A non-quenched and tempered hot work die steel and its preparation method

Abstract

This invention relates to a non-quenched and tempered hot work die steel and its preparation method, belonging to the field of steel production technology. This invention addresses the shortcomings of existing hot work die steels in terms of strength and red hardness. The chemical composition of the non-quenched and tempered hot work die steel, by mass percentage, is: C 0.44-0.48%, Si 0.50-0.70%, Mn 0.40-0.60%, Cr 4.1-4.5%, V 0.4-1.0%, Nb 0.06-0.12%, Mo 2.6-2.8%, Ni 0.3-0.5%, P ≤ 0.025%, S ≤ 0.02%. At 600℃, the tensile strength is 1332 MPa to 1386 MPa, the yield strength is 1055 MPa to 1104 MPa, and the elongation is 11% to 15%. The strength and red hardness of the non-quenched and tempered hot work die steel meet the requirements.

Description

Technical Field

[0001] This invention relates to a non-quenched and tempered hot work die steel and its preparation method, belonging to the field of steel production technology. Background Technology

[0002] Hot work die steels typically possess high strength and hardness, and are widely used in tooling applications such as die casting, hot extrusion, hot forging, and hot stamping. During use, the die surface is subjected to significant cyclic mechanical and thermal stresses, adhesion, wear, and thermal melting. Red hardness represents the die steel's ability to resist hardness reduction during subsequent heating, and it plays a crucial role in long-term service life. However, the strength and red hardness of current hot work die steels are no longer sufficient to meet existing requirements.

[0003] Therefore, there is an urgent need to propose a non-quenched and tempered hot work die steel and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0004] This invention addresses the shortcomings of existing hot work die steels, whose strength and red hardness no longer meet the requirements. It provides a non-quenched and tempered hot work die steel and its preparation method. A brief overview of the invention is given below to provide a basic understanding of certain aspects. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention.

[0005] The technical solution of the present invention:

[0006] A non-quenched and tempered hot work die steel, the chemical composition of which, by mass percentage, is: C 0.44-0.48%, Si 0.50-0.70%, Mn 0.40-0.60%, Cr 4.1-4.5%, V 0.4-1.0%, Nb 0.06-0.12%, Mo 2.6-2.8%, Ni 0.3-0.5%, P≤0.025%, S≤0.02%.

[0007] A method for preparing non-quenched and tempered hot work die steel includes the following steps:

[0008] Step 1: Vacuum Melting

[0009] Chemical components are added, and the mixture is smelted in a furnace to obtain ingots;

[0010] Step 2: Annealing and Cooling

[0011] The ingot is diffused annealed, and then buried in sand to allow it to cool slowly.

[0012] Step 3: Forging

[0013] The ingot is heated to a specified temperature, held at that temperature, and then forged. The ingot is then subjected to an upsetting and drawing process, and finally the ingot is formed into a rectangular bar.

[0014] Preferred: In step one, the melting furnace is a ZGL-25Z vacuum induction melting furnace, and the resulting ingot is a 19Kg cylindrical shape with a volume of 150mm and a height of 180mm. The diameter of the circle at the riser of the ingot is slightly larger than the diameter of the circle above.

[0015] Preferred method: In step one, volatile, molten, and oxidizable chemical components are added in two stages to ensure accurate composition.

[0016] Preferred method: In step two, the ingot is subjected to diffusion annealing at 1150°C for 1.5 hours.

[0017] Preferred method: In step three, the ingot is heated to 1100℃ and held at that temperature for two hours;

[0018] The forging ratio is greater than 3:1, and the dimensions of the rectangular bar are 40×40×600mm.

[0019] The present invention has the following beneficial effects:

[0020] The tensile strength of this non-quenched and tempered steel in the forged state is 1909 MPa–2158 MPa, the yield strength is 1178 MPa–1347 MPa, the elongation is 8%–12%, and the hardness is 54.2–57.8 HRC. After tempering at 600℃ once and then undergoing a red hardness test, the hardness is 52 HRC–57.4 HRC; after tempering at 600℃ twice and then undergoing a red hardness test, the hardness is 51.1 HRC–56.5 HRC; after tempering at 600℃ three times and then undergoing a red hardness test, the hardness is 49.4 HRC–55.4 HRC; and after tempering at 600℃ four times and then undergoing a red hardness test, the hardness is 48.7 HRC–55.2 HRC. After red hardening treatment, the room temperature tensile strength is 1874 MPa–2158 MPa, the yield strength is 1285 MPa–1541 MPa, and the elongation is 8%–13%. After four red hardening treatments at 600℃, the room temperature tensile strength is 1725 MPa–1974 MPa, the yield strength is 1452 MPa–1649 MPa, and the elongation is 11%–15%. At 600℃, the high-temperature tensile strength is 1332 MPa–1386 MPa, the yield strength is 1055 MPa–1104 MPa, and the elongation is 11%–15%. The strength and red hardness of the non-quenched and tempered hot work die steel meet the requirements. Attached Figure Description

