Alloying of high manganese stainless steel with sulphur 1

[Martinos]

Dear all
Have you some experiences with alloying of hign manganese stainless steel (about 10% Mn) with sulphur (to 0,2 %S after solidification)? There is very strong reaction of manganese and sulphur which creates slaggy MnS layer and reduce content of both the elements. Exist some known method how to slightly avoid this reaction - make it not so strong?

Thank you!

 

[MagBen]

how did you get that high S? S normally should be lower than 0.02%.

 

[Martinos]

High level of S is required to improve very bad machinability which is provided by a lot of globular manganese sulphides. Sulphur is alloyed as FeS

 

[EdStainless]

You know that this will destroy both the mechanical properties and corrosion resistance.
You will have very little toughness left.
And pitting initiation at the inclusions that are open to the surface will be very rapid, you will probably get rust staining.
If you keep the pouring temp minimized, aggressively stir the S in right before the pour, and get rapid solidification the damage will be minimized.
Honestly anything over 0.05% S will cause such massive MnS in the structure that They will not help.

How much worse does this machine than any other stainless?
You use either carbide or ceramic tooling, take very deep cuts, with as much feed as your power will allow.
Don't make a second machining pass unless it is also a very deep cut. The surface will work harden greatly.

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Plymouth Tube

 

[arunmrao]

303 grade exists with or without Se for improved machinability. S of 0.2% is specified, but why 10%Mn ? Is this a substitute for Ni ?
The affinity of S to Mn is very high thermodynamically . I think your 10%Mn is the problem in slag formation.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[MagBen]

10% Mn SS is not uncommon, but S is normally < .02%
.2%S SS (magnetic grades for solenoid quality) is not uncommon either, but Mn is normally <1%.
P is another element added intentionly for improved machinbility.

Adding Al, V at melting may be able to help to keep both Mn and S higher.

 

[MagBen]

just a food for thought:
adding S at pouring, not at melting

 

[Martinos]

Thank you guys for your feedback. Of course I cannot write here the Details, but Yes Mn is there as the replace for Nickel. We are steelmakers only. It is customer's standard which require chemical composition like these. I was surprised, but it looks this material is working very well. The problem is that tensile strength, hardness and elongation is higher than in standard CrNi types which are replaced (as HK30 or PL23). Machining is worse. I think machining department do not want to do some trials and they only think that sulphur solve it. But you know the situation: a lot of MnS Slag, sulphur dioxide and we have reduced mostly both, Mn and S as well in the melt.
Wew will try Al. Vanadium is in the standard about 0,7

 

[Martinos]

Adding S during pouring made our tubes slaggy.

 

[arunmrao]

Martinos, how about adding Mn at a late stage, perhaps this can delay the slag formation.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[Martinos]

arunmrao, we are doing it like that, plus we cover the FeS with scrap. We found the way how to reduce the sulphur content after pouring as more as possible, but still we did not reach requested level 0,15 - 0,25 %. We have level from 0,1 to 0,12 %.
In past we reached level min. 0,15% on poured tubes, but it was in about 20-30% cases and it totally destroyed our productivity. (multiple alloying and re-alloying with FeMn / FeS)

I am trying to find metallurgic way to reach satisfactory level with satisfactory productivity, but it looks like we have to request the deviation to sulphur content. We have proved that machinability of tube wit 0,5 % S and 0,12 % S is totally the same... the same bad.

We are going to try to lead the melt as a low manganese and to alloy the FeMn at the very end of melting process. We have another heat resistant steels with very high sulphur level and Mn up-to 2%, so, of course, there is no problem like that.

 

[Martinos]

Sorry for 2 mistakes. Here are 2 corrections from my previous post:
1. We found the way how to reduce the sulphur content... = of course, I thought to get the sulphur content as high as possible
2. 0,5 % S and 0,12 % S = 0,05 % S and 0,12 % S

I will appreciate every opinion or experience from you!

Thank you guys once more!

 

[EdStainless]

The addition of S will only improve machinability if you can control the morphology.
The sulfides must be thin and evenly dispersed. Large thick sulfides will be just as bad (or worse) than none since you will have abrupt changes in loading on the tooling.
Tell you machine shop to fix their tooling.
You do know that these alloys will have very poor fatigue strength and terrible corrosion resistance.

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Plymouth Tube

 

[Martinos]

Thank you Ed.
For understanding, our customer developed steel like these. It is for parts used as stators. Only they know why steel like this is used. We only have to make steel according to customers standard. This is our problem.

 

[MagBen]

Do you use arc or vacuum melting? and what are the slag compositions? slag normall includes both oxides and sulfides, if you can keep oxygen in a very low level, MnS may not float out to form slag. (note MnO has a higher melting point than MnS). So using Al, Mg, or Ca (note it can be sucked out in vacuum) to kill oxygen to a low level could help MnS stay or other sulfides (CaS can also improve machniability).

a higher tapping temperature could also be helpful

 

[Martinos]

MagBen, thank you!
We are limited because we are using atmospheric induction melting furnaces. I do not know if Ca and other deoxidizers can be helpful in this case. What is your opinion?
What about temperatures, our melt has 1560 deg. Celsius before pouring to the tranfer ladle. Lower temperature used results to cold joints and a lot of melt stays in ladle, higher temperature means very low viscosity (a lot of manganese in melt)...

 

[arunmrao]

1560C is a good temperature. Do not exceed. You can consider adding Se, not only it removes the gases, it also helps improve machinability.

For critical applications, vacuum induction melting is preferred.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)