Iron Nitriding
10-17-05, 10:23 PM
#1
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Iron Nitriding
I have the equipment to regrind my irons but I don't want to take off what I can't put back on (Nitride). The problem is that there are many differnt nitride variations; titanium, boron, aluminum, chrome, silicon... what is used from the factory and does anyone know if success has had with any other industrial metal treatments?
10-18-05, 01:41 PM
#2
spoon!
Stock housings are gas nitrided, which is a type of case hardening and is different than a TiN (or whichever) coating. Ammonia's introduced into a furnace, disassociates, and deposits the nitrogens on the iron.
I know of people doing cermet coatings, and really have been meaning to look into getting things nitrided but... time and all.
Hope that helps some.
I know of people doing cermet coatings, and really have been meaning to look into getting things nitrided but... time and all.
Hope that helps some.
10-18-05, 07:37 PM
#4
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Thanks Kenku, I've been reading about JBH & scalliwag's stuff. For a streetported NA I just can't see spending that much $$ on coatings when I can have good as new for... well we'll have to see how much nitriding costs.
Good luck in the middle east BoostedRex
John
Good luck in the middle east BoostedRex
John
10-19-05, 07:19 AM
#5
Please somebody help!!!
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there's a company out of decatur, IL that does some sort of cryo treatment that is supposed to harden and damageproof parts. Don't know what they're called though.
10-19-05, 09:00 AM
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Gas Nitriding is available at a reasonable price, the cost comes in from the cost of shipping to the nitrider; then to a lapping shop {Nitriding Process can mildly "warp" the housing, due to the temps involved} and then shipping the housings back to you. It has been recommended to me, from my discussions with various builders to to a very small "clean-up lap to ensure a perfectly flat plate after nitriding.
Another point to consider, most nitriding providers charge buy the pound with a 125 lb min. charge.
Another point to consider, most nitriding providers charge buy the pound with a 125 lb min. charge.
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10-19-05, 10:38 AM
#8
spoon!
Hrm, so just have to get all of the junkyard scavenged irons ground and nitrided at the same time to get my money's worth. 
There's probably 125 pounds worth of them hanging around...
There's probably 125 pounds worth of them hanging around...
10-20-05, 12:52 PM
#9
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Thread Starter
$100 min charge, .002 deep. Should I go deeper?
I'll have to get some pics up of some NA exhaust inserts I've worked over.
torch the diffuser, grind it smooth, tig weld extra meat on the lip that faces toward the port then open the port and match the sleeve.
smooooth
I'll have to get some pics up of some NA exhaust inserts I've worked over.
torch the diffuser, grind it smooth, tig weld extra meat on the lip that faces toward the port then open the port and match the sleeve.
smooooth
10-21-05, 03:49 PM
#12
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Thread Starter
surface grinder with adequate coolant. I'm going to take very shallow slow to prevent heat build-up. It is extremly precise and makes a very smooth surface finish.
11-04-05, 10:43 PM
#13
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Thread Starter
Just checked the magnetic table of the grinder, Within a thou all the way around. 
I just finished porting so now it's time to get these irons flat again. Pics comming soon.
13B-RX3: chrome will not take the heat of combustion, not an option.
I just finished porting so now it's time to get these irons flat again. Pics comming soon.
13B-RX3: chrome will not take the heat of combustion, not an option.
11-06-05, 04:24 PM
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Liquid Nitriding is probably a better option. The one I use is done with sulphur in the process for self lubrication. Gas nitriding gives about 0.006" - 0.008" of hardness and liquid nitriding gives about 0.004" of hardness. The liquid nitriding process I have used does not cause distortion and the 0.004" will wear as good or better than 0.008" done in gas. The frost plugs should be left in and replaced after nitriding. The oil passage plugs on the front and rear plate should be removed, milled out and tapped to fit a 1/4" NPT plug prior to nitriding. This is necessary as the sulphur will stay in most of the openings and will have to be blasted with a pressure washer to dissolve and remove the residual sulphur.
