CN114875302B - Low-alloy steel and preparation method and application thereof - Google Patents
Low-alloy steel and preparation method 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
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0006—Adding metallic additives
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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
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses low alloy steel and a preparation method and application thereof, belonging to the field of cast steel. The low alloy steel comprises the following element components in percentage by mass: c:0.15 to 0.22%, mn:0.8 to 1.6%, si:0.3 to 0.5%, al:0.015 to 0.06%, cu:0.2 to 0.4%, zr:0.01 to 0.03%, Y:0.01 to 0.03 percent of iron, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities. According to the invention, by adding a small amount of Cu and Zr, the strength, toughness and corrosion resistance of the low alloy steel are improved while the cost is controlled; zr and Y are used as alterants, so that the cleanliness of the low alloy steel is improved, and the low temperature fracture resistance of the low alloy steel is improved.
Description
Technical Field
The invention belongs to the field of cast steel, and particularly relates to low alloy steel and a preparation method and application thereof.
Background
The low-alloy manganese-containing cast steel is widely applied to the preparation of stressed structural members, such as container corner fittings, lifting hooks, suspension bridge cable clamps, steel chain rings and the like. As a force-receiving and force-transmitting member, the steel grade needs to have sufficient strength. In addition, when the related components such as container corner fittings, cable clips, etc. are used in the offshore environment or high-altitude areas, the components are prone to corrosion and low-temperature fracture due to corrosive atmosphere/moisture and low-temperature environment, resulting in unexpected failure and difficulty in meeting the operation requirements. Therefore, the high-end of these members requires steel materials having not only high strength but also low-temperature fracture resistance and corrosion resistance. The existing cast steel material and the preparation process are difficult to manufacture the novel steel which simultaneously considers the performances.
Patent CN 110042324 discloses a production process of container corner fittings. The container corner fitting steel comprises the following components: 0.09-0.15% by weight of C, 0.96-1.37% by weight of Mn, 0.32-0.36% by weight of Si, 0.19-0.26% by weight of Ni, 0.18-0.21% by weight of Cr, 0.007-0.015% by weight of Al, 0.015% by weight of P at most, 0.015% by weight of S at most, 0.08% by weight of Mo at most, 0.17% by weight of Cu at most, 0.01% by weight of V at most, and the balance of Fe and inevitable impurities. The steel grade is prepared by the working procedures of smelting, casting, carburizing heat treatment, salt bath heat treatment and the like, and has better strength and low-temperature toughness. However, the high-cost elements such as Ni and Cr are added into the steel, so that the cost of the steel is increased; and the carburizing heat treatment and the salt bath heat treatment process complicate the preparation process, especially the salt bath heat treatment has a severe working environment, and has hidden danger of waste salt pollution, which is not environment-friendly enough.
Patent CN 103184390 discloses a high-strength metal alloy and a corner fitting made of the same, wherein the main alloy comprises the following components in percentage by weight: 0.1 to 0.22% by weight of C,0.6 to 1.5% by weight of Mn,0.2 to 1.0% by weight of Si,0 to 0.6% by weight of Cr,0 to 0.6% by weight of Ni,0.1 to 1.0% by weight of Mo, and the balance of Fe and inevitable impurities. The alloy corner fitting prepared by the method has high tensile strength and yield strength and good low-temperature impact performance. However, high-cost elements such as Ni and Mo are introduced into the invention, a matched proper heat treatment process is not needed, and the corrosion resistance is not considered in a targeted manner. In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides low alloy steel and a preparation method and application thereof. On the basis of controlling the steel cost, the strength and the toughness of the steel are improved through precipitation strengthening and fine-grain strengthening effects by synergistically adding a small amount of Cu and Zr in chemical components; meanwhile, the corrosion resistance of the steel is improved by virtue of the effects of easily forming a protective corrosion product film of Cu, promoting the generation of a film layer by Zr and the like; through the compound modification treatment of trace Zr and rare earth, the cleanliness of steel is improved, and the low-temperature fracture resistance of steel is improved. The performance of the cast steel is further comprehensively regulated and controlled by combining three simple heat treatment processes, so that the cast steel has high strength, low temperature resistance and corrosion resistance. Therefore, the low-alloy cast steel which can be applied to components such as corner fittings, steel chain rings, lifting hooks and the like of the container in a low-temperature corrosive atmosphere severe environment is prepared.
