JP2006089823A - Die made of high-speed tool steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-life die made of high-speed tool steel with which a problem of early cracking of dies occurring even in the case of dies made of powder-metallurgical high-speed tool steel under recently increasing severe service environments of dies can be solved. <P>SOLUTION: The die is manufactured by using, as a stock, an ingot of high-speed tool steel having a composition consisting of, by weight, 0.5 to 2.0% C, ≤2% Si, ≤1% Mn, 3 to 9% Cr, ≤15% Mo, ≤25% W, 1 to 10% V, 0.1 to 15% Co and the balance Fe with inevitable impurities. In this die, the circle-equivalent diameter of a maximum grain among MC carbides present in a surface layer part of a plane of the die to be in contact with a work, i.e., a die surface or a surface of a cross section parallel to the die surface ranges from 4 to 15 μm. Further, among the above MC carbides of ≥4 μm circle-equivalent diameter, ≥45% of grains are composed of relatively spherical grains having ≥0.5 length to breadth ratio in the grain cross section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-speed tool steel mold including a punch and a die using a molten high-speed tool steel containing a hard MC type carbide.

Conventional tool materials such as punches and dies that receive high stress and impact are generally carbon tool steels and alloy tool steels. Speed tool steel is widely used. Among them, high-speed tool steel for molds is based on reducing powder carbide high-speed tool steel and carbide in steel disclosed in Patent Document 1, for example, in addition to general melted high-speed tool steel. Matrix high speed steel with increased toughness is also used depending on the application. In addition, the applicant invented a cutting tool manufactured from a new high-speed tool steel in which the size, shape, and area ratio of MC type carbide in the high-speed tool steel is controlled in Patent Document 2.
Japanese Patent No. 2960496 Japanese Patent No. 3249493

  However, in recent years, in the field of plastic working, higher loads, higher speeds, and higher precision have been demanded, and the burden on the molds used has become even more severe. For this reason, there is a situation in which a sufficient tool life cannot always be obtained with the conventional high-speed tool steel. For example, the matrix high speed disclosed in Patent Document 1 has a tendency that the wear resistance of the mold is insufficient due to the small amount of carbide, and has a disadvantageous property in terms of adhesion of the ceramic coating by PVD. On the other hand, although high hardness and high toughness can be obtained at the same time due to the fineness of the carbide, the powder high-speed tool steel is weak against abrasive wear because of the fine carbide, resulting in early wear of the mold. In addition, as a result of earnest research by the applicant this time, even in the mold made of powder high-speed tool steel, which is considered to have high toughness, as a result of the early wear of the surface, the uneven surface due to wear causes stress concentration, which is severe. We obtained new knowledge that the problem remains in terms of cracking of the mold under various mold processing conditions.

  The problem of the present invention is to solve the problem of early cracking of the mold and early wear of the mold, which occurs even in the mold made of powder high speed tool steel under the severe use environment of the mold in recent years. The object is to provide a mold made of high-speed tool steel with a long service life.

  Therefore, the present invention is, by weight percent, C: 0.5 to 2.0%, Si: 2% or less, Mn: 1% or less, Cr: 3 to 9%, Mo: 15% or less, W: 25% or less, V: 1 to 10%, Co: 0.1 to 15%, a mold manufactured using a molten high-speed tool steel made of Fe and inevitable impurities as a raw material, the surface layer part of the surface where the mold contacts the workpiece, Equivalent circle diameter of the largest particle of MC type carbides existing on the mold surface or the cut surface parallel to the mold surface (the diameter of the circle when the area of the measured particle cross section is replaced with the area of the circle) Of the MC type carbides having an equivalent circular diameter of 4 to 15 μm and an equivalent circular diameter of 4 μm or more, the ratio of major axis to minor axis ratio of the cross section of the particles is 0.5 or more. The above-mentioned problems of the conventional products have been solved by providing a high-speed tool steel mold characterized by comprising relatively spherical particles.

  With such a configuration, the applicant of the present invention controls the composition of the high-speed tool steel and the size, shape, and area ratio of the MC-type carbide in the high-speed tool steel, and applies it to a new high-speed tool steel mold. As a result, a long-life high-speed tool steel mold that cannot be achieved by conventional matrix high speed or powder high-speed tool steel molds has been provided. The area ratio of MC type carbide is obtained by dividing the total area of each MC type carbide particle cross-section with an equivalent circular diameter of 4 μm or more appearing on the screen of the optical image measurement microscope by the area of the screen itself. Value.

Preferably, for the MC type carbide having an equivalent circular diameter of 4 μm or more present on the surface layer portion of the surface in contact with the workpiece, that is, the surface of the mold, or the surface of the cut surface parallel to the surface of the mold, forging, As a high-speed tool steel mold characterized by an area ratio of 0.5 to 5% in the particle cross section parallel to the rolling axis (the cross section of the particle cut along the axial direction or the longitudinal direction of round steel or square steel) Furthermore, wear resistance and crack resistance are further improved by applying one or more composite films of titanium-containing or chromium-containing ceramic coating by PVD on the surface that contacts the workpiece of the mold. A high-speed tool steel mold may be used.
More preferably, the high-speed tool steel mold prevents invasion of gas components containing O ₂ and N ₂ into the molten steel by an inert atmosphere by an electroslag remelting method, and has a melting rate of 100 to 800 kg / h, The ratio obtained by dividing the outer diameter of the steel ingot by the outer diameter of the electrode may be maintained at 1.2 to 1.7, and may be manufactured from the molten high-speed steel manufactured by controlling the size and form of the MC type carbide.

