CN116043106A - High-purity high-toughness long-service-period cold work die steel and preparation method thereof - Google Patents

High-purity high-toughness long-service-period cold work die steel and preparation method thereof Download PDF

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CN116043106A
CN116043106A CN202211388206.7A CN202211388206A CN116043106A CN 116043106 A CN116043106 A CN 116043106A CN 202211388206 A CN202211388206 A CN 202211388206A CN 116043106 A CN116043106 A CN 116043106A
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CN116043106B (en
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刘海松
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Hubei Nantiangong Mould Technology Co ltd
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
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    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising
    • C—CHEMISTRY; METALLURGY
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    • 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
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    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/18—Electroslag remelting
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C33/04—Making ferrous alloys by melting
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    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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Abstract

The invention relates to high-purity high-toughness long-service-period cold-working die steel and a preparation method thereof, wherein the cold-working die steel comprises the following elements in percentage by mass: c:1.3 to 1.5 percent, si:0.60 to 0.80 percent, S is less than or equal to 0.030 percent, P is less than or equal to 0.030 percent, mn:0.40 to 0.60 percent, cr:9.0 to 10.0 percent, V:0.2 to 0.3 percent, mo:0.8 to 1.2 percent of Al:0.1 to 0.2 percent, ti: 0.3-0.5%, T [ O ]]≤10ppm，[N]Less than or equal to 40ppm, and the balance of Fe and unavoidable impurities; the preparation method of the cold work die steel comprises the following steps: intermediate frequency furnace smelting, die casting, electrode preparation, electroslag remelting, annealing, forging, spheroidizing annealing, quenching and tempering; the cold-work die steel finished product prepared by the components and the method has good performance: the hardness of the alloy can reach HRC more than or equal to 58, and the impact toughness a k The service cycle of the die made of the cold-working die steel is more than or equal to 60J and more than or equal to 15000 times, the impact work is improved by more than 3 times compared with the original Cr12MoV steel, the toughness is obviously improved, and the service cycle is greatly improved compared with the existing Cr12 and Cr8 die steel.

Description

High-purity high-toughness long-service-period cold work die steel and preparation method thereof
Technical Field
The invention relates to the technical field of die steel manufacturing, in particular to high-purity high-toughness long-service-period cold-work die steel and a preparation method thereof.
Background
Cold work die steel is mainly used for manufacturing various dies for press forming of metal materials at room temperature, and comprises a stamping die, a stretching die, a bending and flanging die, an imprinting die, a cold extrusion die, a cold heading die, a rolling die, a powder pressing die and the like. At present, various industries develop a great deal of work in the aspects of high reinforcement and reduction of materials, and the reaction forces of punching, pulling, pressing, bending and the like applied to a cold working die in the processing process are also increased, so that the requirements on the comprehensive performance of the die materials are higher and higher in order to ensure the longer service period of the die.
The series of die steel based on Cr-containing alloy is the main raw material of cold-working die, the strength and wear resistance of the die are increased along with the increase of Cr content, but the hardenability and toughness are correspondingly deteriorated, while along with the increase of the strength of the metal material to be processed, a series of die materials such as Cr12 series are needed to be used as the base material of the cold-working die steel, and the series of die materials have the advantages of high strength and good wear resistance, but very developed netlike carbide, insufficient toughness, easy occurrence of fracture failure in the process of processing the die, and serious influence on the service period of the die.
Internationally, developed countries such as Japan, austrian and Swedish develop a series of cold-work die steels with high wear resistance, high toughness and long service period, and most of multi-dimensional composite alloy steels are based on Cr8, and the impact toughness of the multi-dimensional composite alloy steels is greatly improved on the premise of ensuring the wear resistance of the die steels by mainly adjusting the content ratio of elements such as C, cr, mo, V or adding a certain amount of microalloy elements such as Nb and Al, etc., so that carbide distribution and uniformity are better than those of the traditional Cr5 and Cr8 steels. Such as DC53 developed by Dain Special steels, sweden, ASSAB88, austrian, K340, K360, etc. In China, in order to ensure the strength and wear resistance level of the initial mold, cr12 series is most used as the first choice of cold-working mold steel, and because of the high carbon, eutectic carbide densely distributed in a steel base is generated, the toughness and fatigue resistance of the series of mold steel are poor, and failure phenomena such as cracking, tool breakage and the like are easy to occur after a certain period of service, and maintenance and repair are needed through welding repair and the like, so that the maintenance cost and the time cost are increased for processing enterprises.
