CN114875335A - Pre-hardened mirror plastic die steel with uniform section hardness - Google Patents
Pre-hardened mirror plastic die steel with uniform section hardness Download PDFInfo
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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Abstract
The invention relates to pre-hardened mirror plastic die steel with uniform section hardness, which consists of the following elements in percentage by mass: c: 0.27-0.35%, Si: 0.30-0.50%, Mn: 1.00-1.50%, S is less than or equal to 0.005, P is less than or equal to 0.015, Cr: 2.0-3.0%, Mo: 0.60-0.80%, Ni: 1.20-1.50%, Ti: 0.015-0.030%, Al is less than or equal to 0.010%, N is less than or equal to 0.0050, B: 00008-0.0015%, and the balance of Fe and inevitable impurities, and the chemical composition also needs to satisfy the formula: 3.13 percent to 6.12 percent of C + Mn is less than or equal to 3.20 percent, 2.83 percent to (2.3 percent of C + Cr + Mo)/Ni is less than or equal to 2.96 percent; the thickness of the die steel prepared by the method is 50-100 mm, the Rockwell hardness is HRC28-34, the maximum section hardness difference is less than or equal to 3HRC, the level of inclusions is low, and the surface roughness Ra of the machined and molded surface is less than or equal to 0.20 mu m.
Description
Technical Field
The invention relates to the technical field of plastic die steel, in particular to pre-hardened mirror plastic die steel with uniform section hardness.
Background
Plastic molding is an important component of the plastic industry, and only by molding can plastic be converted into useful articles. With the development of the plastic industry, the demand for transparent plastic parts and bright parts is rapidly increased, the requirement for the roughness value of the cavity surface of an injection mold is higher and higher, and the mirror surface performance becomes an important index for evaluating the technological performance of plastic mold steel. The manufacturing process of the die comprises die design, die material selection, material milling, die rough machining, die finish machining, wire cutting, electric spark and the like, and the last processing procedure is polishing. The polishing process can remove the grinding marks, cutter marks and discharge marks remained on the surface of the die part, and the white layer on the surface of the discharge machining, improve the surface roughness and meet the requirement of a mirror surface on the surface of the die. The high mirror surface mold can improve the corrosion resistance and the wear resistance of the surface of a mold cavity besides improving the attractiveness of a workpiece, so that a plastic product is easy to demould, and the injection molding period is shortened.
Relevant researches find that the good mirror finish property of the die steel mainly depends on factors such as structural compactness, hardness uniformity, purity, inclusion morphology and the like of the steel, and DS type large-particle inclusions are not allowed to exist in the die steel. The high-quality die is manufactured by combining various advanced polishing processes on the basis that the die steel has excellent metallurgical quality. Therefore, in the case of steels for mirror surface plastic molds, in addition to the uniformity of hardness in the cross-sectional direction of the steel material, the type and size of inclusions are also controlled. That is to say, on the basis of guaranteeing the service performance of the die steel, it is very important to improve the metallurgical quality. The steel purity is high, various inclusions and air holes in the steel are few, and the polishing effect of the material can be improved.
The pre-hardening means that the steel mill can meet the hardness requirement of the mold during use through heat treatment, so that the large and medium plastic molds with complex and precise shapes do not need heat treatment after the manufacture is finished, and the deformation and cracking of the molds in the heat treatment process are avoided, thereby ensuring the manufacturing precision of the molds.
The strict control of metallurgical process can raise the purity of steel, reduce gas and impurity in steel and raise the mirror performance of die steel. However, various metallurgical processes are subject to final use performance, the comprehensive performance meeting the final use requirement has practical significance, and the design of proper chemical components is a source for comprehensively solving the pre-hardened mirror surface plastic die steel. According to the different Ni content, the pre-hardened mirror plastic die steel in China can be divided into two series of low Ni and high Ni, and the scheme adopted by the scheme is a low Ni type.
The pre-hardened mirror plastic die steel is a small product, and related reports in the prior art are relatively few.
