Research On Determination System For Welding Thermal Cycle Curve And Phase Transformation Point

A computer-aided system for testing and analyzing weld thermal cycle is presented in this paper. The system can collect and process data conveniently. Its hardware part consists of thermocouples, a date acquisition card and a microcomputer. To simulate the parameters of weld thermal cycle, some programs are developed using C++ Builder 7.0 language. The system is the integration of data collecting, data processing and data analyzing. It has the advantages of high precision, easy to use and high ratio of quality to price.To smooth the random noise, a circuitry of filter is desiged and a method named mean-value filter is used, and a Twi-differential algorithm is used for data analyzing. For the first time, a transformation temperature point 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.It seemed that the phenomenon of sudden temperature changing can not be found on the welding themrcal cycle cooling curves by different testing experiment.By analyzing Twi-differential algorithm, a very marked inflexion can be found on the temperature zone of 800~300C .Comparing with lots of experiments, the temperature of the inflexion should be the point of Bainitic phase transformation by analyzing the SH-CCT graph if the absolute value of Twi-differential is more 4.5 than that of mean value of Twi-differential.By analysis of SH-CCT graph and microstructure of HAZ of the experiment material, the result of experiment accords with the anticipation of the theory, that is to say the system is reliability and practicability.The system may be helpful for establishing and enriching the welding CCT curves for metal material because temperature points of phase transformation can be obtained in the thermal cycle curves of HAZ by using the system. It is also applicable to research on the microstructures and mechanical properties of HAZ.