In addition, high titanium content (0.096%) will cause hot cracks when cutting castings. But the D-type graphite cast iron with titanium has good oxidation resistance, growth resistance and thermal fatigue resistance. Compared with common CrMoCu cast iron, the service life can be increased by 3 times at 500 ~ 700 ℃. Titanium is strictly prohibited as an interfering element in nodular cast iron.
But in some vermicular cast iron, titanium is added to the creep agent as a useful element to expand the scope of creep treatment. Under the condition of high carbon equivalent, microtitanium alloy can improve the strength and hardness of gray cast iron, and improve the uniformity of section. A small amount of titanium can also neutralize excessive nitrogen in cast iron to reduce the frequency of fractured nitrogen pores. The role of titanium in cast iron has both advantages and disadvantages. In this paper, the effects of titanium on graphite morphology and mechanical properties of middle and low carbon equivalent gray cast iron under different molding conditions were studied by experiments, and the effects of different titanium content on the densification of gray cast iron were quantitatively analyzed.
Test conditions and methods
Because titanium can increase the mechanical properties of high carbon equivalent gray cast iron, this experiment selected middle and low carbon equivalent gray cast iron as the object to study the change of casting structure under different sand type conditions. The test uses 250kg medium-frequency induction furnace melting, the ratio of charge: Z14 pig iron 40%, return charge 30%, scrap 30%, part of the carburizing agent and chromium, copper alloy. The temperature is measured by immersion thermocouple, the iron output temperature is 1500 ~ 1530 ℃, the pouring temperature is 1360 ~ 1400 ℃, and the inoculating treatment of 75 ferrosilicon with 0.5% adding amount is adopted before the furnace.
The castings are molded with water glass sand and clay coal silt respectively. The clay sand properties are controlled in the following parameters: moisture 4.0% ~ 5.0%, compactness 50% ~ 70%, air permeability 120-130, wet compressive strength 0.12 ~ 0.14MPa. Sand mold hardness is controlled between 65 and 85, plane hardness is in the upper limit, elevation hardness is around the middle limit. The mechanical property samples were made of sodium silicate sand, and the inner cavity with a diameter of 30 mm was made of alcohol based paint.
Figure 1 Casting structure and process
Test content and result analysis
1. Influence of titanium on microstructure and mechanical properties of gray cast iron
Titanium can increase the austenite core and refine the primary austenite grain in gray cast iron. American Association of Foundry Workers data pointed out: for cast iron titanium can play the role of graphitizing agent and reducing agent, but also can refine grain, improve the tensile strength and bending strength of cast iron. When the residual titanium content is 0.08% ~ 0.25%, the tensile strength of cast iron with high carbon equivalent can be increased, while the strength of cast iron with low carbon equivalent can be decreased. However, the discussion does not point out the influence of titanium on the middle carbon equivalent gray cast iron, so the test is carried out from the middle and low carbon equivalent gray cast iron. Scheme: 3 to 4 boxes of liquid iron were poured in each furnace for comparison. The first box generally adopted basic HT250 liquid iron composition, only adding inoculated agent without adding titanium alloy. The second to fourth boxes added titanium alloy with different contents, and the alloys were added into the furnace successively. Each pack pours 2 ~ 4 test rods and 1 box of castings.
The first two castings were made of water glass sand, and the last two were made of clay and coal silt.
The comparison of the average mechanical properties of the four tests shows that the average strength of the first and second tests decreases with the increase of titanium content, while the average strength of the third and fourth tests increases with the increase of titanium content. This is because the addition of titanium increases the supercooling tendency of liquid iron. The titanium content of the first two tests is relatively low, and there is less type A and type D graphite and more type E graphite in the test rod structure, resulting in a decrease in strength. In particular, the carbon equivalent of the first test was the lowest and the strength decreased the most, up to 41 MPa. The titanium content of the last two tests was relatively high, and there were more type A and type D graphite and less type E graphite in the test rod structure, resulting in increased strength. In addition, the overall strength of the third test is relatively high because the Si/C of the three samples is between 0.72% and 0.76%. The results show that the mechanical properties of titanium-bearing cast iron can be significantly improved when Si/C ≥ 0.64%.
