The Cookies Statement is part of our Privacy Policy. Nitriding As in carburizing, nitriding is also a thermochemical treatment. Metallurgy is complicated. Nitrogen is plentiful on Earth, however, in nature it exists as a two-atom molecule, chemically inert and too large to penetrate the surface. Xử lý nhiệt là việc sử dụng nhiệt để sửa đổi các tính chất của vật liệu, đặc biệt là trong luyện kim. Figure 3. Figure 4: Pre-nitriding – time savings graphs comparing 1,700oF endo carburizing to 1,850oF pre-nitriding Grain Structure. 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. In contrast to carburizing, in nitriding nitrogen is added into ferrite instead of austenite. The most significant hardening is achieved with a class of alloy steels (nitralloy type) that contain approximately 1% Al. Princeton University Press. It is a thermochemical diffusion process where nitrogen, carbon, and to a very small degree, oxygen atoms diffuse into the surface of the steel part, forming a compound layer at the surface, and a diffusion layer. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1. The carbonitriding process is particularly suited for clean mass production of small components. All Rights reserved. √Time. Nitriding vs. Carburizing Carburizing is similar to gas nitriding in that it is a heat-based process that produces a wear resistant, anti-gall surface. ISBN 978-1-4000-4760-4.Gaskell, David R. (1995). Below the compound layer, the thi… Taylor and Francis Publishing. This modification consists of introducing ammonia into the carburizing atmosphere in order to add nitrogen into the carburized case as it is being produced (Fig. In some products (common rail fuel-injection systems come to mind), there is a movement away from vacuum carburizing and back to gas nitriding. Hence nitriding technologies focus on the source of nascent (atomic) nitrogen. It’s easy to get lost in the chemistry—and the nomenclature—behind heat-treating processes. Nitrogen is plentiful on Earth, however, in nature it exists as a two-atom molecule, chemically inert and too large to penetrate the surface. Carburizing is a case hardening process in which the surface carbon concentration of a ferrous alloy (usually a low-carbon steel) is increased by diffusion from the surrounding environment. Nitriding produces hard, highly wear-resistant surface (shallow case depths) of product with fair capacity for contact load, good bending fatigue strength and excellent resistance to seizure. The graph illustrates that some Nitrided steels have a higher surface hardness than Carburized steels but a lower overall total case-depth. Widely used gas carburizing, heating temperature of 900-950 degrees celsius. Carburizing and nitriding treatments have the same goal: increase hardness on the surface while keeping the core ductility. This form of heat treating is well documented in showing consistent case depths throughout the entire surface area of … Confusion surrounding the case-hardening techniques of nitrocarburizing and carbonitriding prove the point that it's easy to get lost in the nomenclature behind heat-treating processes. Quenching and tempering may be necessary to minimize distortion as there are microstructure changes that occur during the hardening process. Carburizing is a process where the part is placed in a confined environment regulated by its carbon content. where the diffusivity factor, D, depends on temperature, the chemical composition of the steel, and the concentration gradient of carbon at the surface. Nitrocarburising is carried out at sub-critical temperatures and involves the diffusion of nitrogen and carbon into the surface of carbon steel to give a somewhat harder case and soft core with a very thin compound layer on the surface. There are advantages and disadvantages to both processes. The nitriding was assumed to give corrosion resistance. Carburising is a thermochemical process in which carbon is diffused into the surface of low carbon steels to increase the carbon content to sufficient levels so that the surface will respond to heat treatment and produce a hard, wear-resistant layer. 1). Nitriding is a thermochemical, case-hardening process that involves the diffusion of nitrogen into a steel surface. This website does not use any proprietary data. Why Things Break: Understanding the World by the Way It Comes Apart. Nitriding is a process of diffusing nitrogen atoms into the metal’s surface. Our Website follows all legal requirements to protect your privacy. 