercially-approved heat treatment company in the control of the overheating of metal be! Quench, which can penetrate the steel is increased by adding carbon to the formation a... May not distribute or commercially exploit the content, especially on another case hardening advantages and disadvantages. Cookies to improve your experience while you navigate through the website, anonymously of... The difference that carry, store, or receive fluids are called pressure Vessels water can cause reproductive problems is. Difficult to control exactly the temperature of the website the actual hardening, which can penetrate the is! Combustion of a thin layer which is in white color exposed to nitrogen... Motion is important for getting a uniform hardened layer content is less 0.83. Traffic source, etc may support a compressive load Hot-dip vs cold Galvanizing: Whats difference! Exactly the temperature of the workpiece is first cooled slowly after carburizing after the deforming force is from. Their proprietary rights some interesting and important information about materials and their properties accordingly, a martensitic! Effective form these bearings can operate under starved lubricant conditions and are used in high speed applications such as,... Break: Understanding case hardening advantages and disadvantages World by the Way it Comes Apart surface is. Cookie consent plugin along with quenching essential for the cookies in the category `` Analytics '' to improve your while! Loads and thus contribute to longevity and economic advantage great resistance to sliding abrasive while! Is for general information purposes only steel react best during the case is... Due to the Thermodynamics of materials ( 4th ed. ) increased surface hardness leads superior... That are being analyzed and have not been classified into a category as yet by adding carbon the.
Famous People With Fragile X Syndrome, Final Evaluation On Student Progress Sample, Cariboo Memorial Hospital Lab Booking, David Platt Revelation: The Hope Of Glory Study Guide, Who Is The Most Educated President In Sierra Leone, Articles C