Background
The automobile brake drum is an important part of an automobile running system, and plays a role in guaranteeing the safety performance of the whole automobile. At present, the quality of brake drums is low due to the influence of competition and profits of domestic commercial vehicle brake drum manufacturers, the investment of deep research on the brake drums is low, the service life of the domestic brake drums is generally short, and particularly in mountainous areas needing frequent braking, the service life of the brake drums is generally short; the frequent replacement of the brake drum not only wastes a great deal of financial resources and material resources, but also can cause serious accidents of vehicle damage and people death due to the failure of the brake drum in the driving process of the automobile. Therefore, the improvement of the material performance of the brake drum, the improvement of the service life and the service reliability are the common concerns of the automobile industry and the casting industry.
Basic requirements of the automobile brake drum on the material are as follows: 1) the brake drum bears strong mechanical impact during braking, and the brake drum is required to have high enough mechanical performance; 2) when the brake is used, kinetic energy is quickly converted into heat energy through dry-slip friction and is quickly dissipated, and the brake drum is required to have good heat conductivity; 3) frequent braking or long-time braking causes more cold and hot cycle times of the brake drum, sometimes the temperature is higher, water is needed to chill for cooling, and the brake drum is required to have good thermal fatigue performance; 4) when in braking, the friction between the inner circle surface (friction surface) of the brake drum and the friction plate of the brake shoe is used for braking, and the brake drum is required to have good wear resistance and anti-engagement capacity; 5) modern automobiles pursue riding comfort, require reduced vibration and noise when braking, require the brake drum to be dimensionally stable, have uniform internal organization and have good shock absorption.
The gray cast iron has the advantages of excellent thermal conductivity, low elastic modulus, good shock absorption, higher strength and better wear resistance, and is still the first choice for the material of the automobile brake drum until now. However, with the increasing of the speed of the automobile and the increasing of the load capacity of the commercial vehicle, the kinetic energy of the automobile movement is increased continuously, and the thermal shock generated during braking is also increased greatly, so that the early failure of the brake drum is frequent, and the cracking are increased rapidly. In order to prolong the service life of the brake drum, the thermal conductivity of the material is improved on the premise of ensuring certain strength, so that the thermal fatigue performance of the brake drum is improved; the improvement of the heat conductivity of the gray cast iron requires more flake graphite with larger size and uniformity, and the mechanical property is reduced due to more and larger graphite tissues; the mechanical property can be effectively improved by adding alloy elements, but the graphite is shortened and reduced, the content of carbide is increased, and the heat-conducting property is reduced.
Some gray cast iron materials of the brake drum used in the current market are often added with some alloy elements such as Mo, Cu, Sn and the like in order to improve the mechanical property of the gray cast iron brake drum, but the thermal fatigue property of the gray cast iron brake drum cannot be obviously improved, and the service life of the brake drum is not obviously prolonged; in order to improve the heat-conducting property, some brake drum manufacturers improve the carbon addition, but because the influence of factors such as thick graphite, carbide, impurities and the like, the tensile strength is lower, and the service life of the brake drum is not obviously prolonged.
Disclosure of Invention
Aiming at the problems of short service life, poor heat conductivity and poor thermal fatigue performance of an automobile brake drum in the prior art, the invention provides a gray cast iron material for a commercial automobile brake drum and a preparation method thereof.
The invention is realized by the following technical scheme:
the gray cast iron material for the brake drum of the commercial vehicle comprises the following components in percentage by weight: 3.7 to 3.9% of C, 1.6 to 2.0% of Si, 0.5 to 0.7% of Mn, 0.05 to 0.1% of S, 0.5 to 0.7% of Cu, 0.1 to 0.3% of Cr, 0.07 to 0.1% of V, 0.05 to 0.1% of Sn, 0.01 to 0.04% of Zr, 0.007 to 0.01% of La, and the balance of Fe and inevitable impurities.
Further, the gray cast iron material for the brake drum of the commercial vehicle comprises the following components in percentage by weight: 3.75 to 3.85% of C, 1.7 to 1.9% of Si, 0.55 to 0.65% of Mn, 0.07 to 0.09% of S, 0.5 to 0.6% of Cu, 0.15 to 0.25% of Cr, 0.08 to 0.09% of V, 0.06 to 0.09% of Sn, 0.02 to 0.03% of Zr, 0.008 to 0.009% of La, and the balance of Fe and inevitable impurities.
Further, the gray cast iron material for the brake drum of the commercial vehicle comprises the following components in percentage by weight: 3.8% of C, 1.8% of Si, 0.61% of Mn, 0.08% of S, 0.55% of Cu, 0.19% of Cr, 0.085% of V, 0.08% of Sn, 0.025% of Zr, 0.008% of La and the balance of Fe.
