In a previous paper, data on the movement of fluorine during the smelting of Pao-Tou ironore in a 1 M~3 experimental blast-furnace has been reported. This paper provides further infor-mation on the mechanism of volatilization of fluorine and its movement in a 11 M~3 blast-furnaceduring two campaigns of smelting of the same ore. The conclusion of the previous paper is confirmed by the results of the present investigation inthat the fluorine content of the blast-furnace gas depends primarily on temperature, and approachesequilibrium with lime or limestone in the furnace charge. It has also been found that this state-ment holds true only at those temperatures when a slag phase has not been formed, and that thefluorine content of the furnace, gas decreases rapidly at the appearance of a liquid slag phase. From the analysis of the ore samples taken at different levels of the blast-furnace, it has beenfound that the CaO/F ratio increases as the ore moves downward, and that there is a parallelrelationship between the SiO_2 and the F contents of the ore samples. These facts seem to indicatethat fluorine volatilizes from the ore chiefly as SiF_4, which subsequently reacts with H_2O in thefurnace gas to form HF and SiO_2. The mechanism of volatilization of fluorine from the liquid slag is also briefly discussed.

The results of investigation of the behaviour of fluorine in blast-furnace smelting have beenreported in a series of previous papers. The purpose of the present research is to investigatethe slag-forming processes in a 11 M~3 blast-furnace smelting Pao-Tou iron ore. Petrographical examinations supplemented by White test studies show that the chief mineralconstituents present in the primary slag are calcium oxide, fluorite and wustite. From a comparison of the slag-forming processes in a 11 M~3 blast-furnace smelting Pao-Touiron ore with that smelting an ordinary acid ore, a new mechanism for the formation of theprimary slag in smelting the former ore has been proposed. In addition, it has been found thatthe plastic region in smelting Pao-Tou iron ore is smaller than that in the usual case, thereby,considerably facilitating the driving of the blast-furnace by improving the penetrability of thecharge column.

Under the works condition, ghost lines in the billets of a low-alloy structural steel, 30 Cr Mn Si,made in basic electric arc furnace were investigated. A statistical analysis of the production datashows that there exists a linear relationship between the average length of ghost lines and the sizeof billets, i. e., after ingots of a given size being forged, the smaller the diameter of billets, thelonger the ghost lines. For ingots of 340×340 millimeter top size, after being forged into billetsof 60 to 70 millimeter diameter, the probability of the occurance of ghost lines appears to be maxi-mum. Meanwhile, it was also observed that the different parts of the ingots have bearing uponthe formation of ghost lines. Ghost lines usually originated from the kind of chain-type non-metallic inclusions, such asspinel of iron and aluminum oxides (Al_2O_3·FeO) and mixture of the spinel and corundum(Al_2O_3·FeO; Al_2O_3). Results of works experiments show that by means of the improvement ofdeoxidation, the adoption of an optimum degree of forgeability and the removal of the surfacelayer of ingots at certain stage during forgoing, ghost lines in billets can be greatly reduced orcompletely removed.

A study has been made on the effects of hot working conditions on the austenitic grainsize and mechanical properties of carbon steels. At the same time, the cumulative effect ofsuccessive reductions and the effect of austenitic grain size on such hot working characteristics asplasticity, resistance to deformation and the impact values have also been investigated. Thefollowing are the results obtained. Specimens having coarse austenitic grain size, besides the general tendency of giving greatergrain size with the increase in cooling speed, also give nonuniform long grains, banded structuresand widmanstatten structures. Specimens having higher carbon contents (0.66％C) give sorbitic,pearlitic and ferritic structures with different cooling speeds. With the increase in the austenitic grain size, there is a notable lowering in the yield pointand the impact values at—20℃. Tensile tests with specimens having the same austenitic grainsize show that the cooling speed after rolling has little effect on the reduction in area, but withthe increase in cooling speed there is a raise in the yield point, the ultimate strength and theimpact values at room temperature and at—20℃. When steels with different carbon contents are rolled at 1050℃, there appears a criticalreduction range between 0 and 10％, in which the austenitic grains become coarse. However,under the same hot working conditions and within the same critical reduction range, there is alarge difference in the largest grain size obtained with different carbon steels. The soaking timehas also different effects on different steels. In all steels investigated, there is a marked cumulative effect of reduction, but the reductionin the last hot working operation has the greatest effect on the austenitic grain size. Hence it isimportant to avoid critical reduction in the last rolling pass. Specimens from carbon steels having No. 0 and No. 8 grain sizes respectively show littledifference in their hot working characteristics: at 900℃, the difference in impact values betweenthese two specimens amounts only to 8％, the difference in the resistance to deformation to 3％and the difference in the critical reduction in height at fracture in the impact compression testamounts only to 2％.

By using the normal-pressure chlorine method in conjunction with the electrolytic method,the problem of the quantitative determination of non-metallic inclusions in low-chromium steelsand steels with carbon content more than 0.5％ was successfully solved. With the arrangementand procedures being simplified, the low-pressure chlorine method has also been found successfulin the determination of non-metallic inclusions in ball-bearing steel. The practicability of ferrous-sulfate electrolytic method has been further comfirmed.

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