Online pre-hardening process and preparation method of 4Cr13 type plastic die steel

Abstract

The invention discloses an online pre-hardening process and a preparation method of 4Cr13 type plastic die steel, and belongs to the technical field of ferrous metallurgy. The on-line pre-hardening process comprises the steps of blank heating, rolling forming and tempering, and the specific flow of the rolling forming procedure comprises the steps of rolling cogging, plate blank heating, continuous rolling, relaxation after rolling and quenching. The preparation method comprises the following steps: smelting by adopting a non-vacuum induction furnace, and pouring by adopting a lower casting method to obtain a 4Cr13 type steel ingot; then carrying out treatment according to an online pre-hardening process to obtain a steel billet; and the steel billet is straightened after being cooled, oxide skin is removed, and the 4Cr13 type plastic die steel is obtained. According to the 4Cr13 type plastic die steel prepared through the online pre-hardening process method, the banded structure is obviously improved, and the polishing performance of the 4Cr13 type plastic die steel is equivalent to that of the 4Cr13 type plastic die steel subjected to thermal refining.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to an online pre-hardening process and a preparation method of 4Cr13 type plastic mould steel. Background Art

[0002] Moulds are known as the "mother of industry" and are the foundation of a country's industrial development. According to statistics, more than 80% of industrial products require moulding. General moulding methods include injection, forging, stamping, extrusion, printing, etc., among which injection moulding is closely related to the development of the chemical and plastic industries. Due to the excellent processing performance and variety of plastics, it has become the fastest growing material among the four major materials (wood, cement, steel, and plastics) widely used in society. With the rapid development of various industries' demand for plastics and their products, plastic moulds have also become the largest variety in the mould industry in recent years.

[0003] The shape of plastic molds is relatively complex, and the positions of various parts in the service process are different, and the required material properties are also different. Therefore, the basic performance requirements of plastic molds generally include: sufficient surface hardness and wear resistance, sufficient strength and toughness, good cutting performance, good polishing performance, small heat treatment deformation, good corrosion resistance, etc.

[0004] 4Cr13 steel is a commonly used corrosion-resistant plastic mold steel. It belongs to martensitic stainless steel. The steel has good mechanical processing performance. After heat treatment, it has excellent corrosion resistance, polishing performance, high strength and wear resistance. It is suitable for manufacturing plastic molds that bear high loads, high wear resistance and corrosive media, as well as transparent plastic product molds. The current 4Cr13 heat treatment process is long and costly, mainly including billet heating - rolling into products - spheroidizing annealing - quenching and tempering (high temperature quenching + tempering), and after directly using the original rolling process and tempering process, a large number of banded structures appear, which seriously affects the polishing performance.

[0005] As upstream and downstream mold companies are increasingly calling for mold cost reduction, online pre-hardening has emerged in recent years to replace offline quenching and tempering heat treatment processes. Online pre-hardening refers to the process of directly quenching mold flat steel after rolling using rolling waste heat without compensating heating. Due to its advantages such as short process flow, low energy consumption and excellent product characteristics, it has gradually been adopted by the market.

[0006] CN112226667A discloses a method for preparing chromium stainless pre-hardened plastic mold steel. It produces high-quality pre-hardened plastic mold steel by controlling the purity of smelting, heating the steel ingot at high temperature, ensuring the amount of deformation during rolling and blanking, and online pre-hardening. This patent only describes the general offline pre-hardening method and does not use online pre-hardening technology.

[0007] CN116219123A discloses a quenching and tempering process for 1.2316MOD martensitic-ferrite corrosion-resistant plastic mold flat steel, eliminating the subsequent mold steel oil quenching and tempering process. The specific technical scheme is as follows: process route: mold flat steel rolling → online cooling (air cooling or water mist cooling) → roller hearth furnace primary tempering → roller hearth furnace secondary tempering. This method is only applicable to 1.2316MOD martensitic steel, not to 4Cr13 series plastic mold steel.

