The author investigated cracks in billets of semi-killed steel and obtained following results as the causes:
1. Variation of the crack index between ladles were larger than tbat within them.
2. The crack index of 2nd ladles were larger than 1st ladles.
3. The crack index became maximum at 0.20-0.21% C content, and it increased with the Scontent under the same conditions of rolling temperature.
4. Under normal operations of soaking pit, a prolonged soaking time increased the crack index of charges.
5. The rolling temperature index "h" had positive correlation with the crack index of normal charges.
6. On variation of the crack index within ladle, it was found that Al charged into molds had increased the crack index of ingots.

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A subsurface blowhole is a defect which has been encountered in almost every heat of killed steel and become the cause of rejection, especially in I-beam steels rolled directly from the small ingot in one heat without billeting. Its distribution is not equal in all ingots of one heat, nor in all ingots of one teeming group, nor in all portions of one ingot. Of course, insufficient deoxidation is the most powerful cause of the subsurface blowhole, but the above irregular distribution shows that the most important cause of the subsurface blowhole comes not from our melting practice, but from our pouring practice. The effect of the following variabies on the subsurface blowhole wsa investigated from the standpoint of operation control, such as the life of ingot moulds, various coatings, teeming rate, ingot size, mixed water in coating etc.

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In Japan, the recommended method for the microscopic estimation of slag inclusions in steel was established by the 19th Sectional Committee of the Japan Society for the Promotion of Scientiflc Research, in 1940. In that case, it was prescribed that the test specimen which was cut off should be hardened before polishing, as the preparation of test specimens, in order to harden to the polished surface. This prescription is similar to the Jernkontoret's method of the Iron and Steel Insitute of Sweden and to other methods.
The author, however, always suspected whenever he measured the cleanliness of inclusions that the cleanliness might be changed by hardening. The author examined the infiuence of various heat-treatments on the cleanliness to solve the doubt, with regard to forged specimens of bearing steel (1.10%C, 0.28%Si, 0.38%Mn, 0.008%P, 0.014%S, 1.73% Cr). Results of these tests were summarized as follows:
(1) Both Type A (those easily plastic-elongated by forging) and Type B (left unelongated by forging) increased index numbers of cleanliness and enlarged the thickness of inclusion by hardening. Namely, cleanliness of steel was deteriorated by hardening.
(2) In that case, the higher rose up the hardening temperature the worse became cleanliness.
(3) Inclusion of Type A before hardening were mainly Mn-sulphide and they had visible dove colour. But inclusions of Type A in specimens after hardening exhibited a dark colour, and they were different both in colour and form from sulphide.
(4) From the results of these examinations, the author considered as follows. In estimating the cleanliness of steel, if the self-hardening tendency of the material was great, hardening should be avoided, since hardening might deteriorate the cleanliness in case of such material.
It is necessary to study and investigate again preparation of the test specimen in the recommended method for the microscopic estimation of slag inclusions.

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(1) To substitute the bend fracture test of flat test pieces (flat 10×20×length 55mm, distance between the two supporting points 40mm) at the place of ring crushing test (standard size of rings: outer dia. 80×inner dia 60×height 20mm) of the ball bearing steels, the author studied experimentally the relation between the crushing strength P and the bend fracture strength Q, measuring the both in parallel, changing the quenching and tempering temperatures, with the ring and flat test pieces, both shaped out and forged. (2) Then the author calculated the relation equation between P and Q, considering the test pieces as the perfect elastic body. From the idea that the test pieces broke when the max. tensile skin stress on the section at the loading point increased beyond the strength of this material, the author obtained From the idea that the test pieces broke when the deformation energy on the section at the loading point increased beyond a limit value, the author obtained where α and α' were the coefficients which were determined according with their manufacturing conditions, for example, fibre direction etc. (3) Next the author determined the values α and α' so that these theoretical equations accommodated well with the values practically measured. Considering the statistically measured results of the forged test pieces from the production billets of about 110 charges, rather than the test results of the several charges above mentioned in (1), the author obtained α=0.85 and α'=0.75. Then P≅0.6763 Q: so, when P=4, 000kg, Q≅6, 000kg. By these data, the author proposed to substitute the bend fracture test of flat test pieces in place of ring crushing test and to define that the bend fracture strength must be more than 6, 000kg. (4) The author checked the coefficient α by means of the resistance wire type strain gauge. (5) The author checked the relations between the size of rings and their crushing strengths theoretically obtained, comparing with the values practically measured. (7) At last, the author studied the influences of rolling or forging conditions of the billets etc. on their ring crushing strengths.