Chinese patent application No. 200810060480.5 discloses a quench-hardened free-cutting mirror plastic die steel, which is a novel plastic die steel with hardenability, free-cutting property, mirror polishing property and corrosion resistance, and adopts chemical components (weight percentage, percent) C: 0.30-0.70, Si is less than or equal to 1.0, Mn is less than or equal to 0.90, Cr: 7.0-11.5, Cu is less than or equal to 1.0, Ni is less than or equal to 2.5, B: 0.30-0.75 percent of Fe, less than or equal to 0.10 percent of S, less than or equal to 0.04 percent of P, and the balance of Fe and inevitable impurities. The production process comprises the steps of electric furnace-die casting-forging and cogging-annealing-secondary forging-spheroidizing annealing-quenching and tempering heat treatment, the typical metallographic structure comprises a martensite matrix and a small amount of eutectic B compounds, the hardness of steel is 56-58HRC, and the milling surface quality reaches Ra less than or equal to 0.20 mu m. The alloy of the scheme has high cost and contains Cr: 7.0-11.5 percent of Ni, less than or equal to 2.5 percent of Ni, long process flow, low yield caused by die casting, forging and cogging, and multiple heat treatments, not only increase the process cost, but also increase the burning loss.
Chinese patent application No. 201110175031.7 discloses a process for producing mirror plastic mold steel, which comprises the following chemical components (by weight percent): 0.26-0.42, Si: 0.30-0.50, Mn: 1.40-2.10, Cr: 1.40-2.10, Mo: 0.20-0.50, Ni: 0.80-1.30 percent of Fe, less than or equal to 0.012 percent of S, less than or equal to 0.015 percent of P, and the balance of Fe and inevitable impurities. The production process comprises the steps of electric furnace smelting, VD refining and electroslag casting, wherein the steel ingot heating temperature is not more than 1240 ℃, the initial forging temperature is 1050-. The scheme adopts electroslag pouring, has high requirements on skills of equipment and operators, has high requirements on equipment technology in forging and forming, has long process time of sand cooling for 72 hours, and ensures that the obtained mirror surface plastic die steel has good cutting performance, but does not introduce the actual performance of the surface roughness after processing.
The chinese patent application No. 200810048359.0 discloses "a corrosion-resistant high-mirror-surface plastic extrusion die steel", which adopts chemical components (weight percentage, percent) C: 0.18 to 0.26, Si: 0.80-1.20, Mn: 0.20-0.40, Cr: 13.0-15.0, Mo: 1.85-2.50, Ni is less than or equal to 0.60, Cu: 0.80-1.20, V: 0.07-0.15 percent, less than or equal to 0.0070 percent, less than or equal to 0.008 percent of S, less than or equal to 0.015 percent of P, and the balance of Fe and inevitable impurities. The production process comprises the following steps: electric furnace-VD-electroslag remelting-high temperature annealing-forging (rolling) into steel bar-QT or T treatment. The invention belongs to medium-carbon martensitic stainless steel, precipitates a large amount of dispersed carbide through tempering to generate high secondary hardness and high-temperature strength, and also has better oxidation resistance, heat strength and mechanical processing performance. Only the chemical components are claimed and no description is made of the properties.
The application number CN201810833317.1 chinese patent application discloses a corrosion-resistant mirror surface die steel and a preparation method thereof, the mirror surface die steel comprises the following components (weight percentage, percent): 0.35-0.45, Si: 0.35-0.55, Mn: 0.40-0.70, Cr: 12.0-15.0, Mo: 0.08-0.20, Ni: 0.10-0.30, W: 0.08-0.30, V: 0.10-0.30, Ti: 0.01 to 0.05 percent, less than or equal to 0.012 percent of S, less than or equal to 0.020 percent of P, and the balance of Fe and inevitable impurities. The production process comprises the steps of electric furnace smelting, argon protection pouring and VD furnace refining, electroslag remelting, annealing, forging and annealing, quenching and tempering heat treatment, wherein quenching and heating are carried out to 1120-fluid-containing 1200 ℃, the heating time is 12-20 hours, and tempering is carried out at 500-fluid-containing 590 ℃, and the time is 5-20 hours; in the cooling process after quenching, a comprehensive mode of spray cooling, water spray cooling and air blast cooling is also adopted, and the hardness range of the obtained die steel is HRC 45-50. The proposal is provided for solving the problem that rare earth and a large amount of alloy elements are required to be added in the prior art, but noble elements such as Ni, Mo, W, V and the like are added, so that the production cost is increased; the process routes of electroslag remelting, forging and the like are adopted, so that the production cost is greatly increased, and the yield is low; after quenching, fog cooling, water cooling and air cooling are alternately adopted, the requirements on cooling equipment and operation level are high, and the production period is long.
