Talk:Case-hardening

Sorbitizing

What is sorbitizing

My first guess is that it's treatment with sorbic acid, which looks like it would infuse carbon into the surface of the object being treated. I'll do some more digging and see what I can find. scot 15:07, 28 November 2006 (UTC)

Re recent edit - should case hardening link to Surface engineering so directly, as the first link in the list? Is it really a "surface process" in the same sense as the category uses it? It's really a bulk process that just has very limited access to the bulk of the material. Is this a pure "surface" treatment in the way that ion implantation etc. are? Andy Dingley 01:30, 14 November 2007 (UTC)

Chemistry: dubious tag

Is the chemical "reaction" described in this section really correct? Case hardening is a similar process to the production of blister steel. Since all materials are in the solid state there is no means by which CO could diffuse into iron, and no means of it being persuaded to lose its oxygen when it arrived. My understanding of the process is that the migration took place entirely in the solid state. My assumption is that vibrating carbon atoms became detached from the charcoal and incorporated into the iron. Such high temperature solid-state processes are not within the sort of chem,istry that I was taught either at school or university. If this section is not to be deleted it needs to cite some reliable source. Peterkingiron (talk) 15:40, 12 July 2009 (UTC)

Yes, it's right. Andy Dingley (talk) 16:22, 12 July 2009 (UTC)

This is face hardening, right?

Face-hardening redirects here, and I believe that is a synonym, right? If so, I'd like to add that to the intro statement. Maury Markowitz (talk) 16:15, 6 July 2010 (UTC)

Face-hardening is one form of hardening, but they're not synonyms. Case-hardening is a method of hardening, specifically for hardening low carbon steels that can't otherwise be hardened. Face-hardening is a requirement for hardening, for instance where a cam rocker needs to be hardened over a specific area. If the rockers are mild steel, they could indeed be hardened by case-hardening. However there are other ways too these days: other ways of upping the carbon content, also just using a higher carbon steel, machining most of it soft and then selectively hardening the tips, probably by induction.

It ought to be added, if it's a redirect, but the wording should be careful. Andy Dingley (talk) 20:29, 6 July 2010 (UTC)

This may be a "cross the pond" issue... many sources I have read on tank armor talk about "face hardening" (note the use as a verb) using a process identical to the one described here. It's commonly used to describe late-war German armors for instance. If this is an incorrect usage of the term, that might be worth pointing out too. Maury Markowitz (talk) 20:18, 7 July 2010 (UTC)

Ah, the naval use. Yes, that's certainly a pretty direct synonym, albeit limited in scope. I've only heard it applied to armour plate. Andy Dingley (talk) 20:22, 7 July 2010 (UTC)

• It sounds to me as if they are nearly synonyms, but not quite. If so, it may be best to keep them both in one article, but to add a section explaining the technical difference. Peterkingiron (talk) 23:03, 12 July 2010 (UTC)

Chemistry section

If the chemistry section isn't in reference to carburizing, then what process is it? Wizard191 (talk) 01:45, 26 July 2010 (UTC)

Ferrocyanide

A nit here. Ferrocyanides are not "potentially toxic cyanide compounds" - they are essentially nontoxic both in vivo and in the environment. Addition of strong acids cat cause release of actually toxic hydrogen cyanide gas. The reason that ferrocyanides were used in the first place was because potassium cyanide - which case hardens really well btw - is in fact quite toxic. See ec.europa.eu/food/fs/sc/scan/out70_en.pdf‎ about cyanoferrates. Norm Reitzel (talk) 21:33, 4 December 2013 (UTC)

I removed the phrase "such as ferrocyanide". The ferrocyanide article gibes with what you said. I left the rest of the sentence alone on the fair chance that it may be accurate (newer formulas less toxic than older ones), especially since it has refs, but it would be good if anyone could knowledgeably say which specific molecules made the old formulas more toxic. — ¾-10 01:25, 5 December 2013 (UTC)

The information in the article Carbonitriding and that of the carbonitriding section of this article

This article states it (carbonitriding) can be done with, or without quenching, the carbonitriding article however makes no mention of a process in which you don't quench the steel afterwards. This article as states that the steel is heated to a temp. between 649 degrees Celsius, and 885 degrees Celsius, and the carbonitriding article states only that it is done at ~850 degrees Celsius. There're are also no references provided in either article for this process. I am only a student of power engineering, and don't know enough to clarify, could someone else do so? Thanks, Jahelistbro (talk) 18:43, 12 December 2016 (UTC)

Carbonitriding is done to produce a surface that has much higher quench-hardenability than the steel normally would with normal quenching. It is particularly effective on low carbon or low-hardenability steels, to increase the amount of surface carbon allowing the full formation of martensite upon quenching. Carbonitriding is really a carburizing process rather than a nitriding process, in that the goal is primarily to increase the surface carbon-content. It is done with rather low amounts of ammonia, because the nitrogen is an austenite stabilize thus has a tendency to lower the wear resistance (increase galling) at high doses.

