High hardness plastic mold steel and method of making same

Abstract

The application discloses a high-hardness plastic die steel and a preparation method thereof. In one aspect, the application provides a high-hardness plastic die steel, wherein the mass fraction of each component of the plastic die steel is as follows: C is 0.35-0.45%, Si is 0.4-0.6%, Mn is 0.6-0.8%, Cr is 12-14%, Ni is 0.4-0.6%, Cu is 0.8-1.0%, the content of P is not more than 0.05%, the content of S is not more than 0.05%, and the balance is Fe; the plastic die steel is subjected to quenching and tempering treatment, the proportion of tempered martensite in the metallographic structure is more than 80%, and the surface of the plastic die steel contains Cu hardening phases. In another aspect, the application also provides a preparation method of the high-hardness plastic die steel. The application has relatively low cost, high hardness, and the surface hardness can reach more than 65HRC.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of die steel, in particular to a high-hardness plastic die steel and a preparation method thereof. BACKGROUND

[0002] In plastic forming processing, the quality of a die has a great influence on the quality of a product. The parts of a plastic die are divided into two categories: one category is structural parts, including a pouring system, a guide part, a top die plate, an ejection mechanism, a supporting part and the like; and the other category is forming parts, including a cavity, a core, an inlay part and the like. With the continuous updating of material technology and the increasing requirement for the processing precision of plastic forming processing, the performance requirement for die steel is becoming more and more strict.

[0003] The plastic die steel currently used in China is mainly a die steel with the brand No. 4Cr13. According to the current national standard GB / T 1299-2014 'Die Steel', the surface hardness of the 4Cr13 die steel in the annealed state can reach 235HBW, and after special heat treatment, the hardness thereof can reach 50HRC, and the hardenability is relatively excellent, the polishing performance is better, and the cost is relatively low. However, the hardness of 50HRC cannot meet the current requirement for high processing precision, and the die steel with a hardness of more than 60HRC is required for the current high-precision processing.

[0004] However, in the current national standard GB / T 1299-2014 'Die Steel', only two types of die steels with the brand Nos. 8Cr2MnWMoVS and 5CrNiMnMoVSCa can reach the above hardness after quenching. The two types of die steels need to add Mo and V, and the market price is relatively high, which greatly increases the production cost of plastic precision processing enterprises.

[0005] Therefore, it is necessary to develop a plastic die steel with relatively low cost and high hardness. SUMMARY

[0006] In order to solve the above at least one technical problem, a plastic die steel with relatively low cost, high hardness and a surface hardness of more than 65HRC is developed, and the application provides a high-hardness plastic die steel and a preparation method thereof.

[0007] In one aspect, the application provides a high-hardness plastic mold steel, the mass fraction of each component of the plastic mold steel is as follows: C is 0.35-0.45%, Si is 0.4-0.6%, Mn is 0.6-0.8%, Cr is 12-14%, Ni is 0.4-0.6%, Cu is 0.8-1.0%, the content of P is not more than 0.05%, the content of S is not more than 0.05%, and the balance is Fe; the plastic mold steel is subjected to quenching and tempering treatment, the proportion of tempered martensite in the metallographic structure is more than 80%, and the surface of the plastic mold steel contains Cu hardening phase.

[0008] In another aspect, the application further provides a preparation method of the high-hardness plastic mold steel, comprising the following steps:

[0009] S1, according to the formula amount, the amount of each metal raw material required for smelting the plastic mold steel is calculated, and each metal raw material is accurately weighed;

[0010] S2, all the metal raw materials except Cu are put into a smelting furnace to smelt into an alloy liquid;

[0011] S3, the Cu raw material is put into the alloy liquid of step S2, after the Cu is completely melted into the alloy liquid, the alloy liquid is poured into a ladle to be cast into a mold steel blank;

[0012] S4, the mold steel blank cast in step S3 is first heated to 520-560℃ at a heating rate of 6-10℃ / min in a heating furnace, and then heated to 910-930℃ at a heating rate of 8-12℃ / min, and kept for 1-1.5h, and after oil quenching, it is placed to room temperature;

[0013] S5, step S4 is repeated 1-2 times;

[0014] S6, the mold steel blank treated in step S5 is heated to 500-540℃ at a heating rate of 4-8℃ / min in a heating furnace, and kept for 10-30min, and then naturally cooled to room temperature;

[0015] S7, the mold steel blank treated in step S6 is machined, polished and polished to obtain a finished mold steel piece.

