JPH11152549A - Hot work tool steel and high temperature members made of the hot work tool steel - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To increase the durability of molds and structural members used for casting and injection molding. SOLUTION: C: 0.10 to 0.50%, Si: 0.
5% or less, Mn: 1.5% or less, Ni: 1.5% or less,
Cr: 3.0 to 13.0%, Mo: 0 to 3.0%, W:
1.0 to 8.0%, V: 0.01 to 1.0%, Nb:
0.01 to 1.0%, Co: 1.0 to 10.0%, B:
0.003 to 0.04%, N: 0.005 to 0.05%
And, optionally, REM: 0.001-0.05%, M
g: 0.001 to 0.05%, Ca: 0.001 to 0.
Alloy steel containing at least one type of nickel and at least 05%, with the balance being Fe and unavoidable impurities. [Effect] The softening resistance at high temperatures, the heat check resistance, and the erosion resistance are improved, and the life of a casting machine or an injection molding machine using this steel is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hot tool steel used at a relatively high temperature, a casting mold and a structural member for a casting machine, and a mold and a structure for an injection molding machine made of the hot tool steel. The present invention relates to a member, a hot forging die, an extrusion die, and the like.

[0002]

2. Description of the Related Art Light metals such as aluminum and alloys containing aluminum as a main component, magnesium and alloys containing magnesium as a main component (hereinafter simply referred to as light metals), or lead and lead. Of low-melting-point metals, such as alloys containing tin as a main component, tin or alloys containing tin as a main component, and alloys containing low-melting-point metals (hereinafter, simply referred to as low-melting-point metals) by casting. At this time, 5% Cr-based JIS-
SKDJ61 steel has been employed. Recently, an injection molding machine has been used to produce such light metals and low melting point metals, but at that time, an injection molding machine mold or an injection molding machine structural member is also used. Adopts JIS-SKD61 steel. Further, as a die for hot forging such as a steel material, JIS-
SKD61 steel has been employed.

[0003] When JIS-SKD61 steel is used for such a purpose, the life is extended by various factors. The factors are roughly classified into the following three. The first factor is softening with prolonged use at high temperatures. JIS
-The SKD61 steel is strengthened by dispersing carbides finely in tempered martensite, but when used at high temperatures for a long time, recovery of dislocations and aggregation and coarsening of carbides occur. This is because it cannot be maintained and gradually softens. The second factor is a crack called heat check. The heat check is a tortoise-shaped crack generated on the surface of a material, and is said to be caused by repeated heating and cooling cycles. The third factor is the erosion phenomenon. This is because the metal or alloy in the molten state is very reactive, and when it comes into contact with the surface of the material, the surface of the material is gradually transformed and consumed by the reaction.

[0004]

As described above, the conventionally used JIS-SKD61 steel has insufficient softening resistance at high temperatures, heat check resistance, and erosion resistance. There is a problem that the life may be reached. The present invention has been made in view of such circumstances, and its object is to provide a hot tool steel and a hot tool steel having excellent softening resistance at high temperatures, heat check resistance, and erosion resistance. It is to provide a high temperature member.

[0005]

In order to achieve this object, the present inventors have used a number of test materials based on SKD61 steel to obtain softening resistance at high temperatures, heat check resistance, erosion resistance. A detailed investigation on the effect of alloying elements on properties was conducted. As a result, by optimizing the balance of the amounts of alloying elements, a new alloy composition far superior to SKD61 steel was found for each of these characteristics,
The present invention has been reached.

That is, the first invention of the present invention is:
By weight%, C: 0.10 to 0.50%, Si: 0.5%
Mn: 1.5% or less, Ni: 1.5% or less, C
r: 3.0 to 13.0%, Mo: 0 to 3.0%, W:
1.0 to 8.0%, V: 0.01 to 1.0%, Nb:
0.01 to 1.0%, Co: 1.0 to 10.0%, B:
0.003 to 0.04%, N: 0.005 to 0.05%
And the balance consists of Fe and inevitable impurities. The second invention is the first invention, further comprising, as a component, in weight%, REM:
0.001-0.05%, Mg: 0.001-0.05
%, Ca: at least one of 0.001 to 0.05%. The third invention is the first or second invention.
In the invention, the total of the Co content and the W content is 5.
0% or more. In a fourth aspect based on the first, second, or third aspect, the ratio of the B content to the N content, B / N is in the range of 0.2 to 1.0, and
The total of the B content and the N content, that is, B + N is 0.05% or less. The fifth invention is the first, second, and third inventions.
Alternatively, in the fourth invention, it is preferable that the total amount of all the alloying elements except Fe is 15.0% or more. According to a sixth aspect of the present invention, a high-temperature member such as a casting mold and a structural member for a casting machine, a mold and a structural member for an injection molding machine, a hot forging die, an extrusion die, or the like is used for the first, second, third, or fourth. It is characterized by being made of the hot tool steel of the fifth invention.

