Tag Archives: cementite

Preventing corrosion in oil pipelines at the nanoscale

A June 7, 2019 news item on Azonano announces research into the process of oil pipeline corrosion at the nanoscale (Note: A link has been removed),

Steel pipes tend to rust and sooner or later fail. To anticipate disasters, oil companies and others have developed computer models to foretell when replacement is necessary. However, if the models themselves are incorrect, they can be amended only through experience, an expensive problem if detection happens too late.

Currently, scientists at Sandia National Laboratories, the Department of Energy’s Center for Integrated Nanotechnologies and the Aramco Research Center in Boston, have discovered that a specific form of nanoscale corrosion is responsible for suddenly diminishing the working life of steel pipes, according to a paper recently published in Nature’s Materials Degradation journal.

A June 6, 2019 Sandia National Laboratories news release (also on EurekAlert), which originated the news item, provides more technical detail,

Using transmission electron microscopes, which shoot electrons through targets to take pictures, the researchers were able to pin the root of the problem on a triple junction formed by a grain of cementite — a compound of carbon and iron — and two grains of ferrite, a type of iron. This junction forms frequently during most methods of fashioning steel pipe.

Iron atoms slip-sliding away

The researchers found that disorder in the atomic structure of those triple junctions made it easier for the corrosive solution to remove iron atoms along that interface.
In the experiment, the corrosive process stopped when the triple junction had been consumed by corrosion, but the crevice left behind allowed the corrosive solution to attack the interior of the steel.

“We thought of a possible solution for forming new pipe, based on changing the microstructure of the steel surface during forging, but it still needs to be tested and have a patent filed if it works,” said Sandia’s principle investigator Katherine Jungjohann, a paper author and lead microscopist. “But now we think we know where the major problem is.”

Aramco senior research scientist Steven Hayden added, “This was the world’s first real-time observation of nanoscale corrosion in a real-world material — carbon steel — which is the most prevalent type of steel used in infrastructure worldwide. Through it, we identified the types of interfaces and mechanisms that play a role in the initiation and progression of localized steel corrosion. The work is already being translated into models used to prevent corrosion-related catastrophes like infrastructure collapse and pipeline breaks.”

To mimic the chemical exposure of pipe in the field, where the expensive, delicate microscopes could not be moved, very thin pipe samples were exposed at Sandia to a variety of chemicals known to pass through oil pipelines.

Sandia researcher and paper author Khalid Hattar put a dry sample in a vacuum and used a transmission electron microscope to create maps of the steel grain types and their orientation, much as a pilot in a plane might use a camera to create area maps of farmland and roads, except that Hattar’s maps had approximately 6 nanometers resolution. (A nanometer is one-billionth of a meter.)

“By comparing these maps before and after the liquid corrosion experiments, a direct identification of the first phase that fell out of the samples could be identified, essentially identifying the weakest link in the internal microstructure,” Hattar said.

Sandia researcher and paper author Paul Kotula said, “The sample we analyzed was considered a low-carbon steel, but it has relatively high-carbon inclusions of cementite which are the sites of localized corrosion attacks.

“Our transmission electron microscopes were a key piece of this work, allowing us to image the sample, observe the corrosion process, and do microanalysis before and after the corrosion occurred to identify the part played by the ferrite and cementite grains and the corrosion product.”

When Hayden first started working in corrosion research, he said, “I was daunted at how complex and poorly understood corrosion is. This is largely because realistic experiments would involve observing complex materials like steel in liquid environments and with nanoscale resolution, and the technology to accomplish such a feat had only recently been developed and yet to be applied to corrosion. Now we are optimistic that further work at Sandia and the Center for Integrated Nanotechnologies will allow us to rethink manufacturing processes to minimize the expression of the susceptible nanostructures that render the steel vulnerable to accelerated decay mechanisms.”

Invisible path of localized corrosion

Localized corrosion is different from uniform corrosion. The latter occurs in bulk form and is highly predictable. The former is invisible, creating a pathway observable only at its endpoint and increasing bulk corrosion rates by making it easier for corrosion to spread.

“A better understanding of the mechanisms by which corrosion initiates and progresses at these types of interfaces in steel will be key to mitigating corrosion-related losses,” according to the paper.

Here’s a link to and a citation for the paper,

Localized corrosion of low-carbon steel at the nanoscale by Steven C. Hayden, Claire Chisholm, Rachael O. Grudt, Jeffery A. Aguiar, William M. Mook, Paul G. Kotula, Tatiana S. Pilyugina, Daniel C. Bufford, Khalid Hattar, Timothy J. Kucharski, Ihsan M. Taie, Michele L. Ostraat & Katherine L. Jungjohann. npj Materials Degradation volume 3, Article number: 17 (2019) DOI: https://doi.org/10.1038/s41529-019-0078-1 Published 12 April 2019

This paper is open access.