In order to achieve the purpose, the invention adopts the technical scheme that:
in a first aspect, a low alloy steel is provided, which is characterized in that the low alloy steel comprises the following elements by mass percent: c:0.15 to 0.22%, mn:0.8 to 1.6%, si:0.3 to 0.5%, al:0.015 to 0.06%, cu:0.2 to 0.4%, zr:0.01 to 0.03%, Y:0.01 to 0.03 percent of iron, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities.
The low-alloy steel is added with low-content Cu and Zr so as to introduce dispersed precipitated phases into the steel, the existence of the dispersed precipitated phases can play a role in precipitation strengthening, and the dispersed precipitated phases can block the growth of grains to play a role in fine grain strengthening, so that the strength of the steel is ensured. Meanwhile, the corrosion resistance of the steel is improved due to the effects of easy formation of a protective corrosion product film of Cu, generation of a film promoting layer of Zr and the like. The Zr and the rare earth Y are added in a compounding way, so that the steel structure can be modified, and the low-temperature toughness of the steel is further improved.
The theoretical basis for determining the chemical components in the low alloy steel is as follows:
carbon: the C element is one of the most basic elements in steel, the content of the C element greatly affects the structure and the mechanical property of the steel, and in the case of low alloy steel, enough carbon needs to be added to ensure the strength of the steel, but the too high content of the carbon can cause the plasticity to be reduced and the welding property to be deteriorated. Comprehensively, the content of C is controlled to be 0.15-0.22%.
Manganese: mn can play a role in reinforcing steel within a certain range, and can improve the strength, hardness and wear resistance of steel materials, but excessive addition can influence weldability and toughness. Comprehensively, the content of Mn is controlled to be 0.8-1.6 percent.
Silicon: si is one of deoxidizing elements of steel, and proper addition of Si can enhance the strength of steel while ensuring no detailed deterioration of the toughness of steel, but too high addition reduces the toughness of steel. The content range of the invention is controlled to be 0.3-0.5%.
Aluminum: al element is generally brought into low alloy steel due to deoxidation, and too high Al content can cause too much oxide inclusion in the steel, and has great influence on the toughness of the steel. Therefore, the content of the invention is controlled to be 0.015 to 0.06 percent.
Copper: cu can improve the strength and toughness, especially the atmospheric corrosion performance, of the steel. The disadvantages are that hot brittleness is easily generated during hot processing, and the steel plasticity is obviously reduced when the copper content exceeds 0.5 percent. When the copper content is less than 0.50%, the weldability is not affected. The content range of the invention is controlled to be 0.2-0.4%.
Zirconium: zr element is C, N, O affinity element, only can play deoxidation effect when directly added into molten steel, and burning loss is serious. But by adding the additive in cooperation with other elements, a composite modified phase can be generated in the steel, the size and distribution of inclusions in the steel are optimized, the wear resistance and toughness of the steel can be improved by reasonably adding a small amount of the additive, but the excessive addition can cause the increase of the inclusions and influence various properties of the steel. The content range of the invention is controlled to be 0.01-0.03%.
Rare earth: the rare earth elements can play a good role in desulfurization and deoxidation in steel, purify the steel and change the form and distribution of inclusions in the steel. Particularly, Y in the rare earth elements can act together with Zr to compound the inclusions Y-Zr in the steel, and the inclusions are more uniformly dispersed and have low conductivity, thereby having an important effect on improving the mechanical property and the corrosion resistance of the steel. The content range of the invention is controlled to be 0.01-0.03%.
P and S are taken as impurity elements to seriously damage the toughness and plasticity of the steel, and the content is controlled to be less than or equal to 0.035 percent.
In a second aspect, a method for preparing a low alloy steel is provided, comprising the following steps:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into an intermediate frequency smelting furnace for smelting, wherein the smelting temperature is 1630-1660 ℃, deoxidizing the obtained molten steel by using a deoxidizing agent, adjusting the temperature of the molten steel to 1580-1620 ℃, and discharging;
(2) Placing a modifier inside the casting ladle, and modifying the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) And (3) casting the molten steel obtained in the step (2) at 1550-1580 ℃ to form cast steel, and carrying out heat treatment on the obtained cast steel to obtain the low alloy steel.
Preferably, in said step (2), the modifier is located at the top, middle and bottom of the inner edge of the ladle.
The alterant is arranged at the top, the middle and the bottom of the inner edge of the casting ladle, so that the molten steel injected into the casting ladle can fully react with the alterant.
