1963 Perspective of Production and Technique of Iron and Steel in Japan
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|Publisher:||The Iron and Steel Institute of Japan|
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05 Dec. (Last 30 Days)
Koretaka KODAMA, Akitoshi SHIGEMI, Toshimitsu OGATA
We studied on the use of iron sand in the blast furnace.
In the case of pig iron making with a high rate charge of iron sand, it is well known thatpig iron runs out of the slag tapping hole at slagging. Therefore in actual operation, it isnot practicuble to use iron sand in large quantities. Thorough investigation of this problemshows that viscosity of pig iron grows worse with the increase of Ti in pig iron, and stickyiron does not flow out well at tapping, and as the result pig iron surface becomes higherthan the slag tap hole of the furnace and pig iron runs out of the slag tap hole. We studiedhow to decrease Ti content of pig iron and improve iron viscosity, and found that blowingof fines ore through the pig iron layer was the most effective for oxidization (slagging) of Ti in pig iron. As the first step to industrialization of this method, we applied it to thesmall blast furnace (inner volume 50m3) and found that blast furnace operation could bemade successfully even with 50% iron sand charging. This method is being applied for apatent.
Koin ITO, Kokichi SANO
As a continuation of the preceding paper, the authors have studied the kinetics of gas/molten iron reactions. In the present work, we measured the rates of oxygen transfer from H2O-H2-Ar atmopheres into molten iron. On the basis of the 2-film theory, it was supposedthat there were gas and liquid diffusion layers on each side of gas/molten iron interface, andthat each of the layers had resistance to the mass transfer between both phases. When gasmixtures of PH2O/PH2O·7 are used, there are linear relations similar to Henry's rule betweenH20 and 0, and then the rate equation: was derived. Experimental results obtained here could be expressed by this equation andgave the rate constants KL which were in good agreement with the values calculated fromthe data in the preceding paper.
Yasushi KOJIMA, Kokichi SANO
Recently, physico-chemical researches have been done by many laboratories for stainlesssteel making practice. Chromium and silicon are the most important elements in acidic steelmaking but it is not well known how they react eacl other. So long as the structures of slag are not fully understood physically and chemically, the various reactions between theacidic slag and the liquid iron-chromium alloy will not be solved definitely. However, theauthors tried to observe accurately these various reactions and to obtain fundamental datafor acidic steel making practice.
Although generally chromic oxide is dissolved in ionic state in the silica saturated slag, and chromium ion could not be measured directly in the present work its reactivity, characterand component were examined from experimental data, and compared with the resultsof other works.
The relation between the distribution of chromium in two phases and FeO in slag showsthat the oxide of chromium in the slag was dissolved, with its component nearly equal tothat of CrO.
The equilibrium data for silicon and chromium with acidic slag showed that the follomingchemical reaction occurred in two phases, log K'=5738/T-3·179
In the range of above 5 weight per cent chromium, the experimental data agreed with thevalues, calculated values using the equilibrium formula, but under 5 weight per cent, theexperimental data were smaller than the calculated.
The solubility of oxygen showed a good agreement with the previous data in the rangeabove 3 per cent chromium but under that the experimental value was higher than in theother reports.
Through a series of experiments and theoretidal calculations we disovered that 1·4 t circularingots (400mm_??_×1, 500mm) and 1.7t square ingots (400mm_??_×1, 500mm) of highcarbon-chromium steel suffer cracking due to to thermal stress when heated to the rollingtemperature in a reheating furnace.
The results obtained are as follows:
(1) To find out the period and the surface-center temperature difference at which theinternal cracking may take place, we heated the ingots at varios heating speeds in a Batchtype furnace. Cracks developed only in the ingots in which transformation had been completed, and whose surface-center temperature difference at the completion of transformationwas over 230°C-240°in calculated value. And this critical temperature difference wasidentical with both of the circular and the spuare ingots.
