An overview: the so-called sintering, the powder is heated to a certain temperature, and maintain a certain amount of time, and then cooling, to get the required materials or products, this special heat treatment method called sintering.
Carbide sintered belongs to the liquid phase sintering of multicomponent system, sintering on alloy products play a decisive role.
1, the sintering process of the change of the sintered body: smaller pressure fast volume shrinkage, and strength increase, alloy surface is metal luster, usually, pressure fast porosity is 50%, the products should be less than 0.2%. Sintering process, the qualitative changes between powder particles, the combination of alloy intergranular instead of the contact between the powder particles to form alloy strong overall, which has excellent physical properties.
1, the sintering process of several stages:
(1) removal agent and presintering stage (800 ℃) or less:
The early stage of sintering, with the temperature increases, cracking, gradually forming agent out of the sintered body side by side, at the same time, forming agent increased carbon sintered body more or less. When hydrogen sintering, under 800 ℃ can restore oxide on the surface of the powder, at the same time, the contact stress between powder gradually eliminate, bonding metal powder to produce responses and recrystallization, particle surface diffusion, increase strength.
(2) solid phase sintering stage eutectic temperature (800 ℃ -- 800 ℃) : eutectic temperature refers to the gradual thawing to started to the temperature of the eutectic liquid phase sintered body.
(3) the liquid phase sintering stage (eutectic temperature sintering temperature) : when there is liquid phase sintered body after sintered body contraction finished quickly, carbide grain growth and formation of the skeleton, which laid the basic organization structure of alloy.
(4) cooling stage (sintering temperature - room temperature), the organization of the alloy and binding phase composition varies with the different cooling condition and produce some. After cooling, to get final alloy.
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2014年2月26日星期三
2014年2月5日星期三
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2014年2月3日星期一
SIX - Metallographic examination
1, sample preparation, coarse grinding with coarser silicon carbide grinding wheel grinding, grinding surface to 2-3 mm. The internal organization of the proof alloy; Set sample is coarse grinding sample with sulfur circle insert samples, sample set samples should make all polished in a plane. Circle will be set with sample set samples, on special sample device of fine grinding, to eliminate coarse grinding water grinding crack. When the fine grinding of abrasive has two kinds: one is containing silicon carbide (120-180 mesh) and potassium permanganate solution; Another kind is boron carbide (180-220 mesh) with kerosene or a mixture of transformer oil. Polishing can be conducted on similar to the fine grinding device. Mill pad on the canvas, and drop into the zirconia powder (150 mesh) and potassium permanganate solution, no streaks of light should be after polishing grinding surface, further on the iron plate in woolen cloth fine grinding, to eliminate grinding polishing is the formation of the turbidity, drip continuously in the process of fine grinding abrasive (less than 3 micron boron carbide) and lubrication oil, transformer oil or edible vegetable oil), after fine grinding of grinding should be smooth as a mirror.
2, the corrosion of grinding
Porosity is A field of pore area percentage, namely X = A/B * 100%; X for porosity, A is the area of the field of pore, B is the area of the field. Generally choose a field of most pore and the known standard photos to compare and determine porosity. Dirt degree is to put the above 40 microns, irregular shape but the clarity of the edge of black holes. Graphite inclusions generally or tiny dot gathered in nests, its edge is clear, in the process of grinding, flake graphite inclusions are usually the pore, some national standards will even graphite inclusions as the secondary pore. Other defects, layered like dirt under a microscope, but longer than dirt, dirt than straight edges. Crack is thin and long black stripes. Not good pressure caused by the pore usually triangular or water chestnut, if pore focused particularly on the sharp edge of place, usually is not good. Owe to burn the pore generally smaller, about 5 microns, concentrated in the middle of specimen. Burnt generally does not affect the porosity, but serious when burnt, average porosity is larger, in 10-20 microns, and most of the surface.
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2, the corrosion of grinding
Porosity is A field of pore area percentage, namely X = A/B * 100%; X for porosity, A is the area of the field of pore, B is the area of the field. Generally choose a field of most pore and the known standard photos to compare and determine porosity. Dirt degree is to put the above 40 microns, irregular shape but the clarity of the edge of black holes. Graphite inclusions generally or tiny dot gathered in nests, its edge is clear, in the process of grinding, flake graphite inclusions are usually the pore, some national standards will even graphite inclusions as the secondary pore. Other defects, layered like dirt under a microscope, but longer than dirt, dirt than straight edges. Crack is thin and long black stripes. Not good pressure caused by the pore usually triangular or water chestnut, if pore focused particularly on the sharp edge of place, usually is not good. Owe to burn the pore generally smaller, about 5 microns, concentrated in the middle of specimen. Burnt generally does not affect the porosity, but serious when burnt, average porosity is larger, in 10-20 microns, and most of the surface.
