JP6797465B2 - High hardness matrix highs with excellent toughness and high temperature strength - Google Patents

Description

The present invention relates to a matrix height suitable for dies such as cold forging, warm forging, hot forging, hot extrusion, and die casting.

For example, JIS-SKH51 is a high-speed sheet that can obtain hardness and wear resistance, but since a large amount of alloying elements such as Mo, V, and W are added, it crystallizes during solidification and remains after homogenization heat treatment or quenching. Carbides (hereinafter referred to as coarse carbides) tended to increase and toughness tended to decrease. Matrix highs are used as highs with increased toughness while obtaining hardness equivalent to that of highs. Matrix high-speed steel is a component system in which alloying elements such as Mo, V, and W are reduced with reference to the base (matrix) composition of high-speed tool steel such as JIS-SKH51, and is a tool steel with high strength and toughness. Yes, for example, the following prior arts 1 to 3 are known.

Looking at the problems seen from the present invention from the viewpoint of the technology of the published patent publication as a conventional technique, it is an alloy high-speed tool steel having little variation in characteristics depending on the product dimensions, and Cr and Cr are used as components shown in the examples. A component system having a high upper limit value such as the amount of V has been proposed (see, for example, Patent Document 1). However, this alloy high-speed tool steel has a problem that high-temperature strength and toughness are lowered.

On the other hand, some high-speed tool steels having high toughness have been studied for the particle size and distribution density of carbides precipitated in the matrix with respect to the toughness (see, for example, Patent Document 2). By the way, the component shown in this high-speed tool steel has an extremely low amount of C, and has a problem that a practical hardness (hardness of 62 HRC or more) such as a cold forging die cannot be obtained.

Further, in the matrix highs having excellent high-temperature strength, the components shown in the examples mainly contain a large amount of Mo, W, and V, so that high-temperature strength can be obtained (for example, Patent Documents). See 3.). However, on the other hand, this matrix highs has a problem that coarse carbides generated during solidification remain and the toughness is lowered.

As a conventional technique, matrix highs having excellent toughness and high-temperature strength as described above have been developed, but none of them satisfy all the characteristics of hardness, toughness, and high-temperature strength.

Japanese Unexamined Patent Publication No. 2004-285444 Japanese Unexamined Patent Publication No. 2004-307963 Japanese Unexamined Patent Publication No. 2005-20913

The problem to be solved by the present invention is to propose a matrix highs having excellent hardness, high temperature strength and toughness, which have been problems of the prior art.

In order to increase the hardness and high-temperature strength, C and carbide-forming elements Cr, Mo, and V may be increased, but excessive addition promotes coarse carbide formation during solidification and causes a decrease in toughness. It becomes. From this, we focused on the area ratio of coarse carbides, clarified the relationship between the area ratio of coarse carbides and toughness after applying the homogenization treatment to the ingot, and further optimized the amount of alloying elements added based on this relationship. That is, 1. Carbide forming elements are adjusted from the viewpoint of reducing coarse carbides generated during solidification and promoting solid dissolution of coarse carbides in homogenization heat treatment, and the components of matrix high steel having excellent hardness, high temperature strength, and toughness. I found a range.

Therefore, in the first means, the means for solving the above-mentioned problems are C: 0.55 to 0.75%, Si: 0.50 to 1.50%, Mn: 0.10. ~ 1.00%, Cr: 3.00 to 5.00%, Mo: 2.00 to 3.00% and W: 2.00% or less, 2Mo + W: 4.00 to 6.00% , V: 0.80 to 1.30%, P: 0.30% or less, S: 0.01% or less, O: 0.0050%, N: 0.0300 or less, and the balance is Fe and unavoidable. It is an impurity and is a carbide remaining inside in the steel ingot state. It is 3.0% per 1 μm ² of MX type and / and M ₆ X (X is C or N) type with a circle equivalent diameter of 2.0 μm or more. The following is a matrix highs having excellent toughness and high strength, characterized in that the hardness of the steel material after hot forging of the ingot after quenching and tempering is 62 HRC or more.

