我想問iron同steel有何分別?

Steel, an alloy, consists mostly of iron, with a carbon content between 0.2 and 1.7 or 2.04% by weight depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese and tungsten. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron (in austenite region) is 2.14% by weight, occurring at 1149 °C; higher concentrations of carbon or lower temperatures will produce cementite. Alloys with higher carbon content than this are known as cast iron because of their lower melting point.

Iron係element(原素), steel係一種有iron同carbon既alloy(合金), steel有既carbon大約係2.04% by wieght. 加左carbon可以控制到resulting material既硬度, 韌度同拉伸強度而變成steel. 至於點解, 係一個materials science既問題, 簡單黎講, 因為carbon atom係細粒過iron atom, carbon atom就會填左iron結昌體裡面d空位, 而令到出黎既合金(steel), 變得堅硬, 但同時會變得較brittle(脆), 因為carbon係一種brittle material. 所以carbon既份量要睇應用情況而加減. 當carbon既份量再高d, 高過2.14% by weight, 就會變左另一種alloy - cast iron.

有興趣既可以去借一d materials science or engineering既書睇, 會有更詳細解釋~

source: http://en.wikipedia.org/wiki/Steel

2007-11-21 12:25:06 補充：
補充少少, iron + carbon會變左乜野呢個問題, 除左要睇有幾多carbon, 仲要睇埋個加熱既溫度, 呢個係我之前冇講到既, 至於點知咩溫度, 咩carbon content, 會變咩, 就會睇返個phase diagram: http://upload.wikimedia.org/wikipedia/en/c/c3/Phase_diag_iron_carbon-color_temp.png

Steel is material, it's one kind of iron--we can say,as it's is iron that got some percentage of carbon to make it become hard~