Grain direction in steel

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levernut

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When I purchase steel from the usual knife supply businesses, the grain direction of the blank appears to be random. In other words, it can be perpendicular to the length or parallel. Does anyone specify the grain direction when they order steel?
 
Grain direction is set when the steel is rolled out at the foundry. I'm not sure if they pay attention to the direction of the grain when they sheer sheets into bars. As far as can you order steel with a certain grain direction in relation to it's length, I have no idea why you would want to do this but if you wanted to pay enough money, as in thousands of dollars for a large run, you could probably get it done. Remember that you are dealing with a metal not wood; the grain is totally different in the two.

Doug
 
What you are seeing are the rolling marks from the mill on the outside of the steel. Not really a directional grain pattern. The steel is transformed into its final grain structure during the heat treat process as the elements are realigned on a molecular level.

Laurence

www.rhinoknives.com
 
When you buy bar steel, the direction is normally with the bar in common carbon steels. I suppose thin stock could be from sheet. As I understand the process, sheet steel is rolled one way, then the other, by which the grain ends up mixed or random. How did you determine the grain direction, and what steel did you see cross grain in? Grain direction is set by the rolling, and is set in a directional pattern. No amount of heat treat or hammering will change it. Heat treating only changes it's size and internal structure. Not it's directional pattern.
 
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Let me put this another way.

Yes, When I have 440C stainless heat treated The heat treat does change the internal makeup of the steel and any directional pattern from the mill is simply cosmetic and has no being on the performance of the steel.

Laurence

www.rhinoknives.com
 
Acually, the grain direction is not just cosmetic, but adds only a little more strength than cross grain does, and does have a slight advantage over cross grain. Slight, but is there. That is why when used in applications requireing max strength, forging is used for the primary shaping. Such as in crankshafts and landing gear struts in aircraft. As far as cosmetic, you cannot see grain direction in steel with the naked eye anyway, unless you see alloy banding, or some similar flaw that might follow grain direction, or after using acid on it.
 
Laurence is absolutly right.
What you see on the surface is from the rolling mill , and has nothing to do with the "grain" structure in the steel.
Thats why we anneal before we start working a piece of stee , then we know what the structure is like.
YOU set the grain structure YOU would like through thermal cycles and heat treatment.
You CANNOT forge in the structure of the "grain" , you CAN through the forging processes of thermal cycling change the grain, but its all on a molecular level , and can be done without a hammer.
Your right you cant see it.
 
I think I agree, but you cannot change the direction of the grain by any method short of re-hot rolling, and just as point of nit picking, there are no molecules involved in metals. It is atomically arranged crystals that form grains.
 
Grain from the pour is randomly shaped with no particular direction. When the steel is formed into bar or sheet, the rolling process elongates them to the direction of the roll. Controlled heat through thermal cycling determines the size of the grains, and properly done makes them of a uniform size, whether that be large or small, depending at which step the process is at. Forging mechanical parts or tools can change the direction of the steel, but not the direction of the grains. Directional grain does impart a tad bit more load resistance in high stressed parts and tools. Cast steel parts and tools have a random grain direction and are in some applications, such as springs or pry bars, inferior to forged steel, even if only slightly.
 
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I think I agree, but you cannot change the direction of the grain by any method short of re-hot rolling, and just as point of nit picking, there are no molecules involved in metals. It is atomically arranged crystals that form grains.

Of course there are molecules involved in metals! That is what is realigned and forms or elongates the crystals & grains.

Laurence

www.rhinoknives.com
 
Mmmmm, me thinks you need to do a wee bit more homework on basic metallurgy. Lesson one. Groups of atoms make up crystals. Groups of crystals make up grains. groups of grains make up the steel.
 
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Sorry, Laurence, no molecules in metals, crystals. Molecules are like building blocks with no linkage between them other than maybe electrical charges. Crystals are linked atomically to each other. Think of it as Tinker Toys. With molecules you could have something like a cube, just as an example, formed with eight blocks linked together together with twelve sticks to form a cube. The blocks would represent atoms and the sticks atomic bonds. Each molecule will be an identical cubic structure of eight blocks held together by twelve sticks floating free around each other, more or less. With a crystal you would start out with the same cubic structure but you expand the structure by attaching a square of four blocks and four sticks to the original cube with four other sticks so that you will have a double cube that share corner blocks. Of course there are other shapes for the basic crystals in different crystalline substances but a cube is the basic shape of an iron crystal and iron crystals form the matrix for steel. From there it starts to get complicated a little. If you want to do some reading on it, I would recommend Metallurgy Fundamentals. It sort of like Cliff Notes on the subject.