11-06-05, 10:47 PM
#16
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Thread Starter
Glassman, thanks for the good info, I'll talk to the shop about availability, liquid sounds like the way to go. The metal treatment place said .002 is standard depth but deeper is available (gas nitriding). I was worried about warping as well, both grinding and nitriding. I am heading to this place on tuesday: http://www.abrasivebrokers.com/about.htm
to see about getting a proper wheel that will cut the best and produce the least heat. I am also going to resurface the surface grinder magnetic table while I'm at it just to get everything as precise as possible.
I just topped off the hydraulic system, oiled all the ways, and greased all the zerks, should be good to go soon enough.
to see about getting a proper wheel that will cut the best and produce the least heat. I am also going to resurface the surface grinder magnetic table while I'm at it just to get everything as precise as possible.
I just topped off the hydraulic system, oiled all the ways, and greased all the zerks, should be good to go soon enough.
11-07-05, 08:43 PM
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Originally Posted by patman
what is the hardness rating of the nitride compared to the base hardness of the castings?
11-07-05, 09:13 PM
#18
Nitriding
Abstract:
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. Thus, nitriding is similar to carburizing in that surface composition is altered, but different in that nitrogen is added into ferrite instead of austenite.
Because nitriding does not involve heating into the austenite phase field and a subsequent quench to form martensite, nitriding can be accomplished with a minimum of distortion and with excellent dimensional control.
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. Thus, nitriding is similar to carburizing in that surface composition is altered, but different in that nitrogen is added into ferrite instead of austenite. Because nitriding does not involve heating into the austenite phase field and a subsequent quench to form martensite, nitriding can be accomplished with a minimum of distortion and with excellent dimensional control.
The mechanism of nitriding is generally known, but the specific reactions that occur in different steels and with different nitriding media are not always known. Nitrogen has partial solubility in iron. It can form a solid solution with ferrite at nitrogen contents up to about 6%. At about 6% N, a compound called gamma prime (γ’), with a composition of Fe4N is formed.
At nitrogen contents greater than 8%, the equilibrium reaction product is ε compound, Fe3N. Nitrided cases are stratified. The outermost surface can be all γ’ and if this is the case, it is referred to as the white layer. Such a surface layer is undesirable: it is very hard profiles but is so brittle that it may spall in use. Usually it is removed; special nitriding processes are used to reduce this layer or make it less brittle. The ε zone of the case is hardened by the formation of the Fe3N compound, and below this layer there is some solid solution strengthening from the nitrogen in solid solution.
Principal reasons for nitriding are:
To obtain high surface hardness
To increase wear resistance
To improve fatigue life
To improve corrosion resistance (except for stainless steels)
To obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature
Nitridable Steels
Nitrided steels are generally medium-carbon (quenched and tempered) steels that contain strong nitride-forming elements such as aluminum, chromium, vanadium, and molybdenum.
The most significant hardening is achieved with a class of alloy steels (nitralloy type) that contain about 1% Al. When these steels are nitrided the aluminum forms AlN particles, which strain the ferrite lattice and create strengthening dislocations. Titanium and chromium are also used to enhance case hardness although case depth decreases as alloy content increases.
Of the alloying elements commonly used in commercial steels, aluminum, chromium, vanadium, tungsten and molybdenum are beneficial in nitriding because they form nitrides that are stable at nitriding temperatures. Molybdenum in addition to its contribution as a nitride former also reduces the risk of embrittlement at nitriding temperatures. Other alloying elements such as nickel, copper, silicon and manganese have little, if any, effect on nitriding characteristics.
Although at suitable temperatures all steels are capable of forming iron nitrides in the presence of nascent nitrogen, the nitriding results are more favorable in those steels that contain one or more of the major nitride-forming alloying elements. Because aluminum is the strongest nitride former of the common alloying elements, aluminum containing steels (0.85 to 1.50% Al) yield the best nitriding results in terms of total alloy content.
