Etches and the people who love them

R

Rex

Joined
Dec 21, 1999
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Etching is an extremely valuable tool in the metals industry. Many defects are found during processing with the aid of etches. Flaws such as cracks, porousity, chemical segregation, poor grain flow, and numerous other defects are revealed with an etch.
Steel producers and end users such as JOHN DEERE, CATEPILLAR, and many other manufacturers have very exacting and specific requirements for the etching of their products. If these specifications cannot be met, material will not be accepted. Etching is also used in failure analysis. If a gear in your transmission breaks, or an engine falls off a plane, you can bet that someone somewhere will be etching samples for evaluation.
Police use etching to raise serial numbers which have been filed off firearms. The metal under where the stamp was struck is in a stressed condition and will etch differently than the surrounding matrix. This is similar to what Ed mentions about scratches showing up after his blades have been etched. This has been an interesting topic. If you would like to discuss further aspects or have any questions, let me know.
Thanks, Rex
 
I agree with what you have posted here. In A thread That I started called The Telltale Etch there has been quite the discussion about the benefits of etching. You may want to check it out. It is just a little farther down the page. Please feel free to add your own comments as they would be very much appreciated.
 
Yes, I'm that Rex. I tried posting in the other thread but For some reason I can't get it to work.
:( :confused:
 
Darn Rex, I don't know what to say. I just tried to post on that thread and had no problem. It sure would be great to get your input as Ed feels the work you two have done has helped him tremendously in understanding 52100 much better.
 
Four years ago I remember making the statement that in all probability there were no great leaps in the high performance knife to be realized. Any advances I felt would be slow and gradual.

In three short years filled with hundreds of intricate experiments we have more than doubled the levels of performance that I had once considered manifestations of the high performance knife.

All of these events occured as a consequence of Rex Walter, Bill Burke and I working as a team. Rex the scientist evaluating the work Bill and I did. Rex suggested variables that we needed to explore and explore we did. When we completed the evaluation of our latest test blade that is reported in the April issue of Blade Magazine, I got kind of blue, feeling that the performance qualities of this blade left little room for future improvement.

I mentioned my feelings to Rex. He immediately voiced the miriad of variables that ever so quietly await exploration. The frontiers of the forged blade will continue to challenge us.

Any of you who have questions now have an opportunity to request opinions from a man of science I greatly admire. The high performance blade would not be where it is now without his guidance.

Ask and we will all have the opportuity to learn.
 
Hello Ed
Thanks for the nice compliments. This has been a very interesting topic and I feel that there is a lot to share. I hope others will join in with questions.

Take care,
Rex
 
Rex: Night before last we discussed the Baussinger Effect and its significance in the forged blade. You were able to bring to light more facts concerning its significance. How about dislcussing some on the forums? the first time I noticed its influence was in some 2,000 layer experimental Damascus made from mild roller bearings and ball bearings. It chipped in ribbons.
 
Hello Bill and Ed. Thanks to all for their intrest.
The Bauschinger Effect
For both single crystal and polycrystalline metals,any change in the stress-strain characteristics that can be ascribed to changes in the microscopic stress distribution within the metal,as distinguished from changes caused by strain hardening.In the narrow sense,the process whereby plastic deformation in one direction causes a reduction in yield strength when when stress is applied in the opposite direction.
ASM METALS REFRENCE BOOK SECOND EDITION
WHEW-what a mouthful. In a nutshell what it means -in broad terms that relate to us- when material is moved enough to permently deform,thats the plastic deformation part,by forging bending etc.you lose ductility.Ductility is the reduction in yield strength mentioned in the last part. Kindof-Its not exactly the same but works for this example. If an edge is too hard it will chip when flexed on the brass rod test. Pretty simple in concept. The trick is to get the edge as hard as possible and then reintoduce ductility by tempering. This is what seperates the good ones from the also rans. Testing by flexing gives immediate feedback to the maker as to where this line is at.
If you don't chip edges at the begining of your experiments you are either not getting the maximum hardness possible or else you are overtempering. The trick is to sneak up on it a little at a time until you are satisfied with the results. After a few trials it is then possible to reproduce the results repeatedly. Different lots of steel will need to have times and temperatures adjusted . This makes it a good idea to work with known material. The learning cure will be much faster and you avoid the variables caused by material, which can leave you schratching you head wondering what went wrong.
Rex
 
Hello Rex: Seems like folks are bashful so I will ask a question. I hear tell and its true I'm sure.
"Each and every hammer blow leaves its memory in the steel". What do we look for when examining a forged blade and wish some insight into the forging practices that led to that blade?
 
As steel is forged,its grain structure will "flow".A good forger will take advantage of this and control it to achieve maximun strength.

