CN112795722A - Austempering technology for austempered ductile iron - Google Patents
Austempering technology for austempered ductile iron Download PDFInfo
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- CN112795722A CN112795722A CN202011548315.1A CN202011548315A CN112795722A CN 112795722 A CN112795722 A CN 112795722A CN 202011548315 A CN202011548315 A CN 202011548315A CN 112795722 A CN112795722 A CN 112795722A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
- C21C1/105—Nodularising additive agents
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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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
-
- 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
-
- 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
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- Metallurgy (AREA)
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Abstract
The invention discloses an austempering technique for austempered ductile iron, which specifically comprises the following steps: s1, smelting: putting the raw materials into an electric furnace, heating and smelting to a molten state to form an alloy liquid; s2, placing the alloy liquid into a spheroidizing bag for spheroidizing and inoculation; s3, pouring: casting and molding the alloy liquid by using a casting mold; s4, isothermal quenching treatment: the invention relates to the technical field of austempered ductile iron processing, in particular to a method for processing austempered ductile iron, which comprises the steps of heating a casting blank, then preserving heat, carrying out isothermal salt bath treatment on the casting blank after heat treatment, and finally cooling to room temperature. According to the austempering technology for austempered ductile iron, molybdenum with different contents is added, so that the casting has better hardenability in the heat treatment process, the heat treatment effect is improved, copper and nickel with different contents are added, the processed casting has good toughness, the casting is subjected to heat treatment and isothermal treatment at different temperatures, the heat preservation time is controlled, the casting has better mechanical properties, and the service life of the casting is prolonged.
Description
Technical Field
The invention relates to the technical field of austempering ductile iron processing, in particular to an austempering technique for austempering ductile iron.
Background
The austempered ductile iron is a novel engineering material with excellent comprehensive mechanical properties, has high strength, hardness, wear resistance, better plasticity and low-temperature toughness, has higher bending fatigue strength compared with cast iron of other materials and heat-treated cast steel and forged steel, and has higher contact fatigue strength than pearlite and ferrite cast iron. The material is widely applied to the mechanical manufacturing industry and various structural parts with high tensile strength and high elongation, and compared with alloy steel, the austenite-bainite nodular cast iron has higher cost performance.
In the meshing and friction process of the austempered ductile iron gear, residual austenite contained in the cast iron material is converted into martensite, and the service life of the austempered ductile iron gear is greatly prolonged as a wear-resistant layer with high hardness is formed on the surface, and meanwhile, plasticity, toughness and high bending fatigue strength are kept in the gear; the deformation and the warpage are small in the heat treatment process, so that the gear precision requirement can be completely met by giving the grinding amount of the primary processing according to experimental experience values for the deformation of the existing gear without using a special tool fixture (quenching press) during quenching; the noise is lower than that of a steel material in the using process, and the weight of the austempered ductile iron is 7 to 10 percent lighter than that of a steel part; the production cost of the gear made of austempered ductile iron is about 30 percent lower than that of a carburized gear made of forged steel, the machining performance can be improved, the service life of the product can be prolonged, and the cost can be reduced.
However, in the existing austempering technology of austempering ductile iron, due to the fact that the finished austempering ductile iron products are poor in toughness and mechanical properties due to different addition amounts of molybdenum, nickel and copper alloy elements and different heating temperatures and heat preservation times of heat treatment, the invention provides an austempering technology of austempering ductile iron, and aims to solve the problems.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides an austempering technology for austempered ductile iron, which solves the problem of poor toughness and mechanical property of finished products of austempered ductile iron castings.
(II) technical scheme
In order to achieve the purpose, the invention is realized by the following technical scheme: an austempering technique for austempered ductile iron specifically comprises the following steps:
s1, smelting: putting the raw materials into an electric furnace, heating up and smelting, and melting the raw materials to a molten state to form an alloy liquid, wherein the alloy liquid comprises the following components in percentage by weight: carbon: 3.6-4.0%, silicon: 2.3-2.9%, molybdenum: less than or equal to 0.35 percent, copper: less than or equal to 1.3 percent, nickel: less than or equal to 1.3 percent, phosphorus: less than or equal to 0.05 percent, sulfur: less than or equal to 0.03 percent, the balance being iron, the smelting being one of the casting production processes, putting metal materials and other auxiliary materials into a heating furnace for melting and tempering, the furnace burden generating certain physical and chemical changes in the furnace burden at high temperature (1300-1600K), producing crude metal or metal enrichment and a pyrometallurgical process of furnace slag;
s2, spheroidizing and inoculating: pouring the alloy liquid prepared in the step S1 into a spheroidizing bag, and adding 1.2-1.6% of a spheroidizing agent and 0.8-1.5% of an inoculant for spheroidizing and inoculating, wherein the spheroidizing grade is as follows: 1-2 grade, and the number of graphite nodules per square centimeter is more than or equal to 100.