The following steels can be gas nitrided for specific applications:
Aluminum-containing low-alloy steels
Medium-carbon, chromium-containing low-alloy steels of the 4100, 4300, 5100, 6100, 8600, 8700 and 9800 series
Hot-work die steels containing 5% chromium such as HI1, HI2, and HI3
Low-carbon, chromium-containing low-alloy steels of the 3300, 8600, and 9300 series
Air-hardening tool steels such as A-2, A-6, D-2, D-3 and S-7
High-speed tool steels such as M-2 and M-4
Nitronic stainless steels such as 30, 40, 50, and 60
Ferritic and martensitic stainless steels of the 400 and 500 series
Austenitic stainless steels of the 200 and 300 series
Precipitation-hardening stainless steels such as 13-8 PH, 15-5 PH, 17-4 PH, 17-7 PH, A-286, AM350 and AM355.
Nitriding processes
Process methods for nitriding include:
gas (box furnace or fluidized bed),
liquid (salt bath),
plasma (ion) nitriding.
The advantages and disadvantages of these techniques are similar to those of carburizing. However, times for gas nitriding can be quire long, that is, from 10 to 130 h depending on the application, and the case depths are relatively shallow, usually less than 0.5 mm. Plasma nitriding allows faster nitriding times, and the quickly attained surface saturation of the plasma process results in faster diffusion. Plasma nitriding can also clean the surface by sputtering.
Gas Nitriding
Gas nitriding is a case-hardening process whereby nitrogen is introduced into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. Quenching is not required for the production of a hard case. The nitriding temperature for all steels is between 495 and 565°C.
Because of the absence of a quenching requirement with attendant volume changes, and the comparatively low temperatures employed in this process, nitriding of steels produces less distortion and deformation than either carburizing or conventional hardening. Some growth occurs as a result of nitriding but volumetric changes are relatively small.
Prior Heat Treatment. All hardenable steels must be hardened and tempered before being nitrided. The tempering temperature must be high enough to guarantee structural stability at the nitriding temperature: the minimum tempering temperature is usually at least 30°C (50°F) higher than the maximum temperature to be used in nitriding.
Single-Stage and Double-Stage Nitriding. Either a single- or a double-stage process may be employed when nitriding with anhydrous ammonia. In the single-stage process, a temperature in the range of about 495 to 525°C is used and the dissociation rate ranges from 15 to 30%. This process produces a brittle nitrogen-rich layer known as the white nitride layer at the surface of the nitrided case.
The double-stage process, known also as the Floe process, has the advantage of reducing the thickness of the white nitrided layer.
The first stage of the double-stage process is, except for time, a duplication of the single-stage process. The second stage may proceed at the nitriding temperature employed for the first stage or the temperature may be increased to from 550 to 565°C; however, at either temperature, the rate of dissociation in the second stage is increased to 65 to 80% (preferably 75 to 80%). Generally, an external ammonia dissociator is necessary for obtaining the required higher second-stage dissociation.
The principal purpose of double-stage nitriding is to reduce the depth of the white layer produced on the surface of the case. Except for a reduction in the amount of ammonia consumed per hour, there is no advantage in using the double-stage process unless the amount of white layer produced in single-stage nitriding cannot be tolerated on the finished part or unless the amount of finishing required after nitriding is substantially reduced.
To summarize, the use of a higher temperature during the second stage:
Lowers the case hardness
Increases the case depth
May lower the core hardness depending on the prior tempering temperature and the total nitriding cycle time
May lower the apparent effective case depth because of the loss of core hardness depending on how effective case depth is defined.
Operating Procedures. After hardening and tempering and before nitriding, parts should be thoroughly cleaned. Most parts can be successfully nitrided immediately after vapor degreasing.
Bright Nitriding
Bright nitriding is a modified form of gas nitriding employing ammonia and hydrogen gases. Atmosphere gas is continually withdrawn from the nitriding furnace and passed through a temperature-controlled scrubber containing a water solution of sodium hydroxide (NaOH). Trace amounts of hydrogen cyanide (HCN) formed in the nitriding furnaces are removed in the scrubber thus improving the rate of nitriding.