A great deal of work is done by the students in the industry in the aspects of cold work die steel composition design and performance optimization, such as the patent with the application number of CN201910379977.1, and a cold work die steel is designed, wherein the cold work die steel comprises the following components in percentage by mass: c:0.90 to 1.20 percent, si:0.90 to 1.20 percent, mn:0.30 to 0.60 percent, cr: 7.00-9.00%, W:0.20 to 0.60 percent, mo:0.60 to 1.20 percent, ni:0.40 to 1.20 percent, S:0.05 to 0.15 percent, cu:0.20 to 0.60 percent of Al:0.20 to 0.50 percent, P is less than or equal to 0.02 percent, and the balance is Fe. The preparation method of the cold work die steel comprises the following steps: batching, smelting, casting, electroslag remelting, forging, spheroidizing annealing, and finally quenching and tempering heat treatment. Compared with common Cr12, cr8 and Cr5 series cold-working die steel, the cold-working die steel disclosed by the invention has the advantages that the high toughness ratio is ensured, the abrasion resistance is improved by more than 1 time compared with Cr8Mo2VSi, the cutting performance is improved by more than 3 times compared with Cr12MoV, and the overall service life of the die is prolonged by 0.5-3 times.
Patent application number is CN200710171694.5 relates to a high-strength and high-toughness cold-working die steel and a manufacturing method thereof, and belongs to the technical field of alloy steel manufacturing processes. The alloy steel comprises the following chemical components in percentage by weight: c:0.9 to 1.0 percent, cr: 9-10%, mo:2.0%, V:0.8 to 1.0 percent, si:1.0%, P < 0.02%, S < 0.02%, and Fe in balance. The preparation process and the steps of the cold work die steel are as follows: (1) smelting, (2) electroslag remelting, (3) annealing, (4) rough forging, (5) re-annealing, (6) spheroidizing annealing, and (7) quenching tempering. The method of the invention can prepareThe hardness of the alloy steel can reach 61-63 HRC, and the impact power a K The impact strength can reach 61-85J, the impact strength is improved by more than 3 times compared with the original Cr12MoV steel, and the toughness is obviously improved.
There is also a method of composite strengthening by microalloy components, such as the patent with application number CN201410797731.3, which designs a C-N-B composite hardened high wear resistant cold work die steel comprising the following specific chemical components in weight percent: c:1.5 to 1.9 percent, si:0.5 to 1.5 percent, S is less than or equal to 0.030 percent, P is less than or equal to 0.030 percent, mn is less than or equal to 0.5 percent, cr:8.5 to 11.0 percent, V:0.1 to 0.8 percent, N:0.05 to 0.15 percent, B:0 to 0.1 percent, and the balance of Fe and unavoidable impurities. Compared with the prior art, the invention has higher hardness and wear resistance and good comprehensive performance while keeping toughness. Compared with the existing Cr12MoV cold-working die steel, the invention optimizes the Cr content and the C content, and adopts the thought and the method of C-N-B composite reinforcement, so that the hardness of the steel is increased on the premise of not deteriorating eutectic carbide, and the material has higher wear resistance. The content of Si is increased to improve the hardness and the wear resistance. Through the implementation of the technology, the wear resistance of the material can be effectively improved, and the long-life requirement of a user is met. The steel has a combination of properties that is more excellent than Cr12MoV steel.
Some documents also prepare die steel with excellent performance by adding elements such as Zn, ti and the like to carry out modification treatment on Cr12MoV and combining an optimized heat treatment process. As in paper (study of heat treatment process of modified Cr12MoV die steel) (heat treatment of materials), the modification treatment of Cr12MoV die steel by Zn is performed to improve the form of eutectic carbide, and the die steel with excellent hardness and toughness is prepared by performing the treatment by the optimal tempering heat treatment process of 1080 ℃ quenching and 250 ℃. The paper "influence of Ti modification treatment on the structure and performance of Cr12MoV die steel" and "influence of Ti addition on the mechanical performance of Cr12MoV die steel" both show that the addition of a certain amount of Ti has a direct effect on the improvement of impact toughness of die steel, but also show that the yield of Ti has obvious fluctuation.
