hardening and tempering

[liveaboard]

I read the theory online; and found a site with specific recommendation for C45.

To harden I heated to 840C [1544F], quenched in water.
To temper. I heated again to 600C [1022F] for 2 hours and let cool in air. The page said between 550 and 660.

After treatment it doesn't seem very hard; I have no objective way to tell, I used a file, a punch and a drill to compare to known mild steel and a hard bolt.

The treated parts are harder [or tougher] than mild steel for sure, 2 rods I made for my press didn't bend at full force like the first mild steel ones did.

A previous test piece that I heated orange with a torch and dropped into a bucket of water is so hard that a drill bit skitters off and a file won't touch it. I know that much hardness is undesirable because it must also be very brittle, but I feel that somewhere in between would be a good place to be.

So I'm thinking, maybe that tempering temperature was a bit high?

[GlennW]

What alloy steel?

45 isn't really all that hard. Off the shelf pre-hardened 4140 is 38-42RC and is nice to work with.

How did you regulate the temps?

[Russ Hanscom]

From what little I have done, your tempering temperature seems to be on the high side. But it all depends on the strength/ductility combination you want.

[liveaboard]

I used my OH's computer controlled ceramic kiln. It's very precise.
I had some trouble with it as it hadn't been used for a while, I thought the computer might be kaput so I looked up prices; oh my, don't want to go there. Opened it up and shot some air through and it's alive again.

The bit I heated with the torch was at a similar color.

So I guess what I need is some reading on temps to achieve hardness / ductility levels, and some hints about what levels are good for what.

[Russ Hanscom]

For most alloys, there are charts of hardness vs tempering temp. There is also a rough chart of hardness vs strength. You should be able to find tables or charts on line. I will try to find a sample cahrt,

[Russ Hanscom]

Got a chart for a 1040 steel, closest that I could find. 5 mb pdf file. email address?

[liveaboard]

Sent it on PM, thanks.

[tornitore45]

I agree with Russ about 600C taking most of the hardness out.
Small parts that need no soaking can be tempered by color.
Polish to show bright metal + heat with torch on the side that you want less hard + look for the color to travel from the torch side to the tip + quench when the color you want reach the tip.
To keep things simple Straw Yellow for cutting tools Blue for springs and something less brittle and more resilient
The end where the heat is applied will be less hard

Larger parts can't be done with this method. I place them in the kitchen oven at 400F when wife is out.

[David Merrill]

According to the TTT chart in this reference C45 equivalent steel needs to have its temperature reduced (quenched) from 850°C to less than about 300°C within about two seconds to achieve its maximum potential hardness. Surface temperature will drop faster than core temperature, more so if the part is thicker. Quench rate depends also on part handling technique from furnace to quench bath, on agitation of quench bath, and on thermal properties of the quench bath.

https://www.theworldmaterial.com/1-0503 ... c45-steel/

David Merrill

[liveaboard]

Heating, + quenching for hardness is clear; like I said, a piece that was not subsequently tempered is very hard.

It's the tempering process that I think I have wrong, but the chart Russ sent me [thanks Russ] seems to indicate I was correct.

[tornitore45]

Are we sure we are not confusing Celsius with Fahrenheit?

[NP317]

C vs F?
It's not like such a mistake would destroy a Mars probe...
RussN