CN114058937B - Low-temperature high-toughness nodular cast iron and application thereof - Google Patents
Low-temperature high-toughness nodular cast iron and application thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/10—Cast-iron alloys containing aluminium or silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B61—RAILWAYS
- B61F—RAIL VEHICLE SUSPENSIONS, e.g. UNDERFRAMES, BOGIES OR ARRANGEMENTS OF WHEEL AXLES; RAIL VEHICLES FOR USE ON TRACKS OF DIFFERENT WIDTH; PREVENTING DERAILING OF RAIL VEHICLES; WHEEL GUARDS, OBSTRUCTION REMOVERS OR THE LIKE FOR RAIL VEHICLES
- B61F15/00—Axle-boxes
- B61F15/20—Details
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
- C22C33/10—Making cast-iron alloys including procedures for adding magnesium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/04—Cast-iron alloys containing spheroidal graphite
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03D—WIND MOTORS
- F03D13/00—Assembly, mounting or commissioning of wind motors; Arrangements specially adapted for transporting wind motor components
- F03D13/20—Arrangements for mounting or supporting wind motors; Masts or towers for wind motors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03D—WIND MOTORS
- F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention relates to low-temperature high-toughness nodular cast iron and application thereof, wherein the nodular cast iron comprises the following chemical components: c: 3.5-3.9%, Si: 1.6-2.2%, Mn is less than or equal to 0.18%, Mg: 0.03-0.05%, RE: 0.03-0.06%, Bi: 0.001-0.005%, B: 0.003-0.008% and the balance of Fe and inevitable impurities, wherein the nodular cast iron is in an annealed state, and can be applied to hubs, gear boxes, racks, bases and the like of wind driven generators or axle suspension bearing covers, bogie axle boxes, gear boxes and the like of railway locomotives.
Description
Technical Field
The invention relates to low-temperature high-toughness nodular cast iron and application thereof, wherein the nodular cast iron has excellent room temperature strength and low-temperature toughness, and is particularly suitable for hubs, gear boxes, racks, bases and the like of wind driven generators and working conditions with high requirements on low-temperature toughness such as axle-suspension bearing covers, bogie axle boxes, gear boxes and the like of railway locomotives.
Background
The nodular cast iron is widely applied in the fields of rail transit, wind power, oil drilling and production and the like. In recent years, when the wind generating sets are increasingly arranged in high-altitude, high-cold and extreme environment areas, such as the opening of the Hadamard high-speed iron and the Lanxin high-speed iron which pass through high-altitude and high-cold areas, the nodular cast iron applied to the working conditions has high requirements on the room temperature strength characteristics of the nodular cast iron, and simultaneously has excellent low-temperature toughness, and particularly has higher requirements on the low-temperature toughness at minus 40 ℃.
QT400-18L low temperature nodular cast iron is regarded as being applied to the material that the operating mode is comparatively ideal, and its-40 ℃ impact toughness reaches 12J, and room temperature tensile strength reaches 400MPa, but along with the gradual improvement of operating mode load, for example high-speed railway locomotive speed is faster and more high, wind power installation power is higher and more, its requirement to nodular cast iron intensity and low temperature toughness also improves thereupon, and conventional QT400-18L has can't satisfy the high load high speed requirement in low temperature severe cold district.
In order to solve the above problems, in the prior art, nodular cast iron is usually strengthened with elements such as Ni and Cu, but both Ni and Cu are elements that increase the ductile-brittle transition temperature of the nodular cast iron and have the effect of stabilizing pearlite, and although the room temperature strength of the nodular cast iron can be increased, they are extremely disadvantageous for the low temperature toughness of the nodular cast iron, and both the room temperature strength and the low temperature toughness cannot be achieved.
Based on the knowledge, the nodular cast iron which can give consideration to both room temperature strength and low temperature toughness is provided so as to be fully suitable for the application working conditions of low temperature, high cold and high speed and heavy load.
