from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A solid solution of iron and up to one percent of carbon, the chief constituent of hardened carbon tool steels.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A solid solution of carbon in iron; the chief constituent of steel
- n. Any crystal structure formed by a martensitic transition
from The Century Dictionary and Cyclopedia
- n. A very hard carbide of iron, approximately of the composition Fe24C, formed in the recalescenee of steel at 850° C. in cooling from a temperature of 1,000° C. or over. It remains unchanged if the metal is then suddenly cooled, as by plunging it into cold water, but on slow cooling is decomposed into iron and the carbide Fe3C. On the other hand, it appears that this latter compound, known as cementite, may split into martensite and carbon in the form of graphite.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a solid solution of carbon in alpha-iron that is formed when steel is cooled so rapidly that the change from austenite to pearlite is suppressed; responsible for the hardness of quenched steel
This structure is called martensite and is desired when maximum hardness is essential.
In the ordinary practice of hardening steels, the quenching is not so drastic, and the transformation of austenite back to ferrite and cementite is more or less completely effected, giving rise to certain transitory forms which are known as "martensite," "troostite," "sorbite," and finally, pearlite.
The engineers are running programs that show how adding tiny amounts of alloys to ferrite and martensite—crystalline structures of iron—during the steelmaking process changes the steel's strength, as well as its ability to be shaped into different parts.
When cooled rapidly, however, as in the tempering of steel, martensite remains a homogeneous solid solution, or hard steel.
When cooled slowly below 670 degrees, martensite yields a heterogeneous mixture of pearlite and ferrite (or cementite, if the original mixture contained between 0.8 per cent. and two per cent. of carbon).
When heated to 670 degrees, it becomes homogeneous, an amount of carbon up to two per cent. dissolves in the iron, and hard steel or martensite is formed.
Moderate reheating or annealing changes this structure largely into troostite, which is a partly transformed martensite, possessing much of the hardness of martensite, but with
The structure is then austenite and the air-cooled structure of this steel is martensite.
Troostite is of doubtful composition, but possibly is an unstable mixture of untransformed martensite with sorbite.
This toughness is the chief characteristic of the next material in the transformation series, sorbite, which is merely martensite wholly transformed into