Reactivity of Steel At Elevated Temperatures

Most of us know If you dump a ton of oxygen, heat, and fuel on steel it can burn. Burn may be technically arguable but a very violent reaction resulting in loss of material in its original form results.

Some of us may know that there is some steel loss from reactions at a lower temperature when using a steel crucible for things like casting aluminum and even some material loss with steel molds used for casting aluminum many times. ...

--------------------- Steel wool burns.

Steel's tempering colors result from oxidation.

The blacksmith told me to temper the quench hardened froe blade I made from a leaf spring at ~350F for an hour, twice, and the high areas I had ground down became faintly yellow from incipient oxidation.

I absolutely believe what I was taught, that steel burns. That reactiveness of steel premise was originally shared with a tackle making group which tends to be more "craftsy" than technical. Sometimes its easier to allow for some grudging disagreement than to parrot "facts."

Of course its obvious that steel(iron alloys) becomes more reactive at temperatures as low as molten lead. If for no other reason than an old gunsmith's trick for tempering flat springs (simple carbon spring steels) is to dunk them in molten lead until they change color. That's more than twice the temperature than knife makers tend to temper knife steel, but a much faster temper. (seconds)

I suspect molten lead tempering is over tempering which is more likely to result in a loss of spring tension over time as opposed to a broken spring from under tempering. Of course can I argue with any spring that has lasted a hundred years? One of my other hobbies is buying old junk guns and fixing them. Not selling them. LOL. Maybe someday. Just fixing them.

I absolutely believe what I was taught, that steel burns. [[[ Pinch off a bit of steel wool and light it. When forging if the steel is yellow hot and gets into the air stream it can burn and spark. ]]]

That reactiveness of steel premise was originally shared with a tackle making group which tends to be more "craftsy" than technical. Sometimes its easier to allow for some grudging disagreement than to parrot "facts."

Of course its obvious that steel(iron alloys) becomes more reactive at temperatures as low as molten lead. If for no other reason than an old gunsmith's trick for tempering flat springs (simple carbon spring steels) is to dunk them in molten lead until they change color. That's more than twice the temperature than knife makers tend to temper knife steel, but a much faster temper. (seconds)

I suspect molten lead tempering is over tempering which is more likely to result in a loss of spring tension over time as opposed to a broken spring from under tempering. Of course can I argue with any spring that has lasted a hundred years? One of my other hobbies is buying old junk guns and fixing them. Not selling them. LOL. Maybe someday. Just fixing them.

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This gives 600-650F for gun spring temper, which puts molten pure lead in the middle. Alloys have lower melting points.

Knives aren't expected to bend much so they can be tempered harder.

That of course leads me to wonder then why steel baking in the southern Arizona Sun will get hot enough to harm you if you pick it up and hold it for very long, but just develops a light surface rust and lasts for decades. LOL.

We joke about it developing its light coating of protective rust. Okay maybe two of us make that joke.

At a boy scout jamboree many years ago groups of us were challenged to start fires and the winner did what the leaders frowned on but it got a fire going quickly, he had brought along a D cell and some wire wool and shorted the wire wool across the cell and had a fire going in no time.

That of course leads me to wonder then why steel baking in the southern Arizona Sun will get hot enough to harm you if you pick it up and hold it for very long, but just develops a light surface rust and lasts for decades. LOL.

Bob La Londe

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As a general rule, the rate of a chemical reaction doubles with a temperature rise of 10 degrees C (18F). I mentioned that 2 hours at 350F gave a barely visible yellow tinge to bare spring steel. The jump from 150F to 350F is more than 10 such doublings, or 1000 times faster. Steel can oxidize in several ways (oxidation states) under different conditions to give red, brown, yellow->purple or black oxide coatings. Around room temperature the overall energy level is low so rust forms preferentially at irregularities with slightly higher energy, hot steel has enough overall energy to overwhelm the slight differences and it oxidizes more evenly, for example mill scale and temper color.

That's a vast oversimplification of the complex subject of chemical thermodynamics.

