Quenched and tempered plastic mold steel plate with excellent weldability and production method thereof

Abstract

The invention discloses a quenched and tempered plastic mold steel plate with excellent weldability and a production method of the quenched and tempered plastic mold steel plate. The quenched and tempered plastic mold steel plate comprises the following chemical components in percentage by mass: 0.20-0.22% of C, 0.50-0.80% of Mn, 0.21-0.51% of Si, less than or equal to 0.004% of S, less than or equal to 0.009% of P, 1.30-1.40% of Cr, 0.0021-0.0031% of B, 0.54-0.63% of CEV and the balance of Fe and inevitable impurities. The production method comprises the working procedures of converter smelting, refining, continuous casting, heating, rolling, quenching and tempering. The plastic mold steel plate alloy is low in cost and excellent in welding performance and low-temperature impact toughness, and the market competitiveness of plastic mold steel is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic mold steel, and particularly relates to a quenched and tempered plastic mold steel plate with excellent weldability and a production method thereof. Background Art

[0002] The development level of mold materials largely depends on the development of plastic molds. The development of the mold industry is closely related to industries such as petrochemical, electronic machinery, and construction, and the development of these industries relies on the development of mold steel. With the development and progress of China's industry, the demand for plastic mold steel in the market is also continuously increasing. In order to fill the gap of domestic plastic mold steel, China introduced the American plastic mold steel P20 with good versatility. Its tempered structure is a uniform and fine tempered troostite structure, with good polishing performance and good machining performance after pre-hardening treatment. Therefore, P20 steel is widely used in plastic molds of household appliances such as washing machines. In recent years, the output value and consumption of plastic mold steel far exceed those of hot work mold steel and cold work mold steel, accounting for about 50% of the mold steel market share.

[0003] However, at present, the carbon content of medium and high-end plastic mold steels at home and abroad is generally C: 0.37 - 0.43%, the carbon equivalent CEV: 0.9 - 1.15%, and the weldability and low-temperature impact toughness are poor, and even welding is impossible; some exported plastic mold steels require good low-temperature impact toughness, which cannot be met by domestic-produced plastic mold steels, and a high Cr, Mo composition system is designed; in order to improve the hardness of plastic mold steel, expensive elements such as Nb, V, Ni are also added, and the cost of alloy materials is relatively high.

[0004] In view of the above deficiencies, the present invention explores that when designing the composition, the carbon content is lower than that of plastic mold steel plates such as 1.2311 / 1.2738 / P20 circulating in the market, the carbon content is controlled at C: 0.20 - 0.22%, and the carbon equivalent is controlled at CEV: 0.54 - 0.63%. The produced plastic mold steel has excellent weldability and low-temperature impact toughness, and does not add expensive elements such as Mo, Nb, V, Ni; in order to meet the hardness requirements of plastic mold steel plates, the present invention adopts a quenching + tempering process for production, and the product meets the technical requirements of plastic mold steel plates, so it has important social and economic benefits. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a quenched and tempered plastic mold steel plate with excellent weldability and a production method thereof, which not only has low alloy cost, but also has excellent weldability and low-temperature impact toughness.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: A quenched and tempered plastic mold steel plate with excellent weldability, its chemical composition and mass percentage are as follows: C: 0.20 - 0.22%, Mn: 0.50 - 0.80%, Si: 0.21 - 0.51%, S ≤ 0.004%, P ≤ 0.009%, Cr: 1.30 - 1.40%, B: 0.0021 - 0.0031%, CEV: 0.54 - 0.63%, and the balance is Fe and inevitable impurities.

[0007] The thickness of the quenched and tempered plastic mold steel plate with excellent weldability described in the present invention is 10 - 120 mm.

[0008] The hardness of the quenched and tempered plastic mold steel plate with excellent weldability described in the present invention is 28 - 34 HRC, and the hardness difference of the whole plate is ≤ 3 HRC; the low-temperature impact energy at -20 °C is 36 - 66 J.

[0009] The production method of the quenched and tempered plastic mold steel plate with excellent weldability described in the present invention includes converter smelting, refining, continuous casting, heating, rolling, quenching, and tempering processes.

[0010] Furthermore, for the quenching process described in the present invention, the quenching heating temperature is 870 - 890 °C, the quenching heating coefficient is 1.8 - 2.5 min / mm, and the final cooling temperature is ≤ 40 °C.

[0011] Furthermore, for the tempering process described in the present invention, the tempering temperature is 380 - 480 °C, and the tempering heating coefficient is 3.0 - 4.0 min / mm.

[0012] The performance detection method of the quenched and tempered plastic mold steel plate described in the present invention refers to GB / T231.1.