Disclosure of Invention
The invention provides a nodular cast iron with room temperature strength and low temperature toughness, which is suitable for the wheel hub, the gear box, the rack, the base and the like of a wind driven generator, and the working conditions of axle-hung bearing cover, bogie axle box, gear box and the like of a railway locomotive with higher requirements on room temperature strength and low temperature toughness, and is particularly suitable for the parts working in low-temperature, high-cold and high-speed heavy-load areas.
The technical object of the present invention is achieved by the following means.
The invention provides low-temperature high-toughness nodular cast iron which comprises the following chemical components: c: 3.5-3.9%, Si: 1.6-2.2%, Mn is less than or equal to 0.18%, Mg: 0.03-0.05%, RE: 0.03 to 0.06%, Bi: 0.001-0.005%, B: 0.003-0.008% and the balance of Fe and inevitable impurities, wherein the nodular cast iron is in an annealed state.
The design principle of the composition, content and proportion relationship of the invention is described below.
C: carbon is an element constituting a graphite structure, has the function of strengthening graphite, can reduce the chilling tendency, increase the ferrite content and improve the toughness of the nodular cast iron, and is beneficial to improving the molten iron fluidity of the nodular cast iron. The impact toughness of nodular cast iron is influenced by carbon: the carbon content is too high, the number and the sphere diameter of graphite spheres in the structure are increased and increased, the vacancy growth is reduced, the plastic deformation in the aggregation process is reduced, the plastic deformation energy in the ductile iron fracture process is reduced, and the impact energy is reduced. However, when the carbon content is too low, the brittle transition temperature of the material increases, which is disadvantageous in low-temperature impact toughness. Suitable C contents according to the invention are 3.5-3.9%, preferably 3.6-3.8%, more preferably 3.65-3.75%.
Si: silicon is an element that promotes graphitization and promotes ferrite formation, inhibiting pearlite formation. Increasing the Si content increases the strength, but decreases the impact toughness. The influence of silicon on the impact toughness of the nodular cast iron has two aspects. On one hand, the silicon can obviously improve the ductile-brittle transition temperature of the ferritic matrix nodular cast iron, and the silicon content is reduced, so that better low-temperature impact toughness can be obtained; on the other hand, as the silicon content decreases, the amount of ferrite in the nodular cast iron structure also decreases, which leads to a decrease in the plasticity and toughness of the material. However, silicon has an adverse effect on low-temperature toughness as a whole, and therefore, it is required to be as low as possible. However, in the conventional spheroidal graphite cast iron containing pearlite-forming elements such as Cu and Ni, too low Si affects the ferrite content, so that it is not practical to reduce Si. The present invention provides a low-silicon nodular cast iron which does not contain Cu, Ni, etc., and has excellent low-temperature toughness. The Si content in the present invention is limited to 1.6 to 2.2%, preferably 1.7 to 2.1%, more preferably 1.8 to 2.0%.
Mn: the increase in manganese will lead to an increase in the ductile-brittle transition temperature of the nodular cast iron, which promotes the formation of carbides and pearlite in the matrix, with a very negative effect on the impact toughness, in particular under low temperature conditions. Therefore, the lower the Mn content is, the better, the invention limits the Mn content to 0.18% or less, more preferably 0.15% or less, particularly preferably 0.1% or less and the lower the Mn content, the better, but the Mn content of 0.01% or more is acceptable in view of the raw material conditions and the economic efficiency.
Mg: magnesium is a spheroidizing element, and a proper amount of magnesium is advantageous for low-temperature toughness. Too high magnesium adversely affects toughness, decreases low-temperature impact energy, increases slag inclusion and shrinkage tendency, affects mechanical properties, and too low magnesium causes insufficient spheroidization effect. When the Mg content of the invention is limited to 0.03-0.05%, better spheroidization rate and low-temperature toughness property can be obtained, and 0.035-0.045% is preferred.
