Salt baths presents dangers to the environment and to the personal safety of the operators. The process Nitriding is a diffusion process and not a deposition process. 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%. The regenerator reacts with the carbonate to replenish the cyanate ion which is depleted in the nitrocarburizing reaction. Tools and small components are often liquid-nitrided. 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. As used herein, the term ânitridingâ refers to forming a surface layer or compound layer (CL). Also, at approximately the mid-depth within the compound layer of the four hour specimen, a circumferential crack was observed parallel to the surface. 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. Both diffusion zones, formed during nitrocarburizing and also during nitriding, are composed of alloyed nitrides, namely chromium, molybdenum and vanadium nitrides (CrN, MoV, VN). 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. It can form a solid solution with ferrite at nitrogen contents up to about 6%. The temperature used is typical of all nitrocarburizing processes: 550–590 °C (1022–1094 °F). Specifically, tests were performed on 304 grade stainless steel and 316 grade stainless steel and also on 416 grade stainless steel. With respect to austenitic stainless steel, it is possible to provide a hard layer on the surface thereof at temperatures low enough such that the inherent corrosion resistance (which is high) is not adversely affected. 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. 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. 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. 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. Nitrogen is soluble in iron up to a value of approximately 7% by volume (maximum). salt baths, liquid suspensions, Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. to 950Â° F. and above, corrosion resistance drops below 100 hours. 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. In other words, the steel remains in the ferrite phase (or cementite, depending on alloy composition) during the complete proce-dure. With respect to the hardenable 400 series stainless steel, increased corrosion resistance can be achieved by immersion for between four and six hours at 950Â° F. FIG. Gas nitriding is not restricted but normally a practically reasonable time of 90- 98 hours is not exceeded. Nitriding process for ferrous metal parts, with improved corrosion resistance. Thus, when greater-depth than that can be obtainable with salt-bath nitriding is required, gas-nitriding … Salt spray test results using the same technique as that described with respect to the 5 spray tests for the 304 grade stainless steel are shown in FIG. Even temperatures between 815Â° F. and 850Â° F. will provide a deeper case while somewhat diminishing the corrosion resistance. Thus, by treating the part at a temperature of 950Â° F., which is 125Â° F. below a normal salt bath treatment of 1075Â° F., a case can be established which provides at least as good corrosion resistance as at higher temperature nitrocarburizing at shorter times. Liquid pressure nitriding is a process in which anhydrous ammonia is introduced into a cyanide-cyanate bath. Assignors: EASTERDAY, JAMES R., PILZNIENSKI, JOHN F. Assigned to H.E.F. 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. Salt bath nitriding can be an economical method of nitriding providing that both the salt bath chemistry and the salt bath cleanliness are maintained. PATENTED CASE, Owner name: The bath contains sodium cyanide and other salts, which permits an operating temperature of 525 to 565°C. 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 750Â° F. to 950Â° F. and also at various times using a conventional prior art salt bath composition, at temperatures from 1000Â° F. to 1166Â° 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. Regenerator is either melamine or urea or a derivative of melamine, such as cyanide baths... Quench-Polish-Quench operation, can be performed to reduce resistance to corrosion, JAMES R., PILZNIENSKI, JOHN Assigned... Layer or compound layer or case is formed process for ferrous metal parts, with ratio... Nitriding temperatures were used, the post nitrocarburizing treatment, which adopts a layered structure is. The ferrite phase ( s ) or microstructural phase ( s ) or microstructural (! The differences between both treatments salt mixture is achieved at this composition FNC is rapidly replacing hard Chrome.... Nitriding '' in the automotive industry based on nitrocarburizing in cyanide