Salt bath nitriding. It is believed that this may explain the excellent test results of the 304 stainless steel at 750° F. and the somewhat decreased corrosion resistance at 850° F. and the much poorer corrosion resistance at 950° F. Thus, if a sufficient case can be provided at below about 815° F., a hardened surface can be provided without degradation of the corrosion resistance characteristics. Thus, when greater-depth than that can be obtainable with salt-bath nitriding is required, gas-nitriding … This result may be acceptable. Liquid nitriding increases wear resistance properties from 200% to 1000% , depending upon composition of base metal and fatigue strength by 20% to 100%. There is no maximum amount of carbonate that needs to be present, provided, however, that the amount is within the soluble range of carbonate. The melting temperature of this composition is below 750° F. However, a fluid bath at 750° F with significant carbonate can be achieved with 48% CNO— and, since lower nitrocarburizing temperatures have not been shown to be useful with stainless steel, 48% CNO— is the preferred weight percentage of CNO—. With respect to hardenable grades of stainless steels, such as the 400 series stainless steel, corrosion resistance in the hardened and tempered condition can be increased and a compound layer formed on the surface at a temperature low enough to prevent degradation of the core hardness in certain conventional hardened and tempered conditions of the stainless steel part. Del-Quench™ Standard is a proprietary salt consisting of alkaline nitrate and hydroxide compounds. Ferritic nitrocarburizing or FNC, also known by the proprietary names Tenifer, Tufftride and Melonite as well as ARCOR, is a range of proprietary case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures during a salt bath. All salt bath nitriding performed at temperatures from 1000° F. to 1166° F. were performed in a fused salt bath having about 38% by weight of cyanate ions and at least 1% by weight of carbonate ions, again with the ratio of potassium to sodium being about 3.9 to 1.0. The samples were immersed in salt bath for ten different times (1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h ) at 580 °C, salt bath nitriding treatments applied to 42CrMo4 steel are given in Fig. In FNC and Gas Nitriding, the source of Nitrogen comes from Ammonia. Liquid nitriding is the process of diffusion enrichment of the surface layer of a part with Nitrogen provided by a molten cyanide base salt (extremely toxic substance). A composition for nitrocarburizing stainless steel parts and a method for producing a nitride or hard case on such parts using the composition, are provided. As can be seen in FIG. PVD Coatings PVD coatings involve the deposition of thin (2-10 microns; 0.0001" – 0.0004") films on the surface of tools and components. However, with the same treatment of austenitic stainless steels at 1075° F. to increase the compound layer, a degradation of the corrosion resistance results. Low temperature nitriding salt and method of use. The workpiece is immersed in the fused bath and left in until a satisfactory compound layer or case is formed. Assignors: EASTERDAY, JAMES R., PILZNIENSKI, JOHN F. Assigned to H.E.F. At nitrogen contents greater than 8%, the equilibrium reaction product is ε compound, Fe 3 N. Nitrided cases are stratified. Liquid nitriding increases wear resistance properties from 200% to 1000% , depending upon composition of base metal and fatigue strength by 20% to 100%. ... alloy composition and the pre-nitriding steel microstructure. providing a fused bath of alkali metal cyanate, and alkali metal carbonate, wherein said cyanate ion is present in a weight percentage of greater than 45% and less than 55.2%, maintained at a temperature of between 750° F. and 950° F., and immersing a workpiece in said bath for a sufficient time to form a hard case thereon. It is estimated that this file hard surface was probably about HRC 65 (R. Further examination of the 950° F. and 1075 ° F. test specimens disclosed a dark microstructural phase. The salt bath composition for the improved nitrocarburizing bath, which is useful at temperatures between about 750° F. and about 950° F., comprises an alkali metal cyanate and an alkali metal carbonate, wherein the cyanate ion is present in a weight percentage of greater than 45% and less than 53%, preferably between 48% and 50%, and more preferably at about 48%. Salt baths presents dangers to the environment and to the personal safety of the operators. Again, the composition of the salt bath for those specimens treated at 750° F. to 950° F. was a salt bath according to the present invention, including alkaline metal cyanate with 48% cyanate ion and at least 1% carbonate ion with the potassium to sodium ratio being 3.9 to 1.0. Thus, a benefit is derived in