Reheating and Forging of High Temperature Alloy
High temperature alloy is a kind of metal material with excellent mechanical properties, which is widely used in aerospace, aviation, automobile and other industries. In order to ensure the property of high temperature alloy, the proper pre-treatment and heat treatment process are essential. In this paper, the pre-treatment process of high temperature alloy forging is studied.
High temperature alloy has very high requirements for purity and uniformity of chemical composition, and inclusions should be strictly controlled. In order to reduce the inclusion and improve the performance of high temperature alloy, pre-treatment process such as smelting and refining is generally adopted. Below the melting point of high temperature alloy, the reduction of oxygen content and the elimination of inclusions can be carried out by secondary smelting process, meanwhile uniform alloy composition can be obtained by adding necessary elements.
Forging usually requires preheating of high temperature alloy before processing. Due to the high strength of high temperature alloy, preheating is necessary to reduce the strain between metal crystal grains caused by plastic deformation and ensure the forming quality. Reheating of the high temperature alloy should be conducted by different methods according to its chemical composition, state of delivery and use requirements. The commonly used methods of preheating high temperature alloy are medium frequency induction heating, gas heating, electric heating, etc.
Reheating high temperature alloy is mainly to obtain the relative soft state and appropriate structural organization of the alloy. The heating temperature range is controlled between the lower critical temperature of the alloy and the upper critical temperature, which is generally isothermal heating or heating and insulation combined. The former is mainly for fully annealed and partially annealed alloys, and the latter is mainly for alloys in the cold state and isothermal holding. The heating cycle should be controlled so that heating and insulation should not be too short or too long. In addition, continuous forging should be carried out as soon as possible after preheating to avoid re-aging treatment.
In summary, the preheating temperature should be appropriate, the heating time should be moderate, the heating rate should be appropriate, and the insulation time should also be reasonable when dealing with high temperature alloy. Paying attention to the above conditions is conducive to the improvement of properties and quality of high temperature alloy.