Preferably, the modificator consists of ferrozirconium and yttrium. The quantity, shape, size and distribution of inclusions in the steel are improved by adopting the synergistic modification of trace zirconium iron and rare earth yttrium, so that the effect of increasing the low-temperature toughness of the steel is achieved.
Preferably, the preparation method of the alterant comprises the following steps: respectively crushing the zirconium iron and the yttrium into powder by adopting mechanical crushing, wherein the particle size of the obtained powder is less than or equal to 2mm, and then uniformly mixing the two kinds of powder, and wrapping the mixture by using an iron sheet to obtain the alterant.
The powdery alterant can be more uniformly dispersed in the molten steel, and the ability of modification treatment is improved.
Preferably, in the step (3), the heat treatment step is:
a, placing the obtained cast steel in a heat treatment furnace, heating to 650 ℃, keeping the temperature for 3-5h, continuing heating to 910-930 ℃, keeping the temperature for 3-5h, discharging from the furnace, and carrying out air cooling or water cooling to room temperature;
b, placing the cast steel obtained in the step a in a heat treatment furnace, heating to 510-530 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air-cooling to room temperature;
and c, placing the cast steel obtained in the step b in a heat treatment furnace, heating to 530-560 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air cooling to room temperature.
Preferably, in the step a, the time for the first temperature rise is 6-8h, and the time for the second temperature rise is 3h.
Preferably, in the step b and the step c, the temperature rise time is 5-6h.
The invention adopts three times of heat treatment processes, combines air cooling/water cooling quenching with two times of tempering treatment processes, and reasonably matches the two times of tempering processes to realize the purpose of removing residual stress and fully recovering the toughness structure in the cast steel, thereby further improving the low-temperature toughness of the low-alloy steel.
Optionally, the deoxidizer is a calcium silicate powder.
In a third aspect, the use of low alloy steel in container corners, steel links, hooks is provided.
Compared with the prior art, the invention has the beneficial effects that:
1. the low alloy steel provided by the embodiment of the invention can integrate high strength, high and low temperature toughness and corrosion resistance, and compared with low alloy steel for a low temperature structure applied in the current industry, the low alloy steel has the advantages of less addition of precious metal elements and lower cost.
2. According to the low alloy steel provided by the embodiment of the invention, a small amount of Cu and trace Zr are added to form a dispersed precipitated phase in the steel, and the strength of the steel is improved by virtue of strengthening effects such as precipitation strengthening, fine grain strengthening and the like.
(3) The low alloy steel provided by the embodiment of the invention develops a new way, and from the angle of constructing a protective corrosion product film, a Cu element which is easy to form the protective corrosion product film and a Zr element which promotes the film layer to generate are added, so that the low alloy steel with good corrosion resistance is obtained.
(4) The low-temperature resistance of the low-alloy cast steel is the key point of the application, and the invention adopts the trace amount of zirconium iron and rare earth yttrium to modify the quantity, shape, size and distribution of inclusions in the steel in the process of material smelting preparation, thereby achieving the effect of increasing the low-temperature toughness of the steel.
(5) The invention improves the traditional normalizing or quenching and tempering heat treatment of the low alloy steel into a three-pass heat treatment process, adopts the air cooling/water cooling quenching combined two-pass tempering treatment process, and reasonably matches the two-pass tempering process to realize the purposes of removing residual stress and fully recovering the toughness structure, thereby further improving the low-temperature toughness of the alloy steel.
Detailed Description
To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to the following embodiments.
The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The method for preparing the alterant used in the following examples is as follows: respectively crushing the ferrozirconium and the yttrium into powder by mechanical crushing, wherein the particle size of the obtained powder is less than or equal to 2mm, and then uniformly mixing the two powders and wrapping the mixture by an iron sheet to obtain the alterant.
The deoxidizer used in the following examples was calcium silico powder.
The method for testing various performances of the low alloy steel comprises the following steps:
mechanical properties: GB/T228 metal material room temperature tensile test method; GB/T229 metal material Charpy pendulum impact test method;
atmospheric corrosion rate: GB/T19292.4 corrosive atmospheric corrosion of metals and alloys part 4.
Example 1
The embodiment provides a low alloy steel, which comprises the following chemical components in percentage by mass: c:0.19%, mn:1.2%, si:0.5%, al:0.015%, cu:0.4%, zr:0.03%, rare earth Y:0.03 percent of the total weight of the alloy, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities.
