surface hardening treatments of steels

[Mattymecc]

Good morning to all, I have a few questions to ask you about the thermal treatments of steels. in this period at school I am facing them, but compared to what I knew from before I noticed several discrepancies in the description of some treatments:
1) in nitriding we have been told that the pieces are reclaimed after the surface enrichment of nitrogen, I knew that it was the opposite because at 500°c there are no distortions of the piece and the microstructure does not undergo changes;
2) thermal treatments following cementation: I thought in a previous post of clarifying my ideas, but I was punctually denied. we have been told that after the surface enrichment of carbon, we perform a double tempering (an ac3 heart tempering + ac1 ac1 surface enriched layer) or a single tempering (at a halfway temperature between the two preceding ones), in order to have martensite throughout the piece. to these treatments follows a referral to 150-250°c.

Do you not have both the heart and the surface hard and fragile? the heart of the piece will be very tense or not?

how I was told in other discussions is no longer logical to do so? :
1) harden on all the piece at ac3 temperature of the heart;
2) referral to about 550-650°c to have the heart of the tenacious piece
3) surface tempering for induction or flame of the cemented layer;
4) 150-250°c extension to decrease internal tensions without affecting the hardness reached by the cemented layer after the tempering.

an example that seems quite appropriate to me is that of a cementing steel tree-pignon: If you followed the method that was explained to me at school you would have beyond that the surface of the teeth also the heart of the hard and little tense tree. with the other method would not be better the tenacity of the piece?

thank you in advance to those who will answer me.

 

[meccanicamg]

with regard to the treatment of nitriding, the following is indicated in this guide:and, however, being a superficial treatment, it is necessary first to reclaim the heart and then to sharpen the few tenths of superficial millimeter. this is practically the classic example of gears with base and bonified core to withstand bending and superficially nitrated to withstand wear.

for cementing steels it is necessary first to atomize the outer layer with carbon cementing in salts or gas and then by force of things it is necessary to tempt twice to have fine carbides on the outer layer and harden the heart. later it becomes tempted to give stability to the compounds and refine the grains as well as to give a more tenacious structure. the lower temperature and the harder the material remains.

 

[Mattymecc]

thanks for the answer, for nitroration is as I thought, but regarding cementation after tempering it hardens to induction or so leaves the surface layer? If, for example, I look at 600° the cemented layer loses a lot of hardness, should it not be re-tempractor induction? Thank you again.

 

[meccanicamg]

Usually the tempra is total and is made in oil. practically never a localized induction tempering. Otherwise there would not be the process of cementing and tempering.

 

[Mattymecc]

thanks for the explanation, usually with these treatments at what temperature you find 250-300°?

 

[PIETRO2002]

for the treatment of cementation is enriched with carbon only the surface part, the heart having low carbon content fails to assume important hardness and therefore does not "tempra". in the treatment of cementation you do not tempt but you do distension on the 150 / 200 ° c

 

[PIETRO2002]

thanks for the answer, for nitroration is as I thought, but regarding cementation after tempering it hardens to induction or so leaves the surface layer? If, for example, I look at 600° the cemented layer loses a lot of hardness, should it not be re-tempractor induction? Thank you again.

treatment is done on steels which have a carbon percentage of approximately 0.25 %.
the pieces are put in the oven, where in controlled atmosphere, they are enriched with carbon in the surface, time is defined by several factors, required cement depth, size of the pieces, material to be treated etc. etc.
after carbon enrichment, the pieces are brought to the appropriate tempering temperature and are normally cooled in the oil bath.
in the end they are put in the oven for distension, otherwise the surface would remain too fragile.
Then according to the type of pieces, as the treatment induces deformations, we proceed to any correction operations.
I've never seen cemented pieces hardened to induction, maybe someone with more experience can deny me. :

 

[IronMike87]

of amenity and beastliness I have seen make many...
I saw later nitrated hardened pieces, as well as later nitrated cemented pieces with soft nitroration ... but vain, these are dysfunctions of people who want to reinvent the wheel.


if we have to orchestrate a "standard" cycle for a sharp piece:
normalization + remediationnormalization: preheating - austenization 900°c - air cooling
remediation: preheat - austenization 870°c - tempering in oil at 60°c - cooling in air
finding: > 570÷600°c - air cooling
stabilization - any treatments to release tensions accumulated during mechanical processing
always lower than the tempting temperature: for example 550°c
gas nitridetemperature rise - maintenance approx. 500°c - cooling
or
Soft nitriding in salt bathrise in temperature - stay in room 550÷570°c - neutralization in the bath of salts

then be careful, that the variations on the theme are "infinite". for what I know, for example, some manufacturers of hot stamping molds, after remediation perform 3 phases of referral, at 3 different temperatures, with the last cryogenic, to sharpen as much as possible the size of the grain, and subsequently sharpen everything.



