Several problems in heat treatment of pressure vessels (3)
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The heat treatment method of high temperature tempering after quenching is called quenching and tempering treatment. High temperature tempering refers to tempering between 500 and 650 °C. Quenching and tempering can greatly adjust the properties and materials of steel, and its strength, plasticity and toughness are good, and it has good comprehensive mechanical properties. After quenching and tempering treatment, tempered sorbite is obtained. Tempered sorbite is formed when martensite is tempered and magnified 500 to 600 times under an optical metallographic microscope. It is a carbide (including carburizing) in the ferrite matrix. Body) The composite structure of the spherules. It is also a tempering structure of martensite, a mixture of ferrite and granular carbide. At this time, the ferrite has substantially no carbon supersaturation, and the carbide is also a stable carbide, which is an equilibrium structure at normal temperature.
Quenching and tempering is often used in medium carbon (low alloy) structural steels and low alloy cast steels. In general, structural parts with high mechanical requirements must be quenched and tempered. The purpose of the quenching and tempering treatment is to make the steel parts have high toughness and sufficient strength, and have comprehensive excellent mechanical properties. For example, alloy steels such as 40MnB and 35CrMoA, which are usually used for high-pressure fasteners and anchor bolts, can be quenched and tempered to achieve the required mechanical properties.
According to the actual situation of our factory, the steel may change the supply state of the steel after hot processing, and the necessary heat treatment of the pressed components after hot working may be performed according to the state of use of the steel required by the design.
(1) For steels used in hot rolling, the pressure-receiving elements after hot working are generally not heat-treated.
(2) The steel used in the normalizing state needs to be renormalized after hot working. If the heating temperature during hot working is equivalent to the normalizing temperature of the steel, and the hot plate of the furnace is qualified, the normalizing treatment may not be repeated.
(3) Steel for normalizing and tempering use, after normalizing, it is necessary to re-normalize and temper. If the heating temperature during hot working is equivalent to the normalizing temperature of the steel, and the test piece of the hot working process of the furnace is qualified after the normalizing treatment, the pressed element may be subjected to tempering only after hot working.
(4) Steel used in quenching and tempering state, the pressure-receiving component should be re-tempered after hot working.
(5) The hot working pressure components of austenitic stainless steel should be controlled at a temperature above 850 °C, and should be cooled quickly after heating. If there is a requirement for intergranular corrosion test, the pressure-receiving element itself or the hot-worked process test plate shall be tested and evaluated after hot working. If the test result is unqualified, it shall be subjected to solution treatment (plus stabilization heat treatment).
Heat treatment is the process of heating, holding and then cooling the metal material. The effect of heating temperature, heating rate, holding time and cooling rate on performance should be grasped in essence. Quenching (adding tempering), normalizing (adding tempering), and solid solution treatment (plus stabilizing treatment) have a common feature, that is, after heating to the required temperature, after a period of heat preservation, it should be quickly cooled. Achieve the purpose of improving the microstructure of the steel and making it uniform. However, it is difficult to achieve rapid cooling of the pressure vessel due to the confined space, and it is often necessary to use the above-mentioned material state to manufacture a pressure vessel which is often important, and it is particularly important to ensure that the steel supply state required by the design document is not damaged.
Second, the solution of the problem
(1) If the pressure component may change the material state and mechanical properties of the material during processing, the necessary heat treatment shall be performed after processing to restore its supply state.
(2) For the design department, the material selection needs to consider the adverse factors affecting the performance of the material, so that the final use state of the material meets the design selection requirements.
(3) Whether it is “pre-heat treatment†or “final heat treatment†is a description of the heat treatment process of metal in actual production. But what matters is not the expression of the concept, but the explicit connotation, and the heat treatment object corresponding to the concept. Previous page 1 2 3