cracked pump-hardfacing effects? 2

[791018]

i used a hardface welding (300 Amp)inside our dredgepump housing to avoid wear on pump inner surface. however, after several months, the crack line occured on the surface of the unwelded. Could this things happen because of the hardfacing weld? we are using the pump casing which made by maxidur 5 material which can withstand a friction of materials from 0.06mm to 6mm for at least 2 years.

 

[metengr]

Yes, most likely. I did a search of the Maxidur 5 pump cast material. Apparently, this is a highly abrasion resistant chromium carbide cast iron. The abrasion resistance is from the chromium carbides embedded in a martensite matrix. The stated hardness is 55-65 HRc scale.

Based on the above information, this cast iron has very poor weldability. You are in a tough situation because having performed hardface welding and attempting to re-repair will be difficult, at best.

The only repair scenario I can think of is to remove the crack from the pump case, and locally weld restore using a Nickel-base weld rod under a high preheat (500 deg F). If you can deposit this nickel-base weld layer over the repair area, you can deposit the hardface on top of this material.

I would start looking at replacement pump casings.

 

[arunmrao]

I agree with you metengr. Very little choice but to look for a new casing. This time try ceramic coating on the abrasion surface instead of hard facing.

I make these pump castings and any increase in heat input during rough grinding causes the parts to crack. Welding is never a good option,though I have got away with it in non working areas and in stationary parts.

 

[791018]

thanks for the fact. its mean a lot. For your info, i was replaced the casing just after the pump found crack. this means, i got nothing to improve on my pump casing. just let it be. do the properties are the same between maxidur 5 and maxidur 3? i'm not yet ordered the new casing for standby, but if you can advice, let see if i try to use maxidur 3 material.

 

[gieter]

Maxidur 3 is lower in alloy content than Max 5 and lacks the Molybdenen you need for sufficient hardness throughout the complete wall thickness.
At this moment Molybdenen is extremely expensive. For this reason Max 5 is very tricky. If it's content is reduced or completely left out of the alloy (and we have seen this), it produces a hard case (60-65 HRC) around a softer core. Most dredgers only look at hardness values in there acceptance criteria and will not notice this. In service the hard surface will wear off exposing the softer material.

A good and at this moment cheaper alternative can be Nihard 4. This alloy does not contain Molybdenen and is precipition hardened leaving a uniform hardeness throughout the wall thickness. I dont think it is possible, or at least economically feasable, to sheat on this alloy. The hardness you measure at the surface is the same (within a marginal reduction of 2 or 3 points) as at the inside.
The patterns used for Max 5 can also be used for Nihard 4.

 

[arunmrao]

Gieter a star for you on your comments about Mo content. I have been advising my customers to switch over from high chrome irons to NiHard. There are few takers. The only issue will be in NiHard you have M7Ce type of carbides as against M23C6 type of carbides in high chrome irons.

 

[gieter]

Arunmrao,

Thank you for the star, I'm flatered.

What do you mean with the issue on the carbide types?

 

[791018]

metenger,
i just follows the references i made to the smit-weld which claims that the maxidur 5 can be hardfaced by using the sterno 40FMC welding electrodes with some precautions. when the pumps start cracking, i aware that something going wrong during the process. i not yet analyse in the materials used for the electrodes.

gieter,
where can i refer the contetnt and material composition for
1. Maxidur 5
2. Maxidur Top
3. Maxidur R
4. Nihard
one thing, i'll discuss with a local pump manufacturer here to fabricate a new pump casing for my usage. What factor should we pay a lot of attention in order to improved our maxidur 5? any suggestions?

 

[gieter]

Max 5 is close to GX300CrMo15.3 meaning it has about 3% C, 14-17% Cr and 1-3% Mo.

There are different grades of Nihard developed by NIDI. The most used is grade 4 which is a GX300CrNiSi9.5.2 containing about 3% C, 8-10% Cr, 4-7 Ni and 1.5-2% Si.
This material is very well documented by NIDI. Have a look at their site

http://www.nidi.org

Both alloys are high alloyed white cast irons and only obtain their optimum properties after appropriate heat treatment.

Maxidur TOP is some sort of steel plate with an abrassion resistant cladding (I think welded) and Maxidur R is claimed to be a bimetalic cast material with a soft carrier material and a hard top. Both are not suted for dredging pump housings at this time.

 

[791018]

dear metengr
i can weld the casing but, as you said, now its time to look for replacements. gieter proposed to used Nihard grade 4. How 'bout you? any suggestion to improved my pump rather than max 5 or nihard?

 

[arunmrao]

15Cr-3Mo grade will be better than NiHard for wear life. Ofcourse I still doubt the benefit of welding a cracked casing. It will eventually be an exercise in vain.

 

[791018]

the casing that i'll weld is completely removed from the system. so, it'll be part of my analysis. just need some exercise to do the precaution to weld the things.

 

[metengr]

791018;
If it was me, I would go with arunmrao's recommendation in using the 15Cr-3Mo grade of casting for this application. He is involved with supplying castings, so I would follow his advice.

 

[791018]

dear arunmrao and metengr,
thanks for your recommendation. in order to get the best performance, many consideration has to be made. either using 15Cr-3Mo or Nihard, both have thier own advantage and disadvantage. However, i need to consider the market price and availability for all materials involved such as Mo, Si, Ni (not including Cr, Carbon and iron as base materials)in asian region. And i have no doubt to again use max 5 with some other precaution in the system itself. Sometimes, doesn't mean the best is the 'best'. sometimes, the worst could be best. The best way for us (maybe) to think the way to improve our existing parts by applying suggestion and experiences which was discussed in this forums.
your kind comments and recommendation is always welcome.

 

[791018]

Dear all
Below are list of the links to image taken for failed pumps for you to get the clear pictures for comments
1.

http://tinypic.com/kf31ch.jpg

- Failures on wearing plate
2.

http://tinypic.com/kf32th.jpg

- Location of the fails
3.

http://tinypic.com/kf32x5.jpg

- Cracked casing
4.

http://tinypic.com/kf333k.jpg

- Crack

*Please post yout comments

 

[arunmrao]

It is best if you could discuss with your pump manufacturer the concerns that you have raised. They will be able to provide the right recommendation. To make a unit casting will be uneconomical as pattern and tooling costs will be high. Also spares suppliers like me may not have the proper drawings. Machining hard metals is difficult and then the heat treatment for increasing the hardness of the casting. This will call for a high level of experience.

Hence your attempt in knowing the price of Mo,Ni etc may not be very useful.