The scrubber also establishes a predetermined moisture content in the nitriding atmosphere reducing the rate of cyanide formation and inhibiting the cracking of ammonia to molecular nitrogen and hydrogen. By this technique control over the nitrogen activity of the furnace atmosphere is enhanced and nitrided parts can be produced with little or no white layer at the surface. If present, the white layer will be composed of only the more ductile Fe4N (gamma prime) phase.
Pack Nitriding
Pack nitriding is a process analogous to pack carburizing. It employs certain nitrogen-bearing organic compounds as a source of nitrogen. Upon heating, the compounds used in the process form reaction products that are relatively stable at temperatures up to 570°C.
Slow decomposition of the reaction products at the nitriding temperature provides a source of nitrogen. Nitriding times of 2 to 16 h can be employed. Pans are packed in glass ceramic or aluminum containers with the nitriding compound, which is often dispersed in an inert packing media.
Ion (or Plasma) Nitriding
Since the mid-1960s, nitriding equipment utilizing the glow-discharge phenomenon has been commercially available. Initially termed glow-discharge nitriding, the process is now generally known as ion, or plasma, nitriding. The term plasma nitriding is gaining acceptance.
Ion nitriding is an extension of conventional nitriding processes using plasma-discharge physics. In vacuum, high-voltage electrical energy is used to form a plasma, through which nitrogen ions are accelerated to impinge on the workpiece. This ion bombardment heats the workpiece, cleans the surface, and provides active nitrogen.
Metallurgically versatile, the process provides excellent dimensional control and retention of surface finish. Ion nitriding can be conducted at temperatures lower than those conventionally employed. Control of white-layer composition and thickness enhances fatigue properties. The span of ion-nitriding applications includes conventional ammonia- gas nitriding, short-cycle nitriding in salt bath or gas, and the nitriding of stainless steels.
Ion nitriding lends itself to total process automation, ensuring repetitive metallurgical results. The absence of pollution and insignificant gas consumption are important economic and public policy factors. Moreover, selective nitriding accomplished by simple masking techniques may yield significant economies.
Comparison of Ion Nitriding and Ammonia-Gas Nitriding
Ammonia-gas nitriding produces a compound zone that is a mixture of both epsilon and gamma-prime structures. High internal stresses result from differences in volume growth associated with the formation of each phase. The interfaces between the two crystal structures are weak. Thicker compound zones, formed by ammonia-gas nitriding, limit accommodation of the internal stresses resulting from the mixed structure.
Under cyclic loading, cracks in the compound zone can serve as initiation points for the propagation of fatigue cracks. The single-phase gamma-prime compound zone, which is thin and more ductile, exhibits superior fatigue properties. Reducing the thickness of the ion-nitrided compound zone further improves fatigue performance. Maximization occurs at the limiting condition, where compound zone depth equals zero.
Case Hardness. The bulk of the thickness of the nitride case is the diffusion zone where fine iron/alloy nitride precipitates impart increased hardness and strength. Compressive stresses are also developed, as in other nitriding processes. Hardness profiles resulting from ion nitriding are similar to ammonia-gas nitriding but near-surface hardness may be greater with ion nitriding, a result of lower processing temperature.
Advantages and Disadvantages of Ion Nitriding. Ion nitriding achieves repetitive metallurgical results and complete control of the nitrided layers. This control results in superior fatigue performance, wear resistance, and hard layer ductility. Moreover, the process ensures high dimensional stability, eliminates secondary operations, offers low operating-temperature capability and produces parts that retain surface finish.
Among operating benefits are:
Total absence of pollution
Efficient use of gas and electrical energy
Total process automation
Selective nitriding by simple masking techniques
Process span that encompasses all sub-critical nitriding
Reduced nitriding time
The limitations of ion nitriding include high capital cost, need for precision fixturing with electrical connections, long processing times compared to other short-cycle nitrocarburizing processes, and lack of feasibility of liquid quenching for carbon steels.
