The effect of mill scale addition into molten iron was investigated in comparison with the oxygen blowing process as reported previously (Tetsu-to-Hagane, Vol. 41, 1955, No. 4, p. 407). The scale Was added at the high temperature (about 1450°C)into molten iron to decrease the undesirable effect of oxidation. As the results, it was found that by the treatment of adequate scale addition into molten iron the amount of Ti, and V in the iron decreased and so even the unsuitable irons as rnaterials for ductile cast iron were easily nodulized by magnesium treatment after the scale addition, as well as in the case of oxygen blowing treatment. And also found that the above effects of the scale addition were inferior in comparison with the case of oxygen blowing treatment in which the temperature of molten iron rose remarkably.
It was found in the first report that there were some times defects in segregated line of ingot such as sands and cavities appeared at the time of ingot solidification. In the course of forging, some of them disappeared by forging effect, while some of them remained as flaws in forged steel. The opinion that the latter are nothing but segregation-flaws of forging, is born out from comparing the result of observation about defects in segregated line of ingots with that about segregation-flaws of forging. In order to confirm this opinion, the author makes a complementary consideration about defects in segregated line of ingots, and investigates behaviours of defects in ingots and those of segregation-flaws in the course of forging and tries to describe theoretically the relation between segregation-flaws and type of annular segregations. Finally he describes the methods of reducing segregation-flaws on the basis of above-mentioned opinion in the form of conclusion.
Blowholes in iron and steel are due to CO, H2, N2 gas. In rimmed steel, blowholes are mainly due to CO gas, because oxygen content in molten steel is much higher than its solubility in solid steel, and the pressure of CO gas in molten steel is high. Eut in semi-killed or killed steel, hydrogen or nitrogen gas becomes a factor of blowhole formation, because the pressure of CO gas in molten steel is very low and the solubilty difference of H2 or N2 gas between molten steel and solid steel is large. As to blowholes caused by CO gas, the relation between formation of blowholes and Si, Mn, Al deoxidation was explained experimentally and the results of experiments were compared with calculation values from equilibrium constant (Report III). In this report, to study formation of blowholes by H2, N2 gas, H2 or N2 gas was lanced into molten steel, and the relation between blowhole formation by H2, N2 gas and deoxidation was explained. Blowhole samples were melted by a 100kg basic high frequency electric furnace similarly to Report III. When the temperature of molten steel attained to 1600°C, deoxidation reagents (Si, Al) were added in different quantities. Some time after deoxidation, H2 or N2 gas was lanced into molten steel for a time. 25kg of molten steel was immediately tapped to a ladle and then poured to a 16kg ingot. In succession four ingots were cast, similarly. The results obtained from this experiments were as follows. 1) Blowholes caused by hydrogen a) Si deoxidation...As hydrogen content increased, the limit of blowhole formation increased to 0.2% Si from 0.1% Si. But when Si content was more than 0.2%, blowhole by hydrogen gas did never grow under 80×10-5% H2. b) Al deoxidation...When Al content was more than 0.01%, blowhole by hydrogen gas did not grow under 80×10-5% H2. Accordingly when H2 content was less than 80×10-5% H2, hydrogen was not the main cause to blowhole formation if the molten steel was deoxidized fully. 2) Blowholes caused by nitrogen a) Si deoxidation...As N2 content iacreased, the limit of blowhole formation increased to 0.2% Si from 0.1% Si. But when Si content was more than 0.2%, blowhole by N2 gas did never grow under 100×10-4% N2. b) Al deoxidation…As N2 content increased, the limit of blowhole formation increased to 0.08% Al from 0.01% Al. Accordingly, in case of Al deoxidation N2 gas probably became the main cause of blowhole formation.
Attempts to find methods of protecting the refractory lining wall were made. The authors studied the formation of a permanent wall at the lining surface with compulsory cooling. In this paper, the experimental results on erosion of lining bricks were reported. The results indicated that water cooling method would be applied to the elimination of lining erosion. Using this method, the permanent wall would be formed at the lining surface, and it would be neutral during melting operation. The authors tried to carry out the melting test by using the small of cupola in which water cooling method was applied to its melting zone. The results obtained were summarized as follows; 1. By applying the water cooling method to protection of refractory lining wall, erosion loss was almost entirely eliminated and the quantity of repair materials and labour for maintenance was reduced. 2. Application of water cooling method to the melting zone of the cupola was very effective. It was recognized that it might obtain a permanent refractory layer at the wall surface and retain the constant diameter in the zone. 3. The melting zone unchanged gave a greater uniformity of furnace condition. This implied that prolonged melting could be operated. 4. Control of cooling water was easy and the life of the system would be unlimited. 5. A greater degree of control of slag composition being obtained, it was economically possible to charge steel scrap to a great extent and to produce high grade castings.
The cast rolls made of special steel containing chromium and molybdenum has been manufactured since the year of 1927 by the Yawata Iron & Steel Works. At present, these products have the life of rolling 70, 000 tons in average in contrast with 38, 000 tons of the past, and on some occasions 120, 000 tons of billets could be passed. It is widely known that the quality of cast steel is not improved in the course of forging or rolling to the favorable extent of eliminating their coarse structure and internal stress of casting. But they could be improved by means of such heat treatments as spheroidizing, normalizing and tempering which influenced mainly on the toughness and hardness. Special cast steel rolls manufactured recently by Yawata Works having the chemical composition of 0.8%C, 1.0%Cr, 0.3%Mo, etc. and Shore hardness number of 40 after such heat treatments as mentioned above, were found to have the longer life in comparison with the others. However, the chemical composition and hardness were not always regarded as the prime factors having an influence upon the defect of crack. It was considered therefore this kind of crack was due not only to the methods and techniques of rolling operation but to the segregation of chemical composition at the stage of casting. Accordingly, the anthors investigated the segregation of these rolls under various thermal Conditions. As the result, they studied quantitatively each characteristics of segregated elements at the longitudinal and transverse sections of some of rolls cast under different conditions and made clear the solidifying and cooling process by means of chemical analysis, microscopic inspection and mechanical test.
In continuance to the lst report, (No. 2 of this Journa1, 1956, p. 105-110) the authors studied the statical and dynamical mechanical properties of four spring steels, using the same specimens as before. The results were as follows: 1) At quenching and tempering, AISI 6150 showed the greater resistanee to tempering than other steels. As to the toughness (elongation, reduction of area and Charpy impact value) at the same hardness, AISI 6150 was the greatest and other three steels showed little difference. 2) On the tensile test with notched specimen, AISI 6150 had the greater resistance to tempering and at BHN 400 TS50 B60 was the best. 3) On the impact test at low temperature, AISI 6150 and TS50 B60 were good, and they had no clear transition points. 4) As to the resistance to hot deformation, TS50 B60 was the least and AISI 6150 was the greatest. 5) Fatigue limits found by the Schenck's repeated bending tester were 55kg/mm2 for AISI 6150 and TS50 B6O, and 53kg/mm2 for AISI 5160 and SUP 6. 6) Using the Sawai's fatigue machine of resonance type, the authors examined the test pieces of TS50 B60 and SUP 6 with the real size and heat-treated surface. The results of TS50 B60 were better than SUP 6, because the former had very thinner decarburized layer of surface than the latter. From the above points, TS50 B60 were found to be very good spring steel.
Reactions between the cyanide salt and the oxidizing agent in heating steels in a closed vessel were studied from the case-hardenability. The optimum ratio (estimated theoretically) of the salt to the oxidizing agent was found to give maximum hardness to steels.