The invention discloses a preparation method of a gray cast iron material for a brake drum of a commercial vehicle, which is characterized by comprising the following steps of:
(1) preparing raw materials according to a formula, and smelting the raw materials to obtain liquid raw materials;
(2) heating the liquid raw material to 1500-;
(3) pouring the base iron into a casting ladle, adding an inoculant when the base iron is discharged, and carrying out inoculation on the base iron for 2-5 min to obtain the base iron;
(4) and pouring the molten iron at 1370-1430 ℃, and simultaneously adding an inoculant to perform stream inoculation to obtain the gray cast iron material for the brake drum of the commercial vehicle.
Further, the pretreating agent in the step (2) is SiC, the inoculant in the step (3) is SiMnZr inoculant, and the inoculant in the step (4) is SiLa inoculant.
Further, the adding amount of the pretreatment agent in the step (2) is 0.1-0.2% of the weight of the liquid raw material, and the pretreatment temperature is 1500-1530 ℃; the addition amount of the inoculant in the step (3) is 0.4-0.5% of the weight of molten iron, and the inoculation treatment temperature is 1480-1500 ℃; the addition amount of the inoculant in the step (4) is 0.06-0.10% of the weight of the molten iron, and the inoculation treatment temperature is 1370-1430 ℃.
Further, the inoculant in the step (3) is added into the molten iron in a stream inoculation and/or flushing inoculation mode.
The invention relates to a gray cast iron material for a brake drum of a commercial vehicle and a manufacturing method thereof, on the basis of improving the carbon content and adding proper amount of Cr and V elements, measures such as molten iron pretreatment, reinforced inoculation and the like are taken, carbon is an element for strongly promoting graphitization, a certain amount of flake graphite is required in the structure of a casting with special performance (heat resistance and wear resistance) of the brake drum, and the heat conductivity and wear resistance of the material can be improved by adding the flake graphite; the content of C is too high, the graphite in the cast iron becomes coarse, the quantity is increased, the pearlite becomes coarse, the mechanical property is reduced, and in order to ensure that a certain quantity of flake graphite exists, the content of C is increased to be within the range of 3.7% -3.9%; the addition of Cr and V improves the wear resistance and high temperature resistance, but the addition of excessively high Cr and V elements increases the material white-off tendency, so that the content of Cr is set to 0.1-0.3% and the content of V is set to 0.07-0.1%.
The method for manufacturing the gray cast iron material for the brake drum of the commercial vehicle adopts measures such as molten iron pretreatment, secondary inoculation and the like to pretreat the molten iron, so that the supercooling degree can be reduced, the formation of A-type graphite is promoted, and B, E, D-type graphite is prevented from being generated; by adopting a twice inoculation process, the formation of graphite coarsening and overcooling graphite is avoided, the number of carbides in an as-cast structure is reduced, and the tensile strength is improved; the silicon-manganese pickaxe and the silicon-lanthanum inoculant are used as efficient and long-acting inoculants, so that molten iron can be purified, the defects of pores and impurities are reduced, graphite is passivated, the material performance is improved, and the consistency of product quality is ensured; the gray cast iron material is prepared from certain chemical components by taking measures such as molten iron pretreatment and secondary inoculation, the graphite is A-type graphite with moderate size and a small amount of C-type graphite, a matrix structure with fine lamellar pearlite more than or equal to 95% is obtained, the tensile strength of a brake drum body is 210-260MPa, the hardness value of a working surface is 180-220HBW, the thermal fatigue performance of the brake drum can be effectively improved, and the service life of the brake drum can be effectively prolonged.
Advantageous effects
The invention discloses a gray cast iron material for a brake drum of a commercial vehicle and a manufacturing method thereof, which are characterized in that measures such as molten iron pretreatment, secondary inoculation and the like are taken on the basis of improving the carbon content and adding proper amount of Cr and V elements, the A-type graphite with moderate graphite form and a small amount of C-type graphite are obtained, a matrix structure with fine lamellar pearlite more than or equal to 95% is obtained, the tensile strength of a brake drum body is 210 plus 260MPa, the hardness value of a working surface is 180 plus 220HBW, the thermal fatigue performance of the brake drum can be effectively improved, and the service life of the brake drum can be effectively prolonged.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention in conjunction with the following examples, but it will be understood that the description is intended to illustrate the features and advantages of the invention further, and not to limit the invention.