Doug
 
I had basic physics in school my friends.
My terminology may be in question ?
But my original statement that "the roll marks from the rolling mill are comedic" and the internal strength and make up of the steel is transformed into it's final state during Heat treat.

I went thru this testing knives to destruction in my shop and found no difference in the strength or toughness of the blades made ether way of roll stock 440C. Granted I am not a trained scientist with a doctorate and have no real lab type equipment.

Do one of you has a doctorate in metallurgy? If so, I am willing to listen, If not?

Laurence

www.rhinoknives.com
 
I have never been concerned with the grain direction just grain size.
Untitled-1.jpg

I'm a simple guy so I like simple terms. This picture is of two pieces of 1084 from the same bar. The bottom one has an enlarged grain from overheating. The top piece shows proper grain structure. The coarse grain is far more fragile and a knife made from it would not be half as good as a knife with proper grain size. The grain direction of both pieces has no practical impact on the quality of knife made from the steel. Give this a read it is not directly related to your question but it explains a lot about proper heating and grain structure.
http://www.caffreyknives.net/journeymanarticle.html

I will stay out of the molecule debate, I got through high school by the skin of my teeth. I do have a doctorate in tree felling:)
 
A doctorate in tree felling is good!:35:

Thanks for posting a picture of the internal process I was referring too. this doesn't show any external rolls marks, but it shows that the grain structure is determined in the HT process.

Laurence

www.rhinoknives.com
 
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How the steel was rolled does not have anything to do with the actual grain of the metal, which is reset by proper HT, but it does affect any slag or small inclusions in the billet. This is far less of an issue than it was in the past. The amount of these in current tool steel is close to non existent. Forging modern steel that has been rolled will not improve its grain. I have had 13 sheets of D2 all 12"x39" and have some sheared, laser cut and cut up with a band saw in various directions. I can't tell a lick of difference which way a blade came of the sheet. Least of my worries. The reason they forge somethings is because they start from a billet. A cast steel crank shaft was never rolled and therefore any impurities, inclusions, slag remain as cast and never broken down in a forging process, a forged crank doesn't get that many hits from a hammer though. It isn't many wacks with the huge dies before it goes to machining. Most of the forging improvement happens when the roll the billet into rounds before it is forged into a crankshaft shape.
http://www.youtube.com/watch?v=fy6CxszXCjw&feature=related

If you want to really understand metals get the book Metallurgy Fundamentals by Daniel A. Brandt, J.C. Warner, J. C. Warner. Gives the information very clearly and even has quizzes for each chapter so you can check to see if you "got it" It covers steel very well and the other metals as well.

Look at metal this way
This fits well with my understanding of metallic bonding - the nuclei are surrounded by a 'sea' of electrons so there is no 'molecule' to identify, just a repeating pattern of nuclei sites (the unit cell). Basicallly, the concept of molecule has no meaning for metallic bonding. It's useful for covalent & ionic bonding however. A sodium & a chlorine atom make a 'salt' molecule but two iron atoms don't make a metallic unit cell. T

I have read where metals can form molecules when "doped" to become insulators or superconductors in electronics
 
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Laurence, as far as differences in a forged blade and a stock removal blade, you're preaching to the choir. There is no difference, all things being equal in steel and HT. All mill bar steel is already forged by the rolling process. Further forging will add nothing to the steel, however the elongated grain shape is not formed in HT. The rolling has already done that, and it will not change in shape or direction during HT. Only in size.
 
The steel grains themselves can re-formed in the heat treating operation. The "grain direction" being discussed here is the distribution of alloying elements, those alloying elements with larger atoms are more or less bound into place between the steel grains wherever they end up in the rolled bar or sheet.
These alloying elements are not always evenly distributed in the original pour, and during rolling they tend to get drawn out into long strands that run lengthwise to the rolling direction. You can re-form the steel grains around these strands of alloys but the strands themselves, once formed, cannot be dealt with effectively using common heat treating practices. This is known as alloy banding and many makers have seen it in a bar of steel at one point or another. Highly alloyed steels are especially suceptible to this.
 
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