Chemical uniformity in Forged bar

[leizhou]

I have got a few low carbon steel forged bar with 620mm diameter and 3m long. It has been found that the chemical composition is varies from one end to the other with a difference of about 0.02% for carbon. Other elements are not varies considerably.

The material was already edge cutted and grinded before the PMI test, so shouldn't be oxidation of the surface. Is this effect due to the density of the alloying element?

Can anyone give some idea please?

Many thanks

Lei

 

[arunmrao]

The only possible reason could be decarburization. However,0.02% should not be a major concern if it is within the limits..

How reliable is the sampling procedure?

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

 

[leizhou]

Can you explain a bit more detail about how decarburization would affect the composition on both end?

Sampling are carried in the company by bodycote, i think they are quite reliable.

Thanks

 

[tomwalz]

You add carbon to iron to make steel. The process takes place as the materials are heated. If the materials are reheated there is a tendency for the carbon to come back out. We see this in blacksmithing and in laser cutting as well.

I would agree with your opinion of Bodycote with the caveat that no one is perfect.

Just a hunch but something sounds off a bit in the 0.02%. Might there be a couple minor errors that compound?


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[metengr]

Sampling error.

 

[arunmrao]

Why should you not give another set of samples to another lab for conformity?

Another issue how is this variation in carbon affecting your end product or performance?

As an aside my son works for Bodycote in one of their testing labs in their mechanical testing group !!

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

 

[leizhou]

I agree with the carbon come out, but both test are on the end of the bar.

I had 10 tests they all showing the same.

It does not bring me problems, just want to understand it

 

[Metalmeister]

Sounds like a combination of sampling variability and typical inhomogeneity of chemical constituents in the steel product.

An outfit by that name near Chicago made 3 critical mistakes in a job that we had run through their shop not so long ago. But I would not be concerned with this chemical variation unless it was a significant percentage of the total amount such as in a low C stainless.

 

[leizhou]

I have just realised there is a 0.05 varies in Cu and Mn for some materials as well.

I know there must be a issue of sampling and testing.

But apart from that what can be the basic reason. Decarburization can explain carbon content, how about other elements.

These materials are experienced some problem in the past. That's after HTs. Chemical can be one of the issue.

Thanks

 

[CoryPad]

Variation of 0.05 mass percent for Cu & Mn and 0.02 mass percent for C can be typical variations in composition within a part, especially one as massive (~ 7100 kg) as yours.

Regards,

Cory

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

 

[arunmrao]

leizhou,your expectation of 0/0 variation in chemistry may be difficult to find in text book samples. What are you planning to achieve by this super homogeneity levels.

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

 

[arunmrao]

An after thought, how successful will it be to zone refine low alloy steel. (Is it too naive a question?)

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

 

[steelmtllrgst]

Was this material forged from ingot or billet? What is the carbon level (what is your low carbon)?

 

[ulyssess]

At my knowledge 630mm forged bar is only produced from ingots. In ingots macrosegregations resulting in differences of 0,02% C between top and bottom is not unusual. For ferritic steel cast in heavy ingots (50 to 100 t) you can find differences of 0,04% C

 

[steelmtllrgst]

agree with ulyssess. Assuming that these are forged from ingots, and that there is a reasonable amount of carbon in the material bulk, 2 pt difference in carbon is very reasonable.

 

[leizhou]

Thanks everyone, I think I did find useful information here.

 

[swall]

Leizhou--you might take a look at SAE J408 and SAE J409. These describe sampling methods for steel products and allowable variation in the product analysis as compared to the heat analysis.