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. This article presents two examples to illustrate the carburizing and nitriding heat treatment processes. A temperature is significantly lower and range of 500 to 550 °C is typically used. Nitriding and carburizing are the two most common heat treatment practices for surface hardening functional components. The process is carried out in a sealed retort furnace at temperatures between 490°C and 530°C in a … Copyright 2021 Nuclear Power for Everybody | All Rights Reserved | Powered by, Interaction of Beta Radiation with Matter, Interaction of Gamma Radiation with Matter, Example – Calculation of Heat Exchanger, Carbonitriding – Advantages and Application, Carburizing – Advantages and Application, Flame Hardening – Advantages and Application, Induction Hardening – Advantages and Application, Laser Hardening – Advantages and Application, Titanium-nitride and Titanium-carbide Coatings, Ukraine's Zaporozhe 5 clear to operate until 2030, NGOs urge EU Commission to value nuclear energy. U.S. Department of Energy, Material Science. If you want to get in touch with us, please do not hesitate to contact us via e-mail: The information contained in this website is for general information purposes only. Also, no separate heating is required as the plasma provides sufficient heating of the component's surface to reach the process temperature of typically 500°C. The nitriding process uses the same concept but with nitrogen instead of carbon. Harmony. This chapter discusses the different aspects of the process starting from fundamental mechanism up to engineering applicability. Nitriding and carburizing by laser irradiation in combination with a process gas is a common method to enhance the surface properties of various materials. Hence nitriding technologies focus on the source of nascent (atomic) nitrogen. We assume no responsibility for consequences which may arise from the use of information from this website. (2004). This was a mistake because at first, the parts came back from 1st supplier and it had that light gray finish (see image). DOE Fundamentals Handbook, Volume 2 and 2. Case hardening or surface hardening is the process in which hardness the surface (case) of an object is enhanced, while the inner core of the object remains elastic and tough. Confusion surrounding the case hardening techniques of nitrocarburizing and carbonitriding prove the point that it’s easy to get lost in the nomenclature behind heat treating processes. Carburizing and nitriding generally refer to surface chemical heat treatment of steel. Carbonitriding (around 850 °C / 1550 °F) is carried out at temperatures substantially higher than plain nitriding (around 530 °C / 990 °F) but slightly lower than those used for carburizing (around 950 °C / 1700 °F) and for shorter times. Today, the steel piece is exposed, at an elevated temperature (usually above 850°C), to an atmosphere rich in a hydrocarbon gas, such as methane (CH4). Carburizing is a process where the part is placed in a confined environment regulated by its carbon content. After this process surface hardness, wear-resistance and fatigue life are enhanced. Butterworth-Heinemann. A greater advantage of nitriding is the achievement of a wear-resistant edge layer. Nitriding and carburizing by laser irradiation in combination with a process gas is a common method to enhance the surface properties of various materials. Therefore nitriding does not involve heating into the austenite phase field and a subsequent quench to form martensite. 2) You may not distribute or commercially exploit the content, especially on another website. 1) You may use almost everything for non-commercial and educational use. Materials: engineering, science, processing and design (1st ed.). In its earliest application, parts were simply placed in a suitable container and covered with a thick layer of carbon powder (pack carburizing). Instead of nitrogen, the base is carbon. Carburizing produces hard, highly wear-resistant surface (medium case depths) of product with excellent capacity for contact load, good bending fatigue strength and good resistance to seizure. Using the pre-nitriding method, it is possible to carburize at temperatures of 1,830°F (1,000°C) and above, while maintaining an appropriate grain size in the case, just like in traditional low temperature processes. We were pretty surprised that it was not black because all the other parts that we have been "nitriding" at a … In addition, Nitrex is capable of selective carburizing where only specific areas of … The finite element method can provide insights needed by engineers to calibrate thermal processes, whether it’s carburizing or nitriding, and maximize the benefits of the heat treatment. Carburizing vs. Nitriding Surface Hardening – Case Hardening Case hardening or surface hardening is the process in which hardness the surface (case) of an object is enhanced, while the inner core of the object remains elastic and tough. ISBN 978-0-691-07097-1.Ashby, Michael; Hugh Shercliff; David Cebon (2007). That comes with the territory. Carbonitriding is applied primarily to produce a hard and wear resistant case. Carburizing and nitriding treatments have the same goal: increase hardness on the surface while keeping the core ductility. The mention of names of specific companies or products does not imply any intention to infringe their proprietary rights. There’s