However, from the industrial production point of view, the invention and the literature have certain problems, and the addition of Ni can improve the impact toughness, but obviously increases the alloy cost; the addition of S is beneficial to cutting performance, but the component control difficulty is increased, direct high S pollution is caused to a furnace body, and the cutting performance is not a main difficulty of die processing under the background that the current numerical control machine tool processing level is continuously improved; however, segregation of Cu in grain boundaries is one of the important reasons for forming inter-grain cracks of castings; as for the method for preparing the high-wear-resistance cold-work die steel by using N, B composite hardening, the solubility of N in non-austenitic steel is limited, and although V and N can form nitride precipitation strengthening, the V/N ratio is strictly controlled, so that N atoms are prevented from precipitating to form internal pores, and the internal quality and performance of the die steel are seriously deteriorated; b is beneficial to hardenability, but also is extremely easy to increase the brittleness of the casting, is unfavorable for improving toughness, and even causes the failure of the casting. Both papers mention the action of Ti in die steel, titanium reacts with carbon to produce a large amount of dispersed titanium carbide, titanium nitride, titanium carbide and titanium nitride as effective heterogeneous cores of carbide nucleation, so that the morphology and distribution of eutectic carbide are improved, the impact toughness of the die steel can be obviously improved, and the service period is prolonged, but in industrial production, the open casting of an intermediate frequency furnace is generally used as the main part, the yield of Ti is difficult to ensure, tiOx is generated after oxidation and exists as inclusions in the steel to influence the quality and performance of the die steel.
Therefore, developing a cold-work die steel with high toughness, high hardness and long service period and an industrialized sustainable preparation method thereof become a problem to be solved in industry.
Disclosure of Invention
The invention aims to provide high-purity high-toughness long-service-period cold-working die steel and a preparation method thereof, aiming at the problems of more eutectic carbides, insufficient impact toughness and short effective service period of the existing cold-working die steel.
The invention relates to high-purity high-toughness long-service-period cold working die steel, which consists of the following elements in percentage by mass: c:1.3 to 1.5 percent, si:0.60 to 0.80 percent, S is less than or equal to 0.030 percent, P is less than or equal to 0.030 percent, mn:0.40 to 0.60 percent, cr:9.0 to 10.0 percent, V:0.2 to 0.3 percent, mo:0.8 to 1.2 percent of Al:0.1 to 0.2 percent, ti: 0.3-0.5%, T [ O ] less than or equal to 10ppm, N less than or equal to 40ppm, and Fe and unavoidable impurities as the rest.
The hardness HRC of the cold working die steel is more than or equal to 58, and the impact toughness a is higher than or equal to 58 k And the service period of the mold made of the cold-work mold steel is more than or equal to 60J and is more than or equal to 15000 times.