RE: the rare earth has the effect of assisting spheroidization, the magnesium has the effect of main spheroidization, and simultaneously has the effects of desulfurizing and degassing, purifying molten iron and resisting spheroidization interference elements, when the RE content is too low, the spheroidization and spheroidization interference elements have unobvious effect, and when the RE content is too high, the tissues easily generate pearlite tendency, oxide, sulfide inclusion and the like are easily generated, and various mechanical properties of the nodular cast iron are seriously reduced. The amount of rare earth added is usually 0.03% or less. On the basis of intentionally adding trace spheroidization interference elements B and Bi, the RE content is slightly increased, and the harm of Bi and B to spheroidization is eliminated, wherein the RE addition amount is 0.03-0.06%, preferably 0.035-0.055%, and more preferably 0.04-0.05%.
Bi: and a trace amount of bismuth is added, and the bismuth is added, so that the refinement and homogenization of the graphite are facilitated. Bi has little influence on a ferrite matrix and can obviously improve the form of graphite and refine the structure, thereby improving the low-temperature toughness and the room-temperature strength of the nodular cast iron. However, Bi is an element that interferes with spheroidization, and when Bi is too high, flake graphite is easily produced and spheroidization rate is difficult to ensure, and when Bi is too low, refining and homogenization effects are difficult to ensure. The method ensures the functions of Bi thinning graphite and graphite homogenization while eliminating the harm of Bi interfering spheroidization by intentionally introducing Bi and slightly increasing the addition amount of RE, and is beneficial to obtaining excellent room temperature strength and low temperature toughness of the nodular cast iron, and the Bi content is set to be 0.001-0.005%, preferably 0.002-0.004%, and more preferably 0.0025-0.0035%.
B: trace boron can promote graphitization and refine graphite; meanwhile, trace boron is a favorable element for improving the strength. The trace boron has little influence on the ferrite matrix and can obviously improve the form of graphite and refine the structure, so that the nodular cast iron can give consideration to both room temperature strength and low-temperature impact toughness. Similarly, B is also an element which interferes with spheroidization, in order to eliminate the disadvantage of interfering with spheroidization caused by adding B, the invention slightly increases the addition amount of RE, can avoid the interference of B on spheroidization on the basis of ensuring the beneficial effect of B, and is beneficial to the nodular cast iron to obtain excellent room temperature strength and low temperature toughness, and the content of B in the invention is set to be 0.003-0.008%, preferably 0.004-0.007%, and more preferably 0.0045-0.0065%.
In the present invention, a non-exhaustive list of the inevitable impurity elements is P, S, and the contents of the inevitable impurity elements are defined as P: 0.05% or less, S: below 0.03%, the lower the content of impurities, the better, but the higher the requirements on raw materials and smelting, which leads to an increase in cost, and the preferred P: 0.03% or less, S: 0.02% or less.
P: phosphorus is a harmful element, and is easily segregated in the nodular cast iron to form a phosphorus eutectic, so that the ductile-brittle transition temperature of the nodular cast iron is significantly increased, and the low-temperature toughness of the nodular cast iron is rapidly decreased, and therefore, P is controlled to 0.05% or less, preferably 0.03% or less, more preferably 0.02% or less, and particularly preferably 0.015% or less and 0.01% or less.
S: sulfur and phosphorus are harmful elements, are one of strong reverse spheroidizing elements, consume spheroidizing elements of magnesium and rare earth in molten iron, reduce spheroidization rate and indirectly influence product performance. Low S is also advantageous for controlling casting defects. In order to ensure good spheroidization effect and low casting defects, the present invention limits S to 0.02% or less, preferably 0.01% or less, and more preferably 0.008% or less.
