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For a limited time we are now offering free freight on all SHEL LAB ovens as well as Cress Single Chamber and Cress Dual Chamber Heat Treat Furnaces.

The SHEL LAB oven series offers a diverse choice of forced air ovens (floor models and bench-top units), gravity convection, clean room ovens, nitrogen purge ovens, and vacuum ovens. You will often hear the terms drying oven, curing oven, or bake out oven being used in industrial applications. These are generic terms that can be represented across multiple heat processing applications.  Click here for help finding the SHEL LAB Oven that will best fit your application.

Cress Heat treat (Hardening) furnaces have higher heat output power than draw furnaces due to the elevated temperatures at which they operate. Heat transfer to the tool steel is accomplished by a very efficient process called direct radiation. Temperature uniformity in these furnaces is best in the red heat range. Normal maximum temperature is 1232°C (2250°F). Optional 1316°C (2400°F.

For a free quote or questions about EPS Ovens Contact Us Here

Our company is using a commercial heat treater and we’re getting good results. Why should we buy a Cress furnace and do the heat treating in house?

This is one question that we hear over and over again and there are arguments to steer the answer in both directions.  We’re going to look at several scenarios so that you can select the correct solution for your company.  Not all heat treaters operate this way, but with the high cost of energy, some are forced to take steps to keep costs low to stay competitive.

Background

You’ve created a tool, a part or series of parts in your machine shop that you need for your operations, or your customer’s requirements.   The designer has chosen A2 tool steel and specifies a hardness of 60 to 62 Rc is needed.  The part or parts could weigh 2 pounds, or 50 pounds and may have taken five hours, five days, or five weeks to make.  Regardless of the time, your company has invested time and money into producing the parts to satisfy a need.  You package the parts up, ship them off to the heat treater and ask them to be heat treated to 60 to 62 Rc.

Scenario Number Two

This is one of my biggest complaints about commercial heat treaters.  The parts arrive, a job ticket is written up.  The job is assigned to a person on the floor who often has no formal training in handling parts or heat treating for that matter.  The company metallurgist sat in their lab and only is called to verify the process to be applied if the leadman, or shop foreman can’t find the process in his private notebook.  The only time the metallurgist gets involved is if the hardness level is incorrect, and you know that the owner of the company will always be in his office concerned with bill paying or sales.

Bottom line of this scenario….. Even if the hardness reads correctly, you have no absolute assurance the times, temperatures, pre-heat, quench or tempering cycles were followed to the prescribed recipe.  Your part quality is at risk.  The life of the part is at risk along with your reputation. Your only hope is to request and pay extra for strip chart recordings of every step of the parts in process.  Even then there are things that can effect the quality of the finished product.

DISCLAIMER OF LIABILITY
The material presented in this article is intended for general educational information only.  It should not be used for a specific application without careful analysis and study of the in¬tended use.  Anyone using this information or relying on it assumes all risk and any liability arising from their applications and use.

Our company is using a commercial heat treater and we’re getting good results. Why should we buy a Cress furnace and do the heat treating in house?

This is one question that we hear over and over again and there are arguments to steer the answer in both directions.  We’re going to look at several scenarios so that you can select the correct solution for your company.  Not all heat treaters operate this way, but with the high cost of energy, some are forced to take steps to keep costs low to stay competitive.

Background
You’ve created a tool, a part or series of parts in your machine shop that you need for your operations, or your customer’s requirements.   The designer has chosen A2 tool steel and specifies a hardness of 60 to 62 Rc is needed.  The part, or parts, could weigh 2 pounds, or 50 pounds and may have taken five hours , five days, or five weeks to make.  Regardless of the time, your company has invested time and money into producing the parts to satisfy a need.  You package the parts up, ship them off to the heat treater and ask them to be heat treated to 60 to 62 Rc.

Scenario Number One
The heat treater receives your package and analyzes what you’re asking for.  Their furnace can hold 500 to 1,000 pounds of steel per load.  So, your material goes into a queue waiting for other material from other customers in order to make the run profitable.

After two or three days, other materials do arrive, but there is only 120 pounds of A2 to run.  So, he loads the 120 pounds, which requires a 1750oF soak.  He has 75 pounds of D2 which requires an 1850°F soak, and 60 pounds of S7, which requires a 1750°F soak.

It’s not a full load, but it’s enough to process for this week and take care of their customers.  Of those steels the D2 is the most difficult to treat because of its high chemistry content; so the decision is made to process the load at the D2 temperature of 1850°.  It’s also decided that the size of the parts in the D2 load will be the controlling soak time factor.  That means your A2 and the S7 will get overcooked, creating excessive amounts of retained austenite and a very course grain structure will be created.  If your parts are somewhat larger in size, it will possibly offset a portion of the higher temperature, but the 1850°F is still going to have a very bad effect.