[0008] The literature (Wang Yongsheng, Jin Weisong, Sun Shengyu, et al. Research on pre-hardening process and microstructure of corrosion-resistant plastic mold steel [J]. Mold Manufacturing, 2021, 21(08): 79-82) mainly introduces an online pre-hardening process for 4Cr13 steel to replace the offline quenching and tempering process. The online pre-hardening process mainly uses the residual temperature of the final rolling for quenching, and the temperature is 830℃-850℃; followed by two tempering. However, the literature does not introduce the specific starting rolling temperature and final rolling temperature, as well as the tempering time. Moreover, after online pre-hardening, the microstructure still has banded segregation, and can only be used as plastic mold steel with general requirements. Summary of the invention

[0009] The technical problem to be solved by the present invention is that the existing online pre-hardening process of 4Cr13 type plastic mold steel cannot improve the banded segregation of the structure, resulting in poor polishing performance; although 4Cr13 type plastic mold steel with good polishing performance can be obtained through tempering treatment, the existing tempering treatment process of 4Cr13 type plastic mold steel is long, the production efficiency is low and the cost is high.

[0010] The technical solution adopted by the present invention to solve its technical problem is:

[0011] In a first aspect, the present invention provides an online pre-hardening process for 4Cr13 type plastic mold steel, comprising blank heating, rolling into a product and tempering.

[0012] In the above-mentioned online pre-hardening process, the billet heating process is specifically to perform diffusion annealing treatment on the steel ingot, the diffusion annealing temperature is 1280°C to 1300°C, and the holding time is 5 to 6 hours.

[0013] Furthermore, the amount of the steel ingot subjected to the diffusion annealing treatment is 3.2 to 5 t.

[0014] In the above-mentioned online pre-hardening process, the specific process of the rolling process is rolling blank-slab heating-continuous rolling-relaxation after rolling-quenching.

[0015] Furthermore, the thickness of the slab obtained by rolling is 100 to 120 mm.

[0016] Furthermore, the heating temperature of the slab is 1220° C. to 1250° C., and the insulation time is 3 to 5 hours.

[0017] Furthermore, the above continuous rolling is carried out using two rolling mills, and the final rolling temperature is 950°C to 1000°C.

[0018] Furthermore, during continuous rolling, when the product thickness is 30≤δ≤50mm, the reduction in the first pass is ΔH×60%≤Δh1≤ΔH×80%, and the reduction in the second pass is ΔH×20%≤Δh2≤ΔH×40%.

[0019] Furthermore, during continuous rolling, when the product thickness is 50<δ≤80mm, the reduction in the first pass is ΔH×80%<Δh1≤ΔH×100%, and the reduction in the second pass is ΔH×0%≤Δh2<ΔH×20%.

[0020] Among them, δ represents the product thickness, Δh1 represents the reduction in the first pass, Δh2 represents the reduction in the second pass, and ΔH represents the total reduction in continuous rolling.

[0021] Furthermore, the steel is relaxed for 3 to 5 minutes after rolling, and the surface temperature of the steel is controlled to be 850°C to 900°C.

[0022] Furthermore, the quenching is performed by water quenching for 3 to 5 minutes, the surface temperature of the steel is controlled to be lower than 500°C, and then air-cooled to room temperature.

[0023] In the above-mentioned online pre-hardening process, the tempering process is specifically double-pass tempering, the first-pass tempering temperature is 620°C to 650°C, the tempering time is 90 to 120 minutes, and the second-pass tempering temperature is 480°C to 520°C, and the tempering time is 8 to 10 hours.

[0024] In a second aspect, the present invention provides a method for preparing 4Cr13 type plastic mold steel, which adopts non-vacuum induction furnace smelting and bottom casting method to obtain 4Cr13 type steel ingot; then, the above-mentioned 4Cr13 type plastic mold steel is processed by online pre-hardening process to obtain steel billet; after the steel billet is cooled, it is straightened and the oxide scale is removed to obtain 4Cr13 type plastic mold steel.