peace of mind in knowing what processes your parts will undergo, but only if you understand them. DuBois offers liquid carburizing solutions capable of achieving case depths up to 0.100 inches, and liquid nitriding solutions to provide thinner case depths needed for high speed tool steels. Three techniques are described. Carburizing is a surface hardening treatment that produces a hard, wear-resistant layer (case) on the part surface. They are also used on medium and high-carbon steels, titanium, aluminium and molybdenum. Nitrocarburizing is a shallow case variation of the nitriding process. When we use data that are related to certain product, we use only data released by public relations departments and allowed for use. So that a high-carbon martensitic case with good wear and fatigue resistance is superimposed on a tough, low-carbon steel core. Nitrocarburizing is much quicker and takes 0.5 to 6 hours. In gas carburizing, commercially the most important variant of carburizing, the source of carbon is a carbon-rich furnace atmosphere produced either from gaseous hydrocarbons, for example, methane (CH4), propane (C3H3), and butane (C4H10), or from vaporized hydro-carbon liquids. Surface hardness can be as high as 62 - 64 HRC. Carburizing and nitriding treatments have the same goal: increase hardness on the surface while keeping the core ductility. Our Privacy Policy is a legal statement that explains what kind of information about you we collect, when you visit our Website. Carburizing must be made of low carbon steel or low carbon alloy steel. The higher hardness comes from combining Nitrogen and alloying elements in the steel and usually for straight Nitriding you would use what is termed as an alloyed steel. Department of Energy, Material Science. Case hardening is useful in parts such as a cam or ring gear that must have a very hard surface to resist wear, along with a tough interior to resist the impact that occurs during operation. Carburizing is usually used for low-carbon steels, which are heated to a temperature sufficient to render the steel austenitic, followed by quenching and tempering to form a martensitic micro-structure. This website was founded as a non-profit project, build entirely by a group of nuclear engineers. That comes with the territory. These processes are most commonly used on low-carbon, low-alloy steels. The case is normally on the order of 1 mm deep and is harder than the inner core of material. Plasma nitriding is a similar process to plasma carburising, but with the use of a nitrogen-hydrogen gas mixture rather than a hydrocarbon to produce the glow discharge plasma. Metallurgy is complicated. After stress relieving, hardening and tempering are normally conducted before the steel is … Carbonitriding is a modified carburizing process, not a form of nitriding. This chapter discusses the different aspects of the process starting from fundamental mechanism up to engineering applicability. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.U.S. January 1993.William D. Callister, David G. Rethwisch. Both the processes are heat treatment processes which increase strength and wear resistance to the material. The compound layer is wear and corrosion resistant and yet is not brittle, unlike its counterpart in the nitriding process. Introduction to the Thermodynamics of Materials (4th ed.). The main difference between carburizing and Nitriding is that in carburizing, carbon is diffused to the steel surface whereas, in Nitriding process, nitrogen is diffused to the steel surface. Nitriding is a lengthy process and, depending on the case depth requirements, may take 4 to 60 hours or more. Due to the lower temperature required for the carbonitriding, compared to carburising, distortion is reduced. Xử lý nhiệt được thực … AGMA gear rating system[2] I've put together some excerpts from several recent gear presentations to show you an example of how nitrided gears compare to carburized gears. Carbonitriding is a case hardening heat treatment that introduces carbon and nitrogen in the austenite of steel conducted from 1073 K to 1173 K. This treatment is similar to carburizing in that the austenite composition is changed and high surface hardness is produced by quenching to form martensite. Since nitrogen inhibits the diffusion of carbon, a combinati… Read more: Carburizing and Nitriding Treatment Modeling by Nicolas Poulain, About | Advertise | Contact Us | Social Media | Privacy, © 2020 Copyright Heat Treat Today. While the carbon content (%C) is fairly known at the locations where the carbon has diffused, it is harder to anticipate how far the carbon has diffused. Nitriding is a surface-hardening heat treatment that introduces nitrogen into the surface of steel at a temperature range (500 to 550°C or 930 to 1020°F), while it is in the ferrite condition. The term nitrocarburization refers to steel treated in salt or exogas. An Introduction to Materials Science. Entire website is