using the present invention in treating austenitic grade stainless steels in that a hardened case can be provided without sacrificing the corrosion resistance and, in the case of hardenable stainless steel, it is possible to maintain the corrosion resistance obtained at normal nitrocarburizing temperatures while not adversely affecting the core hardness in the hardened and tempered condition. Nitriding technology has gone a long way, from the old gas nitriding to the relatively recently developed plasma nitriding. It provides similar advantages as gas nitriding. Thus, nitriding is similar to carburizing in that surface composition is altered, but different in that nitrogen is added into ferrite instead of austenite. However, as has been noted previously, in the heating of austenitic grade stainless steel, there are two transition temperatures that are dependent on alloy composition of the stainless steel which have been identified in this lower range of temperatures. With respect to the 304 stainless steel, specimens were salt bath nitrided in the as-processed annealed condition. Thus, when greater-depth than that can be obtainable with salt-bath nitriding is required, gas-nitriding … USA;REEL/FRAME:026719/0538. DNS team members have a wealth of experience in salt bath nitriding and understand the importance of starting your nitriding process with high quality salts. The outside layer is called a compound layer (or white layer) and its thickness generally falls between zero and 0.001” (25 µm). In an alkali metal cyanate mixture, with a potassium to sodium ratio of about 3.9 to 1 by weight, what appears to be a eutectic composition forms. The workpiece is immersed in the fused bath and left in there for a time, typically from about two hours to about eight hours until a satisfactory compound layer or case is formed. Because the molten salts are diffused with anhydrous ammonia, a new bath does not require aging and may be put into immediate The theoretical maximum of CNO— is about 55.2 weight percent, at which percentage there is no carbonate. Liquid Nitriding: It is a nitriding process using molten salt baths containing cyanides or cyanates in range of 510 to 580°C. The process Nitriding is a diffusion process and not a deposition process. conversion coatings, passivation of metals using liquids, e.g. The surface of the four hour specimen appeared to be file hard. In performing the test, the test specimens were immersed in the fused bath at various temperatures for various times and then various properties of the test specimens were measured, such as case hardness, case depth and, in the case of hardenable stainless steel, core strength of the specimen. As used herein, the term “nitriding” refers to forming a surface layer or compound layer (CL). Could be observed that the surface hardness of AISI 1045 steel is increased up to 50% by the salt bath nitriding process at … 4 is a set of curves of depth of the contact layer or case formed using various temperatures and various salt bath nitriding compositions at various times on various samples of 416 stainless steel; and. Tools and small components are often liquid-nitrided. However, comparable treatment of austenitic stainless steels is known to reduce resistance to corrosion. Thus, by treating the part at a temperature of 950° F., which is 125° F. below a normal salt bath treatment of 1075° F., a case can be established which provides at least as good corrosion resistance as at higher temperature nitrocarburizing at shorter times. According to the present invention, a composition for nitrocarburizing stainless steel parts and a method for producing a nitride or hard case on such parts using the composition, sometimes referred to as salt bath nitriding, are provided. Similar tests were performed on 316 grade stainless steel, which gave results similar to the results of the tests performed on the 304 grade stainless steel, except that there was no decrease of corrosion resistance at temperatures as high as 850° F. It is believed that this is because molybdenum is present in 316 grade stainless steel and has a stabilizing effect on the expanded austenite. The phases formed within this surface layer are epsilon (e) and gamma prime (g¢). Nitriding. The processes are named after the medium used to donate. With austenitic stainless steel, the piece is immersed from about four hours to about six hours at temperatures between about 750° F. and about 950° F., preferably between 750° F. and 850° F. to maintain corrosion resistance. Gas nitriding is not restricted but normally a practically reasonable time of 90- 98 hours is not exceeded. The best results are achieved with austenitic stainless steel wherein the piece is immersed from about three hours to about eight hours at temperatures between about 750° F. and about 850° F. With temperatures above 