[0025] In the above preparation method, the chemical composition of the 4Cr13 steel ingot is as follows by weight: C 0.36%-0.45%, Si 0.25%-0.5%, Mn 0.30%-0.50%, Cr 11.50%-13.50%, S≤0.01%, V≤0.5%, Mo≤0.4%, and the balance is Fe and unavoidable impurities.

[0026] In the above preparation method, the raw materials for smelting 4Cr13 steel ingots include 4Cr13 steel return material, alloy return material with a composition similar to that of 4Cr13 steel, and industrial pure iron.

[0027] The beneficial effect of the present invention is that the method of the present invention can shorten the production process of 4Cr13 plastic mold steel, and shorten the original production process of "blank heating - rolling into shape - spheroidizing annealing - tempering treatment (high temperature quenching + tempering)" to an online pre-hardening process of "blank heating - rolling into shape - tempering". The method of the present invention can improve production efficiency and save production costs.

[0028] The 4Cr13 plastic mold steel prepared by the online pre-hardening process of the present invention has a carbide banded structure that tends to be uniform, a significantly improved banded structure, and a polishing performance that is equivalent to that of the 4Cr13 plastic mold steel that has been quenched and tempered, and a greatly reduced cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the microstructure of the steel after the online pre-hardening process in Example 1;

[0030] Figure 2 This is the microstructure of the steel after the online pre-hardening process in Example 2;

[0031] Figure 3 This is the microstructure of the steel treated by the conventional online pre-hardening process in Comparative Example 1;

[0032] Figure 4 This is the microstructure of the steel after quenching and tempering treatment in comparative example 2. DETAILED DESCRIPTION

[0033] The technical solution of the present invention can be specifically implemented in the following manner.

[0034] The size of the 4Cr13 type plastic mold steel involved in the present invention is a thickness between 30 and 80 mm. The preparation method of the 4Cr13 type plastic mold steel comprises the following specific steps:

[0035] 1. Non-vacuum induction furnace smelting. The raw materials of this manufacturing method are mainly Benxi Steel returns and Benxi Steel similar alloy returns and industrial pure iron; the chemical composition of the steel billet is calculated by weight percentage: C 0.36%~0.45%, Si0.25%~0.5%, Mn0.30%~0.50%, Cr 11.50%~13.50%, S≤0.01%, V≤0.5%, Mo≤0.4%, and the balance is Fe and unavoidable impurities; then the steel ingot is cast by the bottom casting method.

[0036] 2. Diffusion annealing is performed on steel ingots of 3.2t to 5t at a temperature of 1280℃ to 1300℃ for 5 to 6h to eliminate liquid carbides.

[0037] 3. Rolling: After the insulation is completed, the steel ingot is rolled. The purpose of the initial rolling is to break the dendrites and reduce segregation, and finally it is rolled into a slab with a thickness of 100 to 120 mm.

[0038] 4. Heat the slab at a temperature of 1220°C to 1250°C, keep it warm for 3 to 5 hours, and then start rolling.

[0039] 5. Two rolling mills are used for continuous rolling, and the final rolling temperature is 950℃~1000℃:

[0040] When the product thickness is 30≤δ≤50mm, the first pass reduction is ΔH×60%≤Δh1≤ΔH×80%, and the second pass reduction is ΔH×20%≤Δh2≤ΔH×40%;

[0041] When the product thickness is 50<δ≤80mm, the first pass reduction is ΔH×80%<Δh1≤ΔH×100%, and the second pass reduction is ΔH×0%≤Δh2<ΔH×20%;

[0042] Among them, δ represents the product thickness, Δh1 represents the reduction in the first pass, Δh2 represents the reduction in the second pass, and ΔH represents the total reduction in continuous rolling.

[0043] 6. Relax for 3 to 5 minutes after rolling, control the surface temperature at 850℃~900℃, and wait for the austenite to complete recrystallization.