[0013] The beneficial effects of adopting the above technical solutions are as follows: (1) For the plastic mold steel plate provided by the present invention, the carbon content is lower than that of plastic mold steel plates such as 1.2311 / 1.2738 / P20 in the market circulation. The carbon content is controlled at C: 0.20 - 0.22%, and the carbon equivalent is controlled at CEV: 0.54 - 0.63%, with excellent welding performance and low-temperature impact toughness.

[0014] (2) The plastic mold steel plate provided by the present invention does not add expensive elements such as Mo, Nb, V, Ni, etc., with low alloy cost and high market competitiveness.

[0015] (3) In order to meet the hardness requirements of the plastic mold steel plate, the present invention adopts the quenching + tempering process for production, and the produced plastic mold steel plate has excellent performance. Specific Embodiments

[0016] The following further elaborates on the present invention in combination with specific embodiments. Example 1

[0017] In this embodiment, the thickness of the plastic mold steel plate is 10 mm, and the chemical composition and mass percentage are shown in Table 1. Its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching and tempering processes. The key process parameters are controlled as follows: (1) Quenching process: The quenching heating temperature is 890 °C, the quenching heating coefficient is 2.5 min / mm, and the final cooling temperature is ≤ 27 °C; (2) Tempering process: The tempering temperature is 480 °C, and the tempering heating coefficient is 3.5 min / mm.

[0018] After heat treatment, the hardness of the plastic mold steel plate in this embodiment is 32.7 - 34 HRC, the average hardness is 33.2 HRC, and the hardness difference of the whole plate is ≤ 1.3 HRC. The low-temperature impact energy at -20 °C is 53 J / 58 J / 51 J, with an average of 54 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 2

[0019] In this embodiment, the thickness of the plastic mold steel plate is 30 mm, and the chemical composition and mass percentage are shown in Table 1. Its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching and tempering processes. The key process parameters are controlled as follows: (1) Quenching process: The quenching heating temperature is 890 °C, the quenching heating coefficient is 2.3 min / mm, and the final cooling temperature is ≤ 35 °C; (2) Tempering process: The tempering temperature is 470 °C, and the tempering heating coefficient is 3.3 min / mm.

[0020] After heat treatment, the hardness of the quenched and tempered plastic mold steel plate in this embodiment is 30.3 - 33.3 HRC, the average hardness is 32.2 HRC, and the hardness difference of the whole plate is ≤ 3 HRC. The low-temperature impact energy at -20 °C is 58 J / 47 J / 49 J, with an average of 51 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 3

[0021] In this embodiment, the thickness of the plastic mold steel plate is 50 mm, and the chemical composition and mass percentage are shown in Table 1. Its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching and tempering processes. The key process parameters are controlled as follows: (1) Quenching process: The quenching heating temperature is 880 °C, the quenching heating coefficient is 2.0 min / mm, and the final cooling temperature is ≤ 33 °C; (2) Tempering process: The tempering temperature is 450 °C, and the tempering heating coefficient is 3.0 min / mm.

[0022] After heat treatment in this example, the quenched and tempered plastic mold steel plate has a hardness of 30.5 - 32.1 HRC, an average hardness of 31.5 HRC, and the hardness difference across the whole plate is ≤ 1.6 HRC; the low-temperature impact energy at -20°C is 66 J / 59 J / 62 J, with an average of 62 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 4

[0023] The thickness of the plastic mold steel plate in this example is 70 mm, and the chemical composition and mass percentage are shown in Table 1; its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching, and tempering processes, and the key process parameter controls are as follows: (1) Quenching process: The quenching heating temperature is 880°C, the quenching heating coefficient is 2.0 min / mm, and the final cooling temperature is ≤ 37°C; (2) Tempering process: The tempering temperature is 420°C, and the tempering heating coefficient is 3.7 min / mm.

[0024] After heat treatment in this example, the quenched and tempered plastic mold steel plate has a hardness of 29.8 - 31 HRC, an average hardness of 30.5 HRC, and the hardness difference across the whole plate is ≤ 1.2 HRC; the low-temperature impact energy at -20°C is 49 J / 59 J / 46 J, with an average of 51 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 5

[0025] The thickness of the plastic mold steel plate in this example is 90 mm, and the chemical composition and mass percentage are shown in Table 1; its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching, and tempering processes, and the key process parameter controls are as follows: (1) Quenching process: The quenching heating temperature is 880°C, the quenching heating coefficient is 2.0 min / mm, and the final cooling temperature is ≤ 36°C; (2) Tempering process: The tempering temperature is 410°C, and the tempering heating coefficient is 3.8 min / mm.