[0007]

The limited range of the components in the present invention will be described below in detail.

C is an element that forms a solid solution in the matrix and promotes martensitic transformation, and is an essential element for ensuring hardenability. At the same time, Fe, C in the alloy
It is an indispensable element for forming carbides by combining with r, Mo, W, V, Nb, and the like, and increasing the high-temperature strength. That is, it is an indispensable element in order to guarantee the minimum strength, hardness, wear resistance, and the like that are required as hot tool steel. In order to exert its effect, the addition amount must be at least 0.10% or more. However, an excessively large addition amount tends to cause excessive coarsening of the carbides and lowers the high-temperature strength, so that the softening resistance at high temperatures and the heat check resistance are adversely affected. Therefore, the addition amount is 0.10
The range is limited to 0.50%. For the same reason,
It is desirable to set the lower limit to 0.15% and the upper limit to 0.40%.

[0009] Si is used as a deoxidizing element when melting and refining the alloy, and as a result, Si is inevitably contained as an impurity. However, Si promotes coarsening of carbides and forms an intermetallic compound called a Laves phase, thereby significantly lowering the toughness of the alloy. Therefore, it is desirable to reduce as much as possible, and the content of Si is limited to 0.5% or less. For the same reason, it is desirable to set the upper limit to 0.3%.

Mn is an element useful as a deoxidizing element like Si, and also contributes to improvement of hardenability.
However, an excessive amount of addition causes deterioration of toughness and lowers high-temperature strength, thereby adversely affecting softening resistance at high temperatures and heat check resistance. Therefore, the addition amount is limited to 1.5% or less. For the same reason, it is desirable to set the upper limit to 1.0%.

Ni is an effective additive element for improving toughness, increasing hardenability, and suppressing the formation of δ ferrite. However, an excessively added amount causes deterioration of the structure stability at a high temperature, so that it tends to change with time, which adversely affects the softening resistance and the heat check resistance at a high temperature. Therefore, the addition amount is limited to 1.5% or less. For the same reason, it is desirable to set the upper limit to 1.0%.

[0012] Cr is an indispensable additive element for hot work tool steel in order to ensure oxidation resistance and corrosion resistance at high temperatures and to increase the strength of the alloy by forming carbides by combining with C. is there. Further, the high stability to the molten metal improves the erosion resistance of the alloy. In order to exhibit the effect, it is necessary to add at least 3.0% or more. However, an excessive amount promotes the formation of δ-ferrite, resulting in a decrease in toughness and a decrease in high-temperature strength. Therefore, the amount added is limited to the range of 3.0 to 13.0%. For the same reason, it is desirable to set the lower limit to 5.0% and the upper limit to 11.0%.

[0013] Mo has the effect of improving the high-temperature strength by forming a solid solution in the matrix, promoting the fine precipitation of carbides and preventing its aggregation, and has a high stability to the molten metal. Is added as desired because it improves the resistance to erosion. However, an excessive amount promotes the formation of δ-ferrite, resulting in a decrease in toughness and a decrease in high-temperature strength. Therefore, the amount of addition is limited to the range of 3.0% or less. For the same reason, the upper limit is 2.
It is desirable to set it to 0%.

W has the effect of improving the high-temperature strength by forming a solid solution in the matrix, promoting the fine precipitation of carbides, and preventing its aggregation. In addition, since the alloy has high stability to a molten metal, the erosion resistance of the alloy is improved.
Moreover, since such an effect is greater than Mo, all of the resistance to softening at high temperatures, the heat check resistance, and the erosion resistance are significantly improved. Therefore, W must be added without fail, and in order to exert its effect sufficiently, an addition amount of at least 1.0% or more is required. However,
If the amount is too large, the formation of δ-ferrite and Laves phase is promoted, so that the toughness and the high-temperature strength are reduced. Therefore, the amount of addition is limited to the range of 1.0 to 8.0%. For the same reason, the lower limit is 2.0% and the upper limit is 7.
It is desirable to set it to 0%.