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2014年1月31日星期五
FIVE - Cemented carbide with determination and analysis of the nature of particular average
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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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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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2014年1月29日星期三
Four - phase composition and structure of carbide
Carbide of the binding phase composition is mainly refers to the content of W, W content and carbon content of alloy and alloy cooling rate;
1, the relationship between binding phase composition and alloy properties: W content on the hardness of alloy impact is not big, but obviously change the strength of the alloy, for high cobalt alloy, its strength increase with the increase of W content, while the opposite was true for low cobalt alloy. Abrasion resistance and W content relationship: W content is higher, the higher wear resistance; Alloy has a small amount of eta does not prevent use of wear resistance, but eta, alloy brittle.
2, the factors influencing the bond:
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The effects of carbon content:
(1) alloy normal two-phase (WC + Y) WC - CO alloy W content and carbon content of the binding phase relationship: bonding phase increased with the decreasing carbon content and the W content.
(2) the influence of cooling rate: if the cooling speed is too fast, WC can not afford time to precipitation, or the amount of precipitation is less, so that more W content binding phase. But when there are free carbon alloy, binding phase of W content is very low. At this time, the cooling speed of binding phase composition had little influence.
3, hard alloy heat treatment (annealing) : alloy after heat treatment, the bending strength of WC - CO alloy can improve 5-20%; Hardness increase by 3-9%; Impact toughness increase 15-30%; Fracture under alternating load capability is more apparent, can achieve 1 to 6 times.
1, the relationship between binding phase composition and alloy properties: W content on the hardness of alloy impact is not big, but obviously change the strength of the alloy, for high cobalt alloy, its strength increase with the increase of W content, while the opposite was true for low cobalt alloy. Abrasion resistance and W content relationship: W content is higher, the higher wear resistance; Alloy has a small amount of eta does not prevent use of wear resistance, but eta, alloy brittle.
2, the factors influencing the bond:
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The effects of carbon content:
(1) alloy normal two-phase (WC + Y) WC - CO alloy W content and carbon content of the binding phase relationship: bonding phase increased with the decreasing carbon content and the W content.
(2) the influence of cooling rate: if the cooling speed is too fast, WC can not afford time to precipitation, or the amount of precipitation is less, so that more W content binding phase. But when there are free carbon alloy, binding phase of W content is very low. At this time, the cooling speed of binding phase composition had little influence.
3, hard alloy heat treatment (annealing) : alloy after heat treatment, the bending strength of WC - CO alloy can improve 5-20%; Hardness increase by 3-9%; Impact toughness increase 15-30%; Fracture under alternating load capability is more apparent, can achieve 1 to 6 times.
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2014年1月27日星期一
III WC - CO alloy sintered grain growth
1, WC grain grew up mechanism: after sintered alloy average grain size is greater than average size carbide mixture called grain growth.
(1) gather recrystallization: mainly in liquid phase, this process is a solid phase sintering stage. Interface between WC particles increases, due to the diffusion bonding of polycrystalline WC particles into a larger particles, with the diffusion and grain boundary line of large particles gradually eliminate, the formation of large size of WC grain; The higher the temperature, sintering time and the greater the coalescence of recrystallization; Mixture, the smaller the grain size, the longer the wet milling, gathered at a speed of recrystallization, the greater the grew up and gather the recrystallization phenomenon, the more obvious.
(2) liquid recrystallization: in liquid phase sintered body, after some WC grain to dissolve in the liquid phase, and then in other precipitation on the grain, make the latter grew up, this is dissolved precipitation process, this process is very fierce, there are two reasons:
A, WC have larger solubility in liquid cobalt; B, the size of the WC grain uneven, uneven, gathered after recrystallization, produce a small amount of large grain WC; Uneven energy, because of the mixture was strong during the grain in wet grinding in deformation; Irregular shape, such as Angle and protruding parts, larger than the flat parts of energy; When there is liquid phase sintering, the tiny, high-energy first dissolving, has been saturated, the heat preservation time, dissolution and precipitation of WC, the cause of dynamic balance, the size of grain disappearing as a result, the coarse WC particle size increasing. Liquid recrystallization than gathered recrystallization process strongly.
2, the influence of WC grain growth factors:
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(1) the number of liquid: improve the sintering body liquid quantity of various factors, can promote the WC grain growth;
(2) sintering temperature: raise the temperature, make the WC increases the solubility and dissolution rate in the liquid phase, the WC particles increased obviously.