This control of grain flow is one of the big benifits of forging.
To observe this grain flow is fairly easy. Start with some scrap to practice and forge a small bend or curve. A shape like a drop point works well. Grind to a 220grit finish,a little finer or coarser won't hurt anything.
CAUTION THE FOLLOWING SHOULD BE DONE IN A WELL VENTALATED AREA WITH EYE PROTECTION. A FULL FACE SHIELD WORKS WELL. RUBBER GLOVES ARE RECOMMENDED.THIS IS A MILD ACID SOLUTION AT A TEMPERATURE THAT CAN BURN IF SPLASHED ON YOUR SKIN. IT WILL ALSO PUT SMALL HOLES IN YOUR CLOTHES REMEMBER WHEN MIXING, ADD THE ACID TO THE WATER-DO NOT POUR WATER INTO ACID!!REMEMBER ACID TO WATER- DO WHAT YOU OTTER
For the etch use hydrochloric acid mixed 50:50with water. Heat to about 150-180 degrees for about 10 minutes. Hydrochloric is a purer grade of Muratic Acid which is sold in hardware stores for scrubbing cement floors and it will work almost as well.The exact time and temperature is not critical.you need a fair amount of heat to get the reaction going but you don't need it to boil. BOILING ACID WILL CAUSES BURNS AND LEAVE SCARS. ASK ME HOW I KNOW. Experiment and see what works. When you have a good etch action going you will get a white frothy bubbling. When this stops the etching is complete. Rinse the piece in cool water and you will see a grey scum on the sample Use a stiff bristle brush and scrub this off in the cool water bath. The flow pattern is then visable and will reveal a great deal about the forging.Forging faults like small cracks,uneven grain distribution,grain flow etc. will be easy to spot.
DO NOT USE BATTERY ACID !!!!EVER!!
This is not meant to sound like you are in extreme danger doing this. You fellows all play with sharp pointy things and things that glow red hot. Just use some common sense and caution. In our mill the etchers job is considered an entry level position which means that people with no prior training are entrusted to do this with minimal training.Be careful and have fun.
Rex
 
Rex,

In another post somewhere someone was talking about the difference between a piece of steel work out on a press and one forged out on a hammer I am in the process of running a test on the performance difrential. What are your thoughts? Will the grain flow be the same? What of the Bossinger effect?

Bill
 
Wow, now that was one of the most interesting posts that I have seen anywhere on Bladeforums. This may seem like a stupid question, but does bringing out the flow pattern in a blade like that destroy the blade, or can it still somehow be made into a knife. I know that something like this is done to learn how to forgw a better blade and that to do this you must destroy a large number of blades. Is doing this one of the way in which you will make the blade unusable for making a knife?
 
I am not bashful, it is just that the language you folks now speak is "Greek" to someone like me, who up until very recently did not even understand the difference between "stock removal" and "Forged"

My confusion right now does not deal specifically with "etching" but deals more with the types of steels currently available. Of great interest is the new steels and why they are being touted as "new". Aren't they all just dendritic cobalts instead of High carbons?

And, Is etching one of the newer "steels" as beneficial as it is with 52100, 154-CM or ATS-34?

Thanks, and Rex, you are an amzing walking Enclyopedia, stick atound will ya???;) ;) .................Ira
 
First to answer some questions. Etching the blade will not ruin it for a knife. It is a surface condition only. The steel will be VERY prone to rusting, sometimes in only an hour or two if humditiy is high.
The muratic acid should be mixed 50:50 with water. If the solution is a little weak it will take a little longer to etch.Straight acid does not etch very well. It works better with water Old solution does not give as clean an etch as fresh and does not show structure as well. If you leave the sample in the acid too long it will have a dark burnt appearance.
Pressing and hammering will leave different properties in the steel.
Note that there is a lot of overlap but GENERALLY a press is more powerful and slower than a hammer.A press will move material both longitudinally and transversly{It squashes things}, A hammer moves less material per cycle but the force is more directed. Yhe sharp rapid blow of a hammer will tend to breakup inclusions and refine the grain more than a press will. Different dies can be used to help direct the metal flow. The BAUSCHSINGER EFFECT is really a kind of red-herring . It mainly manifests itself in material that has been cold worked . In oil country tubes its most notable after a tube has been heattreated and then needs run through a straightening process. At this point it is given a quick stress relief in a furnace . A complete heattreat will almost always prevent this phenomenon from occuring.
Rex
 
Rex: your comments on the difference between steel formed via a hydraulic press and hammer addressed a debate that has been going on for years. That was an experiment I was going to run some time in the future. Thanks for saving me the time.
 
Rex: I know you have been busy, but you got to sweep your thread. I know you will read this cause I am going to call you again and remind you.
 
Hello Ed and all.Sorry for the delay in getting back.
Etching to bring out grain flow works best before heattreating. As a learning experiment etch the blade after forging and see what it looks like. Then,heattreat and reetch and note the change.
Etching rolled steel may show defects and prevent you from wasting time on a poor piece of steel. For makers who like to recycle auto aprings and other low cost sources of stsrting material,etching before using some of this material can save a lot of wasted work and help sort defective stock. Etching by itself does not make a better blade but it can be one of the most powerful tools in a makers arsenal .
Thanks
Rex
 
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