[0044] 7. After relaxation, water quench for 3 to 5 minutes. After the steel surface temperature is lower than 500°C, air cool to room temperature.

[0045] 8. The steel billet is subjected to double tempering, the first tempering temperature is 620℃~650℃, and the tempering time is 90~120min; followed by the second tempering, the tempering temperature is 480℃~520℃, and the tempering time is 8~10h.

[0046] 9. After the billet is cooled, it is straightened and the oxide scale is removed to obtain the finished product of 4Cr13 plastic mold steel.

[0047] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0048] Example

[0049] The size of the 4Cr13 plastic mold steel involved in the present invention is a thickness between 30 and 80 mm. The chemical composition of the steel billet in the embodiment is shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0050] Table 1 Chemical composition (by mass percentage, %)

[0051] C Si Mn Cr S V Mo Example 1 0.41 0.32 0.4 13.1 0.002 0.35 0.3 Example 2 0.45 0.31 0.35 12.8 0.002 0.5 0.4 Example 3 0.37 0.28 0.36 13.2 0.002 0.03 0.35 Example 4 0.42 0.31 0.42 13.5 0.002 0.35 0.32

[0052] Example 1

[0053] 1. According to the chemical composition shown in Table 1, smelting is carried out in a non-vacuum induction furnace, and then the steel ingot is cast by the bottom casting method;

[0054] 2. Diffusion annealing of 5t steel ingot, the diffusion annealing temperature is 1300℃, and the holding time is 5h;

[0055] 3. After the insulation is completed, the steel ingot is rolled into a 120 mm thick slab;

[0056] 4. Heat the slab to 1250°C, keep it warm for 5 hours, and then start rolling;

[0057] 5. Two rolling mills are used for continuous rolling, the product thickness is 50mm, the first pass reduction is 80%, the second pass reduction is 20%, and the final rolling temperature is 980℃;

[0058] 6. Relax for 5 minutes after rolling, and control the surface temperature at 870℃;

[0059] 7. After relaxation, water quench for 5 minutes. After the steel surface temperature is lower than 500°C, air cool to room temperature.

[0060] 8. Double tempering is performed, the first tempering temperature is 620℃, and the tempering time is 90min; then the second tempering is performed, the tempering temperature is 500℃, and the tempering time is 9h;

[0061] 9. After the billet is cooled, it is straightened and the oxide scale is removed to obtain the finished product with a finish of up to 15000#.

[0062] Example 1 The microstructure of the 4Cr13 plastic mold steel is as follows: Figure 1 As shown by Figure 1 It can be seen that the structure of the 4Cr13 plastic mold steel obtained in Example 1 is uniform and has no obvious banded structure.

[0063] Example 2

[0064] 1. According to the chemical composition shown in Table 1, smelting is carried out in a non-vacuum induction furnace, and then the steel ingot is cast by the bottom casting method;

[0065] 2. Diffusion annealing of 3.2t steel ingot, the diffusion annealing temperature is 1300℃, and the holding time is 5h;

[0066] 3. After the insulation is completed, the steel ingot is rolled into a 100 mm thick slab;

[0067] 4. Heat the slab to 1230°C, keep it warm for 3 hours, and then start rolling;

[0068] 5. Two rolling mills are used for continuous rolling, the product thickness is 50mm, the first pass reduction is 80%, the second pass reduction is 20%, and the final rolling temperature is 960℃;

[0069] 6. Relax for 4 minutes after rolling, and control the surface temperature at 850℃;

[0070] 7. After relaxation, water quench for 3 minutes. After the steel surface temperature is lower than 500°C, air cool to room temperature.

[0071] 8. Double tempering is performed, the first tempering temperature is 650℃, and the tempering time is 90min; followed by the second tempering, the tempering temperature is 520℃, and the tempering time is 8h;

[0072] 9. After the billet is cooled, it is straightened and the oxide scale is removed to obtain the finished product with a finish of up to 15000#.