In the fourth test, the titanium content in liquid iron is 0.11%, and the average increase of the test rod is 17MPa. This is because more than 90% of the high titanium test rod structure is D-type graphite, so the mechanical properties are increased. Because of the fast cooling of the castings using clay wet molding sand, a large amount of D-type graphite is generated in the hot joint of the castings. Due to the effect of chromium and copper alloys, the pearlite content in the matrix of most thick D-shaped castings is more than 90%, which offsets the influence of D-type graphite on the matrix structure.
The experimental results show that, in the dry mold casting with low titanium content, the undercooling tendency of liquid iron is small, and type A and type E graphite are mostly produced. However, with the increase of titanium content, the undercooling tendency is increased, which promotes the increase of D-type graphite. When the D-type graphite is more than 90%, the mechanical properties of the casting are obviously improved. Due to the large tendency of wet sand to undercool and the increase of titanium content, a large amount of D-type graphite also appears in the thick hot joint of the casting.
Titanium increases the supercooling tendency of gray cast iron liquid iron, resulting in a large number of branches of graphite, and a large number of short, curved D-type graphite shortens the diffusion distance of carbon, so that the austenite near the graphite is converted into ferrite during the cooling process of castings, resulting in the decrease of mechanical properties. However, because of the large number of austenitic dendrites and the small D-type graphite, the matrix cleavage is small. In addition, the D-type graphite eutectic group has a good spheroid shape, and compared with the same matrix of cast iron, D-type graphite eutectic group has higher strength.
2. Influence of titanium and aluminum on densification
The titanium brought in by pig iron or scrap in smelting not only affects the workability of gray cast iron, but also affects the compactness of castings. By adding a certain amount of ferrotitanium, the probability of shrinkage of gray iron parts under different titanium content was studied. Since titanium alloy contains a certain amount of aluminum, and a certain amount of aluminum may also affect the shrinkage of castings, the factor of aluminum is taken into account in the analysis of influencing factors and chemical testing.
Smelting using the main charge ratio: pig iron 45%, return charge 20%, scrap steel 35% and part of the high temperature graphitization carburizer. 3 ~ 4 boxes of castings were poured at the same time in each furnace, so as to analyze the probability of shrinkage and loosening of castings.
The comparative test results of different titanium contents show that there is no internal shrinkage in gray cast iron with lower titanium content, and the surface shrinkage is lighter. With the increase of titanium content, the probability of internal shrinkage in cast iron is increasing. At 0.056% Ti and 0.016% Al, the shrinkage probability is only 50%. When the content of titanium and aluminum in gray cast iron reaches 0.17% and 0.023%, the probability of internal shrinkage is 75%. At this time, not only the hot joint part of the casting appears shrinkage loosening, but also the non-hot joint and small hot joint part. The shrinkage and loosening characteristics of different parts of the casting are shown in Figure 5 and Figure 6.
There is no clear mechanism analysis on the cause of shrinkage and porosity of titanium. As for the influence of aluminum, the data indicate that the increase of aluminum content in liquid iron reacts with the inoculant and water molecules in wet sand under the action of hot liquid iron to form hydrogen. The hydrogen content of the metal liquid is high, and the dissolved hydrogen in the residual liquid phase is constantly enriched during the solidification process, so that the hydrogen content in the liquid phase is higher in the isolated small molten pool. When the small molten pool changes from liquid phase to solid phase, the volume loss occurs at the same time, dissolved hydrogen will also precipitate and occupy the space of the small molten pool, becoming the precipitation pore. At this time, the intergranular porosity and hydrogen precipitated porosity defects are symbiotic and difficult to distinguish. Therefore, in order to eliminate intergranular shrinkage, it is necessary to take measures to prevent pore precipitation and reduce the hydrogen content of metal liquid as far as possible. Therefore, the combined action of titanium and aluminum is easy to form the complex defects of microporosity and microporosity.
