High thermal conductivity hot forming die steel

Abstract

The application discloses a high-thermal-conductivity hot forming die steel and belongs to the technical field of hot working of metal materials. The formula comprises, in percentage by weight, C 0.14-0.30%, Si 0.05-0.08%, Mn 0.10-0.40%, V 0.10-0.20%, Cr 1.40-2.30%, Mo 0.80-1.50%, Ni 0.12-2.00%, Cu 1.50-2.50%, Ce 0.01-0.05%, SiC 1.25-2.40%, and the balance of Fe. The hot forming die steel prepared by the scheme has the characteristics of high strength and high thermal conductivity, the tensile strength is up to 1920 MPa, the thermal conductivity can reach 59.7 W·m ‑1 ·K ‑1 , and the manufacturing cost is low.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hot working of metal materials, and particularly relates to a high-thermal-conductivity hot forming die steel. BACKGROUND

[0002] Die steel is the "mother of industry" in manufacturing industry, and as the core basic material for manufacturing various types of dies, the quality of the die steel directly determines the precision, service life and production efficiency of the die. As an important branch of special steel, die steel refers to a steel type specially used for manufacturing cold punching dies, hot forging dies, die casting dies and various types of dies, and plays a crucial role in industrial production. According to statistics, more than 75% of rough machining parts and more than 50% of finished machining parts in modern manufacturing industry need to be manufactured through die forming, and the quality of the die directly affects the quality of the machining process, the precision of the product, the yield and the production cost. The performance of the die steel is mainly affected by the die material itself and the heat treatment process in addition to reasonable die structure design and machining precision.

[0003] Die steel is divided into three categories according to the use: cold working die steel, hot working die steel and plastic die steel. Cold working die steel is mainly used for manufacturing dies for pressure processing of materials at room temperature, such as blanking dies, cold extrusion dies and the like, and requires high hardness, high strength and high wear resistance; hot working die steel is used for manufacturing dies working at high temperature, such as die casting dies, hot forging dies and the like, and in addition to high temperature strength, also needs to have good heat fatigue resistance; plastic die steel is specially used for manufacturing plastic product forming dies, and has high requirements for polishing property and corrosion resistance.

[0004] Patent CN116426837A discloses a high-strength high-toughness corrosion-resistant plastic die steel and a preparation method thereof, the die steel prepared by the method has high grain size, can reach grade 10, the transverse notch impact can reach 50J, the quenched and tempered hardness reaches 50HRC, and the corrosion resistance can reach ≤0.01mm / a. Patent document CN116716542A discloses a heat-resistant and corrosion-resistant high-strength and high-toughness plastic die steel and a preparation process thereof, the die steel prepared by the method has transverse notch impact of 310J, quenched and tempered hardness of 49HRC, and excellent heat-resistant and corrosion-resistant properties. Patent CN108950413A discloses a die steel material and a preparation method and use thereof, the die steel material prepared by the method has a significantly reduced thermal fatigue damage factor and greatly improved thermal fatigue resistance.

[0005] Traditional hot working die steel relies on high Cr, Mo and V alloy elements to improve high temperature strength, but high alloying leads to low thermal conductivity, which affects the heat dissipation efficiency of the die and aggravates the thermal fatigue cracks. Low thermal conductivity leads to local overheating of the die, shortens the service life and increases the energy consumption. The addition of Mo, W and other elements can improve the thermal conductivity, but the addition of high content of Mo, W and other elements leads to high production cost of the die steel and limited processing performance. SUMMARY

[0006] The present application aims to provide a high-thermal-conductivity hot forming die steel to solve the problem of low thermal conductivity caused by high alloying of conventional die steel, aggravating thermal fatigue cracks and short service life.

[0007] Technical scheme: A high-thermal-conductivity hot forming die steel, the formula of which comprises, by weight percentage: C 0.14-0.30%, Si 0.05-0.08%, Mn 0.10-0.40%, V 0.10-0.20%, Cr 1.40-2.30%, Mo 0.80-1.50%, Ni 0.12-2.00%, Cu 1.50-2.50%, Ce 0.01-0.05%, SiC 1.25-2.40%, and the balance being Fe.

[0008] The preparation method of the high-thermal-conductivity hot forming die steel comprises the following steps: melting, electrode rod preparation, surface oxidation layer removal, electroslag remelting, segmented quenching, three times of tempering, and cyclic quenching.

[0009] Preferably, the melting mode is vacuum melting furnace melting, and the melting temperature is 1600-1650℃.

[0010] Preferably, the electrode rod diameter is 610-700mm.

