Grain direction testing

[steamingspud]

Howdy again,

 

We've been working with grain direction in materials science this week, the same used on turbine blades and aircraft parts to get the max strength. A few of us wanted to try testing what this process does and doesn't do for steel, and whether it can actually be done on a forge. Thing is, we've only gone into the chemical concepts on atomic bonding and grain patterns, so we're not subject matter experts...

 

My question for you guys:

 

Has anyone ever tried doing a heat treating to produce a 'parallel' grain structure? I realize it's one of those less-than-microscopic things that's only a tiny bit beneficial, but it'd be interesting to try. 

 

The experiment would use 3/8 inch bar stock about 6 inches long a piece, probably something like 1037 or what we have in the shop. We'd try several kinds of treatments on the forge, then test the shear and bending strength of each piece. This would include a control test. 

 

Problem is, I have no idea how to treat the steel correctly to get a single grain direction. The idea is to cool it from one side of the bar to the other, but it sounded like it needs to be slower than quenching. Maybe some of you have seen the process and can explain it?

 

We'll probably try a few tests on an annealed piece, an piece annealed then quenched, and a piece quenched only, just for comparison. 

 

Any suggestions welcome, it's not academic either so don't worry bout that. I'll post results if I get any, haha

 

Cheers.

 

C/Purdy

[Rich Hale]

You have not mentioned wot the piece will be used for if you are successful. But regardless.....heat treating steel is for sure an involved process and a key factor is the amount of carbon it contains, Wot you have projected,,1037 will contain the same amount of carbon as 1036,,I consider that a mild steel,,,Or it may contain less. The makers have tolerances that are allowable. I am not familiar with that steel but for example each of the two steels may have an upper and lower limit of carbon that will pass company or ordered specifications for shipping. Let us 'spose that the upper limit of 1036 is .40 and the lower for 1037 is .33.In that case the 1036 would actually be a better choice for heat treat testing. And the next batch may be quite different. Now to a big thing for me...When I Heat treat steels it is to attain specific properties and performance for a carbon steel to perform in its intended usage. For me that is tools or blades. Steel containing less than .40 may work out for certain kinds of tools...If I am going to use for a hacking blade i may choose something below .50 but probable not. For blades that need ability to hold and edge and work in a lot of different situations I personally stick with .70  and most times above that. There is a large group of folks that make nice working knives from steel containing about .60 C, I say about due to the makers tolerance mentioned above.

Another thing to keep in mind: When you quench steel it shrinks,,,makers can tell you how much if you let them know exact dimensions, rate of cooling and wot quenchant. That is important as you said you may wish to cool one side....The hot side has expanded and the cool side will shrink,,,it will warp,,,Youi could pre bend to offset this,,and you can let us know if that creates internal stresses in the final piece.

i think you have a great mind and it will lead you forward. But for now you could really use some shop time working with steel using methods that work..At least until there are better ones for us all. Keep us posted. 

[steamingspud]

If the experiment is successful... well I guess it's just to see if it works. I'm thinking in terms of statics, so bridge parts and crane beams. We have a bridge building team that does competitions that involve building the strongest bridge with the least amount of materials, built in the fastest time. If we could manufacture parts for the joints that were smaller than ones made from mill steel, every ounce counts.

[John McPherson]

Steel grain type and direction can be imparted and refined by rolling or forging as the metal drops below the critical temperature, as in a rolling mill (parallel grains) or a drop forge or press (flowing grains). This working heat zone for each alloy is easily seen on a TTT chart.

 

Polishing and acid etching the bar stock or plate should reveal it's present grain structure. Ferric chloride solution, or even lemon juice will work.

 

Overheating the steel results in a loss of all grain structure, and forming new grains as it cools. How do you propose to induce a new parallel grain structure in the bar stock without reforging or reshaping it?

[DSW]

I had a welding instructor about 10 years back whose full time job was doing welding repairs on cranes. Some of the steels the manufacturers use for newer cranes can often top 160 KSI and he mentioned they have had some issues with some that top 180KSI. Most of those steels get their strength thru heat treatment and tempering, but I don't know the exact specs. Lots of his comments went way over my head at the time. Maintaining strict weld parameters was really important with these steels, especially pre and post heat and cooling rates.

