ABSTRACT
When compare with conventional cemented carbide（middle grain or fine grain carbides）, coarse grain carbides demonstrate a special properties and application, with a serials merits, such as high micro-hardness, low micro-strain, few stuctural defects.Thus, it attracts more attention from different departments in the area of industry.Currently, it is widely applied into many fields and found increasing usage in areas such as milling tools, punching dies, boring drills, hard-surface materials. The study and development on coarse grain carbides improve the properties of WC powder,accompanied by the ameliorating the quality of carbides.
In this paper, the properties and structural features of coarse grain WC powder are discussed, followed by the optimization and adjustifacation of the processing conditions. And, by study, check and analysis the relationship between processing parameters and the properties of WC powder, the new method of production WC powder were founded in that high quality coarse grain WC powder were obtained, with which high quality carbides were manufactured. Also, it was investigated the main factors and mechnism that influence the production process of WC powder. All kinds of properties of coarse grain WC powder are investigated by means of TEM, electron probe, stereoscan, metallographic examination, etc, with the conclusion that two-step carburization is optimum to obtain high quality coarse WC powder:
By adoption follow parameters: first apportion carbon 4.5%(weight), first carburization temperature: 1900~2000 ℃ , second carburization temperature:1800~1900℃, loose pack, the high quality WC powder with Fsss grain size 35~45 µ m,can be manufactured whose grain growth completely and have few defects.High quality WC powder can be producted by two-step carburization., which reduce the opportunity of bombard of W powder during the process of carburization.And, WC powder producted by two-step carburization have some special properties,such as, high content of carbide carbon, low content of free carbon, pure phase, low content of impurities, homogeneous crystal grain, homogeneous subgrain size, few micro-defects and low dislocation density, which also prevent the bombard of W powder. Now, the quality of carbides reach the plateau in China that are synthesised by this kind of high quality WC powder.
And, the experiment shows that trace element play a vital role in the process of growth of WC particle. The contrast experiments are carried that are relvant to the effect of Na, Li and P as catalyst in the process of WC nuclear growth. Also, the standard of high quality coarse crystal WC powder was presented accompanied by technological design and key technology for high quality coarse crystal WC powder production.
The high quality coarse grain cemented carbides are manufactured with this high quality coarse WC powder, whose average grain size is much more than 3.2 µ m,demonstrating greater toughness. The total footage of dill bits, which was made by the coarse grain carbides, surpassed the advance product in China. The results of consumer test revealed that the alloy’s property have reached the plateau nationally.
KEY WORDS: cemented carbide, high quality coarse grain, two-step carburiation,trace element, catalyst
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