CN115011872B - Manufacturing method of cold drawn round steel bar for high-dimensional-stability hydraulic valve core - Google Patents
Manufacturing method of cold drawn round steel bar for high-dimensional-stability hydraulic valve core 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
- C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
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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
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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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
- C21C7/10—Handling in a vacuum
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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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
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Abstract
The invention relates to a manufacturing method of a cold drawn round steel bar for a high-dimensional stability hydraulic valve core, wherein the diameter range of a hot rolled wire rod is 5.5-25mm. The production process flow comprises the following steps: converter or electric furnace smelting, LF refining, RH or VD degassing, continuous casting, blank surface treatment, high-temperature wire rolling and wire laying, controlled cooling and cold drawing. The cold drawn round steel bar for the hydraulic valve core produced by the invention has excellent dimensional stability in the subsequent machining and surface heat treatment processes, and can cancel the normalizing process of the hot rolled wire rod, thereby avoiding the surface decarburization caused by the normalizing process. The hot rolled wire rod and the cold drawn round steel rod for the hydraulic valve core are produced in a full-flow and all-round manner at low cost and high quality, and the purposes of energy conservation and consumption reduction are achieved.
Description
Technical Field
The present invention relates to a method for producing round steel, and more particularly to a method for producing round steel bars suitable for cold drawing.
Background
In hydraulic valves, it is necessary to achieve movement of the control mechanism by controlling movement of the hydraulic spool. The hydraulic valve core continuously makes linear reciprocating motion in the hydraulic valve. This requires the hydraulic spool to have excellent coaxiality and surface wear resistance. The production process of the hydraulic valve core comprises the following steps: chip machining- (carburization or nitridation) surface heat treatment-surface finish grinding of the core machine. Because the hydraulic valve core is a slender part with complex shape, the phenomenon of exceeding standard of size fluctuation or bending easily occurs in the carburization or nitriding surface heat treatment process, and the part processing is scrapped. The current common practice for solving the problem is to carry out off-line normalizing on the steel for the hydraulic valve core before machining, wherein the off-line normalizing can increase the decarburization on the surface of the cold drawn round steel, the corresponding requirement after normalizing increases the surface cutting quantity of the round steel, and the off-line normalizing is energy waste, so that the production cost of the steel rod for the hydraulic valve core is increased.
Therefore, the development of the cold drawn round steel bar for the hydraulic valve core with higher dimensional stability can save off-line normalizing heat treatment.
Disclosure of Invention
The invention aims to provide a manufacturing method of a cold drawn round steel bar for a high-dimensional stability hydraulic valve core, which is used for improving the dimensional stability of the round steel bar after carburization or nitriding surface heat treatment, realizing low-cost and high-quality production of a hot rolled wire rod and a cold drawn round steel bar for the hydraulic valve core, and achieving energy conservation and consumption reduction.
The invention solves the problems by adopting the following technical scheme: a manufacturing method of a hot rolled wire rod for a high dimensional stability hydraulic valve core comprises the following steps:
step one, designing element components: the weight percentage is as follows: 0.13-0.18%, si:0.15-0.35%, mn:0.60-0.90%, P: less than or equal to 0.030 percent, S:0.015-0.020%, cr:0.90-1.20%, mo:0.15-0.25%, al 0.030-0.040%, N:0.0060% -0.0200%, the balance being Fe and unavoidable impurity elements;
step two, smelting molten steel: smelting molten steel according to the element components in the first step, wherein the smelting involves primary smelting, refining and vacuum degassing;
casting: casting the molten steel into a steel billet;
step four, rolling the steel billet: the method comprises a heating process and a rolling process, wherein AlN begins to precipitate in a small amount in the heating process, the temperature of a temperature equalizing section is controlled to be 1000-1200 ℃, the heating time of the temperature equalizing section is controlled to be 30-50min, and the AlN particles are prevented from growing; the billet is heated and then is descaled by high-pressure water, and then is rolled, wherein the rolling is divided into rough rolling, medium rolling, pre-finish rolling and finish rolling, the rough rolling temperature is controlled to be 900-1000 ℃, the medium rolling temperature and the pre-finish rolling temperature are controlled to be 900-950 ℃, the wire rod spinning temperature is controlled to be 900-950 ℃, and the specification of the wire rod is 5.5-25mm;
step five, cooling after rolling: the rolled wire rod is firstly rapidly cooled and passes through a high temperature region, the cooling speed is 1.5 ℃/s-6 ℃/s, the surface of the wire rod is controlled to not generate a full decarburized layer, the depth of the full decarburized layer is controlled to be within 0.7% D, and D represents the diameter of the wire rod; when the temperature is reduced to 700-800 ℃, the slow cooling is started, the structure before the wire rod slow cooling is still in a full austenite state, no decomposition occurs, the cooling speed of the slow cooling is 0.1 ℃/s-0.5 ℃/s, the slow cooling is performed to below 500 ℃, alN is separated out again in a fine particle form in the slow cooling process, and the coil is collected and naturally cooled after the wire rod is covered, so that the balance structure of ferrite, pearlite and punctiform carbide is obtained.