The chinese patent application No. 201010501576.8 discloses a method for smelting mirror surface plastic die steel, wherein the components of the smelted mirror surface plastic die steel are (weight percentage): 0.06-0.16, Si is less than or equal to 0.40, Mn: 1.40-1.70, Cr is less than or equal to 0.30, Mo: 0.20-0.40, Ni: 2.90-3.40, Cu: 0.80-1.00, Al: 0.70 to 1.30 percent, N is less than or equal to 0.0070, S is less than or equal to 0.030, P is less than or equal to 0.030, and the balance is Fe and inevitable impurities. The production process adopts an EBT electric furnace-LF (deoxidation, slagging-component adjustment-Al wire feeding) -VD, aluminum powder and aluminum pills are deoxidized and slagging are adopted in the LF after tapping of the EBT electric furnace, Cu, C, Mn, Mo and Ni elements are preferentially adjusted in the LF, argon stirring operation is adopted, after the elements are uniform, Al wires are fed to adjust the Al content, and argon stirring is weakened after the Al content is adjusted; and carrying out vacuum treatment in a VD furnace, still adopting small argon gas for stirring in order to avoid the Al layering problem, and opening a VD station for steel casting after the temperature reaches the requirement. The scheme only puts forward a claim on the smelting method, introduces the technical scheme in detail, and does not introduce the surface roughness condition of the processed die.
As can be seen, the above mirror plastic mold steels all strictly limited the S, P impurity content, and only a single invention case limited the [ N ] content. If the compound formed by gas and some microelements in the steel is aggregated or the compound inclusion with micron-sized size is formed by taking the high-melting point compound as the core, the compound inclusion can affect the surface quality of the milled mirror plastic die steel, and the figure 1 shows that the roughness value is increased by the inclusion in the mirror processing process.
Therefore, to control the type and size of inclusions in the steel, the proper chemical composition is the first step of the comprehensive solution of the pre-hardened mirror plastic mold steel in addition to controlling the metallurgical quality.
Disclosure of Invention
The invention aims to provide pre-hardened mirror surface plastic die steel with uniform section hardness, and the pre-hardened mirror surface plastic die steel can comprehensively solve the problem of high mirror surface performance of pre-hardened plastic die steel. The invention aims to solve the problem that high-quality pre-hardened mirror surface plastic die steel is a unified body with uniform internal quality and section hardness, and the design of proper chemical components is the first step of comprehensively solving the pre-hardened mirror surface plastic die steel.
The invention relates to pre-hardened mirror plastic die steel with uniform section hardness, which consists of the following elements in percentage by mass: c: 0.27-0.35%, Si: 0.30-0.50%, Mn: 1.00-1.50%, S is less than or equal to 0.005, P is less than or equal to 0.015, Cr: 2.0-3.0%, Mo: 0.60-0.80%, Ni: 1.20-1.50%, Ti: 0.015-0.030%, Al is less than or equal to 0.010%, N is less than or equal to 0.0050, B: 00008-0.0015%, and the balance of Fe and inevitable impurities, and the chemical composition also needs to satisfy the formula: 3.13 percent to 6.12 percent of C + Mn is less than or equal to 3.20 percent, 2.83 percent to (2.3 percent of C + Cr + Mo)/Ni is less than or equal to 2.96 percent.
The thickness of the die steel prepared by the method is 50-100 mm, the Rockwell hardness is HRC28-34, the maximum section hardness difference is less than or equal to 3HRC, the level of inclusions is low, and the surface roughness Ra of the machined and molded surface is less than or equal to 0.20 mu m.
The invention relates to a production method of pre-hardened mirror plastic die steel, which comprises the following steps: molten iron desulphurization, converter smelting, vacuum treatment, continuous casting, casting blank heating, rolling, normalizing and tempering heat treatment, wherein:
(1) heating a casting blank: controlling the heating temperature of the casting blank to 1150-1250 ℃ and the heat preservation time to be 30-40 min;
(2) tempering heat treatment: the tempering temperature is 600-650 ℃, and the heat preservation time is 1.5-3.0 min/mm.
