Low-Mo plastic mold steel plate and production method thereof

Abstract

The invention discloses a low-Mo plastic mold steel plate and a production method thereof. The steel plate comprises the following chemical components in percentage by weight: 0.32 to 0.42 percent of C, 0.2 to 0.4 percent of Si, 1.1 to 1.6 percent of Mn, 0.01 to 0.05 percent of Al, 1.5 to 2.0 percent of Cr, 0.10 to 0.30 percent of Mo, 0.9 to 1.1 percent of Ni, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe and inevitable impurity elements. The production method disclosed by the invention has the advantages of good performance uniformity, low production cost and the like, and has great popularization and application values.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a low-Mo plastic mould steel plate and a production method thereof. Background Art

[0002] Moulds are the basic process equipment for mass production of industrial products. 70% of rough processing and 5% of fine processing of parts in the machinery manufacturing industry need to be completed by moulds. Plastic mould steel is an important mould material, which is widely used in various industries such as household appliances, electronic and communication equipment, plastic products, automobiles and motorcycles. With the rapid growth of world steel production, the soaring prices of metal raw materials such as Mo, Ni, and V have caused the price of plastic mould steel to continue to rise.

[0003] At present, the market has a certain demand for low-Mo plastic mold steel S1.2738. S1.2738 is a non-standard grade of plastic mold steel, which can replace Sweden's 718H and Germany's 1.2738. With the development and optimization of S1.2738, the use of downstream customers and subsequent promotion, it has a good market prospect and will provide a new growth point for Shagang's plastic mold steel products. In the existing technology, the amount of Mo precious metal alloy added is large, and the internal quality and uniformity of the hardness of the cross-section of the plastic mold steel plate produced by the existing technology are poor, which is not conducive to market development and promotion. Summary of the invention

[0004] Technical problem solved: In view of the above technical problems, the present invention provides a low Mo plastic mold steel plate and a production method thereof, which can effectively solve the shortcomings of the above plastic mold steel plate such as high production cost, poor internal quality, and poor cross-sectional hardness uniformity.

[0005] Technical solution: In the first aspect, the present invention provides a low-Mo plastic mold steel plate, the chemical composition of the steel plate in weight percentage is as follows: C: 0.32-0.42%, Si: 0.2-0.4%, Mn: 1.1-1.6%, Al: 0.01-0.05%, Cr: 1.5-2.0%, Mo: 0.10-0.30%, Ni: 0.9-1.1%, P: ≤0.02%, S: ≤0.01%, and the rest are Fe and unavoidable impurity elements.

[0006] Preferably, the thickness of the steel plate is ≤121 mm.

[0007] In a second aspect, the present invention provides a method for producing the steel plate according to the first aspect, wherein the parameters are controlled as follows:

[0008] (1) Hot metal KR mechanical stirring desulfurization, after KR desulfurization treatment, the sulfur content of hot metal is ≤0.005%;

[0009] (2) Converter oxygen smelting and LF furnace refining. After treatment in the LF refining furnace, the S content of the molten steel is ≤ 0.005%;

[0010] (3) RH furnace vacuum dehydrogenation treatment. After RH vacuum treatment, the H content in the steel is less than 2ppm;

[0011] (4) After the RH is completed, calcium silicon wire is fed and soft stirring is performed for no less than 8 minutes;

[0012] (5) During the slab continuous casting stage, non-oxidation protection pouring is carried out, the superheat of the tundish is controlled at 20±5℃, and the casting speed is 0.6~0.7m / min;

[0013] (6) During the slab reheating stage, the temperature is controlled at 1180-1250°C and the furnace time is not less than 1.0 min / mm;

[0014] (7) During the rolling stage, the billet is continuously rolled directly to the finished product thickness and the total number of passes and the amount of reduction per pass are strictly controlled;

[0015] (8) After rolling, the steel plates are quickly stacked and slowly cooled down, with the stacking temperature being greater than 300°C and the stacking height being greater than 800mm;

[0016] (9) The steel plates are piled and slowly cooled to room temperature for finishing and flaw detection before being sent to the heat treatment raw material warehouse;

[0017] (10) After pretreatment, the steel plate is subjected to normalizing heat treatment, the normalizing temperature is controlled at 900-920°C, and the furnace time is not less than 2.0 min / mm;

[0018] (11) The tempering temperature of the steel plate is controlled between 530 and 560°C, and the time in the furnace is not less than 3.5 min / mm.