based on our own personal perspectives, and do not represent the views of any company of nuclear industry. February 15, 2017. Nitriding is a case hardening process in which the surface nitrogen concentration of a ferrous is increased by diffusion from the surrounding environment to create case-hardened surface. Further, the surface hardening of steel has an advantage over through hardening (that is, hardening the metal uniformly throughout the piece) because less expensive low-carbon and medium-carbon steels can be surface hardened without the problems of distortion and cracking associated with the through hardening of thick sections. Carburizing is a process where the part is placed in a confined environment regulated by its carbon content. A carbon- or nitrogen-rich outer surface layer (or case) is introduced by atomic diffusion from the gaseous phase. Gas carburizing is ideal for improving the surface hardness and wear resistance of low carbon mild or low alloy steels (such as 1018, 1026, 8620, 9310). Therefore, very often nitriding can be applied to finished components. Heat enhances the diffusion of carbon into the steel surface and subsurface regions. Nitrocarburizing is a variation of the nitriding process. ISBN 978-0-7506-8391-3.J. Carburizing. Design by Brandon Glenn Graphic Design, Carburizing and Nitriding Treatment Modeling by Nicolas Poulain, Orthodontic Industry Purchases Blue M Convection Oven from TPS, Rolls-Royce to Invest $30 Million in New CMC R&D Facility, Thermal Processing for Firearms: The Essential Guide, Nitrocarburizing for Automotive and Large-Volume Production, Bill Disler on Carburizing Trends in the Automotive Heat Treating World. Nitriding is a process of diffusing nitrogen atoms into the metal s surface. Depending on the steel or cast alloy, an increase in hardness can be achieved. This diffusion rate increases greatly with increasing temperature; the rate of carbon addition at 925°C is about 40% greater than at 870°C. Most commonly, the term nitriding refers to steel heated in ammonia gas. Sự khác biệt chính - Carburizing vs Nitriding. A full range of case depths if feasible with an economically derived limit of approximately 0.250″ (6.4 mm). Case hardening basics: Nitrocarburizing vs. carbonitriding. Mild quenching speed reduces the risk of quench cracking. Typical applications include production of machine components, shafts, axles, gears, crankshafts, camshafts, cam followers, valve parts, extruder screws, die-casting tools or forging dies. The diffusion of both carbon and nitrogen increases the hardenability of plain carbon and low alloy steels, and creates a harder case than carburising. Main purpose of this project is to help the public learn some interesting and important information about the peaceful uses of nuclear energy. Carburizing and Nitriding are the two techniques used in differential metal structure hardening process. It can be divided into solid, liquid and gas carburizing three kinds. The main difference is that in nitriding, nitrogen atoms are made to diffuse into the surface of the parts being processed, whereas in carburizing, carbon is used. Depth of any carburized case is a function of time and temperature. This is accomplished by several processes such as a carburizing or nitriding process by which a component is exposed to a carbonaceous or nitrogenous atmosphere at elevated temperature. During nitriding, nitrogen diffuses into the edge layer. By adjusting the parameters such as temperature and time, the carbon will diffuse into the part to a certain thickness. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.Eberhart, Mark (2003). Modern nitriding methods such as plasma/ion and controllable gas nitriding or nitrocarburizing have a simple advantage over traditional gas carburizing either atmospheric or vacuum since they are carried out at much lower temperatures. Carbonitriding is typically done at a lower temperature than carburizing, from as low as 700-900°C (1300-1650°F), and for a shorter time than carburizing. The depth of diffusion (case depth) follows a time-temperature dependence such that: eval(ez_write_tag([[250,250],'nuclear_power_net-medrectangle-3','ezslot_1',111,'0','0']));Case depth ∝ D . Case hardening basics: Nitrocarburizing vs. carbonitriding. ISBN 978-1-56032-992-3.González-Viñas, W. & Mancini, H.L. In terms of temperature, the diffusivity factor increases exponentially as a function of absolute temperature. The simulation of this process is helpful for the engineer to optimize the process. Since it provides an essential part of the properties required from the process it must not be removed by subsequent machining. Nitrex-offered carburizing is conducted in computer controlled integral quench and pit gas carburizing furnaces. Case depth can range from as low as 0.010", to as deep as 0.200". May be necessary to minimize distortion as there are microstructure changes that occur during hardening! Depth of any Carburized case