1987 Fiscal Year Final Research Report Summary
Behavior of Nb during Synthetic Weld Thermal Cycling and HAZ Toushness
| Project/Area Number |
61850135
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| Research Category |
Grant-in-Aid for Developmental Scientific Research
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| Allocation Type | Single-year Grants |
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| Research Field |
溶接工学
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| Research Institution | Kyushu Institute of Technology |
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Principal Investigator |
MUKAE Shizuo Kyushu Institute of Technology President, 学長 (20039027)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIO Kazumasa Kyushu Institute of Technology Research Instructor, 工学部, 助手 (50039145)
KATOH Mitsuaki Kyushu Institute of Technology Associate Porfessor, 工学部, 助教授 (90039107)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Nb besaring stell / NbC / Nb carbides / HAZ toughness / Weld thermal cycle / precipitation curve / Mild steel / C-M系鋼 / TMCP鋼 |
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| Research Abstract |
Effects of C and Mn contrnts of mild steels containing less than 0.01%C on syntheticv weld heas affected zone(HAZ) toughness have been inverstigated. And also, effect of NB on HAZ toughness of mild steels containing low C content and NbC precipitaion, changes of HAZ tougheness and microstructures when the second thermal cycling was given to the HAZ habe been studied. Results obtained are as follows;
(1) HAZ toughness was higher when combinations of C and Mn contents were optimum, HAZ toughness of a stell habing 0.06%c and 1.2%Mn was the highest in this stdudy.
(2) Addition of Nb to steels having more then 0.06%C lowered the HAZ toushness. When Nb was added to steels having less than 0.03%C, the HAZ toughness was improved because intergranular polygonal ferrites and fine boundary ferrites were precipitated. %addigion of much amount of Nb, however, lowered the HAZ toughness besacse of fromation of M-A constituents.
(3) NbC precipitation represented a C-curve having a nose at 900 ゜C. When the sysnthetic weld thermal cycling such as 1350 ゜C x 5 sa nd cooling time of 40 s from 800 to 500 ゜C was given to the sample NbC was hardly precipitated, 50 to 80 % of total Nb content, however, was precipitated as NbC by the following second thermal cycling of peak temperature of 800 or 900 ゜C. The toughness of HAZ when the second thermal cycling of peak temperature of 800 ゜C was given was lower than that of HAZ given only the first thermal cycling by both formations of NbC and M-A constituents.
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