As for cementing, we always talk about cementing+tempra+reinvention for heat treatment in the oven.
The standard is oil shutdown, mainly because shutting off in the salt bath entails very high management costs for the treatment of the exhaust solution of the same. Of course, a shutdown in the salt bath, contains the deformations of the pieces and improves the quality of the grain. we consider that cementation is an always very intrusive treatment ... I saw materials stretching even 2mm on 1m

Tempra of course can be made by induction, but we talk about a completely different process, so-called special, on plants with considerable cost.
it is heated very quickly (by induction precisely) an area of the piece, and "spegnendola" immediately after in a solution of water to polymers: aqua-quench. the polymer becomes insoluble exceeded a certain temperature, while it returns completely miscible below it.
the most advanced plants, after this tempering phase, are able to perform the tempering phase always in the same station, heating at a much lower temperature the area previously tempered.
Otherwise it is appropriate to treat the pieces, t<200°c for about 2h, to remove the accumulated tensions.

 

[Mattymecc]

thanks to both for clarifying my ideas about these two treatments, but I would have a few things to ask you:

the heart having low carbon content fails to assume important hardness and therefore does not "tempra"

This seems true to me for steels like the c10, but if they are tied as the 16nicr11 tempts even the heart or am I wrong?

As for cementing, we always talk about cementing+tempra+reinvention for heat treatment in the oven.

what temperatures are you talking about? lower than those used in the reclamation, which as you said, are around 570-60°?

 

[PIETRO2002]

thanks to both for clarifying my ideas about these two treatments, but I would have a few things to ask you:



This seems true to me for steels like the c10, but if they are tied as the 16nicr11 tempts even the heart or am I wrong?



what temperatures are you talking about? lower than those used in the reclamation, which as you said, are around 570-60°?

with alloy steels, with addition of cr and ni the temprability is increased, but the purpose of a cemented piece is to have a good heart tenacity and high hardness on the surface, logically the alloy steels are better than a c10. the hardness obtained however depends on the percentage of carbon.
with regard to cementation, according to me the right definition is cementation+tempra+distension.
a cemented piece is never found as you mean at temperatures 570/600 °C but is spread at temperatures from 150 to 200 °C.
tempered steels or tool steels are tempered.
at the base of all thermal treatments is the understanding of the "carbon iron state chart and its ttt curves". a beautiful book, according to me, is that published by matteoli leno, published by Italian association of metallurgia.
The title is my quote.

 

[Mattymecc]

thanks again to both for the explanations, now I am a little lighter this heat treatment.

I had never heard of it.
Ironmike87 excuses if I only write it now but first I was traveling and I forgot. . .

 

[meccanicamg]

with alloy steels, with addition of cr and ni the temprability is increased, but the purpose of a cemented piece is to have a good heart tenacity and high hardness on the surface, logically the alloy steels are better than a c10. the hardness obtained however depends on the percentage of carbon.
with regard to cementation, according to me the right definition is cementation+tempra+distension.
a cemented piece is never found as you mean at temperatures 570/600 °C but is spread at temperatures from 150 to 200 °C.
tempered steels or tool steels are tempered.
at the base of all thermal treatments is the understanding of the "carbon iron state chart and its ttt curves". a beautiful book, according to me, is that published by matteoli leno, published by Italian association of metallurgia.
The title is my quote.

But unfortunately in literature there is often the definition of finding in place of distension because they call it "revenience at low temperature" which in itself is correct the definition because it prevents heating to soften, refine, relax etc. The temperature is important.

 

[PIETRO2002]

But unfortunately in literature there is often the definition of finding in place of distension because they call it "revenience at low temperature" which in itself is correct the definition because it prevents heating to soften, refine, relax etc. The temperature is important.

for accuracy allego copy page of a metallurgy book.

 

[PIETRO2002]

But unfortunately in literature there is often the definition of finding in place of distension because they call it "revenience at low temperature" which in itself is correct the definition because it prevents heating to soften, refine, relax etc. The temperature is important.

on a school text I also found the definition: decretioning.

 

[IronMike87]

with alloy steels, with addition of cr and ni the temprability is increased, but the purpose of a cemented piece is to have a good heart tenacity and high hardness on the surface, logically the alloy steels are better than a c10. the hardness obtained however depends on the percentage of carbon.
with regard to cementation, according to me the right definition is cementation+tempra+distension.
a cemented piece is never found as you mean at temperatures 570/600 °C but is spread at temperatures from 150 to 200 °C.
tempered steels or tool steels are tempered.
at the base of all thermal treatments is the understanding of the "carbon iron state chart and its ttt curves". a beautiful book, according to me, is that published by matteoli leno, published by Italian association of metallurgia.
The title is my quote.

we say that I agree on a theoretical level, but on a practical and working level, it is more times that I have heard the acronym ctr than that ctd.
Let's say that if you use English (for once I bend to the language of albione) and use "case-hardening" we'll get stuck

I've got it. ninjato mechanical response? ?

thanks again to both for the explanations, now I am a little lighter this heat treatment.

