CN106978564A - A kind of precipitation hardening type plastic die steel and preparation method thereof - Google Patents

Abstract

A precipitation hardening plastic mold steel and a preparation method thereof belong to the field of mold steel. The specific chemical composition (weight%) of the steel is as follows: C: 0.08-0.25%, Si: 0.8-1.5%, S: ≤0.030%, P: ≤0.030%, Mn: 0.4-0.8%, Ni: 2.0-4.0 %, Mo: 0-1.5%, Cr: 1.0-2.8%, Cu: 0.5-1.5%, Al: 0.5-2.0%, V: 0-0.2%, and the balance is Fe and unavoidable impurities. Compared with the prior art, the invention has higher strength, toughness and corrosion resistance, and has good comprehensive performance. Through age hardening treatment, the steel can obtain higher service hardness, higher impact toughness, and better corrosion resistance than the existing Ni-Cu-Al precipitation hardening steel, and the comprehensive performance is more excellent. Through the implementation of the above technologies, the comprehensive performance of the material can be effectively improved to meet the needs of users.

Description

A kind of precipitation hardening type plastic mold steel and preparation method thereof

technical field

The invention belongs to the technical field of mold steel, and in particular relates to a precipitation-hardening plastic mold steel and a preparation method thereof, which has excellent comprehensive performance of corrosion resistance and is suitable for various plastic mold steels with high mirror polishing performance.

Background technique

Plastic products are now widely used as substitutes for metal products, and the amount of high-strength engineering plastics, ultra-high-strength engineering plastics, and resins added with a large amount of GF is increasing. With the rapid popularization of information technology (IT) products, plastic products used in connection with IT have increased significantly, such as manufacturing LCD screen protective films, CD, DVD digital video discs, etc. Driven by plastic products, the demand for steel for plastic molds continues to increase. Compared with the past, the current plastic products require more stringent and extremely high optical specularity. The Ni-Al-Cu composite precipitation hardening plastic mold steel represented by 10Ni3MnCuAl steel can obtain a polishing performance of more than 8000#, and has good machinability, engraving and electrical discharge machinability at the same time, and has been widely used. However, at present, the steel has the problems of being prone to overheating, poor corrosion resistance of cooling holes, and low toughness during use. The purpose of the present invention is to invent a new type of age-hardening plastic mold steel with corrosion resistance and excellent comprehensive performance in all aspects by adding an appropriate amount of corrosion-resistant element Cr and rationally configuring alloy elements.

Contents of the invention

The purpose of the present invention is to provide a precipitation-hardening plastic mold steel and a preparation method thereof, which have excellent comprehensive properties of corrosion resistance.

According to above-mentioned purpose, the overall technical scheme of the present invention is:

On the basis of 10Ni3MnCuAl steel, the present invention adds element Cr and strictly controls its content to obtain corrosion resistance without affecting other properties; adding Mo element, the M ₂ C type carbide formed mainly by Mo element is the secondary element in steel. An important precipitate of the secondary hardening effect. By adding Mo element, the steel will precipitate M ₂ C carbides during the aging treatment process, which will increase the strengthening effect of the steel and increase the precipitation hardening hardness of the steel. At the same time, it also increases the hardenability of steel, which is easy to produce large-scale mold steel; adding V elements, refines austenite grains, and improves impact toughness. At the same time, the structure is refined and the polishing performance is improved. The corrosion resistance of the mold steel has good toughness, polishability and other mechanical and service properties, and it becomes a pre-hardened plastic mold steel with excellent comprehensive performance, which has good usability and application prospects.

According to above-mentioned purpose and overall technical scheme, the concrete technical scheme of the present invention is:

The chemical composition (weight %) of steel of the present invention is as follows: C: 0.08～0.25%, Si: 0.8～1.5%, S:≤0.030%, P:≤0.030%, Mn: 0.4～0.8%, Ni: 2.0～4.0 %, Mo: 0-1.5%, Cr: 1.0-2.8%, Cu: 0.5-1.5%, Al: 0.5-2.0%, V: 0-0.2%, and the balance is Fe and unavoidable impurities.

The role and proportioning basis of the above-mentioned elements are as follows:

C: Carbon has an important influence on the strength and toughness of steel. When the carbon content in the steel is low, the structure of the steel at room temperature after quenching is fine lath martensite, and the low-carbon lath martensite is strong and strong. Tough, as the carbon content increases, the degree of supersaturation of martensite increases, and the degree of distortion increases. High-carbon martensite is generally needle-shaped, hard and brittle. Excessive carbon content will damage the weldability of the steel. Precipitation hardened steels often increase the strength by adding other alloying elements to form precipitation strengthening phases, which only require a lower carbon content. The Mo element is added in the present invention, and one of the main purposes is to form M ₂ C carbide strengthening phase with C, so an appropriate amount of C element must be added, and the C content is determined to be 0.08-0.25%.

Ni: An important precipitation hardening-forming element in age-hardening steel. It combines with Al to form a Ni ₃ Al intermetallic compound strengthening phase, which precipitates during the aging process, so that the steel can obtain the expected strength and hardness. In order to ensure that the steel can obtain a hardness above 40HRC, the Ni content in the steel of the present invention is determined to be 2.0-4.0%.

