[TheForge] Tempering and hardness

[Andrew Vida]

As I recall, some steels display double peaks.  Draw to some temperature 
and the hardness is diminished.  Draw further to a point and hardness 
has increased.  Further still and hardness continues to fall.  I do not 
recall this a being characteristic of any stainless steel, but rather 
some high-alloy material though I cannot recall specifically the 
specification at this time.

As for the obstreperous spectator, I will suggest to you that they are 
one of the reasons that iron bars exist.

On 12/5/2011 9:59 PM, Paul Novorolsky wrote:
> During a public demonstration last weekend, I was explaining to someone
> about hardening and tempering in pretty general terms. When I said that
> tempering sacrifices some hardness for toughness, a spectator told me I
> was wrong. He pretty much said "No it doesn't, tempering makes it harder".
>
> I disagreed assuming he had hardness and toughness confused, stating
> that the heat treating charts for common steels show a reduction in
> hardness at various tempering levels. He continued to tell me I was
> wrong, because he had bought 100's of tons of "full hard stainless
> steel" and asked how I explain that material. I told him I had no
> knowledge of it, but tool steels will lose some hardness during
> tempering. He repeated that I was wrong. At that point I was agitated,
> and told him to do some research and he'll see that tempering does
> result in loss of hardness, at which time his wife seemed annoyed with
> him and dragged him out of our shop. (amusing in itself, as he was a big
> man)
>
> While I could have handled that a little better, probably by asking for
> a detailed explanation of the process used for "full hard stainless",
> which I'm sure he had no clue.
>
> Anyway, I'm looking for more education. When I got home, I did some
> research, but I'm still short on details. If I understood what I read,
> "full hard stainless" is tempered, and then maybe cold rolled to work
> harden back hardness. I'm not really looking for tremendous detail here,
> just an explanation "in blacksmith terms" about what this stuff is.
>
> I also came across a statement in one search that popped up that said
> that some alloys will become harder by tempering. Being an internet
> source and therefore dubious in my eyes, I tried unsuccessfully to find
> additional sources to provide some verification. (and then lost the link
> that had that statement in the first place). So question 2 is "are there
> steels that become harder by tempering?"
>
> It's been awhile since I read anything on metallurgy, and since I tend
> to use macro processes for my heat treating, I tend to forget a lot of
> the details, but I'm hoping there are a few bits of knowledge, or maybe
> rumors to be had from the list. Any help?
>
> **Paul
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