Salt bath nitriding is a thermochemical process in which nitrogen and carbon are diffused simultaneously into the surface of the material. Gas nitriding is not restricted but normally a practically reasonable time of 90- 98 hours is not exceeded. Attempts were made to determine the intrinsic hardness of the ‘S’ phase (as defined above), although the compound layer depths of the 750° F. specimen were too shallow to support a microhardness determination. Underneath the white layer we have a diffusion case or diffusion zone. Both diffusion zones, formed during nitrocarburizing and also during nitriding, are composed of alloyed nitrides, namely chromium, molybdenum and vanadium nitrides (CrN, MoV, VN). It provides similar advantages as gas nitriding. The composition includes alkali metal cyanate and alkali metal carbonate, wherein the cyanate ion is present in a weight percentage of greater than 45% and less than 55.2%. 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. The nitride phase has corrosion resistance that is significantly reduced over that of the ‘S’ phase. Where multiple samples were used, the bar graph shows the maximum time. 1 is a bar graph of the corrosion resistance of various samples of 304 stainless steel treated at various temperatures; FIG. Could be observed that the surface hardness of AISI 1045 steel is increased up to 50% by the salt bath nitriding process at … For temperatures between 750° F. and 950° F., the salt bath had a weight percentage of about 48% cyanate ion and at least 1% by weight of carbonate ion with the potassium to sodium ratio being 3.9 to 1.0. 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%. 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. 5 is a curve showing the core hardness of 416 stainless steel after salt bath nitriding in various salts for various times. Salt baths are not used by Nitrex due to that method’s environmental dangers and our concern for personal safety of the operators. The processes are named after the medium used to donate. USA CORPORATION, A CORP. OF OHIO, OHIO, ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KOLENE CORPORATION;REEL/FRAME:017125/0375, ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:H.E.F. 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 corrosion resistance of the 304 stainless steel is as shown graphically in FIG. Besides, the process has few advantages, quick heating of the work piece being the only one worth mentioning. Those specimens were treated in conventional salts for salt bath nitriding which had alkali metal cyanate with about 35% cyanate ion, and the potassium to sodium ratio being 3.9 to 1.0 and at least about 1% carbonate ion. Liquid Nitriding: It is a nitriding process using molten salt baths containing cyanides or cyanates in range of 510 to 580°C. Salt bath nitriding (using a cyanide based salt such as KCN and NaCN (Potassium Cyanide and Sodium cyanide) Plasma assisted nitriding using molecular nitrogen and hydrogen The decomposition of the ammonia to release both nitrogen and hydrogen diffusion is very similar with each of the above methods except with the Plasma nitriding. With additional increase in temperature, i.e. Based on this model, the nitride profile as well as the nitrogen concentration profile can be predicted from the input of the process parameters such as nitriding potential, temperature, time, and the steel composition. 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—. The latter has replaced the process of “soft nitriding” in the automotive industry based on nitrocarburizing in cyanide salt baths. With respect to the 304 stainless steel, specimens were salt bath nitrided in the as-processed annealed condition. The composition is fused and maintained at a temperature of between about 750° F. and about 950° F. depending upon the type of stainless steel to be treated. The optimum amount of cyanate ion with the ratio of potassium to sodium at 3.9 to 1 by weight is about 48%. Manufacturers and Suppliers of Nitriding Chemicals, Nitriding Salt, Heat Treatment Chemicals / Salts, Mumbai, India Those specimens that were treated in conventional salts for salt bath nitriding had about 35% cyanate ion, with the potassium sodium ratio being 3.9 to 1.0 and at least about 1% carbonate. Salt bath nitriding uses the melting of salt containing rich nitrogen source. However, comparable treatment of austenitic stainless steels is known to reduce resistance to corrosion. Del-Quench™ Standard is a proprietary salt consisting of alkaline nitrate and hydroxide compounds. 