Cold work tool steel and preparation method thereof

Abstract

The invention discloses cold work tool steel and a preparation method thereof. The cold work tool steel comprises the following elements in percentage by weight: 0.75 to 1.15 percent of C, 0.45 to 1.50 percent of Si, less than or equal to 1.50 percent of Mn, 4.50 to 7.00 percent of Cr, 3.00 to 6.00 percent of Mo, less than or equal to 3.00 percent of W, 0.50 to 2.50 percent of V and the balance of Fe and inevitable impurities. The preparation method comprises the steps that C, Si, Mn, Cr, Mo, W, V and Fe are added into a furnace to be smelted, and molten steel is obtained; deoxidizing, desulfurizing and deoxidizing the molten steel; carrying out vacuum degassing on the molten steel, pouring into a steel ingot, and annealing, forging and rolling the steel ingot to obtain a finished product; and quenching the rolled material at 1140-1170 DEG C, and tempering for three times at 540 DEG C after quenching, and tempering for one hour each time. The cold work tool steel has high hardness and high toughness, and is suitable for machining tools of materials difficult to machine.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to a cold work tool steel and its preparation method. Background Technology

[0002] High-strength bolts and fasteners with a strength of 12.5 or higher are widely used in aerospace, heavy machinery, mining, and ocean-going engineering machinery. With the rise of high-end manufacturing in China, the requirements for machining tools for high-strength bolts have become more stringent. Using traditional cold work steel with a hardness of 62HRC to machine high-strength bolts can no longer meet industry demands. While using high-speed steel with a hardness of 65HRC can solve the strength problem, the alloy cost is relatively high.

[0003] Traditional low-alloy cold work steel (such as SKD11) typically has a heat treatment hardness of 62 HRC. However, due to the increasing number of applications with high load stress (such as the machining of high-strength 12.5 grade bolts), the strength of traditional low-alloy cold work steel cannot meet the requirements. Although high-speed steel M2 can reach a heat treatment hardness of 65 HRC, its high alloy cost and low chromium content result in poor hardenability when using vacuum heat treatment, which affects the size and large-scale of tools and makes it difficult to realize its performance. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a cold work tool steel and a method for preparing the same.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a cold work tool steel, wherein the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: ≤1.50%, Cr: 4.50-7.00%, Mo: 3.00-6.00%, W: ≤3.00%, V: 0.50-2.50%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the contents of W, Mo and Cr in the cold work tool steel satisfy the following: 8 ≤ tungsten equivalent (Weq) ≤ 14, and tungsten equivalent (Weq) ≤ -2.4Cr + 26, wherein tungsten equivalent (Weq) = 2Mo + W.

[0008] Furthermore, the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.5%, Mn: 0.30-1.50%, Cr: 4.50-5.50%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities;

[0009] Preferably, the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: 0.30-1.00%, Cr: 4.50-5.40%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities;

[0010] Preferably, the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: 0.30-0.80%, Cr: 4.90-5.40%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.20%, with the balance being Fe and unavoidable impurities.

[0011] Furthermore, the unavoidable impurities include P and S.

[0012] Furthermore, the weight percentages of P and S are: P: ≤0.028%, S: ≤0.01%.

[0013] The present invention also provides a method for preparing the aforementioned cold work tool steel, comprising the following steps:

[0014] (1) C, Si, Mn, Cr, Mo, W, V and Fe are added to the furnace according to the weight percentage content to smelt steel.

[0015] (2) After the furnace charge is melted to 80-90%, slag is added to cover the furnace charge. Aluminum is added to the ladle at 0.15% of the total amount of molten steel for deoxidation. After the molten steel enters the refining furnace (LF refining), desulfurization and deoxidation are carried out. White slag from the refining furnace is taken as a prerequisite for tapping the steel.

[0016] (3) Molten steel enters the VD furnace for vacuum degassing, removing harmful gases such as oxygen and nitrogen from the molten steel under negative pressure, and then is cast into steel ingots. The steel ingots are annealed and finally forged and rolled into finished products to obtain rolled products.

[0017] (4) The rolled material is quenched at 1140-1170℃, and then tempered three times at 540℃ for one hour each time to obtain the final product.

[0018] Furthermore, the quenching time T = coefficient (seconds) * D (mm) workpiece thickness.

[0019] Furthermore, the annealing temperature is 840-880℃.

[0020] Furthermore, the forging temperature is 1080-1140℃.

[0021] Furthermore, the rolling temperature is 1050-1120℃.

[0022] The present invention also provides the application of the cold work tool steel described herein or the cold work tool steel prepared by the method described herein in the manufacture of cutting tools.