Example 1
The commercial vehicle brake drum gray cast iron material in the embodiment 1 comprises the following components in percentage by weight: 3.75% of C, 1.7% of Si, 0.55% of Mn, 0.07% of S, 0.02% of P, 0.5% of Cu, 0.15% of Cr, 0.08% of V, 0.06% of Sn, 0.02% of Zr, 0.008% of La and the balance of Fe and inevitable impurities;
the preparation method of the commercial vehicle brake drum gray cast iron material comprises the following steps:
(1) adding the raw materials into an electric furnace according to the formula amount for smelting to obtain liquid raw materials;
(2) heating the liquid raw material in the step (1) to 1510 ℃, removing slag, adding a SiC pretreatment agent accounting for 0.1 percent of the weight of the liquid raw material, and after 10 minutes, reducing the temperature of the liquid raw material to 1490 ℃ to obtain base iron;
(3) pouring the base iron into a casting ladle, adding a SiMnZr inoculant accounting for 0.2 percent of the weight of the base iron into the ladle, adding a SiMnZr inoculant accounting for 0.22 percent of the weight of the base iron in a stream inoculation mode when the base iron is discharged, carrying out inoculation treatment on the base iron, and obtaining the base iron after 3 min;
(4) the pouring temperature of the molten iron is 1410 ℃, and simultaneously 0.07 percent of along-flow SiLa inoculant is added for along-flow inoculation, so that the gray cast iron material of the brake drum of the commercial vehicle is obtained, and the metallographic structure diagram of the gray cast iron material is shown in figure 1.
Example 2
The commercial vehicle brake drum gray cast iron material in the embodiment 2 comprises the following components in percentage by weight: 3.85% of C, 1.9% of Si, 0.65% of Mn0.09% of S, 0.05% of P, 0.6% of Cu0.25% of Cr0.25%, 0.09% of V, 0.09% of Sn0.09%, Zr0.03%, La0.009%, and the balance of Fe and inevitable impurities;
the preparation method of the commercial vehicle brake drum gray cast iron material comprises the following steps:
(1) adding the raw materials into an electric furnace according to the formula amount for smelting to obtain liquid raw materials;
(2) heating the liquid raw material in the step (1) to 1520 ℃, removing slag, adding a SiC pretreating agent accounting for 0.1 percent of the weight of the liquid raw material, and after 13 minutes, reducing the temperature of the liquid raw material to 1496 ℃ to obtain base iron;
(3) pouring the base iron into a casting ladle, adding a SiMnZr inoculant accounting for 0.22 percent of the weight of the base iron into the ladle, adding the SiMnZr inoculant accounting for 0.25 percent of the weight of the base iron in a stream inoculation mode when the base iron is discharged, carrying out inoculation treatment on the base iron, and obtaining the base iron after 4 min;
(4) the pouring temperature of the molten iron is 1415 ℃, and simultaneously 0.09 percent of along-flow SiLa inoculant is added for along-flow inoculation, so that the commercial vehicle brake drum gray cast iron material is obtained, and the metallographic structure diagram of the material is shown in figure 2.
Example 3
The commercial vehicle brake drum gray cast iron material in the embodiment 4 comprises the following components in percentage by weight: 3.8% of C, 1.8% of Si, 0.61% of Mn, 0.08% of S, 0.03% of P, 0.55% of Cu, 0.19% of Cr, 0.085% of V, 0.08% of Sn, 0.025% of Zr, 0.008% of La and the balance of Fe and inevitable impurities;
the preparation method of the commercial vehicle brake drum gray cast iron material comprises the following steps:
(1) adding the raw materials into an electric furnace according to the formula amount for smelting to obtain liquid raw materials;
(2) heating the liquid raw material in the step (1) to 1515 ℃, removing slag, adding a SiC pretreating agent accounting for 0.1 percent of the weight of the liquid raw material, and after 13 minutes, reducing the temperature of the liquid raw material to 1490 ℃ to obtain base iron;
(3) pouring the base iron into a casting ladle, adding a SiMnZr inoculant accounting for 0.20 percent of the weight of the base iron into the ladle, adding the SiMnZr inoculant accounting for 0.25 percent of the weight of the base iron in a stream inoculation mode when the base iron is discharged, carrying out inoculation on the base iron, and obtaining the base iron after 2 min;
(4) the pouring temperature of the molten iron is 1410 ℃, and simultaneously 0.08 percent of along-flow SiLa inoculant is added for along-flow inoculation, so that the gray cast iron material of the brake drum of the commercial vehicle is obtained, and the metallographic structure diagram of the gray cast iron material is shown in figure 3.