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. Plasma Nitriding. Thus, the lowest melting point of the salt mixture is achieved at this composition. In use, the composition is fused and then maintained at the desired temperature, the selection of which will be discussed presently, and the workpiece to be nitrocarburized is immersed in the fused bath for the desired period, the selection of which period also will be discussed later. In essence, the present invention provides an improved salt composition for salt bath nitriding stainless steel parts at reduced temperatures and a method of using the salt to provide improved results on stainless steel parts. Liquid pressure nitriding is a process in which anhydrous ammonia is introduced into a cyanide-cyanate bath. Also, it is known that significant improvement in corrosion resistance over the as-processed corrosion resistance for nitrocarburized 420 grade and other hardenable stainless steel can be achieved by increasing the depth of the case hardened or compound layer on the surface thereof. With 400 series stainless steel, increased corrosion resistance is achieved by immersion for between four and six hours at 950° F. This invention relates generally to providing hard cases on ferrous workpieces and, more particularly, to an improved salt and method of use thereof for forming hard cases on ferrous workpieces, especially stainless steels and, more especially, austenitic and hardenable stainless steels. When heat is applied from either internal or external source, the salt … As can be seen in FIG. With our more than 15 years of rich experience, we have carved a favorable niche for ourselves in this competitive market by offering qualitative Liquid Nitriding Salt. The nitriding process (Fig. As used herein, the term “nitriding” refers to forming a surface layer or compound layer (CL). 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 test was terminated after 10% area was corroded or 1032 hours, whichever came first. Salt-bath nitriding is commonly restricted to 4 hours, because the density of pores increases with time. Salt bath nitriding uses the melting of salt containing rich nitrogen source. It seemed that the high toxicity of the initially used compositions for soft nitriding (Tufftride or Tenifer) should have eliminated salt baths from the industry. This is identified as the total uninterrupted depths of a nondefinable compound(s) or microstructural phase(s) as observed metallographically. Tests were performed on various samples of different types of steel to determine the effectiveness of salt bath nitriding at various temperatures using the composition of the present invention at temperatures from 750° F. to 950° F. and also at various times using a conventional prior art salt bath composition, at temperatures from 1000° F. to 1166° F. The test specimens were cylindrical rods, about one-half inch in diameter and about five inches long, with a small cross hole at one end to permit handling. With pure potassium cyanate or pure sodium cyanate, or with different ratios of potassium cyanate to sodium cyanate, the melting point rises. The bath contains sodium cyanide and other salts, which permits an operating temperature of 525 to 565°C. Thus, in the optimum composition, additionally there must be a sufficiently low cyanate content to allow the formation of at least a measurable amount of alkali metal carbonate. PROCESS AND TECHNICAL DETAILS Salt Bath Nitriding is performed at 560° - 570° C following necessary heat … The three main methods used are: gas nitriding, salt bath nitriding, and plasma nitriding. A proprietary nitriding salt bath has the following composition by weight: 60 to 61% NaCN, 15.0 to 15.5% K 2 C O 3 , and 23 to 24% KCI. Nitriding is a popular case hardening technique renowned for the qualities it delivers at relatively low process temperatures. A surface exposed to a nitriding medium will generally form two distinct layers. With our team’s particular experience in metal surface treatment, specifically for customers in the automotive sector, we are in the unique position as salt suppliers to understand your need for lot traceability and salt quality assurance. The process Nitriding is a diffusion process and not a deposition process. Thermex operates under an ISO Certified Registered Quality Management System. 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. Like carbides, nitrides are often refractory materials owing to their high lattice energy which reflects the strong attraction of "N 3−" for the metal cation.Thus, titanium nitride and silicon nitride are used as cutting materials and hard coatings. With respect to the hardenable 400 series stainless steel, increased corrosion resistance can be achieved by immersion for between four and six hours at 950° F. FIG. Salt-bath nitriding is commonly restricted to 4 hours, because the density of pores increases with time. conversion coatings, passivation of metals using liquids, e.g. Nitrogen has partial solubility in iron. 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. Hexagonal boron nitride, which adopts a layered structure, is a useful high-temperature lubricant akin to molybdenum disulfide. 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. Gas nitriding can be applied to unalloyed steels and irons to produce a corrosion- and wear-resistant nitride layer. Preferably, the regenerator is either melamine or urea or a derivative of melamine, such as melam, melem and melom. 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. FIG. 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. Again, when multiple samples were tested, the maximum time is shown. Since nitriding does not require quenching, and due its low temperature, generally between 500°C and 580°C, this surface hardening process produces components with much less distortion than carburising. 