V combines with C to form a carbide and contributes to improvement in high-temperature strength and wear resistance. In order to exert the effect, the addition amount is required to be at least 0.01% or more. However, an excessively added amount tends to cause excessive coarsening of the carbide, and conversely lowers the high-temperature strength, which adversely affects softening resistance at high temperatures and heat check resistance. Therefore, the amount of addition is 0.01-1.0.
%. For the same reason, the lower limit is set to 0.
It is desirable to set the upper limit to 1% and the upper limit to 0.5%.

Nb combines with C to form fine carbides and contributes to improvement of high-temperature strength and miniaturization of crystal grains. In order to exert the effect, the addition amount is required to be at least 0.01% or more. However, an excessively added amount tends to cause excessive coarsening of carbides, resulting in a decrease in high-temperature strength and a decrease in toughness, and thus adversely affects softening resistance at high temperatures and heat check resistance. Therefore, the addition amount is limited to the range of 0.01 to 1.0%. For the same reason, it is desirable to set the lower limit to 0.05% and the upper limit to 0.5%.

Co improves the softening resistance at high temperatures and the heat check resistance in order to increase the high-temperature strength and impact resistance by forming a solid solution in the matrix. Further, it suppresses precipitation of δ ferrite and prevents a decrease in strength and toughness at high temperatures. Further, the high stability to the molten metal improves the erosion resistance of the alloy. Therefore, Co must be added without fail, and at least 1.0% or more of Co must be added to exhibit its effect. However, since Co is a very expensive element, excessive addition significantly increases the cost of the alloy. Therefore, the amount of addition is limited to the range of 1.0 to 10.0%. For the same reason, it is desirable to set the lower limit to 2.0% and the upper limit to 8.0%.

Thus, Co has resistance to softening at high temperatures,
Since it has a favorable effect on all of the heat check resistance and the erosion resistance, in order to further improve these properties, it is desirable to increase the amount of Co to be added within the above-mentioned limited range. However, there is a certain degree of complementarity between W and Co having the same effect, and C and C are expensive alloy elements.
Part of o can be replaced by W. Therefore, especially softening resistance at high temperature, heat check resistance,
If you want to improve the erosion resistance and obtain excellent properties, use Co
It is desirable that the total of the content and the W content be 5.0% or more. For the same reason, it is more desirable that the total of the Co content and the W content be 8.0% or more.

B has a function of stabilizing the grain boundaries by segregating mainly at the grain boundaries even when a small amount of B is added. By this action, the braided temporal change at high temperature is suppressed to maintain the high-temperature strength for a long time, and the generation and propagation of cracks are suppressed. Therefore, the softening resistance at high temperatures and the heat check resistance are significantly improved. In order to show the effect,
A minimum amount of 0.003% or more is required. However, an excessively added amount causes a reduction in ductility and toughness, and conversely adversely affects softening resistance at high temperatures and heat check resistance. Therefore, the amount of addition is 0.003 to
Limited to the range of 0.04%. For the same reason, it is desirable to set the lower limit to 0.005% and the upper limit to 0.02%.

N combines with Cr, V, Nb and the like in the alloy to form a nitride or a carbonitride, thereby increasing the high-temperature strength and strengthening the matrix. Further, the corrosion resistance and strength at high temperatures are improved. In order to exert the effect, it is necessary to add at least 0.005% or more. However, an excessive amount of addition causes deterioration of welding characteristics and deterioration of hot workability. Therefore, its addition amount is 0.005
Limited to the range of 0.05%. For the same reason,
It is desirable to set the lower limit to 0.01% and the upper limit to 0.04%.

In addition, there is a specific correlation between B and N, and in order to secure a sufficient improvement effect of the softening resistance at high temperature and the heat check resistance, the B content and the N content are required. And the B / N ratio are preferably in the range of 0.2 to 1.0. The exact reason is unknown at this time,
This fact suggests that a compound composed of B and / or N is formed in the alloy of the present invention, or that co-segregation of B and N at grain boundaries and around carbides is suggested. For the same reason, the ratio of the B content to the N content, B / N
More preferably, the ratio is in the range of 0.3 to 0.7.

Here, as described above, if both B and N are added in too large amounts, the ductility and toughness of the alloy at high temperatures are reduced. This tendency is observed when B and N are added simultaneously.
Synergistically stronger. In particular, when the total of the B content and the N content exceeds 0.05%, toughness and ductility at high temperatures are reduced, and hot workability is deteriorated, which causes a new problem in manufacturing. There is. Therefore, it is desirable that the total of the B content and the N content is 0.05% or less. In addition, for the same reason, the total of the B content and the N content is 0.1%.
More preferably, it is not more than 04%.

