Charpy test

I just recently started working in a steel Foundry, I'm not familiar with the Charpy Test. I have read some specs(asme sa352 for grade LCC and A-370. Recently we've seen failures in one of the tree test bars. The bars are being poured in a sandcasting mold. Would you know what could make them fail?

Thanks for the help! Mario

 

[arunmrao]

Your question is not clear. are you experiencing problem with the grade LCC alloy or testing procedure. Sand casting should have no influence on test failure. Please elaborate so that the reply can be more specific.

 

[5123]

This is Mario E, Thank you for the help. I guess I was not clear on the question. The spec for the charpy test on the LCC is 12-16 (Impact Strength/foot-pounds), the average of three test bars. The three test bars are from the same area and usually 1 or two of the three fail, this makes the average fall below spec. We have done chemistry on these material and all the time is within spec. The difference of failure between one test bar and the other is big, where one could fall around 14 the other could be 5, Is this typical?. As you can see it is very easy to fail with these numbers. I'm not familiar with Sand castings, my background in the foundry has been with Titanium (Investment casting)only for 14 years, this is the reason I brought up sand casting, would any loose sand affect this test?.
One of the other Question is, What other factors may contribute to the failure one test bar vs. th other? other than chemistry. Thank you for taking the time and patience to answer and most of all thank you for sharing your knowledge.
Sincerely, Mario E.

 

[vanci]

if you have the time, go out on the floor and observe how the material is being handled from begining to end. some one might be overlooking something.

 

[GRoberts]

Mario,

Assuming you are tesing at -50F per A352, for a good clean heat of steel, you should be getting 50 to 150 ft-lb. Although, even with good steel, the lower strength steels like LCC, LCB, etc. seem to get quite a bit more scatter in the results than higher strength steel like A487 Gr. 4B, for instance. Most important is to have P and S low in chemistry. Also take a look at your specimens before testing. Is the notch machined properly? Does is have the correct radius at the root of the notch. Does the notch have any tool chatter in it?
Good luck,

G Roberts

 

[castingmet]

There are many reasons for low charpy values. Here are the most obvious ones in order of importance.
Discontinuities such as shrinkage/porosity or macro-inclusions at the location near the notch.
Normalized and tempered condition rather than quenched and tempered condition. Q&T gives much better impact properties than N&T.
Sulfur and phosphorus levels greater than 0.015wt% each.
AlN embrittlement large dull facets on fracture.
Improper heat treatment- not austenitized properly or tempered properly.
Hope this helps