[0073] Example 2 The microstructure of the 4Cr13 plastic mold steel is as follows: Figure 2 As shown by Figure 2 It can be seen that the structure of the 4Cr13 plastic mold steel obtained in Example 2 is uniform and has no obvious banded structure.

[0074] Example 3

[0075] 1. According to the chemical composition shown in Table 1, smelting is carried out in a non-vacuum induction furnace, and then the steel ingot is cast by the bottom casting method;

[0076] 2. Diffusion annealing of 3.2t steel ingot, the diffusion annealing temperature is 1280℃, and the holding time is 5h;

[0077] 3. After the insulation is completed, the steel ingot is rolled into a 120 mm thick slab;

[0078] 4. Heat the slab to 1225°C, keep it warm for 5 hours, and then start rolling;

[0079] 5. Two rolling mills are used for continuous rolling, the product thickness is 30mm, the first pass reduction is 60%, the second pass reduction is 40%, and the final rolling temperature is 960℃;

[0080] 6. Relax for 5 minutes after rolling, and control the surface temperature at 860℃;

[0081] 7. After relaxation, water quench for 3 minutes. After the steel surface temperature is lower than 500°C, air cool to room temperature.

[0082] 8. Double tempering is performed, the first tempering temperature is 620℃, and the tempering time is 120min; then the second tempering is performed, the tempering temperature is 480℃, and the tempering time is 10h;

[0083] 9. After the billet is cooled, it is straightened and the oxide scale is removed to obtain the finished product with a finish of up to 14000#.

[0084] Example 4

[0085] 1. According to the chemical composition shown in Table 1, smelting is carried out in a non-vacuum induction furnace, and then the steel ingot is cast by the bottom casting method;

[0086] 2. Diffusion annealing of 5t steel ingot, the diffusion annealing temperature is 1300℃, and the holding time is 5h;

[0087] 3. After the insulation is completed, the steel ingot is rolled into a 120 mm thick slab;

[0088] 4. Heat the slab to 1250°C, keep it warm for 5 hours, and then start rolling;

[0089] 5. Two rolling mills are used for continuous rolling, the product thickness is 80 mm, the first pass reduction is 100%, the second pass reduction is 0, and the final rolling temperature is 1000°C;

[0090] 6. Relax for 5 minutes after rolling, and control the surface temperature at 900℃;

[0091] 7. After relaxation, water quench for 5 minutes. After the steel surface temperature is lower than 500°C, air cool to room temperature.

[0092] 8. Double tempering is performed, the first tempering temperature is 620℃, and the tempering time is 90min; then the second tempering is performed, the tempering temperature is 500℃, and the tempering time is 9h;

[0093] 9. After the billet is cooled, it is straightened and the oxide scale is removed to obtain the finished product with a finish of up to 16000#.

[0094] Comparative Example 1

[0095] According to the chemical composition of Example 1 shown in Table 1, the ingot is smelted and cast, and the finished product is prepared by a common online pre-hardening process. The specific differences from the preparation process of Example 1 are as follows:

[0096] (1) The first pass of continuous rolling has a reduction of 50%, the second pass has a reduction of 50%, and the final rolling temperature is 920°C;

[0097] (2) No relaxation treatment after rolling, direct quenching.

[0098] Except for the above differences, the rest of the preparation process in Comparative Example 1 is the same as that in Example 1. The microstructure of the 4Cr13 plastic mold steel obtained in Comparative Example 1 is as follows: Figure 3 As shown by Figure 3It can be seen that the 4Cr13 plastic mold steel obtained in Comparative Example 1 contains obvious banded structure.

