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of iron at room temperature, but up to 2 percent carbon is soluble in the face-
centered cubic lattice which is stable above 1330°F. The second is the solid-state
eutectoid reaction in which a solid solution at a certain temperature can react to form
two new solid phases. In the case of carbon steels, the -phase, austenite, transforms
to -iron (ferrite) and cementite, (Fe3C) by the eutectoid reaction. The eutectoid
reaction is common in many materials, but only steel exhibits such a marked change
in properties.
Thus, when iron with 0.8 percent carbon is heated above 1330°F, the carbon
dissolves and the resulting solid solution is called austenite or -iron. If the austenite
is suddenly quenched in water, the carbon cannot escape and thus is trapped within
the lattice structure as an interstitial atom that strains the lattice because of the
increased volume it must occupy in the new body-centered tetragonal structure
called martensite, which is characterized by a needlelike microstructure (Fig. 3.5).
Martensite is a hard, brittle, metastable structure, i.e., a nonequilibrium structure,
that is a supersaturated solid solution of cementite, Fe
3
C, in a body-centered
tetragonal iron. In the presence of a moderate temperature rise (300 to 400°F),
tempering or recovery occurs and the brittle structure becomes tougher, while still
retaining its strength and hardness.
Glossary
№ English word Translation
1. ferrous «черный»
2. alloy сплав
3. steel сталь
4. soft мягкий
5. ductile ковкий
6. machine обрабатывать резанием
7. heat treatment термообработка
8. hard/ness твердость
9. tough прочный, плотный
10. shape форма
11. iron железо
12. undergo подвергать
13. allotropic аллотропный
14. carbon углерод
15. solubility растворимость
16. body-centered объемноцентрированный
17. cubic кубический
18. lattice решётка
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