Hardness test results 3

[deco0404]

Guys,

we just ran some production test plates as part of our current welding project.

On one of the samples the hardness results are a little high. We have one reading (out of 45) which is 378Hv. Our max allowable is 350Hv. We are working to DNV C401.

My query; There were 3 readings taken in this particular location (weld HAZ), the average of the 3 readings is 314Hv. I have done hardness testing down the years, and as it is quite a subjective test, we have always worked on average readings, and not individual readings.

Does my test plate pass the test or not?

regards

Declan

 

[Eddycurrentguy]

I would take additional readings close to, (but not too close, lol) to the high reading, or take another traverse above/below for comparison. Hardness tests can be affected by many factors...its possible you hit a patch of transformation product that is not representative of the remainder.

 

[metengr]

What does DNV C401 require??????

 

[deco0404]

Sorry, max 350Hv.

 

[SJones]

Neither DNV-OS-C401, nor ISO 6507-1, indicate that average hardness is the criterion. Values are to be reported per individual indentation. As per the applicable standard, the test has failed to meet the stipulated criteria. How such a failure can be redressed will be for agreement between the contracting parties. If it were EEMUA 158 as the applicable specification, two further complete macro-hardness tests would be required.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[Metaljon]

Yes retest macro hardness required. Could be inadequate preheating. What preheating temperature did you use?

 

[deco0404]

Preheating is only 50deg C

 

[Metaljon]

What material plate grade are you using?

 

[deco0404]

just a standard grade NV D36. .15C, 1.5Mn..shipbuilding steel, normalised and rolled.

 

[Duwe6]

"hard spots" in steel plate are not unknown, even with today's Slab-Cast steel. I don't know their origin, just that you find them on occasion. These occasions are pretty rare in the last 2 decades, but they still [barely] exist. The ones I find are less than 10mm in diameter, as when I move over a little [5mm or less] the steel is 'normal'.

 

[Guest102023]

I'm not familiar with the material, but a limit of 350 HV in the HAZ tells me this steel is something more hardenable than garden variety structural. Therefore 50°C sounds like very inadequate preheat.

378 over 350 is a significant miss. I assume you are using Vickers with a 10kg indentation load. Hopefully you are not running into the dreaded and much-debated local brittle zones (LBZ).

My philosophy on HAZ testing is that you report the hardest result, unless it is clearly an outlier. Maximum hardness often lies near the plate surface, where it matters most.

I have seen many sloppy, metallurgically ignorant lab techs (and some engineers) get weld hardness testing criminally wrong. (I'm not suggesting you are in that group.)

 

[QAFitz]

As noted in this thread, "hard spots" in steel plate are not uncommon and, from what I know about welding, throw in all of the variables in any heat affected zone, wow. I suppose anybody could find whatever reading they desire. I don't dabble in DNV C401 to know of what I speak except as I stated in this post.

 

[Viking5711]

By the sounds of it you are using a Vickers hardness, in that case I would make sure the hardness values meet the requirements.

If you are doing field hardness using a MIC 10 I would consider looking into ASTM A1038 at the proper calibration requirements for this equipment. Using an incorrect calibration standard can drastically change the results