white cast iron vs. ductile iron

[macmet]

i'm looking at using a cast iron material for a high wear component. The wear is occuring where one component overlaps another and sits on it for support. On top of the this, there is probably 100-200 pounds of wood sitting on top.

I was told to look at ductile iron, but I think that a high chrome white iron might be better. Can anyone give me any sort of cost comparison on the two? I would like to contact our supplier to ask them as well, but I'm not sure yet what grade of white iron I should be looking at, any suggestions? Is the top grade of white iron overkill? Has anyone ever used both of these for the same application, and if you did which worked better?

Operating temperature is probably less than 200 deg. C. We currently use 297 HH which is wearing too quickly, but we use continue to use it now because these same components are also used for high temp applications.

The wear we see now is only where metal rests on either another components or on a wear plate below made of HSS.

 

[swall]

White iron, particularly martensitic white iron, will offer outstanding resistance to abrasive wear. Ductile iron will need to surface hardened (induction or flame hardened)to offer significant resistance to abrasive wear. Keep in mind that a martensitic white iron will be extremely brittle and have zero resistance to impact failure.

 

[arunmrao]

Agree with swall in recommending high chrome irons. This could be 27% Cr or 15Cr/3Mo grade. I hope the part does not need any machining for seating. You can do a facing operation but no drilling or tapping. If holes are required then provide cast ms inserts and drill the holes.

 

[EdStainless]

As long as there is no impact loading white iron should work.
You might also consider cast Mn steel for the parts. The high Mn grades are hard to start with and work harden like mad.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

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[macmet]

Thanks for you help guys.

A couple questions,

1. How brittle is brittle? In use there will be no impact, but we have to get the casting to site, install it. Just how sensitive is it?

2. What is the cost comparison of Mn steel parts compared to white iron?

 

[metengr]

Answer to Question 1).
We have bottom ash or slag lines from our boilers that are constructed of white iron piping with victaulic couplings to handle abrasive wear conditions. Because of the very poor ductility of this material, handle it with care; do not drop, do not attempt to apply external bending forces to this material to correct misalignment or install in service with external bending forces. It is designed for very low service stress or in compression with no dynamic or impact loads.

 

[arunmrao]

Transportation of white iron parts is truly a challenge especially if there are thin long projections. They need to be individually packed,and handled with extreme care until installatio is complete.

mn steel castings should be 1.2-1.5 times costlier to white iron(no alloying) castings.

 

[EdStainless]

I am not sure I understand your comment on the cost Arunmrao.
Ductile iron (unalloyed) will be the lowest cost. Either White cast iron (high Cr) or Mn steel will be more expensive. These days Cr costs more than Mn, but irons are easier to cast than steels, but white iron is a pain, I am not sure which way it will come out.

Remember, any white irons are brittle, don't load them in bending or tension.


= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[arunmrao]

Ed !
Thanks for pointing out the anomaly in cost mentioned earlier.

White iron : Normally chill cast grey iron or cast white with a low CE.(Small amounts of Cr ,0.5%). Cost 750-800USD/ton.


I have made a comparison in costs with this grade.

In real terms Mn steel castings are sold at 1200USD/ton.

High chrome irons 27% Cr variety at 1200-1600USD.

Since these are high volume items and thanks to China these are the prevailing costs. I often regret such enquiries as I get a better price in domestic market.


I hope I have clarified.


While on the topic of costs,can you please explain the upsurge in 304 costs for the past 2 weeks and is exxpected to go higher by month end.

Will Mo price climb down ever. It is a huge drain on my finances. I am exhausted!!.

 

[EdStainless]

Mo is relaxing, not as fast as I had thought it would, but it is comming down. Most Mo is a mined as a byproduct along with Cu. This is similar to Co, and it is changing. People are now starting to look at mines with an eye toward the Mo first. This will bring more supply on the market, in a year or two.