S3, pouring: casting and molding the alloy solution obtained in the step S2 by using a casting mold to obtain a casting blank with a matrix structure of ferrite and pearlite, wherein the casting refers to casting of a metal part by injecting molten metal into a casting mold produced by a mold, the ferrite is pure iron with body-centered cubic lattice at a temperature below 912 ℃, interstitial solid solution with carbon dissolved in alpha-Fe is called ferrite, the pearlite is a mechanical mixture consisting of the ferrite and cementite, the pearlite is precipitated by eutectoid transformation of austenite at the same time, and the structure between the ferrite and cementite layers is one of the most basic five structures in the iron-carbon alloy;
s4, isothermal quenching treatment: heating the casting blank obtained in the step S3 to 900-910 ℃, then preserving heat to convert ferrite and pearlite into austenite, then carrying out isothermal salt bath treatment at the temperature of 340-350 ℃ to convert part of austenite into bainite to obtain a finished product, cooling the finished product to room temperature by using air, and carrying out isothermal treatment, namely isothermal quenching, namely completing isothermal transformation of austenite if the temperature of the lower bainite transformation zone is kept for a long time after the workpiece is quenched and heated to obtain a lower bainite structure, wherein the quenching is called isothermal quenching.
Preferably, the smelting temperature in the step S1 is 1550-.
Preferably, the spheroidization level in step S2 is: 1-2 grade, and the number of graphite nodules per square centimeter is more than or equal to 100.
Preferably, the pouring temperature in the step S3 is 1400-1450 ℃.
Preferably, in the step S4, the heating speed is 80-90 ℃/h, and the heat preservation time is 3-4 h.
Preferably, in the finished product obtained in step S4, the austenite content is 20 to 30%, the austenite is an interstitial solid solution of carbon in γ -Fe, the austenite has a face-centered cubic structure, the austenite exists above the eutectoid temperature, the eutectoid temperature of ordinary carbon steel is 1000K (727 ℃), the alloy steel has different eutectoid temperatures, the bainite content is 70 to 80%, the bainite is a product after austempering of austenitic steel, the bainite has higher toughness matching, the wear resistance of the bainite structure is obviously better than that of martensite under the condition of the same hardness, which can reach 1 to 3 times of martensite, and the austenite in the product is transformed into martensite by mechanical action during use, the martensite is also called martensite (if the parent phase element is iron, it can be called martensite), which is a structure name of a black metal material, accelerated cooling in medium-high carbon steel generally makes it possible to obtain such a structure, which is the product of the transformation of a pure metal or alloy from one solid phase to another; during the transformation, atoms do not diffuse, the chemical composition does not change, but the crystal lattice changes, and the old and new phases maintain a certain orientation relation and have the characteristic of shear coherence.
(III) advantageous effects
The invention provides an austempering technique for austempered ductile iron. Compared with the prior art, the method has the following beneficial effects:
(1) the austempering technology of the austempered ductile iron comprises the following steps of S1: putting the raw materials into an electric furnace, heating up and smelting, and melting the raw materials to a molten state to form an alloy liquid, wherein the alloy liquid comprises the following components in percentage by weight: carbon: 3.6-4.0%, silicon: 2.3-2.9%, molybdenum: less than or equal to 0.35 percent, copper: less than or equal to 1.3 percent, nickel: less than or equal to 1.3 percent, phosphorus: less than or equal to 0.05 percent, sulfur: less than or equal to 0.03 percent, and the balance being iron; s2, spheroidizing and inoculating: pouring the alloy liquid prepared in the step S1 into a spheroidizing bag, and adding 1.2-1.6% of a spheroidizing agent and 0.8-1.5% of an inoculant for spheroidizing and inoculating, wherein the spheroidizing grade is as follows: 1-2 level, the number of graphite nodules per square centimeter is more than or equal to 100; s3, pouring: and (4) casting and molding the alloy liquid prepared in the step (S2) by using a casting mold to obtain a casting blank with a matrix structure of ferrite and pearlite, adding molybdenum with different contents to ensure that the casting has better hardenability in the heat treatment process so as to improve the heat treatment effect, and adding copper and nickel with different contents to ensure that the processed casting has good toughness and higher tooth root bending fatigue strength, thereby being beneficial to prolonging the service life of the casting.