The invention of the present application is a matrix height suitable for dies such as cold forging, warm forging, hot forging, hot extrusion, die casting, etc., which are excellent in all characteristics of hardness, high temperature strength and toughness. ..

Prior to the embodiment for carrying out the invention, the reasons for limiting the chemical components of the present invention will be described. The% of the chemical component is mass%.

C: 0.55 to 075%
C is an element for ensuring sufficient hardenability and quenching tempering hardness and forming carbides to obtain wear resistance and high temperature strength. However, if the C content is too less than 0.55%, sufficient hardness, high temperature strength, and wear resistance cannot be obtained for the obtained steel material. On the other hand, if the C content is more than 0.75%, the amount of coarse carbides crystallized increases during solidification, and the toughness of the obtained steel material decreases. Therefore, C is 0.55 to 075%, preferably 0.60 to 0.70%.

Si: 0.50 to 1.50%
Si is an element necessary for ensuring the deoxidizing effect and hardenability in steelmaking, and if Si is less than 0.50%, these effects cannot be sufficiently obtained. On the other hand, if the amount of Si is more than 1.50%, the solid solution temperature of the MX (X is C or N) type carbide is raised, so that the effect of the homogenized heat treatment of the obtained steel material is reduced and the toughness is lowered. .. Therefore, Si is set to 0.50 to 1.50%, preferably 0.75 to 1.25%.

Mn: 0.10 to 1.00%
Mn is an element necessary for ensuring hardenability, and if Mn is less than 0.10%, this curing cannot be sufficiently obtained. On the other hand, excessive addition of Mn more than 1.00% lowers workability. Therefore, Mn is set to 0.10 to 1.00%.

Cr: 3.00 to 5.00%
Cr is an element that improves hardenability, and if it is less than 3.00%, the hardenability is insufficient, a structure such as bainite is formed during quenching cooling, and the toughness is lowered. On the other hand, if the amount of Cr is too large, a large amount of Cr-based relatively fine carbides are precipitated during quenching and tempering. Since this carbide tends to be coarsened at a high temperature, the hardness is greatly reduced in a high temperature environment. That is, if the amount of Cr is too large, the high temperature strength and softening resistance are lowered. Therefore, Cr is set to 3.00 to 5.00%, preferably 3.50 to 4.50%.

Mo: 2.00 to 3.00% and W: 2.00 or less, 2Mo + W: 4.00 to 6.00%
Mo and W are elements that contribute to hardenability, secondary hardening during tempering, abrasion resistance, high-temperature strength, and softening resistance, and fine carbides that have become unsolidified during quenching are crystal grains. Suppresses the coarsening of. However, these effects cannot be obtained when Mo is 2.00 to 3.00% and W is 2.00 or less and 2Mo + W is less than 4.00 to 6.00%. On the other hand, if it is too large, the amount of crystallization of M ₆ X (X is C or N) type coarse carbide increases during solidification, the stability of the carbide itself increases, and the effect of the homogenizing heat treatment decreases. As a result, residual carbides increase, and due to these synergistic effects, toughness decreases. Therefore, within the range where Mo is 2.00 to 3.00% and W is 2.00 or less, 2Mo + W: 4.00 to 6.00%, preferably Mo is 2.4 to 3.0. % And W is within the range of 1.00% or less, and 2Mo + W: 4.80 to 6.00%.

V: 0.80-1.30%
V is an element that contributes to high temperature strength and abrasion resistance by precipitating fine and hard MX (X is C or N) type carbides, nitrides, and carbonitrides during tempering, and is unsolidified during quenching. The resulting fine carbides and carbonitrides suppress the coarsening of crystal grains and suppress the decrease in toughness. However, if V is less than 0.80%, these effects cannot be obtained. On the other hand, if V is more than 1.30%, the amount of crystallization of MX (X is C or N) type coarse carbide increases during solidification, and the stability of the carbide itself also increases. As the effect of the heat treatment decreases, the residual carbide increases. Due to these synergistic effects, toughness is reduced. Further, if V is more than 1.30%, the amount of C consumed as MC-type carbide increases and the hardness decreases. Therefore, V is set to 0.80 to 1.30%, preferably 0.90 to 1.20%.