(3) the cobalt content: sintered body fluid phase quantity increases with increase of cobalt content;
(4) carbon content: sintering liquid phase increase with the increase of carbon content in the body, keep the liquid phase time extended, with the increase of carbon content of b improve the carbon content can promote the WC grain growth.
(5) mixture state: A, the smaller the original powder particles, grow up the more serious when sintering; B, the larger the size inhomogeneity, grow up the more serious (still uneven grew up); Grew up, the greater the degree C, grinding and the greater the tendency (still grew up uneven energy);
(6) additive: supplying the alloy with refractory metal carbides, can prevent the WC grain grew up uneven, in order to get the granularity of the fine grain of alloy; Because of adding carbide was adsorbed on the surface of WC particles, can reduce the surface of the WC, bring down the WC solubility in the liquid phase, hinder the WC dissolved in the liquid phase. Hinder recrystallization dissolution mechanism.
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(1) gather recrystallization: mainly in liquid phase, this process is a solid phase sintering stage. Interface between WC particles increases, due to the diffusion bonding of polycrystalline WC particles into a larger particles, with the diffusion and grain boundary line of large particles gradually eliminate, the formation of large size of WC grain; The higher the temperature, sintering time and the greater the coalescence of recrystallization; Mixture, the smaller the grain size, the longer the wet milling, gathered at a speed of recrystallization, the greater the grew up and gather the recrystallization phenomenon, the more obvious.
(2) liquid recrystallization: in liquid phase sintered body, after some WC grain to dissolve in the liquid phase, and then in other precipitation on the grain, make the latter grew up, this is dissolved precipitation process, this process is very fierce, there are two reasons:
A, WC have larger solubility in liquid cobalt; B, the size of the WC grain uneven, uneven, gathered after recrystallization, produce a small amount of large grain WC; Uneven energy, because of the mixture was strong during the grain in wet grinding in deformation; Irregular shape, such as Angle and protruding parts, larger than the flat parts of energy; When there is liquid phase sintering, the tiny, high-energy first dissolving, has been saturated, the heat preservation time, dissolution and precipitation of WC, the cause of dynamic balance, the size of grain disappearing as a result, the coarse WC particle size increasing. Liquid recrystallization than gathered recrystallization process strongly.
2, the influence of WC grain growth factors:
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(1) the number of liquid: improve the sintering body liquid quantity of various factors, can promote the WC grain growth;
(2) sintering temperature: raise the temperature, make the WC increases the solubility and dissolution rate in the liquid phase, the WC particles increased obviously.
(3) the cobalt content: sintered body fluid phase quantity increases with increase of cobalt content;
(4) carbon content: sintering liquid phase increase with the increase of carbon content in the body, keep the liquid phase time extended, with the increase of carbon content of b improve the carbon content can promote the WC grain growth.
(5) mixture state: A, the smaller the original powder particles, grow up the more serious when sintering; B, the larger the size inhomogeneity, grow up the more serious (still uneven grew up); Grew up, the greater the degree C, grinding and the greater the tendency (still grew up uneven energy);
(6) additive: supplying the alloy with refractory metal carbides, can prevent the WC grain grew up uneven, in order to get the granularity of the fine grain of alloy; Because of adding carbide was adsorbed on the surface of WC particles, can reduce the surface of the WC, bring down the WC solubility in the liquid phase, hinder the WC dissolved in the liquid phase. Hinder recrystallization dissolution mechanism.
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2014年1月22日星期三
The sintering waste in cemented carbide production.
1, peeling, alloy surface by edge crack, crack or become warped shell, serious when the scales of small thin skin, critical crack, even pulverization peeling;
Reason: due to the effect of contact of the briquetting of cobalt, decompose carbon gases in which the free carbon, resulting in briquetting strength decreased, resulting in a peeling.
Take the following measures to prevent peeling:
(1) the increase of hydrogen flow rate, lower water content in the hydrogen;
(2) reduce the subjective quantity, strictly control the forming agent addition amount;
(3) open the oven door sintering, the furnace air flow is laminar state;
(4) the guiding strictly control the furnace temperature, slow speed, decompose completely forming agent in the area;
(5) the boat close to block, or sprinkle a thick layer of packing, or reduce the amount of products on either side of the boat forward end;
2, drum up bubble: alloy products internal holes, and on the surface of its corresponding parts of a convex surface, this phenomenon is called drum up bubble;
Reason: there is a concentration of gas, sintered body usually has two kinds:
(1), gathered in the sintering process, the body in the process of sintering shrinkage, air from inside to the surface. If the sintered body has a certain size of impurities, such as alloy scrap, scrap iron, cobalt scrap, air to focus here already, until the liquid phase sintered body appeared, and densification, unable to discharge air, at least resistance of sintered body surface drum up bubble;
(2) the sintered body has generated a large amount of gas chemical reaction, when some oxide sintered body, in the event of a liquid phase after the reduction, the generated gas, this makes the products drum up bubble; WC - CO alloy is generally caused by a mixture of oxide agglomerate.