The results show that the gray cast iron under the condition of 3.65% ~ 3.85% CE:
(1) A certain amount of titanium increased the supercooling tendency of liquid iron and promoted the formation of D-type graphite in gray cast iron. The D-type graphite in wet sand was significantly more than that in dry sand.
(2) With the increase of titanium content in liquid iron, the D-type graphite in gray cast iron increases continuously. When the D-type graphite reaches a high proportion, the thick and large hot joints in castings also appear a large number of D-type graphite, and the mechanical properties of castings with high carbon equivalent and silicon-carbon ratios increase obviously. When the carbon equivalent decreases to 3.66%, the strength decreases greatly with the increase of titanium content.
(3) With the increase of titanium and aluminum content, the densification of gray cast iron decreases and the shrinkage probability increases obviously. When Ti is 0.17% and Al is 0.023%, the shrinkage probability of the ash casting is 70%.
What is the influence of titanium on the quality of gray iron castings
Under the condition of high carbon equivalent (above 4.10% CE), a small amount of titanium can improve the mechanical properties of gray cast iron and improve the uniformity of different sections. The effects of titanium content on microstructure, mechanical properties and densification of gray cast iron were studied in the medium and low carbon equivalent (3.65% ~ 3.85% CE) condition.
The results show that titanium promotes the formation of D-type graphite in cast iron. When D type graphite reaches a certain proportion, especially when Si/C is high, its mechanical properties increase obviously. With the increase of the amount of titanium and aluminum, the densification of gray cast iron decreases and the probability of shrinkage increases.This is Titanium seamless Tube.
In the production process of cast iron, with the mass use of metal charges such as pig iron and scrap steel, titanium more or less enters the liquid iron. A large number of research data indicate that most titanium compounds exist in the metal matrix after the addition of titanium in gray cast iron, but some titanium nitrides or carbonitrides exist in the ferrite and graphite interfacial layer. Titanium compounds with hardness of 3200 HV or higher greatly reduce the machinability of cast iron.
In addition, high titanium content (0.096%) will cause hot cracks when cutting castings. But the D-type graphite cast iron with titanium has good oxidation resistance, growth resistance and thermal fatigue resistance. Compared with common CrMoCu cast iron, the service life can be increased by 3 times at 500 ~ 700 ℃. Titanium is strictly prohibited as an interfering element in nodular cast iron.
But in some vermicular cast iron, titanium is added to the creep agent as a useful element to expand the scope of creep treatment. Under the condition of high carbon equivalent, microtitanium alloy can improve the strength and hardness of gray cast iron, and improve the uniformity of section. A small amount of titanium can also neutralize excessive nitrogen in cast iron to reduce the frequency of fractured nitrogen pores. The role of titanium in cast iron has both advantages and disadvantages. In this paper, the effects of titanium on graphite morphology and mechanical properties of middle and low carbon equivalent gray cast iron under different molding conditions were studied by experiments, and the effects of different titanium content on the densification of gray cast iron were quantitatively analyzed.
Test conditions and methods
Because titanium can increase the mechanical properties of high carbon equivalent gray cast iron, this experiment selected middle and low carbon equivalent gray cast iron as the object to study the change of casting structure under different sand type conditions. The test uses 250kg medium-frequency induction furnace melting, the ratio of charge: Z14 pig iron 40%, return charge 30%, scrap 30%, part of the carburizing agent and chromium, copper alloy. The temperature is measured by immersion thermocouple, the iron output temperature is 1500 ~ 1530 ℃, the pouring temperature is 1360 ~ 1400 ℃, and the inoculating treatment of 75 ferrosilicon with 0.5% adding amount is adopted before the furnace.
The castings are molded with water glass sand and clay coal silt respectively. The clay sand properties are controlled in the following parameters: moisture 4.0% ~ 5.0%, compactness 50% ~ 70%, air permeability 120-130, wet compressive strength 0.12 ~ 0.14MPa. Sand mold hardness is controlled between 65 and 85, plane hardness is in the upper limit, elevation hardness is around the middle limit. The mechanical property samples were made of sodium silicate sand, and the inner cavity with a diameter of 30 mm was made of alcohol based paint.