The embodiment also provides a preparation method of the low alloy steel, which comprises the following steps:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into a medium-frequency smelting furnace for smelting, wherein the smelting temperature is 1630 ℃, deoxidizing the obtained molten steel for 3 times by using a deoxidizing agent, adjusting the temperature of the molten steel to 1590 ℃ after adjusting the components of the obtained molten steel to meet the mass percentage, and discharging;
(2) Placing alterant on the top, middle and bottom of the inner edge of the casting ladle, preheating for 2h at 600 ℃, and then carrying out modification treatment on the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) Pouring the molten steel obtained in the step (2) at 1550 ℃ to form cast steel, and carrying out heat treatment on the obtained cast steel to obtain low alloy steel;
wherein, the heat treatment in the step (3) comprises the following steps:
a, placing the obtained cast steel in a heat treatment furnace, heating the cast steel to 650 ℃ from room temperature for 8h, preserving heat for 3h, heating the cast steel to 920 ℃ for 3h, preserving heat for 3h, discharging the cast steel out of the furnace, and air cooling the cast steel to room temperature;
b, immediately placing the cast steel obtained in the step a into a heat treatment furnace, heating the cast steel from room temperature to 530 ℃ after 6 hours, keeping the temperature for 3 hours, discharging the cast steel out of the furnace, and air-cooling the cast steel to room temperature;
and c, immediately placing the cast steel obtained in the step b into a heat treatment furnace, heating from room temperature to 560 ℃ for 6h, keeping the temperature for 5h, discharging the cast steel out of the furnace, and air-cooling to room temperature.
The properties of the low alloy steel obtained in this example were measured and the results were as follows: the yield strength of the low alloy steel is 385MPa, the tensile strength is 560MPa, the elongation after fracture is 36 percent, and the low-temperature impact absorption energy A is at minus 40 DEG C kv 49J, the annual corrosion rate in the marine atmospheric environment is 0.018mm/a, and the corrosion resistance is improved by more than 3 times compared with 20Mn steel with similar components in GB/T699.
Example 2
The embodiment provides a low alloy steel, which comprises the following chemical components in percentage by mass: c:0.22%, mn:0.8%, si:0.3%, al:0.06%, cu:0.2%, zr:0.01%, rare earth Y:0.02 percent of the total weight of the alloy, less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities.
The embodiment also provides a preparation method of the low alloy steel, which comprises the following steps:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into a medium-frequency smelting furnace for smelting, wherein the smelting temperature is 1660 ℃, deoxidizing the obtained molten steel for 3 times by using a deoxidizing agent, adjusting the temperature of the molten steel to 1620 ℃ after the components of the obtained molten steel meet the mass percentage, and discharging the molten steel;
(2) Putting alterant on the top, middle and bottom of the inner edge of the casting ladle, preheating for 2h at 600 ℃, and then carrying out modification treatment on the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) Pouring the molten steel obtained in the step (2) at 1580 ℃ to obtain cast steel, and carrying out heat treatment on the obtained cast steel to obtain low alloy steel;
wherein, the heat treatment in the step (3) comprises the following steps:
a, placing the obtained cast steel in a heat treatment furnace, heating the cast steel from room temperature to 650 ℃ within 6h, preserving heat for 5h, heating the cast steel to 930 ℃ within 3h, preserving heat for 5h, discharging the cast steel out of the furnace, and cooling the cast steel to room temperature by water;
b, immediately placing the cast steel obtained in the step a into a heat treatment furnace, heating the cast steel from room temperature to 510 ℃ for 5 hours, keeping the temperature for 5 hours, discharging the cast steel out of the furnace, and air-cooling the cast steel to the room temperature;
and c, immediately placing the cast steel obtained in the step b into a heat treatment furnace, heating the cast steel from room temperature to 550 ℃ for 5 hours, keeping the temperature for 3 hours, discharging the cast steel out of the furnace, and air-cooling the cast steel to the room temperature.
The properties of the low alloy steel obtained in this example were measured and the results were as follows: the yield strength of the low alloy steel is 464MPa, the tensile strength is 597MPa, the elongation after fracture is 28.5 percent, and the low-temperature impact absorption energy A is at the temperature of minus 40 DEG C kv 41J, the annual corrosion rate in the marine atmospheric environment is 0.035mm/a, and the corrosion resistance is improved by more than 1 time compared with 20Mn steel with similar components in GB/T699.
Example 3
The embodiment provides a low alloy steel, which comprises the following chemical components in percentage by mass: c:0.15%, mn:1.6%, si:0.4%, al:0.03%, cu:0.3%, zr:0.02%, rare earth Y:0.01 percent of S is less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities.