[0099] Comparative Example 2

[0100] According to the chemical composition of Example 2 shown in Table 1, the ingot is smelted and cast, and the finished product is prepared according to the traditional quenching and tempering process. The specific differences from the preparation process of Example 2 are as follows:

[0101] (1) The first pass of continuous rolling has a reduction of 50%, the second pass has a reduction of 50%, and the final rolling temperature is 900°C;

[0102] (2) No relaxation treatment after rolling, direct water quenching;

[0103] (3) annealing treatment by water quenching, keeping at 830°C for 6 hours, cooling to 550°C at 30°C / h, cooling to room temperature in air, keeping at 1030°C for 2 hours, and then quenching;

[0104] (4) Double tempering is performed, and the first tempering temperature is 540°C

[0105] Except for the above differences, the rest of the preparation process in Comparative Example 2 is the same as that in Example 2, and the finished product is finally obtained, and the finish can reach 15000#. The microstructure of the 4Cr13 plastic mold steel obtained in Comparative Example 2 is as follows Figure 4 As shown by Figure 4 It can be seen that the 4Cr13 plastic mold steel obtained in Comparative Example 2 has a uniform structure without obvious banded structure.

[0106] It can be seen that the polishing performance of the 4Cr13 plastic mold steel prepared by the online pre-hardening process of the present invention is equivalent to that of the mold steel prepared by quenching and tempering treatment, but the process treatment process of the present invention is simpler than the traditional modulation treatment, which significantly shortens the process flow, improves production efficiency, and saves production costs.

Claims

The online pre-hardening process of 1.4Cr13 plastic mold steel is characterized by: The online pre-hardening process includes billet heating, rolling and tempering. The specific process of rolling is billet opening - slab heating - continuous rolling - relaxation after rolling - quenching. Among them, continuous rolling uses two rolling mills for rolling, and the final rolling temperature is 950℃~1000℃; When the product thickness is 30≤δ≤50mm, the first pass reduction is ΔH×60%≤Δh1≤ΔH×80%, and the second pass reduction is ΔH×20%≤Δh2≤ΔH×40%; When the product thickness is 50<δ≤80mm, the reduction in the first pass is ΔH×80%<Δh1≤ΔH×100%, and the reduction in the second pass is ΔH×0%≤Δh2<ΔH×20%.

2. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: The billet heating process specifically involves diffusion annealing the steel ingot, with a diffusion annealing temperature of 1280°C to 1300°C and a holding time of 5 to 6 hours.

3. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: The tempering process is specifically double-pass tempering, the first tempering temperature is 620℃~650℃, the tempering time is 90~120min, the second tempering temperature is 480℃~520℃, and the tempering time is 8~10h.

4. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: The thickness of the slab obtained by rolling is 100 to 120 mm.

5. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: The heating temperature of the slab is 1220℃~1250℃, and the holding time is 3~5h.

6. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: Relax for 3 to 5 minutes after rolling and control the steel surface temperature to 850℃ to 900℃.

7. The online pre-hardening process of 4Cr13 type plastic mold steel according to claim 1 is characterized in that: The quenching is done by water quenching for 3 to 5 minutes, the surface temperature of the steel is controlled below 500°C, and then air-cooled to room temperature. The preparation method of 8.4Cr13 type plastic mold steel is characterized by: A 4Cr13 steel ingot is obtained by smelting in a non-vacuum induction furnace and casting by a bottom casting method; then a steel billet is obtained by an online pre-hardening process according to any one of claims 1 to 7; after the steel billet is cooled, it is straightened and the oxide scale is removed to obtain a 4Cr13 plastic mold steel.

9. The method for preparing 4Cr13 plastic mold steel according to claim 8, characterized in that: The chemical composition of the 4Cr13 steel ingot is as follows by weight: C 0.36%-0.45%, Si 0.25%-0.5%, Mn 0.30%-0.50%, Cr11.50%-13.50%, S≤0.01%, V≤0.5%, Mo≤0.4%, and the balance is Fe and unavoidable impurities.

10. The method for preparing 4Cr13 plastic mold steel according to claim 8, characterized in that: The raw materials for smelting 4Cr13 steel ingots include 4Cr13 steel return materials, alloy return materials with similar composition to 4Cr13 steel and industrial pure iron.

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