The invention relates to a preparation method of high-purity high-toughness long-service-period cold work die steel, which comprises the following steps:
(1) Intermediate frequency furnace smelting
The alloy except aluminum and titanium is added step by step according to the target composition, after melting, aluminum particles are added into molten steel, the adding amount is 1kg/t molten steel, the alloy is mainly used for deep deoxidization, al and Ti are added to the target composition range, and an electrode steel ingot is poured;
(2) Electroslag remelting
After electrode assembly welding is finished, spraying Al+Ti mixed powder with the spraying amount of 40-60 g/t steel on the surface of the electrode, and starting electroslag remelting after the coating is dried, wherein the mass ratio of Al to Ti in the Al+Ti mixed powder is 1:3, the Al+Ti mixed powder is sprayed by a high-pressure spray gun, the solvent is water, and the solid-water mass ratio is 1:2; the slag system of electroslag remelting is 60% CaF by mass 2 +25%Al 2 O 3 +6～10%CaO+5～9%TiO 2 Argon sealing protection is carried out in the whole process; ending electroslag remelting, and T [ O ] in molten steel]≤10ppm，[N]Less than or equal to 40ppm, electrolytic inclusion Al 2 O 3 The content is less than or equal to 0.003 percent, and the finished product is consistent with the content;
(3) Forging
Directly transferring the electroslag remelted steel ingot into a furnace for annealing treatment, wherein the annealing temperature is 800-820 ℃ and the annealing time is 6-10 h (the annealing temperature and the annealing time are related to the diameter of the steel ingot, specifically the diameter is 0.3m or less, the annealing temperature is 800 ℃, the annealing time is 6h, the annealing temperature is increased along with the increase of the diameter, the annealing time is prolonged to the diameter of 0.6m or more, the annealing temperature is 820 ℃, the annealing time is 10 h), and cooling along with the furnace after annealing; heating the annealed steel ingot to 1230-1250 ℃, forging by adopting a three-upsetting three-drawing process, and forging into a cuboid blank with the required external dimension manufactured by a die at the final satin temperature of 900-920 ℃;
(4) Spheroidizing annealing
Spheroidizing annealing: heating the steel forging blank to 800-820 ℃, preserving heat for 4-5 h, cooling to 450-500 ℃ by a cooling speed furnace of 30-40 ℃/s, discharging from the furnace, and cooling to room temperature by air;
(5) Quenching and tempering
Heating the material in stages: heating to 550-560 ℃ at a heating rate of 10-12 ℃/min, preserving heat for 50-100 min, heating to 800-820 ℃ at a heating rate of 15-20 ℃/s, preserving heat for 60-90 min, heating to 980-1020 ℃ at a heating rate of 30-40 ℃/s, preserving heat for 40-60 min, cooling to room temperature after oil quenching, tempering at 180-200 ℃ and tempering time of 3-4 h.
The chemical components adopted in the cold working die steel of the invention are as follows:
c: carbon is an indispensable element in cold work die steel. Carbon is the most effective solid solution strengthening element in steel on the one hand, and on the other hand, is the forming element for forming various carbides, especially in cold work die steel, to ensure a sufficient carbide content for wear resistance. However, the negative effect of too high a carbon content is to reduce the impact toughness of the steel, especially if the carbon and alloy contents are simultaneously high to some extent, eutectic reactions will occur, coarse eutectic carbides are formed, and the toughness of the steel is significantly reduced. Therefore, from the comprehensive consideration of toughness matching, the carbon content is determined to be 1.3-1.5 percent in the invention.
Cr: chromium is the most important carbide forming element in cold work die steels. Chromium has a carbide forming ability with carbon greater than iron and manganese and less than tungsten, molybdenum, etc. When the chromium content reaches a certain range, it can form (Fe, cr) 7 C 3 And (Fe, cr) 23 C 6 Is very beneficial to improving the wear resistance of the steel. Thus, the chromium content is generally greater than 5% for cold work die steels that require particularly wear resistance. However, if the Cr content is too high, a eutectic reaction can occur to form coarse eutectic carbide, the toughness is deteriorated, the larger the eutectic carbide particles are, the worse the distribution uniformity is, the worse the impact toughness is, and the Cr content is 9.0-10.0% by comprehensively considering the reasons.
Mo: molybdenum is also an important carbide forming element, can effectively improve the hardenability, improves the wear resistance of die steel together with Cr carbide, and simultaneously can optimize the distribution of the carbide, reduce the number of oversized massive Cr carbide, thereby obviously improving the toughness, and limiting the Mo content to 0.8-1.2 percent.
V: vanadium has very strong affinity with C, N and can form stable carbide with it. The melting point of VC is 2830 ℃. Therefore, at austenitizing temperatures, VC is preformed, effectively preventing grain growth while increasing the wear resistance of the steel. In addition, vanadium also increases tempering stability, improves the service stability of the die and prolongs the service period, but if a large amount of N exists in steel, V (C, N) and VN are easy to form, strong grain boundary segregation tendency exists in the forging temperature range (900-1200 ℃), and the defect of tearing along the grain boundary in the forging process is easy to cause early failure of the die, so that the N content is reduced, or N in the steel is fixed in other ways, so that the method becomes an important way for reducing the adverse effect of precipitates of V; in the invention, after electroslag remelting, the content of [ N ] is less than or equal to 40ppm, and the content of V is limited to be 0.2-0.3%.
