Tempering understanding

T

tr3yanderson

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Mar 6, 2017
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Hey guys, Just wanted to better understand something with regards to tempering. I can find many tempering temperature charts such as this one for 1084 from Cashen.

http://www.cashenblades.com/steel/1084.html

Now I understand these numbers are estimates and that there are many variables in play. I also know the chart is assuming you are able to harden to max hardness for this steel. My question is less on the specific numbers and more on the underlying principle relationship.

So using the 1084 chart from Cashen as an theoretical example. Maximum hardness is about 65 RC and tempering to 400 gets you to about 60-61 RC. now if I, as a beginner using my homemade forge, do not get a perfect heat treat (very likely), let's say I was only able to get a hardness of 63 after the quench. If I tempered at 400 would I still get around a 60-61 RC or would the temper also be lower at about 58-59RC?

Does this make sense? Again I'm not focused on what numbers I'd actually get but want to understand the principle here. Thanks,
 
I think the loss in RC for a given tempering temperature (in your example 4-5 points) is closer to being a constant than the hardness for a given tempering temperature. But there are other conditions that apply. In general, with 1084 I think it would be reasonably safe to say that a 400F temper is going to drop your as quenched hardness 4-5 points. The closer your as quenched hardness is to 65, the more that drop will be constant. If your as quenched temperature is drastically out of wack, say 55 RC, then I think it's kind of up in the air as to what a 400F temper will do.

But this is why on the more complex steels that LN and a low temperature temper is being used (400F say) the final RC is varied by varying the austenitizing temperature (and as quenched hardness) so that the tempering temperature can remain constant and avoid either tempering martensite embrittlement or the high temperature (900F+) tempers.
 
It would be either the same amount of hardness drop or more (ie 4 Rc or greater). The reason is if you underaustenitized it then there would be less alloy in solution. The Mn, Si, Cr, Mo, etc all contribute to temper resistance, so having less of it would lead to more hardness drop. The extent to which this matters depends on the steel, look up different datasheets that include tempering curves for different austenitizing temperatures and you can see for yourself.
 
Thanks, this makes sense what you are both saying. I appreciate you helping me understand the craft a bit more
 
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