[0021] Figure 1 Metallographic structure of non-quenched and tempered steel after forging;

[0022] Figure 2 This is a microstructure diagram of non-quenched and tempered steel after forging. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0024] Specific implementation method one: Combining Figure 1-2 This embodiment describes a non-quenched and tempered hot work die steel. The chemical composition of this non-quenched and tempered hot work die steel, by mass percentage, is: C 0.44-0.48%, Si 0.50-0.70%, Mn 0.40-0.60%, Cr 4.1-4.5%, V 0.4-1.0%, Nb 0.06-0.12%, Mo 2.6-2.8%, Ni 0.3-0.5%, P≤0.025%, S≤0.02%.

[0025] Specific Implementation Method Two: Combining Figure 1-2 This embodiment describes a method for preparing a non-quenched and tempered hot work die steel, which includes the following steps:

[0026] Step 1: Vacuum Melting

[0027] Pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, ferromolybdenum, and ferroniobium are added and smelted in a ZGL-25Z vacuum induction furnace. Some volatile, molten, and oxidizable chemical components are added in two stages to ensure accurate composition. The resulting ingot is a 19kg cylindrical shape with a volume of approximately 150mm and a height of 180mm. The diameter of the circle at the riser of the ingot is slightly larger than the diameter of the circle above it.

[0028] Step 2: Annealing and Cooling

[0029] The ingot was subjected to diffusion annealing at 1150℃ for 1.5 hours, and then buried in sand and allowed to cool slowly.

[0030] Step 3: Forging

[0031] The ingot was heated to 1100℃ and held for two hours before forging. The sample was then subjected to an upsetting and drawing forging process to achieve a forging ratio greater than 3:1. Finally, the sample was formed into a rectangular bar of 40×40×600 mm.

[0032] Example 1: The chemical composition of a non-quenched and tempered hot work die steel, by mass percentage, is: C 0.47%, Si 0.54%, Mn 0.53%, Cr 4.1%, V 0.88%, Nb 0.11%, Mo 2.39%, Ni 0.39%, P 0.009%, S 0.006%;

[0033] A method for preparing non-quenched and tempered hot work die steel, the raw materials of which are pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, as well as ferromolybdenum and ferroniobium, are added. The steel is smelted in a ZGL-25Z vacuum induction melting furnace. Some easily volatile, molten, and oxidized elements are added in two stages to ensure accurate composition. The resulting 19 kg cylindrical ingot has a volume of approximately 150 mm² and a height of 180 mm. The diameter of the riser circle is slightly larger than the diameter of the upper circle. The ingot is subjected to diffusion annealing at 1150℃ for 1.5 hours, then buried in sand to allow slow cooling. Afterward, the ingot is heated to 1100℃, held for two hours, and then forged. The sample undergoes an upsetting and drawing forging process to achieve a forging ratio greater than 3:1. Finally, the sample is formed into a rectangular bar of 40×40×600 mm.

[0034] The actual effects of this invention are as follows: Forged tensile strength is 1971 MPa, yield strength is 1178 MPa, elongation is 10.5%, and hardness is 55.1 HRC; after tempering at 600℃ once, the red hardness test shows 52.9 HRC; after tempering at 600℃ twice, the red hardness test shows 51.7 HRC; after tempering at 600℃ three times, the red hardness test shows 50.6 HRC; after tempering at 600℃ four times, the red hardness test shows 49.8 HRC; at 600℃, the high-temperature tensile strength is 1335 MPa, yield strength is 1083 MPa, and elongation is 12%.