Figure 1 Casting structure and process
Test content and result analysis
1. Influence of titanium on microstructure and mechanical properties of gray cast iron
Titanium can increase the austenite core and refine the primary austenite grain in gray cast iron. American Association of Foundry Workers data pointed out: for cast iron titanium can play the role of graphitizing agent and reducing agent, but also can refine grain, improve the tensile strength and bending strength of cast iron. When the residual titanium content is 0.08% ~ 0.25%, the tensile strength of cast iron with high carbon equivalent can be increased, while the strength of cast iron with low carbon equivalent can be decreased. However, the discussion does not point out the influence of titanium on the middle carbon equivalent gray cast iron, so the test is carried out from the middle and low carbon equivalent gray cast iron. Scheme: 3 to 4 boxes of liquid iron were poured in each furnace for comparison. The first box generally adopted basic HT250 liquid iron composition, only adding inoculated agent without adding titanium alloy. The second to fourth boxes added titanium alloy with different contents, and the alloys were added into the furnace successively. Each pack pours 2 ~ 4 test rods and 1 box of castings.
The first two castings were made of water glass sand, and the last two were made of clay and coal silt.
The comparison of the average mechanical properties of the four tests shows that the average strength of the first and second tests decreases with the increase of titanium content, while the average strength of the third and fourth tests increases with the increase of titanium content. This is because the addition of titanium increases the supercooling tendency of liquid iron. The titanium content of the first two tests is relatively low, and there is less type A and type D graphite and more type E graphite in the test rod structure, resulting in a decrease in strength. In particular, the carbon equivalent of the first test was the lowest and the strength decreased the most, up to 41 MPa. The titanium content of the last two tests was relatively high, and there were more type A and type D graphite and less type E graphite in the test rod structure, resulting in increased strength. In addition, the overall strength of the third test is relatively high because the Si/C of the three samples is between 0.72% and 0.76%. The results show that the mechanical properties of titanium-bearing cast iron can be significantly improved when Si/C ≥ 0.64%.
In the fourth test, the titanium content in liquid iron is 0.11%, and the average increase of the test rod is 17MPa. This is because more than 90% of the high titanium test rod structure is D-type graphite, so the mechanical properties are increased. Because of the fast cooling of the castings using clay wet molding sand, a large amount of D-type graphite is generated in the hot joint of the castings. Due to the effect of chromium and copper alloys, the pearlite content in the matrix of most thick D-shaped castings is more than 90%, which offsets the influence of D-type graphite on the matrix structure.
The experimental results show that, in the dry mold casting with low titanium content, the undercooling tendency of liquid iron is small, and type A and type E graphite are mostly produced. However, with the increase of titanium content, the undercooling tendency is increased, which promotes the increase of D-type graphite. When the D-type graphite is more than 90%, the mechanical properties of the casting are obviously improved. Due to the large tendency of wet sand to undercool and the increase of titanium content, a large amount of D-type graphite also appears in the thick hot joint of the casting.
Titanium increases the supercooling tendency of gray cast iron liquid iron, resulting in a large number of branches of graphite, and a large number of short, curved D-type graphite shortens the diffusion distance of carbon, so that the austenite near the graphite is converted into ferrite during the cooling process of castings, resulting in the decrease of mechanical properties. However, because of the large number of austenitic dendrites and the small D-type graphite, the matrix cleavage is small. In addition, the D-type graphite eutectic group has a good spheroid shape, and compared with the same matrix of cast iron, D-type graphite eutectic group has higher strength.
2. Influence of titanium and aluminum on densification
The titanium brought in by pig iron or scrap in smelting not only affects the workability of gray cast iron, but also affects the compactness of castings. By adding a certain amount of ferrotitanium, the probability of shrinkage of gray iron parts under different titanium content was studied. Since titanium alloy contains a certain amount of aluminum, and a certain amount of aluminum may also affect the shrinkage of castings, the factor of aluminum is taken into account in the analysis of influencing factors and chemical testing.
