Wear-enhanced hydrogen evolution from mild steel
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I.
INTRODUCTION
H Y D R O G E N in steel can cause catastrophic failure to structures in service. Therefore, the hydrogen content of steel should be kept below a safe limit by applying a degassing process while it is in the liquid or solid state. These processes may require very complicated heat treatment. m Recent studies reported the possibilities for removal of most of the hydrogen in steel at room temperature during the w e a r p r o c e s s , [2,3,41 suggesting wear-induced hydrogen effusion. In their proposed phenomenon t2'3'41 the wear process enhances hydrogen effusion by the removal of effusionretarding oxide layers on the one hand, and retards hydrogen effusion by the formation of effusion-retarding oxide layers on the other hand. These hydrogen effusion enhancing and retarding effects of the wear process probably depend on the wear conditions such as temperature and oxygen partial pressure. During a particular wear process either one or the other of these effects will be predominant. However, the causes and kinetics of wear-induced hydrogen effusion still have not been fully elucidated. Therefore, it is appropriate in the present work to differentiate between the factors contributing to the wear-enhanced hydrogen evolution as a function of sliding time and applied load, and thus to clarify the main causes of wear-enhanced hydrogen evolution from mild steel. There are two conceivable experimental methods to study these problems. The first is an integrated wear-production system, I41 composed of a rotating wear system and a mass spectrometer for hydrogen gas analysis; the other is a method using separated wear production and hydrogen measurement systems. In spite of the advantages of the integrated system, that system cannot be used to evaluate the precise value of the apparent diffusivity for hydrogen due to the wear process and the amount of hydrogen in wear debris. In the present KWANG-KI BAEK, formerly with the Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Seout, Korea, is Research Associate, Hyundai Welding and Materials Research Institute, Ulsan, Korea. SU-IL PYUN, Professor, and JONG-SANG KIM, Research Assistant, are with the Department of Materials Science and Engineering. Korea Advanced Institute of Science and Technology (KAIST), Seoul, Korea. Manuscript submitted February 4, 1986. METALLURGICALTRANSACTIONS A
study, the latter system has been employed. The cathodically hydrogen-charged specimens were put either to the wear test or to dry air for the same length of duration, and then the amount of hydrogen extracted from the specimen was measured. In addition, the apparent diffusivity of hydrogen was calculated from the transient analysis of the hydrogen permeation of unexposed specimens. Hydrogen extraction and permeation experiments have been carried out by an electrochemical detection technique.
II.
EXPERIMENTAL PROCEDURE
The experimental procedure for hydrogen extraction was divided into three stages, cathodic hydrogen charging into
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