A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put ...A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put into the plasma nitriding furnace as sputter sources during nitriding of 722M24 steel. a variety of experimental and analytical techniques were employed to evaluate the structures and hardening response of the nitrided lavers which included metallography for structural examination, glow discharge spectrometry and secondary ion mass spectrometry for chemical composition profile analysis, X-ray diffraction for phase identification and microhardness testing for hardness profile measurements. The results show that the incorporation of rare earth metals in the glow discharge. during plasma nitriding not only influences the discharge characteristics but also results in the deposition of rare earth atoms and their compounds onto the specimen surface. These significantly affect the response of the investigated steel to plasma nitriding. The extent of the influence on plasma nitriding varies with different rare earth metals.展开更多
A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas...A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.展开更多
文摘A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put into the plasma nitriding furnace as sputter sources during nitriding of 722M24 steel. a variety of experimental and analytical techniques were employed to evaluate the structures and hardening response of the nitrided lavers which included metallography for structural examination, glow discharge spectrometry and secondary ion mass spectrometry for chemical composition profile analysis, X-ray diffraction for phase identification and microhardness testing for hardness profile measurements. The results show that the incorporation of rare earth metals in the glow discharge. during plasma nitriding not only influences the discharge characteristics but also results in the deposition of rare earth atoms and their compounds onto the specimen surface. These significantly affect the response of the investigated steel to plasma nitriding. The extent of the influence on plasma nitriding varies with different rare earth metals.
基金Item Sponsored by National Natural Science Foundation of China(50534010)
文摘A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.