[0011] Preferably, the slag system component used for electroslag remelting is CaF2-CaO-Al2O3-MgO, the dissolution speed is 5kg / min, the slag pool depth is 80mm, and the cooling water flow is 1.0m 3 / h.

[0012] Preferably, the segmented quenching preheating temperature is 400-500℃, and the austenitizing temperature is 1100-1150℃.

[0013] Preferably, the first tempering temperature is 750℃, the second tempering temperature is 700℃, and the third tempering temperature is 600℃.

[0014] Preferably, the cyclic quenching temperature is 1200-1250℃, and the cycle number is 4.

[0015] Beneficial effects: the formula of the present application is based on the traditional die steel formula, reduces the content of Si in the formula, thereby reducing the lattice distortion, at the same time, the formula adds a large amount of Cu and a proper amount of Ni, which can greatly improve the thermal conductivity of the alloy. However, due to the addition of Cu, the strength of the alloy will be reduced, therefore, the formula adds Ni and SiC, Cu and Ni can improve the thermal conductivity of the die steel, SiC greatly improves the strength of the die steel, while retaining high thermal conductivity, avoiding the negative effect of strength reduction caused by Cu. At the same time, combined with the segmented quenching and high temperature cyclic quenching process in the preparation process, the alloy is rapidly heated to austenitizing temperature for multiple times and then rapidly cooled, the alloy is refined by multiple phase change processes, further improving the thermal conductivity of the die steel. The formula of the present application does not contain expensive metal elements or rare earth elements, and a die steel material with high strength and high thermal conductivity is prepared, which not only has excellent performance, but also reduces the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Optical microscope photo of the die steel prepared in Example 1.

[0017] Figure 2 Optical microscope photo of the die steel prepared in Comparative Example 4. DETAILED DESCRIPTION

[0018] In order to make the technical scheme of the present application clearer, the present application will be further described in detail below in combination with specific examples.

[0019] Example 1

[0020] The materials are added into a vacuum induction melting furnace according to the formula 1 in Table 1, the furnace cover is closed, vacuum is extracted to a vacuum degree of 20 Pa, the melting temperature is set to 1650℃, the melting time is 40 min, and the melting chamber swing angle is 55°. After the melting is completed, the steel is poured to form a 700mm electrode rod, the surface oxide layer is first physically removed, and then polished to a metal phase using a polisher. The electrode rod is placed in an ESR furnace, a small piece of metal is used to arc, the slag system is CaF2-CaO-Al2O3-MgO (the ratio is about 60%-20%-15%-5%), the slag pool depth is 80mm, the electrode feeding speed and melting rate are synchronized at 3mm / s, the input power is 25KW, the time is 15min, the dissolution speed is 5kg / min, the slag pool depth is 80mm, the cooling water flow is 1.0m 3The material is added into a vacuum induction melting furnace according to the formula 2 in Table 1, the furnace cover is closed, vacuum is extracted to a vacuum degree of 20 Pa, the melting temperature is set to 1600 ℃, the melting time is set to 50 min, and the melting chamber swing angle is set to 55°. After the melting is completed, the electrode rod is poured out and the surface oxide layer is removed. The electrode rod is placed in an ESR furnace, a small piece of metal is used to arc, the slag system is CaF2-CaO-Al2O3-MgO (the ratio is about 60%-20%-15%-5%), the slag pool depth is 80 mm, the electrode feeding speed is synchronized with the melting rate, the speed is 3 mm / s, the input power is 25 KW, the time is 15 min, and an electroslag ingot is prepared. Under nitrogen protection, the material is subjected to segmented quenching, the preheating temperature is 500 ℃, the austenitizing temperature is 1150 ℃, after being poured out, the material is temporarily stayed in air for about 20 seconds, the surface temperature is reduced to 900 ℃, the material is placed in 80 ℃ hot oil, then placed in PAG solution and cooled to 80 ℃. Once tempering is performed at 750 ℃, twice tempering is performed at 700 ℃, and three times tempering is performed at 600 ℃, and the material is air cooled to room temperature. The mold steel 1 is obtained through box furnace cyclic quenching, the temperature is 1250 ℃, the time is 6 h, the cycle number is 4 times, and the cooling method is furnace cooling. The optical microscope photograph is shown in Figure 2. Figure 1 .

