How Accurate is Steel Media Hardness Testing?

摘要

I was recently asked why there were variations among laboratory hardness reports for steel peening media. What I discovered in a brief investigation of the supplied reports was interesting and suggests that we need to pay attention to these findings. The hardness range of the sample is 45-52 HRc (Hardness Rockwell C scale). The accompanying illustrations indicate two areas of concern. First, there is a disparity among the laboratory results despite that all the labs were Nadcap accredited. Second, the sample had a higher hardness level than allowed in specifications. An initial data analysis using only hardness averages indicated that there is, indeed, data scatter. A lab might accept the media if it looks only at the average values and claims that the results are within spec limits. I gained more insight into the data scatter with the histograms on page 41. The histograms made it easier to see that there is something drastically wrong. There should be a way for the labs to synchronize their readings since they are Nadcap accredited.