Competitive Phenomenon of Hydrogen Trapping and Carbon Segregation in Dislocations Introduced by Drawing or Martensitic Transformation of 0.35 mass% and 0.8 mass% C Steels

• Published in: ISIJ International Vol. 56; no. 2; pp. 359 - 365
• Main Authors: Hirakami, Daisuke, Yamasaki, Shingo, Tarui, Toshimi, Ushioda, Kohsaku
• Format: Journal Article
• Language: English
• Published: The Iron and Steel Institute of Japan 01.01.2016
• Subjects: delayed fracture; high strength steel; hydrogen analysis; hydrogen embrittlement; hydrogen trapping site
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2015-555

Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. Many studies have been conducted on the mechanism of hydrogen embrittlement. Because the elucidation of the state of hydrogen is important to understand the mechanism, the states of hydrogen in the steels investigated were controlled. In the present study, 0.35 mass% C and 0.8 mass% C steels annealed in the hydrogen atmosphere followed by quenching from the austenite region together with drawn pearlitic steel of 0.8 mass% C were used to analyze the state of the hydrogen contributing to the emission peak, in particular, at about 300°C in the Thermal Desorption Analysis (TDA) curve. The peak at 300°C was significant for quenched 0.8 mass% C steel with low Ms temperature; however, the peak decreased with aging at room temperature. However, in 0.35 mass% C steel with high Ms temperature, the peak at 300°C was no longer observed. Moreover, in the hydrogen charged as drawn 0.8 mass% pearlitic steel, the peak at 300°C did not change with aging at room temperature because of no significant carbon in solid solution, while the peak at 100°C decreased with the increase in aging time. Taking into account the competitive phenomenon of hydrogen trapping at the dislocation core and C segregation to dislocations during room temperature aging or during quenching from Ms temperature, it was concluded that the hydrogen peak at about 300°C is hydrogen trapped in the dislocation core, while the other hydrogen peak at 100°C is attributed to the hydrogen trapped by the stress field generated by dislocation.