Different Steel Lot Effects on Projection Weld Performance

The secret of steel is carbon carbon carbon and you have not provided us with the Carbon. Also the residual elements nickel chrome and moly can add to the carbon equivalent which could affect weldability.

See my blog:

http://pmpaspeakingofprecision.com/2009/12/29/carbon-equivalent-and-weldability/

Of the data that you have given, the difference between the aluminum on these two lots could indicate a difference in austenitic grain size.

but its a minor difference, as 0.015 min Aluminum is the minimum I specified to assure Fine Austenitic grain size. 0.014% is sooo close to 0.015% that clearly the 0.035 is plenty of aluminum to assure fine grain.

Given the facts presented, my only idea is the difference in grain size as implied by the Aluminum values reported.

My guess. milo

Best would be to do a complete spectro and the micro of both.

Additionally - you are doing electric resistance welding? Any surface coating eg preservative on one of the lots?

Hello,

Unfortunately the Carbon content is not listed in the chemistry supplied by the steel mill. Type 1 enameling steel has a spec. limit of .008% Carbon. I am told it takes a more sophisticated (costly) test to measure Carbon levels that low so the mills don't check that for each heat of type 1 steel. The steel is lightly coated in mil-oil and all of the blanks were very light to almost bare. I suspect part of the difference may lie in the fact that the different lots of steel may have come from different steel mills but I would like to know what difference in makeup would give us such different results.

Enamelman

I donot believe that 0.008% is the Carbon spec.

If it were grade 1008 it would be 0.08 weight percent Carbon.

That is a credible number. 0.008% is not even a single point of carbon.

Regardless, if the Carbon is in the range of 0.08 wt % or below, then it is highly unlikely that the weldability issue is a result of Chemistry.

The possibility of different coatings was pointed out is very likely, and a difference of grain size is also possible explanation.

I also do not believe that the steel mill doesn't have a leco carbon analyzer to run production analyses. But I know my market, not yours.

milo

There may be a metallurgical reason for the behavioral difference between the two steels. However, before reaching that conclusion, I suggest you look at other possible causes. These steels are usually coated with corrosion inhibitors. Were they the same, and were they removed the same way? Was the surface finish the same on both lots? Could the sample welding sequence be related to the problem?

Hello,

The welders used in the trial are electric resistance welders and the welds in question are projection welds. The steel thickness is .033. The component parts are stamped. The welders are fixtured and programmed for these parts. The different lots of steel was the difference between porcelain failure or not. There were no failures on one lot on either welder and many failures on the other lot on either welder. Surface cleanliness and mill oil coverage was light. I may have to have the two lots tested for more specific chemistry. My hope was to use the data I have in hand in order to understand why there could be such difference in effects on the porcelain enamel over the welds.

Enamelman

I understand all this. The question I was asking was whether the two lots of steel came from the same supplier, or is there a possibility that the mill oil residue had different chemistry and was not effectively removed by the cleaning process. In other words, I'm suggesting that you look at other causes in addition to steel chemistry as the cause of your observation.

Hello Welderman,

Thank you for your insights. I do not know if the steel came from a different mill but I suspect it. If that is the case, the mill oil would probably be of slightly different chemistry as well. The slitting house where the steel is blanked for us is not commenting on the origin of the lots of material. The amounts of mill oil present on the blanks is minimal (almost no indication of actual coverage) but maybe it's enough to affect the weld. The parts are not cleaned until after they are welded. The finishing is not done in house. These parts sat in totes for a few days down at the finisher (this is typical for all of our enameling steel coating).

Enamelman

Now there are many rust inhibiters that will not be visible (like oil) and the thickness will be micron level. Unforrunately even at this thickness welding may be a problem. Can you try to clean some test runs with organic solvent and check?

And for steel, carbon is spectro-able. I will also suggest microstructure. Especially in view of some recent problems I am facing with 34CrNiMo6 (1.6582) that I am going to send for micro, and I am sure that will come out to be under-tempered.

Welderman,

I will see if I can get the materials tested and also if I can get my supplier to certify what mill the material came from. I will also try a preclean on the formed parts prior to welding to see if the mill oils play into this.

Thank you for your suggestions.

Enamelman

Better than getting a certificate from the supplier, _{(there are certain sources from which any cerificates in original, including those certified by reputed agencies are available)} I will advice you to get it tested yourself.

I assume that you don't have your own lab, but you may take help from a local lab. The charges are nominal only (at least around here) , of course that depends on the elements , but should still be not very pocket unfriendly. Micro also may be recommended (as Milo said) it will give you some idea about the grain refinement condition.

Keep us posted about your research results.

Thank you all for your replies. I am learning the value of CR4 and all the knowledge and experience that can be tapped. I have forwarded this website to a colleague as well.

I will update if I can get the authorization to get the steel lots tested.

Thanks again,

Enamelman