[0016] Optionally, in step S1, the metal raw materials are scrap steel, manganese plate, chromium plate, nickel plate and copper plate.

[0017] Optionally, in step S2, the smelting temperature is controlled at 1420-1480℃.

[0018] Optionally, in step S3, after the alloy liquid is poured into the ladle, it is placed for 3-5min, and then the mold steel blank is cast.

[0019] Optionally, in the step S4, inert gas protection is passed through the heating furnace.

[0020] Optionally, in the step S4, inert gas protection is passed through the heating furnace.

[0021] Optionally, in the step S4, the temperature is first raised to 530-540 DEG C at a temperature raising speed of 8-10 DEG C / min.

[0022] Optionally, in the step S4, the temperature is raised to 922-924 DEG C at a temperature raising speed of 10-12 DEG C / min, and the temperature is kept for 1-1.2 h.

[0023] Optionally, in the step S6, inert gas protection is passed through the heating furnace.

[0024] In summary, the present application has at least one of the following beneficial technical effects:

[0025] 1. The present application is based on the existing 4Cr13 die steel ratio, and the alloy element ratio is fine-tuned, and then Cu element is added as a hardening phase incubation element, so that the plastic mold steel of the present application is prepared. After a specific heat treatment process, a hardening phase can be formed on the surface, the surface hardness is high, far exceeding the current 4Cr13 die steel.

[0026] 2. The element ratio of the die steel of the present application is basically the same as that of the existing 4Cr13 die steel, only a small amount of Cu element is added, and the alloy does not contain Nb, Mo and V elements, and the raw material for melting the alloy can be mainly scrap steel, and the cost is relatively low.

[0027] 3. The heat treatment process of the present application adopts a high-temperature oil quenching treatment after a medium-temperature stress relief, and the hardening phase is incubated by more than twice quenching treatment, so that the surface of the alloy forms a metallographic structure mainly composed of tempered martensite and hardening phase. Finally, the heat stress is removed by medium-temperature tempering treatment, so that the surface hardness of the alloy is greatly improved, and the surface hardness can reach more than 65HRC. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a 50 mu m electron microscope graph of the plastic mold steel of the embodiment 12 of the present application. DETAILED DESCRIPTION

[0029] The present application will be further described in combination with the following embodiments.

[0030] The application designs a high-hardness plastic mold steel, and each component of the plastic mold steel is proportioned in mass fraction as follows: C is 0.35-0.45%, Si is 0.4-0.6%, Mn is 0.6-0.8%, Cr is 12-14%, Ni is 0.4-0.6%, Cu is 0.8-1.0%, the content of P is not more than 0.05%, the content of S is not more than 0.05%, and the balance is Fe.

[0031] The application inventors have found through experiments that the alloy formula of the application and the proportioning of alloy elements in the formula have very little influence on the performance of the finally prepared plastic mold steel.

[0032] Therefore, the embodiments of the application uniformly adopt the following formula to calculate the amount of raw materials: C is 0.40%, Si is 0.5%, Mn is 0.7%, Cr is 13%, Ni is 0.5%, Cu is 0.9%, the content of P is not more than 0.05%, the content of S is not more than 0.05%, and the balance is Fe.

[0033] The core of the application is to improve the surface hardness of the alloy, and the application inventors have designed the alloy heat treatment process of the application through a large number of experimental researches, and through a specific quenching process, the alloy is quenched for multiple times, so that the hardening phase is inducted and the hardening phase can be gathered to the surface of the alloy, a metallographic structure mainly composed of tempered martensite and containing Cu element hardening phase on the surface is formed, and then the surface hardness of the alloy is improved.