Specifically, for the annealing process of spheroidal graphite cast iron, one-stage annealing or two-stage annealing is preferable. The one-stage annealing process comprises the following steps: the nodular cast iron is insulated for 2-5h at 900-950 ℃, then cooled to 595-605 ℃ in a furnace and then cooled to room temperature in air; the two-stage annealing process comprises the following steps: the nodular cast iron is insulated for 2-5h at 950 ℃ under 900-760 ℃, then cooled to 605 ℃ under 595 ℃ and 605 ℃ under the furnace temperature after being cooled to 720-760 ℃ and then cooled to room temperature. The high-temperature graphitization annealing can eliminate cementite, and carbon atoms are fully diffused, so that the segregation of components and the nonuniformity of tissues are eliminated, the internal stress of the casting is eliminated, and the high-toughness ferritic nodular iron casting is obtained. And (3) eliminating cementite, ternary phosphorus eutectic and composite phosphorus eutectic at a high temperature stage, converting the structure from austenite to ferrite at a low temperature stage, and performing a high-temperature graphitization annealing process to obtain a ferrite and fine spherical graphite structure.
The mechanical property of the nodular cast iron in an annealing state can reach: the room temperature tensile strength is more than 440MPa, the room temperature elongation is more than 20 percent, the room temperature yield strength is more than 260MPa, and the impact toughness at minus 40 ℃ is 22J/cm2The graphite size grade of the nodular cast iron is 6-7 grades, the spheroidization grade is 1-2 grades, and the matrix structure is ferrite.
In addition, based on the technical effects obtained by the above scheme, the inventors of the present invention further found that it is very advantageous to obtain the optimum room temperature strength and low temperature toughness matching by controlling the ratio of B and Bi in the nodular cast iron to be proper. Thus, the invention further controls the ratio of B/Bi to be 1-3,preferably 1.2-2.5, and the room-temperature tensile strength of the obtained annealed nodular cast iron is above 460MPa, the room-temperature elongation is above 20 percent, the room-temperature yield strength is above 280MPa, and the-40 ℃ impact toughness is 24J/cm2The above is advantageous.
The invention has the following beneficial effects.
According to the nodular cast iron, trace B and Bi are added, the RE content is slightly increased, excellent room temperature strength and low temperature toughness are obtained, no strengthening element is added, pearlite forming elements such as Ni and Cu are added, the Si content is reduced, no deterioration influence is brought to the low temperature toughness, and the room temperature strength can be ensured. The addition of a trace amount of bismuth is beneficial to the refinement and homogenization of graphite, the bismuth has little influence on a ferrite matrix and can obviously improve the form of the graphite and refine the structure, thereby improving the low-temperature toughness and the room-temperature strength of the nodular cast iron. The trace boron can promote graphitization and refine graphite, is a favorable element for improving strength, has little influence on a ferrite matrix, can obviously improve the form of the graphite and refine the structure, and ensures that the nodular cast iron can give consideration to both room temperature strength and low-temperature impact toughness. Although B and Bi are elements which interfere spheroidization, trace B and Bi are intentionally added, and the RE content is slightly increased, so that the spheroidization interference hazard of Bi and B is eliminated, and the full play of the Bi and B is ensured without affecting spheroidization. In conclusion, the invention ensures that the ductile cast iron can give consideration to both room temperature strength and low temperature toughness by reasonably controlling the content matching of RE, Bi and B.
Detailed Description
In order to make those skilled in the art fully understand the technical scheme and the beneficial effects of the present invention, the following further description is made in combination with specific test examples.
And manufacturing the nodular cast iron according to the design components, wherein all P elements are qualified if controlled to be 0.015% +/-0.002%, and all S elements are qualified if controlled to be 0.01% +/-0.002%. The specific manufacturing method is as follows.
The first step, chemical composition design: selecting high-purity pig iron, high-quality carbon steel scrap, foundry returns and the like as raw materials according to target chemical components, and calculating the consumption of each raw material, wherein the high-purity pig iron requires: si less than 0.3%, Mn less than 0.2%, P less than 0.02%, S less than 0.015%.
Step two, smelting in an intermediate frequency furnace: smelting each component into molten iron by adopting a medium-frequency induction furnace, sampling and analyzing the temperature of the molten iron at 1480 +/-5 ℃, discharging the molten iron at 1505 +/-5 ℃ after the components of the molten iron are qualified, and preparing for spheroidization.
