Technical Papers and Discussions - Gases in Steel - Effect of Hydrogen on the Ductility of Cast Steels (Metals Tech., October, 1948, T. P. 2454)

During the past several years, the steel casting industry has made studies of heavy castings in which the test bar has been taken from heavy sections rather than from attached or separately cast coupons. It has been noted that the ductility properties of these heavy sections are often lower than those normally expected. Such lowered ductility is usually accompanied by a spotty test bar fracture, and the ductility values can often be greatly improved if a low-temperature aging treatment is given to the casting. A loss of ductility of this type is considered "abnormal," since it is not accompanied by an increase of tensile strength or hardness, and "temporary" when the ductility can be restored by aging. The cure of such an abnormal condition represents a real improvement in the quality of the steel. Several types of abnormal loss of duetility can be distinguished, of which those caused by excessive amounts of inclusions of undesirable type and those caused by unsuitable grain size and inget structure are well known. The particular type of abnormal lowered ductility currently under consideration may be distinguished by the fact that the low-temperature aging treatment necessary for its relief is insufficient to cause any visible change in the micro-structure as ordinarily observed. As this aging will in fact eventually occur at room temperature, the phenomenon of present interest may be given the symptomatic definition, ''Temporary Abnormal Low Ductility." Some hundreds of previous investigations, largely qualitative in nature, have established, beyond reasonable doubt, that hydrogen is normally present in newly manufactured steel and that this gas, in small amounts, can cause a temporary abnormal loss of ductility. The commonly observed association of high gas content and low ductility has given strong evidence for the presumption that hydrogen, possibly assisted by other gases, is the primary cause of the low ductility observed. Accordingly, The Steel Founders' Society of America has, since Nov. 1, 1944, sponsored investigations at Battelle Memorial Institute whose primary objective is to obtain quantitative information on the relation of the amount of hydrogen and nitrogen in steel, together with associated methods of steelmaking and treatment, to low-duetility effects and porosity. The interest of this investigation thus extends to permanent abnormal losses of ductility, such as are caused by the inclusions which sometimes result from special deoxidizing practices and possibly from metallic nitrides, but as these can he distinguished from the temporary effect of hydrogen, they have been excluded from the work reported here except when they