Thermodynamics can be hard to understand. 200 years ago the best minds believed that heat was an invisible fluid called Caloric or Phlogiston that could be squeezed out of the steel by cutting or hammering it. The concept that heat and temperature were the kinetic energy of molecular motion took a while to be accepted, and longer to be well understood. Chemistry is an example of pure reason utterly failing to discover the truth although it had succeeded for math and physics.

At a boy scout jamboree many years ago groups of us were challenged to start fires and the winner did what the leaders frowned on but it got a fire going quickly, he had brought along a D cell and some wire wool and shorted the wire wool across the cell and had a fire going in no time.

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That was also a college contest. The winning technique was soaking charcoal with liquid oxygen.

While on the subject, the oxidation of iron can be enhanced or retarded by other materials that react with it. Chloride in sea or road salt is the common example, water is another that makes oxidation easier while phosphorus helps protect from oxidation. Cast iron for wood stoves often contains significant phosphorus which makes it fill the mold better and reduces oxidation of the hot stove. Some peoples' fingerprint oil protects bare steel, mine for instance, while others' makes it rust more easily in the fingerprint ridge pattern.

The Parkerizing on military equipment is a phosphate conversion coating. Naval Jelly contains phosphoric acid to remove existing rust and reduce subsequent corrosion.

And while its totally wrong its still a good analogy for getting the point across. Its not just angry punk rockers in a mosh pit. Its a volume of angry punk rockers in a mosh pit. Not to technical people who will stop listening and start trashing you to show how smart/educated they are the instant you use an analogy so they can tell you how wrong you are. Its good for practical people who need a feel of how the a large volume of a substance at a particular temperature has more heat to manage than a small volume of that substance at the exact same temperature. Its not just angry punkers or the level of their anger. Its about a whole bunch of angry punkers.

People sometimes struggle with heat management in injection molding because they can't understand why their skinny rubber worm comes out fine, but their thick heavy swimbait dents or pulls air. The people I am dealing with are often not technical experts, but sometimes they are or are becoming practical experts.

Think of heat as having volume. The more volume there is, and the less transmission media there is the longer its going to take to drain the heat away.

Yes I know that's wrong, and if anybody will feel better about themselves by telling me I am wrong have at it.

called Caloric or Phlogiston

And while its totally wrong its still a good analogy for getting the point across. Its not just angry punk rockers in a mosh pit. Its a volume of angry punk rockers in a mosh pit. Not to technical people who will stop listening and start trashing you to show how smart/educated they are the instant you use an analogy so they can tell you how wrong you are. Its good for practical people who need a feel of how the a large volume of a substance at a particular temperature has more heat to manage than a small volume of that substance at the exact same temperature. Its not just angry punkers or the level of their anger. Its about a whole bunch of angry punkers.

People sometimes struggle with heat management in injection molding because they can't understand why their skinny rubber worm comes out fine, but their thick heavy swimbait dents or pulls air. The people I am dealing with are often not technical experts, but sometimes they are or are becoming practical experts.

Think of heat as having volume. The more volume there is, and the less transmission media there is the longer its going to take to drain the heat away.

Yes I know that's wrong, and if anybody will feel better about themselves by telling me I am wrong have at it.

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I see your point, electricity is often introduced to beginners as behaving like water as long as you don't try to stretch the analogy very far, for instance electricity within conductors has no weight. If your study will go further you have to forget the water analogy and learn the mathematical models so you can make things that work, if not it's useful to fit new ideas into a familiar framework.

We dove straight into specific heat, thermal mass and conductivity and the atom-level basis for them, but Phlogiston looked good enough to be the generally agreed on nature of heat until the late 1700's when experiments proved otherwise. So did Earth, Air, Fire and Water despite the excessively convoluted arguments dreamed up to defend that relic of Aristotle. The understanding of chemistry developed slowly and much later than that of physics which Newton codified. Among other hindrances to progress the natural mixtures of isotopes of different weights confused researchers who tried to accurately measure the expected small integer weight ratios of elements in simple compounds. The reason, the neutron, wasn't discovered until 1932.

People sometimes struggle with heat management in injection molding because they can't understand why their skinny rubber worm comes out fine, but their thick heavy swimbait dents or pulls air. The people I am dealing with are often not technical experts, but sometimes they are or are becoming practical experts.

