| It is well know that, in the manufacturing of the low C-special steels as the case-hardening steels and the stainless steels, the ingots are apt to be not killed by the hydrogen boiling, especially in the humid seasons. I saw these problems last year in a plant in this country. We suffered formerly, too, about these troublesome hydrogen problems for a long time before vacuum remelting and vacuum degaussing installations. Here I want to introduce the considerations on our bitter experiences to help your practical operations. 1) P_(H₂O)(㎜Hg)=Mean value of the partial pressures of the moisture in the atmosphere in each month measured every day through a year. [H]_(Tap) (cc/100g Fe)=Mean value of the hydrogen contents at the tapping of the low alloy special steels melted by the basic electric are furnaces (B.E.F.) (10-15 ton) in each month. There can be seen relatively higher degree correlations between [H]_(Tap) and P_(H₂O) (n≒380), when we calculate the regression equation, assuming that both keep the linear relation. Of course, the histograms of [H]_(Tap) differ according to the kinds of steels, the melting furnaces and the terms of sampling. 2) Generally [H]_(MD) (at the melt-down) decreases a little by O₂-blowing, then increases very much suddenly at the reducing period and increases a little again at the tapping (n≒135). These amounts of increase of [H] at the reducing period and at the tapping are larger as when P_(H₂O) is higher. However when we check, for example, about the casehardening steels melted only in Jan. -Mar. (n= 120), there seems almost no correlation between [H]_(Tap) and P_(H₂O) when P_(H₂O) is under than about l0㎜Hg. Therefore, to decrease [H]_(Tap), we must investigate the counter-measures in both cases, that is to say, the manuals to decrease [H] in the ordinary melting processes and the special instructions in the humid seasons. The limits of [H]_(Tap) to avoid the hydrogen boiling are about 9-l0cc/100g in the ordinary case-hardening steels and about 12-14cc/100g in the stainless steels. 3) [H]_(MD) is driven out by the agitation of O₂-blowing and by the floating actions of the produced CO bubbles. Although Δ[H] is much smaller than those theoretically calculated from the decarburized amounts, it is sure that the effective conditions of O₂-blowing for decarburization are also effective for dehydrogenation. The ratio of [H]²× [O] at the end of oxidizing period to [H]²×[O] at the earlier period of reduction is kept about 1:1 for the low C-special steels and about 1:0.5 for the medium and high C steels. So that it suppresses the increase of [H] at the earlier period of reduction to decrease not only [H] but also [O] at the end of oxidizing period. 4) About the influences of the amounts of oxidizing slags which are brought into the reducing period, of the exposed area of the bath open to the atmosphere and the exposing time, or of the charging sequences of reducing slag-forming materials, it was difficult to obtain the distinct conclusion in our many practical operations. Next it is unsufficient to emphasize, only abstractively, the effects of the moisture contained in the charging materials, especially in humid seasons, so that I want to warn their importance, showing the test results of the practical operations. Of course, the most important points of ordinary melting processes, that is to say, how to control the temperatures and the basicities in the reducing period, are also very important for dehydrogenation. 5) If [H] increases over the limited value and the bath can not be killed in the humid seasons, even when the sufficients cautions are taken in the melting stages, the forced dehydrogenation methods are introduced, for example, using the dehydrogenation agent Freon 12 (C-CL₂-F₂) or the argon-blowing. Originally hydrogen is driven out only by the mechanical methods, but, in this case, the dehydrogenation is achieved chemically by formation of the hydrogen-halides. In our tes |
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