Abstract:
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. Thus, nitriding is similar to carburizing in that surface composition is altered, but different in that nitrogen is added into ferrite instead of austenite.
Because nitriding does not involve heating into the austenite phase field and a subsequent quench to form martensite, nitriding can be accomplished with a minimum of distortion and with excellent dimensional control.
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. Thus, nitriding is similar to carburizing in that surface composition is altered, but different in that nitrogen is added into ferrite instead of austenite. Because nitriding does not involve heating into the austenite phase field and a subsequent quench to form martensite, nitriding can be accomplished with a minimum of distortion and with excellent dimensional control.
The mechanism of nitriding is generally known, but the specific reactions that occur in different steels and with different nitriding media are not always known. Nitrogen has partial solubility in iron. It can form a solid solution with ferrite at nitrogen contents up to about 6%. At about 6% N, a compound called gamma prime (γ’), with a composition of Fe4N is formed.
At nitrogen contents greater than 8%, the equilibrium reaction product is ε compound, Fe3N. Nitrided cases are stratified. The outermost surface can be all γ’ and if this is the case, it is referred to as the white layer. Such a surface layer is undesirable: it is very hard profiles but is so brittle that it may spall in use. Usually it is removed; special nitriding processes are used to reduce this layer or make it less brittle. The ε zone of the case is hardened by the formation of the Fe3N compound, and below this layer there is some solid solution strengthening from the nitrogen in solid solution.
Principal reasons for nitriding are:
To obtain high surface hardness
To increase wear resistance
To improve fatigue life
To improve corrosion resistance (except for stainless steels)
To obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature
Nitridable Steels
Nitrided steels are generally medium-carbon (quenched and tempered) steels that contain strong nitride-forming elements such as aluminum, chromium, vanadium, and molybdenum.
The most significant hardening is achieved with a class of alloy steels (nitralloy type) that contain about 1% Al. When these steels are nitrided the aluminum forms AlN particles, which strain the ferrite lattice and create strengthening dislocations. Titanium and chromium are also used to enhance case hardness although case depth decreases as alloy content increases.
Of the alloying elements commonly used in commercial steels, aluminum, chromium, vanadium, tungsten and molybdenum are beneficial in nitriding because they form nitrides that are stable at nitriding temperatures. Molybdenum in addition to its contribution as a nitride former also reduces the risk of embrittlement at nitriding temperatures. Other alloying elements such as nickel, copper, silicon and manganese have little, if any, effect on nitriding characteristics.
Although at suitable temperatures all steels are capable of forming iron nitrides in the presence of nascent nitrogen, the nitriding results are more favorable in those steels that contain one or more of the major nitride-forming alloying elements. Because aluminum is the strongest nitride former of the common alloying elements, aluminum containing steels (0.85 to 1.50% Al) yield the best nitriding results in terms of total alloy content.
The following steels can be gas nitrided for specific applications:
Aluminum-containing low-alloy steels
Medium-carbon, chromium-containing low-alloy steels of the 4100, 4300, 5100, 6100, 8600, 8700 and 9800 series
Hot-work die steels containing 5% chromium such as HI1, HI2, and HI3
Low-carbon, chromium-containing low-alloy steels of the 3300, 8600, and 9300 series
Air-hardening tool steels such as A-2, A-6, D-2, D-3 and S-7
High-speed tool steels such as M-2 and M-4
Nitronic stainless steels such as 30, 40, 50, and 60
Ferritic and martensitic stainless steels of the 400 and 500 series
Austenitic stainless steels of the 200 and 300 series
Precipitation-hardening stainless steels such as 13-8 PH, 15-5 PH, 17-4 PH, 17-7 PH, A-286, AM350 and AM355.
Nitriding processes
Process methods for nitriding include:
gas (box furnace or fluidized bed),
liquid (salt bath),
plasma (ion) nitriding.