So, after the heat treated parts are quenched, the commercial heat treater will take your A2 and the S7 parts and put them into a mechanical freezer and freeze them at -150°F for a couple hours.  (Nearly 100% of commercial heat treaters have a mechanical freezer in a back room. It is also used to stabilize Aluminum parts.) This sub-zero treatment will convert some of the retained austenite into martensite and also make a partial correction to the hardness.  They will then perform a hardness test to determine at what temperature to temper the parts in order to produce the hardness that you requested.

When you receive the parts back, you may verify the hardness to be within specification and think that everything is fine.  Unfortunately, because of their action, the internal grain structure of your A2 and the S7 parts will still be large, coarse grained, and still contain a good deal of retained austenite that will refuse to transform.  The parts will go into service, but will never wear as they were intended to wear and you’ll soon be making the parts over again or, worst case, you may be looking for a new customer.

Bottom line of this scenario….. Hardness in ferrous metal is not what generates great wear resistance. Wear is the result of the finest-grained structure produced, martensite transformation, and excellent carbide creation and distribution.  If you want good results, use a Cress furnace and make sure your parts are processed correctly.

 DISCLAIMER OF LIABILITY
The material presented in this article is intended for general educational information only.  It should not be used for a specific application without careful analysis and study of the in¬tended use.  Anyone using this information or relying on it assumes all risk and any liability arising from their applications and use.

Following a few basic rules can often minimize troublesome distortion that takes place during the steel heat treat process. There are three major areas where distortion can take place, assuming the part is straight prior to heat treatment.

1. The pre-heat step is the first critical distortion prevention step. The pre-heat step, as specified by the steel producer, prepares the metal to transform through the heat treat phase changes, but also reduces the stress introduced by machining, forming, or other processes. Just by programming the controller on your Cress furnace for a 10 minute stop, gives the temperature inside the metal’s mass a chance to catch up to its surface temperature, reducing the tugging and pulling distortion from taking place.

2. At the austenizing temperature, the molecules in steel are ‘in-solution’. That is. they are in a molten state within the shape of the part. That also means they will deform, or sag, to the surface of what they are resting upon. Heat treating is not meant to be done on the Cress hearth plate. That’s an insulation and is not going to allow uniform heat penetration of a part if it’s laying on the hearth plate. A rack should be built that allows even temperature transfer. If the rack becomes distorted, then it needs to be straightened to support the parts in a flat manner.

3. Taking the part from the Cress furnace and transporting it to an air quench rack, or to water or oil quench is next. Because the part is coming from the furnace in the ‘in-solution’ condition, picking the part up has to be done with great care; and if it’s an air hardening metal, needs a flat rack for quenching to prevent sag. If it’s being water or oil quenched, it needs to enter the water or oil straight up and down to avoid cooling one side earlier than the other. Oil or water hard metals may still deform, but it will be less.

If you are heat treating very thin flat parts, often the best way to treat them is to press quench them. How that is accomplished is by removing a single part from austenization and quickly placing it on a flat, heavy plate of steel. Immediately place another heavy plate of steel on top of it. As soon as it loses heat color, proceed with your normal quench method. Remove each piece from the furnace and press quench that same way.

If the part is round or of a peculiar shape, consider making a fixture to hold the part through the heat treat and quench process. For instance, if you have a ¼” diameter rod, 16” long, take a steel pipe with a good schedule wall, drill and tap 3 holes around the pipe every 6 to 8”. Using three bolts in these holes will hold the rod straight in the center of the tube, allowing quenching and a straight part.

If you want practical information on the heat treatment process in understandable everyday language, inquiry to: Advisor In Metals or via e-mail at thegateway@metrocast.net. Information about the book or seminars is available on line at: Advisor In Metals

COPYRIGHT © August 2008, by Advisor In Metals

The author, Bill Bryson, Advisor In Metals has had numerous years and extensive experience in the heat treating of tool steels.

Decarburization is an oxidizing surface condition caused whenever ferrous (carbon based) metal is heated to temperatures above the visible heat (960^oF) zone, and is exposed to atmosphere. The depth of decarburization penetrates deeper as temperature and time of exposure increases. The surface in this condition has lost carbon composition (de-carbon-ized) and scale (loose flaking surface which resembles the scales on a fish) will also become evident. Hardness in this layer is poor to none, and tool life is definitely and dramatically sacrificed. In fact, if a tool is put into service with any appreciable decarburization, it is guaranteed to fail and can show surface breakdown quickly.

