Determination methods of admissible thermal cycles of welding based on study results of austenite phase transformations kinetics

The kinetics of austenite phase transformations of the heat affected zone metal is investigated. It is shown that at characteristic duration cooling in the austenite phase transformations range tsub(8-5) corresponding to appeaarance of tsub(p) pearlite in the structure, the structure of metal of HAZ of carbon and low alloy steel welded joints is characterized approximately by the following phase composition: 20% of ferrite, 70% bainite, 10% martensite. At cooling duration tsub(8-5) corresponding or less than tsub(p), impact strength of the HAZ metal is above the standardizied level for welded joints of carbon and low alloy steels. In connection with this the tsub(p) value may be accepted for an upper level of admissible cooling duration values in the phase transformations range tsub(8-5) at the analysis of various welding variants while the low level during welding with subsequent tempering may attain the values corresponding to tsub(σ) (if there is no danger of appearance of hot cracks )