Ti: titanium is one of the most important microalloying elements in steel. In combination with the effect of V in the previous paragraph, V, ti composite microalloying has become an important steel reinforcement way in the actual combined production of steel based on converter smelting. Specifically, in the preparation process of the die steel, tiN can be precipitated earlier than V (C, N) and VN, the stability is excellent, and the effect of preventing austenite from growing can be partially played, so that the precipitation of V (C, N) and VN in the forging process is reduced, the grain boundary binding force is reduced, and even the tendency of grain boundary tearing is generated, and TiC with high hardness is also one of important precipitates for improving the hardness of the die steel due to the existence of C. However, the stability control of the Ti content in the die steel smelting and electroslag remelting processes is a great difficult problem, and is one of the important contents of the invention.
The vanadium, tungsten and molybdenum are dissolved into the matrix to improve the self-diffusion activation energy of alpha-Fe, and in addition, the vanadium, tungsten and molybdenum are biased to form air clusters near dislocation lines, and interact with dislocation to prevent dislocation slip and dislocation network rearrangement to form a cellular substructure, so that the recovery recrystallization resistance of martensite is increased, and the tempering stability is improved. Vanadium is also an important secondary hardening element, when the addition amount exceeds 0.5%, a secondary hardening effect can be generated through precipitation of VC, the secondary hardening peak temperature tends to shift towards high temperature along with the increase of the vanadium amount, the hardening strength is improved, and the overaging speed is low. The invention mainly considers that V and C, N are utilized to form carbide V (C, N) with high melting point and high hardness, thereby preventing austenite grains from growing and refining the grains in the quenching and heating process of steel, and simultaneously increasing the wear resistance. However, too much V not only tends to produce stable eutectic carbide particles, but also combines C and N, thereby affecting the solution hardening effect of C and N. Therefore, the V content in the steel of the present invention is controlled to be 0.2 to 0.3%.
N: the radius of nitrogen atoms is very small (0.07 nm), very similar to carbon, and is the interstitial solid solution element in steel, so many properties are similar to carbon. Solid solution hardening is one of the most effective hardening modes in steel, and the effect of adding a part of carbon is supplemented by solid solution strengthening action of nitrogen, so that the hardness and wear resistance of the steel can be remarkably increased. However, too high N greatly affects the impact toughness of the steel, and as a die steel, the service life is significantly reduced. Therefore, the invention adopts an ultra-low nitrogen control mode, namely N is less than or equal to 40ppm.
On the one hand, the other elements Mn and Si are derived from raw materials and also play a part of deoxidization alloying effect, while P, S is an unavoidable impurity and should be controlled to the lower limit as much as possible.
The adoption of the component system and the preparation method of the invention can continuously and stably produce the cold-work die steel with high purity, and the T [ O ] in the finished steel]≤10ppm，[N]Less than or equal to 40ppm, electrolytic inclusion Al 2 O 3 The content is less than or equal to 0.003 percent.
The main invention points and principles of the preparation method of the invention are explained as follows:
(1) Intermediate frequency furnace smelting
The alloy except aluminum and titanium is added step by step according to the target components, after melting, aluminum particles are added into molten steel, the addition amount is 1kg/t, and the alloy is mainly used for deep deoxidization. And then Al and Ti are added to the target range, and steel ingots (electrodes) are cast. Step-by-step aluminum addition is performed toIn the first step, when aluminum is added for deep deoxidization, al 2 O 3 The inclusions float up under better dynamic conditions.
