A laboratory scale shaft furnace was constructed for examining the operational characteristics. Some series of reduction experiments of iron oxide pellets with gas mixture of H₂, CO and others were carried out under various operational conditions varying temperature, flow rate and composition of inlet gas and pressure applied. Overall data of operation and distributions of process variables were obtained for the steady-state operations. After cooling down the furnace, the pellets were sampled from various levels in the furnace. Then, the measurement of crushing strength and the observation of reduction fashion of the pellets were conducted.
On the other hand, a one dimensional mathematical model was derived for the process simulation of the shaft furnace. The rate parameters for the reduction of the pellets and the side reactions which were measured by independent experiments were incorporated in the model. Reasonable simulation results were obtained for ordinary pressure operation when appropriate values of the rate parameters were given for the reduction of iron oxide pellets and side reactions.

View full abstract

An electrochemical permeation method using molten sodium hydroxide has been developed to detect hydrogen in a steel at elevated temperatures in the range of practical interest for hydrogen attack. A test for a steel in the tubular shape with different wall-thickness gives the following results:
(1) The most suitable range for detecting hydrogen is from -0.8 to -0.6V vs. air/O²-(ZrO₂).
(2) The permeation curves measured for a 6.5-mm thick steel agree fairly well with the theoretical ones.
(3) Diffusivities of hydrogen in the 6.5-mm thick steel are in good agreement with the values obtained from a conventional gaseous method.
(4) The detection limit of hydrogen content in the steel is 0.1ppm.
(5) Therefore, this electrochemical method will be useful for predicting the hydrogen attack in steels.

View full abstract

Finite difference equations are derived based on the direct finite difference method for solving fluid flow during solidification of alloys. In the analysis the darcy and laminar flows are assumed in the solid-liquid coexisting and liquid regions, respectively. Numerical examples revealed some features and effects of the fluid flow during solidification of steel ingots. These finite difference equations are applicable to solidification problems of complicated shape and boundary conditions.

View full abstract

Application of accelerated cooling combined with controlled rolling (ACC) to X70 linepipe steel plates was tried using conventional Nb- and V-containing steels. Firstly, stability of the properties of ACC plates to possible rolling and cooling condition changes in commercial mass-production, uniformity of the properties along, across, and through a plate, weldability, and changes in the properties due to roller bending as a simulation of pipe forming were examined. Then, mill trial for UOE pipe forming was carried out. As a result, ACC plates had enough stability for mass-production and sufficient uniformity as pipe plates. Accelerated cooling increased tensile strength by 3 to 5kg f/mm² at the finish-rolling temperature of 740 to 780°C, the cooling rate of approximately 9 deg C/sec, and the finish-cooling temperature of about 550°C. In the mill trial, no difference was found in UOE pipe formability between the ACC plates and the controlled rolled one. Dimensions of the ACC pipes satisfied the API specification. Mechanical properties of the base metal in the ACC pipe also met the API specification. A combination of Mn-Ni-Mo-Ti type and low Mn type wires with SiO₂-CaO-CaF₂ Al₂O₃ MgO type flux provided the SAW seam weld of the ACC pipe with sufficient strength and toughness for an X70 linepipe. It is concluded that there are no problems in applying ACC to X70 linepipe steel plates.

View full abstract

Texture formation and aging behavior in a cold rolled 18% Ni maraging steel have been studied to apply a continuous annealing process to austenitization of this type of steel sheet. The results obtained are summarized as follows.
(1) Austenitization of the cold rolled 18% Ni maraging steel can be performed in a continuous annealing line to provide the mechanical property comparable to that obtained in the conventional austenitizing condition of 820°C×1h if the austenitizing temperature is higher than 900°C.
(2) The {111}<uvw> orientations, which strongly developed during cold rolling, gradually change into the near (557)[110] and (554) [156] orientations and the (001)[010] orientation evolves with progress of austenitizing.
(3) A marked hardness increase of about 40% from the as-annealed state was observed in the early stage of aging at 480°C, irrespective of the prior austenitizing conditions.
(4) The number of Fe atoms with Mo neighbors decreases within 3min of aging at 480°C, as evidenced by the Mössbauer spectrometry. The marked hardening in the early stage of aging is suggested to be a result of lattice distortion by clustering of Mo atoms.

View full abstract

The effects of surface microstructure and chemical compositions on characteristics of Fe-Zn compounds which formed on continuously galvanized steel sheets have been investigated by using ultra low carbon and low carbon steels.
From SEM observation, morphology of Fe-Zn compounds formed at interface between steel and plating layer were classified into three types; outburst structure, fine granular structure, and pillar-like structure.
The amount of outburst structure increases with decreasing solute carbon content in steels. Phosphorus inhibited the formation of outburst structure when solute carbon was combined with a carbide forming element such as Nb or Ti.
A comparison between distribution of Fe-Zn compounds and corresponding steel surface indicated that the outburst structure formed preferentially at grain boundaries exposed on the steel surface, whereas fine granular structure formed mainly at the interior of surface grains.

View full abstract

The effect of heat treatment on the tensile properties and fracture toughness of Ti-10V-2Fe-3Al, a near β titanium alloy, was studied to establish the optimum manufacturing process. Fatigue properties were also investigated using heat treated specimens specified by Aerospace Material Specifications.
It is found that aging at 400°C causes embrittlement by the precipitation of extremely fine secondary α particles from the β matrix. Aging at 490°C gives the best combination of strength and fracture toughness, while aging at 600°C causes overaging. Fracture toughness obtained under as-solution treated condition is lower than that estimated from the relationship between strength and fracture toughness for materials produced with aging after solution treatment. Therefore, an adequate aging is indispensable to obtain the high strength and high fracture toughness expected from this alloy.

View full abstract

Because of improved strength-ductility combination over HSLA steels, dual phase steels have recently become of commercial importance to both the sheet users and producers. These steels possess good properties by virtue of their microstructure which consists, typically, of about 15-20% martensite uniformly distributed in a soft matrix of ferrite. Although, the desired microstructural features of a dual phase steel can be obtained by various process routes, the most economical method is the production of this steel in as hot rolled condition. The sucessful production of dual phase steels in the hot strip mill, however, requires a careful control of process parameters particularly the finishing temperature, the cooling of the sheet on the runout table, the coiling temperature and the subsequent cooling of the coils.
As a development effort some commercial heats of dual phase steel in C-Mn-Si-Cr-Mo chemistry have been produced in as hot rolled condition at Rourkela Steel Plant. The effect of coiling temperature and cooling rate on the final structure and properties of the steel has been discussed in detail. All the coils coiled at lower temperatures of about 470°C or less showed dual phase structure with uniform properties where as coiling at about 500°C or above did not yield the desired microstructure and properties. Possible reasons have been given to explain the effect of coiling temperature on microstructure. Acceleration of the cooling rate of the coil, after coiling, has been found to improve the tensile strength without significantly affecting the ductility of the material.

View full abstract

Based on the void growth and damage mechanics, the rupture time t_r is derived as a function of the creep exponent n and the reference stress σ_o and the corresponding time t_o, for materials obeying exponential and power law creep. The analysis is extended to obtain parameters for prediction of long time behaviour. For materials which obey a simple power law creep, the parameter is shown as P=log t_r+(n- n_r)log(1-D_c) and for materials which obey an exponential function the parameter is given as P=log t_r+(n_r-n) D_c where n_r is the reference creep exponent and D_c is the critical size of the void at fracture, which is related to the applied stress σ as D_c=1-σ/σ_o

View full abstract