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It is usual that a Jominy hardenability curve continuously decreases its hardness as the distance from the water-cooled end increases, however, sometimes abnormal hardness reverse appears especially in Jominy curves on low alloy steels containing carbide-forming elements and also in the case of plain high-carbon steels. The author made a number of observations on the relation between hardenability curves and microstructures along Jominy bars, and also investigated on the continuous cooling transformation and isothermal transformation diagrams of these steels. The results of observations were concluded as follows:
1. The anomaly of the hardness curve appeared both in Jominy curves and in the relation curves between hardness of isothermal decomposition products and transformation temperatures, only in the range where the intermediate transformation product and pearlite structure co-existed.
2. The hardness reverse was considered to be attributed to the discontinuity of hardness vs. transformation-temperature curves in pearlite and intermediate transformation ranges. And fine pearlite seemed rather harder than coarse bainite, although the formation temperature of the former was higher than that of the latter.
3. Alloying of carbide forming elements such as Cr, V, Mo etc. seemed to exaggerate the anomaly probable due to their influences on the shapes of S-curves and nature of carbide in pearlite, however, it could not be considered as essential reason, because plain high carbon steels also had such tendency.
4. In the end-quenched structure of plain high-carbon steels, intermediate transformation structure was also observed as well as in the isothermal transformation structure. The author considered that the more accurate study on the S-curves of plain carbon steels, which might indicate pearlite and intermediate transformations separately, would enable to explain the phenomenon.

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Greyness of tin plates which were manufactured from semi-killed steel ingots was investigated. The authors could not find the influence of Cr, Ni, and Cu ordinally included in normal raw materials.
The appearance of the defects was studied mainly by the microscopic examination and it was recognized that there is a thin oxide layer of about 1-40μ thickness. Then it was investigated whether greyness in rimmed tin plates had the similar oxide layer or not, and the existence of that oxide was clarified. Finally, the differenoe of oxidizing degree of various low carbon steel was studied by annealing test, and the knowledge of the effect of chemical composition on oxidizing was examined.
In conclusion, it was confirmed that the very existence of the thin oxide layer was the most important and direct causes of greyness.

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In the first report (Tetsu-to-Hagné, 39, Sept. 1953, No. 9, 948-953), the relations between the fluidity of molten pig and the temperature, the composition and the degree of deoxidation of pig were observed by the weight which flowed out through the capillary. In this report, the author carried out this research farther with the same apparatus and by the same method.
Here Z, L and T were defined as follows
Z: the time required to let flow out 0.3kg molten iron through the capillary at the constant pressure.
L: the length of the melt which flowed along the mould until solidification. The fluidity of pig was usually measured by this method.
T: the temperature of the molten iron.
The following results were obtained
(1) Z-L relations was shown in one curve, when the samples were taken from the same melt. At the measurement on the samples from the different melts, their relations showed difierent curve at each case. This is due to the fact that Z mainly depended upon the viscosity of pig at the molten state, but L chiefly depended upon the temperature range until solidification from molten state.
2 Z-T relations of the normally used pig were shown in two almost linear relations which were closed at the liquidus point. The curve at the temperature above liquidus point showed an easy grade, but their inclination under the liquidus point became very steep, because the primary crystals appeared in the melt. When 0.7kg Al per 100kg steel was added to the normal molten pig, their Z-T relations became one curve which was steep as same as the Z-T curve under the liquidus point about the normal pig
(3) The sand (non-metallic inclusion) in the molten pig which had nearly same composition and yet showed the different fluidity were analized by the HNO3 method. When the fluidity of pig was high, in general the pig contained high [FeO] within the range of this experiment.
(4) The value of Z obtained about 0.3-0.4% carbone steel at 1540°C by the same method was nearly 9.2. When 0.2kg Al per 100kg steel was added to these molten steel, Z increased so about 13.0. That is to say, the fluidity of the steel deoxidized sufficiently by Al was smaller than that of the steel which was not deoxidized.

