Iron oxysulfide melt saturated with iron was reduced in N2-H2 mixtures at 10001300°C using a thermobalance to obtain both chemical reaction parameters concerning deoxidation and desulfurization of the melt with hydrogen. Gas mixture flow rate of 24 l/min was employed to lower mass transfer resistance in gas phase. Decrement of overall reaction rate using hydrogen diluted by nitrogen (PH2= 0.0200.30 atm ) was of advantage to avoid forming of melt and clarify reaction area. Both the rate parameters were obtained in consideration of mass transfer resistance in gas phase estimated by a dimensionless equation. The parameters of deoxidation depended on temperature, not on oxygen activity in melt of 0.200.55, and amounted to nearly one tenth less than those extrapolated from the results of liquid wustite by earlier workers, while the influence of sulfur diminished with increasing temperature. The parameters of desulfurization were nearly two orders magnitude lower than those of deoxidation and rised with increasing sulfur activity in melt of 0.640.93 and temperature. The deoxidation process of wustite in coexistence of the melt showing extremely reaction retardation is discussed kinematically.
Measurements have been made to study the effect of the addition of alkaline or alkaline earth metal sulfide such as Li2S, K2S, MgS, CaS, SrS or BaS to FeS flux on the copper distribution ratio between FeS flux and carbon saturated liquid iron at 1673 K. Since each solubility of MgS and CaS in liquid FeS was limited, no apparent effect of MgS or CaS on the copper distribution ratio was observed. Similar to the effect of Na2S studied in our previous work, the addition of Li2S, K2S, SrS or BaS to FeS increased the copper distribution ratio, LCu=(mass%Cu)flux/[mass%Cu]Fe, and LCu reached maximum value at certain content of these additives in each flux. The maximum values of LCu measured in each flux were 30, 20, 22 and 19 in FeS-LiS0.5, -KS0.5, -SrS and -BaS fluxes, respectively. The sulfur content in liquid iron also decreased by the addition of these sulfides to FeS.
A frictional thermal shock simulator of drop weight type, by rubbing mild steelbar reproduces slipping accident occurres on cold strip mill work rolls and imposes a thermal shock on a specimen, was made and used to study thermal shock cracking phenomenon on high carbon high chromium hardened steel. A thermal shock produces two heat affected layers below the roll surface, one is rehardened layer and the other is succeeding tempered layer. The maximum depth of crack (dmax) occurred in a thermal shocked area, as a criterion for the resistance to thermal shock cracking, correlates to the thickness of the tempered layer. The initiation site of thermal shock cracking is the upper position within the tempered layer where just below the boundary between these two layers. There seems to be coincidence of the position between above initiation site and a peak of tensile residual stress generated in the tempered layer. When a martensitic specimen, with greater degree of supersaturation with carbon results from higher quenching temperature or lower subzero treatment temperature, is imposed a thermal shock on, dmax become larger. While high temperature tempering decreases dmax. The degree of supersaturation with carbon of martensite is considered to be the governing factor of thermal shock cracking resistance.
Effect of roll diameter in cold rolling on r-value and specular glossiness on 17%Cr stainless steel sheet has been investigated. It was found that r-value increased with increasing roll diameter in the cold rolling and the specular glossiness increased when cold rolled with small diameter roll in the later part of cold rolling. Combination of large diameter roll in the former stage of cold rolling and small diameter in the later stage of cold rolling gave better r-value and higher specular glossiness than cold rolled only by small or large diameter roll.
In view of inverse sigmoidal form of stress vs. time to rupture curve, long-term creep strength of ferritic heat resistant steels has been investigated using a large number of long-term creep data in the NRIM Creep Data Sheets. It was observed that the inverse sigmoidal form of stress vs. time to rupture curve was caused not by the change in mechanisms of strengthening or deformation, but by the decrease in creep strength and by the approach to steady internal stress due to microstructural change. At lower stresses, the complex form of creep rate vs. time curve which had two minima in creep rate was found and attributed to the inverse sigmoidal form of stress vs. time to rupture curve. Comparing the creep rupture strength for the different kind of steels, the large difference in creep rupture life of about four orders of magnitudes was found at lower temperatures and higher stresses. At higher temperatures and lower stresses, however, the creep rupture strength of all ferritic steels investigated was almost the same. It was concluded that the creep strength of the ferritic heat resistant steels was reduced by the microstructural change and approached to the inherent values which were nearly the same for all ferritic steels investigated.
The precipitation behavior of Nb in deformed austenite and the effect of precipitation on rolling load and mechanical properties were studied in two Nb treated steels and a Nb free steel. The steel slabs were solution treated at 1250°C, hot rolled in a five pass schedule and cooled at 40°C/s. Precipitation treatment of Nb was performed between third and fourth passes at 950°C for 020 min. Nb (CN) was quantitatively analysed as Insol. Nb by using electrolysis method. Sol. Nb( Total Nb-Insol. Nb), rolling load and tensile strength(TS) decrease with holding time at 950°C. The decreasing rate of these values measured for 0.03%Nb steel are larger than that for 0.02%Nb steel. This result shows that the amount of Nb disolved in austenite accelerates the rate of precipitation. TS increase with increasing Sol. Nb and in case of 0.03%Nb steel the increment of TS depending on an increase in precipitation hardening in ferrite is estimated at 12 kgf/mm2. These results show that Sol. Nb is able to be used for the prediction of the mechanical properties of Nb treated hot rolled steel sheet.