According to the book Surface Hardening of Steels: Understanding the basics(page 127), carbonitriding is done at very low temps compared to plain carburizing, between 775 °C (1,427 °F) and 900 °C (1,650 °F). This low temp-range causes very slow rates of diffusion, so the case will be extremely shallow; and even less so as temperature decreases. However, at higher temperatures the absorption of nitrogen becomes too great and the proper levels cannot be controlled. When done at very low temperatures, quenching is often unnecessary because the surface layer becomes a completely separate composite-layer. The problem is that the holding time is very long, usually making it impractical, and the depth is extremely shallow. The benefit is that a very hard surface can be applied to a metal that is otherwise unquenched and remains very soft and tough. Zaereth (talk) 19:39, 12 December 2016 (UTC)

History outdated

The cited article by Ayres does not talk about steel production before Bessemer, and modern archaeological studies show that the carburized parts of blooms have been used to make tools and weapons in western Eurasia for at least 3000 years. See handbooks like Moorey's "Ancient Mesopotamian Materials and Industries: The Archaeological Evidence" or Vagn Fabritius Buchwald, "Iron and steel in ancient times" (Copenhagen, 2005). Prof. Helmut Föll's "Iron, Steel, and Swords" is more of a 'lecture note turned hypertext' but has an OK section on Smelting Wrought Iron, Steel, and Cast Iron https://www.tf.uni-kiel.de/matwis/amat/iss/index.html

How much steel was made in the smelter, and how much case-hardened, is controversial. Moorey, Buchwald, or Föll give a much better sense for the state of the debate than this article on economic cycles from 1989. 193.170.51.199 (talk) 00:01, 1 February 2018 (UTC)

While true, I think that differs considerably from the definition of case-hardening, which is to provide a hard outer-shell, providing better wear resistance at the surface, while leaving a majority of the object softer and far tougher. For example, the bearing surfaces (journals) of an automotive crankshaft are induction hardened to provide a very hard, wear-resistant surface. However, if the entire crankshaft was treated that hard it would shatter under the blows from the pistons. A gun barrel may be case hardened to protect its surface while keeping a majority of the steel tough enough to avoid exploding when the bullet is fired.

The steel produced in bloomery smelting was more of an accidental byproduct. It was typically very high in carbon content (typically from 1 to 2% carbon, averaging around 1.5%), and due to this had a much lower welding temperature. Thus, in the making of wrought iron it was more of an impurity that needed to be removed from the bloom before being wrought. True, at some point people discovered the unique properties of steel and began using it on its own (and even smelting iron just for it) but this is different from case hardening. Similarly, blister steel is far more like case hardening than a bloom of sponge iron, but the creation of such a hard shell was not the purpose. It was actually useless for most applications until people began making shear steel out of it in an attempt to homogenize the steel.

I have no doubt the use of case-hardening began very early. The mystery of why steel behaved as it did was very misunderstood and seemed almost magical to ancient people. Some believe they should only quench the steel in a certain river at a specific time of year, while others thought you needed the urine of a young page with light complexion. Others thought mercury was the best quench. At some point someone had to have tried oil. Still, I don't really think bloomery smelting or the cementation process can be compared because it's like apples and oranges. (And the yield is dependent on many factors, such as the exact method of smelting and the composition of the ore used.) Zaereth (talk) 00:31, 1 February 2018 (UTC)

It may also be worth mentioning that differential hardening is a form of case hardening that began nearly 2000 years ago in Asia. I think it's also worth pointing out that, to really understand the history and development of steel in Europe, it's important to understand the work of Johann Becher, the Einstein of his time. His phlogiston theory is an excellent example of how a theory can be completely backwards and still give correct results almost identical to the current theory. Zaereth (talk) 02:49, 2 February 2018 (UTC)