Ahoy me hearties! A new theory for Damascus steel

I hope I got that right. It’s been a long time since I’ve seen a pirate movie but talk of Damascus steel meant that I had to have at least one movie pirate-type phrase in this piece.

I first came across Damascus steel outside the pirate movie domain in 2007 about the time that researchers declared blades made of Damascus steel sported carbon nanotubes giving  the blades their legendary qualities. From a Nov. 16, 2006 National Geographic article by Mason Inman,

New studies of Damascus swords are revealing that the legendary blades contain nanowires, carbon nanotubes, and other extremely small, intricate structures that might explain their unique features.

Damascus swords, first made in the eighth century A.D., are renowned for their complex surface patterns and sharpness. According to legend, the blades can cut a piece of silk in half as it falls to the ground and maintain their edge after cleaving through stone, metal, or even other swords.

Now studies of the swords’ molecular structure are uncovering the tiny structures that may explain these properties.

Peter Paufler, a crystallographer at Technical University in Dresden, Germany, and his colleagues had previously found tiny nanowires and nanotubes when they used an electron microscope to examine samples from a Damascus blade made in the 17th century.

It seems that while researchers were able to answer some questions about the blade’s qualities, researchers in China believe they may have answered the question about the blade’s unique patterns, from a March 12, 2014 news release on EurekAlert,

Blacksmiths and metallurgists in the West have been puzzled for centuries as to how the unique patterns on the famous Damascus steel blades were formed. Different mechanisms for the formation of the patterns and many methods for making the swords have been suggested and attempted, but none has produced blades with patterns matching those of the Damascus swords in the museums. The debate over the mechanism of formation of the Damascus patterns is still ongoing today. Using modern metallurgical computational software (Thermo-Calc, Stockholm, Sweden), Professor Haiwen Luo of the Central Iron and Steel Research Institute in Beijing, together with his collaborator, have analyzed the relevant published data relevant to the Damascus blades, and present a new explanation that is different from other proposed mechanisms.

Before the development of tanks, guns, and cannons, humans fought with swords, and there was one type of sword in particular that everyone wanted, a Damascus sword. Western Europeans first encountered these swords in the hands of Muslim warriors in Damascus about a thousand years ago. Damascus swords were prized for their strength and sharpness. They were famous for being so sharp that they could cut a silk scarf in half as it fell to ground, something that European swords could not do. Both Mediterranean and European blacksmiths believed that the outstanding strength and sharpness of the swords resulted from their beauty, i.e., the Damascus pattern. This presents as a wavy pattern like a rose and ladder on the surface of Damascus blades, as shown in Fig. 1. It was recorded that blacksmiths in Persia made the best Damascus steel swords by hammering a small cake of Wootz steel, which was a high-quality steel ingot imported from ancient India. The best European blade smiths from the Middle Ages onwards were not able to fabricate similar blades, even though they carefully studied examples made in the East. Damascus blades became even more mysterious when the art of making them actually died out. Despite all the knowledge and technological advances of the 21st century, people are still debating the mechanism through which such beautiful patterns were formed on Damascus blades.

Here’s the figure showing a blade and its pattern,

Caption: This is an example of a Damascus sword with a typical Damascus pattern of Muhammad ladder and rose. Microstructural examination of the blade indicates that rows of cementite particles (in black) form the Damascus patterns[11]. Credit: ©Science China Press

Caption: This is an example of a Damascus sword with a typical Damascus pattern of Muhammad ladder and rose. Microstructural examination of the blade indicates that rows of cementite particles (in black) form the Damascus patterns[11].
Credit: ©Science China Press

The news release goes on,

The compositions and microstructures of many existing Damascus steel blades have been examined previously. Their C contents are within the range of 1 wt.%, and often around 1.6 wt.%. It is also known that the Damascus pattern results from the band-like formation of coarse cementite particles. The high C content leads to a large amount of cementite particles being precipitated during hot hammering. After proper etching, the coarse cementite bands appear white within the dark matrix, such that they form a visible pattern on the surface. After the 1970s, the mechanism for the formation of the Damascus pattern was revisited and debated, particularly by Professors Verhoeven from Iowa State University and Sherby from Stanford University. Sherby and his co-workers[1-4] thought that a coarse cementite network was formed around the large austenite grains, when the Wootz steel cake was cooled slowly in crucibles for several days after melting. Later, the continuous cementite network was broken into spheroidal particles during extensive hammering at relatively low temperatures between cherry (850 °C) and blood red (650 °C), rather than the white heat customarily used by European blacksmiths. Furthermore, Wootz steel cake must be used in the manufacture of genuine Damascus blades. The low-temperature hammering was also a key technology, by which Wootz steels were easily hot deformed without cracking, and finer carbide particles precipitated to make the steel stronger and tougher. However, Verhoeven et al. though that the Damascus pattern was related to the microsegregation of solutes during solidification. They carried out experiments on two genuine Damascus blades during which the carbides were removed completely by dissolution treatment, followed by quenching. It was shown that the planar arrays of carbide particles could be made to return, together with the surface pattern, by thermal cycling, whereas the Sherby mechanism requires the cementite particles formed on the boundaries of the large austenite grains to be retained during deformation. Hence, they argued strongly that the surface patterns formed on genuine Damascus steel blades should result from a type of microsegregation-induced carbide banding that requires thermal cycling[5-10]. In particular, the dendritic segregation of V was considered the most likely reason for carbide banding[11].