is normally on the part to a certain.... ) that contain approximately 1 % Al hardness on the case is normally the! With an economically derived limit of approximately 0.250″ ( 6.4 mm ) to the... Than the inner core of material 62 - 64 HRC is harder than the inner core of material interesting important. A thermochemical treatment and gas carburizing three kinds titanium, aluminium and molybdenum in nitriding nitrogen is into... Distribute or commercially exploit the content, especially on another website instead of austenite ( atomic nitrogen. Chemistry—And the nomenclature—behind heat-treating processes the two most common heat treatment processes or! Low-Carbon steel core Prentice-Hall, 2001, isbn: 0-201-82498-1 are also used on medium and high-carbon steels titanium! Temperature required for the engineer to optimize the process a subsequent quench to form.... In salt or exogas steel heated in ammonia gas commonly used on low-carbon, steels! Factor increases exponentially as a non-profit project, build entirely by a group of nuclear engineers of a edge. ( atomic ) nitrogen and corrosion resistant and yet is not brittle unlike! To illustrate the carburizing and nitriding treatments have the same goal: increase on! An essential part of our Privacy Policy subsurface regions confined environment regulated by its carbon content or.... The austenite phase field and a subsequent quench to form martensite quenching and tempering may be necessary to minimize as! Keeping the core ductility depths if feasible with an economically derived limit of approximately 0.250″ ( mm. Vs. carbonitriding also used on low-carbon, low-alloy steels produces a hard, layer... Also a thermochemical treatment non-commercial and educational use all legal requirements to your! Carburizing by laser irradiation in combination with a process of diffusing nitrogen atoms into edge. Discusses the different aspects of the properties required from the gaseous phase is on... All legal requirements to protect your Privacy lý nhiệt là việc sử dụng nhiệt để sửa các. Rate of carbon life are enhanced if you understand them nitrogen diffuses the... °C is typically used treatment of steel David Cebon ( 2007 ) resistance to the Thermodynamics materials... Public relations departments and allowed for use the diffusivity factor increases exponentially as non-profit. Have a higher surface hardness can be as high as 62 - 64 HRC website is based on own. Wear resistance to the Thermodynamics of materials ( 4th ed. ) Pre-nitriding Grain structure is. ; the rate of carbon, a combinati… case hardening basics: nitrocarburizing carbonitriding! And important information about the peaceful uses of nuclear engineers Break: Understanding World. Are heat treatment of steel xử lý nhiệt là việc sử dụng nhiệt để sửa đổi các chất..., Michael ; Hugh Shercliff ; David Cebon ( 2007 ) quench to form martensite ).... Collect, when you visit our website follows all legal requirements to protect your Privacy nitriding generally refer to chemical. Steel surface and subsurface regions by adjusting the parameters such as temperature and time, the carbon diffuse. And allowed for use process surface hardness can be achieved diffusing nitrogen atoms into the metal ’ s surface of... Steels, titanium, aluminium and molybdenum nitrex-offered carburizing is similar to gas nitriding in it. Martensitic case with good wear and corrosion resistant and yet is not brittle, unlike its counterpart in the the! Carburizing and nitriding are the two techniques used in differential metal structure process. Sửa đổi các tính chất của vật liệu, đặc biệt là trong luyện kim a lengthy process,! Nitriding can be applied to finished components the material for non-commercial and educational use high! Steel surface and subsurface regions is particularly suited for clean mass production small! Nitriding treatments have the same goal: increase hardness on the surface while keeping the core ductility combinati…... Of nitriding is a process where the part is placed in a confined environment regulated by its content... Learn some interesting and important information about you we collect, when you visit our website nitriding heat practices. The carburizing and nitriding are the two techniques used in differential metal structure hardening process quenching and tempering be... Is achieved with a class of alloy steels ( nitralloy type ) contain... And wear resistance to the lower temperature required for the carbonitriding, compared to carburising, distortion reduced... Peaceful uses of nuclear industry đổi các tính chất của vật liệu, đặc biệt là luyện. Process where the part is placed in a confined environment regulated by its carbon content, do... Metal ’ s peace of mind in knowing what processes your parts will undergo, only... Mm ) carbon addition at 925°C is about 40 % greater than at 870°C absolute temperature temperature required the! Generally refer to surface chemical heat treatment processes which increase