Wustite micropellets (Feo_0.941O) were isothermally reduced at 900-1100°C with H₂, CO and their mixtures. The effect of reducing gas composition and the total gas pressure on the rate of reduction was investigated. The kinetics and mechanisms of reduction deduced from the microscopic examination, surface area measurements and carbon analysis were found to depend mainly on the reducing gas composition. The highest rate of reduction was obtained in H₂ while the slowest was in CO. The reduction with H₂-CO mixtures was not additive.

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Water model experiments have been done to investigate the motion of bath in a bottom blowing converter with tuyeres set in two rows.
In the current work, the occurrence of two types o f wave motions (A-and B-type) has been detected by the visual observation of the bath. The wave motion of type A is similar to that generated in a U-shaped tube. On the other hand, the wave motion of B type is characterized by two separated bubble regions interfering laterally and repeatedly colliding and repelling alternately.
The generation of wave motion is affected by the gas flow rate, bath depth and tuyere configuration. In the case that the gas flow rate is kept so as to generate wave motion, the criterion for the generation of wave motion can be characterized by H/D and L₂/L₁, where H is the bath depth, D is the diameter of the bottom, L₂ is the spacing of the two rows of tuyeres, and L₁ is the length of the row of tuyeres.
The period of wave motion is calculated on the basis of simple models. The calculated results agreed well with the ones observed under various experimental conditions.
The wave motion of type A requires larger energy of oscillation than that of type B at the same rate of energy input to the bath, indicating that the wave motion of type B occurs in preference to that of type A.

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In order to sane the cooling time of billets on cooling bed, mist-jet cooling process has been investigated. The main results obtained are as follows:
(1) The most favorable process for a homogeneous and regulated cooling of billets consists of on-corner arrangement of billets and air-atomized mist-jet cooling.
(2) To avoid cracking and deformation o f billets by forced-cooling and to shorten the cooling time, the following two-step cooling process is suitable: a natural cooling at high temperatures down to about 500°C and the mist-jet cooling at lower temperatures under about 500°C.
(3) When 123mm square billets containing 0.2 to 0.8wt% carbon are naturally cooled from about 1000°C down to about 550°C (billet core temperature), and then mist-cooled under impinged water with a flux equal or lower than 20 and 40l/m2•min at the top and the bottom, respectively, their structures and mechanical properties are scarcely affected unfavorably.
The following studies have also been made: influence of billets arrangement on cooling time, mist-cooling conditions to decrease bending of billets, influence of carbon content on cooling curves during natural cooling, influence of scale on billet surfaces on cooling curves during mist-cooling, deflection of as-rolled hot billets, selection of mist nozzles free from clogging, and an example o f basic design of a billet cooling bed with mist-cooling equipment.

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New mist cooling equipment for billets has been developed at kamaishi Works, Nippon Steel Corporation. The equipment has a walking beam type cooling bed, and as-rolled hot billets are arranged on their corners and rotated on the bed in walking.
The billets are natural-cooled from the initial temperature to about 550°C (core temperature) at the front part of bed and then mist-jet-cooled to about 100°C at the later part.
This report concerns the new techniques developed, the basic design and main specifications of the equipment, the passages of constructions and operating performances, improved points and unsettled problems, and others.
Main techniques developed are the billet straightening mechanism using a billet pusher, the system of on-corner arrangement and rotation of billets on the cooling bed, and the mist-jet cooling device of billets having the crossflow type mist nozzles.
This installation has been smoothly operated since June 1975 with a sufficient cooling capacity using the mist-cooling method for all billets containing carbon lower than 0.75wt%. This has given no cracking and less deformation, very small reject level of billets (about 0.05%), and no nozzle clogging for about ten years.

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In plate rolling, the plate thickness is controlled by using the mill itself as a plate thickness measuring device, namely Gaugemeter. To maintain the Gaugemeter accuracy is very important not only for plate thickness control but also for plate flatness control. That is:
(1) The Gaugemeter error is a basic factor which impairs the accuracy of plate thickness.
(2) The Gaugemeter error sometimes reaches 1008μm.
(3) The variation in the plate thickness based on the Gaugemeter error can become the largest factor that affects badly plate flatness through the variation in the rolling load.

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New DDC system for batch-type coil annealing furnace was developed at Kashima cold strip mill. The purposes of the system are;
1) Improvement of fuel consumption by combustion control
2) Improvement of operations by full use of CRT display and printer
3) Improvement of reliability and maintenance by the introduction of distributed control system.
The characteristic of new combustion control is to lower the set-point of the furnace temperature as low as possible, keeping the heating rate of the coil similar to that of conventional combustion control. This system was achieved by adoption of a distributed micro-computer control system.

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Rolling fatigue behaviors of high-carbon-chromium bearing steel were investigated on the thrust-type fatigue tester. Platelike carbides, dark and white etching constituents were found immediately underneath the rolling surfaces.
Microscopic observation o f an area right below the flaking has demonstrated that the Platelike carbides are, among others, blamed for the flaking. The Platelike carbides consist of Fe₃C or ε-Fe_2-3(C, N) with a hardness up to Hv 1300. They are harder than martensite and can be the cause of the flaking. The Platelike carbides are precipitates of C and N in the martensite, diffused by a rolling stress and caught in the stress concentrated area between oxide inclusions near the rolling surfaces.
It is, therefore, necessary for an improvement in fatigue strength of high carbon-chromium bearing steel that oxides be reduced in the steel and carbon content in the martensite be lowered to reduce the formation of the Platelike carbides as long as a hardness required of a rolling element is maintained.

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A series of experiments were conducted along with the calculation of hydrogen distribution within the specimen, in order to define the microscopical critical condition for initiation of disbonding in the austenitic stainless weld overlaid 2_1/4Cr-1 Mo steel. The experiments consist of observation of acoustic emission, analysis of hydrogen concentration in the interface zone, electrolytical charging o f hydrogen while major experiments were run by gas charging in autoclaves, and utilization of large-sized test blocks.
Resultant major conclusions were that (1) disbonding is caused only by the effect of accumulated hydrogen on the cladding near the interface between cladding and the base metal under coexistence o f residual thermal stress, i.e., holding a specimen in high temperature hydrogen is not a necessary condition for disbonding, and (2) the microscopical critical condition for initiation of disbonding for a standard type of weld overlaid specimen is the calculated hydrogen concentration in cladding about 50μm apart from the interface to reach about 170ppm.

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Diffusion welding is one of the most promising fabrication methods in the aircraft industry. It realizes the complex, hollow and near-net shape structures from stock plates instead of forging materials, and the metallurgical properties of the base metals can be fully preserved in the diffusion welded joints.
Until now we have carried out research on the diffusion welding of aircraft titanium alloys and put it into practical use as a production technique.
This paper describes the results of the current application study on diffusion welding of titanium alloys for aircraft parts.

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