這可不是....錯誤，，剛剛出爐,how can be 柔著呢 ~ ~

yes, that called tempering

Tempering is a heat treatment technique for metals, alloys and glass. In steels, tempering is done to "toughen" the metal by transforming brittle martensite or bainite into a combination of ferrite and cementite or sometimes Tempered martensite. Precipitation hardening alloys, like many grades of aluminum and superalloys, are tempered to precipitate intermetallic particles which strengthen the metal. Tempering is accomplished by a controlled reheating of the work piece to a temperature below its lower critical temperature.

The brittle martensite becomes tough and ductile after it is tempered. Carbon atoms were trapped in the austenite when it was rapidly cooled, typically by oil or water quenching, forming the martensite. The martensite becomes strong after being tempered because when reheated, the microstructure can rearrange and the carbon atoms can diffuse out of the distorted body-centred-tetragonal (BCT) structure. After the carbon diffuses, the result is nearly pure ferrite with body-centred structure.

In metallurgy and materials science, there is always a trade-off between strength and ductility. This delicate balance highlights many of the subtleties inherent to the tempering process. Precise control of time and temperature during the tempering process are critical to achieve a metal with well balanced mechanical properties

所有跟帖： 

• 剛剛出爐, bread, and metal, are 柔著呢！:-) -肖莊- ♀ (39 bytes) () 12/02/2011 postreply 08:30:05

• The people are iron, meal is metal :-) -走馬讀人- ♂ (136 bytes) () 12/02/2011 postreply 11:16:50

• Good one. Thanks. -肖莊- ♀ (0 bytes) () 12/02/2011 postreply 12:15:41