Preferably, in the second step, primary smelting is converter or electric furnace smelting, and slag, alloy blocks and deoxidizing agent are added along the steel flow during tapping; the refining is LF refining, and nitrogen is supplemented into molten steel by feeding nitrogen increasing lines after or near the end; nitrogen is used as lift gas or low-gassing gas in vacuum degassing.
Preferably, the third step adopts a continuous casting process, the molten steel in the second step is transferred to a tundish to be cast into a continuous casting blank, the superheat degree of the molten steel is controlled at 15-40 ℃, argon is adopted in the whole continuous casting process to prevent the molten steel from contacting oxygen, and the continuous casting blank is cooled by hot cutting and then stacking or cooling in a slow cooling pit.
Preferably, in the fourth step, a step heating furnace is adopted for heating, the temperature of a preheating section of the heating furnace is controlled to be less than or equal to 650 ℃, the temperature of a heating temperature equalizing section of the heating furnace is controlled to be 1000-1200 ℃, and the total heating time is controlled to be 90-160min.
Preferably, in the fifth step, the rolled wire rod is cooled by a Steyr cooling line, 4-6 heat preservation covers are opened at the front section of the heat preservation cover of the cooling line, the heat preservation covers at the back are fully closed, the roller speed is 0.15-0.3m/s, the front 4-6 fans are opened for more than 20% of air quantity for quick cooling, the stay time of the wire rod in a high temperature state is shortened for controlling decarburization, and after the quick cooling is finished, the wire rod enters the heat preservation cover for slow cooling, austenite is decomposed into ferrite and pearlite in the slow cooling process, and spot carbide is generated.
The cold drawn round steel rod is obtained by cold drawing the wire rod obtained by the method, the drawing reduction ratio is set to be 5% -15%, preferably 8%, the wire rod is straightened after drawing, and the bending runout of the whole cold drawn round steel rod is controlled within 0.3 mm/m. For better cold drawing, the hot rolled wire rod is pickled and lubricated before drawing.
The application has the characteristics that:
(1) The addition of a certain amount of sulfur to the steel can improve the chip property of the steel, but the upper limit of the sulfur content is limited, and the excessive sulfur content easily causes the increase of brittleness of the material, which is unfavorable for drawing. In addition, aluminum and nitrogen with a certain proportion are added into the steel, alN precipitates are formed in the rolling process, austenite grain boundaries are pinned, coarse grains of the hydraulic valve core in the surface heat treatment process can be effectively prevented, and the deformation of the size of the part is reduced.
(2) The final structure of the wire rod is ferrite + lamellar pearlite + small amount of punctiform carbide, which is similar to the equilibrium structure, and the formation of the structure is that austenite is decomposed into ferrite + pearlite structure during slow cooling in the cover. The formation of punctiform carbides is a residue of austenite during heating, and individual points precipitate during subsequent cooling. Its presence has no effect on the performance of the wire rod.
(3) The high-temperature rolling process is adopted, alN is separated out during high-temperature rolling, the stability of austenite is improved, the decomposition potential energy behind the austenite is increased, unstable tissues such as bainite are avoided, internal stress is reduced, and the decomposed tissues tend to be in an equilibrium state as much as possible.
(4) In the processing procedure of further hydraulic valve cores, the hot rolled wire rod can improve the processability and the dimensional stability after carburization or nitriding heat treatment.
Compared with the prior art, the invention has the advantages that: al and N elements are added into the existing steel, and the high-temperature rolling, the high-temperature wire laying and the control of a quick cooling process and a slow cooling process are combined. By adopting the high-temperature rolling and high-temperature wire-spinning processes, the wire rod can obtain uniform austenite grains with the austenite grain size of 5-6 levels after actual rolling. And combining a blank heating process and a cooling process of fast and slow after wire rod wire spinning, al and N added in steel are ensured, and fine and dispersed AlN particles can be formed to pin the prior austenite grain boundary. The austenite grain size of the hydraulic valve core is ensured to be stable in carburizing heat treatment. The metallographic structure of the wire rod is consistent with that after the normalizing heat treatment, and compared with the off-line normalizing heat treatment, the off-line normalizing heat treatment can reduce the additional decarburization brought by the off-line normalizing heat treatment. The off-line normalizing can be canceled, the surface peeling process of the cold-drawn round steel can be canceled, and the size and bending deformation of the hydraulic valve core in the machining and surface heat treatment processes can be ensured.
