Further Considerations of Hydrogen as a Cause of Enamel Defects, V

Abstract

Hydrogen as a Cause of Enamel Defects, V 205 scaling. Higgins and Deringer, however, collected the hydrogen evolved from the fish scales of specimens which were deliberately fired so that the bond was a maximum. Kautz intimates that shiner scales occur only after excessive overfiring, but shiner scales are found in industry in normally fired ware. Kautz, moreover, appears to miss a fine point in the behavior of hydrogen when he states that excessive firing should tend to remove the gas so that less would remain than in normally fired ware. In the first place, as has been shown in metallurgical experiments with hydrogen in steel, prolonged heating a t enamel-firing temperatures may not evolve appreciable quantities of hydrogen. On the other hand, overfiring burns the enamel to a thinner and more impervious coat, weakens the enamel, and eliminates the bubble structure which otherwise serves to entrap large quantities of hydrogen and thereby defeats the development of gas pressure.The fact that thin sheets and sheets coated only on one side may show shiner scale from overfiring but will not develop fish scales from underfiring is in no way a rebuttal for the hydrogen theory. The explanation is simply that less hydrogen is required to cause a shiner. The importance of critical quantities and pressures of hydrogen in causing these defects must be taken into consideration.Kautz's suggestion is factual and interesting but probably relatively unimportant, and his conclusions are drawn from excessively abnormal conditions and from few and indecisive tests. He has shown only that local intrinsic stresses may also crack the glass-type aggregates, and this is admittedly true.The systematically occurring chips, fish scales, and shiners, however, the authors still believe to be generically identical. They are caused by hydrogen gas exuding from the steel, and they differ in appearance only in accordance with the physical differences of the enamels and the nature of the gas effusion. ABSTRACTThe argument that reboiling is primarily a function of hydrogen is expanded with additional evidence obtained from metallurgical research during the past year. The behavior of hydrogen in rimming-steel enameling stock is discussed, and an explanation is given for the varying behavior of the edge and center sections of rimming-steel sheet in the development of certain hydrogen-caused defects.

Fragilização por hidrogênio de parafusos cementados

“…Autores como Zapffe & Sims (1941) Este modelo de fragilização por hidrogênio pode ser certamente associado às situações em que há a ocorrência de falhas pelo mecanismo do empolamento por hidrogênio do material ("hydrogen blistering") (Smialowski, 1977apud Hirth, 1984. Neste contexto, de acordo com a ASTM G15 (2008), define-se empolamento por hidrogênio ("hydrogen blistering") como a formação de defeitos como bolhas ("blisters") na superfície, ou em regiões abaixo dela, por meio de uma pressão local excessiva de hidrogênio.…”

“…Teorias como o "Planar Pressure Mechanism" (Zapffe & Sims, 1941apud Hertzberg, 1996, o "Hydrogen-Enhanced Plasticity Mechanism -HELP Mechanism" (Beachem, 1972apud Hertzberg, 1996 e a "Hydride-Induced Embrittlement" (Fujita, 1977apud Hertzberg, 1996 também constituem alguns dos vários exemplos de esforços concentrados na busca do entendimento dos mecanismos da fragilização por hidrogênio.…”