[0034] The preparation method of the high-hardness plastic mold steel of the application comprises the following steps:

[0035] S1, the amount of each metal raw material required for smelting the plastic mold steel is calculated according to the formula amount, and each metal raw material is accurately weighed;

[0036] S2, each metal raw material except Cu weighed in step S1 is put into a smelting furnace to smelt into an alloy liquid;

[0037] S3, the Cu raw material is put into the alloy liquid in step S2, and after the Cu is completely melted into the alloy liquid, the alloy liquid is poured into a ladle to be cast into a mold steel blank;

[0038] S4, the mold steel blank cast in step S3 is first heated to 520-560℃ at a heating rate of 6-10℃ / min, and then heated to 910-930℃ at a heating rate of 8-12℃ / min, and kept for 1-1.5h, and then taken out and oil quenched and placed at room temperature;

[0039] S5, step S4 is repeated for 1-2 times;

[0040] S6, the mold steel blank processed in step S5 is heated to 500-540 DEG C at a heating rate of 4-8 DEG C / min in a heating furnace, and kept for 10-30 min, and then naturally cooled to room temperature;

[0041] S7, the mold steel blank processed in step S6 is machined, polished and polished to obtain a finished mold steel piece.

[0042] The raw materials of each part of the embodiment are as follows:

[0043] The main raw materials of the application are purchased waste stainless steel; Mn plate, Cr plate, Ni plate and Cu plate are purchased from Jiangsu Xinchangrun Metal Co., Ltd.

[0044] The following is a preparation example of the application, which prepares a mold steel blank.

[0045] Preparation example 1

[0046] The preparation of the mold steel blank of the preparation example includes the following steps:

[0047] S1, according to the formula amount, the amount of waste stainless steel, Mn plate, Cr plate, Ni plate and Cu plate required for plastic mold steel smelting is calculated, and accurate cutting and weighing is carried out;

[0048] S2, all the raw materials except Cu plate are put into the smelting furnace, heated to 1420-1480 DEG C, and the raw materials are smelted into alloy liquid;

[0049] S3, the Cu plate is put into the alloy liquid, and after the Cu plate is completely melted into the alloy liquid, the alloy liquid is immediately poured into the ladle, and then cast into a mold steel blank.

[0050] In step S2 of the preparation example, the content of Si in the alloy liquid needs to be detected, and the content of Si is controlled within the proportioning range by adding desiliconizing agent.

[0051] Preparation example 2

[0052] The preparation of the mold steel blank of the preparation example includes the following steps:

[0053] S1, according to the formula amount, the amount of waste stainless steel, Mn plate, Cr plate, Ni plate and Cu plate required for plastic mold steel smelting is calculated, and accurate cutting and weighing is carried out;

[0054] S2, all the raw materials except Cu plate are put into the smelting furnace, heated to 1420-1480 DEG C, and the raw materials are smelted into alloy liquid;

[0055] S3, put the Cu plate into the alloy liquid, after the Cu plate is completely melted into the alloy liquid, immediately pour the alloy liquid into the ladle, stand for 3 min, and then cast into the die steel blank.

[0056] In the step S2 of the preparation example, the content of Si in the alloy liquid needs to be detected, and the content of Si is controlled within the proportioning range by adding silicon removal agent.

[0057] Preparation Example 3

[0058] The preparation of the die steel blank of the preparation example comprises the following steps:

[0059] S1, according to the formula amount, calculate the amount of waste stainless steel, Mn plate, Cr plate, Ni plate and Cu plate required for plastic mold steel smelting, and accurately cut and weigh;

[0060] S2, put all the raw materials except the Cu plate into the smelting furnace, heat to 1420-1480℃, and smelt the raw materials into an alloy liquid;

[0061] S3, put the Cu plate into the alloy liquid, after the Cu plate is completely melted into the alloy liquid, immediately pour the alloy liquid into the ladle, stand for 5 min, and then cast into the die steel blank.