The embodiment also provides a preparation method of the low alloy steel, which comprises the following steps:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into a medium-frequency smelting furnace for smelting, wherein the smelting temperature is 1640 ℃, deoxidizing the obtained molten steel for 3 times by using a deoxidizing agent, adjusting the temperature of the molten steel to 1580 ℃ after adjusting the components of the obtained molten steel to meet the mass percentage, and discharging the molten steel;
(2) Putting alterant on the top, middle and bottom of the inner edge of the casting ladle, preheating for 3h at 600 ℃, and then carrying out modification treatment on the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) Pouring the molten steel obtained in the step (2) at 1550 ℃ to form cast steel, and carrying out heat treatment on the obtained cast steel to obtain low alloy steel;
wherein, the heat treatment in the step (3) comprises the following steps:
a, placing the obtained cast steel in a heat treatment furnace, heating from room temperature to 650 ℃ within 6h, preserving heat for 3h, heating to 910 ℃ within 3h, preserving heat for 3h, discharging from the furnace, and air-cooling to room temperature;
b, immediately placing the cast steel obtained in the step a into a heat treatment furnace, heating the cast steel from room temperature to 510 ℃ for 5h, keeping the temperature for 3h, discharging the cast steel out of the furnace, and air-cooling the cast steel to room temperature;
and c, immediately placing the cast steel obtained in the step b into a heat treatment furnace, heating the cast steel to 530 ℃ from room temperature for 5h, keeping the temperature for 3h, discharging the cast steel out of the furnace, and air-cooling the cast steel to the room temperature.
The properties of the low alloy steel obtained in this example were measured and the results were as follows: the yield strength of the low alloy steel is 350MPa, the tensile strength is 539MPa, the elongation after fracture is 38 percent, and the low-temperature impact absorption energy A is at the temperature of minus 40 DEG C kv 56J, the annual corrosion rate in the marine atmospheric environment is 0.025mm/a, and the corrosion resistance is improved by more than 2 times compared with 20Mn steel with similar components in GB/T699.
Comparative example 1
The comparative example is low alloy steel 20Mn steel which is similar to the components of the invention in GB/T699, and the chemical components of the comparative example are as follows by mass percent: c:0.2%, mn:1.0%, si:0.35%, cr:0.2%, ni:0.2 percent of S is less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities.
The preparation method adopts the normalizing treatment at 910 ℃ recommended by the national standard.
The properties of the obtained low alloy steel were measured, and the results were as follows: the yield strength of the obtained low alloy steel is 302MPa, the tensile strength is 475MPa, the elongation after fracture is 25 percent, the low-temperature impact absorption power Akv is 21J at the temperature of minus 40 ℃, and the annual corrosion rate in the marine atmospheric environment is 0.075mm/a.
Comparative example 2
The low-alloy steel in the comparative example comprises the following chemical components in percentage by mass: c:0.19%, mn:1.2%, si:0.5%, al:0.015%, cu:0.4 percent of S is less than or equal to 0.035 percent of P, and the balance is iron and inevitable impurities.
This comparative example differs from the preparation method of example 1 in that: the chemical composition does not contain Zr and Y, and the preparation step does not comprise the step (2).
The properties of the obtained low alloy steel were measured, and the results were as follows: the yield strength of the low alloy steel is 320MPa, the tensile strength is 502MPa, the elongation after fracture is 19.5 percent, and the low-temperature impact absorption energy A is realized at the temperature of minus 40 DEG C kv 18J, annual corrosion rate in marine atmospheric environment of 0.055mm/a. The low alloy steel obtained by the comparative example has general strength and lower toughness at minus 40 ℃, and is difficult to meet the use requirement in severe low-temperature environment.
Example 4
The low alloy steel in the embodiment comprises the following chemical components in percentage by mass: c:0.19%, mn:1.2%, si:0.5%, al:0.015%, cu:0.4%, zr:0.03%, rare earth Y:0.03 percent of S is less than or equal to 0.035 percent, P is less than or equal to 0.035 percent, and the balance of iron and inevitable impurities.
The only difference between this example and the preparation method of example 1 is that: the heat treatment in the step (3) comprises the following steps:
a, placing the obtained cast steel in a heat treatment furnace, heating the cast steel to 650 ℃ from room temperature for 8h, preserving heat for 3h, heating the cast steel to 920 ℃ for 3h, preserving heat for 3h, discharging the cast steel out of the furnace, and air cooling the cast steel to room temperature;
b, immediately placing the cast steel obtained in the step a into a heat treatment furnace, heating the cast steel from room temperature to 550 ℃ after 6 hours, keeping the temperature for 3 hours, discharging the cast steel out of the furnace, and air-cooling the cast steel to the room temperature.
