High Temperature Deformation Mechanism of a High-Purity Fe–50 mass% Cr Alloy

Abstract

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.

Effect of Tungsten on Mechanical Properties of High-Purity 60 mass%Cr-Fe Alloys

“…Figure 1 shows the tensile strength and the reduction in area of 60Cr-Fe-4W (I) after Gleeble testing at temperatures between 1273 K and 1573 K, together with the data of 50Cr-Fe and 60Cr-Fe. 3,4) The data of 50Cr-Fe-5W and 50Cr-Fe-8W alloys 5) were also shown in the same Figure. It was found from the present investigation that the tensile strength of 60Cr-Fe increases by the addition of tungsten at temperatures between 1273 K and 1573 K. The reduction in area of 50Cr-Fe increases by the addition of tungsten; however, the Effect of Tungsten on Mechanical Properties of High-Purity 60 mass%Cr-Fe Alloys 143 and Fig. 4(b).…”

“…6, the nominal stress gradually decreases until fracture after the stress drop at the end of the elastic deformation. Isozaki et al and Kano et al discussed the deformation mechanism of high-purity 50Cr-Fe and 60Cr-Fe between 873 K and 1073 K, respectively, 4,5) that is, the stress drop after yield is due to grain boundary sliding. The gradual stress decreases after the stress drop is due to uniform dislocation slip through the specimen.…”

“…Isozaki et al found that the addition of tungsten to high purity 50 mass%Cr-Fe alloys was effective in improving strength and ductility at high temperatures. 5,6) Kako et al reported that the amount of twinning increased with the addition of tungsten.…”

Effects of Radiation on Tensile Properties and Damage: Microstructures in High-Purity Fe-(9-70)Cr Alloys

“…These high-purity alloys were prepared from high-purity metals of 99.995 mass% iron, 99.98 mass% chromium, and 99.98 mass% tungsten in a high vacuum of 10 À6 Torr in a high-frequency induction furnace. Further details of the preparation may be found elsewhere [7,8,12,13]. The ingots were heated at 1323 K for 1.8 Â 10 3 s in a high-purity argon atmosphere, then forged and rolled to sheets of 7 mm thickness.…”

“…No precipitation formation of the s-phase was observed in the matrix or even at grain boundaries during the heat treatment in the Fe-50Cr alloys aged at 973 K for 5000 h [6]. Kako et al [7] and Isozaki et al [8] investigated the effect of tungsten atoms in the Fe-50Cr alloys on the tensile properties. The tensile strength increased with tungsten content, and the ductility of the Fe-50Cr-8W alloy was better than that of the Fe-50Cr alloy at above 673 K. phys.…”