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I've known about copes and drags and core prints and riddles and sprues and runners and vents and shrinkage voids since I was 5, watching the foundry workers sand-cast aluminum and describe the process to me. When I was apprenticing as a machinery designer I looked at casting design again and noticed that the descriptions assumed no scientific education, which I had plenty of by then. They gave rules of thumb about max and min web thickness and where to feed to keep potential voids supplied until they solidify, things a draftsman who may have been a failed artist needed to know.

Circuit board layout and routing was similar. It was a bonus to the company that I knew how the circuit worked, but that wasn't essential to become a successful PC board designer. They just had to learn and follow the rules.

And while its totally wrong its still a good analogy for getting the point across. Its not just angry punk rockers in a mosh pit. Its a volume of angry punk rockers in a mosh pit. Not to technical people who will stop listening and start trashing you to show how smart/educated they are the instant you use an analogy so they can tell you how wrong you are. Its good for practical people who need a feel of how the a large volume of a substance at a particular temperature has more heat to manage than a small volume of that substance at the exact same temperature. Its not just angry punkers or the level of their anger. Its about a whole bunch of angry punkers.

People sometimes struggle with heat management in injection molding because they can't understand why their skinny rubber worm comes out fine, but their thick heavy swimbait dents or pulls air. The people I am dealing with are often not technical experts, but sometimes they are or are becoming practical experts.

Think of heat as having volume. The more volume there is, and the less transmission media there is the longer its going to take to drain the heat away.

Yes I know that's wrong, and if anybody will feel better about themselves by telling me I am wrong have at it.

---------------------------- Not wrong, actually pretty close to reality. Heat capacity is usually specified by mass, the easily determined weight of material, but in fact it's nearly constant per atom so lighter elements have higher specific heats. All metals would have about the same heat capacity per volume if their atoms were the same size, but they do vary somewhat. Their heat capacity runs around 2 to 3.5 Joules per cubic centimeter to change the temperature by one Celsius (Kelvin, K) degree. A Joule is 1 Watt for 1 Second.

Measuring in cubic centimeters is a historical practice, they are equal to milliliters.

Yes, the "Molar Heat Capacity"; the heat capacity for a certain reference number of atoms. Is almost identical across metals. I've seen that at least approximately across a few common metals.

"Jim Wilkins" snipped-for-privacy@gmail.com writes: ...

Yes, the "Molar Heat Capacity"; the heat capacity for a certain reference number of atoms. Is almost identical across metals. I've seen that at least approximately across a few common metals.

-------------------------- Which tends to support the belief that heat is a separate undetectable fluid that infiltrates the volume of the metal. They weren't too far off since conduction band electrons do just that.

I was left wondering whether the conduction-band electrons of a metal are responsible for the surreal rapid diffusion of hydrogen (element number one - it's a proton with an electron circulating around it)

During my Doctoral study years on hydrogen in steels - where I was looking at weld hydrogen initially in the weld zone and what becomes of it - but found apparently also uncovered why modern low-carbon TMCP (Thermo-Mechanically Controlled-Processed) microalloyed steels are highly resistant to "sour" crude oils.

I was left wondering whether the conduction-band electrons of a metal are responsible for the surreal rapid diffusion of hydrogen (element number one - it's a proton with an electron circulating around it)

During my Doctoral study years on hydrogen in steels - where I was looking at weld hydrogen initially in the weld zone and what becomes of it - but found apparently also uncovered why modern low-carbon TMCP (Thermo-Mechanically Controlled-Processed) microalloyed steels are highly resistant to "sour" crude oils.

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I'm not sure hydrogen's interactions with metals were that well understood when I learned it. What I took away was that under the certain conditions hydrogen may shift from a diatomic gas to metallic or nearly so and can share loose electrons like a metal or double bonded carbon, and its naked protons could move around similarly to but slower than electrons, like positively charged holes in a semiconductor. That's only my partly educated guess, or SWAG. I don't have the theoretical background in quantum mechanics (or interest) to pursue it.

Catalytic action with hydrogen in general was very difficult to analyze with the available instruments of the 1960's. Even the molecular clumping of water near the freezing point was uncertain, which was the basis of Kurt Vonnegut's Ice 9 in "Cat's Cradle".

