How can Macrosegregation affects the mechanical properties

[stanislasdz]

What would be the difference betwen the mechanical properties of a sample from the top and other from from the bottom of the ingot, in steel forging ?

 

[redpicker]

I've found the top of the ingot to usually be a bit richer in alloying elements as it is usually the last to solidify. This makes the parts from the top higher in hardenss and tensile strength than those from the bottom (with the same heat treatment).

I think advances in process control and better solidification modeling has reduced this effect. I remembeber 20-30 years ago, I'd see 10,000 PSI difference in Q&T yeild strengths between the top and bottom.

I'm guessing your diagram is showing carbon distribution?

rp

 

[stanislasdz]

".... This makes the parts from the top higher in hardenss and tensile strength than those from the bottom..."

What about the CHAPPY IMPACT TEST ?

" I'm guessing your diagram is showing carbon distribution? "

YES !

From this paper :

http://www.tms.org/pubs/journals/JOM/0612/Wu/Wu-0612.html

 

[metengr]

stanislasdz;
As you are aware, there is a direct correlation between CVN impact energy and carbon content. As the carbon content increases, the upper shelf decreases in value and typically shifts to the right (meaning the ductile to brittle transition temperature would increase).

 

[arunmrao]

stanisladz,

Macrosegregation defect is not the only one to occur in an ingot. There are others, like porosities,inclusions, large columnar grains sometimes cracks which combinedly affect the mechanical properties.

It will be rather too simple to conclude a study based only on macro segrgation effect.



Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[redpicker]

The effect on impact can vary. Metengr is correct that, in general, higher carbon results in lower impacts, but that correlation assumes comparable microstructures. This isn't always the case, particualr with quench and temper heat treatments. I've seen the situation where the material at the bottom of the ingot is so lean that it doesn't adequately harden in a Q & T where the material at the top does. In this situation, the impact strength of the material from the top can be considerably better than that from the bottom.

The macro seggregation of the other alloying elements will follow that of the carbon, so the areas rich in carbon will also be richer in Cr, Mn, Ni, and, to a lesser extent, Mo. This can affect the hardenability of the material.

rp

 

[stanislasdz]

Hi metenger !

" As you are aware, there is a direct correlation between CVN impact energy and carbon content "

Yes, but don(t forget also the impact of residuals elements;

Sorry but in my samples, i always found that CVN in the top of the ingot are higer than the bottom !!!!! very strange !

 

[CoryPad]

Does the ingot get homogenized before forging?

Carbon concentration varying from 0.23 % to 0.45 % is enormous and will have a huge effect on properties.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[stanislasdz]

@ Corpad !

Does the ingot get homogenized before forging?

YES !

" Carbon concentration varying from 0.23 % to 0.45 % is enormous and will have a huge effect on properties. "

it's my forging, just an picture wich show the macrosgregation !


@ Arunmrao

Absolutly, macrosegregation is not the only effect !
But i want to measure the impact of the macrosegregation on the mechnaical properties !

 

[CoryPad]

If the part gets homogenized, then redpicker has mentioned an important factor. Carbon diffuses easily, while Cr, Mn, Mo, and Ni don't. This affects formability, hardenability, and mechanical properties.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Robertmet]

Back in my steel mill days the tops and bottoms of the ingots were cut off due to segregation problems .Later that was dealt with by going to continuous casting.