I had never heard of it.
Ironmike87 excuses if I only write it now but first I was traveling and I forgot. . .

polymer-quench (because aqua-quench is a brand) simply act as heat exhaust vectors.
It is obvious that I could soak banally in water as the ancients did, but it is equally obvious that this would involve: evaporation of part of the water (with fumes not exactly salubri) and heating of the water itself. Whereas induction tempering is a special heat treatment that is adopted in case of large mass productions with high volumes, it is understood that it is not the maximum. this without taking into account possible problems of corrosion of the treated pieces.

said this, putting a heated piece into the water+polymer mixture is this:
a water vapor coltre will be formed around the piece when it is turned off, as in any other medium. when the temperature of the steel drops and the polymer warms up, and the boiling phase begins. At this point, the polymer layer is interrupted allowing the piece to get in touch with a more water-rich concentration. after the temperature of the metal has fallen below the boiling point, part of the liquid around the piece can still be above the cloud point, causing the presence of a limit layer (film) with high viscosity that allows heat transfer for convection.

these limits are extremely viscous (and quite shaky to clean!!!): this viscosity directly impacts the cooling speed.
The higher the concentration, the slower the cooling due to the viscosity and thickness of the film. in fact the more the film is often, the more difficult to break, allowing the piece to cool for a fraction of a second more before the water hit the piece = depth and hardness of different tempers


all induction tempering plants use polymer-quench for cooling.

some sawuzzo:

below you will find the video of a madonna plant (eye >1.5mln): first tempra station, second distension station.

 

[PIETRO2002]

we say that I agree on a theoretical level, but on a practical and working level, it is more times that I have heard the acronym ctr than that ctd.
Let's say that if you use English (for once I bend to the language of albione) and use "case-hardening" we'll get stuck

I've got it. ninjato mechanical response? ?



polymer-quench (because aqua-quench is a brand) simply act as heat exhaust vectors.
It is obvious that I could soak banally in water as the ancients did, but it is equally obvious that this would involve: evaporation of part of the water (with fumes not exactly salubri) and heating of the water itself. Whereas induction tempering is a special heat treatment that is adopted in case of large mass productions with high volumes, it is understood that it is not the maximum. this without taking into account possible problems of corrosion of the treated pieces.

said this, putting a heated piece into the water+polymer mixture is this:
a water vapor coltre will be formed around the piece when it is turned off, as in any other medium. when the temperature of the steel drops and the polymer warms up, and the boiling phase begins. At this point, the polymer layer is interrupted allowing the piece to get in touch with a more water-rich concentration. after the temperature of the metal has fallen below the boiling point, part of the liquid around the piece can still be above the cloud point, causing the presence of a limit layer (film) with high viscosity that allows heat transfer for convection.

these limits are extremely viscous (and quite shaky to clean!!!): this viscosity directly impacts the cooling speed.
The higher the concentration, the slower the cooling due to the viscosity and thickness of the film. in fact the more the film is often, the more difficult to break, allowing the piece to cool for a fraction of a second more before the water hit the piece = depth and hardness of different tempers


all induction tempering plants use polymer-quench for cooling.

some sawuzzo:

below you will find the video of a madonna plant (eye >1.5mln): first tempra station, second distension station.

It's not to be stubborn, but the books I didn't write them, I posted a copy of a page found on a famous metallurgy book, I wait for a copy where I see quoted your definition! possibly in Italian and not in English! Thank you.

 

[IronMike87]

far from me want to make controversy. I just wanted to say that in my working experience I almost always found myself talking, with suppliers of thermal treatments, of cement+tempra+finding rather than cement+tempra + extensionI do not think I have knowledge in my pocket, therefore it was only an observation.

That said:

Cementazione in atmosfera controllata – Bodycote plc

La cementazione è un processo che aumenta la resistenza all'usura, la durezza superficiale e la resistenza alla fatica, creando uno strato superficiale indurito e un nucleo tenace.

www.bodycote.com

Carbonitrurazione - Carbocementazione Tempra e distensione - Bodycote

La carbonitrurazione è un processo di carbocementazione austenitica (al di sopra di A3) simile alla cementazione, con l'aggiunta di azoto (tramite gas NH3), utilizzato per aumentare la resistenza all'usura e la durezza superficiale attraverso la creazione di uno strato superficiale indurito.

www.bodycote.com

http://www.fa-fe.com/files/pdf/libri_articoli/it/8-gli_acciai_da_cementazione.pdf

Cementazione e tempra di acciaio | Nuova Oria Trattamenti Termici

www.nuovaoria.com

?

in the end, which commands, is always and only the temperature and thermal cycles of pre-heat, rise in temperature, maintenance and cooling ... and most times you can just have the peak temperature max of the single phase (also rightly since it represents the know-how of the individual supplier)


I have certain suppliers that if you see the company you give him "Rutamàtt" while they treat valuable components :roflmao:
the magical world of thermal treatments...

 

[PIETRO2002]

Fortunately I had the opportunity to work in a company where among other operations we also had the plant for the heat treatment of cementation, having to fill out the working cycles I have always written distension.
I would say it's always better to use the right terms, we came to this point of the discussion because the good morningymecc was confused by the word "revenue".

 

[Chris_BRB]

when it is written on the "manual of treatments and finishings" of new techniques regarding the "diatriba" distension/revenue

 

[PIETRO2002]

when it is written on the "manual of treatments and finishings" of new techniques regarding the "diatriba" distension/revenue

Perfect!