Cress Furnaces are atmospheric box furnaces which means they have air, or heated air in them and there is no protection from decarburization in the furnace. There are several optional methods to protect against decarburization when using a Cress Furnace. They are:

Cress Stainless Steel Inert Atmosphere Tube: You can order your Cress Furnace with a stainless steel inert atmosphere tube used to pump Nitrogen or inert gas into the chamber. It helps, but does not solve the decarb problem because box furnaces are not sealed vessels and are built using fire bricks and contain ceramic element walls that are very porous and full of air and water molecules that cause the surface corrosion.  Purging the chamber does not remove all the air and water molecules and thus decarb will take place. Installing a retort (metal box) inside the chamber and pumping inert gas into the retort works better because the porous fire brick is taken out of the equation; but a thin gray, smutty surface will still prevail because the retort is not air tight.

Stainless Steel Foil, formed by triple folding the edges into an envelope, gives relatively safe atmospheric protection. The disadvantage of SST foil is that the SST is razor sharp, and not particularly inexpensive to use. It provides very good protection, but there is often a grayish surface color that needs to be removed before the tool is used.

Protective Powder is applied to the metal when it is 450^oF which, when it melts, creates a protective barrier around the part. After the heat treat and tempering is completed, the powder may be washed off with hot water for clean up.  Results reported are bright shiny parts, but it’s imperative in all protection methods to remove all traces of cutting fluids, oils or even finger prints.

Protective Paints can be applied to the parts.  After heat treatment is complete, the paint is removed by sand blasting.

DISCLAIMER OF LIABILITY
The material presented in this article is intended for general educational information only. It should not be used for a specific application without careful analysis and study of the in¬tended use. Anyone using this information or relying on it assumes all risk and any liability arising from their applications and use.

COPYRIGHT © April 2007, by Advisor In Metals

ALL RIGHTS RESERVED. No part of this publication may be reproduced, transmitted or copied without prior written permission of the author and publisher.

If you put your steel parts into a Cress Draw Furnace and set the temperature for 600oF because you want to draw down the hardness a few points to make the part a little tougher, you may get a surprise you don’t expect.

Few people even realize there is a range of dangerous tempering temperatures that exist. All mill sources publish tempering charts that show hardness levels that can be obtained from ‘as quenched’ temperatures to as high as 12000 F. What they don’t tell you, is you should avoid using temperatures between 5000 and 7000 F. This zone of tempering can cause a weakness in the finished part from what is called ‘Blue Brittleness’ or ‘Temper Enbrittlement’. It is most severe when Chromium is present in steel and these temperatures should always be considered ‘off limits’ to any of these steels.

In fact, every heat treated metal has an optimum operating range. If you are lowering the hardness level to induce properties the steel isn’t made for, you are most likely using the wrong grade of metal. All of the tool steels developed by the mills were originally developed to accomplish certain attributes. Look at every application for what it demands and then select the best metal to do the job.

COPYRIGHT © April 2007, by Advisor In Metals

ALL RIGHTS RESERVED. No part of this publication may be reproduced, transmitted or copied without prior written permission of the author and publisher.

Water in quenching oils can be very dangerous, and even more so when martempering using oils at temperatures above 212oF. Where does water come from? Generally it is from condensation due to the heating and cooling cycles the oil goes through. The colder the climate the worse the problem can be if the quench tank is sitting on a cold floor. Water in oil generally collects and settles to the bottom of the quench tank, but can also become emulsified in a circulating tank. If the oil is stagnant, or not circulated, the red hot parts in the bottom of the quench basket can be quenched in water, which in turn can cause non-uniform hardness, improper as-quenched hardness of the parts, and very often cracks will also occur from the faster quench. If the water level is high enough that red-hot parts cause the water to boil, an explosion can take place from the large amounts of steam that is formed.

A larger amount of water can exist with less chance of explosion, in a tank with circulating oil because the steam cannot form; however, it can create foam. However, foam is also a very dangerous fire hazard since oil foam can catch on fire very easily.

It is generally a good practice to check your quench tank every 6 months to make sure your water level is under control. The best method is to pump the quench oil out and observe the mixture at the bottom of the quench tank. You will be looking for water, muck, dirt or any contamination which, if found, should be removed and disposed of properly. Muck and sludge in the bottom of the tank also can affect the effectiveness of the hardenability of the oil. If the oil becomes emulsified, it cannot be salvaged and must be replaced.

Another quick method is to attach a long handle to a shallow container which you lower to the bottom of your quench tank. It must go deeper than the bottom of your quench basket, and by removing it slowly and carefully, you can bring a sample of the bottom of your tank to the surface.

COPYRIGHT © April 2007, by Advisor In Metals

ALL RIGHTS RESERVED. No part of this publication may be reproduced, transmitted or copied without prior written permission of the author and publisher.