The design principle analysis of the chemical components of the invention is as follows:
C. n is both a gap element and a strong austenite forming element, and has certain effects on improving hardenability, high-temperature austenite stability and strength; the fine carbide and nitride are main precipitation strengthening phases in the steel, can improve the hardness of the pre-hardened mirror plastic die steel, and are favorable for improving the mirror performance. However, excessive M (CN) can cause uneven aging hardness of the pre-hardened mirror plastic die steel, and C, N is not easy to be too high according to the requirement of service hardness of the pre-hardened mirror plastic die steel (HRC 28-34), so that the content of C in the invention is controlled to be 0.27-0.35%, and N is less than or equal to 0.0050%.
Si: the process of using silicon as a deoxidizer in the steelmaking process is mature, and the cost is low; si exists in a solid solution form in the steel, the strength and the hardness of the steel can be obviously improved, and the lower limit of the Si content is 0.30%; the high Si content brings the risk of cracks on the casting blank and the steel plate and great inconvenience to the production structure, so the upper limit of the Si content is 0.50%.
Mn: solid solution in ferrite and austenite, thereby enlarging the austenite region, reducing the phase change point in the steel cooling process, improving the hardenability of the steel, and obviously improving the strength and hardness of the steel; mn can also form MnS with a higher melting point with S in steel, so that a FeS film is prevented from being formed on a crystal boundary, and the hot brittleness of the steel is eliminated, so that the lower limit of the Mn content is 1.00%; however, if the Mn content is too high, the fluidity of the cast slab is lowered, and internal quality defects such as shrinkage cavities and bubbles are generated, so the upper limit of the Mn content is 1.50%.
P: p is a harmful element in steel, increases the cold brittleness of the steel, reduces the plasticity, and also causes cold cracks on a steel plate due to the segregation to a crystal boundary, but the reduction of the P content increases the production cost, so that the phosphorus content in the steel is required to be less than or equal to 0.015 percent.
S: s is also a harmful element in steel, so that the steel generates hot brittleness, the ductility and the toughness of the steel are reduced, the steel generates anisotropy, the molten iron S removal technology is mature, the production cost is not greatly influenced, and the upper limit of the S content is 0.005%.
Cr: strong ferrite forming elements, austenite area reducing elements and a certain content of Cr can enable steel to form martensite under the air cooling condition, so that the strength and the hardness of the steel are improved; cr can improve the hardenability of steel and can also ensure that the die steel has certain corrosion resistance, and a certain amount of Cr needs to be added for a thick steel plate to improve the hardenability so as to make up for the loss of strength and hardness caused by thickness; cr is also a medium-strength carbide-forming element that can form carbides in steel to increase the strength and hardness of the steel, but too high Cr and Mn are added to steel at the same time, and surface cracks are easily formed during rolling, so that the Cr content is limited to 2.0-3.0%.
Mo: mo forms M in steel 6 C type compound, so as to increase the solid solubility of Cr and improve the wear resistance; the dispersion hardening can be caused after tempering, which is beneficial to improving the hardness and the thermal stability, improving the tempering brittleness temperature and avoiding the tempering brittleness; mo is a noble metal element, and the Mo content is limited to 0.60-0.80% for cost reasons.
Ni: the steel has extremely strong capability of stabilizing austenite and expanding austenite, can improve the toughness of steel, improve the thermal fatigue performance of a die and also improve the hardenability of the steel; however, the excessive Ni increases the production cost, the mirror surface die steel in China can be divided into two series of low-nickel and high-nickel according to the different Ni content, the scheme adopted by the scheme is of a low-Ni type, and the Ni content is controlled to be 1.20-1.50%.
Ti: the steel is a strong carbide and nitride forming element, a formed compound can prevent austenite grains from growing when a casting blank is heated, microalloy carbonitride precipitated by strain induction in the rolling process can prevent deformed austenite from recrystallizing or prevent recrystallized grains from growing, rolling is controlled in a non-recrystallization region, the uniformity of the structure can be improved, better comprehensive performance is obtained, and 0.015-0.030% of Ti can play a better role. In addition, Ti has higher affinity to S than Mn, forms Ti sulfide in steel to fix sulfur, and the Ti sulfide is spherical to reduce the harm of inclusion.
