Study on the Weldability of Aluminum Nitride Bearing Steel (Report 2)

Effect of AlN on the Continuous-Cooling Transformation of Carbon Steel

Abstract

In the previous work, it was concluded that the microstructures of A1N bearing low carbon steel (AN-1) were almost similar to those of aluminum killed low carbon steel (AN-IC) after various weld thermal cycles (max. heating temp.: 1350°C).
AN-1 and AN-1C being affected by various weld thermal cycles (max. heating temp.: 1150°C), the microstructures of AN-1 were ferrite+pearlite, but those of AN-1 C were mainly intermediate.
These results indicate that AIN will probably affect the transformation process of carbon steel.
In this study, continuous cooling transformation diagrams of AN-1 and AN-1C were made using a particular equipment applying magnetic analysis and the effect of A1N on the continuous cooling transformation of carbon steel was investigated.
Also the effect of A1N on the Ar3 transformation of carbon steel was researched.
The results obtained in this study are summarized as follows.:
(1) AN-1 and AN-IC being rapidly heated to 1350°C and cooled under various conditions, the difference between C.C.T. diagram of AN-1 and that of AN-1C was little.
(2) AN-I and AN-IC being rapidly heated to 1200°C and cooled under various conditions, the critical cooling times of AN-1 to nucleate intermediate structure, ferrite and pearlite were shorter than those of AN-IC and respectively 0.42, 0.86 and 3 sec.
(3) After heattreated at 1350°C for 10. min, quenched to 730°C and held at 730°C, the Ar₃ transformation velocity of AN-I was almost the same as that of AN-IC.
(4) After heat-treated at 1200°C for 10 min, quenched to 730°C and held at 730°C, the Ar₃ transformation velocity of AN-l was larger than that of AN-IC for about 9 sec after the beginning of Ar₃ transformation.
Especially, the Ar₃ transformation velocity of AN-1 was 2-2.5 times larger than that of AN-1C for several initial seconds after the beginning of Ar₃ teransformation.