heated steel debate

[Irondragon Forge ClayWorks]

Mystery steel… gotta love it.

Today I decided to make a “hoop” to hang a very large caldron. I had a half circle ½ inch round bar that would fit the bill so I began drawing out the ends and putting hooks on them. I finished the first one and quenched it in water so I could work on the other. While drawing the second end a piece of the first snapped off.

I thought ok high carbon spring steel that doesn’t like water quench. I reformed the end and let both cool in air. I then began to heat the center with both ends up, planing to swage a hump for the chain and when the metal got to orange heat it fell apart.

A spark test showed it is high carbon steel and it has a very fine grain and rings like a bell.

Any ideas? Never had metal just fall apart while heating it.

 

Photos were lost in a forum up date.

 

 

 

 

 

 

[jlpservicesinc]

Yup, use mild steel..  Save that for other projects..   I will be putting out a  "How to" video on figuring out mystery metal and how to use it but it's not going to be ready till mid summer.. 

Ideally you need to figure out what metal it is before you use it..   without testing it myself and not knowing what temp you forged/bent it at from your description, I'd guess it's an air hardening steel..  

Looks like a spring from an old hay rake.. 

[patrick]

It's been a while since I've posted here so I'll briefly provide my background before answering the original question. I am a professanal metallurgical engineer and have been working as the plant metallurgist for one of the Scot Forge facilites for the past 14 years. We make forgings up to about 150 tons these days. Prior to that I worked for Timken for 2 years. I've been forging by hand and with power hammers for the last 20 years. Hat tip to Thomas Powers who got me started...

The orginal question had to do with a precieved difference in strength between forged blades and those ground directly from bar which lead to a more general discussion of the various merrits of forged products vs. those produced by other methods. To properly answer this question we first have to define "strength". There are multiple types of strength and ways of measuring it. Tensile properties are determiend by stretching. There are 4 properties tyically obtained from a tensile test: Ultamate tensile strength, yield strength, elongation and reduction of area.

Utimate tensile strength: The maximum load applied before the specimen breaks

Yield strength: The load necessary to cause permanent deformation of the specimen

Elongation: The % change in length from the starting length to the final length after the specimen breaks

Reduction of area: The % change in cross sectional area from the starting area to that after the specimen breaks.

Additoinal Types of Strength:

Fatigue Strength: The ability to withstand repeated bending when the amound of bend does NOT result in any plastic deformation

Imapct strength: A measure of the amount of energy needed to break a notch bar specimen of standard dimension. This property is temperature dependant for the carbon and alloy steels under discussion here.

When comparing forgings to products made from machined bars, assuming that is the only difference is in how the shape was achieved, the differences in "strength" will not be differences in utimate tensile or yield strength. Nor will there be differences in the elongation, reduction of area or impact strength. The difference will be in the fatigue properties. The reason for this is becuase in a forged product, the metal is forced to flow around corners. This flow around the corners does align the non-metallic inclusions in the streel in a preferential way which results in resistance to fatigue failures.

It is true that steel today is not like steel from years ago and is particularly different from wrought iron. It is much cleaner so the behaviours we see in wrought iron are not encountered when hand forging steel. However, inspite of the much cleaner materials we have today most steel still has some amount of non-metallic inclusions. These are microscopic, but they still do affect properties. In particular they affect the elongation, reduction of area and impact properties. If you are dealing with a forged or rolled bar these micro inclusions are oriented in line with the long axis of the bar. If you cut a specimen parrellel to this axis you will get one set of properteis. If you cut your specimen at 90 degrees to this axis you will find that ultamite tensile and yield are about the same but the elongation, reduction of area and impact properties are reduced. Today it is possible to produce steel that is so clean you have very little difference in properties regardless of test orientation, but those materials are more costly to produce and are not as widely used.

With respect to the original question where the starting stock is a rolled bar which is then either forged into a blade or ground into a blade there will be almost no measureable difference in properties assuming that is the only differnece in manufacturing. IF there are difference in heat treat then yes you can get major differeces in performance.

Additional questions were raised about grain size and grain flow and there seems to be some confusion on these subjects:

Grain size is the actual size of an individual crystal of iron. This is measured via standard methods and is given an ASTM size rating. The larger the number the smaller the actual crystal. In general smaller grains are prefered for most applications because smaller grained materials will have better elongation, reduction of area and impact properties. Industrially grain size is controlled through a combination of heat treatment and chemistry. Provided you have elements in the steel that limit grain growth during heat treatment (aluminum, vanadium, niobium) you can refine the grains by normalizing prior to austentizing for the quench. In industry there are times when multiple normalizing cycles are used for the purpose of refining the grains. Generaly we don't see a benefit to doing more than two cycles, and even that is a special case. Most of the time a single normalize cyle is sufficient.

Grain flow is what I noted about about forcing the metal to go around corners.

Edge "packing"-This is really a confusing term because you are not making the steel more dense. What you are doing is locally deforming and breaking the grains into smaller sizes. It is a technique that is not necessary with modern steels since grain refinement can be achieved through heat treatment.

 

[JHCC]

1 hour ago, patrick said:

To properly answer this question we first have to define "strength".

@patrick, thank you very much for an informed and thorough answer both to the original question and to the issues raised in the subsequent discussion.

1 hour ago, patrick said:

[Non-metallic inclusions] affect the elongation, reduction of area and impact properties. If you are dealing with a forged or rolled bar these micro inclusions are oriented in line with the long axis of the bar. If you cut a specimen parrellel to this axis you will get one set of properteis. If you cut your specimen at 90 degrees to this axis you will find that ultamite tensile and yield are about the same but the elongation, reduction of area and impact properties are reduced.

This raises an interesting (if largely academic question) about the strength of pattern-welded blades, especially those mosaic damascus blades where the billets are cut, rotated, stacked, welded, lathered, rinsed, and repeated for visual effect. 

[jlpservicesinc]

Patrick, thanks for voicing..   This is where it would be nice to have a +1 or thumbs up button..  

[Charles R. Stevens]

One of the many joys of IFI, it dosnt matter the subject there is an honest to god expert lurking around here! Lol

Patric, out of curiosity can you put a $ value on your time to answer the OP,s question and to prove TP and JLP both right? It goes to something I try to point out to new folks about the respect a fellow smith shows you, even if s/he climes your ears for not paying attention. 

[ThomasPowers]

Hey Patrick; I hope Melody and the kids are doing great; I'm due to have an 8th grandchild in October (and my Daughter Megan's 4th boy). I'm not getting to Q-S this year as my surgery and Death of my Father has burned up all my vacation.

And just remember "not everything has to be made into a knife"!

[Irondragon Forge ClayWorks]

On 4/24/2017 at 8:42 PM, Irondragon ForgeClay Works said:

Photos were lost in a forum up date.

I figured if anyone was interested in this, I would add the pictures again.