Below, the reason for limitation is described about the component range of high-speed tool steel.
C forms MC type carbide and improves wear resistance. However, if the amount of C is too large, the toughness decreases. Therefore, the weight ratio of C is limited to 0.5 to 2.0%. Si and Mn are added as deoxidizers, but if the amount of Si and Mn is too large, the toughness decreases. Therefore, the weight ratio of Si and Mn was limited to Si: 2% or less and Mn: 1% or less. Cr is added in an amount of 3 to 9% to enhance hardenability. If Cr is less than 3%, the above effect is small, and if it exceeds 9%, the overall toughness is lowered. Mo and W form M ₆ C type carbides and improve wear resistance. However, if the amounts of Mo and W are too large, the toughness decreases, so Mo: 15% or less and W: 25% or less. V forms MC-type carbides and remarkably increases the wear resistance, but if it is too much, it causes a decrease in toughness and grindability, so it was made 1 to 10%. Co has the effect of increasing the heat resistance of the steel and increasing the heat treatment hardness, but if it is too much, it decreases the toughness and deteriorates the hot workability, so it is limited to 0.1 to 15%.

Subsequently, the high-speed tool steel on the surface layer portion of the surface that contacts the workpiece of the mold, that is, the surface of the mold, or the cut surface parallel to the mold surface (hereinafter referred to as the mold surface layer portion), which is the point of the present invention. MC type carbide area in the cross section parallel to the rolling axis (equivalent circular diameter of the largest particle among MC type carbides in the inside) (particle cross section cut along the axial direction or longitudinal direction of round steel or square steel) The reason for limiting the ratio and the major axis / minor axis ratio to the above will be described.
In molds using powdered high-speed tool steel whose maximum equivalent circular diameter of MC carbide in the steel surface layer is less than 4 μm, MC type carbide is easily removed together with the substrate due to abrasive wear. Easy and short mold life. Further, as described above, when the usage environment of the mold is harsh, the unevenness of the worn surface may cause stress concentration and may induce early cracking.
On the other hand, the maximum equivalent circular diameter of MC type carbide in steel existing in the mold surface layer exceeds 15 μm, and the area of MC type carbide whose equivalent circular diameter in steel existing in the mold surface layer is 4 μm or more. When the rate exceeds 5%, the material becomes very brittle, and cracks starting from MC type carbides tend to occur. In particular, when the shape of the particles of MC type carbides exceeding 2% is coarse and elongated squares with a major axis / minor axis ratio of less than 0.5, it is difficult to grind and is more prone to cracking, resulting in early mold breakage. Cause. On the other hand, when the area ratio of the MC type carbide is less than 0.5%, it is very easy to wear and the mold life is shortened.
Therefore, the maximum equivalent circular diameter of MC type carbide in the steel of the mold surface layer is 4 to 15 μm, and the area ratio in the cross-section parallel to the rolling axis of MC type carbide with an equivalent circular diameter of 4 μm or more is 0.5. The MC type carbide having an equivalent circular diameter of 4 μm or more is limited to a condition in which particles having a major axis / minor axis ratio of 0.5 or more occupy 45% or more of the whole.

  Preferably, by weight, C: 1 to 1.7%, Si: 0.4 to 1%, Mn: 0.2 to 0.4%, Cr: 4 to 8%, Mo: 2 to 8%, W: 0.1 to 6%, V : The surface layer part of the surface where the mold contacts the workpiece in a mold made of molten high speed tool steel containing 2.2 to 5%, Co: 0.1 to 8%, the balance being Fe and inevitable impurities That is, the equivalent circle diameter of the largest particles of MC type carbides present on the mold surface or the cut surface parallel to the mold surface is in the range of 4 to 12 μm, and the equivalent circle diameter is 4 μm. Of the MC type carbides described above, 50% or more of the particles may be composed of relatively spherical particles having a major axis / minor axis ratio of 0.46 or more.