Smelting using the main charge ratio: pig iron 45%, return charge 20%, scrap steel 35% and part of the high temperature graphitization carburizer. 3 ~ 4 boxes of castings were poured at the same time in each furnace, so as to analyze the probability of shrinkage and loosening of castings.
The comparative test results of different titanium contents show that there is no internal shrinkage in gray cast iron with lower titanium content, and the surface shrinkage is lighter. With the increase of titanium content, the probability of internal shrinkage in cast iron is increasing. At 0.056% Ti and 0.016% Al, the shrinkage probability is only 50%. When the content of titanium and aluminum in gray cast iron reaches 0.17% and 0.023%, the probability of internal shrinkage is 75%. At this time, not only the hot joint part of the casting appears shrinkage loosening, but also the non-hot joint and small hot joint part. The shrinkage and loosening characteristics of different parts of the casting are shown in Figure 5 and Figure 6.
There is no clear mechanism analysis on the cause of shrinkage and porosity of titanium. As for the influence of aluminum, the data indicate that the increase of aluminum content in liquid iron reacts with the inoculant and water molecules in wet sand under the action of hot liquid iron to form hydrogen. The hydrogen content of the metal liquid is high, and the dissolved hydrogen in the residual liquid phase is constantly enriched during the solidification process, so that the hydrogen content in the liquid phase is higher in the isolated small molten pool. When the small molten pool changes from liquid phase to solid phase, the volume loss occurs at the same time, dissolved hydrogen will also precipitate and occupy the space of the small molten pool, becoming the precipitation pore. At this time, the intergranular porosity and hydrogen precipitated porosity defects are symbiotic and difficult to distinguish. Therefore, in order to eliminate intergranular shrinkage, it is necessary to take measures to prevent pore precipitation and reduce the hydrogen content of metal liquid as far as possible. Therefore, the combined action of titanium and aluminum is easy to form the complex defects of microporosity and microporosity.
The results show that the gray cast iron under the condition of 3.65% ~ 3.85% CE:
(1) A certain amount of titanium increased the supercooling tendency of liquid iron and promoted the formation of D-type graphite in gray cast iron. The D-type graphite in wet sand was significantly more than that in dry sand.
(2) With the increase of titanium content in liquid iron, the D-type graphite in gray cast iron increases continuously. When the D-type graphite reaches a high proportion, the thick and large hot joints in castings also appear a large number of D-type graphite, and the mechanical properties of castings with high carbon equivalent and silicon-carbon ratios increase obviously. When the carbon equivalent decreases to 3.66%, the strength decreases greatly with the increase of titanium content.
(3) With the increase of titanium and aluminum content, the densification of gray cast iron decreases and the shrinkage probability increases obviously. When Ti is 0.17% and Al is 0.023%, the shrinkage probability of the ash casting is 70%.
In addition, high titanium content (0.096%) will cause hot cracks when cutting castings. But the D-type graphite cast iron with titanium has good oxidation resistance, growth resistance and thermal fatigue resistance. Compared with common CrMoCu cast iron, the service life can be increased by 3 times at 500 ~ 700 ℃. Titanium is strictly prohibited as an interfering element in nodular cast iron.
But in some vermicular cast iron, titanium is added to the creep agent as a useful element to expand the scope of creep treatment. Under the condition of high carbon equivalent, microtitanium alloy can improve the strength and hardness of gray cast iron, and improve the uniformity of section. A small amount of titanium can also neutralize excessive nitrogen in cast iron to reduce the frequency of fractured nitrogen pores. The role of titanium in cast iron has both advantages and disadvantages. In this paper, the effects of titanium on graphite morphology and mechanical properties of middle and low carbon equivalent gray cast iron under different molding conditions were studied by experiments, and the effects of different titanium content on the densification of gray cast iron were quantitatively analyzed.
