high temp oxidation 1

[49078]

First I'd like to just say that this is my favorite forum on the webpage. You can learn a lot by just reading the posts in here.

I have question though, currently we are using an astm 297 HH for a high temperature application. I have investigating possible alternatives given relatively the same budget. What are some possible alternatives should i consider in hoping to find a longer resistance to high temperature oxidation.

Applicatin has low loads, little abrasion. Combustion chamber environment.

Currently I am planning on using other astm 297 grades, but I don't know which ones would be better off hand, but i can change from 297, i'm just not sure what i should look at.

Cheers

 

[metengr]

Can you provide some additional information as to your environment? Specifically service temperature range and combustion products? This would help to explore alternative materials.

 

[49078]

Sorry, I meant to add that too. The material will be exposed to 600-900 deg. C. depending on the particular system.

The chamber is wood fueled. Fuel is sorted to minimize contaminates added.

 

[metengr]

Well, for a maximum exposure of 900 deg C and for a combustion chamber one of your options could be Inconel 601 or Inconel 601GC, which are supplied by Special Metals.

http://www.specialmetals.com/products/

There are other high temperature, nickel-chromium alloys like Hastelloy X or Haynes 230 , offered by Haynes.

http://www.haynesintl.com/guestbooknew.asp

Either way, these will be expensive because of the alloy content.

 

[EdStainless]

I presume that you need to stay with a cast alloy. A297 is the right place.
For some improvement you could move to HL. The higher Cr will give better overall corrosion resistance.
With all of these alloys, and HH most, the exact chemistry balance is very critical. The Ni and Cr contents must be right or you will have poor performance.

Another option, but more expensive would be cast Alloy X (45%Ni, 22%Cr, 9%Mo). This is the best greneral service high temp alloy.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[49078]

EdStainless,

This Alloy X, is it easy to find? Our current supplier has a limited selection, but I am looking to find a new supplier. Do you know where it is available in USA/Canada?

 

[EdStainless]

How complex are the castings? How large? Is it investment cast of sand cast?
There are many high alloy cast sources in the US. Give me some info and maybe I can point you.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[49078]

they are relatively simple cast slabs with a ridge on one side, and a support on the other. Difficult to descirbe on here, but they are pretty simple casts. They are about 2ft long, 6 inches wide, and range from 2-4 in thick along the length.

As far as I know we have never used sand casts.

Do surface coatings help in environments like this? Is it possible that a cheaper base material with a proper coating might help?

 

[EdStainless]

The trouble with coatings is when the fail it is catostrophic. At least with an alloy the degridation is fairly predictable.

If you are looking for these parts to be investment cast you might try

http://www.oicc-co.com/

I have worked with them in the past and they always did a good job.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[49078]

I will look into them. Thanks for your help.

 

[49078]

EdStainless, earlier you said that for HH to be effective the portions of Cr and Ni must be exact or poor performance can be seen.

I just got the chemical analysis back of the ASTM A-297 HH alloy we had been using. The proper portions of Cr and Ni are 25% and 12% respectively, and our material contained 24% and 13.5%. Are these errors great enough to make a noticable difference?

 

[stanweld]

The Chrome content is a little on the low side for your HH material - would like to see it above 25%.

As has been noted, %Cr is the key to high temperature oxidation resistance of the iron base chrome-nickel cast alloys listed under A-297. More similar in cost to HH are grades HI and HE both having more chromium. Somewhat more expensive are HK and HL. Note that the high chrome -low nickel alloys will have considerable delta ferrite, which may prove detrimental to your service conditions (greater potential for formation of the brittle constituent-sigma.

 

[EdStainless]

HH should be fully austenitic. Are your pieces magnetic? Can you measure how magnetic?
The other thing to do is age some samples at 2000F and 1400F. They should both be non-magnetic and have reasonable tensile ductilities.
I suggested HL becuase it will offer the best oxidation resistance while still staying with a reasonable Ni content (read cost). It is also a fully austenitic alloy.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[rolledalloy]

One could argue with Alloy X being listed as a good general alloy for high temperature service. At 9% molybdenum it has the potential to suffer catastrophic oxidation, when the conditions are stagnant. Which is not uncommon in many furnaces applications. It is primarily used in places like gas turbines where there is consistent air flow.