P: 0.030% or less P is an impurity element, but segregates at the grain boundaries and reduces toughness. Therefore, P is set to 0.030% or less.

S: 0.010% or less S is an impurity element, but forms sulfide and lowers toughness and hot workability. Therefore, S is set to 0.01% or less.

O: 0.0050% or less O is an impurity element, but it forms an oxide, becomes a starting point of fracture, and lowers toughness and fatigue strength. Therefore, O is set to 0.0050% or less.

N: 0.0300% or less N is an impurity element, but if it is more than 0.0300%, MN-type nitride, which is more stable at a higher temperature than MC-type, crystallizes during the solidification process and inhibits toughness. .. Therefore, N is set to 0.0300% or less.

Carbide remaining inside in the steel ingot state, with a diameter equivalent to a circle of 2.0 μm or more, MX type and / and M ₆ X (X is C or N) type per 1 μm ² : 3.0% or less In matrix highs. Coarse carbide tends to be a starting point of fracture and promotes crack growth, so it is desirable to reduce it as much as possible from the viewpoint of toughness. With respect to the coarse carbide remaining inside in the ingot state, when it is 3.0% or less per 1 μm ² of MX type and / and M ₆ X (X is C or N) type with a diameter equivalent to a circle of 2.0 μm or more. Excellent toughness was obtained. Therefore, the area ratio is set to 3.0% or less per 1 μm ² .

Hardness after quenching and tempering of steel material after hot forging: 62 HRC or more The present invention relates to a matrix highs that is intended not only for hot and warm dies but also for cold forging. For cold forging applications, it is desirable that the practical hardness of the die is 62 HRC or more. Therefore, the hardness of the steel material after hot forging after quenching and tempering is 62 HRC or more.

Here, a mode for carrying out the invention of the present application will be described. For example, the following manufacturing illegalities such as (1) and (2) can be applied.

(1) A cast material composed of the chemical components of the steel of the present invention by primary melting is secondarily melted and resolidified by a vacuum arc remelting method (VAR) or an electroslag remelting method (ESR). In this method, since solidification after re-dissolution is performed in a short time by the secondary dissolution, solidification segregation is unlikely to occur, and local coagulation and segregation of carbides can be suppressed.

(2) This is a manufacturing method in which the steel melted and resolidified by the method of (1) above is soaked at 1150 to 1250 ° C. for 10 hours or more. This manufacturing method is the most suitable manufacturing method for controlling the size of coarse carbides precipitated in steel to an appropriate range. This soaking process needs to be carried out at a temperature higher than the quenching temperature and lower than the melting point. Appropriate soaking treatment makes it possible to reduce the size of the formed coarse carbides and further reduce the amount of carbides to uniformly disperse them. The appropriate values for the temperature and time of the soaking process differ depending on the components.

For the characteristics of the steel materials in Table 1 shown below, the manufacturing method using the soaking treatment shown in (2) was applied. That is, the chemical components, the balance Fe, and the unavoidable impurities, which are the composition of 11 kinds of the symbols A, C, E, G, H, JO of the steel of the present invention and 1 to 17 kinds of the symbols of the comparative steel shown in Table 1. An ingot made of steel is ingot in a 1-ton vacuum melting furnace, and the ingot obtained by this melting is soaked at 1200 ° C. for 15 hours, and then heated to a diameter of 140 mm so that the forging ratio is about 6S. Steel was manufactured by interforging.