The recent rise in 304 prices is Econ 101, supply and demand. Mill capacity is still tight and lead times are long, so they raised base prices again. The sheet guys have done it twice this year already.
The comodity prices, Ni and Mo mostly, will come down slowly as additional capacity comes on line. Neither comodity prices or base prices will fall significantly until the next global recession.
Wait and see how much iron ore goes up this year. It jumped 70% last year and the word is that this years rise will be singificant.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[arunmrao]

Ed a small interesting news. Until a few years ago,ironore mine owners were a neglected lot. Now they have personal helicopters,with helipads to hip hop around merrilly. There is a whole society living picking up the fines spilled from the trucks during transportation.

 

[EdStainless]

Amazing isn't it.
years ago I was casting high Co alloys. We tumbled the castings to remove the sand. We paid a guy to haul it away. When Co went from $2/lb to $10/lb he offered to haul it for nothing. When it went to $20/lb we installed seperators and trapped all of the metalic fines that we had been sending out in the sand. It took our hauler about 3 months to catch on. We went back to paying him to take the sand away.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[macmet]

I have been looking into possibly using Mn steel as suggested. I'm curious about how work hardening increases a materials abrasion resistance. I was always told about work hardening increasing a materials strength, but I don't recall it increasing hardness - which I understand to be a good indicator of abrasion resistance.

 

[arunmrao]

Mn steel castings when supplied have a hardness of 210 BHN max.. Due to workhardening,the hardness level increases to near 500 BHN range.

 

[kenvlach]

macmet,
The original austenitic manganese steel containing 1.2% C and 12% Mn was invented by Sir Robert Hadfield in 1882. The first major use was railroad rail. Lots of literature since. Google for 'Hadfield steel properties,' 'manganese steel properties,' 'manganese steel hardening,' etc.

Also, ASTM A128/A128M-93(2003) Standard Specification for Steel Castings, Austenitic Manganese

http://www.astm.org/cgi-bin/SoftCar...EDLINE_PAGES/A128A128M.htm?L+mystore+uqij8913

Table 1 gives compositions of the casting grades.
It references ASTM A781 for common requirements of steel castings, including testing.

 

[macmet]

Well, I went to our supplier and discussed this further with them.

They recommend a white alloy with 15%Cr and 3%Mo. But they also mentioned a ductile iron "100-70-03", ASTM A536. BHN ~300. Cost is only slightly less than the white iron.

How much of a performance drop can I see in the ductile compared the white? The white iron is spec'd to be hardenalbe to 700BHN.

I'm worried about the brittleness of the white iron, not while it's in service but actually getting it into service.

 

[arunmrao]

macmet,
what is the casting you are looking for and the application or service condition. I have given you indicative costs for straight white iron and the difficulties in handling.

15Cr/3Mo is a good alloy ,but this is also susceptible to breakages in handling. just today a few VSI parts were damaged by my boys,the edges were chipped.

I fail to understand the utility of ductile iron for abrasion wear application.

 

[macmet]

Arunmrao,

The casting is for moving material, such as wood, using a step system.

The reason I was considering ductile iron is b/c I was asked to look into it. I have gone to my supplier and it is marginally cheaper than the CrMo alloy. Unfortunately, where I work, that is often enough to make it the best option. So I am trying to put together a case for going with the slightly more expensive CrMo alloy.

I am not worried about small chips breaking off, appearance makes no difference to me. What I am worried about is the possibility that in the field whoever installs it may decide that the best way to get them into position is to smash them into position and destroy the cast.

These are not small castings, I don't have the drawings here but I would assume the smallest cross section is 5/8" (min) and some of them weigh up close to 200 pounds.

 

[arunmrao]

If your installation is going to be so crude and violent,it will be better , you use Mn steel or 4140 grade casting. This would stand the rigours of a tough installation and will not give way. DI casting is also susceptible to cracking under impact.

 

[macmet]

I'd like to thank everyone for their help with this topic, I really appreciate it.

Cheers