Al: An important precipitation hardening forming element in age hardening steel, which combines with Ni to form a Ni ₃ Al intermetallic compound strengthening phase, which precipitates during the aging process, so that the steel can obtain the expected strength and hardness. In order to match the Ni content in the steel of the invention, the content of Al in the steel of the invention is determined to be 0.5-2.0%.

Cu: Copper has two strengthening mechanisms in steel, namely solid solution strengthening and aging precipitation strengthening. Before aging treatment, most of the copper remains in the supersaturated ferrite, which acts as solid solution strengthening. After aging, copper is precipitated in the form of ε-Cu fine and dispersed particles, resulting in significant precipitation strengthening. The maximum solubility of Cu in α-Fe is 2.2%. As the temperature decreases, the solubility of Cu in α phase decreases sharply, which creates conditions for Cu to produce aging precipitation strengthening. The contribution of solid solution strengthening to ferrite strength is only 3.8Pa for every 0.1% Cu added. Every 1% of Cu in the steel is precipitated from the supersaturated matrix, and the strength of the steel increases by 248MPa, which is much higher than the solid solution strengthening effect of Cu in the steel. Therefore, the addition of Cu to the invention steel produces aging precipitation strengthening, and the content of Cu is controlled at 0.5-1.5%.

Cr: Chromium is an important alloying element added to steel. The most significant function of Cr is to improve the corrosion resistance of steel, but at the same time it is easy to reduce the plasticity and toughness of steel. Cr has two major destinations in steel, and part of it will dissolve into ferrite to play a role of solid solution strengthening, improve the strength and hardness of ferrite matrix, and increase corrosion resistance. There is also a part of the replacement of iron atoms to form alloy cementite or alloy carbide with C. In addition, a small amount of Cr can also refine the M/A island structure in bainitic steel, and improve the influence of M/A island on the strength and toughness of steel. The main purpose of adding Cr in the present invention is to increase the corrosion resistance of steel, especially the cavitation resistance. However, the content of added Cr must be strictly controlled. If Cr is too high, it will form alloy carbides with C, which not only seriously deteriorates the impact toughness, but also reduces the content of solid solution Cr, so that it cannot exert the effect of corrosion resistance. Therefore, considering the above reasons, its content is controlled at 1.0-2.8%.

Mn: Manganese mainly exists in the matrix in the form of solid solution, which has a strong effect on stabilizing austenite. After adding a large amount of Mn to the steel, the austenite structure can be obtained at room temperature; when a small amount of Mn is added, the γ phase region and Reducing the equilibrium phase transition temperature of A ₁ and A ₃ can obtain relatively fine ferrite grains in low carbon steel by reducing the final rolling temperature of the steel; Mn can also improve the hardenability of the steel and has a certain solid solution strengthening effect. Therefore, only need to control 0.4 ~ 0.8%.

Si: Silicon is a non-carbide-forming element. Si atom substitution and solid solution can effectively reduce the diffusion rate and solubility of carbon in ferrite. Even if carbon atoms are easier to precipitate and diffuse, it is easy to change from carbonization during tempering. The precipitation in the carbide is enriched around it, thereby promoting the formation of small carbides and hindering the growth and coarsening of carbides at high temperatures. Therefore, the designed Si content is 0.8-1.5%.

P: Phosphorus forms microscopic segregation when the molten steel solidifies, and then segregates at the grain boundary when heated at the austenitizing temperature, which significantly increases the brittleness of the steel. The content of P is controlled below 0.030%, and the lower the content, the better.

S: Sulfur is an unavoidable impurity, forms FeS, and brings hot embrittlement to steel. Control the S content below 0.030%, and the lower the content, the better.

Mo: When molybdenum dissolves in ferrite, it has a solid solution strengthening effect, and when it forms carbides, it can improve the stability of carbides, and when it dissolves in austenite, it can also improve hardenability. Molybdenum is an important secondary hardening element, which forms secondary hardening by precipitation of Mo ₂ C carbides in the martensite matrix through high temperature tempering. Molybdenum can increase the resistance of steel to temper softening, that is, improve the temper stability of steel. In addition, the effect of molybdenum on temper brittleness is quite complicated. When present in steel as a single alloying element, molybdenum increases the temper brittleness of steel; but when it coexists with other elements that cause temper brittleness, such as chromium and manganese, molybdenum reduces or inhibits the temper brittleness caused by other elements. In the steel of the present invention, it is beneficial to precipitate Mo ₂ C type carbides in the aging process of the steel to improve the aging hardness of the steel, and further improve the polishing performance, and the Mo content is controlled at 0-1.5%.