Step three, spheroidizing: the nodulizer is a rare earth magnesium silicon nodulizer with the granularity of 5-15mm, the nodulizing method is to perform nodulizing by adopting a flushing method, the nodulizing temperature is 1450-.
Step four, inoculation treatment and pouring: controlling the pouring temperature at 1360-1380 ℃, and carrying out instantaneous stream inoculation by adopting a ferrosilicon bismuth inoculant with the granularity of 0.3-0.5 mm; and (3) sand casting is adopted, the nodular cast iron ingot samples are obtained by pouring, and three ingot samples are poured for each furnace sample.
Step five, annealing treatment: and (3) adopting a one-stage annealing process, keeping the temperature of the nodular cast iron cast ingot sample in an annealing furnace at 910 ℃ for 4 hours, cooling the nodular cast iron cast ingot sample to 600 ℃ along with the furnace, and then air-cooling the nodular cast iron cast ingot sample to room temperature to obtain the nodular cast iron sample in an annealed state.
And (3) analyzing chemical components of one annealed ductile iron sample, detecting the strength and the elongation (plasticity) and observing and analyzing a microstructure, detecting the-40 ℃ low-temperature impact toughness property of all three annealed ductile iron samples, and calculating an average value, wherein the sample adopts a V-shaped notch. The analysis of chemical components, the test of room temperature strength, room temperature elongation (plasticity), low temperature toughness performance and the observation and analysis of microstructure are carried out according to the national standard GB/T1348-2009 and the cited standard requirements thereof. The results of the analysis of the chemical components of the spheroidal graphite cast irons of test nos. 1 to 25 are recorded in table 1, and the results of the various mechanical property tests and the structure observation are shown in table 2.
Table 1 (the components are in percentage by mass, and the balance is Fe)
In the above test examples, the components numbered 1 to 12 and the element ratio elements all meet the requirements of the present invention and are the invention examples of the present invention. 13-25, one of the elements in the composition does not meet the content requirements of the present invention, and thus test example nos. 13-25 are comparative examples of the present invention.
Table 2 shows the mechanical properties and microstructure of test nos. 1 to 25, and the tensile strength, yield strength and elongation in table 2 represent the room-temperature tensile strength, room-temperature yield strength and room-temperature elongation, respectively.
TABLE 2
Further analysis is described below with reference to the chemical composition of table 1 and the mechanical properties and microstructure of table 2.
The numbers 1 to 12 in the table 1 are all inventive examples of the present invention, which satisfy the requirements of the present invention for the content and the ratio of each element. The mechanical properties of the ductile cast iron of each invention example in an annealing state in the table 2 can reach: the room temperature tensile strength is more than 440MPa, the room temperature elongation is more than 20 percent, the room temperature yield strength is more than 260MPa, and the impact toughness is 22J/cm at minus 40 DEG C2The graphite grade is 6-7, the spheroidization grade is 1-2, and the matrix structure is ferrite; particularly, for invention examples 1-2, 6-7 and 10-12 with B/Bi within the range of 1-3, the mechanical properties of the ductile cast iron in the annealing state of each invention example can reach as follows: the room temperature tensile strength is more than 460MPa, the room temperature elongation is more than 20 percent, the room temperature yield strength is more than 280MPa, and the impact toughness is more than 24J/cm at minus 40 DEG C2The above shows that controlling B/Bi reasonably within a reasonable range results in a more excellent cellIt is advantageous to match the warm strength to the low temperature toughness.
Comparative examples of the present invention are analyzed one by one in conjunction with tables 1 and 2 below.
The comparative example 13 is the comparative example of the invention example 10, the content of B in the invention example 10 is reduced, the effects of promoting graphitization and thinning graphite are insufficient if the content of B is too low, the mechanical properties of the nodular cast iron cannot be effectively guaranteed, so that the room temperature tensile strength, the room temperature yield strength, the room temperature elongation and the-40 ℃ low temperature toughness of the nodular cast iron cannot meet the requirements of the invention, but due to the existence of sufficient RE and Mg and the implementation of the annealing process, the spheroidization rate and the graphite size grade can still be guaranteed, the mechanical properties of the nodular cast iron can still meet the requirements of QT400-18L, and it can be seen that the reasonable content of B is very important for ensuring the room temperature tensile strength, the room temperature yield strength, the room temperature elongation and the-40 ℃ low temperature toughness of the nodular cast iron.