Test conditions and methods
Because titanium can increase the mechanical properties of high carbon equivalent gray cast iron, this experiment selected middle and low carbon equivalent gray cast iron as the object to study the change of casting structure under different sand type conditions. The test uses 250kg medium-frequency induction furnace melting, the ratio of charge: Z14 pig iron 40%, return charge 30%, scrap 30%, part of the carburizing agent and chromium, copper alloy. The temperature is measured by immersion thermocouple, the iron output temperature is 1500 ~ 1530 ℃, the pouring temperature is 1360 ~ 1400 ℃, and the inoculating treatment of 75 ferrosilicon with 0.5% adding amount is adopted before the furnace.
The castings are molded with water glass sand and clay coal silt respectively. The clay sand properties are controlled in the following parameters: moisture 4.0% ~ 5.0%, compactness 50% ~ 70%, air permeability 120-130, wet compressive strength 0.12 ~ 0.14MPa. Sand mold hardness is controlled between 65 and 85, plane hardness is in the upper limit, elevation hardness is around the middle limit. The mechanical property samples were made of sodium silicate sand, and the inner cavity with a diameter of 30 mm was made of alcohol based paint.
Figure 1 Casting structure and process
Test content and result analysis
1. Influence of titanium on microstructure and mechanical properties of gray cast iron
Titanium can increase the austenite core and refine the primary austenite grain in gray cast iron. American Association of Foundry Workers data pointed out: for cast iron titanium can play the role of graphitizing agent and reducing agent, but also can refine grain, improve the tensile strength and bending strength of cast iron. When the residual titanium content is 0.08% ~ 0.25%, the tensile strength of cast iron with high carbon equivalent can be increased, while the strength of cast iron with low carbon equivalent can be decreased. However, the discussion does not point out the influence of titanium on the middle carbon equivalent gray cast iron, so the test is carried out from the middle and low carbon equivalent gray cast iron. Scheme: 3 to 4 boxes of liquid iron were poured in each furnace for comparison. The first box generally adopted basic HT250 liquid iron composition, only adding inoculated agent without adding titanium alloy. The second to fourth boxes added titanium alloy with different contents, and the alloys were added into the furnace successively. Each pack pours 2 ~ 4 test rods and 1 box of castings.
The first two castings were made of water glass sand, and the last two were made of clay and coal silt.
The comparison of the average mechanical properties of the four tests shows that the average strength of the first and second tests decreases with the increase of titanium content, while the average strength of the third and fourth tests increases with the increase of titanium content. This is because the addition of titanium increases the supercooling tendency of liquid iron. The titanium content of the first two tests is relatively low, and there is less type A and type D graphite and more type E graphite in the test rod structure, resulting in a decrease in strength. In particular, the carbon equivalent of the first test was the lowest and the strength decreased the most, up to 41 MPa. The titanium content of the last two tests was relatively high, and there were more type A and type D graphite and less type E graphite in the test rod structure, resulting in increased strength. In addition, the overall strength of the third test is relatively high because the Si/C of the three samples is between 0.72% and 0.76%. The results show that the mechanical properties of titanium-bearing cast iron can be significantly improved when Si/C ≥ 0.64%.
In the fourth test, the titanium content in liquid iron is 0.11%, and the average increase of the test rod is 17MPa. This is because more than 90% of the high titanium test rod structure is D-type graphite, so the mechanical properties are increased. Because of the fast cooling of the castings using clay wet molding sand, a large amount of D-type graphite is generated in the hot joint of the castings. Due to the effect of chromium and copper alloys, the pearlite content in the matrix of most thick D-shaped castings is more than 90%, which offsets the influence of D-type graphite on the matrix structure.
The experimental results show that, in the dry mold casting with low titanium content, the undercooling tendency of liquid iron is small, and type A and type E graphite are mostly produced. However, with the increase of titanium content, the undercooling tendency is increased, which promotes the increase of D-type graphite. When the D-type graphite is more than 90%, the mechanical properties of the casting are obviously improved. Due to the large tendency of wet sand to undercool and the increase of titanium content, a large amount of D-type graphite also appears in the thick hot joint of the casting.
