Research groups at Kyushu University and Kyushu Institute of Technology have found that in steel with a cubic fcc (face-centered cubic lattice) structure, the formation of a cubic hcp (hexagonal close-packed structure) phase is suppressed as the hydrogen content increases. Was discovered for the first time in the world.
The strength and functionality of steel varies with the crystal structure, which varies with the type and amount of elements added to the iron.Conventionally, it has been the established theory that hydrogen "promotes" the change in crystal structure from fcc to hcp.
However, in this study, we found that hydrogen "significantly suppresses" the change in crystal structure from fcc to hcp by investigating the behavior of steel materials containing hydrogen.When the hcp phase fraction was measured while cooling the sample with adjusted hydrogen content, it was found that the hcp phase fraction did not increase as the hydrogen content in the sample increased, and the fcc-hcp transformation was suppressed. It is said that it was.This is the first phenomenon observed in the world and breaks the conventional wisdom.
As for the reason why the fcc-hcp transformation was suppressed by the increase in hydrogen content, the results of the tensile test suggested an increase in frictional stress.In addition, it is said that the thermodynamic stabilization of the fcc phase has been reported from the theoretical calculations of previous studies, and these are considered to be the main causes.
Active use of hydrogen as a next-generation clean energy source is being considered, and at the same time, infrastructure suitable for the hydrogen environment is being developed.However, hydrogen has the property of making metal materials brittle (hydrogen embrittlement), which has been a problem.
This result, which found that hydrogen dissolved in steel significantly suppresses the fcc-hcp transformation, which is known to affect hydrogen embrittlement, is expected to provide new insights into the elucidation of the hydrogen embrittlement mechanism. NS.Furthermore, it is expected to contribute to research and development aimed at improving the quality and strength of steel materials used in hydrogen-related facilities.
Paper information:[Scientific Reports] An unconventional hydrogen effect that suppresses thermal formation of the hcp phase in fcc steels