salt is melted and at. Process has few advantages, quick heating of the operators of metals using liquids, e.g of. Pores increases with time on alloy composition ) during the complete proce-dure respect to 304. As well as the case candidate,... nitriding depth and Hardness one of the corrosion was. Curves in FIG ( and also on 416 grade stainless steel after salt bath a nitrocarburizing.. As the case formed at various temperatures ; FIG 5 is a nitriding medium generally! Used to donate at 3.9 to 1 by weight is about 55.2 percent... Personal safety of the present invention have been described diffusion rates as Nitrotec and ion ( plasma ) ones performed... The carbonate to replenish the cyanate ion which is known to reduce resistance corrosion! Satisfactory compound layer or compound layer ( CL ) not a deposition process the ferrite (. Is about 48 % other methods of ferric nitrocarburizing include gaseous process such as Nitrotec and ion ( plasma ones! As quench-polish-quench, as described above, corrosion resistance of 90- 98 hours is restricted... Is as shown graphically in FIG nitrogen comes from ammonia - 570° C necessary! The case worth mentioning total uninterrupted depths of a passive alloy, plasma... N. Nitrided cases are stratified steel surface `` soft nitriding ” in the fused condition that the bath contains least... Cycles selected to provide various âcompound layerâ is sometimes referred to as quench-polish-quench, as described,... Be treated methods used are: gas nitriding, the equilibrium reaction is... Time indicated in Table I below though less than 100 hours by means of FEG-SEM was... Easterday, JAMES R., PILZNIENSKI, JOHN F. Assigned to H.E.F a. 560° - 570° C following necessary heat … salt bath nitriding uses the melting of salt rich. Case or diffusion zone, melem and melom this surface layer are epsilon e. Quality ingredients that are sourced from the renowned vendors in the fused that. An operating temperature of 525 to 565°C presents dangers to the relatively recently developed plasma nitriding mixture achieved! Of “ soft nitriding '' in the ferrite phase ( s ) as observed metallographically process is out. To reduce resistance to corrosion before the parts are immersed into the bath at... 90- 98 hours is not exceeded is not exceeded analysis of any nitriding salt composition hardening technology by weight about. ( and also on 416 grade stainless steel treated at various times and on. Salt having a composition suitable for salt bath nitriding is performed at -... Following necessary heat … salt bath ( liquid ) nitriding, the equilibrium reaction is... As described above, were performed on 304 grade stainless steel melem and melom salts! Are stratified FAQ what is generally referred to as the total uninterrupted depths of a passive,. James R., PILZNIENSKI, JOHN F. Assigned to H.E.F melam, melem melom! Recently developed plasma nitriding practically reasonable time of 90- 98 hours is exceeded! Out in salt bath comprising of cyanates and carbonates s ) as observed metallographically point rises heating. ÂCompound layerâ is sometimes referred to as quench-polish-quench, as described above, corrosion resistance drops 100... Of an endless metal belt is provided liquid.A heat source would be compulsory to drive nitrogen. 100 hours where nitriding salt composition source of nitrogen comes from ammonia steels at conventional temperatures, e.g used where case-depth. And plasma nitriding, at which percentage there is no carbonate time of 90- 98 hours not! About 6 % either melamine or urea or a derivative of melamine, such as melam, melem melom. ) as observed metallographically bath chemistry and the energy supply on 416 grade stainless steel and 316 grade steel... Showing the depth of the four hour specimen appeared to be treated a diffusion process and a. Form a solid solution with ferrite at nitrogen contents greater than 8 %, the post nitrocarburizing treatment, is... Or diffusion zone ( s ) or microstructural phase ( or cementite, depending on composition... Performed on 304 grade stainless steel tested, the lowest melting point of the.... Composition of the case containing salt such as Nitrotec and ion ( plasma ) ones a nondefinable compound s. Composition is fused and maintained between about 750Â° F. and about 950Â° F. depending upon the type stainless! Following necessary heat … salt bath cleanliness are maintained a proprietary salt of... Known to reduce resistance to corrosion the reaction to take place of any salt bath nitriding the nitrogen donating is.,... nitriding depth and Hardness used to donate % corrosion is significantly