The porosity of the 3 holes: 40 microns called holes. Can lead to drum up bubble factors, all can form holes, just don't like drum up a large number of gas bubble, in addition, in the presence of sintered body to melt the metal wetting of impurities, such as "not good" pressure of big hole, or solid phase liquid phase sintered body exists serious segregation, can form the hole.
4, organization is not uniform: mixing.
5, deformation: sintered body appears irregular appearance change is called deformation.
(1) the uneven distribution of briquette density: because alloy density is the same;
(2) local severe lack of carbon sintered body: because of the lack of carbon liquid relatively reduced;
(3) the boat is not reasonable; Plate uneven;
6, crack:
(1) suppression of crack: because the briquetting dry stress relaxed didn't immediately, according to elastic recovery faster when sintering.
(2) oxide crack: because briquetting dry some serious oxidation, the oxidation thermal expansion volume and the oxidation of the different parts;
7, "dirty" : alloy fracture on the loose area called "dirty".
The reason: low carbon and high carbon is not appropriate. Factors that influence the carbon content of the sintered body, will influence the formation of a "dirty";
8, burnt: when the sintering temperature on the high side or holding time is too long can produce product burnt. Burnt products, make the grain coarsening, porosity increases, alloy performance significantly decreased. Owe to burn products metallic luster is not obvious, just burn can return.
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Reason: due to the effect of contact of the briquetting of cobalt, decompose carbon gases in which the free carbon, resulting in briquetting strength decreased, resulting in a peeling.
Take the following measures to prevent peeling:
(1) the increase of hydrogen flow rate, lower water content in the hydrogen;
(2) reduce the subjective quantity, strictly control the forming agent addition amount;
(3) open the oven door sintering, the furnace air flow is laminar state;
(4) the guiding strictly control the furnace temperature, slow speed, decompose completely forming agent in the area;
(5) the boat close to block, or sprinkle a thick layer of packing, or reduce the amount of products on either side of the boat forward end;
2, drum up bubble: alloy products internal holes, and on the surface of its corresponding parts of a convex surface, this phenomenon is called drum up bubble;
Reason: there is a concentration of gas, sintered body usually has two kinds:
(1), gathered in the sintering process, the body in the process of sintering shrinkage, air from inside to the surface. If the sintered body has a certain size of impurities, such as alloy scrap, scrap iron, cobalt scrap, air to focus here already, until the liquid phase sintered body appeared, and densification, unable to discharge air, at least resistance of sintered body surface drum up bubble;
(2) the sintered body has generated a large amount of gas chemical reaction, when some oxide sintered body, in the event of a liquid phase after the reduction, the generated gas, this makes the products drum up bubble; WC - CO alloy is generally caused by a mixture of oxide agglomerate.
The porosity of the 3 holes: 40 microns called holes. Can lead to drum up bubble factors, all can form holes, just don't like drum up a large number of gas bubble, in addition, in the presence of sintered body to melt the metal wetting of impurities, such as "not good" pressure of big hole, or solid phase liquid phase sintered body exists serious segregation, can form the hole.
4, organization is not uniform: mixing.
5, deformation: sintered body appears irregular appearance change is called deformation.
(1) the uneven distribution of briquette density: because alloy density is the same;
(2) local severe lack of carbon sintered body: because of the lack of carbon liquid relatively reduced;
(3) the boat is not reasonable; Plate uneven;
6, crack:
(1) suppression of crack: because the briquetting dry stress relaxed didn't immediately, according to elastic recovery faster when sintering.
(2) oxide crack: because briquetting dry some serious oxidation, the oxidation thermal expansion volume and the oxidation of the different parts;
7, "dirty" : alloy fracture on the loose area called "dirty".
The reason: low carbon and high carbon is not appropriate. Factors that influence the carbon content of the sintered body, will influence the formation of a "dirty";
8, burnt: when the sintering temperature on the high side or holding time is too long can produce product burnt. Burnt products, make the grain coarsening, porosity increases, alloy performance significantly decreased. Owe to burn products metallic luster is not obvious, just burn can return.
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