Cast steel Ground Engagement Tool failure after hardfacing 4

[emonje]

Hello,

We make these cast steel tips for dragline buckets. Several failed recently, failure rate much higher than usual.

We had a batch of these tips hardfaced on top, front, side and bottom faces. Hardfacing didn't cover full face, just few ~20 mm wide weld lays of hardfacing metal.
All the failures have been in this batch.

Material is cast steel with Carbon equivalent of 0.7, typical hardness 400-450 BHN (43-47 HRC), typical yield strength around 750 MPa (108 ksi)


Here are some photos of the failed part:

Here's a rendering of the part with hardfacing:

Can anyone please shed some light on possible cause & remedy?

I don't have any info on how the hardfacing was done, if any pre-heat or PWHT applied.

I was thinking this overwhelmingly brittle fracture was because the part was cooled too quickly, making it too hard to the application.
Not sure if pre-heat will help, part is too small to hold heat & remain in high enough temperature may be?
I was more inclined to some form of PWHT after hardfacing, or at least put it in furnace for slow cooling.

Thanks.

 

[EdStainless]

I think that you need to visit the guys doing the hardfacing.
We used to hard face some parts, they were pre-heated, then pulled and placed on insulation while the overlay was being applied, then put into a box furnace an temper temperature. When the batch was done the furnace was shut off and allowed to cool.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

I would not bother or waste time with discussing the above until you have a proper metallurgical failure analysis performed to determine the cause of failure.

 

[Tmoose]

Have checked the failed parts for hardness?
For fun, before sending the parts off to the metallurgical failure analyst, I'd try drilling a few shallow hole in the surfaces near the cracks with a sharp cobalt 1/4 inch drill at slow speed with lubricant. I'd be looking for the drill to form short curly chips, and not dust

 

[arunmrao]

Why blame hard facing, it can be a poor quality casting too. One can see that the fracture is very coarse, typical of high carbon, high hardness material failure.

As suggested by metengr, get the complete analysis, before any inference can be made.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[emonje]

Thanks for the input, highly appreciated.

 

[ibfmining1]

With 0.7 carbon equivalent, you are definitely within zone III of the Graville diagram (attached); therefore, preheating is a must. However, I fully agree with everybody - else`s comments such as:

1. Coarse grain structure - very likely your casting / heat treatment process needs closer attention.

2. Also suggested a WPS/PQR for hardfacing build - up welding.

3. And "yes", root cause analysis is highly recommended to mitigate all possible combined side effects for both casting; heat treatment and hardfacing processes.

IBFmining1.

 

[mrfailure]

For failure analysis, I would suggest in this instance also performing the same characterization testing on a part from a batch that was not experiencing failures. That is an easy way to see what specifically was different in terms of end results and the processing required to achieve them.

 

[gruntguru]

There is a crack in photo 3 which is clearly in parent material and unrelated to the hard facing process.

je suis charlie

 

[priyam07]

HI, the fracture surface indicates this is of typical "rock candy" brittle, intergranular failure because of Aluminum nitride precipitation associated with Quenched and tempered cast steels. This is clearly visible in the visual examination and associated with low toughness values. Of course further root cause analysis can confirm this Aluminum nitride embrittlement and what initiated the crack (such as hardfacing). Check with the casting supplier to find out the Al and N levels?