[0019] Preferably, during the rolling stage in step (7), an intermediate cooling function is used before the first and last rolling passes.

[0020] Preferably, in the rolling stage in step (7), the total number of passes for a thickness of 90 mm or above is ≤ 6, and the maximum reduction in a single pass is 50 mm.

[0021] Preferably, in step (8), the steel plates are stacked in the leeward place and are prohibited from being stacked in the tuyere area to reduce the cooling rate.

[0022] Beneficial effect: The applicable thickness range of the low Mo plastic mold steel plate of the present invention is ≤121mm;

[0023] (2) The steel plate of the present invention strictly controls the content of alloy elements, and the alloy cost is more economical and saved;

[0024] (3) The present invention strictly controls the S content and H content of the process and finished product, uses pure Ca wire for inclusion deformation treatment, and ensures that the soft stirring time is not less than 8 minutes, thereby ensuring the purity and cleanliness of the steel;

[0025] (4) The rolling process of the present invention implements large reduction, that is, increasing the reduction of a single pass during the rolling process, and using an intermediate cooling function before the first and last passes to facilitate deformation and penetration into the core of the ingot, thereby improving the internal quality; for thicknesses of 90 mm and above, the total number of passes is ≤ 6, and the maximum reduction of a single pass is 50 mm;

[0026] (5) After rolling, the steel plates produced by the present invention are quickly stacked and slowly cooled. The stacking temperature is greater than 300°C and the stacking height is greater than 800mm. The steel plates are stacked in the leeward area and are prohibited from being stacked in the tuyere area to reduce the cooling speed and improve the internal quality. The steel plates are slowly cooled to room temperature, finished, and inspected before being sent to the heat treatment raw material warehouse.

[0027] (6) The steel plate produced by the present invention is subjected to normalizing heat treatment after rolling, and the normalizing temperature is controlled at 900-920°C, and the furnace time is not less than 2.0 min / mm; the tempering temperature of the steel plate is controlled between 530-560°C, and the furnace time is 3.5 min / mm. The tempering temperature is adjusted and controlled in different thickness intervals to ensure the tempering effect of the steel plate and the uniformity of hardness performance;

[0028] (7) The final structure of the low Mo plastic mold steel plate is bainite, the hardness of the steel plate is between 32-36HRC, the flaw detection of the steel plate meets the requirements of Level II in GB / T 2970, and the performance meets the relevant standards and customer requirements;

[0029] In summary, the production method of a low-Mo plastic mold steel plate of the present invention has the advantages of good performance uniformity, low production cost, etc., and has great promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a photograph of the steel plate structure of Example 1;

[0031] Figure 2 is a photograph of the steel plate structure of Example 2;

[0032] Figure 3 This is a photograph of the steel plate structure of Example 3. DETAILED DESCRIPTION

[0033] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0034] The process route is: hot metal KR desulfurization, converter smelting, LF refining, RH vacuum treatment, slab continuous casting, slab reheating, rolling, stack cooling, ultrasonic flaw detection, shot blasting, normalizing and tempering. The smelting compositions of the smelting furnaces of Example 1-3 are shown in Table 1 below:

[0035] Table 1 Melting Composition of Examples 1-3 Smelting Furnaces

[0036] Example C％ Si% Mn% P％ S％ Cr％ Ni% Mo% Al％ 1 0.38 0.28 1.41 0.014 0.004 1.89 0.95 0.18 0.018 2 0.37 0.27 1.40 0.013 0.005 1.88 0.94 0.17 0.020 3 0.38 0.28 1.42 0.015 0.004 1.90 0.93 0.18 0.018

