Cast Iron vs. Cast Steel Test

Date 10-21-2005 17:47

Hi everyone - Question:

I was wondering if anyone knew of a reliable test method to determine if a material is cast iron (high carbon) or cast steel (lower carbon).

We are often asked this question in regards to welding repairs of large cast hydrocarbon pump cases and we have struggled with different test methods (observe grinding sparks, chipping with a chisel, etc) with varying results and lots of shrugging shoulders.

I was wondering if there is some reliable method of testing the material to determine the difference of the two, preferably nondestructive.

Also, what methods are others using to determine this?

The pump cases are used in a petroleum refinery and are anywhere from fairly new to 50 years old.

Thanks in advance,

JKH

By jwright650 (*****)

Date 10-21-2005 17:55

http://www.tpub.com/steelworker1/5.htm

Click on "NEXT" to get to the page that talks about using the Spark Test by evaluating the sparks off a grinder.

John Wright

By MDG Custom Weld (***)

Date 10-21-2005 19:54

We have used all of the test that you have mentioned, with limited results. The grind spark test takes some time and experience to understand (especially if one is color blind). We use a drill test and have had great success with it. When you drill steel, it makes chips and shavings that are easy to recognize. When you drill cast iron it will make a fine, graphite like dust. You only need to use a 3/16 or 1/4 drill, and only go deep enough to identify the shavings. It works 99% of the time. Most people assume by the look of a fracture surface that the material is cast iron, more often then not it's cast steel. Cast steel still should be pre-heated and welded with some level of care, but cast iron as you know take much care.

By jwright650 (*****)

Date 10-21-2005 20:03

My opologies....I should have read the original post closer, he mentioned he had the same results from the spark test as you indicated. I was simply passing the link along, as this question has popped up several times in the past. I personally have not tried any of those tests to verify their accuracy.
John Wright

By pipewelder_1999 (****)

Date 10-21-2005 23:13

A ground or milled surface of grey cast iron will leave a smudge of graphite on white paper. Carbon steel will not. This does not apply to other types of cast iron.

Items that have been is service under varying conditions may not apply to this test.

Cutting or forming a puddle with a torch may help.

Have a good day

Gerald
http://www.weldinginspectionsvcs.com/

By weldemup Date 11-25-2005 03:17

Try to remove some metal with a chisel, if it curls its steel, if it chips away its cast iron.

By RonG

Date 12-01-2005 17:00

With out taking samples and sending them to a Lab the Spark Tree test (grinding) is the most reliable. The Carbon content makes for a very large Spark Tree very close to the grinding wheel where as the Cast Steel's Spark tree is sparser with longer tails.

Also the Graphite (as mentioned) is a very good indication of Cast Iron.

Another thought is that unless its a welded fabrication Cast Iron is the prefered material because of the ridigy.

By swnorris (****)

Date 12-01-2005 18:49

Basically, if we could remove the graphite flakes from cast iron and squeeze what is left together, we would have steel.

By Barbosa Norbert (*)

Date 12-03-2005 22:55

I have a pratical resource

1) Weld a 1/2" x 2" Low Carbon Bar over the piece to be tested. Apply a weld bead with E-7018, just by one side.
2) Hit the bar welded by the side against the weld bead until it breaks.
3) a- If the weld bead breaks by the side of the piece being tested it is cast iron.
b- If it breaks by the side of the bar welded or in the middle of the bead, it is cast steel.

By the way: It is necessary to apply 150°C preheating at the area to be welded.

It is used to determine the appropriate temperature when we don't know the type o steel to be welded, raising the preheating temperature
step by step. It is well known as NICK BREAK TEST.

Have a good luck.