Largely taken from Sivan Kartha, ``Disorder--Driven Pretransitional Tweed Microstructures in Martensitic Transformations'', Ph.D. Thesis, Cornell University 1993, chapter 1. Photographs and other information from two articles in G. B. Olson and W. S. Owen, "Martensite", ASM International, 1992: "A History of Martensite: Some Thoughts on the Early Hardening of Iron" by R. Maddin, and "A History of Martensite: Early Ideas on the Structure of Steel", by C. S. Smith.
The word "martensitic" is not familar, except among metallurgists. Its history is a fascinating story, worth telling briefly.
One of the great periods of change in civilization occurred when steel replaced bronze. Yet, it was entirely unknown what gave steel its valuable properties, and for centuries the techniques for making high quality steel were closely held, almost alchemical, secrets. Clearly, iron was its major component, but a myriad of other minor additions were found empirically, and even more mysterious treatments were evolved for cooling the red hot object to room temperature - unlikely manufacturing processes such as adding mixtures of blood, and aging times which depended on the phase of the moon, for example.
Maddin tells us that iron replaced bronze for general use during the 300 year period after about 1200 B.C. Iron was known before this time, but Maddin suggests that it was the discovery of how to make steel that led to the shift. Iron isn't a very useful material. By dissolving carbon into it, one stabilizes highly distorted martensitic domains leading to hard, brittle cast-iron; by tempering to draw out the carbon into precipitates, one then toughens the material making it resistant to cracks, forming steel. Steel is an immense improvement over bronze.
Maddin's earliest example of martensite comes from an excavation in 1976. He says the analysis shows a pretty sophisticated manipulation of iron into steel.
A dig in 1971 found a lot of knives, which seems to indicate that the metallurgists of ancient Cyprus had found a consistant method of "carburizing and quenching".
The technique of quenching the iron into cold water is mentioned in this gruesome description in Homer's Odyssey, describing the blinding of the giant Cyclops (who had imprisoned Odysseus and his men in a cave). After getting Cyclops drunk, they heat an olive stake and plunge it into his one eye:
"The blast and scorch of the burning ball singed all his eyebrows and eyelids, and the fire made the roots of his eye crackle. As when a man who works as a blacksmith plunges a screaming great axe blade or plane into cold water, treating it for temper, since this is the way steel is made strong, even so Cyclops' eye sizzles about the beam of the olive." (Translation after Richard Lattimore.)
(Apparently the translation "treating it for temper" is a translator's anachronism representing our modern viewpoint.)
In the 19th century there were great advances in chemical analysis, and metallurgists had faith that the reasons why steels were different would soon be known through determination of differences in chemical composition. However, these hopes were soon dashed, as it was often found that various steel alloys with very similar compositions could have vastly dissimilar mechanical properties. Chemistry not having provided the answer to the steel puzzle, the answer was to come evenually from a distinctly different area of science - optics.
There were great strides in optics over the same period, particularly in Germany, and in c. 1890, a gifted German microscopist Adolf Martens examined the microstructure, and found, not visible to the naked eye, many varieties of patterns at the micron scale. In particular, hard steels were found to have banded regions of differently oriented, fascinating microcrystalline phases, whereas inferior steels had little coherent patterning. The characteristic patterned regions became known as "martensite," after their discoverer.
The realization that the microscopic patterning might be just as important as compostion in determining a material's properties was a watershed in metallurgy; and a whole new subfield, "metallography" was born. Since that time hundreds of materials with martensitic morphology have been discovered and studied.
Jim Sethna, email@example.com
Statistical Mechanics: Entropy, Order Parameters, and Complexity, now available at Oxford University Press (USA, Europe).