The advantages and disadvantages of these techniques are similar to those of carburizing. However, times for gas nitriding can be quire long, that is, from 10 to 130 h depending on the application, and the case depths are relatively shallow, usually less than 0.5 mm. Plasma nitriding allows faster nitriding times, and the quickly attained surface saturation of the plasma process results in faster diffusion. Plasma nitriding can also clean the surface by sputtering.
Gas Nitriding
Gas nitriding is a case-hardening process whereby nitrogen is introduced into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. Quenching is not required for the production of a hard case. The nitriding temperature for all steels is between 495 and 565°C.
Because of the absence of a quenching requirement with attendant volume changes, and the comparatively low temperatures employed in this process, nitriding of steels produces less distortion and deformation than either carburizing or conventional hardening. Some growth occurs as a result of nitriding but volumetric changes are relatively small.
Prior Heat Treatment. All hardenable steels must be hardened and tempered before being nitrided. The tempering temperature must be high enough to guarantee structural stability at the nitriding temperature: the minimum tempering temperature is usually at least 30°C (50°F) higher than the maximum temperature to be used in nitriding.
Single-Stage and Double-Stage Nitriding. Either a single- or a double-stage process may be employed when nitriding with anhydrous ammonia. In the single-stage process, a temperature in the range of about 495 to 525°C is used and the dissociation rate ranges from 15 to 30%. This process produces a brittle nitrogen-rich layer known as the white nitride layer at the surface of the nitrided case.
The double-stage process, known also as the Floe process, has the advantage of reducing the thickness of the white nitrided layer.
The first stage of the double-stage process is, except for time, a duplication of the single-stage process. The second stage may proceed at the nitriding temperature employed for the first stage or the temperature may be increased to from 550 to 565°C; however, at either temperature, the rate of dissociation in the second stage is increased to 65 to 80% (preferably 75 to 80%). Generally, an external ammonia dissociator is necessary for obtaining the required higher second-stage dissociation.
The principal purpose of double-stage nitriding is to reduce the depth of the white layer produced on the surface of the case. Except for a reduction in the amount of ammonia consumed per hour, there is no advantage in using the double-stage process unless the amount of white layer produced in single-stage nitriding cannot be tolerated on the finished part or unless the amount of finishing required after nitriding is substantially reduced.
To summarize, the use of a higher temperature during the second stage:
Lowers the case hardness
Increases the case depth
May lower the core hardness depending on the prior tempering temperature and the total nitriding cycle time
May lower the apparent effective case depth because of the loss of core hardness depending on how effective case depth is defined.
Operating Procedures. After hardening and tempering and before nitriding, parts should be thoroughly cleaned. Most parts can be successfully nitrided immediately after vapor degreasing.
Bright Nitriding
Bright nitriding is a modified form of gas nitriding employing ammonia and hydrogen gases. Atmosphere gas is continually withdrawn from the nitriding furnace and passed through a temperature-controlled scrubber containing a water solution of sodium hydroxide (NaOH). Trace amounts of hydrogen cyanide (HCN) formed in the nitriding furnaces are removed in the scrubber thus improving the rate of nitriding.
The scrubber also establishes a predetermined moisture content in the nitriding atmosphere reducing the rate of cyanide formation and inhibiting the cracking of ammonia to molecular nitrogen and hydrogen. By this technique control over the nitrogen activity of the furnace atmosphere is enhanced and nitrided parts can be produced with little or no white layer at the surface. If present, the white layer will be composed of only the more ductile Fe4N (gamma prime) phase.
Pack Nitriding
Pack nitriding is a process analogous to pack carburizing. It employs certain nitrogen-bearing organic compounds as a source of nitrogen. Upon heating, the compounds used in the process form reaction products that are relatively stable at temperatures up to 570°C.
Slow decomposition of the reaction products at the nitriding temperature provides a source of nitrogen. Nitriding times of 2 to 16 h can be employed. Pans are packed in glass ceramic or aluminum containers with the nitriding compound, which is often dispersed in an inert packing media.
