I've done a lot of research for a newbie, trying to understand chisels, and how to choose them.
I have discovered along the way that many of the cheap chisels are made with Chrome Vanadium, which as I understand it can get very hard compared to something like simple carbon steel. Yet from my research, I see that CV doesn't hold an edge near as well as good, well tempered carbon steel. So it stands to reason, at least in my small head, that hardness is only one factor in edge retention/sharpness.
I have no clue what metal/alloy the Irwins are manufactured from, but in the case of "the scratch test", shouldn't some kind of measure be taken to ensure that the steels used are at least similar in composition?
Please keep well in mind that I am not responding to the OP's method of testing, it is just that the conversation brought this line of thought into my head. And please be gentle to the newbie; I realize that there is way more I don't know than that which I do.
I have settled on the fact that I prefer a bit softer steel, one easier to sharpen quickly. I keep sharpening media with me, and touch up as often as necessary. Takes very little time, and I'm back to work again.