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A, fracture
Alloy fracture state and quality has a close relationship. Carbide fracture belongs to brittle fracture, compared with the metal material, it has a fine grain, thus the fracture shape is more smooth and detailed. Defect of the organizational structure can be expressed in the alloy profile.
1, holes, (dirty) habits will be larger than 40 microns holes is dirty. Less than 40 micron holes called pores. Check fracture observed holes refers to dirty hole. 40 micron holes under 25 times of the microscope is 1 mm.
Carbide on the cross section of dirty hole, the edge is clear, darker. Hole shape is round, oblique groove, elongated, shape, triangle, half moon, etc., which related to the shape of impurity. Generally speaking, if appear in the liquid phase temperature used to be able to generate carbon and hydrocarbon impurities, holes, which is formed by the general similar to the original; So at low temperature can be hydrogen or carbon reduction of impurities, generated by the hole, its shape is similar to the original is not so. If impurity can only in the presence of liquid phase under high temperature to be restored, the formation of the holes are round or oblique hole; If the impurities are not produce gas into the content, such as cobalt scrap, copper, aluminum, stainless steel scrap, alloy scrap, etc., the formation of the hole, its shape is irregular. Some was not reduction in sintering temperature oxide, basically keep the shape of the original particles. Some big holes in briquette form, is not going to disappear in the sintering process, such as not good pressure caused by the sharp polygonal hole, in good sintered alloy has kept the same.
1, the decarburization
Eta on the fracture characteristics of the 1, usually in the form of silver bright spot. Sometimes a tadpole shaped concave pit. See white highlights from the bottom of the pit. The characteristics of decarburization is easy to recognize. When a serious shortage of carbon, decarburization point doesn't show a tadpole shape window, but the whole fracture is silvery white, very fine grain, it is the characteristics of the matrix of carbon. Another case is fracture presents many concave pit, connect to form a wavy fracture, but not present silvery white window, YN the lack of carbon alloy, fracture is the more features.
Decarburization point size and sintering of liquid phase is related to the number of serious lack of carbon, the relative decline in the liquid phase, eta 1 phase grew up slowly, resulting in fracture of on decarburization point is smaller. On the other hand, slight decarburization, decarburization is larger. This is judgment of decarburization weight a method. Similarly, decarburization point distribution density, and decarburization of the area can illustrate the degree of lack of carbon. Sometimes, only found a few bright spots in the fracture edge, which is characteristic of the alloy surface decarburization. In the case of difficult to determine, cross section can be immersed in potassium ferricyanide solution for a few seconds, and then wash to dry, then under the magnifying glass observation, if there is brown spots on cross section, suggests that lack of carbon, alloy, on the other hand, is the other material produced by the window, this is the most effective way to judge whether alloy with low carbon.
2, the carburizing
Alloy carburizing fracture has two kinds: one is the d-type graphite, the second is the plum blossom shape graphite. D-type graphite is usually produced in low cobalt alloy and fine grain fracture, due to the small and scattered carburizing shape, color, not easy to find, once found, the carburizing is more serious. Plum blossom shape graphite are mostly produced in high cobalt alloy and coarse particle alloys on the fracture surface, because of its shape, size is bigger, so is easily observed, but the carburizing is not serious.
Serious carburizing alloy surface light black, by hand or wipe on white paper, can make hand or white black, in the case of this kind of serious carburizing, the fracture.
Graphite in YT, YN class is usually small and scattered point, fracture is difficult to observe, but if on the grinding slice observation, can be found to have 1.0 1.5% (volume) of graphite impurity, it has to do with fine grain low cobalt alloy carburizing is similar.
3, owe to burn
Owe to burn alloy surface is usually pale, the grain on the cross section were the non-viscous stack, no obvious metallic luster, owe to burn is not obvious, sometimes can see a loose area in the center of the fracture site. But grain and normal alloy has metallic luster. Judge owes to burn the simplest method is to use a drop of ink pen on the cross section point, if the ink bled, absorption, suggests that structure is loose, is characteristic of owe to burn. Will owe to burn the most reliable method is alloy metallographic grinding of porosity determination.
4, burnt
Burnt alloy surface is rough, badly burnt when also can see the grain size of flash, burnt cause alloy grain growth, its section is coarser grains, light person only observed quantity more sparkle, serious a honeycomb, but burnt alloy alloy and coarse grain (such as YG8C YG11C) section is different, the latter more bright spots, but the luster of the bright spots a little dark than burnt, is the white window rather than silver sparkle. It should be pointed out: slightly burnt and owe is difficult to fracture observation method is used to determine whether to burn.
5, mixing
Mixture mixed with another in a greater difference between composition and particle size mixture, this phenomenon is called mixture. Blending alloy fracture usually show the different shapes of small points, some bumps, some depression, but the boundary of the convex and concave into the don't like dirty hole so clear.
6, "dirty"
Alloys on the fracture surface of loose area of organization, macroscopic observation its dark color, and less loose organization, or severe burning fine powder dot carburizing, often appear in the heart of fracture, can also assumes the circular distribution.
7, not pressed
Alloy section were water chestnut sharp triangle, quadrangle and polygon holes, this is due to insufficient material grain deformation when pressing traces of.
8, bulky carbide
Here is not burnt is of coarse grain, but to YT classes the kind of bulky carbide alloy unique. When appear this kind of thick carbide alloy fracture appear similar to owe to burn fracture appear white crystal, sometimes don't have to enlarge, and directly with the naked eye can be observed. Grinding were observed under high power microscopy, the bulky carbide is a kind of special thick needle or flake grain, its shape is similar to the WC grain size.
When the alloy. The above defects, its mechanical performance will be significantly lower, seriously affected the alloy using performance.
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