Ion (or Plasma) Nitriding
Since the mid-1960s, nitriding equipment utilizing the glow-discharge phenomenon has been commercially available. Initially termed glow-discharge nitriding, the process is now generally known as ion, or plasma, nitriding. The term plasma nitriding is gaining acceptance.
Ion nitriding is an extension of conventional nitriding processes using plasma-discharge physics. In vacuum, high-voltage electrical energy is used to form a plasma, through which nitrogen ions are accelerated to impinge on the workpiece. This ion bombardment heats the workpiece, cleans the surface, and provides active nitrogen.
Metallurgically versatile, the process provides excellent dimensional control and retention of surface finish. Ion nitriding can be conducted at temperatures lower than those conventionally employed. Control of white-layer composition and thickness enhances fatigue properties. The span of ion-nitriding applications includes conventional ammonia- gas nitriding, short-cycle nitriding in salt bath or gas, and the nitriding of stainless steels.
Ion nitriding lends itself to total process automation, ensuring repetitive metallurgical results. The absence of pollution and insignificant gas consumption are important economic and public policy factors. Moreover, selective nitriding accomplished by simple masking techniques may yield significant economies.
Comparison of Ion Nitriding and Ammonia-Gas Nitriding
Ammonia-gas nitriding produces a compound zone that is a mixture of both epsilon and gamma-prime structures. High internal stresses result from differences in volume growth associated with the formation of each phase. The interfaces between the two crystal structures are weak. Thicker compound zones, formed by ammonia-gas nitriding, limit accommodation of the internal stresses resulting from the mixed structure.
Under cyclic loading, cracks in the compound zone can serve as initiation points for the propagation of fatigue cracks. The single-phase gamma-prime compound zone, which is thin and more ductile, exhibits superior fatigue properties. Reducing the thickness of the ion-nitrided compound zone further improves fatigue performance. Maximization occurs at the limiting condition, where compound zone depth equals zero.
Case Hardness. The bulk of the thickness of the nitride case is the diffusion zone where fine iron/alloy nitride precipitates impart increased hardness and strength. Compressive stresses are also developed, as in other nitriding processes. Hardness profiles resulting from ion nitriding are similar to ammonia-gas nitriding but near-surface hardness may be greater with ion nitriding, a result of lower processing temperature.
Advantages and Disadvantages of Ion Nitriding. Ion nitriding achieves repetitive metallurgical results and complete control of the nitrided layers. This control results in superior fatigue performance, wear resistance, and hard layer ductility. Moreover, the process ensures high dimensional stability, eliminates secondary operations, offers low operating-temperature capability and produces parts that retain surface finish.
Among operating benefits are:
Total absence of pollution
Efficient use of gas and electrical energy
Total process automation
Selective nitriding by simple masking techniques
Process span that encompasses all sub-critical nitriding
Reduced nitriding time
The limitations of ion nitriding include high capital cost, need for precision fixturing with electrical connections, long processing times compared to other short-cycle nitrocarburizing processes, and lack of feasibility of liquid quenching for carbon steels.
11-08-05, 01:28 PM
#20
the nitriding on the mazda housings has a depth of about 0.0004-0.0007", the nitriding does penetrate a little deeper but the hardness drops off very quickly. The "useful" depth is only about 0.0005" and this varies from part to part. Remember, this is used by mazda for production purposes and is intended for stock engines that will only see the loads associated with stock horsepower. The average cost to properly treat the parts with this method should come to about $300-$400 per face (includes grinding, lapping, nitriding and final lapping) and then add shipping. If you do this (properly) you are getting a good as factory part, but you will not get the advatages of other treatments that are available such as increased wear resistance, lower friction, higher corrosion resistance, uniform coating hardness and depth, self lubricating properties and more.....
11-08-05, 08:43 PM
#21
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There are a number of other versions of nitriding which are mentioned on the first page. Keep in mind of the purpose that you are doing this, primarily wear resistance and hardness. Ceramics are better used for insulating such as on the combustion surface.