[0021] Example 2

[0022] The material is added into a vacuum induction melting furnace according to the formula 2 in Table 1, the furnace cover is closed, vacuum is extracted to a vacuum degree of 20 Pa, the melting temperature is set to 1600 ℃, the melting time is set to 50 min, and the melting chamber swing angle is set to 55°. After the melting is completed, the electrode rod is poured out and the surface oxide layer is removed. The electrode rod is placed in an ESR furnace, a small piece of metal is used to arc, the slag system is CaF2-CaO-Al2O3-MgO (the ratio is about 60%-20%-15%-5%), the slag pool depth is 80 mm, the electrode feeding speed is synchronized with the melting rate, the speed is 3 mm / s, the input power is 25 KW, the time is 15 min, and an electroslag ingot is prepared. Under nitrogen protection, the material is subjected to segmented quenching, the preheating temperature is 500 ℃, the austenitizing temperature is 1150 ℃, after being poured out, the material is temporarily stayed in air for about 20 seconds, the surface temperature is reduced to 900 ℃, the material is placed in 80 ℃ hot oil, then placed in PAG solution and cooled to 80 ℃. Once tempering is performed at 750 ℃, twice tempering is performed at 700 ℃, and three times tempering is performed at 600 ℃, and the material is air cooled to room temperature. The mold steel 1 is obtained through box furnace cyclic quenching, the temperature is 1250 ℃, the time is 6 h, the cycle number is 4 times, and the cooling method is furnace cooling. The optical microscope photograph is shown in Figure 2.

[0023] Comparative Example 1

[0024] The main difference from Example 1 is that no Cu is added in the formula, the specific formula is shown in Table 1 formula 3, and the preparation process is the same as that of Example 1, and the mold steel 3 is obtained.

[0025] Comparative Example 2

[0026] The main difference from Example 1 is that no Ni is added in the formula, the specific formula is shown in Table 1 formula 4, and the preparation process is the same as that of Example 1, and the mold steel 4 is obtained.

[0027] Comparative Example 3

[0028] The main difference from Example 1 is that no SiC is added in the formula, the specific formula is shown in Table 1 formula 5, and the preparation process is the same as that of Example 1, and the mold steel 5 is obtained.

[0029] Comparative Example 4

[0030] The materials were added into a vacuum induction melting furnace according to the formulation 1 in Table 1, the furnace cover was closed, vacuum was extracted to a vacuum degree of 20 Pa, the melting temperature was set to 1650 ℃, the melting time was 40 min, and the melting chamber swing angle was 55°. After the melting was completed, the electrode rod was poured out and cast into a 700 mm electrode rod, and the surface oxide layer was removed. The electrode rod was placed in an ESR furnace, a small piece of metal was used to arc, the slag system was CaF2-CaO-Al2O3-MgO (the ratio was about 60%-20%-15%-5%), the slag pool depth was 80 mm, the electrode feeding speed and the melting rate were synchronized at 3 mm / s, the input power was 25 KW, the time was 15 min, the dissolution rate was 5 kg / min, the slag pool depth was 80 mm, the cooling water flow was 1.0 m 3 / h, and an electroslag ingot was prepared. One tempering was performed at 750 ℃, two tempering was performed at 700 ℃, and three tempering was performed at 600 ℃, and the mold steel 6 was air-cooled to room temperature. The optical microscope photograph of the mold steel 6 is shown in Figure 1. Figure 2 .

[0031] Comparative Example 5

[0032] The main difference from Example 1 is the Cu addition amount in the formulation. The specific formulation is shown in Table 1, formulation 6, and the preparation process is the same as that of Example 1, and the mold steel 7 is obtained.

[0033] Comparative Example 6

[0034] The main difference from Example 1 is the SiC addition amount in the formulation. The specific formulation is shown in Table 1, formulation 7, and the preparation process is the same as that of Example 1, and the mold steel 8 is obtained.

[0035] Comparative Example 7

[0036] The main difference from Example 1 is the Ni addition amount in the formulation. The specific formulation is shown in Table 1, formulation 8, and the preparation process is the same as that of Example 1, and the mold steel 9 is obtained.

[0037] Table 1: Mold Steel Formulation Table

[0038]

[0039] Tensile Test:

[0040] Sample: Length 55 mm, diameter 5 mm;

[0041] Instrument: High temperature universal testing machine (LFM-300KN, Switzerland), single axis tensile test;

[0042] Test: Tensile test was carried out according to GB / T 4338-2006 standard. Before the test, the tensile sample was kept for 7 min to ensure uniform heating. The test rate was 1 mm / min, and the test temperature was 25 °C. The length and diameter of the sample were recorded before and after the test to calculate the elongation. Each sample was tested three times, and the average value was taken. The results are shown in Table 2.

[0043] Hardness test:

[0044] Sample: Length 55 mm, width and thickness 10 mm;

[0045] Instrument: Hardness tester

[0046] Test: The Rockwell hardness (HRC) of the sample surface at three different points was measured using a hardness tester, and the average value was taken. The results are shown in Table 2.