Al: the most economical and effective deoxidizing element, the development of modern detection technology, can quickly and accurately measure the oxygen content in front of the furnace, thereby determining the proper Al addition; the excessive Al may exist in the form of oxide (B-type inclusion) and silicate (C-type inclusion) in the steel, which is extremely disadvantageous to the mirror surface property of the die steel, and therefore, the upper limit of the Al content is less than or equal to 0.010%.
B: is an element which strongly improves the hardenability of steel, and particularly, the pre-hardened mirror plastic die steel sheet is large, and an addition amount of 0.0008% is indispensable. The upper limit of the content of B is limited to 0.0015% because B has a small atomic radius and is easily deviated to grain boundaries, so that the dislocation density of adjacent regions is increased to serve as hydrogen traps to induce cracking of the grain boundaries.
It is also limited to 3.13% to 6.12% C + Mn to 3.20%, 2.83% to (2.3C + Cr + Mo)/Ni to 2.96%, for the following reasons:
C. mn is an element capable of obviously improving the strength and the hardness of steel, and the combined addition of 6.12C + Mn which is more than or equal to 3.13 percent is necessary; the technical requirement of the pre-hardened mirror plastic die steel is that the Rockwell hardness HRC28-34 is narrow, so that the combined addition of 6.12C + Mn is less than or equal to 3.20%.
C. Cr, Mo and Ni are elements for improving the hardenability of steel, and are elements for guaranteeing the uniformity of section hardness. Because the pre-hardened mirror surface plastic die steel is mostly an extra-thick plate (the thickness is more than or equal to 50 mm), under the condition of no hardenability or insufficient hardenability elements, the surface cooling is fast and the core cooling is slow in the cooling process of the steel, so that the surface layer and the core structure are not uniform, the hardness of the cross section direction is not uniform, even the surface hardness meets the technical standard requirement, the core hardness is lower than the technical standard requirement, the delivery technical requirement of the pre-hardened mirror surface plastic die steel cannot be met, and the delivery cannot be carried out, not to mention the use effect of the pre-hardened mirror surface plastic die steel is influenced. Therefore, certain amount of elements C, Cr, Mo and Ni for improving the hardenability of the steel are added into the pre-hardened mirror plastic die steel; in addition, Ni also improves the toughness of the steel and the thermal fatigue performance of the die, and it is necessary that (2.3C + Cr + Mo)/Ni be not less than 2.83%. B is also an element that strongly improves the hardenability of steel, and if the hardenability of steel is improved by B alone, it is necessary to add a large amount of B, and as described above, B easily segregates to grain boundaries, and excessive B easily induces grain boundary cracking, so that the hardenability of steel is improved mainly by C, Cr, Mo, and Ni for pre-hardened mirror plastic mold steel. The Rockwell hardness requirement range of the pre-hardened mirror plastic die steel is very narrow, and is HRC28-34, so the content ranges of C, Cr, Mo and Ni (2.3C + Cr + Mo)/Ni are limited to be less than or equal to 2.96%.
The reasons for controlling the production process parameters of the present invention are detailed below:
the invention relates to a production method of pre-hardened mirror plastic die steel, which comprises the following steps: molten iron desulphurization, converter smelting, vacuum treatment, continuous casting, casting blank heating, rolling, normalizing and tempering heat treatment, wherein:
(1) heating a casting blank: controlling the heating temperature of the casting blank to 1150-1250 ℃ and the heat preservation time to be 30-40 min;
(2) tempering heat treatment: the tempering temperature is 600-650 ℃, and the heat preservation time is 1.5-3.0 min/mm.
The heating temperature of the casting blank is controlled to be 1150-1250 ℃, because the heating temperature is kept high enough, so that elements such as C, Si, Mn, Cr, Ni and the like are fully dissolved and uniformly distributed in high-temperature austenite, conditions are created for obtaining a homogenized steel plate, and the performance of the invention steel is prevented from being deteriorated due to poor structure caused by excessive growth of the high-temperature austenite.
