HRB vs HB
HRB vs HB
(OP)
I work in an automotive manufacturing facility. We get forgings in that have certain hardness specifications. I'm trying to wrap my brain around an issue we're having and cannot find any information. We have a hardness requirement in HB. We use a 2.5mm tip @ 187.5kg load. Upon inspection of the material we've found the hardness to be too high. We contacted the supplier and their records indicate that the material was well within spec during their testing. Their method for measuring hardness is the HRB scale. We've sent samples to two different independent facilities where the HB hardness was well out of specification in the same range that I measured. One of the independent labs measured in HRB but their results showed the hardness to be in specification. The specified tolerance of the steel is 167 - 229HB. The HRB scale shows 86 - 98.2. I guess my question is what is the significant difference between the two measurement methods and why would somebody chose one over the other?
Thanks,
Kevin
Thanks,
Kevin





RE: HRB vs HB
RE: HRB vs HB
Thanks for the help,
Kevin
RE: HRB vs HB
Brinell hardness is measured using a 10mm dia probe and 3000kgf, while Rockwell B-scale is measured using a 1/16" dia probe and 100kgf. For the situation you describe, BHN would seem like the better metric.
However, you note that your inspection procedure involves a large batch of forgings. Typically, there are other factors that matter more with regards to the quality of steel forgings than just surface hardness. Things like forging grain size, material cleanliness, etc, can matter more. With steel forgings, what you should strive for in your as-delivered condition is a forging that has uniform metallurgical properties/quality and is free from retained stresses. If your forging samples are showing excessive hardness at their surface, then you may need to put the forgings thru a stress-relief and normalize after forging.
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
While a common Brinell test uses a 10-mm diameter indenter and 3000 kgf applied force, multiple other indenter sizes and applied forces are allowed within the testing standards like ASTM E10 or ISO 6506. SAmerica has provided the test parameters, 2.5-mm indenter diameter and 187.5 kgf applied force. Those are close to the values for Rockwell B testing (1.588-mm diameter and 100 kgf applied force).
SAmerica,
Since the two hardness methods are similar, you should expect similar results. It is confusing that you are seeing large variation. While ISO 18265 shows 102 HRB conversion for 257 HBW, that is outside the defined range and can be used as an estimate only. Since you are near the upper limit for Rockwell B testing, and since it is possible that some labs still use the banned steel indenter balls for Rockwell B testing, I recommend you consider the Brinell testing to be more reliable.
RE: HRB vs HB
RE: HRB vs HB
Thanks,
Kevin
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
Maui
www.EngineeringMetallurgy.com
RE: HRB vs HB
RE: HRB vs HB
Thanks again for all the help guys,
Kevin
RE: HRB vs HB
SAmerica, as CoryPad correctly pointed out, in your OP you mentioned you are using a 2.5mm dia probe to check hardness. And in a later post you mentioned you are performing the hardness check on a sectioned specimen at 3-5 mm from an adjacent surface. It may be possible that your results are affected by a combination of the probe diameter and the proximity of the indenture location to the edge of the specimen.
Maybe someone familiar with hardness test procedures can confirm if there are guidelines for edge margin of test points with various sizes/shapes of brales/probes/tips.
RE: HRB vs HB
RE: HRB vs HB
Why do you believe that your 2.5 mm (diameter?) tip (indenter) with 187.5 KG load accurately provides the BHN when compared to the 10mm ball indenter and 3000KG load? It will not.
RE: HRB vs HB
Your question is important if the material is heterogeneous on the scale of the indentations produced by the Brinell and Rockwell B tests. The Brinell test they chose is very similar to the Rockwell B test, so the variations between those methods are confusing.
RE: HRB vs HB
The reason I ask is that I have seen many different types of Brinell testers and not all of them (none, actually) would meet this requirement, although I haven't seen one certified for 187.5 KG / 2.5mm ball. The differences in results being seen here, in my opinion, cannot be attributed to steel vs. WC ball or even microstructurial differences. As pointed out by CoryPad, the loads and ball sizes of the two test methods are quite similar, so I would expect the results to be much more similar than what is being reported.
Without knowing anything more, I'd attribute the differences seen to testing errors.
RE: HRB vs HB
Thanks again for all of the help. You guys are very knowledgeable,
Kevin
RE: HRB vs HB
RE: HRB vs HB
RE: HRB vs HB
Maui
www.EngineeringMetallurgy.com
RE: HRB vs HB
RE: HRB vs HB