(2) The austempering technique for austempering austempered ductile iron comprises the following steps of S4: heating the casting blank prepared in the step S3 to 900-910 ℃, and then preserving heat to convert ferrite and pearlite into austenite; s5, isothermal quenching treatment: isothermal salt bath treatment is carried out on the casting blank after heat treatment at the temperature of 340-350 ℃ to convert part of austenite into bainite to prepare a finished product, the finished product is cooled to room temperature by air, heat treatment heating and isothermal quenching treatment are carried out on the casting at different temperatures, and the heat preservation duration is controlled, so that the casting has better mechanical property and higher compressive fatigue strength, and the service life of the casting is further prolonged.
Drawings
FIG. 1 is a process flow diagram of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the embodiment of the present invention provides three technical solutions: an austempering technique for austempered ductile iron specifically comprises the following embodiments:
example 1
S1, smelting: putting the raw materials into an electric furnace, heating to smelt at 1600 ℃, and melting the raw materials to a molten state to form alloy liquid, wherein the alloy liquid comprises the following components in percentage by weight: carbon: 3.6%, silicon: 2.4%, molybdenum: 0.2%, copper: 0.6%, nickel: 0.4%, phosphorus: 0.02%, sulfur: 0.01 percent, the balance of iron, and the total amount of copper and nickel is not more than 1.3 percent;
s2, spheroidizing and inoculating: the treatment is carried out in a bag by adopting a flushing method, the treatment temperature is 1480 ℃, the addition amount of a nodulizer is 1.6 percent, and the addition amount of an inoculant is 1.4 percent;
s3, pouring: casting and molding the alloy liquid prepared in the step S2 by using a casting mold, wherein the casting temperature is 1400 ℃, and a casting blank with a matrix structure of ferrite and pearlite is obtained;
s4, isothermal quenching treatment: heating the casting blank prepared in the step S3 to 900 ℃, heating at the speed of 80 ℃/h, then preserving heat for 3h to convert ferrite and pearlite into austenite, then carrying out isothermal salt bath treatment at the temperature of 340 ℃ to convert part of austenite into bainite to prepare a finished product, and cooling the finished product to room temperature in an air cooling mode, wherein the austenite content in the finished product is 30% and the bainite content in the finished product is 70%.
Example 2
S1, smelting: the method comprises the following steps of putting raw materials into an electric furnace, heating to smelt at 1550-: carbon: 3.9%, silicon: 2.6%, molybdenum: 0.3%, copper: 0.7%, nickel: 0.2%, phosphorus: 0.05%, sulfur: 0.03 percent, the balance being iron, the total amount of copper and nickel not exceeding 1.3 percent;
s2, spheroidizing and inoculating: the treatment temperature is 1480 ℃, the addition amount of the nodulizer is 1.4 percent, and the addition amount of the inoculant is 1.1 percent.
S3, pouring: casting and molding the alloy liquid prepared in the step S2 by using a mold, wherein the casting temperature is 1430 ℃, and 0.1% of inoculant is added in the casting process for stream inoculation to obtain a casting blank with a matrix structure of ferrite and pearlite;
s4, isothermal quenching treatment: heating the casting blank prepared in the step S3 to 910 ℃, wherein the heating rate is 90 ℃/h, and then carrying out heat preservation for 4h to convert ferrite and pearlite into austenite; and then carrying out isothermal salt bath treatment at 350 ℃ to convert part of austenite into bainite to obtain a finished product, and cooling the finished product to room temperature by using an air cooling mode, wherein the austenite content in the finished product is 20% and the bainite content in the finished product is 80%.