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Following the 15th report (Tetsu-to-Hagané, 39, June 1953, No. 6, 614-619), the tempering behaviour of a C 0.65%, W 15.92%, Cr 4.30%, V 0.76% and Co 2.64% high speed steel variously austempered was studied by means of dilatometric and micrographic examination and hardnees test
The results obtained were summarized as follows:
(1) Austempering at 600°C did not cause the isothermal transformation of austenite, but appeared to condition the austenite so that lower-bainite would form on the cooling process at the expense of martensite and austenite, and consequently decreased the amount of martensite and retained austenite at room temperature. As a result, after this austempering the inital softening on tempering at 300°-400°C little occured.
(2) After austempering at the temperature range of 250-300°C with the resultant isothermal transformation of austenite to accicular lower-bainite, the final structure contained a little martensite and appreciable quantities of retained austenite, which decreased the hardness at room temperature and caused a large amount of secondary hardening on tempering.
(3) The formation of lower-bainite in austempering, regardless of either on isothermal process or on cooling process, appeared to increase the stability of retained austenite so that the subsequent secondary Ar″ trausformation was more difficult to occur than that after oil quenching.

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A tentative model of gas-analysis equipment by vacuum-fusion method was developed with a view to investigate effects of the gas contained in the molten cast iron on the structure and character of cast iron product. Recurrence of analysis values was examined as to rimmed steel and cast iron. The following conclusions were obtained.
1) Recurrence of O₂ and N₂ analysis value for cast iron was somewhat lower than that for rimmed steel, the principal cause of difference being considered to be segregation of gas in analysisspecimens.
2) O₂ and N₂ contents of cast iron were both in the order of 0.00 x wt%; thus variations depending upon melting conditions could be detected by the proposed analysis method.
3) To secure higher reliability of gas analysis of cast iron, further studies should be carried out about the following points:
a) To raise gas-extracting temperature.
b) To improve the evacuating rate.
c) To develop a sampling method with less segregation, etc.

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Special features of recent cast iron rolls was briefly outlined as follows:
1) Though grain rolls were used widely in every steel works, such defects as skin roughness and neck-breaking could not be improved for the present in the invetigation of the Roll Research Committee of the Iron and steel Instiute of Japan
2) Plain chilled rolls had become to be manufactured perfectly almost without defects. Alloy chilled rolls of nickel-chromium series or manganse-silicon series had extremely high hardness and superior quality, and in the recent years the effect of additional element as vanadium, titanium, boron, tellurium and zirconium etc, on alloy chilled rolls have been studied in every field.
3) Dead locks in manufacturing technigue of alloy chilled rolls wruld be broken by the development of manufacture of compound rolls.
4) Displaced compound rolls (duplex rolls) became to be put in to practical use in every country recently, and especially they were used as working rolls. The core material of displaced compouud rolls had been changed from cast iron to cast steel.
5) Sleeve chilled rolls were put in to practical use in steel works of America and Germany, but in Japan it was in the stage of trial manufacture.
6) Centrifugal casting chilled rolls were going to be manufatured for trial in America, but its design had not been found in Germany.
7) Cast carbide chilled rolls, of which the shell was a carbide-rich material with high hardness and the core was a tough material, were used as hot-working rolls in Japan.
8) It was very difficult for grooved chilled rolls to be manufactured without defects, and so in Germany grooved grain rolls were substituted for it. In Japau two and three grooved chilled rolls were manufactured with good results and the rolled capacity by it was twice or three times as much as by grooved grain rolls and sand grooved rolls.
9) Though it wes necessary especially to carry out the heat-treatment of alloy chilled rolls in order to eliminate the internal stress of it, it was not put in to practical use yet, but it was carried out in general to heat-treat the neck of rolls for the sake of prevention of neck-breaking.

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