The properties of the obtained low alloy steel were measured, and the results were as follows: the yield strength of the low alloy steel is 403MPa, the tensile strength is 571MPa, the elongation after fracture is 27.6 percent, and the low-temperature impact absorption energy A is at minus 40 DEG C kv At 32J, the annual corrosion rate in a marine atmospheric environment was 0.023mm/a. The toughness is reduced compared to example 1.
Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present invention and not to limit the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (9)
1. The low alloy steel is characterized by comprising the following element components in percentage by mass: c:0.15 to 0.22%, mn:0.8 to 1.6%, si:0.3 to 0.5%, al:0.015 to 0.06%, cu:0.2 to 0.4%, zr:0.01 to 0.03%, Y:0.01 to 0.03 percent of iron, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, and the balance of iron and inevitable impurities;
the preparation method of the low alloy steel comprises the following steps:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into an intermediate frequency smelting furnace for smelting, wherein the smelting temperature is 1630-1660 ℃, deoxidizing the obtained molten steel by using a deoxidizing agent, adjusting the temperature of the molten steel to 1580-1620 ℃, and discharging;
(2) Placing a modifier inside the casting ladle, and modifying the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) Pouring the molten steel obtained in the step (2) at 1550-1580 ℃ to form cast steel, and carrying out heat treatment on the obtained cast steel to obtain low alloy steel;
in the step (3), the heat treatment step is as follows:
a, placing the obtained cast steel in a heat treatment furnace, heating to 650 ℃, keeping the temperature for 3-5h, continuing heating to 910-930 ℃, keeping the temperature for 3-5h, discharging from the furnace, and carrying out air cooling or water cooling to room temperature;
b, placing the cast steel obtained in the step a in a heat treatment furnace, heating to 510-530 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air-cooling to room temperature;
and c, placing the cast steel obtained in the step b in a heat treatment furnace, heating to 530-560 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air cooling to room temperature.
2. A method of making a low alloy steel as claimed in claim 1, comprising the steps of:
(1) Adding a steel source, a manganese source, a silicon source and a copper source into an intermediate frequency smelting furnace for smelting, wherein the smelting temperature is 1630-1660 ℃, deoxidizing the obtained molten steel by using a deoxidizing agent, adjusting the temperature of the molten steel to 1580-1620 ℃, and discharging;
(2) Placing a modifier inside the casting ladle, and modifying the molten steel obtained in the step (1) by using an in-ladle pouring method;
(3) And (3) casting the molten steel obtained in the step (2) at 1550-1580 ℃ to form cast steel, and carrying out heat treatment on the obtained cast steel to obtain the low alloy steel.
3. The method of claim 2, wherein in step (2), the alterant is located at the top, middle and bottom of the inner edge of the ladle.
4. The method according to claim 2 or 3, wherein the modificator consists of ferrozirconium and yttrium.
5. The method of claim 4, wherein the inoculant is prepared by: respectively crushing the zirconium iron and the yttrium into powder by adopting mechanical crushing, wherein the particle size of the obtained powder is less than or equal to 2mm, and then uniformly mixing the two kinds of powder, and wrapping the mixture by using an iron sheet to obtain the alterant.
6. The method according to claim 2, wherein in the step (3), the heat treatment step is:
a, placing the obtained cast steel in a heat treatment furnace, heating to 650 ℃, keeping the temperature for 3-5h, continuing heating to 910-930 ℃, keeping the temperature for 3-5h, discharging from the furnace, and carrying out air cooling or water cooling to room temperature;
b, placing the cast steel obtained in the step a in a heat treatment furnace, heating to 510-530 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air-cooling to room temperature;
and c, placing the cast steel obtained in the step b in a heat treatment furnace, heating to 530-560 ℃, keeping the temperature for 3-5h, discharging from the furnace, and air cooling to room temperature.
7. The method of claim 6, wherein in step a, the first temperature rise is carried out for 6-8h, and the second temperature rise is carried out for 3h.
8. The method according to claim 6, wherein the temperature is increased for 5 to 6 hours in each of the steps b and c.
9. Use of the low alloy steel of claim 1 in container corners, steel links, hooks.
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