[0062] In the step S2 of the preparation example, the content of Si in the alloy liquid needs to be detected, and the content of Si is controlled within the proportioning range by adding silicon removal agent.

[0063] The following are examples 1-8 of the application.

[0064] Example 1

[0065] The high-hardness plastic mold steel of the example is prepared by the following steps:

[0066] S4, using the die steel blank of preparation example 1, first heat to 554-560℃ at a heating rate of 6-8℃ / min, and keep for 10 min; then heat to 910-916℃ at a heating rate of 8-10℃ / min, and keep for 1.5 h, take out and oil quench, and stand to room temperature;

[0067] S5, repeat step S4 once;

[0068] S6, heat the die steel blank treated in step S5 to 500-510℃ at a heating rate of 4-6℃ / min in a heating furnace, keep for 30 min, and then naturally cool to room temperature;

[0069] S7, machine process, polish and polish the die steel blank treated in step S6 to obtain a finished die steel piece.

[0070] Example 2

[0071] The high-hardness plastic mold steel of the present example is prepared by the following steps:

[0072] S4, using the mold steel blank of Preparation Example 1, first heat to 520-526°C at a heating rate of 6-8°C / min in a heating furnace, and keep for 30 min; then heat to 924-930°C at a heating rate of 8-10°C / min, and keep for 1 h, take out and quench in oil, and then stand to room temperature;

[0073] S5, repeat step S4 once;

[0074] S6, heat the mold steel blank treated in step S5 to 530-540°C at a heating rate of 4-6°C / min in a heating furnace, and keep for 10 min, and then cool to room temperature naturally;

[0075] S7, machine, polish and finish the mold steel blank treated in step S6 to obtain a finished mold steel piece.

[0076] Example 3

[0077] The high-hardness plastic mold steel of the present example is prepared by the following steps:

[0078] S4, using the mold steel blank of Preparation Example 1, first heat to 538-544°C at a heating rate of 6-8°C / min in a heating furnace, and keep for 20 min; then heat to 920-926°C at a heating rate of 8-10°C / min, and keep for 1.2 h, take out and quench in oil, and then stand to room temperature;

[0079] S5, repeat step S4 once;

[0080] S6, heat the mold steel blank treated in step S5 to 520-530°C at a heating rate of 6-8°C / min in a heating furnace, and keep for 20 min, and then cool to room temperature naturally;

[0081] S7, machine, polish and finish the mold steel blank treated in step S6 to obtain a finished mold steel piece.

[0082] Example 4

[0083] The high-hardness plastic mold steel of the present example is prepared by the following steps:

[0084] S4, using the mold steel blank of Preparation Example 1, first heat to 530-540°C at a heating rate of 8-10°C / min in a heating furnace, and keep for 15 min; then heat to 920-926°C at a heating rate of 8-10°C / min, and keep for 1.2 h, take out and quench in oil, and then stand to room temperature;

[0085] S5, repeat step S4 once;

[0086] S6, heat the die steel blank after step S5 in a heating furnace at a temperature increasing rate of 6-8°C / min to 520-530°C, keep for 15 min, and then naturally cool to room temperature;

[0087] S7, machine, polish and finish the die steel blank after step S6 to obtain a finished die steel piece.

[0088] Example 5

[0089] The high-hardness plastic die steel of the present example is prepared by the following steps:

[0090] S4, use the die steel blank of Preparation Example 1, first heat in a heating furnace at a temperature increasing rate of 6-8°C / min to 530-540°C, keep for 15 min, then heat at a temperature increasing rate of 10-12°C / min to 922-924°C, keep for 1 h, take out and oil quench, and then stand at room temperature;

[0091] S5, repeat step S4 once;

[0092] S6, heat the die steel blank after step S5 in a heating furnace at a temperature increasing rate of 6-8°C / min to 520-530°C, keep for 15 min, and then naturally cool to room temperature;

[0093] S7, machine, polish and finish the die steel blank after step S6 to obtain a finished die steel piece.