The steel needs tempering heat treatment, the normalized structure of the steel is martensite and bainite, and the uneven hardness performance is caused by the uneven structure. Through tempering, martensite decomposition is promoted, a tempered martensite + tempered sorbite structure is formed, the performances of the two structures are similar, and uniform section hardness can be obtained. The pre-hardened mirror plastic die steel with uniform section hardness, which is obtained by the invention, has Rockwell hardness HRC28-34, maximum section hardness difference of less than or equal to 3HRC, low inclusion level and surface roughness Ra of a machined molding surface of less than or equal to 0.20 mu m.
Compared with the prior art, the invention has the following beneficial effects:
the invention aims to provide a pre-hardened mirror surface plastic die steel which has high mirror surface performance on the premise of uniform section hardness. The elements for ensuring the uniformity of the section hardness, such as C, Mn, Cr, Mo, Ni and B, are elements which must be added, but Cr is a carbide forming element, Mn can cause soft inclusions (such as MnS) to exist in steel, but the difference of deformation between the soft inclusions and a matrix can cause damage, the nucleation, growth and aggregation processes of holes in the matrix finally cause ductile fracture, and the orange peel phenomenon can be generated. The proper chemical components are the first step of comprehensively solving the problem of pre-hardening mirror plastic die steel except controlling the metallurgical quality by controlling the type and the size of inclusions in the steel. The scheme of the invention is to design proper chemical components, and meet the limited formulas of two chemical elements to achieve the uniformity of the internal quality and the section hardness, thereby obtaining the high-quality pre-hardened mirror surface plastic die steel. The Rockwell hardness HRC28-34 of the plastic die super-thick steel plate, the maximum section hardness difference of the plastic die super-thick steel plate is less than or equal to 3HRC, the level of inclusions is low, the surface roughness Ra of a machined molding surface is less than or equal to 0.20 mu m, and the manufacturing requirement of a large die block die is met.
Drawings
FIG. 1 is a schematic view showing an increase in roughness value caused by inclusions during mirror finishing in the background art;
FIG. 2 is a graph showing inclusions in a pre-hardened mirror-finished plastic mold steel produced in example 3 of the present invention, enlarged by a factor of 100.
Detailed Description
In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific examples, which are only exemplary to illustrate the technical solution of the present invention and do not limit the present invention in any way.
The following table 1 is a list of values of chemical components in percentage by mass in each example of the present invention;
table 2 below is a list of values of the main process parameters of the embodiments of the present invention;
table 3 below shows the cross-sectional direction hardness and the milling surface quality and polishing effect of each example of the present invention.
The preparation method comprises the following steps: the components of the molten steel smelted by the converter are finely adjusted in the RH vacuum treatment process, the thickness of the intermediate billet and the finish rolling temperature of the cast billet are controlled to prepare a finished product, and then the normalizing and tempering heat treatment is carried out, wherein:
(1) heating a casting blank: controlling the heating temperature of the casting blank to 1150-1250 ℃ and the heat preservation time to be 30-40 min;
(2) tempering heat treatment: the tempering temperature is 600-650 ℃, and the heat preservation time is 1.5-3.0 min/mm.
TABLE 1 tabulation of chemical composition (wt%) values for die steels of various embodiments of the invention
Table 2 list of values of the main process parameters of the embodiments of the present invention;
TABLE 3 hardness in cross-section direction and quality of milled surface and polishing effect of examples of the present invention
As can be seen from Table 3, the cross-sectional hardness of the pre-hardened mirror plastic die steel prepared by the five embodiments of the invention is uniform, the Rockwell hardness HRC28-34, the maximum cross-sectional hardness difference is less than or equal to 3HRC, the inclusion level is low, and the surface roughness Ra of the machined molding surface is less than or equal to 0.20 μm. The six HRC values measured according to the test standards of the hardness test were less different from each other in terms of the surface hardness and the core hardness of 5 examples. The difference between the maximum and minimum values for the six HRC values of example 2 was 2.9HRC, and the difference between the maximum and minimum values for the six HRC values of example 5 was only 1.7 HRC.
FIG. 2 is a diagram showing inclusions in a pre-hardened mirror plastic die steel prepared in example 3 of the present invention at a magnification of 100 times, and it can be seen that the die steel prepared in the present invention is very pure in steel quality and very few in inclusions under an optical microscope.