(2) Electroslag remelting
After electrode welding is completed, al+Ti (proportion 1:3) mixed powder is coated on the surface of the electrode, the coating amount is 40-60 g/t steel, electroslag remelting is started after the coating is dried, and slag system is 60% CaF 2 +25%Al 2 O 3 +6～10%CaO+5～9%TiO 2 And (5) argon sealing protection is performed in the whole process. In the electroslag remelting process, even though argon is used for protection in the whole process, the phenomenon of mass transfer of air to liquid slag and liquid slag to molten steel inevitably occurs, so that oxidation of Al and Ti in high-temperature molten steel can be caused, and therefore, the Al and Ti coated on the surface of an electrode can continuously enter the molten steel, the stability of components is ensured, and the Al in the slag is formed 2 O 3 And TiO 2 There is a tendency to slow down the oxidation reactions of Al, ti going to the right and thus into the slag. Electroslag remelting is a key link for controlling components and purity and is also a final link. TiO in slag 2 The content of Ti in the electrode is more than or equal to 0.50 percent along with the change of the content of Ti in the electrode, and the content of Ti in the slag is TiO 2 The content is controlled to be 5 percent, and as the Ti content in the electrode is reduced, tiO in the slag 2 The content of Ti in the electrode is less than or equal to 0.35 percent, and the content of TiO in the slag is increased 2 The content was controlled to 9%. CaO and TiO in slag 2 The total amount was kept at 15%.
After the electroslag remelting is finished, the T [ O ] in the steel sample can be controlled]≤10ppm，[N]Less than or equal to 40ppm, electrolytic inclusion Al 2 O 3 The content is less than or equal to 0.003 percent, and the finished product is consistent with the content.
(3) Forging
The internal stress of the casting piece can be eliminated by carrying out full annealing treatment before forging, the internal stress of the casting piece is avoided, meanwhile, the annealing temperature of 800-820 ℃ is lower than the temperature range described in the literature, abnormal growth of crystal grains can be avoided while tissue homogenization is promoted, the larger the casting piece is, the higher the annealing temperature is, the annealing time is prolonged, the variability of the crystal grains in the casting piece can be basically eliminated by the three-heading three-drawing process, and the uniformity of the performance in all directions is ensured.
(4) Spheroidizing annealing
Spheroidizing annealing: heating the steel forging blank to 800-820 ℃, preserving heat for 4-5 h, cooling to 450-500 ℃ by a cooling speed furnace of 30-40 ℃/s, discharging from the furnace, and cooling to room temperature by air; annealing can ensure that the spheroidized structure is obtained, and meanwhile, the non-uniformity and the local abnormal growth of crystal grains are reduced, so that the uniformity of the performance of a finished product is affected.
(5) Quenching and tempering
The material is heated in a grading way, so that internal stress and even cracks caused by asynchronous tissue transformation in different areas in the heating process can be reduced, and the uniformity of the tissue is ensured. The process of quenching at proper temperature and tempering at low temperature ensures that fine martensite and carbide tissues are obtained, and better toughness matching is achieved, namely the impact toughness is obviously improved on the basis of ensuring high hardness and high strength.
Compared with the prior art, the invention solves the following problems in the prior art:
(1) The invention combines the characteristics of the component systems of Cr8 and Cr12 series die steel, optimizes the component systems, and solves the problems of more eutectic carbides, insufficient impact toughness and short effective service cycle of cold work die steel.
(2) Solves the problems that the yield of easily oxidized elements is unstable and the content of inclusions is higher in the multi-element alloying process in the production process system based on intermediate frequency furnace smelting, thereby influencing the impact toughness of the finished product.
(3) The problems of component stability and purity control in the electroslag remelting process are solved through the electroslag remelting slag system and process operation optimization.
The cold-work die steel finished product produced by adopting the components and the preparation method has good performance: hardness HRC is more than or equal to 58, impact toughness a k And more than or equal to 60J. The current most novel high-strength double-phase automobile plate is taken as a base plate for a comparison test (the same roll of cold-rolled base plate is leveled into a specific size), the grade is 600DP, the yield strength is 630MPa, the thickness is 1.4mm, and the surface is not plated; the mold prepared by the mold steel of the invention has a service cycle of 15000 times or more, and the same type of steel has a service cycle of 5000 times or less and a service cycle of 60 times or less of a Cr12MoV mold and a Cr8 mold by adopting the same forming speed, stamping pressure and stroke length and taking the occurrence of excessive scratches, meat drop failure and the like on the surface of the mold as evaluation standards00 times.