Years ago mills supplied alloy and tool steels with a spherodized annealed structure. Due to economic constraints most, if not all, mills have short cut that process. They still anneal, but it isn’t a sphereodize annealed any longer. Today’s annealing yields a pearlitic microstructure with an increased hardness. The result, or effect, is that the metals generally don’t machine as well as they used to a few years back and surface finishes also suffer. In applications that require machining in tough, tight tolerances, difficult design areas, it often would make sense to properly anneal the material either before machining begins or, better still, once the part is roughed out to a near net shape. It is better after being roughed out because it also eliminates most of the stresses and reduces some of the deformation.

To properly spherodize anneal any steel, use the annealing temperature as stated by the manufacture of your steel, or refer to the ASM Standards. The best method is to put the steel in your Cress furnace and heat the steel to the annealing temperature. Then lower the temperature slowly (preferably 25 degrees per hour) to 900 F and then shut off the furnace. Do not open the furnace at all, and allow the furnace to return to room temperature. The process will take 22 to 24 hours but will produce a totally uniform grain structure which contain small, neat and orderly globular shaped carbides in a smooth flowing ferritic matrix.

Low carbon steels are not normally spherodized for machining since they become soft and gummy, but can be spherodized when increased ductility is desired for bending or forming parts.

COPYRIGHT © May 2007, by Advisor In Metals

ALL RIGHTS RESERVED. No part of this publication may be reproduced, transmitted or copied without prior written permission of the author and publisher.

Stress relief heat treatment is used to remove stress induced in metals from various manufacturing methods. Some of these methods include: milling, turning, welding, bending, heating, cooling, shearing, forging, sawing, grinding, not to mention the steel making processes that leave the metal full of residual stresses. These stresses can cause harmful distortion, brittle fracture, and stress corrosion cracking near welds and within some grades of metal.

Removing residual stress is a time/temperature related event with a very controlled cooling cycle using your Cress Furnace. If not carried out correctly, new residual stresses can be produced that will result in greater stresses than the part had originally. To remove stresses it is recommended that you consult the mill literature for the grade of metal to determine what the Ac1 temperature is for your application. There are several methods to remove stresses successfully, but the most commonly used method is heat treat stress relief. The main criteria to use for choosing the correct temperature is to heat below the lower austenizing temperature (Ac1). Decarburization will take place above 960oF, so protect the surfaces if the surface is not going to be removed by machining.

Thus, if we have a 4140 steel part, (4140 has a 1380oF Ac1) that we want to stress relieve, we could place it in our Cress furnace, take it up to 1100oF and soak it for 6 hours, followed by controlled cooling at a rate of lowering it at 50 to 75oF per hour, in a closed furnace, to below 400oF, at which point it can be removed from the furnace, and it would be stress relieved. However, if you heated it to 1300oF, you can soak it for just an hour, followed by the controlled cooling and also stress relieve the part.

Yes, by PACK CARBURIZING. First, let me clarify. There are several ways to carburize low carbon steels, but in an open atmosphere, box type furnaces like Cress furnaces, there are only two ways. One way is to use a carburizing compound. But buyer beware. Many carburizing compounds contain oxidation chemicals that literally eat other chemical elements in stainless steel. And, using these compounds, even just one time, saturates the porous fire brick to a point that if you ever desire to use stainless foil for decarb protection, the chemicals will literally eat holes in the stainless foil.

Now on to pack hardening: Pack hardening is a two step process that works well for low carbon steel carburization. First, you must have a completely sealable steel box. This is often a bolted together box that fits in your Cress Furnace that has sealing insulation rope between sides and ends of the box. A heavy wall pipe with sealable, removable end caps works well.

The box needs to be filled with any good carbon rich material, such as, cast iron turnings or chips, or something like powdered bone meal. When filling the box, parts can be introduced in layers, with no parts touching one another, then more layers upon layers until the box is completely full. The end of the box must be sealed using insulation sealing rope.

Next, the box can be placed in the furnace and heated as required for the grade of steel being treated, usually in the 1700 to 1900oF range. The whole box must come up to temperature, then soaked for 16 to 48 hours, which is dictated by the depth of case needed; the longer it is soaked, the deeper the case will be. The carbon essentially gets absorbed on all exposed surfaces of the parts during the soak process. Once the soak time is complete, the box can be removed from the furnace and cooled. Once cooled to room temperature, the box is opened and the parts can be removed from the box and are then ready to be put through the second step which is the heat treating process as required for the grade of steel being used.

The packing material can be reused several times before it needs to be refreshed for more available carbon.

COPYRIGHT © May 2007, by Advisor In Metals

ALL RIGHTS RESERVED. No part of this publication may be reproduced, transmitted or copied without prior written permission of the author and publisher.