The pre-hardened mirror surface plastic mould cavity is complex and has strict requirements on dimensional accuracy and surface roughness, so the pre-hardened mirror surface plastic mould steel has excellent cutting processability, mirror surface polishing and grinding performance and pattern etching performance; the large-section module has the advantages of uniform hardness distribution along the section, good basic performances such as wear resistance, electric spark processing property, weldability, plastic product corrosion resistance and the like, and the metallurgical essence of the performance requirements is that the structure is stable along the section direction, the hardness distribution is uniform, the level of inclusions is low, the surface roughness value Ra of a processed forming surface is less than or equal to 0.20 mu m, and the large-section module is suitable for manufacturing high-quality pre-hardened mirror surface plastic molds.
The embodiments described above are merely specific examples given for the purpose of illustrating the invention and are not to be construed as limiting the invention in any way, and insubstantial changes from the forms and descriptions set forth above, which do not depart from the scope of the claims, should be construed as being covered thereby. The invention is not limited to the specific embodiments described above.
Claims (3)
1. The pre-hardened mirror plastic die steel with uniform section hardness is composed of the following elements in percentage by mass: c: 0.27-0.35%, Si: 0.30-0.50%, Mn: 1.00-1.50%, S is less than or equal to 0.005, P is less than or equal to 0.015, Cr: 2.0-3.0%, Mo: 0.60-0.80%, Ni: 1.20-1.50%, Ti: 0.015-0.030%, Al is less than or equal to 0.010%, N is less than or equal to 0.0050, B: 00008-0.0015%, and the balance of Fe and inevitable impurities, and the chemical composition also needs to satisfy the formula: 3.13 percent to 6.12 percent of C + Mn is less than or equal to 3.20 percent, 2.83 percent to (2.3 percent of C + Cr + Mo)/Ni is less than or equal to 2.96 percent.
2. The pre-hardened mirror plastic die steel with uniform section hardness as claimed in claim 1, wherein: the thickness of the die steel is 50-100 mm, the Rockwell hardness HRC is 28-34, the maximum section hardness difference is less than or equal to 3HRC, the level of inclusions is low, and the surface roughness Ra of a machined molding surface is less than or equal to 0.20 mu m.
3. A method of producing a pre-hardened mirrored plastic mold steel as claimed in claim 1, comprising: molten iron desulphurization, converter smelting, vacuum treatment, continuous casting, casting blank heating, rolling, normalizing and tempering heat treatment, wherein:
(1) heating a casting blank: controlling the heating temperature of the casting blank to 1150-1250 ℃ and the heat preservation time to be 30-40 min;
(2) tempering heat treatment: the tempering temperature is 600-650 ℃, and the heat preservation time is 1.5-3.0 min/mm.
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| CN115354228A (en) * | 2022-08-29 | 2022-11-18 | 山东钢铁集团日照有限公司 | Production method of high-uniformity pre-hardened plastic die steel |
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| CN1646717A (en) * | 2002-04-03 | 2005-07-27 | 法国安达斯戴乐公司 | Bulk steel for the production of injection moulds for plastic material or for the production of pieces for working metals |
| CN103397261A (en) * | 2013-07-31 | 2013-11-20 | 首钢总公司 | Steel plate for plastic mold for rolling continuous casting slab with thickness of 400mm and production method of steel plate |
| CN113621885A (en) * | 2021-08-18 | 2021-11-09 | 宝武集团鄂城钢铁有限公司 | Boron-treated pre-hardened plastic mold super-thick steel plate and production method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1646717A (en) * | 2002-04-03 | 2005-07-27 | 法国安达斯戴乐公司 | Bulk steel for the production of injection moulds for plastic material or for the production of pieces for working metals |
| CN103397261A (en) * | 2013-07-31 | 2013-11-20 | 首钢总公司 | Steel plate for plastic mold for rolling continuous casting slab with thickness of 400mm and production method of steel plate |
| CN113621885A (en) * | 2021-08-18 | 2021-11-09 | 宝武集团鄂城钢铁有限公司 | Boron-treated pre-hardened plastic mold super-thick steel plate and production method thereof |
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| CN115354228A (en) * | 2022-08-29 | 2022-11-18 | 山东钢铁集团日照有限公司 | Production method of high-uniformity pre-hardened plastic die steel |
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