The comparative example 14 is the comparative example of the invention example 10, the content of B in the invention example 10 is increased, the spheroidization of graphite is seriously interfered due to the excessively high content of B, the interference effect of B cannot be eliminated due to the proper amount of RE, the decrease of the spheroidization rate can remarkably deteriorate various mechanical properties of the nodular cast iron, so that the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron cannot meet the requirements of the invention, and the spheroidization rate and the graphite size grade cannot meet the requirements of the invention due to the interference effect of B, which shows that the reasonable content of B is very important for ensuring the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation, the-40 ℃ low-temperature toughness, the spheroidization rate and the graphite size grade of the nodular cast iron.
The comparative example 15 is the comparative example of the invention example 5, the Bi content in the invention example 5 is reduced, the refining and homogenization effects of graphite with too low Bi content are insufficient, and the mechanical properties of the nodular cast iron cannot be effectively ensured, so that the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron cannot meet the requirements of the invention, but due to the existence of sufficient RE and Mg and the implementation of an annealing process, the spheroidization rate and the graphite size grade can be ensured, the mechanical properties of the nodular cast iron can still meet the requirements of QT400-18L, and the reasonable Bi content is very important for ensuring the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron.
The comparative example 16 is the comparative example of the invention example 5, which increases the content of Bi in the invention example 5, wherein Bi is an element interfering spheroidization, when the content is too high, flake graphite is easily generated, and the spheroidization rate is difficult to be ensured, when a proper amount of RE cannot eliminate the interference effect caused by Bi, the increase of the special-shaped graphite morphology and the reduction of the spheroidization rate can obviously deteriorate various mechanical properties of the nodular cast iron, so that the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron cannot meet the requirements of the invention, and the spheroidization rate and the graphite size grade cannot meet the requirements of the invention due to the interference effect of Bi, thereby showing that the reasonable content of Bi is very important for ensuring the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation, the-40 ℃ low-temperature toughness, the spheroidization rate and the graphite size grade of the nodular cast iron.
The comparative example 17 is a comparative example of the invention example 8, the RE content in the invention example 8 is reduced, the RE has the effects of promoting spheroidization and eliminating the anti-spheroidization effect of the anti-spheroidization interference elements, while the invention example 8 is intentionally added with a certain amount of spheroidization interference elements B and Bi, the spheroidization interference effect of B and Bi is remarkably exerted due to the excessively low RE content, the spheroidization capacity of the nodular cast iron is sharply reduced, the mechanical property of the nodular cast iron is sharply deteriorated, the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation, the-40 ℃ low-temperature toughness, the spheroidization rate and the graphite size grade of the nodular cast iron cannot meet the requirements of the invention, and the reasonable RE content is very important for ensuring the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation, the-40 ℃ low-temperature toughness, the spheroidization rate and the graphite size grade of the nodular cast iron.
The comparative example 18 is the comparative example of invention example 8, which increases the RE content in invention example 8, where RE is a pearlite forming element, and since the RE content is too high, a pearlite structure has already appeared in the structure of the nodular cast iron, and the binding ability of rare earth with oxygen, sulfur, and the like is strong, oxides, sulfide inclusions, and the like are easily generated, and various mechanical properties of the nodular cast iron are seriously reduced, so that the room temperature tensile strength, the room temperature yield strength, the room temperature elongation, the-40 ℃ low temperature toughness of the nodular cast iron cannot meet the requirements of the present invention, indicating that a reasonable RE content is very important for ensuring the room temperature tensile strength, the room temperature yield strength, the room temperature elongation, the-40 ℃ low temperature toughness, and the matrix structure of the nodular cast iron.