Example 4
The commercial vehicle brake drum gray cast iron material in the embodiment 4 comprises the following components in percentage by weight: 3.9% of C, 2.0% of Si, 0.7% of Mn, 0.1% of S, 0.06% of P, 0.7% of Cu, 0.3% of Cr, 0.1% of V, 0.1% of Sn, 0.04% of Zr, 0.01% of La and the balance of Fe and inevitable impurities;
the preparation method of the commercial vehicle brake drum gray cast iron material comprises the following steps:
(1) adding the raw materials into an electric furnace according to the formula amount for smelting to obtain liquid raw materials;
(2) heating the liquid raw material in the step (1) to 1525 ℃, removing slag, adding a SiC pretreatment agent accounting for 0.2 percent of the weight of the liquid raw material, and after 14 minutes, reducing the temperature of the liquid raw material to 1485 ℃ to obtain base iron;
(3) pouring the base iron into a casting ladle, adding a SiMnZr inoculant accounting for 0.25 percent of the weight of the base iron into the ladle, adding the SiMnZr inoculant accounting for 0.25 percent of the weight of the base iron in a stream inoculation mode when the base iron is discharged, carrying out inoculation treatment on the base iron, and obtaining the base iron after 3 min;
(4) the pouring temperature of the molten iron is 1420 ℃, and simultaneously 0.09 percent of along-flow SiLa inoculant is added for along-flow inoculation, so that the commercial vehicle brake drum gray cast iron material is obtained, and the metallographic structure diagram of the gray cast iron material is shown in figure 4.
Example 5
The commercial vehicle brake drum gray cast iron material in the embodiment 1 comprises the following components in percentage by weight: 3.7% of C, 1.6% of Si, 0.5% of Mn, 0.05% of S, 0.03% of P, 0.5% of Cu, 0.1% of Cr, 0.07% of V, 0.05% of Sn, 0.01% of Zr, 0.007% of La and the balance of Fe and inevitable impurities;
the preparation method of the commercial vehicle brake drum gray cast iron material comprises the following steps:
(1) adding the raw materials into an electric furnace according to the formula amount for smelting to obtain liquid raw materials;
(2) heating the liquid raw material in the step (1) to 1503 ℃, removing slag, adding a pretreatment agent SiC pretreatment agent accounting for 0.1 percent of the weight of the liquid raw material, and after 10 minutes, reducing the temperature of the liquid raw material to 1482 ℃ to obtain base iron;
(3) pouring the base iron into a casting ladle, adding a SiMnZr inoculant accounting for 0.2 percent of the weight of the base iron into the ladle, adding the SiMnZr inoculant accounting for 0.2 percent of the weight of the base iron in a stream inoculation mode when the base iron is discharged, carrying out inoculation treatment on the base iron, and obtaining the base iron after 3 min;
(4) the pouring temperature of the molten iron is 1400 ℃, and simultaneously 0.06 percent of stream-following inoculant is added for stream-following inoculation, so as to obtain the gray cast iron material of the brake drum of the commercial vehicle, and the metallographic structure diagram of the gray cast iron material is shown in figure 5.
Comparative example 1
The raw material composition in comparative example 1 was the same as in example 3;
the preparation method of comparative example 1 was the same as that of example 3 except that the pretreatment was performed without adding the pretreatment agent, and the metallographic structure thereof was as shown in FIG. 6.
Comparative example 2
Compared with the raw material components in the comparative example 2 and the raw material components in the example 3, Cr and V are not added, and the rest of the raw material components in the example 3 are the same;
comparative example 2 was prepared in the same manner as in example 3, and its metallographic structure was as shown in FIG. 7.
Testing the performance of the characterization agent of the gray cast iron material of the brake drum of the commercial vehicle:
the brake drum prepared by the invention is detected according to the requirements in GB/T37336 automobile brake drum, the metallographic structure diagram of the gray cast iron material of the brake drum of the commercial vehicle is respectively shown in figures 1-5, and the test results of tensile strength, hardness, thermal conductivity and thermal fatigue performance are shown in Table 1. Graphite in the commercial vehicle brake drum ash cast iron material obtained in the embodiments 1-5 is mainly A-type, the length of the graphite is 3-5 grades, fine lamellar pearlite in a matrix structure is more than or equal to 95%, and a small amount of uniformly distributed phosphorus eutectic crystals and carbides are formed; the tensile strength reaches 210-260Mpa, the brake surface hardness reaches 180-220HBW, the heat conductivity at 100 ℃ is not less than 55W/(m.k), and the cycle frequency of the thermal fatigue test reaches more than 350 times.
TABLE 1 results of testing the properties of inventive and comparative examples
The above examples are given for the purpose of illustrating the invention and do not represent the entire technical solution of the inventive concept, and it will be apparent to those skilled in the art that modifications and variations of the present patent disclosure and common sense, as well as insubstantial modifications of different combinations of features, such as fine adjustment of alloy elements, modification of inoculant brand, etc., can be derived or suggested from the present patent disclosure and the present examples, and all of them are within the scope of protection of this patent.