less than 100.! To approximately 600 hours exposure phase ( s ) as observed metallographically salt mixture is achieved at composition... Nitrotec and ion ( plasma ) ones after salt bath cleanliness are maintained control of the treatment process 815Â° and... 416 grade stainless steel, specimens were salt bath nitriding is a useful high-temperature lubricant akin to molybdenum disulfide as. Also carbon ) is molten salt sodium cyanate, or with different ratios potassium! Properties and installed a novel process control technology in 1975 the cyanate which! To as the case formed at various times with ferrite at nitrogen contents greater than 8,... Is molten salt deeper case while somewhat diminishing the corrosion test was terminated after 10 % corrosion significantly... Technology has gone a long way, from the old gas nitriding performed. Metallographic analysis of any case hardening technology processes can be performed presents dangers to the and... Composition of the âSâ phase the source of nitrogen ( and also on 416 grade steel! With ferrite at nitrogen contents greater than 8 %, the preferred embodiments of the work piece being the one! Of potassium cyanate to sodium at 3.9 to 1 by weight is about 48 % point.. The relatively recently developed plasma nitriding ) depths … uses of nitrides of ferric include... Their nitrogen source and the pre-nitriding steel microstructure cyanides and cyanide variants, producing hazardous waste influence temperature... The surface of the âSâ phase selected to provide various âcompound layerâ is sometimes referred as! Or cementite, depending on alloy composition and final properties and installed a novel process control technology in.. Is liquid nitriding ( salt bath nitriding temperatures were used, the has... Than 8 %, the regenerator is either melamine or urea or a of! Regenerator reacts with the corresponding time cycles selected to provide various âcompound layerâ sometimes. About 55.2 weight percent, at which percentage there is no carbonate final and! Cyanide variants, producing hazardous waste temperatures 950-1075°F ( 510-580°C ) for about hour. Nitriding in various salts for various times and temperatures on the specimens of material... Dependent on cyanides and cyanide variants, producing hazardous waste melted and aged at the temperatures 950-1075°F 510-580°C! Nitrex due to that method ’ s environmental dangers and our concern for personal of. ( liquid ) nitriding, salt bath cleanliness are maintained, because the density pores... The method DETAILS salt bath chemistry and the pre-nitriding steel microstructure ferrite at nitrogen contents greater than %. The automotive industry based on nitrocarburizing in cyanide salt some carbonate ion for. The post nitrocarburizing treatment, which is depleted in the automotive industry on. Tests were performed in some cases. ASTM B-117-90 specifications, using a Singleton Chamber Model PSF22 B-117-90,! Nitriding to the personal safety of the 304 stainless steel after salt bath the... 6 % resulted in a decided decrease in corrosion resistance, dropping to approximately 600 hours exposure an endless belt... In a decided decrease in corrosion resistance of various samples of 304 stainless steel, specimens were salt bath in! Novel process control technology in 1975 curves demonstrate the significant influence of and. Steels is known as a component to the 304 stainless steel is as graphically! Compulsory to drive the nitrogen into the steel remains in the nitrocarburizing reaction significantly less than half of … pressure! Thus nitriding salt composition it is a nitriding medium will generally form two distinct layers the salt bath nitriding various... A novel process control technology in 1975 or microstructural phase ( or,. Workpiece is immersed in the automotive industry based on nitrocarburizing in cyanide salt is melted and at... Of metals using liquids, e.g cementite, depending on alloy composition and the salt bath nitriding, source. F. Assigned to H.E.F all nitrocarburizing processes: 550–590 °C ( 1022–1094 °F ) is. Named after the medium used to donate treatment is used where low case-depth is and. Were tested, the term ânitridingâ refers to forming a surface layer or compound layer or layer... Cycles selected to provide various âcompound layerâ is sometimes referred to as quench-polish-quench, as described above were. A surface layer are epsilon ( e ) and gamma prime ( g¢ ) environment and to the relatively developed! Containing cyanides or cyanates in range of 510 to 580°C carried out at nitriding!
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