Comparative example 19 is a comparative example of invention example 1, in which the Si content in invention example 1 is reduced, Si is a ferrite-forming element and a graphitization-promoting element, too low Si causes a pearlite structure to have appeared in the structure of the nodular cast iron, the graphite size grade is deteriorated as compared with invention example 1, and Si is a strengthening-promoting element and is disadvantageous to the low-temperature toughness, too low Si can ensure that the-40 ℃ low-temperature toughness and the room-temperature elongation of the nodular cast iron can meet the requirements of the invention, but the room-temperature tensile strength and the room-temperature yield strength of the nodular cast iron are remarkably reduced and are lower than the lower limit of the requirements of the invention, indicating that a reasonable Si content is very important to ensure the room-temperature tensile strength, the room-temperature yield strength, the graphite size grade, and the matrix structure of the nodular cast iron.
The comparative example 20 is the comparative example of the invention example 1, the content of Si in the invention example 1 is increased, however, the increase of the Si causes the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron to be obviously reduced while the strength is increased, so that the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron cannot meet the requirements of the invention, and the reasonable content of Si is very important for ensuring the room-temperature elongation and the-40 ℃ low-temperature toughness of the nodular cast iron.
Comparative example 21 is a comparative example of invention example 7, which reduces the C content in invention example 7, however, C is an element ensuring the ferrite content which improves the toughness of nodular cast iron and has the function of strengthening graphite, too low C content causes the pearlite structure to have appeared in the structure of nodular cast iron, and although too low C content causes the elongation at room temperature of nodular cast iron to be improved, the low-temperature toughness at-40 ℃ and the tensile strength at room temperature and the yield strength at room temperature thereof are significantly reduced and are already below the lower limit required by the present invention, indicating that a reasonable C content is important for ensuring the tensile strength at room temperature, the yield strength at room temperature, the toughness at-40 ℃ at low temperature and the matrix structure of nodular cast iron.
Comparative example 22 is a comparative example of invention example 7, which increases the C content in invention example 7, however, C is an element that strengthens graphite, but too high causes a sharp drop in low-temperature toughness and plasticity, and since the C content is too high, the room-temperature elongation, -40 ℃ low-temperature toughness cannot meet the requirements of the present invention, and the graphite size grade, although meeting the requirements of the present invention, is deteriorated compared to invention example 7 due to too high C, indicating that a reasonable C content is important for ensuring the room-temperature elongation, -40 ℃ low-temperature toughness and graphite size grade of spheroidal graphite cast iron.
The comparative example 23 is a comparative example of the invention example 2, which reduces the Mg content in the invention example 2, however, magnesium is a spheroidizing element, and if the magnesium content is too low, the spheroidizing effect cannot be ensured, so that various mechanical properties of the nodular cast iron are affected, the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation percentage, the-40 ℃ low-temperature toughness of the nodular cast iron cannot meet the requirements of the invention, and the spheroidizing rate is also deteriorated relative to the invention example 2, which indicates that the reasonable Mg content is very important for ensuring the room-temperature tensile strength, the room-temperature yield strength, the room-temperature elongation percentage, the-40 ℃ low-temperature toughness and the spheroidizing rate of the nodular cast iron.
Comparative example 24 is a comparative example of invention example 2, which increased the Mg content in invention example 2, however, too high Mg adversely affected toughness, decreased low temperature impact energy, increased slag inclusion and shrinkage porosity tendency, affected mechanical properties, and failed to satisfy the requirements of the present invention in terms of room temperature tensile strength, room temperature yield strength, room temperature elongation, low temperature toughness at-40 ℃, indicating that a reasonable Mg content is important for ensuring room temperature tensile strength, room temperature yield strength, room temperature elongation, low temperature toughness at-40 ℃.
