Cold work die alloy steel and cold work die using the same

Abstract

To provide a cold work die alloy steel and a cold work die using the same that can achieve a high hardness (64 HRC or higher on the Rockwell hardness C scale) by overall quenching at a low temperature (900°C or less) followed by tempering (150 to 200°C) without a carburizing treatment.SOLUTION: A cold work die alloy steel consisting, in terms of weight%, of 0.90% or more and 1.50% or less of C, 0.70% to 2.50% of Si, 0.10% to 1.00% of Mn, 1.00% to 4.00% of Cr, 0.20% to 1.50% of Mo, 0.40% to 3.00% of W+2Mo, and 0.10% to 0.80% of V, with the balance being Fe and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an alloy steel for cold die applications and a cold die using the same. [Background technology]

[0002] Cold forming dies require high wear resistance, so high-hardness materials, such as alloy tool steel and high-speed tool steel, have been used as the base material (see Patent Documents 1 to 3). For example, as the use of high-tensile steel plates (hi-tensile steel) in automobile bodies is increasing, cold forming dies are also required to have high wear resistance in order to process hard materials such as high-tensile steel plates. In addition to the aforementioned automotive field, there is also a growing demand for cost reduction in order to keep up with global prices for wear-resistant parts in electrical and home appliances, hydraulic components, and the construction industry. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4266383 [Patent Document 2] Patent No. 5143531 [Patent Document 3] Patent No. 5276330 Summary of the Invention

[0004] However, conventional alloy tool steels do not provide sufficient wear resistance because their hardness is in the range of 60 to 62 HRC on the Rockwell hardness scale C. In addition, alloys such as high-speed tool steels require quenching at high temperatures of 1100 to 1200°C, which increases the cost of heat treatment and creates problems in terms of manufacturing costs. [Problem to be solved by the invention]

[0005] Therefore, the present invention aims to provide an alloy steel for cold-working dies that can achieve high hardness (64 HRC or higher on the Rockwell hardness C scale) by whole quenching at a low temperature (900°C or lower) without carburizing, followed by tempering (150 to 200°C), and a cold-working die using the same. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the alloy steel of the present invention is an alloy steel for cold working dies which contains, by weight, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, V: 0.10 to 0.80%, with the remainder being Fe and unavoidable impurities.

[0007] Alternatively, the alloy steel for cold tooth dies is composed of, by weight percent, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, Nb: 0.05 to 0.40%, with the remainder being Fe and unavoidable impurities.

[0008] In addition, in the invention of a cold die using the above-mentioned alloy steel for cold die, the surface of the cold die has a Rockwell hardness C scale of 64 HRC or more. [Effects of the Invention]

[0009] The alloy steel for cold work dies of the present invention can be subjected to a full quenching treatment at a low temperature (900°C or less) without carburizing treatment, followed by a tempering treatment (150 to 200°C), thereby achieving sufficient surface and internal hardness (64 HRC or more on the Rockwell hardness C scale) and an appropriate amount of retained austenite.

[0010] In addition, the manufacturing cost of the cold die alloy steel can be reduced by limiting the content of rare metals such as Cr, Mo, and V in the cold die alloy steel to 5% by weight or less. Furthermore, since the cold die alloy steel has excellent tempering softening resistance, the decrease in hardness is small even when the temperature rises. DETAILED DESCRIPTION OF THE INVENTION

[0011] As one embodiment of the present invention, the chemical components of an alloy steel for cold working dies and a cold working die using the alloy steel for cold working dies will be described.

[0012] 《C (Carbon)》 The C (carbon) content in the cold die alloy steel of the present invention is set to 0.90% to 1.50% by weight. Carbon ensures the hardness of the cold die alloy steel after quenching and tempering, and plays a role in ensuring a high fatigue life when used as a die material. If the C content in the cold die alloy steel is less than 0.90%, the required surface and internal hardness cannot be obtained, while if it exceeds 1.50%, the amount of retained austenite (γ amount) increases, deteriorating the fatigue life of the die.

[0013] Silicon The content of Si (silicon) is set to a range of 0.70% to 2.50% by weight. Silicon plays a role in increasing the temper softening resistance of cold die alloy steel. If the Si content in the cold die alloy steel is less than 0.70%, the required temper softening resistance cannot be obtained, and if it exceeds 2.50%, the hot forgeability deteriorates significantly. Preferably, the Si content is 1.50% to 2.50%.

[0014] Manganese (Mn) The content of Mn (manganese) is 0.10% or more and 1.00% or less by weight. Manganese improves the hardenability of cold-working die alloy steel, and is effective in improving fatigue life when used as a die material. If the Mn content in the cold-working die alloy steel is less than 0.10%, the hardenability of the cold-working die alloy steel deteriorates, and if it exceeds 1.00%, the hot forgeability deteriorates significantly.

[0015] 《Cr (Chromium)》 The Cr (chromium) content is set to 1.00% or more and 4.00% or less by weight. Chromium enhances the hardenability of the cold-working die alloy steel and also thermally stabilizes cementite, preventing the cementite from dissolving in the matrix at high temperatures. If the Cr content in the cold-working die alloy steel is less than 1.00%, the hardenability of the cold-working die alloy steel deteriorates, while if it exceeds 4.00%, coarse carbides are generated in the cold-working die alloy steel.

[0016] Mo (Molybdenum) The content of Mo (molybdenum) is 0.20% or more and 1.50% or less by weight. Molybdenum forms carbides in the cold-working die alloy steel, contributing to ensuring hardness. If the Mo content in the cold-working die alloy steel is less than 0.20%, the required tempering hardness and softening resistance cannot be obtained. On the other hand, if the Mo content exceeds 1.50%, coarse carbides are generated.

[0017] "V (Vanadium)" The content of V (vanadium) is 0.10% or more and 0.80% or less by weight. V plays a role in increasing temper softening resistance when added in combination with silicon in the cold die alloy steel. Furthermore, if the V content in the cold die alloy steel is less than 0.10%, the required temper softening resistance cannot be obtained, and if it exceeds 0.80%, coarse carbides are generated. Note that a similar effect can also be achieved by adding Nb (niobium) as a substitute element for V. In this case, the Nb content is preferably in the range of 0.05% or more and 0.40% or less by weight.

[0018] W (Tungsten) W (tungsten) can be contained in the range of 0.40% to 3.00% by weight as the W equivalent (W + 2Mo). In this case, tungsten, like molybdenum, forms carbides in the cold-working die alloy steel, contributing to ensuring hardness. If the W equivalent in the cold-working die alloy steel is less than 0.40%, the required tempering hardness and softening resistance cannot be obtained. On the other hand, if the W equivalent exceeds 3.00%, coarse carbides will form.

Claims

1. An alloy steel for cold working dies, characterized in that it contains, by weight, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, V: 0.10 to 0.80%, with the remainder being Fe and unavoidable impurities.

2. An alloy steel for cold working dies, characterized in that it contains, by weight, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, Nb: 0.05 to 0.40%, with the remainder being Fe and unavoidable impurities.

3. A cold die using the alloy steel for cold die according to claim 1 or 2, wherein the surface of the cold die has a Rockwell hardness C scale of 64 HRC or more.