[0037] The rolling process control parameters of Examples 1-3 are shown in Table 2 below:

[0038] Table 2 Rolling process control parameters of Examples 1-3

[0039]

[0040] The heat treatment process control parameters are shown in Table 3:

[0041] Table 3 Control parameters of heat treatment process of Example 1-3

[0042] Example Thickness mm Normalizing temperature ℃ Normalizing time min Tempering temperature℃ Tempering time min 1 120 912 260 535 430 2 100 913 220 540 360 3 80 912 180 542 290

[0043] The properties of the steel plate after heat treatment are shown in Table 4 below:

[0044] Table 4 Performance of steel plates after heat treatment in Example 1-3:

[0045] Example Thickness mm Hardness HRC Center hardness HRC The hardness HRC in the table below 1 120 34.1 33.7 33.9 2 100 33.8 34.1 34.3 3 80 34.3 34.0 33.9

[0046] The steel plate microstructure photos produced in the above examples 1-3 are as follows: Figure 1-Figure 3 As shown: the microstructure of the steel plate is bainite. It can be seen that the hardness of the steel plate manufactured by this method can be guaranteed to be between 32-36HRC, meeting the pre-hardening requirements, and can be directly processed into products for use. At the same time, the cross-section hardness uniformity can be controlled within ±1.2HRC, and the stability during use is better.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low Mo plastic mold steel plate, characterized in that: The chemical composition of the steel plate in weight percentage is as follows: C: 0.32~0.42%, Si: 0.2~0.4%, Mn: 1.1~1.6%, Al: 0.01~0.05%, Cr: 1.5~2.0%, Mo: 0.10~0.30%, Ni: 0.9~1.1%, P: ≤0.02%, S: ≤0.01%, and the rest are Fe and unavoidable impurity elements.

2. The low Mo plastic mold steel plate according to claim 1, characterized in that: The thickness of the steel plate is ≤121 mm.

3. A method for producing a steel plate according to any one of claims 1 to 2, characterized in that: The parameters are controlled as follows: (1) Hot metal KR mechanical stirring desulfurization, after KR desulfurization treatment, the S content of hot metal is ≤0.005%; (2) Converter oxygen smelting and LF furnace refining. After treatment in the LF refining furnace, the S content of the molten steel is ≤ 0.005%; (3) RH furnace vacuum dehydrogenation treatment. After RH vacuum treatment, the H content in the steel is less than 2ppm; (4) After the RH is over, feed the calcium silicon wire and perform soft stirring for no less than 8 minutes; (5) During the slab continuous casting stage, non-oxidation protection pouring is carried out, the superheat of the tundish is controlled at 20±5℃, and the casting speed is 0.6~0.7m / min; (6) During the slab reheating stage, the temperature is controlled at 1180-1250°C and the furnace time is not less than 1.0 min / mm; (7) During the rolling stage, the billet is continuously rolled directly to the finished product thickness and the total number of passes with load and the amount of reduction per pass are strictly controlled; (8) After rolling, the steel plates are quickly stacked and slowly cooled down, with the stacking temperature being greater than 300°C and the stacking height being greater than 800mm; (9) The steel plates are piled up and slowly cooled to room temperature for finishing and flaw detection before being sent to the heat treatment raw material warehouse; (10) After pretreatment, the steel plate is subjected to normalizing heat treatment, the normalizing temperature is controlled at 900-920°C, and the furnace time is not less than 2.0 min / mm; (11) The tempering temperature of the steel plate is controlled between 530 and 560°C, and the time in the furnace is not less than 3.5 min / mm.

4. The production method according to claim 3, characterized in that: During the rolling stage in step (7), an intermediate cooling function is used before the first and last rolling passes.

5. The production method according to claim 3, characterized in that: In the rolling stage of step (7), for thickness 90 mm and above, the total number of passes is ≤ 6, and the maximum reduction of a single pass is 50 mm.

6. The production method according to claim 3, characterized in that: In step (8), the steel plates are stacked in the leeward direction and are not allowed to be stacked in the tuyere area to reduce the cooling rate.

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