This investigation was carried out to verify the role of liquid metal embrittlement by Pb, Bi and Te on the chip disposability of steel. A computer program using finite difference method to calculate average chip temperature was made, and the results were compared with chip morphology and fractography. It has been verified that the average chip temperature exceeds the melting points of Pb and Bi in most of the cutting conditions tested. As a result, liquid metal embrittlement takes place which reduces the ductility of chip. Consequently, the chip can be broken easily, and its disposability is improved. On the other hand, the Te addition does not improve chip disposability, because the chip temperature does not exceed the melting point of PbTe or the eutectic point of MnS-MnTe. Further, liquid Ag does not embrittle steel, and thus no improvement in chip disposability is observed.
In order to apply diffusion bonding to a radiant tube made of heat resisting steel castings, the relation between bonding strength of joints and Ni content in insert metals has been investigated. Then the bonding strength was evaluated by tensile tests at 1 273 K as well as creep rupture tests of 1 273 K-9.8 MPa. Quantity of voids caused with kirkendall effect at the bonded zones heated at 1273 K either for 1800 ks or 1 224 ks in N2 gas has been investigated. The results obtained are summarized as follows: (1)The joints were bonded with the insert metal of Ni foil or Fe-Ni alloy varied from 10% to 45% of Ni contents in order to improve the bondability. Their tensile strength as bonded was hardly affected with Ni contents. On the contrary, quantity of voids gradually increased in proportion to the difference between Ni contents in the base metal and the insert metals after heating of 1 273 K×1 800 ks. (2)The joint bonded without an insert metal was as excellent as the base metal in the creep strength and the tensile strength. (3)The joint bonded with the insert metal of similar composition to the base metal was as almost strong as the base metal in the high temperature properties. (4)Concerning with bonding atmosphere, the joint bonded in N2 gas was as almost strong as that bonded in vacuum in the high temperature properties.
Cracking may occur in the weld Heat Affected Zone (HAZ) of Alloy 800 H, one of the austenitic heatresistant alloys during long-term service in the temperature range of 600700°C. The authors have conducted a series of restraint cracking tests to consider the mechanism of this crack formation and method of ameliorating the cracking. The following results were obtained. (1)This HAZ cracking can be reproduced by a cylindrical type restraint cracking test. (2)Intergranular oxidation and cracking were detected at the bottom of notched HAZ area of as-welded specimens in the temperature range of 600650°C. The area of cracking coincided with the area of γ' phase precipitation. (3)The intergranular cracking occurs when weld tensile residual stress acts upon grain boundaries whose cohesive forces are severely reduced by the intergranular oxidation and precipitation of γ' phases in matrix. (4) A solution treatment which reduces initial weld residual stress, plating of Ni-1%B for preventing oxidation, and the reduction of Ti and/or Al contents which prevents the precipitation of γ' phases are all effective to reduce this type of cracking.
In order to develop a new low alloy steel for gas turbine rotor disk, considerable studies have been performed. The targets of a new low alloy steel development for disk are to have excellent stress rupture strength which is not required to take account of creep below 400°C, and to have excellent both high temperature strength (Yield strength at 400°C is higher than 60 kgf/mm2) and fracture toughness (FATT is lower than +40°C) at bore of disk. The effect of chemical composition on mechanical properties and the heat treatment characteristics of low alloy steel were investigated. As a result, the 21/4Cr-Mo-V-Nb steel containing low silicon manufactured by VCD or ESR process was found to have the best performance for large size disk. Based on the above results, the 21/4Cr-Mo-V-Nb steel disk for turbine was produced by commercial base. Tensile, impact and metallurgical tests were conducted on this disk, and it is confirmed that this disk has excellent yield strength and impact properties at both rim and bore.
Recently, it is strongly demanded to develop a tester which makes possible to in situ observe the microstructures deformed in the wide temperature range from room temperature to high temperatures. Both Mechanical Engineering Laboratory, Agency of Industrial Science and Technology and Shimadzu Co. have produced such a tester, where a hydraulic machine with a vacuum chamber and a heater is equipped with a scanning electron microscopy. Mod. IN-100, a slightly modified version of IN-100 which has specific points (i.e. transformation and recrystallization temperatures etc.) at high temperatures has been prepared, and in situ observed in the temperature range from room temperature to 1 323 K using an upper type furnace in installation of trapping the thermal electron. Good scanning electron microstructures have been observed up to 1 306 K in both scanning and television mode. Beyond 1 306 K, however, it is difficult to bring its target into focus, because an amount of the detected second electron decreases in using the furnace mentioned above. In television mode, especially, the microstructures are slightly seen.