Not sure why people think that housings get warped from nitriding (Ion Plasma process) but from my experience with my own (and test housings both iron and rotor), there is absolutely no warping whatsoever. This was with junked bad housings and with brand new housings in comparison both pre and post lapping as that was my concern as well. I am personally aware of two engines to have this done and no warping at all measured with a mic.
Not sure why people think that housings get warped from nitriding (Ion Plasma process) but from my experience with my own (and test housings both iron and rotor), there is absolutely no warping whatsoever. This was with junked bad housings and with brand new housings in comparison both pre and post lapping as that was my concern as well. I am personally aware of two engines to have this done and no warping at all measured with a mic.
11-08-05, 08:46 PM
#22
Senior Member
Thread Starter
Ok I got a 12"x1.5" 46H aluminum oxide wheel today. Then I got back to real work and siezed a press (huge bastard with a 3' flywheel) so I spent the rest of the day machining a new dog to replace the 1.25" A2 steel one I sheared in half... oops, the best lessons are learned the hard way.
I'm going to call up the heat treat place tomorow to see about liquid nitriding.
Counturemarc, are you sure it's that shallow? four to seven tenths of a thou? gas nitriding is only $100 for .002 (not sure about the cost of liquid nitriding yet) sounds good to me.
I don't doubt the $300 to $400 per face price, the setup is a bear to make sure everything is as flat and paralell as necessary.
Lapping is another thing I am going to have to figure out, can I actually just sit there with two side housing face to face with lapping compund inbetween and lap away?
I'm going to call up the heat treat place tomorow to see about liquid nitriding.
Counturemarc, are you sure it's that shallow? four to seven tenths of a thou? gas nitriding is only $100 for .002 (not sure about the cost of liquid nitriding yet) sounds good to me.
I don't doubt the $300 to $400 per face price, the setup is a bear to make sure everything is as flat and paralell as necessary.
Lapping is another thing I am going to have to figure out, can I actually just sit there with two side housing face to face with lapping compund inbetween and lap away?
11-08-05, 08:47 PM
#23
Safety Guy
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The difference is that cryo is done to get a complete molecular shift in the entire piece. A coating of any sort is done on the surface and as "rotariesrule" referenced in the encyclopedia, there are a number of different depths obtained from nitriding, but none that are very deep in comparison to a complete material change.
Look up http://www.diversifiedcyrogenics.com/ for some reading material as I am not a material science engineer nor a metallurgist but I have worked with one of each for many years and wouldn't be able to explain it in as great of detail as they could!
Look up http://www.diversifiedcyrogenics.com/ for some reading material as I am not a material science engineer nor a metallurgist but I have worked with one of each for many years and wouldn't be able to explain it in as great of detail as they could!
11-08-05, 09:00 PM
#24
Senior Member
Thread Starter
Turbo 3, It's very reassuring to hear that you have had success with re-nitriding side housings. Uneven heating and cooling of a metal can cause warping, you won't measure the warping with a mic. The easiest method is to lay it on a granite precision table and give it a thump with your fist on the edges, if it thuds solidly it's flat, if it rings it's not. I don't have a grante table but I used a mill table and a dial indicator to obtain a measurement.
11-08-05, 09:31 PM
#25
lapping:
the poor man's way to do it is with a large sheet of glass. i used a 4x5 tempered window i had laying around in my garage. then place it on a flat surface (table) and use that as your lapping surface. glass tends to be very flat, so you can ensure a very square surface. basically just get some compound, squirt it on the glass, and lap away, in a random motion. (i alternate between a circle and figure 8 pattern)
do that till you get a consistantly smooth surface.
pat
the poor man's way to do it is with a large sheet of glass. i used a 4x5 tempered window i had laying around in my garage. then place it on a flat surface (table) and use that as your lapping surface. glass tends to be very flat, so you can ensure a very square surface. basically just get some compound, squirt it on the glass, and lap away, in a random motion. (i alternate between a circle and figure 8 pattern)
do that till you get a consistantly smooth surface.
pat