11 types of symbols A, C, E, G, H, JO of the present invention steel and 10 types of comparative steel symbols 1 to 17 of the steel material obtained by the above hot forging, carbide area ratio, quenching and tempering material The maximum hardness, toughness and softening resistance of the steel are shown in Table 2.

In Table 2, * 1) Carbide area ratio After soaking the ingot at 1200 ° C. for 15 hours or more, the microstructure in the center was photographed, and the carbide area ratio per 1 μm ² was calculated in (%) by screen analysis. .. The carbide area ratio in the present invention is 3.0% or less. Therefore, the carbide area ratio of the comparative example exceeding 3.0% is underlined.

* 2) Quenching Tempering hardness Quenching is performed by using a block of 25 mm × 25 mm × 25 mm indexed from the center of each steel material in Table 2 as a sample, holding at 1140 ° C. for 10 minutes, and stirring. It was carried out by putting it in oil at ℃. For tempering, the operation of holding at 480 to 620 ° C. for 60 minutes and then air cooling was repeated three times. Each of the obtained samples is interrupted, the interrupted surface is used as the measurement surface, the heat-affected zone of the measurement surface and the scale layer on the surface opposite to the measurement surface are removed by a flat surface grinder to improve the parallelism, and then the rock well. The hardness was measured with a hardness meter. The hardness at which the peak of the secondary curing was obtained during tempering at 480 to 620 ° C. was defined as the maximum curing. If it is 62.0 HRC or more, it is evaluated as ◯, if it is less than 62.0 HRC, it is evaluated as ×, and the value is underlined.

* 3) Toughness Toughness was evaluated by the Charpy impact test. A block-shaped test material having a side of 25 mm was indexed from the center of each steel material, quenched at 1140 ° C., and then tempered to be tempered to 58 HRC and then processed into 10 RC notch Charpy. When the Charpy impact value is 100.0 J / cm ² or more, it is marked with ⊚, when it is 80.0 J / cm ² or more and less than 100.0 J / cm ^2, it is marked with ○, and when it is less than 80.0 J / cm ^2. Is x, and its impact value is underlined.

* 4) High temperature strength Softening resistance was used as an evaluation of high temperature strength. The method of the softening resistance test is shown below. A test material on a block with a side of 25 mm is indexed from the center of each steel material, quenched at 1140 ° C., and then tempered to prepare the test material to 57 to 59 HRC, and the test material is tempered at 600 ° C. Hold for 50 hours and air cool these steels. Next, after removing the heat-affected zone on the measurement surface and the scale layer on the surface opposite to the measurement surface with a flat surface grinder, the parallel accuracy is improved, and then the measurement is performed with a Rockwell hardness tester, and the difference from the initial hardness, that is, softening. Evaluated by quantity (ΔHRC). The evaluation was evaluated as ◯ when the softening amount was 12.0 or less and × when it exceeded 12.0, and the value of the softening amount was underlined.

Claims (1)

By mass%, C: 0.55 to 0.75%, Si: 0.50 to 1.50%, Mn: 0.10 to 1.00%, Cr: 3.00 to 5.00%, Mo: Within the range of 2.00 to 3.00% and W: 2.00% or less, 2Mo + W: 4.00 to 6.00%, V: 0.80-1.30%, P: 0.030% or less , S: 0.01% or less, O: 0.0050%, N: 0.0300 or less, the balance is Fe and unavoidable impurities, and the carbide remaining inside is 2.0 μm or more in the equivalent circle diameter. MX type and / and M ₆ X (X is C or N) type is a matrix highs in a steel ingot state with an area ratio of 3.0% or less per 1 μm ² , and the forging ratio of the ingot is 6S. held for 10 minutes to 140mm in diameter steel after hot forging at 1140 ° C., after implementing Re quenching by pouring into 50 ° C. oil, the operation of air cooling after 60 min holding at 480-620 ° C. 3 matrix high-speed steel with excellent toughness and high strength, wherein a hardness of quenching and tempering material obtained when performing the Shi tempering by repeating times is not less than 62HRC.