Cold fusion research of Pons & Fleishman and Rossi's E-Cat were tentatively accepted, subject to verification, because some properties of hydrogen dissolved in or adsorbed on metals are still debated despite over 100 years of hydrogenation experience, e.g high test gasoline, NiMH batteries.

What tipped me that Rossi's results might be a scam or experimental error was the naturally occurring isotopic distribution of the resulting copper, instead of being one pure isotope. When I found that his reactor was brazed copper tubing without internal cleaning or plating I realized that the hot hydrogen was reducing the copper oxide to atomically fine copper mist and blowing it into the nickel, and revealed that to one of his supporters who had asked me to build the apparatus for him.

My personal research experience with hydrogen was limited to substituting deuterium for it so the organic molecule in question could be tracked in the body with MRI to find where it was metabolized. After graduation in 69 I was sucked into the military and given a year of condensed electronics education, which I found I liked better than Chemistry and had much better job prospects. My degree wasn't a complete waste, the only students who passed that demanding course already had technical degrees, and the broad knowledge of matter and energy it gave me has been useful in R&D to complement the deep but narrow education of Ph.Ds.

Rules of thumb often work very well. In fact sometimes its very difficult to get somebody to get past a rule of thumb. Not that there aren't a few cases were a rule of thumb nearly always apply. Just that some people will trust the rule of thumb better if they have some form of understanding they can grasp. Even if its only a general analogy they can put in the back of their mind to make them feel there is some sense to it.

X: Just do this!

Y: Why?

X: Because I said so!

Y: Silence.

Well, that works, but it can also lead to catastrophic runaway situations.

X: Just do this!

Y: Why?

X: Well, I'm not sure 100%, but this is the way I think it works.

Y: Oh, so if we did it at one thousand times that scale we'd melt a hole in the crust of the planet?

X: I hadn't thought of that. Yeah maybe. Within the scope of what we do in this shop just do this, but if you want to go bigger, smaller, faster, or slower perhaps consult somebody more educated than myself.

On 7/6/2023 11:02 AM, Jim Wilkins wrote: ...

Rules of thumb often work very well. In fact sometimes its very difficult to get somebody to get past a rule of thumb. Not that there aren't a few cases were a rule of thumb nearly always apply. Just that some people will trust the rule of thumb better if they have some form of understanding they can grasp. Even if its only a general analogy they can put in the back of their mind to make them feel there is some sense to it.

X: Just do this!

Y: Why?

X: Because I said so!

Y: Silence.

Well, that works, but it can also lead to catastrophic runaway situations.

X: Just do this!

Y: Why?

X: Well, I'm not sure 100%, but this is the way I think it works.

Y: Oh, so if we did it at one thousand times that scale we'd melt a hole in the crust of the planet?

X: I hadn't thought of that. Yeah maybe. Within the scope of what we do in this shop just do this, but if you want to go bigger, smaller, faster, or slower perhaps consult somebody more educated than myself. Bob La Londe

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I do and sometimes post both rough approximations like rules of thumb and exact calculations. The specific heat post was rough ballpark* estimates plus links to find better answers.

The approximations were useful when someone stopped by unexpectedly to ask me if I could build something for them. I had to quickly estimate the magnitude of problems to give them a good answer, then refine it after I knew more. The accuracy of a solution is no better than that of the most uncertain variable.**

For example earlier today I was talking to the owner of a self-driving Tesla, after watching it pull out of its parking space toward me and stop beside him. I had worked for Tesla's previous tech director and chosen a portable DC-AC inverter and jump starter to his spec for a remote presentation, passed through his secretary so I couldn't discuss it, which proved to be too heavy to travel with because he hadn't estimated the consequences of the power output he asked for. Embarrassing the boss is never good so afterwards I avoided him.

• falling within a large space, as opposed to out of it.

** Russian joke. A man orders a car and is told it will be delivered in ten years. He asks if that is ten years in the morning, or afternoon. The salesman screams TEN YEARS, TEN YEARS, WHAT DOES IT MATTER? He replies "Well, the plumber is due ten years from now in the morning."

Local Humidity. There's not really enough water in the air to do more that oxidize the top later.

And then there is the stuff which just rust "a little bit" then stops. Used in some decorative pieces.