Brass Test Blocks & Microdur Field Tester 2

[Guest102023]

I recently ordered Rockwell B standards and (I should have known in advance) received brass, which for the Microdur MIC-10 I use is out of the question. (I'd like to know in general how brass started to be used for calibration blocks.)

I'd like to hear people's experiences and solutions to Microdur's requirement (in their operating manual) that calibration blocks be of 'similar material' to that being tested. By 'similar material' do they merely mean similar elastic (Young's) modulus? I am looking at testing the entire range of Cr-Mo steels up to 10% Cr, including some exotic CSEF alloys.

 

[EdStainless]

In the high B range you can get a lot of different material so watch carefully.
Modulus and strain hardening rate can both impact the hardness readings that you get.

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Plymouth Tube

 

[stanweld]

The MIC-10 is precalibrated for maerials (steels) having a Young's Modulus of approximately 29,000,000. Do not use your brass blocks unless you need to recalibrate for testing materials with similar modulus to the brass test block. The MIC-10 normally comes with a standard steel test block.

 

[Guest102023]

Any thoughts on using Brinell bars for this purpose? They are steel at least.

 

[stanweld]

I've often used the Brinell bars to verify accuracy with the MIC-10 & MIC-20 hardness testers.

A third party Engineering study comparing MIC-10, MIC-20, Rebound hardness, PIN Binell & Brinell indicated that the MIC-20 provided greater test accuracy than the MIC-10. Rebound hardness values were found to be highly inaccurate. Tests were performed on P91 materials and welds.

 

[Guest102023]

Thanks stanweld,

At the GE website, the MIC-20 just seems like two testers in a package - the MIC-10 plus a rebound tester, although with a more elaborate computer attached. Both Mic-10 and MIC-20 use the UCI method, so how would MIC-20 be better? I would love to see that report if it is publicly available. I agree the UCI method (and TIV) are the only ones to use for HAZ, but I have witnessed plenty of techs report HAZ hardnesses on critical refinery equipment without bothering to actually locate the HAZ or even knowing how to do that.

Anyway my concern is more with obtaining reliable blocks (I am stuck with the MIC-10 tester). I recently purchased a bunch of Brinell bars covering the range of 110 to 300 HRB. I cleaned them up to 320 grit using my in situ metallography tools and then had them tested using HV10 and HRB/C. The results were all over the map, to the point where I was even questioning whether they were even labelled correctly by the supplier. I can post the results if you are interested.

 

[stanweld]

I'm not sure that why the differences between MIC-10 and MIC-20 occurred. Both used the same applied load for indentation. Possibly due to improved electronics? By the way the rebound test was done with Equotip.

 

[Metaljon]

The GE instruction manual supplied I think is very poorly written. We have done extensive research on using this instrument and if you are going to use this equipment in the field then you will need to some validation work. The MIC10 uses the Ultrasonic Contact Impedance method and does not use vickers hardness method. Consequently being an impedance measurement it is very sensitive to material type.

If you want to get accurate data then you will have to make your own test blocks using the same material as being tested and then heat treat to different hardness conditions. The UCI method should only be used within a defined hardness range based on your own calibration tests.

The surface finish is also critical. 320 grit finish is not good enough. If you want good results then you need to polish to 1000 grit but replica quality one diamond finish is best. Then etch the surface so that you can clearly see the weld and HAZ. In the field, if you don't have good hardness calibration blocks then use a Pin Brinell hardness tester as the means of cross validation.

Finally if your purpose is to measure HAZ hardness, then this is best measured using a line measurement technique where a series a readings and made across the HAZ.