Comparative example 25 is a comparative example of invention example 11, which increases the Mn content in invention example 11, and although Mn has a strengthening effect, the increase in manganese results in an increase in ductile-brittle transition temperature of ductile iron, promotes the formation of carbide and pearlite in the matrix, exerts a very adverse effect on impact toughness, particularly impact toughness under low temperature conditions, the room temperature elongation, -40 ℃ low temperature toughness of which does not satisfy the requirements of the present invention, and pearlite has already appeared in the structure, indicating that a reasonable Mn content is important for ensuring the room temperature elongation, -40 ℃ low temperature toughness, and the matrix structure of ductile iron.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, it is possible to make various improvements and modifications to the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (5)
1. The low-temperature high-toughness nodular cast iron is characterized by comprising the following chemical components: c: 3.5-3.9%, Si: 1.6-2.2%, Mn is less than or equal to 0.18%, Mg: 0.03-0.05%, RE: 0.042-0.06%, Bi: 0.002-0.005%, B: 0.0056-0.008% and B and Bi contents satisfying B/Bi = 1.2-3; the balance of Fe and inevitable impurities, wherein the nodular cast iron is in an annealing state; the annealing process of the nodular cast iron is one-stage annealing or two-stage annealing;
the one-stage annealing process comprises the following steps: the nodular cast iron is insulated for 2-5h at 900-950 ℃, then cooled to 595-605 ℃ in a furnace and then cooled to room temperature in air;
the two-stage annealing process comprises the following steps: the nodular cast iron is kept at 950 ℃ of 900-760 ℃ for 2-5h, then cooled to 605 ℃ of 595 ℃ after being cooled to 760 ℃ of 720-720 ℃ and then cooled to room temperature by air;
the room temperature tensile strength of the annealed nodular cast iron is more than 460MPa, the room temperature elongation is more than 20 percent, the room temperature yield strength is more than 280MPa, and the impact at minus 40 DEG CToughness of 24J/cm2As described above.
2. The low-temperature high-toughness ductile iron according to claim 1, wherein said B content is 0.0056-0.007%.
3. The spheroidal graphite cast iron with low temperature and high toughness according to claim 1, wherein the Bi content is 0.002-0.004%.
4. The spheroidal graphite cast iron with low temperature and high toughness according to claim 1, wherein the spheroidal graphite cast iron has a graphite size grade of 6-7, a spheroidization grade of 1-2, and a matrix structure of ferrite.
5. The use of the ductile iron with low temperature and high toughness as claimed in any one of claims 1-4, wherein: the nodular cast iron is applied to hubs, gear boxes, racks and bases of wind driven generators, or shaft-hung bearing covers, bogie axle boxes and gear boxes of railway locomotives.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01309939A (en) * | 1988-03-09 | 1989-12-14 | Hitachi Metals Ltd | Spheroidal graphite cast iron and its manufacture |
| JP2015183198A (en) * | 2014-03-20 | 2015-10-22 | 株式会社栗本鐵工所 | Spheroidal graphite cast iron and manufacturing method of spheroidal graphite cast iron |
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| JP3858288B2 (en) * | 1994-10-26 | 2006-12-13 | 日立金属株式会社 | Thin-walled spheroidal graphite cast iron, automotive parts using the same, and method for producing thin-walled spheroidal graphite cast iron |
| CN103757172A (en) * | 2014-02-19 | 2014-04-30 | 恒天重工股份有限公司 | Method for preparing nodular cast iron |
| CN105256220A (en) * | 2015-09-22 | 2016-01-20 | 山东汇丰铸造科技股份有限公司 | Low-temperature high-toughness nodular cast iron winding drum and preparation method thereof |
| CN105838975B (en) * | 2016-05-13 | 2018-08-07 | 北汽福田汽车股份有限公司 | Spheroidal graphite cast-iron and its preparation method and application |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01309939A (en) * | 1988-03-09 | 1989-12-14 | Hitachi Metals Ltd | Spheroidal graphite cast iron and its manufacture |
| JP2015183198A (en) * | 2014-03-20 | 2015-10-22 | 株式会社栗本鐵工所 | Spheroidal graphite cast iron and manufacturing method of spheroidal graphite cast iron |
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