[TheForge] Welding 5160

Tue Aug 26 05:24:00 2003

You can buy large section H13 and such "drop" for about $2/lb around the
Minneapolis area from "The Steel Store."  They will cut it to the size you
need, but I have always had luck picking through the odds and ends.

They also have rounds in various lengths.

It's Uddeholm stuff.  Nice to know it's consistent.

----- Original Message -----
From: "Thomas A. Troszak" <[email protected]>
To: <[email protected]>
Sent: Monday, August 25, 2003 5:58 PM
Subject: Re: Re: [TheForge] Welding 5160

> > From: "David E. Smucker" <[email protected]>
> > Subject: Re: [TheForge] Welding 5160
> > Date: Mon, 25 Aug 2003 08:43:47 -0400
>
> > For most Blacksmithing applications the "hold for one hour per inch of
> > thickness" doesn't make sense.
> > The reason it is required is that to control the temperature in a
industrial
> > heat treat furnace the operator adjusts the set point of the furnace to
the
> > desired critical temperature -- and then expects the work piece to come
up
> > to that temperature over time.  To be sure that the piece fully gets to
the
> > temperature we use that 1 hour per inch of thickness rule of thumb.  "We
let
> > it soak" to be sure that the whole piece reaches critical temperature.
>
> Dave,
>
> There is more to it than that. Even when the entire piece is finally at
> critical temperature, the transformation takes a measurable amount of time
> to spread through a thick section.
>
> Soak times are measured from the point at which the entire piece arrives
at
> critical temp., not from when the piece is tossed in the furnace.
>
> I have used a small volume (about 1 cu ft.), high input (300,000-500,000
> btu.) gas furnace to harden large blocks of tool steel (more than 3 inches
> thick) in 90-120 lb. batches, with manual gas and air controls. In this
> situation, it is possible to set the gas throttle to a fixed heat input.
>
> With fixed heat input, the temperature in the furnace remains relatively
> constant throughout the heating phase, even after the surface of the work
> shows a color matching the color of the furnace interior. This indicates
to
> me that the blocks are still absorbing heat.
>
> 20 minutes or so after the blocks first show color, the furnace temp
> suddenly starts to rise, indicating to me that the blocks are now heated
all
> the way through.  The operator must then throttle back the input, over
> overheat the blocks. I count the "soak time" from the temp spike, not the
> first color.
>
> Rough generalization:
> Think of ice melting in a bucket of water on a hot day. The temp of the
> water will not rise until all of the ice is melted, as all the thermal
input
> is absorbed in melting the ice. With the blocks of steel in the furnace,
the
> temp of the furnace remains remains constant (with a constant heat input)
> until the center of the blocks reach the furnace temp, then the furnace
temp
> suddenly starts to rise.
>
> In actual practice, blocks of H-13, 3 inches thick pulled and quenched as
> soon as color matched furnace temp, rarely got above R 40. Blocks soaked
for
> an hour after the temp spike and quenched get to R 50 or R 55 no problem,
so
> "something important" definitely happens during the soaking, long after
the
> outside of the blocks reached critical temp. Perhaps someone on the list
can
> explain "why", I just know "what happened".
>
> Below one inch of thickness, however, I can find little reason (in my
> experience) to soak any appreciable length of time once the critical temp
is
> reached. I have quenched 1 inch dia. punches as soon as they reached
> critical temp, and I have let them soak for 20 minutes at critical temp,
and
> could not discern a difference in the final product.
>
> Also, according to the tech guys at Uddeholm (whom I hold in high regard),
a
> lot of action takes place between 350-150 degrees F. during the quench, so
> they advise quenching all steels to room temp. before tempering.
>
> I am not an expert, I have just hardened hundreds and hundreds (and
> hundreds) of pieces of tool steel, and I keep good notes, and this is some
> of what I have found out.
>
> Also, the recommended critical temp for a given grade of steel varies
> noticeably from brand to brand, even from batch to batch. The product I
got
> from Crucible was vary variable, and even though it was cheap, it was too
> frustrating to deal with on a production basis. The product I got from
> Uddeholm was incredibly consistent, and never varied from batch to batch.
> If you are buying steel from a reputable manufacturer, ask then for the
heat
> treatment data, and follow it to the letter. If you are using steel from
> scrap, you will have to experiment to find the sweet spot. If you only
have
> one piece, you cross your fingers and hope for the best.
>
> Tom Troszak
>
>
>
>
>
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