Detailed Description
In order to better explain the technical solution of the present invention, the following description of the technical solution of the present invention is given by way of example only and not by way of limitation in any way, in conjunction with specific examples.
Table 1 below shows a list of chemical compositions (wt%) of the steels of each example and the comparative example according to the present invention;
table 2 below is a list of values of main production process parameters of the steels of each example and the comparative example of the present invention;
table 3 below shows a list of the main performance parameters of the steels of each example of the present invention and the comparative example.
The preparation method of the high-purity high-toughness long-service-period cold work die steel comprises the following steps of:
(1) Intermediate frequency furnace smelting
The alloy except aluminum and titanium is added step by step according to the target composition, after melting, aluminum particles are added into molten steel, the adding amount is 1kg/t molten steel, the alloy is mainly used for deep deoxidization, al and Ti are added to the target composition range, and an electrode steel ingot is poured;
(2) Electroslag remelting
After electrode assembly welding is finished, spraying Al+Ti mixed powder with the spraying amount of 40-60 g/t steel on the surface of the electrode, and starting electroslag remelting after the coating is dried, wherein the mass ratio of Al to Ti in the Al+Ti mixed powder is 1:3, the Al+Ti mixed powder is sprayed by a high-pressure spray gun, the solvent is water, and the solid-water mass ratio is 1:2; the slag system of electroslag remelting is 60% CaF by mass 2 +25%Al 2 O 3 +6～10%CaO+5～9%TiO 2 Argon sealing protection is carried out in the whole process; ending electroslag remelting, and T [ O ] in molten steel]≤10ppm，[N]Less than or equal to 40ppm, electrolytic inclusion Al 2 O 3 The content is less than or equal to 0.003 percent, and the finished product is consistent with the content;
(3) Forging
Directly transferring the electroslag remelted steel ingot into a furnace for annealing treatment, wherein the annealing temperature is 800-820 ℃ and the annealing time is 6-10 h (the annealing temperature and the annealing time are related to the diameter of the steel ingot, specifically the diameter is 0.3m or less, the annealing temperature is 800 ℃, the annealing time is 6h, the annealing temperature is increased along with the increase of the diameter, the annealing time is prolonged to the diameter of 0.6m or more, the annealing temperature is 820 ℃, the annealing time is 10 h), and cooling along with the furnace after annealing; heating the annealed steel ingot to 1230-1250 ℃, forging by adopting a three-upsetting three-drawing process, and forging into a cuboid blank with the required external dimension manufactured by a die at the final satin temperature of 900-920 ℃;
(4) Spheroidizing annealing
Spheroidizing annealing: heating the steel forging blank to 800-820 ℃, preserving heat for 4-5 h, cooling to 450-500 ℃ by a cooling speed furnace of 30-40 ℃/s, discharging from the furnace, and cooling to room temperature by air;
(5) Quenching and tempering
Heating the material in stages: heating to 550-560 ℃ at a heating rate of 10-12 ℃/min, preserving heat for 50-100 min, heating to 800-820 ℃ at a heating rate of 15-20 ℃/s, preserving heat for 60-90 min, heating to 980-1020 ℃ at a heating rate of 30-40 ℃/s, preserving heat for 40-60 min, cooling to room temperature after oil quenching, tempering at 180-200 ℃ and tempering time of 3-4 h.
TABLE 1 list of chemical compositions (wt%) of steels of each example and comparative example of the present invention
Figure SMS_1
Table 2 below is a list of values of the main production process parameters of the steels of each example and the comparative example of the present invention
Figure SMS_2
TABLE 3 list of the main performance parameters of the steels of each example and comparative example of the present invention
Figure SMS_3
The service period of the die in the table 3 is 600DP, 630MPa of yield strength and 1.4mm of thickness, and the surface is not coated by taking the current novel high-strength double-phase automobile plate as a substrate for a comparison test (the same roll of cold-rolled substrate is flattened into a specific size). The test was performed using the same forming speed, stamping pressure and stroke length, with the occurrence of overstandard scratches, meat drop failure, etc. on the die surface as evaluation criteria.
