The deformation mechanisms in high‐purity Fe–50Cr(–5W) alloys were investigated between 293 and 773 K by tensile tests and by TEM observations of the fractured specimens. The results of the TEM observation have shown the following. 1. Fe–50Cr alloys deform by dislocation slip and twinning. 2. Four types of twin–matrix interfaces are observed in high‐purity Fe–50Cr(–5W) alloys after deformation, normal type, zigzag type, wavy type and abnormal type. 3. The planar slip traces are seen on the Fe–50Cr alloy after deformation at 293 and 573 K and the addition of tungsten restrains the local deformation. The results of the tensile test have shown the following. 4. The addition of tungsten to an Fe–50Cr alloy increases the amount of twinning at every temperature and the elongation of high‐purity Fe–50Cr alloy increases dramatically at 773 K due to uniform dislocation slip.

SynopsisFor a stable operation of blast furnace and a decrease in fuel rate, the improvement of the qualities of sinter which is the principal charging material is very important. At Wakamatsu Sinter Plant of Nippon Steel Corporation which is equipped with a double-layer charging system, the plant experiment has been made to improve the reducibility of sinter by making uniform and ideal heat pattern in the sintering bed. In this experiment, sinter with excellent properties, 3.7 % FeO, 70 % JIS RI, good hightemperature properties has been manufactured. Findings obtained are summarized as follows:(1) An effective means o f improving the sinter reducibility is to cause porous ore to remain as unmelted ore by lowering the sintering temperature at about 1 250 to 1 300 °C and by increasing the temperature-rise rate in the high-temperature zone.(2) Compact ore should have fine grains to improve the sinter reducibility.(3) The reduction degradation index (RDI) of sinter can be improved by reducing the ratio of A1203JSiO2 in fine raw mix and by lowering the sintering temperature.

The deformation mechanism of a high‐purity Fe–50 mass% Cr alloy and a floating‐zone refined Fe–50 mass% Cr alloy was investigated by tensile testing between 873 and 1073 K and microstructural observation. It is concluded from the present experimental research that: 1. A stress‐drop appears after yielding in both alloys between 873 and 1073 K. The stress‐drop is the result of grain boundary sliding and is related to the formation of dislocation sources at the beginning of deformation. 2. Intergranular cracking occurs in the high‐purity Fe–50 mass% Cr alloy and also in the fine‐grained zone‐refined alloy and the cracking is strongly influenced by grain size. The mechanism is not grain boundary decohesion caused by segregated sulfur. 3. The stress‐drop is also observed in the Fe–50 mass% Cr–8 mass% W alloy, but grain boundary cracks are seldom observed in this alloy. 4. The deformation behavior after the stress‐drop is determined by a competition between increasing dislocation density and dislocation annihilation at high temperatures. No twinning is seen in this temperature range, not even in the W‐doped alloy.

High‐chromium iron‐based alloys have attractive characteristics compared to those of conventional ferritic steels which have been considered to be promising candidate alloys for the next generation machines in place of austenitic stainless steels. Their expected properties of good corrosion resistance, low thermal stress factor, high strength at elevated temperatures, and in some cases low ferromagnetism are very desirable for advanced nuclear reactor application.

The tensile properties of high‐ and low‐purity Fe–9, –18 and –30Cr alloys irradiated by neutrons up to a dose of 5 × 1024 n/m2 (E >1 MeV) at 613, 673, or 763 K have been examined. The yield strength and the ultimate strength are increased and the elongation is decreased by irradiation. The enhancement of these strengths due to the irradiation has a tendency to increase with chromium and impurity content. Large stress drops are often observed, especially at 763 K, in stress–strain curves of high‐purity and high‐chromium‐content alloys except for Fe–9Cr alloys. Irradiation‐induced precipitates, with 2% larger interplanar spacings than the α′‐phase, on dislocation loops are more easily formed in the specimens of higher chromium content and higher purity. The precipitates are formed even in the irradiated Fe–9Cr alloy of high purity. The stress drop behaviour during the tensile tests is predominant in the specimens of higher chromium content and higher purity.