[0094] Example 6

[0095] The high-hardness plastic die steel of the present example is prepared by the following steps:

[0096] S4, use the die steel blank of Preparation Example 1, first heat in a heating furnace at a temperature increasing rate of 6-8°C / min to 530-540°C, keep for 15 min, then heat at a temperature increasing rate of 10-12°C / min to 922-924°C, keep for 1.2 h, take out and oil quench, and then stand at room temperature;

[0097] S5, repeat step S4 once;

[0098] S6, heat the die steel blank after step S5 in a heating furnace at a temperature increasing rate of 6-8°C / min to 520-530°C, keep for 15 min, and then naturally cool to room temperature;

[0099] S7, machining, polishing and polishing the die steel blank processed in step S6 to obtain a die steel finished product.

[0100] Example 7

[0101] The difference between this example and example 6 is that in step S4 of this example, argon gas is passed throughout the heating process.

[0102] Example 8

[0103] The difference between this example and example 7 is that in step S6 of this example, argon gas is passed throughout the heating process.

[0104] Performance test:

[0105] The test uses the method recorded in the national standard GB / T 1299-2014 "Die Steel".

[0106] The die steel of the plastic mold of examples 1-8 of the present application and the die steel of the comparative example were detected for metallographic structure, hardenability and surface hardness, respectively, using the die steel with the brand 4Cr13 as a comparative example. The results are shown in Table 1.

[0107] Table 1: Performance test results of examples 1-8

[0108] Metallographic structure Hardness (850°C, mm) Surface hardness (HRC) Example 1 Tempered martensite 81% 4.2 65 Example 2 Tempered martensite 84% 4.3 66 Example 3 Tempered martensite 86% 4.3 68 Example 4 Tempered martensite 89% 4.5 68 Example 5 Tempered martensite 90% 4.5 69 Example 6 Tempered martensite 91% 4.5 71 Example 7 Tempered martensite 91% 4.7 74 Example 8 Tempered martensite 91% 4.7 74 Comparative Example Martensite 90% 1.8 50

[0109] As can be seen from the data in Table 1, the plastic mold steel of examples 1-8 of the present application has a main tempering martensite and a small amount of Cu hardening phase, and the hardening phase tends to be distributed on the surface of the alloy, has good hardenability, and the hardenability depth can reach more than 4.2mm at 850℃, far exceeding the die steel of the comparative example. In addition, the surface hardness of the plastic mold steel of examples 1-8 of the present application can reach more than 65HRC, which is much higher than that of the die steel of the comparative example.

[0110] As can be seen from the data in Table 1, the material hardness is best after the specific preheating process and the specific quenching process of the present application. Moreover, the hardness can be further improved after the argon gas protection during the heat treatment process.

[0111] Examples 9-15 of the present application are based on example 8 of the present application, using the same preparation method and element ratio, only the process parameters are different.

[0112] Example 9

[0113] The difference between this example and example 8 is that in step S1, the die steel blank of preparation example 2 is used.

[0114] Example 10

[0115] The difference between this embodiment and embodiment 8 is that the mold steel blank of Preparation Example 3 is used in the step S1.

[0116] Embodiment 11

[0117] The difference between this embodiment and embodiment 9 is that the step S4 is repeated twice in the step S5.

[0118] Embodiment 12

[0119] The difference between this embodiment and embodiment 10 is that the step S4 is repeated twice in the step S5.

[0120] Performance detection:

[0121] The surface hardness of the plastic mold steel of embodiments 9-12 of the application is detected, and the results are shown in Table 2.

[0122] Table 2: Performance detection results of embodiments 6-14

[0123]

[0124]

[0125] As can be seen from the data in Table 2, the control of standing for 3-5 minutes after pouring the molten metal into the ladle is critical, and the hardness of the mold steel obtained after casting will be further improved. The applicant speculates that through standing, the Cu element has a good distribution in the alloy, which is more conducive to the subsequent heat treatment, so that the hardening phase is precipitated on the surface of the alloy.