As can be seen from the above Table 3, the cold work die steel finished product prepared by the components and the method has good performance: its hardness can be up to 58-62 HRC, impact power a K The impact power can reach 60-81J, the impact power is improved by more than 3 times compared with the original Cr12MoV steel, the toughness is obviously improved, the service period is more than 15000 times, and compared with the existing Cr12 and Cr8 die steel, the service period is greatly improved.
The above-described embodiments are merely specific examples of the present invention for illustrating the present invention and are not to be construed as limiting the present invention in any way, and any insubstantial changes made in the above-described embodiments without departing from the scope of the claims of the present invention should be construed as falling within the scope of the claims of the present invention.

Claims (3)

1. The cold-work die steel with high purity and high toughness and long service period is characterized by comprising the following elements in percentage by mass: c:1.3 to 1.5 percent, si:0.60 to 0.80 percent, S is less than or equal to 0.030 percent, P is less than or equal to 0.030 percent, mn:0.40 to 0.60 percent, cr:9.0 to 10.0 percent, V:0.2 to 0.3 percent, mo:0.8 to 1.2 percent of Al:0.1 to 0.2 percent, ti: 0.3-0.5%, T [ O ] less than or equal to 10ppm, N less than or equal to 40ppm, and Fe and unavoidable impurities as the rest.
2. The high purity high toughness long service life cold work die steel according to claim 1, wherein: the hardness HRC of the cold working die steel is more than or equal to 58, and the impact toughness a is higher than or equal to 58 k And the service period of the mold made of the cold-work mold steel is more than or equal to 60J and is more than or equal to 15000 times.
3. The method for preparing the high-purity high-toughness long-service-period cold work die steel according to claim 1, which is characterized by comprising the following steps:
(1) Intermediate frequency furnace smelting
The alloy except aluminum and titanium is added step by step according to the target composition, after melting, aluminum particles are added into molten steel, the adding amount is 1kg/t molten steel, the alloy is mainly used for deep deoxidization, al and Ti are added to the target composition range, and an electrode steel ingot is poured;
(2) Electroslag remelting
After electrode assembly welding is finished, spraying Al+Ti mixed powder with the spraying amount of 40-60 g/t steel on the surface of the electrode, and starting electroslag remelting after the coating is dried, wherein the mass ratio of Al to Ti in the Al+Ti mixed powder is 1:3, the Al+Ti mixed powder is sprayed by a high-pressure spray gun, the solvent is water, and the solid-water mass ratio is 1:2; the slag system of electroslag remelting is 60% CaF by mass 2 +25%Al 2 O 3 +6～10%CaO+5～9%TiO 2 Argon sealing protection is carried out in the whole process; ending electroslag remelting, and T [ O ] in molten steel]≤10ppm，[N]Less than or equal to 40ppm, electrolytic inclusion Al 2 O 3 The content is less than or equal to 0.003 percent, and the finished product is consistent with the content;
(3) Forging
Directly transferring the electroslag remelted steel ingot into a furnace for annealing treatment, wherein the annealing temperature is 800-820 ℃, the annealing time is 6-10 h, and cooling along with the furnace after annealing; heating the annealed steel ingot to 1230-1250 ℃, forging by adopting a three-upsetting three-drawing process, and forging into a cuboid blank with the required external dimension manufactured by a die at the final satin temperature of 900-920 ℃;
(4) Spheroidizing annealing
Spheroidizing annealing: heating the steel forging blank to 800-820 ℃, preserving heat for 4-5 h, cooling to 450-500 ℃ by a cooling speed furnace of 30-40 ℃/s, discharging from the furnace, and cooling to room temperature by air;
(5) Quenching and tempering
Heating the material in stages: heating to 550-560 ℃ at a heating rate of 10-12 ℃/min, preserving heat for 50-100 min, heating to 800-820 ℃ at a heating rate of 15-20 ℃/s, preserving heat for 60-90 min, heating to 980-1020 ℃ at a heating rate of 30-40 ℃/s, preserving heat for 40-60 min, cooling to room temperature after oil quenching, tempering at 180-200 ℃ and tempering time of 3-4 h.
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