Re: [CAD_CAM_EDM_DRO] Re:heat treat nomenclature

Hi Marcus;

What you have enlightened us with is the very basic down and dirty and somewhat truncated version of heat treating. It goes much much deeper and temperatures and time left into a cooling process and the coolant itself are quite critical.

Basically when you talk about heat treating you are talking about solution heat treating. What happens is that you take the metal to a point just below the melting point and hold it there for a time specified by the metal, the thickness and density of the metal. What this does is to put the alloy materials into a solution where they are distributed evenly distributed throughout the material. When they are immersed into a cooled liquid for the specified period of time a hardness will be achieved that conforms to a standard that is measured on a rockwell hardness tester.

When annealing or making it the material softer is also done the same way...the metal is heated and held to the "solution" temperature, but allowed to air cool. aluminum rivets with an alloy of 2417 ( used in Aircraft) and I could be wrong on the alloy number are soluthion heated for several hours then put in the freezer to be annealed...when they are removed from the freezer and worked as they come up to room temperature they develop their hardness. They will stay annealed in the freezer for several days.

The purpose for heat treating is to strengthen the metal. When the heat treating process is done incorrectly and not checked the alloy is not sufficiently spread through the metal and results in corrosion and pockets of weaker metal and pockets of more brittle metal.

If you have ever broken a piece a metal and seen the at the break point something that looks like globules on one side and a dull surface on the other you have experienced a heat treating defect. If you have ever seen a metal, especially aluminum start peeling up in layers that is called exfoliation and it is a direct effect of improper heat treating.

There is a whole world these days of heat treating, this includes tempering solution heat treating and annealing that to keep up to date you need to read the most current manuals and journals. I don't know of an oven (kitchen) that will be able to accomplish even the basics of heat treating.

Oh yes when Blacksmiths heat the metal to glowing red and hammered them to a shape, that is forging which is also a method of heat treating that relys more on compressing the metal to force the molecules into a more tightly packed consistency and therefore making it much stronger.

Sorry for the long post but this subject deserves a lot of room.

John McCarthy

Bruce Pigeon <bwpigeon@...> wrote:

These learned arts are especially useful when the closest heat treater is
300 miles away. I have trouble getting them to stop by after work to pick
up and return the next day for $15. I am sure that there are many on this
and other lists who are in the same boat. There are a number of books on
EBay on this subject, if anyone is interested in learning more. While what
I have learned may not be perfect but it has served me well for many years.
So take what I pass on with a grain of salt.

Bruce

-------Original Message-------

From: CAD_CAM_EDM_DRO@yahoogroups.com
Date: 03/01/05 21:27:06
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re:heat treat nomenclature

Hi Wally:
Heating to above the critical temperature "Cherry red" and quenching is
called hardening.
Re-heating a hardened piece to some temperature below (usually substantially
below) the critical temperature and then cooling is called tempering.
Reheating to above the critical temperature and cooling slowly is called
annealing.
This last cycle can also be used for stress relieving or normalizing, but is
normally done at somewhat lower temperatures.
All are heat treating of one sort or another.
Cheers

Marcus





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OFF Topic POSTS: General Machining
If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
http://www.metalworking.com/news_servers.html

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.

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