Example 3
S1, smelting: the method comprises the following steps of putting raw materials into an electric furnace, heating to smelt at 1650-1700 ℃, and melting the raw materials to a molten state to form alloy liquid, wherein the alloy liquid comprises the following components in percentage by weight: carbon: 3.9%, silicon: 2.7%, molybdenum: 0.35%, copper: 0.9%, nickel: 0.6%, phosphorus: 0.05%, sulfur: 0.03 percent, the balance being iron, the total amount of copper and nickel not exceeding 1.3 percent;
s2, spheroidizing and inoculating: the treatment is carried out in a bag by adopting a flushing method, the treatment temperature is 1500 ℃, the addition amount of a nodulizer is 1.2 percent, and the addition amount of an inoculant is 1.3 percent.
S3, pouring: casting and molding the alloy liquid prepared in the step S2 by using a casting mold, wherein the casting temperature is 1400 ℃, and a casting blank with a matrix structure of ferrite and pearlite is obtained;
s4, isothermal treatment: heating the casting blank prepared in the step S3 to 910 ℃, wherein the heating rate is 90 ℃/h, and then carrying out heat preservation for 4h to convert ferrite and pearlite into austenite; and then carrying out isothermal salt bath treatment at 350 ℃ to convert part of austenite into bainite to obtain a finished product, and cooling the finished product to room temperature by using a water cooling mode, wherein the austenite content in the finished product is 20% and the bainite content in the finished product is 80%.
Comparative experiment
A certain mechanical part processing enterprise performs detection work on the compressive fatigue strength and the tooth root bending fatigue strength of the austempered ductile iron gear respectively manufactured in the embodiment 1, the embodiment 2 and the embodiment 3 and a common austempered ductile iron gear in the current market, and in the detection process, the detection data of the four austempered ductile iron gears are counted at the same time, and a table chart 1 is prepared as follows:
table and figure 1
As can be seen from table 1, the compressive fatigue strength and the tooth root bending fatigue strength of the austempered ductile iron gear processed by the embodiment of the invention are both better than those of the common austempered ductile iron gear on the market, the embodiment 2 of the invention has the best performance, the austempered ductile iron gear has better toughness, the gear is not easy to damage in the using process, and the service life is longer, and the austempered ductile iron gear processed by the embodiment 2 of the invention has better mechanical properties, the compressive fatigue strength can reach 1350MPa to the maximum, and the tooth root bending fatigue strength can reach 350MPa to the maximum.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (6)
1. An austempering technique for austempered ductile iron, which is characterized in that: the method specifically comprises the following steps:
s1, smelting: putting the raw materials into an electric furnace, heating up and smelting, and melting the raw materials to a molten state to form an alloy liquid, wherein the alloy liquid comprises the following components in percentage by weight: carbon: 3.6-4.0%, silicon: 2.3-2.9%, molybdenum: less than or equal to 0.5 percent, copper: less than or equal to 1.3 percent, less than or equal to 1.3 percent of nickel, phosphorus: less than or equal to 0.05 percent, sulfur: less than or equal to 0.03 percent, and the balance being iron;
s2, spheroidizing and inoculating: placing the alloy liquid prepared in the step S1 into a spheroidizing bag for spheroidizing and inoculating;
s3, pouring: casting and molding the alloy liquid prepared in the step S2 by using a casting mold to obtain a casting blank with a matrix structure of ferrite and pearlite;
s4, isothermal quenching treatment: heating the casting blank workpiece prepared in the step S3 to 900-910 ℃, then preserving heat to convert ferrite and pearlite into austenite, carrying out isothermal salt bath quenching treatment at the temperature of 340-350 ℃ to convert part of austenite into bainite to prepare a finished product, and air-cooling the finished product to room temperature.
2. The austempering technique of austempered ductile iron as set forth in claim 1, characterized in that: the smelting temperature in the step S1 is 1550-.
3. The austempering technique of austempered ductile iron as set forth in claim 1, characterized in that: the tapping spheroidization temperature in the step S2 is 1480-.
4. The austempering technique of austempered ductile iron as set forth in claim 1, characterized in that: the pouring temperature in the step S3 is 1400-1450 ℃.
5. The austempering technique of austempered ductile iron as set forth in claim 1, characterized in that: in the step S4, the heating speed is 80-90 ℃/h, and the heat preservation time is 3-4 h.
6. The austempering technique of austempered ductile iron as set forth in claim 1, characterized in that: in the finished product prepared in the step S4, the austenite content is 20-30%, and the bainite content is 70-80%.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113400860A (en) * | 2021-06-30 | 2021-09-17 | 东风商用车有限公司 | Commercial vehicle heavy axle ADI hub and casting method and detection method thereof |
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