V: Vanadium has a strong affinity with carbon and nitrogen, and forms extremely stable carbonitrides with them, which also mainly exist in the form of carbides in steel. The melting point of VC is 2830°C. Therefore, even heating VC at a higher austenitizing temperature can effectively prevent grain growth and increase the wear resistance of steel at the same time. Vanadium, like tungsten and molybdenum, can be dissolved into the matrix to increase the self-diffusion activation energy of α-Fe. In addition, it segregates near the dislocation line to form an air mass, which interacts with dislocations to prevent dislocation slippage and dislocation network formation. Rearranged to form a cellular substructure, which increases the recovery and recrystallization resistance of martensite and increases the tempering stability. However, when excessive V is added to the steel, element segregation will increase, and in severe cases, VC primary carbides will be formed. In the steel of the present invention, the V content is controlled at 0-0.2%.

The preparation method of the present invention: smelting by means of electric furnace, induction furnace, out-of-furnace refining, electroslag remelting, etc., casting into steel ingots, and performing slow cooling or 800-900°C heat preservation annealing treatment on the steel ingots. Fully heat the ingot, the temperature rise during heating shall not exceed 30°C/s, the heating temperature is ≤1250°C, the initial forging temperature is ≤1200°C, and the final forging temperature is ≥850°C. After forging, it is heat-preserved at 900-1000°C, slowly cooled to 650°C for heat preservation, and then furnace-cooled to below 400°C for release. Then pre-hardening heat treatment is carried out by solution and aging heat, solution treatment is carried out at 860-900 ℃, water cooling or oil cooling or air cooling is carried out to room temperature, and then heat preservation and aging treatment is carried out at 500-560 ℃.

Compared with the prior art, the present invention has the advantages of excellent comprehensive properties such as corrosion resistance, high impact toughness, high polishing performance and excellent cutting performance. Compared with the existing die steel, the steel of the present invention has higher impact toughness, better polishing performance and corrosion resistance, and can better meet user requirements.

detailed description

According to the chemical composition range designed by the present invention, 3 heats of the steel of the present invention were smelted on a 25kg vacuum induction furnace, and its specific chemical composition is as shown in Table 1. Molten steel is cast into ingots and forged to make bar. After the steel is annealed, it is processed into a sample, and undergoes solution and aging treatment (solution at 820-920°C, aging at 460-600°C). The mechanical properties at room temperature are shown in Tables 2-6.

The steel of the invention has better toughness under the premise of maintaining high hardness.

1. Invention steel 1#, 2# and 3# have higher solid solution hardness than comparative steel 4#. (See Table 2)

2. After solid solution at the same temperature and aging at different temperatures, the inventive steel 1#, 2#, and 3# have higher aging hardness than the comparative steel 4#. (See Table 3, Table 4)

3. After solid solution at the same temperature and aging at 520-560°C, the inventive steel 1#, 2#, and 3# have better impact toughness than the comparative steel 4#, which can better meet the higher toughness requirements of die steel. (See Table 5, Table 6)

Table 1 embodiment and the chemical composition of comparative steel, % by weight

Table 2 The hardness value of solid solution at different temperatures of the embodiment and the contrast steel

Table 3 Hardness values of the examples and comparison steels aged in solid solution at 850°C and aged at different temperatures

Table 4 Hardness values of the examples and comparison steels aged in solid solution at 880°C and aged at different temperatures

Table 5 Impact toughness of the examples and comparison steels aged in solid solution at 850°C and aged at different temperatures

Table 6 Impact toughness of the examples and comparison steels aged in solid solution at 880°C and aged at different temperatures

illustrate:

(1) The solid solution test was carried out in a box-type resistance furnace, kept warm for 2 hours, and cooled in air.

(2) Aging at different temperatures for 4 hours, air cooling.

Claims (3)

1. a kind of precipitation hardening type plastic die steel, it is characterised in that the specific chemical composition weight % of the steel is as follows：

C：0.08~0.25%, Si：0.8~1.5%, S：≤ 0.030%, P：≤ 0.030%, Mn：0.4~0.8%, Ni：2.0 ~4.0%, Mo：0~1.5%, Cr：1.0~2.8%, Cu：0.5~1.5%, Al：0.5~2.0%, V：0~0.2%, surplus For Fe and inevitable impurity.

2. the manufacture method of precipitation hardening type plastic die steel described in a kind of claim 1, it is characterised in that comprise the following steps：

(1) smelt：Melting is carried out using modes such as electric furnace, induction furnace, external refining, electroslag remeltings, steel ingot is cast into, to steel ingot Carry out slow cooling or 800~900 DEG C of insulation annealing processing.

(2) forge：Ingot casting is fully heated, temperature rise must not exceed 30 DEG C/s, heating-up temperature≤1250 DEG C, forging of beginning during heating Temperature≤1200 DEG C, final forging temperature >=850 DEG C.

(3) anneal：With 900~1000 DEG C of isothermal holdings after forging, 650 DEG C of insulations are slowly cooled to, stove is cold to be less than 400 DEG C and come out of the stove.

3. the pre-hardening Technology for Heating Processing of precipitation hardening type plastic die steel and its manufacture method described in a kind of claim 1 and 2, Its feature is as follows：

Pre-hardening Technology for Heating Processing：In 860~900 DEG C of progress solution treatment, water cooling of coming out of the stove or oil cooling or air-cooled to room temperature, then 500~560 DEG C of progress insulation Ageing Treatments.