[0126] As can be seen from the data in Table 2, the alloy of the application has the optimal surface annealing hardness after three times of quenching. The inventor speculates that after three times of quenching treatment, the proportion of tempered martensite in the metallographic structure of the alloy is the largest, and Cu can better inculcate the hardening phase, and form a strengthening point of the hardening phase on the surface of the alloy, thereby improving the surface hardness of the alloy.

[0127] The applicant has carried out electron microscope detection on the alloy of embodiment 14 of the application, and the obtained electron microscope graph is shown in Figure 1 As can be seen from the electron microscope graph, the alloy of embodiment 14 of the application has a needle-shaped tempered martensite as the main surface metallographic structure, and there are blocky Cu hardening phases, and the hardening phases are relatively more on the surface of the alloy, and it can be seen that the hardening phases are precipitated on the surface.

[0128] The above are preferred embodiments of the application, and do not limit the protection scope of the application, so that: any equivalent changes made according to the structure, shape, principle of the application shall be covered within the protection scope of the application.

Claims

1. A high hardness plastic mold steel characterized by, The mass fraction of each component of the plastic mold steel is as follows: C is 0.35-0.45%, Si is 0.4-0.6%, Mn is 0.6-0.8%, Cr is 12-14%, Ni is 0.4-0.6%, Cu is 0.8-1.0%, the content of P is not more than 0.05%, the content of S is not more than 0.05%, and the balance is Fe; the plastic mold steel is subjected to quenching and tempering treatment, the proportion of tempered martensite in the metallographic structure is more than 80%, and the surface of the plastic mold steel contains Cu hardening phase; The application discloses a preparation method of high-hardness plastic mold steel. S1, according to the formula amount, the amount of each metal raw material required for smelting of the plastic mold steel is calculated, and each metal raw material is accurately weighed; S2, all the metal raw materials except Cu are put into a smelting furnace to smelt into an alloy liquid; S3, the Cu raw material is put into the alloy liquid in step S2, after the Cu is completely melted into the alloy liquid, the alloy liquid is poured into a ladle, and a mold steel blank is cast; S4, the mold steel blank cast in step S3 is first heated to 520-560 DEG C at a heating rate of 6-10 DEG C / min in a heating furnace, and then heated to 910-930 DEG C at a heating rate of 8-12 DEG C / min, and after being taken out and oil-quenched, the mold steel blank is placed at room temperature; S5, the step S4 is repeated 1-2 times; S6, the mold steel blank treated in step S5 is heated to 500-540 DEG C at a heating rate of 4-8 DEG C / min in a heating furnace, and then naturally cooled to room temperature; S7, the mold steel blank treated in step S6 is machined, polished and polished to obtain a finished mold steel piece.

2. The high hardness plastic mold steel of claim 1, wherein, In step S1, the metal raw materials are scrap steel, manganese plate, chromium plate, nickel plate and copper plate.

3. The high hardness plastic mold steel of claim 1, wherein, In step S2, the smelting temperature is controlled at 1420-1480 DEG C.

4. The high hardness plastic mold steel of claim 1, wherein, In step S3, after the alloy liquid is poured into the ladle, the mold steel blank is cast after being placed for 3-5 min.

5. The high hardness plastic mold steel of claim 1, wherein, In step S4, inert gas protection is introduced into the heating furnace throughout the whole process.

6. The high hardness plastic mold steel of claim 1, wherein, In step S4, the temperature is first increased to 530-540 DEG C at a heating rate of 8-10 DEG C / min.

7. The high hardness plastic mold steel of claim 1, wherein, In step S4, the temperature is increased to 922-924 DEG C at a heating rate of 10-12 DEG C / min, and the temperature is kept for 1-1.2 h.

8. The high hardness plastic mold steel of claim 1, wherein, In step S6, inert gas protection is introduced into the heating furnace throughout the whole process.

Images