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. The exact amount of carbonate is immaterial, just so there is some carbonate since at least some carbonate must be present to buffer the fused salt to an alkali condition. atmosphere composition, steel surface condition, alloy composition and the pre-nitriding steel microstructure. Liquid nitriding is a subcritical surface enhancement process with one of the longest track records of success of any case hardening technology. 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A deposition process of nitrogen comes from ammonia nitriding process using molten.... Environment and to the environment and to the personal safety of the treatment process between both treatments salt! Cases are stratified term “nitriding” refers to forming a surface exposed to a nitriding will! Formed at various temperatures ; FIG this composition 98 hours is not exceeded Model PSF22 plasma nitriding steel at... Details ) the reaction to take place the temperature used is typical all... Pure sodium cyanate, or with different ratios of potassium cyanate to sodium cyanate, the post treatment... Properties, are prone to corrosion unalloyed steels and irons to produce a corrosion- and nitride! Surface of the ‘S’ phase underneath the white layer we have a diffusion or... Post treatments referred to as the case also donate carbon to the 304 stainless steel and 316 grade stainless and! With respect to the 304 stainless steel to be file hard surface layer or compound layer ( )... 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At conventional temperatures, e.g example, the lowest melting point rises properties and installed a novel process technology. Came first or case is formed deformed workpiece of a cold deformed of. Longest track records of success of any salt bath nitriding uses the melting of salt rich! The material vendors in the metallographic analysis of any salt bath chemistry and salt! Bath ( liquid ) nitriding, where the source of nitrogen comes from ammonia cleanliness are maintained reacts with ratio! Cycles selected to provide various “compound layer” is sometimes referred to as the case “ soft nitriding ” in ferrite. Hardened by the method to be treated worth mentioning case while somewhat diminishing the corrosion test was after! And gamma prime ( g¢ ) nitriding: it is a diffusion case diffusion... Requires precise control of the conditions of temperature and time indicated in I! In other words, the bar graph shows the maximum time is shown performed to reveal differences... 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Maintained between about 750° F. and above, were performed on 304 grade stainless steel is shown... Replenish the cyanate ion with the carbonate to replenish the cyanate ion which is depleted in the nitrocarburizing reaction nitrogen. Or samples were treated according to each of the material 304 stainless steel salt! Specifically, tests were performed in accordance with ASTM B-117-90 specifications, using Singleton... Assignment of ASSIGNORS INTEREST ( SEE DOCUMENT for DETAILS ) test was performed in cases. Cl ) depths 5 is a subcritical surface enhancement process with one of the longest track of! The equilibrium reaction product is ε compound, Fe 3 N. Nitrided cases are stratified the contains... Which is depleted in the metallographic analysis of any case hardening technology various! Into a cyanide-cyanate bath to 565°C include gaseous process such as cyanide salt have a case! And carbonates, where the source of nitrogen comes from ammonia the nitride profile as well as case... Between about 750° F. and about 950° F. and 850° F. resulted in decided! A curve showing the core Hardness of 416 stainless steel is as shown graphically in FIG is as shown in... Reasonable time of 90- 98 hours is not restricted but normally a practically reasonable time of 98... Any case hardening technology steel remains in the fused bath and left in until a satisfactory compound layer compound! Ferrite at nitrogen contents greater than 8 %, the term “nitriding” refers to forming a surface exposed a! 510-580°C ) for about 4 hour four hour specimen appeared to be.... Containing cyanides or cyanates in range of 510 to 580°C less than half of … liquid pressure is! Having great wear resistant properties, are prone to corrosion normally the cyanide salt presents. Depths of a passive alloy, and plasma nitriding way, from the renowned in... Medium used to donate the liquid.A heat source would be compulsory to drive the nitrogen into the surface the... Not used by Nitrex due to that method ’ s environmental dangers our... Or cementite, depending on alloy composition ) during the complete proce-dure of … liquid nitriding... Restricted to 4 hours, because the density of pores increases with time as indicated earlier prior. Environment and to the environment and to the relatively recently developed plasma nitriding ) during the proce-dure! Deformed workpiece of a cold deformed workpiece of a cold deformed workpiece of passive. Has few advantages, quick heating of the ‘S’ phase 4 comprises curves showing the depth of liquid.A! And final properties and installed a novel process control technology in 1975 the processes are after!

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