Drawings
FIG. 1 is a microstructure of a hot rolled wire rod according to an embodiment of the present invention, wherein the microstructure is an equilibrium state of ferrite and pearlite and has a dotted carbide.
Detailed Description
The present invention is described in further detail below with reference to examples, which are exemplary and should not be construed as limiting the technical solutions of the present application.
Example 1
The embodiment relates to a cold drawn round steel bar for producing a high-dimensional-stability hydraulic valve core, which comprises the following components in percentage by weight: c:0.15%, si:0.22%, mn:0.75%, P: less than or equal to 0.013 percent, S: less than or equal to 0.016 percent, cr:1.05%, mo:0.18%, al 0.03%, N:0.0120% and the balance of Fe and unavoidable impurity elements. The diameter of the wire rod is 12mm, and the process flow is as follows: the main raw materials are smelted by a converter, refined outside the LF+RH furnace, fed into a nitrogen increasing line, and nitrogen is used as lifting gas. The molten steel is cast into a continuous casting blank by adopting argon protection in the whole process with low superheat degree of 15-30 ℃, and the blank is subjected to surface treatment after slow cooling to remove surface defects. After the treatment, the blank is heated to 1150 ℃ in a heating furnace, the total heating time is 120min, the blank is discharged from the furnace, the initial rolling temperature is 980 ℃, the intermediate rolling temperature is 920 ℃, the pre-finish rolling temperature is 930 ℃, the finish rolling temperature is 930 ℃, and the spinning temperature is 930 ℃. The Steyr is cooled, the roller speed is set to be 0.15m/s, 4 heat preservation covers at the front section are opened, the air quantity of a fan is opened to 20%, the heat preservation covers at the rear section are fully closed, the temperature of a wire rod entering the heat preservation cover is 780 ℃, and the temperature of the wire rod exiting the heat preservation cover is 480 ℃. And (5) collecting off-line air cooling after the Steyr cooling. And after combined drawing uncoiling and straightening, the drawing reduction rate is 8%. The bending jump of the whole cold drawn round steel bar can be controlled within 0.3 mm/m.
Example 2
The embodiment relates to a cold drawn round steel bar for producing a high-dimensional-stability hydraulic valve core, which comprises the following components in percentage by weight: c:0.16%, si:0.20%, mn:0.75%, P: less than or equal to 0.013 percent, S: less than or equal to 0.018 percent, cr:1.05%, mo:0.18%, al 0.035%, N:0.0180%, the balance being Fe and unavoidable impurity elements. The diameter of the wire rod is 14mm, and the process flow is as follows: the main raw materials are smelted by a converter, refined by LF+RH furnace number, and fed into a nitrogen increasing line, and nitrogen is used as lifting gas. The molten steel is cast into a continuous casting blank by adopting argon protection in the whole process with low superheat degree of 15-30 ℃, the blank is slowly cooled, then surface treatment is carried out, and surface defects are removed by peeling. After the treatment, the blank is heated to 1180 ℃ in a heating furnace, the total heating time is 120min, the blank is discharged from the heating furnace, the soaking section is insulated for 20min, the initial rolling temperature is 1000 ℃, the intermediate rolling temperature is 940 ℃, the pre-finish rolling temperature is 930 ℃, the finish rolling temperature is 950 ℃, and the spinning temperature is 940 ℃.
Cooling on a Steyr cooling line, wherein the roller speed is 0.20m/s, the front 5 heat preservation covers are opened, the air quantity of a fan is 20%, the temperature of a wire rod entering the heat preservation cover is 790 ℃, and the temperature of the wire rod exiting the heat preservation cover is 500 ℃. And (5) collecting the coil rod after the cooling, and performing off-line air cooling. And after combined drawing uncoiling and straightening, the drawing reduction rate is 10%. The bending runout of the whole cold drawn round steel bar is within 0.3 mm/m.
Table 1 mechanical properties of the wire rods of examples 1, 2
| Tensile strength MPa | Hardness HV1 | |
| Example 1 | 613 | 191 |
| Example 2 | 640 | 200 |
Comparative example Using offline normalization
Chemical composition C of hot rolled wire rod: 0.16%, si:0.24%, mn:0.79%, P: less than or equal to 0.018 percent, S: less than or equal to 0.016 percent, cr:1.13%, mo:0.17%, al 0.020%, N:0.0050%, the balance being Fe and unavoidable impurity elements. The diameter of the wire rod is 12mm, and the process flow is as follows: and (3) performing similar smelting continuous casting, and performing surface treatment on the blank after slow cooling. After the treatment, the blank is heated to 1020-1100 ℃ in a heating furnace, the blank is discharged after heat preservation for 120-160min, the initial rolling temperature is 920+/-30 ℃, the intermediate rolling temperature is 900+/-30 ℃, the pre-finish rolling temperature is 880+/-20 ℃, the finish rolling temperature is 880+/-20 ℃, and the spinning temperature is 860+/-10 ℃. The wire rod is unwound into a rod after off-line normalizing, and the surface of the rod is delivered after peeling or turning (removing a surface decarburized layer generated by normalizing) and straightening.
