TAILIEUCHUNG - Material Science_ Vol 1 of 2 - US DOE (1993) Episode 9

Tham khảo tài liệu 'material science_ vol 1 of 2 - us doe (1993) episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Properties of Metals DOE-HDBK-1017 1-93 WORKING OF METALS WORKING OF METALS Heat treatment and working of the metal are discussed as metallurgical processes used to change the properties of metals. Personnel need to understand the effects on metals to select the proper material for a reactor facility. EO STATE how heat treatment affects the properties of heat-treated steel and carbon steel. EO DESCRIBE the adverse effects of welding on metal including types of stress and method s for minimizing stress. Heat Treatment Heat treatment of large carbon steel components is done to take advantage of crystalline defects and their effects and thus obtain certain desirable properties or conditions. During manufacture by varying the rate of cooling quenching of the metal grain size and grain patterns are controlled. Grain characteristics are controlled to produce different levels of hardness and tensile strength. Generally the faster a metal is cooled the smaller the grain sizes will be. This will make the metal harder. As hardness and tensile strength increase in heat-treated steel toughness and ductility decrease. The cooling rate used in quenching depends on the method of cooling and the size of the metal. Uniform cooling is important to prevent distortion. Typically steel components are quenched in oil or water. Because of the crystal pattern of type 304 stainless steel in the reactor tank tritium production facility heat treatment is unsuitable for increasing the hardness and strength. Welding can induce internal stresses that will remain in the material after the welding is completed. In stainless steels such as type 304 the crystal lattice is face-centered cubic austenite . During high temperature welding some surrounding metal may be elevated to between 500 F and 1000 F. In this temperature region the austenite is transformed into a bodycentered cubic lattice structure bainite . When the metal has cooled regions surrounding the weld contain some original .

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