[0035] Example 2: The chemical composition of a non-quenched and tempered hot work die steel, by mass percentage, is: C 0.48%, Si 0.58%, Mn 0.50%, Cr 4.43%, V 1.0%, Nb 0.12%, Mo 2.63%, Ni 0.4%, P 0.0056%, S 0.0014%;

[0036] A method for preparing non-quenched and tempered hot work die steel, the raw materials of which are pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, as well as ferromolybdenum and ferroniobium, are added. The raw materials are smelted in a ZGL-25Z vacuum induction melting furnace. Some easily volatile, melting and oxidizing elements are added in two batches to ensure accurate composition. The resulting cylindrical ingot weighs 19 kg, with a volume of approximately 150 mm and a height of 180 mm. The diameter of the riser circle is slightly larger than the diameter of the upper circle. The ingot is subjected to diffusion annealing at 1150℃ for 1.5 h. After that, the ingot is buried in sand and allowed to cool slowly. Then, the ingot is heated to 1100℃ and held for two hours before forging. The sample is subjected to upsetting and drawing forging process to achieve a forging ratio greater than 3:1. Finally, the sample is formed into a rectangular bar of 40×40×600 mm.

[0037] The actual effects of this invention are as follows: the forged tensile strength is 1972 MPa, the yield strength is 1342 MPa, the elongation is 8%, and the hardness is 57.8 HRC; the hardness after one tempering at 600℃ is 57.4 HRC, after two temperings at 600℃ is 56.5 HRC, after three temperings at 600℃ is 55.4 HRC, and after four temperings at 600℃ is 55.2 HRC; the high-temperature tensile strength at 600℃ is 1332.0 MPa, the yield strength is 1055.0 MPa, and the elongation is 11.2%.

[0038] Example 3: The chemical composition of a non-quenched and tempered hot work die steel, by mass percentage, is: C 0.48%, Si 0.57%, Mn 0.49%, Cr 4.16%, V 0.44%, Nb 0.0063%, Mo 2.45%, Ni 0.41%, P 0.0062%, S 0.0016%.

[0039] A method for preparing non-quenched and tempered hot work die steel, the raw materials of which are pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, as well as ferromolybdenum and ferroniobium, are added. The raw materials are smelted in a ZGL-25Z vacuum induction melting furnace. Some easily volatile, melting and oxidizing elements are added in two batches to ensure accurate composition. The resulting cylindrical ingot weighs 19 kg, with a volume of approximately 150 mm and a height of 180 mm. The diameter of the riser circle is slightly larger than the diameter of the upper circle. The ingot is subjected to diffusion annealing at 1150℃ for 1.5 h. After that, the ingot is buried in sand and allowed to cool slowly. Then, the ingot is heated to 1100℃ and held for two hours before forging. The sample is subjected to upsetting and drawing forging process to achieve a forging ratio greater than 3:1. Finally, the sample is formed into a rectangular bar of 40×40×600 mm.

[0040] The actual effects of this invention are as follows: the forged tensile strength is 2069 MPa, the yield strength is 1285 MPa, the elongation is 9%, and the hardness is 57.8 HRC; the hardness after one tempering at 600℃ is 58.1 HRC, after two temperings at 600℃ is 56.5 HRC, after three temperings at 600℃ is 55.1 HRC, and after four temperings at 600℃ is 54.9 HRC; the high-temperature tensile strength at 600℃ is 1386 MPa, the yield strength is 1105 MPa, and the elongation is 11%.

[0041] Example 4: The chemical composition of a non-quenched and tempered hot work die steel, by mass percentage, is as follows: C: 0.45%, Si: 0.54%, Mn: 0.53%, Cr: 4.25%, V: 0.6%, Nb: 0.09%, Mo: 2.64%, Ni: 0.38%, P: 0.005%, S: 0.0014%.

[0042] A method for preparing a non-quenched and tempered hot work die steel, the raw materials of which are pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, as well as ferromolybdenum and ferroniobium, are added. The raw materials are smelted in a ZGL-25Z vacuum induction melting furnace. Some easily volatile, melting and oxidizing elements are added in two batches to ensure accurate composition. The resulting cylindrical ingot weighs 19 kg, with a volume of approximately 150 mm and a height of 180 mm. The diameter of the riser circle is slightly larger than the diameter of the upper circle. The ingot is subjected to diffusion annealing at 1150℃ for 1.5 h. After that, the ingot is buried in sand and allowed to cool slowly. Then, the ingot is heated to 1100℃ and held for two hours before forging. The sample is subjected to upsetting and drawing forging process to make the forging ratio greater than 3:1. Finally, the sample is made into a rectangular bar of 40×40×600 mm.

[0043] The actual effects of this invention are as follows: Forged tensile strength is 2158 MPa, yield strength is 1347 MPa, elongation is 9%, and hardness is 57.8 HRC; after tempering at 600℃ once, the red hardness test shows 57.3 HRC; after tempering at 600℃ twice, the red hardness test shows 55.9 HRC; after tempering at 600℃ three times, the red hardness test shows 55.4 HRC; after tempering at 600℃ four times, the red hardness test shows 54.7 HRC; at 600℃, the high-temperature tensile strength is 1386 MPa, the yield strength is 1077 MPa, and the elongation is 15%.

