Cracking a carburising pieces

[genesis_32]

Hi,

At work, I have a problem with cracked carburized pieces. Some pieces pass the test and some crack. After carburizing, the piece is resistance welded to the handle. The customer claims that the cause is too high a depth of cementation which is indicated in the figure. 0.25mm is required and the actual is 0.3mm. In my opinion, the load is piece primarily by the core and not the carburised surface. The initiation of the crack is on the lower part of the piece where the part is overheated due to welding. What is your opinion? Is it possible that the depth of cementation is responsible for cracking on the test?

Thanks for your feedback.

 

[bobjustbob]

You stated that 0.25mm is required and 0.30mm is the case read depth. What is the actual minimum and maximum case depth. What is their definition of case depth? For example, we typically use a depth to HRc50. Our Japanese companies use a depth to HRc58. I hope they are looking at a micro and not measuring total case depth with these photos.

 

[EdStainless]

I would focus on the welding. The uniformity of penetration and any pre-heat or PWHT.

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P.E. Metallurgy, consulting work welcomed

 

[genesis_32]

Customer requier is more then 600 HV0,5 on 0,2 mm and less than 600 HV0,5 on 0,3mm. This piece is 650 HV0,5 on 0,3mm. Is it possible that this small difference in depth affects the cracking of the pieces?

 

[EdStainless]

It is possible that the higher C level has resulted in harder (more brittle) welds.
Some cross sections and microhardness traverses of the welds would help inform this discussion.
Where does the cracking start? At the weld or at the open end?
Have they loaded some and them inspected (dye pen) to find initial cracks?


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[3DDave]

Is that a powered metal piece?

 

[mfgenggear]

a little more info on the
what is the material (9130 steel or what?)
what is the hardness of core and case

welding carburized parts is a very bad idea.
is this tool used because of clearance issues?
design change in material required, weldable then heat treat

 

[genesis_32]

Material is 23B2 or. 1.5508. Surface have a 730HV an than hardnes lowering to 600HV on 0.35mm, core have a 460HV.The crack did not start on the weld but on the marked part in the picture.

 

[Martinos]

In fact, welding of carburized components is not the best idea, but if it works in the past, then okay. Anyway, I really don't assume case depth 0,3 mm instead of 0,25 mm plays a role there. As EdStainless wrote, I would suspect welding process.

Also, check (case and core) microstructure and, if possible, make hardness traverse.

 

welding carburized parts is a very bad idea.

Don't even think about it!

And if you insist on welding, carburize after, but most low alloy carburizing steels need special measures to be successfully welded.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[kingnero]

The crack did not start on the weld but on the marked part in the picture.

How sure are you about that?
- That seems like a low stress region (but that's just guessing based on the very first picture), and/but:
- I don't really see a clear initiation on that picture, but perhaps you have other cross sections that show better proof of that?

I'd focus first on other possible root causes...

 

Why is this tool (a homemade socket wrench?) carburized in the first place?

The entire thing needs a complete rethink.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."