[0026] After heat treatment in this example, the quenched and tempered plastic mold steel plate has a hardness of 29.9 - 32.4 HRC, an average hardness of 30.8 HRC, and the hardness difference across the whole plate is ≤ 2.5 HRC; the low-temperature impact energy at -20°C is 39 J / 47 J / 49 J, with an average of 45 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 6

[0027] The thickness of the plastic mold steel plate in this example is 100 mm, and the chemical composition and mass percentage are shown in Table 1; its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching, and tempering processes, and the key process parameter controls are as follows: (1) Quenching process: The quenching heating temperature is 870°C, the quenching heating coefficient is 2.0 min / mm, and the final cooling temperature is ≤ 38°C; (2) Tempering process: Tempering temperature is 400°C, and tempering heating coefficient is 3.9 min / mm.

[0028] After heat treatment in this example, the hardness of the quenched and tempered plastic mold steel plate is 28.9 - 30.7 HRC, the average hardness is 29.7 HRC, and the hardness difference of the whole plate is ≤1.8 HRC; the low-temperature impact energy at -20°C is 44 J / 38 J / 40 J, with an average of 41 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 7

[0029] The thickness of the plastic mold steel plate in this example is 110 mm, and the chemical composition and mass percentage are shown in Table 1; its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching and tempering processes, and the key process parameters are controlled as follows: (1) Quenching process: Quenching heating temperature is 870°C, quenching heating coefficient is 2.0 min / mm, and the final cooling temperature is ≤39°C; (2) Tempering process: Tempering temperature is 390°C, and tempering heating coefficient is 4.0 min / mm.

[0030] After heat treatment in this example, the hardness of the quenched and tempered plastic mold steel plate is 28.4 - 29.8 HRC, the average hardness is 28.9 HRC, and the hardness difference of the whole plate is ≤1.4 HRC; the low-temperature impact energy at -20°C is 39 J / 37 J / 40 J, with an average of 39 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent. Example 8

[0031] The thickness of the plastic mold steel plate in this example is 120 mm, and the chemical composition and mass percentage are shown in Table 1; its production method includes converter smelting, refining, continuous casting, heating, rolling, quenching and tempering processes, and the key process parameters are controlled as follows: (1) Quenching process: Quenching heating temperature is 870°C, quenching heating coefficient is 1.8 min / mm, and the final cooling temperature is ≤39°C; (2) Tempering process: Tempering temperature is 380°C, and tempering heating coefficient is 4.0 min / mm.

[0032] After heat treatment in this example, the hardness of the quenched and tempered plastic mold steel plate is 28.0 - 29.5 HRC, the average hardness is 28.3 HRC, and the hardness difference of the whole plate is ≤1.5 HRC; the low-temperature impact energy at -20°C is 36 J / 38 J / 36 J, with an average of 37 J. The hardness of the whole plate is uniform, and the low-temperature impact toughness is excellent.

[0033] Table 1 Chemical composition of plastic mold steel plates in each example (%)

[0034] The balance in Table 1 is Fe and unavoidable impurities.

[0035] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A quenched and tempered plastic mold steel plate with excellent weldability, characterized in that, The chemical composition and its mass percentage content of the quenched and tempered plastic mold steel plate with excellent weldability are as follows: C: 0.20 - 0.22%, Mn: 0.50 - 0.80%, Si: 0.21 - 0.51%, S ≤ 0.004%, P ≤ 0.009%, Cr: 1.30 - 1.40%, B: 0.0021 - 0.0031%, CEV: 0.54 - 0.63%, and the balance is Fe and inevitable impurities.

2. The quenched and tempered plastic mold steel plate with excellent weldability according to claim 1, wherein The thickness of the quenched and tempered plastic mold steel plate with excellent weldability is 10 - 120 mm.

3. A quenched and tempered plastic mold steel plate with excellent weldability according to claim 1, characterized in that, The hardness of the quenched and tempered plastic mold steel plate with excellent weldability is 28 - 34 HRC, and the hardness difference of the whole plate ≤ 3 HRC; the low-temperature impact energy at -20 °C is 36 - 66 J.

4. The production method of the quenched and tempered plastic mold steel plate with excellent weldability according to any one of claims 1-3, characterized in that, It includes the processes of converter smelting, refining, continuous casting, heating, rolling, quenching and tempering.

5. The production method of the quenched and tempered plastic mold steel plate with excellent weldability according to claim 4, characterized in that, For the quenching process, the quenching heating temperature is 870 - 890 °C, the quenching heating coefficient is 1.8 - 2.5 min / mm, and the final cooling temperature ≤ 40 °C.

6. The production method of the quenched and tempered plastic mold steel plate with excellent weldability according to claim 4, characterized in that, For the tempering process, the tempering temperature is 380 - 480 °C, and the tempering heating coefficient is 3.0 - 4.0 min / mm.

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