[0044] Example 5: The chemical composition of a non-quenched and tempered hot work die steel, by mass percentage, is: C 0.46%, Si 0.55%, Mn 0.54%, Cr 4.4%, V 0.56%, Nb 0.11%, Mo 2.55%, Ni 0.36%, P 0.004%, S 0.007%;

[0045] A method for preparing non-quenched and tempered hot work die steel, the raw materials of which are pure iron, pure silicon, pure chromium, pure manganese, pure nickel, pure vanadium, pure carbon, as well as ferromolybdenum and ferroniobium, are added. The steel is smelted in a ZGL-25Z vacuum induction melting furnace. Some easily volatile, molten, and oxidized elements are added in two stages to ensure accurate composition. The resulting 19 kg cylindrical ingot has a volume of approximately 150 mm² and a height of 180 mm. The diameter of the riser circle is slightly larger than the diameter of the upper circle. The ingot is subjected to diffusion annealing at 1150℃ for 1.5 hours, then buried in sand to allow slow cooling. Afterward, the ingot is heated to 1100℃, held for two hours, and then forged. The sample undergoes an upsetting and drawing forging process to achieve a forging ratio greater than 3:1. Finally, the sample is formed into a rectangular bar of 40×40×600 mm.

[0046] The actual effects of this invention are as follows: Forged tensile strength is 2149 MPa, yield strength is 1323 MPa, elongation is 10%, and hardness is 57.2 HRC; after tempering at 600℃ once, the red hardness test shows 57 HRC; after tempering at 600℃ twice, the red hardness test shows 56.5 HRC; after tempering at 600℃ three times, the red hardness test shows 55.2 HRC; after tempering at 600℃ four times, the red hardness test shows 54.5 HRC; at 600℃, the high-temperature tensile strength is 1355.6 MPa, yield strength is 1090.8 MPa, and elongation is 13.2%.

[0047] As shown in Tables 1 and 2, this invention eliminates the need for quenching and tempering, reducing operational steps. Furthermore, compared to quenched and tempered steel, it achieves better tensile strength, hardness, and other properties, making these parameters the optimal choice.

[0048] Table 1: Chemical Composition of Non-Quenched and Tempered Hot Work Die Steel by Mass Percentage

[0049]

[0050]

[0051] Table 2: Comparison of data between non-quenched and tempered hot work die steel and hot work die steel (H13)

[0052]

[0053] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be permuted and combined. Those skilled in the art can exhaust all possibilities based on the mathematical knowledge of permutation and combination. Therefore, the present invention will not describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing non-quenched and tempered hot work die steel, characterized in that: Based on a non-quenched and tempered hot work die steel, the chemical composition of the non-quenched and tempered hot work die steel, by mass percentage, is: C 0.44-0.48%, Si 0.50-0.70%, Mn 0.40-0.60%, Cr 4.1-4.5%, V 0.4-1.0%, Nb 0.11-0.12%, Mo 2.6-2.8%, Ni 0.3-0.5%, P≤0.025%, S≤0.02%. The method includes the following steps: Step 1: Add chemical components in vacuum melting, and then melt in a melting furnace to obtain an ingot; In step one, the melting furnace is a ZGL-25Z vacuum induction melting furnace. The resulting ingot is a 19Kg cylindrical shape with a volume of 150mm and a height of 180mm. The diameter of the circle at the riser of the ingot is slightly larger than the diameter of the circle above it. Step 2: Annealing and Cooling. The ingot is diffused annealed, and then buried in sand to allow it to cool slowly. In step two, the ingot is subjected to diffusion annealing at 1150℃ for 1.5 hours; Step 3: Forging. The ingot is divided into two halves. One half of the ingot is heated to the specified temperature, held at the temperature, and then forged. The ingot is subjected to upsetting and drawing forging process, and finally the ingot is made into a rectangular bar. The forged tensile strength is 1972 MPa, the yield strength is 1342 MPa, the elongation is 8%, and the hardness is 57.8 HRC. In step one, volatile, molten, and oxidizable chemical components are added in two stages to ensure accurate composition. In step three, the ingot is heated to 1100℃ and held at that temperature for two hours; The forging ratio is greater than 3:1, and the dimensions of the rectangular bar are 40×40×600mm.

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