Establishment and Problem of the Observing System for Boron in Steels by Alpha-particle Track Etching Method Using Pneumatic Tube of JRR-3 and JRR-4

• Published in: Tetsu to hagane Vol. 93; no. 10; pp. 634 - 641
• Main Authors: ASAKURA, Kentaro, KOSEKI, Toshihiko, KAWATE, Minoru, ISHIMOTO, Mitsunori
• Format: Journal Article
• Language: Japanese
• Published: The Iron and Steel Institute of Japan 01.10.2007
• Subjects: alpha-particle track etching; ATE; Boron; cadmium ratio; JRR-3; JRR-4; pneumatic tube; precipitation; segregation; thermal neutron flux
• ISSN: 0021-1575; 1883-2954
• DOI: 10.2355/tetsutohagane.93.634

The addition of small amount of boron to steel is often employed to improve various properties of steel, but there are still many uncertainties in the behavior of boron in steel. It is necessary to clarify the precipitation and segregation behaviors of boron to develop advanced steels. Alpha-particle track etching (ATE) method is effective to observe the behaviors of boron, but as the irradiation equipment of Japan Atomic Energy Agency (JAEA) has been more intensively used for medical research and treatment purposes recently, time available for the ATE method has been limited. In this study, ATE method using the pneumatic tube is investigated to make the analysis of boron in steel easier under such condition. Results indicate that JRR-3 “PN-3” equipment of JAEA is the most applicable to the ATE method using the pneumatic tube. Since the ratio of cadmium of PN-3 is 290, the thermal neutron flux is sufficiently high with low level of background. Boron containing precipitates can be detected as dark spots and the grain boundary segregation of boron as dark lines. It is found, however, that the size of the spots in ATE images is not exactly the same as that of actual precipitates. When the ATE images are compared with TEM images using carbon extraction replica, borides are exaggerated as about hundred-times larger precipitates in the ATE images.