 

He did have one sample he brought in that showed what happens when some of these specialty steels aren't welded properly. Someone simply ran a bead of 7018 on the piece with no preheat/post heat etc to attach a light bracket. Under magnaflux the piece looked like a shattered glass window with a huge spiderweb of micro cracks thru a large section well away ( 4-6") from the weld area.

 

What you are trying to accomplish in general is certainly doable. I'm not sure however you can get the results you are looking for without access to a full heat treatment facility. You are also talking about tiny incremental gains. Max gains will probably come from generic structural design. IE you go lighter with a truss vs using higher strength thinner materials in a conventional wideflange design. You can minimize weight even further in the truss design by isolating tension/ compression members and using say cable for pure tension members and saving your weight for larger lighter stiffer compression members. We've gotten "sloppy" in modern times as far as this is concerned. Look back at an older truss bridge design and you'll notice that they frequently used cables in tension members and built up structures for compression members vs just selecting a generic beam size like is common today.  It's when you have maxed out the structural design that material science will start giving you an edge on average.

[patrick]

Grain flow or direction in metal alloys is not a function of heat treatment but of mechanical deformation. What heat treating will do for you is change individual grain size and shape so you can go from columnar grains to equiaxed grains but the grains will still have a direction that is imparted by the mechanical deformation.

 

The experiment you have described is similar to the jominy end quench test which consists of heating a 1" round 4" long  specimen to predetermined temperature and water quenching one end with a constant, predetermined flow of water. Hardness is measured at 1/16" intervals from the quench end to the mid-length of the specimen. This test is used to compare the hardenability of one grade or heat of steel to another. You end up with a hardness gradient, but there is no change in grain flow because of this heat treatment. For a detailed description of the Jominy end quench test see ASTM specification A255.

 

As a side note, grain flow is not "undone" by overheating since, in today's steels the term "grain flow" has to do primarily with the orientation of micro inclusions such as oxides and sulfides. Overheating does not change the orientation of these particles even though the individual crystals of iron are change as I noted above. That is to say, if I have a closed die forged wrench and I heat it to forging temperatures without forging it, the grain flow is the same before and after that process. The grain size and microstructure (martensite, austenite, pearlite etc.) will not be the same before and after.

[Frank Turley]

What Patrick said. lol  

 

As smiths and not metallurgists, we sometimes confuse metal grains with wood grain, especially when talking about old fashioned wrought iron, the material. I've heard over and over again, smiths talking about wrought iron grain as though it were wood grain. Wrong. Because wrought iron has about 4% iron silicate, a person could break a bar of it cold and a fibrous structure would appear. The fibrous structure is caused in hot rolling lengthwise and the result is micro filaments of silicate which are longitudinal.

 

With present day steels, you get rid of the silicate, a slag, and increase the carbon content. Grain flow is much less 'gross' than the structure in wrought iron. Patrick talked about inclusions such as oxides and sulfides. I have also read that micro slag inclusions can be part of the grain orientation. Grain flow is taken into consideration when designing closed dies.

 

Reference. "Forging Industry Handbook" Cleveland, Ohio, 1970.

 

Sayings and Cornpone

Reference my eating too fast, "like a wolf."

"Hey, put down your fork every now and then."

     My wife, Juanita

[ThomasPowers]

Wrought iron should be considered a composite material like fiberglass!

 

You did have to keep track of the orientation of the silicate spicules as the mechanical properties could vary quite a bit between along the axis and across the axis---why Byers came out with bi-directional rolled wrought iron plate.  I have some I believe is such as when broken you have flat platy chunks instead of fibers.

[Rich Hale]

Something you may, (or may not) wish to add to your testing: 

If you find that you can indeed fashion a grain directional pattern in the steel. and if it a high carbon steel that will undergo heat treat procedures for hardening and tempering. Wot becomes of the directional pattern when HT is complete?

[forgemaster]

Thank you Patrick
A while back there was a discussion on here where various posters maintained that after forging  if you were to normalise or heat treat all grain flow would be lost so why bother about forging to induce grain flow.
After your explanation which is heaps better than mine, I will now have reference to something I can throw back at any non believers.
 
