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/*728*90 created on 2018/5/16*/ var cpro_id = "u3440131"; Home>Bearing knowledge>Special use of ultra-clean bearing steel development Special use of ultra-clean bearing steel
The need for high-speed rotation and miniaturization is increasing; thus, there is a higher need for bearing functions. In particular, the automobile industry has a very high need to reduce the size of the car and reduce the fuel consumption. The electronics industry also needs to have very small bearings to conserve energy and when the electronic instruments are less sensational. /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
Although the use of bearings needs to be higher and higher; but it also needs to be used longer than ever. However, because the bearing balls accidentally fall off; therefore, the extended bearing life is very difficult. In order to satisfy the increasingly severe needs of users; The cleanliness of steel must be improved by reducing the oxide and nitride impurities in the steel.
For cleaner steels, it is difficult to analyze the relationship between fatigue life and steel cleanliness using the traditional ASTM method; therefore, a new method for measuring impurities is needed. This paper will analyze the bearings developed by Kobe Steel Co., Japan. Ultra-clean steel production skills and new measurement skills.
1. Ultra-clean steel production skills for bearings 1. Production of ultra-clean steel Kobe Steel has been trained in Kobe Steel Plant and Kakogawa Plant to continuously cast high-carbon chrome steel for bearings. This steel is not only selected to be more rigorously refined. In order to minimize the oxide and nitride doping; the production process is the same as ordinary steel.
The pre-disposal of demineralized and desulfurized molten iron by hot metal is decarburized in a converter. The converter slag is an oxidized slag. In order to reduce the oxide doping; the slag is blocked; thus the oxide doping does not flow into the ladle. (heating, degassing) and continuous casting; molten steel is shielded by a more strict inert gas than usual to prevent secondary oxidation with air touch. In the essence process; because the alkalinity of the slag is very high; the molten steel is thoroughly mixed; Oxide doping (primarily aluminum oxide) floats into the slag; thus; the steel becomes cleaner; as long as there is a small amount of noisy. In continuous casting; the Kobe plant uses a central tank heater to accelerate the noisy rise in the molten steel; The Kakogawa Plant is a larger central tank.
To reduce nitride doping; it is necessary to minimize the titanium content in the steel. Titanium is mainly derived from ferroalloys; especially ferrochrome used to adjust the chemical composition of steel. Generally; ferrochrome is added to molten steel in the process of ladle essence. Because steel The oxygen content in the water is very low; therefore, it is very difficult to remove titanium in the form of titanium oxide (titanium dioxide). At Kobe Steel, ferrochrome is added and melted during converter blowing; at this moment, the oxygen content is very high; thus titanium and oxygen The repercussions constitute titanium dioxide; they are then absorbed into the converter slag.
2. The function of ultra-clean steel is in ultra-clean steel 52100; the oxygen content can be controlled to a uniform 4. 1ppm; the titanium content is evenly 6.0 ppm. The fatigue life of ultra-clean steel 52100 is compared with the steel of the comparative experiment; L10 is more In addition, many inspection methods were also used to compare the cleanliness of ultra-clean steel and general steel. After comparison, the cleanliness of ultra-clean steel is not much different from that of general bearing steel; however, the fatigue of ultra-clean steel The lifespan should be far better than ordinary steel.
Second, the new method for the determination of impurities in steel because ultra-clean steel has a very low oxygen content; therefore, the traditional ASTM test method for the determination of oxygen content and impurities can not give a good correlation with the fatigue life. This was done by electron beam smelting to determine the impurities in clean steel. At Kobe Steel, the researchers tried to find a new measure to measure cleanliness from the scale and quantity of the impurities. To detect small impurities and detect the number of impurities.
The acid dissolution method involves dissolving the detected data to separate the impurities. The aluminum oxide-rich dopants can be separated; however, the calcium oxide dopants cannot be detected; because they dissolve in the acid.
First; 30-100g samples are dissolved in nitric acid and heated to 90 ° C. The solution is filtered after cooling; the residue in the filter is separated as a dopant. The filter grid size is 10 mesh; the scale is greater than 10 The impurities were left in the filter. The inclusions were investigated by scanning electron microscopy. The inclusions were analyzed by electron probe microdissection.
After selecting these methods; can detect a lot of impurities; and can prevent the influence of carbide. After the acid dissolution method is selected; the researchers can detect the sample with oxygen content below 9ppm for the fatigue life test. It is indicated that the maximum amount of impurities and the maximum scale of impurities in ultra-clean steel are less than or less than that of general steel. When the oxygen content is lower than 9ppm, the acid dissolution method can also determine the difference between the cleanliness of ultra-clean steel and general steel.
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Source: China Bearing Network Time: 2018-02-15