Titanium increases the supercooling tendency of gray cast iron liquid iron, resulting in a large number of branches of graphite, and a large number of short, curved D-type graphite shortens the diffusion distance of carbon, so that the austenite near the graphite is converted into ferrite during the cooling process of castings, resulting in the decrease of mechanical properties. However, because of the large number of austenitic dendrites and the small D-type graphite, the matrix cleavage is small. In addition, the D-type graphite eutectic group has a good spheroid shape, and compared with the same matrix of cast iron, D-type graphite eutectic group has higher strength.
2. Influence of titanium and aluminum on densification
The titanium brought in by pig iron or scrap in smelting not only affects the workability of gray cast iron, but also affects the compactness of castings. By adding a certain amount of ferrotitanium, the probability of shrinkage of gray iron parts under different titanium content was studied. Since titanium alloy contains a certain amount of aluminum, and a certain amount of aluminum may also affect the shrinkage of castings, the factor of aluminum is taken into account in the analysis of influencing factors and chemical testing.
Smelting using the main charge ratio: pig iron 45%, return charge 20%, scrap steel 35% and part of the high temperature graphitization carburizer. 3 ~ 4 boxes of castings were poured at the same time in each furnace, so as to analyze the probability of shrinkage and loosening of castings.
The comparative test results of different titanium contents show that there is no internal shrinkage in gray cast iron with lower titanium content, and the surface shrinkage is lighter. With the increase of titanium content, the probability of internal shrinkage in cast iron is increasing. At 0.056% Ti and 0.016% Al, the shrinkage probability is only 50%. When the content of titanium and aluminum in gray cast iron reaches 0.17% and 0.023%, the probability of internal shrinkage is 75%. At this time, not only the hot joint part of the casting appears shrinkage loosening, but also the non-hot joint and small hot joint part. The shrinkage and loosening characteristics of different parts of the casting are shown in Figure 5 and Figure 6.
There is no clear mechanism analysis on the cause of shrinkage and porosity of titanium. As for the influence of aluminum, the data indicate that the increase of aluminum content in liquid iron reacts with the inoculant and water molecules in wet sand under the action of hot liquid iron to form hydrogen. The hydrogen content of the metal liquid is high, and the dissolved hydrogen in the residual liquid phase is constantly enriched during the solidification process, so that the hydrogen content in the liquid phase is higher in the isolated small molten pool. When the small molten pool changes from liquid phase to solid phase, the volume loss occurs at the same time, dissolved hydrogen will also precipitate and occupy the space of the small molten pool, becoming the precipitation pore. At this time, the intergranular porosity and hydrogen precipitated porosity defects are symbiotic and difficult to distinguish. Therefore, in order to eliminate intergranular shrinkage, it is necessary to take measures to prevent pore precipitation and reduce the hydrogen content of metal liquid as far as possible. Therefore, the combined action of titanium and aluminum is easy to form the complex defects of microporosity and microporosity.
The results show that the gray cast iron under the condition of 3.65% ~ 3.85% CE:
(1) A certain amount of titanium increased the supercooling tendency of liquid iron and promoted the formation of D-type graphite in gray cast iron. The D-type graphite in wet sand was significantly more than that in dry sand.
(2) With the increase of titanium content in liquid iron, the D-type graphite in gray cast iron increases continuously. When the D-type graphite reaches a high proportion, the thick and large hot joints in castings also appear a large number of D-type graphite, and the mechanical properties of castings with high carbon equivalent and silicon-carbon ratios increase obviously. When the carbon equivalent decreases to 3.66%, the strength decreases greatly with the increase of titanium content.
(3) With the increase of titanium and aluminum content, the densification of gray cast iron decreases and the shrinkage probability increases obviously. When Ti is 0.17% and Al is 0.023%, the shrinkage probability of the ash casting is 70%.