(2) From the inspection of many of the ingots of the above two types which had undergone cracking after heating in a continuous reheating furnace, we could find again thatcracking took place only in the ingots whose core had completed transformation with surfacecentertemperature difference of more than about 240°.
Thus we can say that thecontinuous furnace of this type must have the heating capacity smaller than 30t/h to preventcracking.
(3) With several typical examples of heating curves of ingots in the continuous furnace, wemade calculations of the thermal stress which occurs inside the ingots and found that elasticplasticstress and plastic strain increase violently at the core of the ingot when the corecompletes the transformation. But in all the calculations of rapid heating the maximumthermal stress value remains in this case constant at 0.1kg/mm2 with the exception of theincrease of plastic strain.
On the other hand, if the increase of plastic flow delays in proportion to the increase ofplastic strain and strain rate because the plastic flow is retarded by the triaxial tension stressesof the core part, the increase of the stress in the flow state becomes greater than thefracture stress of 13kg/mm2 and consequently it causes thermal stress crackings.
Thus we can explain the occurrence of thermal stress crackings in rapid heating.
(4) From the results of the above experiments and calculations, we could devise the wayof heating effectively and without cracking the ingots which are very liable to crack likethose of high-carbon-chromium steel.By the use of this method we are now able to obtaina heating capacity of more than 40t/h without any crackings.
Taira NAKANO, Tadataka GOTO, Masatoshi MAEDA
Influences of various factors such as solution treatment, cold work and stress relief on flow stress, cold work hardening characteristics and mechanical properties were tesed with the austenitic cold work hardening steels, 8Mn-8Ni-4Cr, 18Mn-4Cr, and 14Mn-6Ni-4Cr, which have been most widely utilized for non-magnetic retaining ring of turbo-generator.After tensile cold working up to 30% redaction of area at various temperatures from 20°C to 500°C tensile properties were studied at room temperature.The results obtained are as follws.
1) At the cold working temperature between 300°C and 500°C 8Mn-8Ni-4Cr showed the highest flow stress and 18Mn-4Cr the lowest, but at room temperature 18Mn-4Cr showed the highest flow stress on the contrary.
2) The investigation of the influence of cooling rate on the mechanical properties of the specimen with a 30mm squre bar cooled from solution temperature revealed that there was no difference between air cooling and water quenching with all of the specimens, except with the steel 18Mn-4Cr cold-worked at a relatively lower temperature, which showed better properties after water quenching.
3) As the result of changing the cold working temperature, tensile and proof strength were increased and elongation and reduction of area were decreased with increasing working temperature for 8Mn-8Ni-4Cr and 14Mn-6Ni-4Cr, but for 18Mn-4Cr, tensile and proof strength were the highest when the specimen was cold worked at room temperature.Therefore cold work hardening was the most remarkable for 8Mn-8Ni-4Cr at the temperatures between 300°C and 500°C and for 18Mn-4Cr at the room temperature.
4) Influence of stress relieving temperature on the mechanical properties of these specimens after cold working at 400°C and 500°C was studied.There was no changes of the mechanical properties when stress relieved at the temperature below cold working temperature, but when stress relieved above cold working temperature, proof strength, elongation and reduction of area were all decreased and especially when relieving at 600°C remarkable brittleness was caused because of carbide precipitation at grain boundary.
Takaji KUSAKAWA, Toshikatsu OTANI
Recent iron and steel alloys are very complicated.It is necessary to research the fundamental properties of iron for the development of these alloys.
For this purpose the properties of various kinds of commercial and trial manufactured pure irons were investigated at first.
Pure iron contains generally C, Si, Mn, P, S, Ni, Mo, V, Ag and Sn as impurities.
Mechanical properties of full annealed pure iron are approximately as follows.Hardness: HRB 30, tensile strength: 30kg/mm2, elongation: 50%, reduction of area: 70%.
Ultrahigh purity iron (Fe>99·99%) is high in work hardening rate and has good corrosion resistance.