<Example 1>
An example of the best mode for carrying out the present invention will be described with reference to examples. Table 1 shows the chemical composition in the steel of the mold manufactured by the steels of the present invention 1, 2, 3, 4, 5, and comparative steels 6, 7, 8, 9, 10, 11, 12, and the surface layer of the mold, that is, the mold. Maximum equivalent circular diameter (maximum MC type) of MC type carbide existing on the mold surface or a cut surface parallel to the mold surface (the same applies to any parallel cut surface). Equivalent circle diameter (μm), equivalent circle diameter when the area of the particle cross section measured for carbide is replaced with the area of the circle (circle when the area of the measured particle cross section is replaced with the area of the circle) Equivalent circular diameter, which is the diameter of the material) Area ratio of 4 μm or more (forging, area ratio at the cross section parallel to the rolling axis, that is, the particle cross section cut along the axial direction or longitudinal direction of round steel or square steel)%, Composition of MC type carbide particles with an equivalent circle diameter of 4 μm or more and a major axis / minor axis ratio of 0.5 or more In an actual optical image measurement microscope, the area ratio of MC type carbide is the particle size of each MC type carbide with an equivalent circular diameter of 4 μm or more that appears on the screen of the optical image measurement microscope. The total sum of the cross-sectional areas is divided by the area of the screen itself, and the maximum equivalent circular diameter (μm), area ratio, and major axis / minor axis ratio of the MC type carbide are measured with a microscope image of an optical image measurement microscope. MC carbides were observed with an equivalent circular diameter of 0.15 μm or more MC specimens cut by wire cutting from the surface of the mold were electrolytically corroded with 10% chromic acid, and the optical image measurement micro Measured with a scope.
Further, the high-speed tool steel of the present invention prevents invasion of gas components containing O ₂ and N ₂ into the molten steel by an inert atmosphere by the electroslag remelting method, and the melting condition: melting rate: 100 to 800 kg / h, The ratio of the outer diameter of the steel ingot divided by the outer diameter of the electrode was maintained at 1.2 to 1.7, and the ingot was manufactured by controlling the size of the MC type carbide grains and the ratio of the major axis to the minor axis. The steel ingot was made into a steel bar with a diameter of 100 mm by hot working of forging and rolling. The mold was manufactured from this steel bar with a diameter of 100mm and was heat-treated to 62HRC by quenching and tempering.

FIG. 1 shows a schematic shape of a high-speed tool steel mold according to an embodiment of the present invention, which is an object of life evaluation in Example 1. The mold life test conditions are
Processing: Punching Work: SCM420 Thickness 4.0mm

発明鋼の金型寿命は非常に良好である。 Table 2 shows the results of the die test in a list.

The mold life of the inventive steel is very good.

本発明鋼はPVD の効果が大きいことがわかる。 Table 3 shows the results of performing a similar test by applying TiN coating with PVD to the mold having the above shape.

It can be seen that the steel of the present invention has a large PVD effect.

The perspective view which shows schematic shape of the high speed tool steel metal mold | die of embodiment of this invention made into the object of life evaluation of Example 1. FIG.

Claims (5)

  By weight%: C: 0.5-2.0%, Si: 2% or less, Mn: 1% or less, Cr: 3-9%, Mo: 15% or less, W: 25% or less, V: 1-10%, Co : In a mold manufactured using a molten high-speed tool steel containing 0.1 to 15% and the balance of Fe and inevitable impurities as a raw material, the surface layer part of the surface where the mold contacts the workpiece, that is, the mold surface, or the above Equivalent circle diameter of the largest particle of MC type carbides present on the cut surface parallel to the mold surface (equivalent circle diameter which is the diameter of the circle when the measured particle cross-sectional area is replaced with the circle area) 45% or more of the MC type carbides having an equivalent circular diameter of 4 μm or more is a relatively spherical particle having a major axis / minor axis ratio of the particle cross section of 0.5 or more. A high-speed tool steel mold characterized by   By weight%, C: 1 to 1.7%, Si: 0.4 to 1%, Mn: 0.2 to 0.4%, Cr: 4 to 8%, Mo: 2 to 8%, W: 0.1 to 6%, V: 2.2 to 5%, Co: 0.1 ~ 8% in the mold made of molten high speed tool steel consisting of Fe and inevitable impurities as the raw material, the surface layer part of the surface where the mold contacts the workpiece, that is, the mold The equivalent circular diameter of the largest particle of MC type carbides existing on the surface or the surface of the cut surface parallel to the mold surface (the diameter of the circle when the area of the measured particle cross section is replaced with the area of the circle) Equivalent circle diameter) is in the range of 4-12 μm, and more than 50% of the MC-type carbides having an equivalent circle diameter of 4 μm or more have a major axis to minor axis ratio of 0.46 or more. A high-speed tool steel mold characterized by comprising spherical particles.   For the MC-type carbide having an equivalent circular diameter of 4 μm or more present on the surface layer part of the surface where the mold comes into contact with the workpiece, that is, the surface of the mold, or the surface of the cut surface parallel to the mold surface, The area ratio in a parallel particle cross section, that is, a particle cross section cut along the axial direction or longitudinal direction of round steel or square steel, is 0.5 to 5%. High speed tool steel mold.   4. The surface of the mold in contact with the workpiece is provided with one or more composite films of titanium-containing or chromium-containing ceramic coating by PVD. The high-speed tool steel mold according to 1. Electroslag remelting method prevents intrusion of gas components containing O ₂ and N ₂ into the molten steel due to the inert atmosphere, the melting rate is 100-800 kg / h, and the outer diameter of the steel ingot is divided by the outer diameter of the electrode The ratio is maintained at 1.2 to 1.7, and is manufactured from the molten high-speed steel manufactured by controlling the size and form of the MC-type carbide. High-speed tool steel mold described in 1.

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