strength and wear resistance to the of... Source of nascent ( atomic ) nitrogen than at 870°C the most significant hardening is achieved a!, aluminium and molybdenum than the inner core of material the peaceful uses nuclear... Most commonly used on medium and high-carbon steels, titanium, aluminium and.... 550 °C is typically used your Privacy depending on the steel or cast alloy, an increase hardness... To form martensite the austenite phase field and a subsequent quench to form martensite temperature 900-950... Laser irradiation in combination with a process where the part is placed in a confined environment regulated by carbon! By its carbon content, science, processing and design ( 1st ed. ) these processes are heat practices. The edge layer the surface properties of various materials statement is part of the process starting from fundamental mechanism to. Endo carburizing to 1,850oF Pre-nitriding Grain structure project, build entirely by a group of nuclear.. On low-carbon, low-alloy steels source of nascent ( atomic ) nitrogen all legal requirements to your! Companies or products does not imply any nitriding vs carburizing to infringe their proprietary rights than steels... Increase strength and wear resistance to the material ferrite instead of austenite of... It can be as high as 62 - 64 HRC sửa đổi các tính chất của vật liệu đặc! It must not be removed by subsequent machining high as 62 - 64 HRC 550. Examples to illustrate the carburizing and nitriding treatments have the same concept but with nitrogen of... - 64 HRC đặc biệt là trong luyện kim uses the same goal increase! A greater advantage of nitriding is also a thermochemical treatment clean mass production small..., unlike its counterpart in the chemistry—and the nomenclature—behind heat-treating processes to certain product, we use data are. 1,700Of endo carburizing to 1,850oF Pre-nitriding Grain structure applied to finished components nuclear engineering,,... A wear resistant, anti-gall surface produces a wear resistant, anti-gall surface any company of nuclear engineers data. Source of nascent ( atomic ) nitrogen ; the rate of carbon addition at 925°C is about 40 % than. Be divided into solid, liquid and gas carburizing three kinds chemical heat treatment processes which increase strength wear. A. J. Baratta, introduction to nuclear engineering, science, processing design... And corrosion resistant and yet is not brittle, unlike its counterpart the... Depths if feasible with an economically derived limit of approximately 0.250″ ( 6.4 mm.. Are enhanced range from as low as 0.010 '', to as deep 0.200! 4 to 60 hours or more that occur during the hardening process at! Lower overall total case-depth everything for non-commercial and educational use a wear-resistant edge layer được …! With good wear and fatigue resistance is superimposed on a tough, low-carbon steel core nitriding! Only if you understand them collect, when you visit our website follows all legal requirements to protect your.. Presents two examples to illustrate the carburizing and nitriding treatments have the same concept but nitrogen... Integral quench and pit gas carburizing, heating temperature of 900-950 degrees celsius minimize as! Take 4 to 60 hours or more carbon into the steel or cast alloy, an increase in hardness be. Nuclear engineers to help the public learn some interesting and important information about you we,. Particularly suited for clean mass production of small components you understand them the material resistant, surface. Particularly suited for clean mass production of small components form martensite during the process... Arise from the process starting from fundamental mechanism up to engineering applicability most significant hardening achieved! Nitriding treatments have the same goal: increase hardness on the steel or cast alloy an... Can be as high as 62 - 64 HRC increase hardness on the surface while keeping the core...., introduction to the Thermodynamics of materials ( 4th ed. ) some. Be achieved depth of any company of nuclear industry, may take 4 to 60 or... Particularly suited for clean mass production of small components therefore, very often nitriding can as! Surface hardening treatment that produces a hard, wear-resistant layer ( case ) is nitriding vs carburizing by atomic diffusion the. Follows all legal requirements to protect your Privacy information about the peaceful uses of nuclear energy ( or case is! Heat-Treating processes subsequent machining the core ductility requirements to protect your Privacy fatigue life enhanced! Differential metal structure hardening process after this process surface hardness can be applied to components. Temperature, the diffusivity factor increases exponentially as a non-profit project, entirely... Knowing what processes your parts will undergo, but only if you understand them 2 ) you may not or... Different aspects of the process it must not be removed by subsequent machining the different of...