Masayoshi HASEGAWA, Ichiro ONODA
In the previous paper, the authors made a study of the influence of uranium addition on low carbon steels, and also suggested:(a) non-metallic inclusions like sulfides and silicates decrease morphologically and also the oxide increases with the addition of uranium;(b) uranium has a solubility in austenite at higher temperature of above 950°and precipitates during tempering at temperature of about 500°C;(c) uranium slightly increases the hardenability of low carbon steels quenched at temperature of above 950°C and (d) corrosion resistance of steel against 5% hydrochloric acid is improved with the increasing content of uranium.
In the present paper, the authors reported on some laboratory tests concerning the inflence of uranium addition up to 0.7% on 0.3-0.4% carbon steels.The results of experiment had been shown as follows:
(1) As far as these small ingots were concerned, no scavenging effect of uranium could be found, but sulfide inclusions decreased, and oxides increased with the addition of uranium.
(2) Uranium refined the austenitic grain size insignificantly as shown in previous works.
(3) Gravitational segregation occurring in a slowly cooled ingot in a melting furnace was revealed through chemical analysis, autoradiograph, β, γ-ray counting and sulfur-print of the longitudinal section.
(4) As-normalized hardness showed an increase through the formation of uranium carbides resulting from uranium addition.
(5) Transformation temperature of steels was not changed by the addition of uranium according to thermal analysis.
(6) Microscopic exermination showed that uranium scavenged the impurities of grain boundary, and the figure of pearlite was changed thereby with a loss of uniformiy. Uranium carbides, UC or UC2, increased with the content of uranium and precipitated at the austenite grain boundaries.
(7) Uranium had no effect on the hardenability of these steels even at the quenching temperature of 1200°C;
(8) No secondary hardening effect was caused even at the quenching temperature of 1200°C and subsequent tempering.From these experiments, it is suggested that uranium carbides were not decomposed and were extremely insoluble to the austenite matrix at higher temperature.
(9) The effect of uranium on the mechanical properties at room temperature was almost negligible, but V-notch Charpy impact strength was reduced with the content of uranium.
(10) The effect of uranium on the corrosion resistance against 5% hydrochloric acid was noticeable, but uranium steel suffered a severe pitting in 5% sulfuric acid. Against 3% nitric acid and 3% sodium chloride aqueous solution, it showed no resistance.
Susumu MINOWA, Mineo KOSAKA
From the standpoint of rate theory, the rate of solution of Cr-steel in liquid aluminium alloy was measured at 750-950°C
The results obtained were as follows:
1) The rate of solution of Cr-steel in liquid pure aluminium was 3.6°-19.4×10-6[cm/s] and in aluminium alloy (Fe 3%, Si 3.1%) was 1.81-17.0×10-6[cm/s].
2) The value of activation energy for solution (EV) is equal to the sum of the value of activation energy for diffusion of iron in liquid metal (ED), heat of solution (ES) and the activation energy for viscosity of liquid metal (Eη).
Values of-EV are equal to 30.1 and 32.4[kcal/mol], respectively.
3) The controlling step of Cr-steel at solution process in liquid aluminium is the rate of diffusion of Fe atom in the diffusion layer.
Kunio KUSAKA, Makoto OSAWA, Mitsuo YAMAZAKI
Some low-chromium steels containing 2% and 5% chromium for inlet valves have been evaluated by short time tensile test at room and high temperature, hot hardness test, cold workability, scaling test, corrosion test and stress-rupture test at 550°C and 600°C.
The steel containing 0.3% C, 1% Si, 5% Cr and 0.5% Mo has a good combination of strength and ductilility, and is found suitable for inlet valves to be operated at under 500°C
05 Dec. (Last 30 Days)
ISIJ International Advance Publication
ISIJ International Advance Publication
ISIJ International Vol.63(2023), No.11
ISIJ International Advance Publication
ISIJ International Vol.63(2023), No.11
MATERIALS TRANSACTIONS Vol.64(2023), No.9
MATERIALS TRANSACTIONS Vol.64(2023), No.11
Tetsu-to-Hagané Vol.109(2023), No.11
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