850° F. to 950° F., corrosion resistance is significantly reduced. In fact, increasing the temperature of the salt bath to about 1166° F. while increasing the depth of the compound layer still resulted in significant degradation of the corrosion resistance of the austenitic stainless steel. For salt bath nitriding, mainly cyanides (sodium cyanide or potassium cyanide) and cyanates (sodium cyanate or potassium cyanate) are used. PROCESS AND TECHNICAL DETAILS. FIG. It has been found that, as the temperature is lowered below 1075° F., the amount of carbonate that can be retained in solution in the bath decreases, thus the amount of CNO— necessitating excess carbonate present in a conventional bath, or starting with a lower initial percent of carbonate, a lower melting point of the salt can be achieved. Manufacturers and Suppliers of Nitriding Chemicals, Nitriding Salt, Heat Treatment Chemicals / Salts, Mumbai, India It can form a solid solution with ferrite at nitrogen contents up to about 6%. drive chain etc. The nitriding process (Fig. Even at temperatures up to 850° F., corrosion resistance is improved over nitrocarburizing at temperatures above 950° F. Diffusion characteristics of the 304 stainless steel resulting in the “compound layer” CL within the 750° F.-1166° F. temperature range were determined by measurement of the “compound layer” CL. Modern practitioners have perfected nitriding into several sub-processes: gas nitriding (the most widely used), salt bath nitriding, and plasma nitriding. Increasing the salt bath temperature to 850° F. resulted in a decided decrease in corrosion resistance, dropping to approximately 600 hours exposure. Nitriding is a popular case hardening technique renowned for the qualities it delivers at relatively low process temperatures. We Sai Chamtech take this opportunity to introduce ourselves as a manufacturer of Nitriding Salts and Automotive Chemicals from the state of Maharashtra (India). A surface exposed to a nitriding medium will generally form two distinct layers. This tool will be designed to predict the nitride profile as well as the nitrogen concentration profile (i.e. Salt Bath Nitriding/Nitrocarburizing was originally created as an alternative to gas nitriding that would produce a more uniform case through surface contact between the substrate and liquid salt. For the 304 stainless, the first is at T1, which occurs at a temperature of about 815° F. The higher transition temperature, known as T2, occurs at about 905° F. It has been postulated that, below 815° F., a microstructural phase termed as ‘S’ phase and defined as expanded austenite exists totally, and provides excellent corrosion resistance. The composition includes alkali metal cyanate and alkali metal carbonate, wherein the cyanate ion (CNO—) is present in a weight percentage of greater than 45% and less than 53%. The bath is used in a fused condition, as indicated above, between about 750° F. and about 950° F. It has been found that the higher the cyanate content, the lower the melting temperature of the salt, such that the cyanate content in the range of greater than 45% allows the bath to be molten and eventually homogeneous at temperatures between 750° F. and 950° F. With the cyanate content at 45% or below, it is difficult to maintain a homogeneous molten salt, especially in the lower part of the range of 750° F. to 950° F. The workpieces are immersed in the fused bath and a nitride or a hard microstructural phase (sometimes referred to as a “compound layer”) is formed. Salt bath nitriding —also known as ferritic nitrocarburizing (FNC)— is one of the most popular ways to achieve these results, but it isn’t the only way. In the metallographic analysis of any salt bath nitride candidate, ... Nitriding Depth and Hardness. Salt bath nitriding is a thermochemical process in which nitrogen and carbon are diffused simultaneously into the surface of the material. has pins, sleeves, rollers, and inner and outer plates all of austenitic stainless steel and surface coating formed by nitrifying process, Salt bath ferritic nitrocarburizing of brake rotors, Fin tube assembly for air cooled heat exchanger and method of manufacturing the same, Steel for nitrocarburization, nitrocarburized components, and production method for same, Founded salt baths for nitriding steel mechanical parts, and method for implementing the same, friction elements particularly resistant to wear by abrasion, Salt bath and method of nitriding steel and cast iron, Process for the treatment of ferrous metal parts to improve their resistance to wear and galling, Process for nitriding iron and steel in salt baths regenerated with triazine polymers, Method of surface hardening stainless steel parts, Method and device for removing alkali nitrite from nitrate salt baths. 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