[0047] Table 2 Test results of performance

[0048]

[0049] The test results in Table 2 show that the tensile strength of die steel 4 is lower than that of die steel 1, indicating that the addition of Ni is beneficial to the tensile strength, which can increase the dislocation density of the material; the tensile strength of die steel 6 is much lower than that of die steels 1 and 2, and the elongation is higher than that of 1 and 2, because the preparation process of die steel 6 does not use segmented quenching and high-temperature cyclic quenching process, and the average grain size of the material is larger than that of die steel 1, which reduces the mechanical properties of the material; the hardness of die steels 4 and 5 is significantly lower than that of die steels 1 and 2, and the addition of Ni or SiC in the formula will cause the hardness to decrease; the tensile strength of die steel 5 is significantly lower than that of die steels 1 and 2, and the elongation is also higher than that of 1 and 2, indicating that SiC can well enhance the strength of the die steel. The mechanical properties of die steels 7 and 9 begin to decrease compared with die steel 1, indicating that too high content of Cu or Ni will cause the mechanical properties of the material to decrease; the mechanical properties of die steel 8 are comparable to those of die steel 1, and after increasing the amount of SiC in the formula to a certain proportion, the mechanical properties no longer increase. Figure 2 Thermal conductivity test:

[0050] Sample: Length and width 12 mm, thickness 2.5 mm, upper and lower surfaces mechanically polished and polished to metallographic surface;

[0051] Instrument: LFA laser thermal conductivity instrument;

[0052] Test: According to ISO 22007-4 standard, pure iron was used as a reference sample, and the thermal conductivity of the test sample at 600 °C was tested. The test was carried out three times, and the average value was taken. The results are shown in Table 3.

[0053] Table 3 Test results of thermal conductivity performance

[0054] ​

[0055]

[0056] The test results of Table 3 above show that the thermal conductivity of the die steel 1 prepared by the formulation and process of the present application can reach 59.7

[0057] W·m -1 ·K -1 The thermal conductivities of the die steels 3 and 4 are both significantly reduced, indicating that the addition of Cu or Ni in the formulation can cause the thermal conductivity to decrease; the thermal conductivity of the die steel 5 is consistent with that of the die steel 1, indicating that SiC has no effect on the thermal conductivity; the preparation process of the die steel 6 does not use segmented quenching and high-temperature cyclic quenching, and the thermal conductivity is lower than that of the die steel 1, indicating that multiple rapid heating to the austenitizing temperature and then rapid cooling can refine the grains of the alloy and enhance the thermal conductivity of the material.

[0058] In summary, the addition of Cu and Ni in the formulation of the present application can significantly enhance the thermal conductivity of the die steel, and further through the segmented quenching and high-temperature cyclic quenching process, the thermal conductivity and strength of the die steel are further enhanced. At the same time, the addition of SiC in the formulation can avoid the negative effect of the decrease in the strength of the material caused by the addition of Cu, and the high thermal conductivity of the die steel is retained.

[0059] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the present patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of protection of the present patent should be subject to the appended claims.

Claims

1. A high thermal conductivity hot forming die steel characterized by, The formula includes by weight percentage: C 0.14-0.30%, Si 0.05-0.08%, Mn 0.10-0.40%, V 0.10-0.20%, Cr 1.40-2.30%, Mo 0.80-1.50%, Ni 0.12-2.00%, Cu 1.50-2.50%, Ce 0.01-0.05%, SiC 1.25-2.40%, the balance being Fe; The preparation method of the high-thermal-conductivity hot forming die steel includes the following steps: smelting, electrode rod preparation, surface oxide layer removal, electroslag remelting, segmented quenching, three times of tempering, and cyclic quenching; wherein the first tempering temperature is 750 DEG C, the second tempering temperature is 700 DEG C, and the third tempering temperature is 600 DEG C.

2. The high thermal conductivity hot forming die steel of claim 1, wherein: The smelting mode is vacuum smelting furnace smelting, and the smelting temperature is 1600-1650 DEG C.

3. The high thermal conductivity hot forming die steel of claim 1, wherein: The electrode rod diameter is 610-700 mm.

4. The high thermal conductivity hot forming die steel of claim 1, wherein: The slag system composition used in electroslag remelting is CaF2-CaO-Al2O3-MgO, the dissolution speed is 5 kg / min, the slag pool depth is 80 mm, and the cooling water flow is 1.0 m 3 / h.

5. The high thermal conductivity hot forming die steel of claim 1, wherein: The segmented quenching preheating temperature is 400-500 DEG C, and the austenitizing temperature is 1100-1150 DEG C.

6. The high thermal conductivity hot forming die steel of claim 1, wherein, The cyclic quenching temperature is 1200-1250 DEG C, and the cycle number is 4 times.

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