[0023] Furthermore, the cutting tool is a tool used for machining high-strength bolts and fasteners with a strength of 12.5 or higher.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention, based on existing cold work tool steel technology, further provides a cold work tool steel with both high hardness and high toughness through composition design. After heat treatment, its hardness can reach 66.5 HRC, while achieving 27-35 J / cm². 2 Impact toughness. Sufficient quenching can be achieved even with vacuum heat treatment (whose quenching effect is typically lower than traditional salt bath quenching). This invention's cold work tool steel enables large tools that have undergone vacuum heat treatment to achieve a high hardness of HRC66.5 while maintaining high toughness. It is suitable for tools used to machine difficult-to-machine materials, particularly cold extrusion tools, cold rolling rolls, and forging dies. Detailed Implementation

[0026] To better understand the present invention, it is now further described with reference to the following embodiments. These embodiments are for illustrative purposes only and do not limit the invention in any way. In the embodiments, all original reagents and materials are commercially available, and experimental methods not specifically described are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0027] This invention provides a cold-working tool steel with the following weight percentage content of each element: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: ≤1.50%, Cr: 4.50-7.00%, Mo: 3.00-6.00%, W: ≤3.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities (P: ≤0.028%, S: ≤0.01%). The W, Mo, and Cr contents in the cold-working tool steel satisfy the following: 8 ≤ tungsten equivalent (Weq) ≤ 14, and tungsten equivalent (Weq) ≤ -2.4Cr + 26, where tungsten equivalent (Weq) = 2Mo + W.

[0028] The present invention also provides a method for preparing cold work tool steel, comprising the following steps:

[0029] (1) C, Si, Mn, Cr, Mo, W, V and Fe are added to the furnace according to the weight percentage of each element to smelt steel.

[0030] (2) After the furnace charge is melted to 80-90%, slag is added to cover the furnace charge. Aluminum is added to the ladle at 0.15% of the total amount of molten steel for deoxidation. After the molten steel enters the refining furnace (LF refining), white slag is produced.

[0031] (3) Molten steel enters the VD furnace for vacuum degassing. Under negative pressure, harmful gases such as oxygen and nitrogen in the molten steel are removed. Then it is cast into steel ingots. The steel ingots are annealed (temperature 850℃), and finally forged (temperature 1100℃) and rolled (temperature 1100℃) into finished products.

[0032] (4) The rolled material is quenched at 1140-1170℃, and then tempered three times at 540℃ for one hour each time to obtain the final product.

[0033] Examples 1-3 and Comparative Examples

[0034] Cold work tool steel was prepared according to the above preparation method, based on the weight percentage content of each element shown in Table 1 and the quenching and tempering conditions.

[0035] Table 1

[0036]

[0037] The heat-treated hardness and impact values ​​of the cold work tool steels prepared in Examples 1-3 and the comparative examples are shown in Table 1. The heat-treated hardness of the cold work tool steel of this invention can reach 66.5 HRC, while the impact toughness is 27-35 J / cm². 2 Compared with the comparative cold work tool steel, the cold work tool steel of the present invention has high hardness and high toughness, and is suitable for tools for processing difficult-to-machine materials, especially cold extrusion tools, cold rolling rolls, and forging dies.

[0038] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A cold work tool steel, characterized in that, The weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: ≤1.50%, Cr: 4.50-7.00%, Mo: 3.00-6.00%, W: ≤3.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities.

2. The cold work tool steel according to claim 1, characterized in that, The contents of W, Mo and Cr in the cold work tool steel satisfy the following: 8 ≤ tungsten equivalent ≤ 14, and tungsten equivalent ≤ -2.4Cr + 26, where tungsten equivalent = 2Mo + W.

3. The cold work tool steel according to claim 1, characterized in that, The weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.5%, Mn: 0.30-1.50%, Cr: 4.50-5.50%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities; Preferably, the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: 0.30-1.00%, Cr: 4.50-5.40%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.50%, with the balance being Fe and unavoidable impurities; Preferably, the weight percentage content of each element in the cold work tool steel is as follows: C: 0.75-1.15%, Si: 0.45-1.50%, Mn: 0.30-0.80%, Cr: 4.90-5.40%, Mo: 4.00-6.00%, W: 0.20-2.00%, V: 0.50-2.20%, with the balance being Fe and unavoidable impurities.

4. The cold work tool steel according to claim 1, characterized in that, The unavoidable impurities include P and S; The weight percentages of P and S are: P: ≤0.028%, S: ≤0.01%.

5. A method for preparing the cold work tool steel according to claim 1, characterized in that, Includes the following steps: (1) C, Si, Mn, Cr, Mo, W, V and Fe are added to a furnace and smelted according to the weight percentage content of claim 1 to obtain molten steel; (2) After the furnace charge is melted to 80-90%, slag is added to cover the furnace charge. Aluminum is added to the ladle at 0.15% of the total amount of molten steel for deoxidation. Desulfurization and deoxidation are carried out after the molten steel enters the refining furnace. White slag from the refining furnace is taken as a prerequisite for tapping the steel. (3) Molten steel enters the VD furnace for vacuum degassing, removing harmful gases such as oxygen and nitrogen from the molten steel under negative pressure, and then is cast into steel ingots. The steel ingots are annealed and finally forged and rolled into finished products to obtain rolled products. (4) The rolled material is quenched at 1140-1170℃, and then tempered three times at 540℃ for one hour each time to obtain the final product.

6. The preparation method according to claim 5, characterized in that, The annealing temperature is 840-880℃.

7. The preparation method according to claim 5, characterized in that, The forging temperature is 1080-1140℃.

8. The preparation method according to claim 5, characterized in that, The rolling temperature is 1050-1120℃.

9. The application of the cold work tool steel according to claim 1 or the cold work tool steel prepared by the preparation method according to any one of claims 5-8 in the preparation of cutting tools.

10. The application according to claim 9, characterized in that, The cutting tool is used for machining high-strength bolts and fasteners with a strength of 12.5 or higher.

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