Phil

[yahoo2]

I have found that a slit and drifted hole that is slit along the grain in a drawn flat bar and normalised afterwards, will resist cracks forming far more effectively than a drilled or punched hole in the same plate. That says to me that the grain structure and all those molecular carbon links are still there.

[AndrewOC]

C/purdy,

How 'bout try this;

1.find out what capacity your local tension or charpy notch test machine takes.

2.obtain a square of plate the thickness that the tester takes.

3.cut two strips at 90 degrees to each other, the width that suits the test machine.

4.test away and compare failure rates.

 

regards,

AndrewOC

[patrick]

In answer to Andrew's proposed the experiment, the results will be that tensile and yield strengths will be about the same in both directions but the impact strength, elongation and reduction of area will all be less in the transverse direction than in the direction parrellel to  the grain flow. The exception to this is that very clean steels, typically those which have very low sulfur contents or those which have been remelted can have uniform properties in all orientations.

 

Note that it is NOT normal for slag to exist as an inclusion element in properly made steel. What is there are oxides such as aluminum and silicon oxides and usually manganese sulfides. I will point out that by adding small amounts of calcium, the manganese sulfides are made spheroidal and they stay way during hot working. This is another way to get uniformity of properties in all directions.

[JNewman]

How much reduction in section is needed to re orient grain direction?  for example a seamless ring originally has  the grain perpendicular to the direction it ends up.  As an example In an eye bolt formed by flattening a bar slot punching and opening up the hole then drawing out the ring does reducing the material to half its section would that be enough to re orient the grain flow on the end of the hole?

[Frosty]

Turbine blades are monocrystalline castings. The most common failure initiation points under stress conditions are most often crystal bounderies. The same monocrystalline casting term applied to steel is "amorphous Iron." I don't know the specific process but it's typically a casting and can be done in many different alloys.

 

My only information regarding monocrystalline casting is in regard to watching a program about making turbine engines and how they make them strong enough to spin in access of 70,000rpm while driving a shaft with a couple K HP and being driven by thousands of lbs. of thrust. It's been a few years but it was an interesting program and stuck with me. As I recall the big trick was the chill time, it had to be quick enough the entire iece formed only one crystal. Intuitively I  would've believed it would've taken a long chill time not quick.

 

While interesting it was obviously NOT something I could even consider doing myself nor afford to purchase so it's filed in an "interesting factoid" file folder of my brain. I did read some about amorphous iron and think the process was very similar but not quite the same. Chill time was still critical and dependent of alloy.

 

Frosty The Lucky.

[patrick]

John- In the forging industry a reduction in area of 3:1 from cast ingot to final forged shape is usually the minimum reduction required to consider a product "wrought". That is probably a good rule of thumb for developing a distinct grain flow as well.

[JNewman]

Thanks Patrick. I am pretty sure the ones I did that way were around 3:1 on the ends.  They were about a 6" id with about a 1/2" or 5/8" round section.  I started with a piece of 2 or 3" round flattened it to about 3/4" flat.  Then I drew out the shank and punched 2 holes  one  over 1" from the end and then slit between the holes.  After opening it enough to grind all the sharp corners off and doing so I drew it out to the section I needed square then octagon till I had my ID.   The drifting from punching then drawing down to my section and then flattening from 3/4" thick all together I am sure ended up with at least a 3:1 reduction.  I did have some extra material that I had to grind off but I did make sure it was at 9 and 3 O clock. 

[scott.livesey]

is important to remember we are talking steel not wood.  there is no grain direction in steel, especially after it has been hot rolled, cut, cold rolled, cut, then ground and sent to your supplier.  what appears to be grain on a sheet of steel is grind marks.  i purchased a large sheet of 80CrV2, cut several blanks top to bottom, then cut the balance left to right.  no difference in performance or how the blades machined.

an old Schuler warrior

[JNewman]

is important to remember we are talking steel not wood.  there is no grain direction in steel, especially after it has been hot rolled, cut, cold rolled, cut, then ground and sent to your supplier.  what appears to be grain on a sheet of steel is grind marks.  i purchased a large sheet of 80CrV2, cut several blanks top to bottom, then cut the balance left to right.  no difference in performance or how the blades machined.

an old Schuler warrior

Then why did the die steel I bought a couple of weeks ago come with the grain flow painted and stamped on the blocks of steel?

