The length and structure of the heat affected zone (HAZ) is determined by thermal cycle of welding. The main parameters of thermal cycles in the HAZ are wH heating rate in the range of phase transformations, the maximal temperature T max, time spent above the temperature of polymorphic transformation and the rate of cooling Tohl in the range of transformations. The heating rate in the weld zone (OSHZ) is very high, and although it varies depending on several factors, but within narrow limits. The main factor affecting the structure and properties of OSHZ is the cooling rate wohl. When welding titanium swim with a high content of p-stabilizer for large values of wohl OSHZ recorded in the metastable structure. At the same time a significant influence on the final structure also has a residence time of metal OSHZ at a temperature below the temperature of polymorphic transformation. Terms of phase transformations in different parts of the HAZ during welding of titanium alloys in many ways similar to those during quenching from different temperatures. In Fig. 4 is a diagram of a change in the phase composition of titanium alloys depending on the content of p-stabnliziruyuschih elements and the temperature quench. Considered the metastable diagram gives an overview of the kinetics of phase transformations in titanium alloys during continuous cooling at rates of quenching. However, in the weld metal cooling rate in different zones of the welded joint is not the same. It depends on the thickness of the metal, welding conditions, welding and construction work piece, etc. Rapid heating and short residence time of metal with a maximum temperature of heating impede the process of stabilization of high-temperature phase. For the analysis of structure transformations during welding using the diagram depending ki kinetics of transformations on the cooling rate. They help to identify areas of formation of brittle phases and to establish regimes of welding to ensure the receipt of the necessary structures and the need for subsequent heat treatment. Simultaneously with the study of the kinetics of phase transformations in the weld zone of influence depending on building cooling rate in the range of phase transformations on the final mechanical properties and structure. There are several methods for determining these dependencies. In domestic practice, the primary use of the method found IMET-1. The test results of samples are summarized in a chart based on the mechanical properties of various welding parameters, most of the cooling rate. These diagrams define an optimal range of cooling rates (Wopt), in which reduction of the properties in the weld zone compared with the base metal is minimal.
See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium
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