Question about heat treatment of castings

[rob768]

I have a casting designated C35CrNiMo6.6. The parts made from these materials (relatively large block of 150x150x700 mm) show extreme poor mechanical properties, with yield and tensile almost equal, elongation <2% and Charpy-V values of average 7-8 J.
Can this material be heat treated (normalizing, followed by quench and teper perhaps) with negative effects such as grain-growth, or this is just "scrap"?

 

[RolMec]

Could you pls. check again for the correctness of the letter C in the denomination? Else without, you'd have an equivalent steel of a SAE 4337 or 4340, going to be Q+T. Annealed a specimen should deliver a tensile strength of around 700+ MPa, but quite better than 2% elongation. Can you have checked the chem. composition of that casting?
Regards


RSVP

 

[rob768]

Sorry, the correct designation is G35CrNiMo6.6
Compostion should be
0.32-0.38%C
0.6-0.8%Mn
1.40-1.70%Cr
1.40-1.70%Ni
0.15-0.35%Mo
I haven't checked compostion (yet) but based on microstructure I assume carcon is ok (the rest i can't see obviously)

 

[arunmrao]

Were the properties checked on cast keel block? This chemistry is close to 4340 or EN24 grade of steel. Have you checked the microstructure and chemistry ?

Your dimensions of 150x150x 700mm is not too big. The weight of the block is just 126 kgs, too small for grain coarsening to happen ( for good foundry practice).

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

Mahatma Gandhi.

 

[rob768]

Chemistry is not checked. Microstructure is quite imhomogeneous.
I am just interested to know if properties can be restored by proper heat treatment. That would save time with regards to repairs.

 

[arunmrao]

Complete metallurgical analysis, study process parameters while producing the casting and then arrive at a decision to salvage or not.

Technically for a rough casting, free from Widmanstatten structure,one should be able to improve the properties by reheatreatment.

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

Mahatma Gandhi.

 

[redpicker]

Are you obtaining mechanical properties in the as-cast condition, or has it been previously heat treated?

If the material is in the as-cast condition, then, yes, the properties can be improved with proper heat treatment. If those are the properties after heat treatment, then it would seem there was a problem with the casting or heat treatment, or both.

 

[RolMec]

Just one thought: Your block is not quite handy, you need a resp. furnace etc. So why not manuf. a small specimen or two, anneal them properly and then do Q+T? Any resp. lab should be able do do this on short notice.
Then, why not divide that block into more handy parts? With a block of that size, mech. properties in themthemselves will vary acc. to thickness.
If chem. composition of low alloy steel is correct, a lot can be done by retreating. However the heating technology for such block might be something for the knowledgeable / experienced company with resp. equipment. I'd seek input from s-one reputable.
Regards

RSVP

 

[JoeyV87]

Normalise at 950C for an hour per inch, air cool - don't quench it, it will crack - then temper at around 620C for an hour per inch. You should get balanced properties from that. Feel free to raise or lower the tempering temperature to raise or lower yield stress