 

http://www.asminternational.org/portal/site/www/AsmStore/ProductDetails/?vgnextoid=4ef77e0e64e18110VgnVCM100000701e010aRCRD

 

Read the description of the ASM Book linked to

"CONTROL OF GRAIN FLOW is one of the major advantages of shaping metal parts by rolling, forging, or extrusion. The strength of these and similar wrought products is almost always greatest in the longitudinal direction (or equivalent) of grain flow, and the maximum load-carrying ability in the finished part is attained by providing a grain flow pattern parallel to the direction of the major applied service loads when, in addition, sound, dense, good-quality metal of satisfactorily fine grain size has been produced throughout".

ASM is the one of if not THE top authorities in metal materials science. 

[John McPherson]

Scott, I beg to differ. I am a professional college welding Instructor, Certified Welding Inspector (CWI) with one of my college degrees in Welding Technology. I have also been the Facility Representative for what was at the time the only AWS Test facility in NC and Virginia.  (So what, you say, all that and $5 will get you a cup of coffee at Starbucks.)

 

So when I say there is a difference in grain orientation and related stress factors found in hot rolled steel, this is not theory, this is observed, repeatable fact, demonstrated in hundreds, if not thousands of welded bend test samples per year. It may not show up in a forged or stock removal then heat treated blade under normal use, but is a factor in testing to destruction welded structures.

[patrick]

Steel does indeed have a grain direction though you normally can't see it without a microscope. It does however make a significant difference in mechanical properties so it is a real cosideration in engineering and component design. I've been dealing with this on a daily basis for the last 10 years in my role as a plant metallugist for Scot Forge.
The term "grain" is a direct reference to wood because, until recent times iron and steel were so dirty that when broken they actually looked almost exactly like wood. We don't see thaft today at the macro level but the condition still exists and the term grain flow is common in steel making and forging.
Patrick

[Ric Furrer]

is important to remember we are talking steel not wood.  there is no grain direction in steel, especially after it has been hot rolled, cut, cold rolled, cut, then ground and sent to your supplier.  what appears to be grain on a sheet of steel is grind marks.  i purchased a large sheet of 80CrV2, cut several blanks top to bottom, then cut the balance left to right.  no difference in performance or how the blades machined.

an old Schuler warrior

Scott,

What you say is a testament to modern steel quality and I can absolutely understand why you would believe this to be the case.

I make steel several ways and it is a factor I must take into account every time I make an item. Modern steels have a long and tortured history of development to have arrived at the wonderful quality they are today.

 

Ric

[Frank Turley]

When I start my wood stove fire in the morning, I usually tear newspaper in strips and use that under the kindling. The newspaper tears easily and fairly straight lengthwise, but I get irregular tears and "tear out" when I've tried tearing the width. Perhaps this is in no way related to steel. Nevertheless, every morning it reminds me of grain flow.

[Dodge]

Scott, I'm with John.

I worked with and many times could see grain direction (especially fresh off the coil) in hot rolled steel daily in the 25 years I worked in the manufacturing biz. There may not be a critical difference of grain direction when using flat pieces but when we bent steel, especially cold, we absolutely had to know the grain direction. I agree that once finished either by grinding, painting, steel shot blasting, galvanizing etc, you can no longer see the grain direction but its there still until the steel is put through heat procedures sufficient enough to change them.

 

Frank, I know what you mean about news paper. Makes tearing news article out of a page very frustrating :D

 

Scott S.

[patrick]

Grain direction is NOT changed by heat treatment. It is a function of the hot (or sometimes cold) deformation processes used prior to heat treatment. Heat treatment changes properties like hardness and ductility, but the grain direction is not changed. This means that properties are generally NOT the same in all directions, regardless of heat treatment. If you perform a tensile test on a plate you will find that there is greater ductility when the test specimen is cut parrellel to the direction that had the greatest deformation than when you perform the same test at 90 degrees to this deformation direction. This is true whether the plate is in the as rolled condition, normalized, quenched and tempered etc. The actual values measured change with these heat treatments, but the fact that the values are different depending on the specimens orientation relative to deformation does not.