While the preferred embodiments of the present invention have been described in detail, it is to be clearly understood that the same may be varied in many ways by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A manufacturing method of a hot-rolled wire rod for a high-dimensional-stability hydraulic valve core is characterized by comprising the following steps of: comprising the steps of (a) a step of,
step one, designing element components: the weight percentage is as follows: 0.13-0.18%, si:0.15-0.35%, mn:0.60-0.90%, P: less than or equal to 0.030 percent, S:0.015-0.020%, cr:0.90-1.20%, mo:0.15-0.25%, al 0.030-0.040%, N:0.0060% -0.0200%, the balance being Fe and unavoidable impurity elements;
step two, smelting molten steel: smelting molten steel according to the element components in the first step, wherein the smelting involves primary smelting, refining and vacuum degassing;
casting: casting the molten steel into a steel billet;
step four, rolling the steel billet: the method comprises a heating process and a rolling process, wherein AlN begins to precipitate in a small amount in the heating process, the temperature of a temperature equalizing section is controlled to be 1000-1200 ℃, the heating time of the temperature equalizing section is controlled to be 30-50min, and the AlN particles are prevented from growing; the billet is heated and then is descaled by high-pressure water, and then is rolled, wherein the rolling is divided into rough rolling, medium rolling, pre-finish rolling and finish rolling, the rough rolling temperature is controlled to be 900-1000 ℃, the medium rolling temperature and the pre-finish rolling temperature are controlled to be 900-950 ℃, the wire rod spinning temperature is controlled to be 900-950 ℃, and the specification of the wire rod is 5.5-25mm;
step five, cooling after rolling: the rolled wire rod is firstly rapidly cooled and passes through a high temperature region, the cooling speed is 1.5 ℃/s-6 ℃/s, the surface of the wire rod is controlled to not generate a full decarburized layer, the depth of the full decarburized layer is controlled to be within 0.7% D, and D represents the diameter of the wire rod; when the temperature is reduced to 700-800 ℃, the slow cooling is started, the structure before the wire rod slow cooling is still in a full austenite state, decomposition does not occur, the cooling speed of the slow cooling is 0.1 ℃/s-0.5 ℃/s, the slow cooling is performed to below 500 ℃, alN is separated out again in a fine particle mode in the slow cooling process, and after the wire rod is covered, the coil is collected and naturally cooled, so that the balance structure of ferrite, pearlite and punctiform carbide is obtained.
2. The method according to claim 1, characterized in that: in the second step, primary smelting is converter or electric furnace smelting, and slag, alloy blocks and deoxidizing agent are added along the steel flow during tapping; the refining is LF refining, and nitrogen is supplemented into molten steel by feeding nitrogen increasing lines after or near the end; nitrogen is used as lift gas or low-gassing gas in vacuum degassing.
3. The method according to claim 1, characterized in that: and thirdly, adopting a continuous casting process, transferring the molten steel in the second step to a tundish for casting into a continuous casting blank, controlling the superheat degree of the molten steel at 15-40 ℃, adopting argon protection to avoid the molten steel from contacting oxygen in the whole continuous casting process, and cooling the continuous casting blank after hot cutting in a stacking way or cooling in a slow cooling pit.
4. The method according to claim 1, characterized in that: and step four, heating by adopting a step heating furnace, wherein the temperature of a preheating section of the heating furnace is controlled to be less than or equal to 650 ℃, the temperature of a heating temperature equalizing section of the heating furnace is controlled to be 1000-1200 ℃, and the total heating time is controlled to be 90-160min.
5. The method according to claim 1, characterized in that: and fifthly, cooling the rolled wire rod in a Steyr cooling line, opening 4-6 heat preservation covers at the front section of the heat preservation cover of the cooling line, closing the heat preservation covers at the rear section, opening the air quantity by more than 20% at the roller speed of 0.15-0.3m/s, and controlling decarburization by shortening the stay time of the wire rod in a high temperature state, wherein the wire rod enters the heat preservation cover for slow cooling after the fast cooling is finished, and austenite is decomposed into ferrite and pearlite in the slow cooling process, and spot carbide is generated.
6. A manufacturing method of a cold drawn round steel bar for a high-dimensional-stability hydraulic valve core is characterized by comprising the following steps of: the wire rod obtained by the method according to claim 1 is subjected to cold drawing, and the drawing reduction rate is set to be 5% -15%, so that the cold drawn round steel rod is obtained.
7. The method according to claim 6, wherein: the draw reduction ratio was 8%.
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