Research And Development Of A New Type System For Testing And Analyzing Weld Thermal Cycle

A new type of computer-aided system for testing and analyzing weld thermal cycle is presented in this paper. To overcome the shortcomings of the traditional method for testing thermal cycle in welding heat affected zone (HAZ), the system employs computer technology which can collect and process data conveniently. It consists of thermocouples, an A/D interface board and a microcomputer. The system is the integration of data collecting, data processing and data analyzing, and which has following advantages: high precision, easy usage and high ratio of quality to price.To simulate the parameters of weld thermal cycle, some programs are developed using C++ language, which adopt such methods as formulation, linear calculation and artificial neural networks. By doing so, it can provide significant aids to establish, qualify and optimize welding procedures.A method named mean-value filter is used to smooth the random noise and an algorithm called variable-length-sliding window is designed for data analyzing. For the first time, obvious temperature plateaus are found in thermal cycle curves of HAZs in a low carbon alloyed steel, and a new idea is thereby put forward to study the phase transformation of HAZ.Analyzing the curves of experiments, a new phenomenon of sudden temperature drop is found before the temperature plateaus appear in weld cooling transformation. In terms of the Martansite pre-transformation theory and Bainite phase theory, explanations are given from the view of energy.Finally, metallograph examinations are given for the explanation of the observed transformation temperature plateau. The results show the consistency between the features obtained in weld cooling transformation by this system and metallographic structures.As a whole, a new type system for testing and analyzing weld thermal cycle is designed and simulating programs are developed in this paper. Most important of all, temperature plateaus are obtained in the thermal cycle curves of HAZ and a new phenomenon of sudden temperature drop is found before solid transformation. By using such enhanced methods, the system is applicable to researching the microstructures and mechanical properties of HAZ. It may also be helpful for establishing the welding CCT curves for new materials.