However, compositional examinations of some existing Damascus steel blades revealed that many of them contain almost no V or any other carbide-forming elements. Moreover, it is apparent that the ancient craftsmen making Wootz steels had no concept of alloying with particular elements such as V. As Wootz steel cakes have been discovered in many parts of the ancient Indian region, it is unlikely that the iron ores in all those places happened to contain V or other certain types of carbide-forming elements. Therefore, the explanation proposed by Verhoeven et al. is also less than convincing.

Luo et al. adopted a new method to approach this puzzle. Using an advanced metallurgical computational software package (Thermo-Calc), all possible factors, such as the influence of S, P, and V elements on the Fe-C phase diagram, precipitation of V(CN), diffusion of V in austenite, and the dendritic segregation of S and P during solidification were quantified, because they have all been considered as possible prerequisites for forming Damascus patterns. The calculations indicated that V(CN) particles precipitate or dissolve at temperatures much lower than cementite in cases with a low content of V, as is commonly found in Damascus steels (see Fig. 2a). Instead, the sulfide and phosphide could precipitate at the dendritic zone because of the severe segregation during slow solidification. In particular, the remaining P-rich liquid at the end of solidification might transform to a eutectic product of phosphide and cementite (Fig. 2b), which cannot be distinguished from cementite under an optical microscope. The high concentration of P will not be homogenized by diffusion after a short dissolution treatment, such that cementite might re-precipitate in the P-segregated regions. Therefore, the dendritic segregation of P influences the spatial distribution of cementite in Damascus blades and thus, the patterns are formed.

Luo et al. also suggested that their method could be widely employed to tackle other puzzles similar to that of the Damascus patterns, because today’s knowledge is so well developed that reliable theoretical computations are now possible. Although people were capable of making Damascus steel swords containing ultrahigh carbon contents (1 wt.%) a long time ago, it is surprising that almost all modern steels in use contain C contents below 1 wt.%. However, with future developments of knowledge and technology, it is expected that ultrahigh carbon steels. e.g., Wootz steels, will once again find important applications, because the best of the new is often the long-forgotten past.

I want to draw attention to two elements that distinguish this news release, the request from the authors and the bibliographic notes (I don’t recall seeing bibliographies appended to a news release before),

Note from the authors: It would be much appreciated if anyone would like to donate a piece of genuine Damascus blade for our research.

Corresponding Author:

LUO Haiwen
Email: haiwenluo@126.com


1. Sherby O D, Wadsworth J. Damascus Steels. Sci Amer, 1985,252:112-118

2. Wadsworth J, Sherby O D. On the Bulat Damascus steels revisited. Prog Mater Sci, 1980,25:35-68

3. Sherby O D, Wadsworth J. Ancient blacksmiths, the Iron Age, Damascus steels, and modern metallurgy. J of Mater Processing Techno, 2001,117:347-352

4. Wadsworth J, Sherby O D. Response to Verhoeven comments on Damascus steel. Mater Charact, 2001, 47: 163

5. Verhoeven J D, Pendary A H. Origin of the Damask pattern in Damascus steel blades. Mater Charact, 2001, 47: 423

6. Verhoeven J D, Pendary A H. On the origin of the Damask pattern of Damascus steels. Mater Charact, 2001, 47: 79

7. Verhoeven J D, Baker H H, Peterson D T, et al. Damascus Steel, Part III—The Wadsworth-Sherby mechanism. Mater Charact, 1990, 24:205

8. Verhoeven J D, Pendary A H, Gibson E D. Wootz Damascus steel blades. Mater Charact, 1996, 37: 9

9. Verhoeven J D, Pendary A H. Studies of Damascus steel blades: Part I—Experiments on reconstructed blades. Mater Charact, 1993, 30:175

10. Verhoeven J D, Pendary A H, Berge P M. Studies of Damascus steel blades: Part II—Destruction and reformation of the patterns. Mater Charact, 1993, 30: 187

11. Verhoeven J D, Pendray A. The mystery of the Damascus sword. Muse, 1998, 2: 35

Here’s a link to and a citation for the paper (you will likely need Chinese language skills to read it, although there is an English language abstract on the page),

Theoretic analysis on the mechanism of particular pattern formed on the ancient Damascus steel blades by LUO HaiWen, QIAN Wei, and DONG Han. Chinese Science Bulletin, 2014(9)

I believe the paper is behind a paywall. Finally, I hope the researchers are able to obtain a piece of genuine Damascus steel blade for their studies.