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Hydrogen trapping at spheroidized and elongated sulphidic inclusions‐matrix interfaces in mild steel
Author(s) -
Pyun SuII,
Kim JeongTae
Publication year - 1991
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199100442
Subject(s) - hydrogen , trapping , matrix (chemical analysis) , volume (thermodynamics) , materials science , analytical chemistry (journal) , metallurgy , chemistry , crystallography , composite material , thermodynamics , physics , ecology , organic chemistry , chromatography , biology
The present work is concerned with those factors which determine the hydrogen trapping at the interfaces between spheroidized and elongated sulphidic inclusions, and matrix in mild steel by using gas‐phase charging and electrochemical detection techniques. Three kinds of specimens A, B and C were prepared from the calcium‐treated mild steel by water quench from 950°C, and from the ordinary mild steel by water quench from 950 and 1150°C, respectively. Specimen A was characterized by the interface between the spheroidized sulphidic inclusions and matrix, but the specimens B and C were characterized by the elongated sulphide‐matrix interface. The values of time‐lag decreased with increasing hydrogen input pressure for the specimens A, B and C. The results indicated that the defects produced at the interfaces act as saturable trap sites for hydrogen. The hydrogen trap density and binding energy were obtained from the plot of [( t T / t L )–1] vs. . The trap densities for the specimens A, B and C were found to be about 5.0 × 10 −8 , 2.1 × 10 −7 and 5.0 × 10 −7 mol cm −3 , respectively. The trap‐binding energy was determined to be −(56.4 ± 1.1) kJ mol −1 for the specimens A, B and C as well. The experimental results indicated that the nature of the interfaces is determined by the number of defects produced in the interfaces per unit volume, regardless of the inclusion shape. The defects distributed in the interfaces included namely microvoids and water‐quench‐created dislocations which act as deep trap sites for hydrogen.