Papers by Keyword: Ferritic Stainless Steel (FSS)

Abstract: With prices for metal resources such as nickel and molybdenum soaring, there is a heightened sense of crisis concerning resource scarcity. While Type304, the most common stainless steel, offers excellent corrosion resistance, its price is affected significantly by the cost of nickel because of its 8% nickel content. The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required. JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel, the world’s first ferritic stainless steel, which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum, two rare metals. The newly developed steel contains 21% chromium with the addition of 0.4% copper. The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition. Copper addition enriches the chromium content in passive films after field exposure. Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304, including commercial kitchenware, building materials and industrial machinery. The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.

Abstract: In order to keep the steel with outstanding antibacterial characteristics, the relationship between the anneal temperatures and the amounts of the precipitated Cu-rich phase was investigated in this work. The SEM analysis of annealing specimens indicated that the microstructure changed with the increase of annealing temperature. At 900°C, the martensite phase appeared along the crystal boundary, but the amount of Cu-rich phase was almost no change. At 920°C, the sizes of the Cu-rich precipitates minished and the amounts of the precipitates reduced gradually. At 940°C, there was only martensite phase existing in the ferrite matrix. Therefore, the optimal final annealing temperature range was chosen from 880°C to 900°C to ensure attaining excellent antibacterial properties and favorable mechanical characteristic of copper-bearing stainless steel.

Abstract: In this study, the toughness of 11Cr ferritic stainless steel weld was evaluated by DBTT (Ductile-Brittle-Transition-Temperature) with the interstitial elements level. DBTT of the weld increased with increasing interstitial level due to the formation of martensite phase and solidsolution strengthening. Interstitial elements level should be limited by the adoption of back shielding gas during welding process because increased C+N level detrimentally affects the toughness of ferritic stainless weld. Adoption of Ar as back shielding gas lowered N content in the weld.

Abstract: Mechanical alloying (MA) process has been examined to synthesize ferritic stainless steel powder dispersed with nano-sized Y2O3 particles. A pilot-scale horizontal mill was fabricated and compared with laboratory-scale ball mills and an attrition mill. Horizontal milling resulted in a much better distribution of particle size and dispersoids than other milling methods. Although horizontal milling is considered as a low-energy process requiring long times, processing time could be markedly reduced with increasing the diameter of horizontal mill with a proper control of milling parameters.

Abstract: Copper is a well-known alloying element which is used to improve the resistance to general corrosion of stainless steels. Our previous experiments show that the increase of copper content can acquire the excellent antibacterial properties and can also increase the tendency to cold formability of the ferritic stainless steels. However, the effect of alloying Cu on the resistance to localized corrosion has not been clarified sufficiently. In order to understand the effect of copper on pitting corrosion resistance of the ferritic antibacterial stainless steel, the electrochemical experiments were carried out and the anodic polarization curves were performed in 3.5% NaCl solution for two kinds of steels. The results reveal that the ε-Cu phase in ferrite matrix diminishes pitting corrosion resistance of the antibacterial stainless steel in the chlorides medium. It is connected with the poor passive behavior of the ε-Cu phase inclusions.

Abstract: 15%Cr ferritic stainless steel was machined in rectangular samples and then processed by multiple forging to a total cumulative strain of 7.2 at an ambient temperature. The large strain deformation resulted in almost equiaxed submicrocrystalline structure with a mean grain/subgrain size of 230 nm and about 2.2×1014 m-2 dislocation density in grain/subgrain interiors. The annealing at a relatively low temperature of 500oC did not lead to any discontinuous recrystallizations. The grain/subgrain size and the interior dislocation density slightly changed to 240 nm and 2.1×1014 m-2, respectively, after annealing for 30 min, while the Vickers hardness decreased from 3140 MPa in the as-processed state to 2900 MPa. This annealing softening was attributed to remarkable release (by 50%) of internal stresses, which are associated with a non-equilibrium character of strain-induced grain/subgrain boundaries.

Abstract: Several studies have shown that recrystallization of cold rolled martensite results in low carbon steels with very fine microstructures. Correspondingly, these materials exhibit promising combinations of strength and elongation. Most of the work on this processing route has focused on low carbon steels (0.1-0.2wt% carbon) where the interstitial content may play an important role in the microstructure refinement. In this note we describe experiments performed on a low interstitial stainless steel containing 0.02wt%C. It has been possible to achieve materials with high strengths (UTS > 1 GPa) and significant uniform elongation (> 8%), however, the microstructures associated with these properties are very different from those previously reported for low carbon steels.

Abstract: This paper showed an example of the phenomena that a strong deformed texture does not change after the annealing process in steels. An Fe – 22%Cr – 3%Ni ferritic stainless steel was processed by bar rolling/swaging to a total strain of 4.4 at an ambient temperature, and its annealing behaviour was studied in a temperature range of 400 ~ 700oC. The deformed sample showed a grain size of 200nm, a fraction of high-angle boundary (HAB) of about 0.6, and a strong fiber texture of <110>{uvw}. This texture showed very little change after annealing which was characterised by the development of continuous recrystallization involving recovery processes and followed by a normal grain growth. On the other hand, by annealing a sample that was deformed to total strain of 2.0 containing rather fine grains (270nm) but without a large enough fraction of HAB (0.3), a discontinuous recrystallization took place, and its deformed texture changed considerably.

Abstract: Preparation of nanocrystalline 430L stainless steel powders by high-energy ball milling has been investigated. The samples were characterized by scanning electron microscope (SEM), X-ray Diffraction (XRD) and Matersizer. The SEM observation confirmed that the cold welding and fragmentation behaviors occurred during high-energy ball milling, which has important effect on the changes of the particle size. In the initial stage (0-10h), particle size increased and crystalline grain size decreased evidently. The mean particle size got to 330μm and the crystalline grain size got to 23nm for sample of 10h ball milling. In the later stage, the particle size decreased and the refinement of crystalline grain became difficult. The crystalline grain size of sample for 50h ball milling only got to 15nm.

Abstract: Effects of Ti and Nb stabilization on the recrystallization and the pitting potential in Fe-21%Cr ferritic stainless steels were studied by using optical microscopy, scanning electron microscopy, transmission electron microscopy and polarization curve measurement. The results show that both Ti and Nb, either in solution or as precipitates, retard the recrystallization and enhance the recrystallization temperature. Substitution of Nb for Ti in Fe-21%Cr ferritic stainless steels increases the recrystallization temperature by 30 to 50°C. Nb and Ti stabilized ferritic steels present higher pitting potential than Ti stabilized steels.