Effects of Alloying Elements on Phase Transformations, Mechanical Properties and Corrosion Behavior in Low-Density FeAlMn-Based Stainless Steels with High Specific Strength and Excellent Thoughness
|Keywords:||鐵鋁錳基不鏽鋼;低密度;高比強度;相變化;析出物;機械性質;腐蝕機制;Fe-Al-Mn based stainless steel;low density;high specific strength;phasetransformation;precipitates;mechanical properties;corrosion mechanism.|
The light metals of aluminum, magnesium, titanium alloys have received considerable attention in recent years because of their much higher specific strength (strength to weight ratio) than carbon steels, which can save much weight in applications. In our previous studies, some important academic results concerning phase transformations in Fe-Al-Mn and Cu-Al-Mn alloys have been achieved and we has obtained licenses of Fe-Al-Mn. hot-rolled alloy steel plates patent from eight countries. Besides, in the past one to two years, we have also successfully developed a new low density stainless steel- "Fe-Al-Mn based stainless steel", which has higher specific strength (150-190 Mpa/(g/cm3)) than most aluminum and magnesium light metals and possesses excellent elongation (20-60％) comparable to austenitic stainless steels The present workers have invent a refining technic to effectively reduce so many aluminum-oxide inclusions that the low density Fe-Al-Mn based stainless steel didn』t get rusty after 48 hours salt spray test (the temperature of testing room is 35℃, the temperature of saturated air barrel is 47℃, the concentration of salt solution is 5 %).Therefore, in 2005, the commercial productions of Fe-Al-Mn based stainless steel forged and precision casting type golf club heads of YAMAHA and KATANA companies have been manufactured by mass and sold over the world. Like the conventional stainless steels, alloying elements and microstructures of the Fe-Al-Mn based stainless steel have significant influences on the corrosion behavior. For the conventional stainless steels, increasing Manganese content has been considered to reduce the pitting resistance and higher carbon content also has been concluded to lead to serious damages on corrosion resistance. However, in the Fe-Al-Mn based stainless steel, with decreasing manganese and carbon contents, the austenite phase would change into unstable state and then might induce the formations of many kinds of precipitates, which could result in the harmful influences on the resistance to corrosion and pitting. On the other hand, the addition of nitrogen to the conventional stainless steels has been found to significantly increase the pitting resistance, but the excess nitrogen more than its solubility in matrix would lead to the precipitation of Cr2N and then the decreasing in corrosion resistance would be followed. However, up to date, the effects of nitrogen addition on phase transformations in the Fe-Al-Mn based stainless steels have never been studied. Therefore, the purposes of the present project in the first year are to investigate the influences of manganese, carbon and nitrogen contents on phase transformations and corrosion mechanisms in the Fe-Al-Mn based stainless steels. The addition of cobalt could increase the corrosion and high temperature oxidation resistance because its similar physic properties and oxidation potential to nickel. Besides, cobalt is mainly considered as one of solid solution strength elements; therefore, cobalt is found in high speed tool steels, high strength maraging steels and superalloys. Moreover, silicon is often added to heat-resisting and stainless steels to improve the corrosion and high temperature oxidation resistance. However, to date, there are few studies in the influences of cobalt and silicon additions on the phase transformations and corrosion behaviors of the Fe-Al-Mn based stainless steels. Therefore, extending the results of this project in the first year, we are going to select some appropriate compositions having higher corrosion resistance and better mechanical properties summarized in the first year』s results, and then add cobalt and silicon to the selected compositions. Accordingly, the purposes of the present project in the second year are to investigate the influences of cobalt and silicon contents on phase transformations and corrosion mechanisms in the Fe-Al-Mn based stainless steels. For conventional stainless steels, molybdenum addition could greatly improve the pitting resistance and magnify the beneficial effects of nitrogen on the resistance to pitting corrosion. Furthermore, titanium plays an important role in the prevention of sensitization of stainless steel since titanium could replace chromium to combine with carbon, which inhibits the precipitations of chromium carbides at grain boundaries. However, so far, there are few studies concering the influences of molybdenum and titanium additions on the phase transformations and corrosion behaviors of Fe-Al-Mn based stainless steels. Therefore, extending the results of this project in the past two year, we are going to select some appropriate compositions having higher corrosion resistance and better mechanical properties summarized in the past two year』s results, and then add molybdenum and titanium to the selected compositions. Accordingly, the aims of the present project in the third year are to investigate the effects of molybdenum and titanium contents on phase transformations and corrosion mechanisms in the Fe-Al-Mn based stainless steels.
|Gov't Doc #:||NSC95-2221-E009-086-MY3|
|Appears in Collections:||Research Plans|