Further, in order to further improve the stability to the molten light metal, the ratio of Fe in the alloy may be relatively reduced. This is because the reaction between the light metal in the molten state and the present alloy mainly consists of Al in the light metal and F in the present alloy.
It is presumed that this is caused by the reaction with e. Therefore, in order to improve the erosion resistance, it is necessary to use Fe
It is desirable that the total amount of addition of all the alloy elements except for the above is 15.0% or more. Further, it is more preferable that the total amount of all the alloying elements except Fe is 18.0% or more.

REM, Mg and Ca act as deoxidizing and desulfurizing elements during melting and smelting. At the same time, it is also highly effective in improving high-temperature strength and high-temperature ductility. Also, REM is an element effective for improving oxidation resistance, and thus hinders the progress of cracks. Since these effects eventually contribute to the improvement of the heat check resistance, one or more of these elements are optionally contained. However, the addition of these elements in too large amounts is a factor that significantly impairs hot workability. Therefore, their contents are each limited to the range of 0.001 to 0.05%. For the same reason, the lower limit is set to 0.0
It is desirable to set the upper limit to 0.05% and the upper limit to 0.03%.

The steel of the present invention can be used as a hot tool steel used at a relatively high temperature. For example, it can be used as a material for a casting mold and a structural member for a casting machine, a mold and a structural member for an injection molding machine, a hot forging die, and an extrusion die. Note that the steel of the present invention is not limited to use in these applications, but can be widely provided for applications premised on use at relatively high temperatures.

In the production of the alloy steel of the present invention,
An ordinary manufacturing method can be employed. For example, the alloy is melted as an alloy having a predetermined composition according to the present invention by ordinary electric furnace melting or vacuum induction melting (VIM), and then cast into a predetermined shape. Or, if necessary, an electroslag remelting furnace (ESR) or a vacuum arc remelting furnace (VA)
After being redissolved in R), it is cast. The cast alloy is subjected to a uniform diffusion treatment as necessary, and then processed into a predetermined shape using various processing methods such as forging, forging, and rolling, and then subjected to an annealing treatment. After that, heat treatment such as quenching and tempering is performed so that desired mechanical characteristics are obtained, and then machining is performed to predetermined dimensions. Alternatively, after mechanical processing is performed in advance, heat treatment such as quenching and tempering is performed so that desired mechanical characteristics are obtained, and further, finishing processing is performed. The casting mold and the structural member for the casting machine, the mold and the structural member for the injection molding machine, and the hot forging die manufactured in this process have excellent softening resistance at high temperatures, heat check resistance and erosion resistance. Therefore, the service life is significantly extended compared to SKD61 steel.

[0027]

Embodiments of the present invention will be described below in detail. A test material having the composition shown in Table 1 was obtained by a vacuum induction melting furnace.
It was melted into a 0 kg steel ingot. Table 2 shows the sum of the Co content and the W content (Co + W), the sum of the B content and the N content (B + N), and the ratio of the B content to the N content of the test material. (B / N) and the total amount (Σ) of the addition amounts of all alloy elements except Fe. Each of the ingots was subjected to a homogenous diffusion treatment and then hot forged to a thickness of 30 mm and a width of 120 m.
m plate material. A test piece collected from this plate material was subjected to a heat treatment at 1050 ° C. for 3 hours as a quenching treatment, followed by air cooling.

[0028]

[Table 1]

[0029]

[Table 2]

First, in order to evaluate the softening resistance of each test material at a high temperature, a test piece after quenching was
After holding for 0 hour, it was air-cooled. After the surface of the cooled test piece is mirror-polished, a Rockwell tester (C scale)
Was used to measure the hardness of the test piece. If the difference between the hardness at this time and the hardness as-quenched is ΔHRC, the smaller the ΔHRC, the better the softening resistance at high temperatures.
FIG. 1 shows the test results, and it is clear that the invented material has better softening resistance at high temperatures than the comparative material and the conventional material.

Next, in order to evaluate the heat check resistance of each test material, a heat check test was performed using a self-made test machine. The process of heating the surface of the test piece to 630 ° C. and immediately cooling with water was defined as one cycle, and the cycle was repeated 1,000 times. The test piece after the test was cut, and cracks generated on the test piece surface by heat check were observed with an optical microscope. The length and number of cracks were all recorded for one 10 mm cross section at the center of each test piece, and the lengths of all cracks were summed to obtain the total crack length. The total crack length of each test material relative to the total crack length of SKD61 steel (test material No. 19), which is a conventional material, was defined as a relative crack coefficient. That is, the smaller the relative crack coefficient, the better the heat check resistance. FIG. 2 shows the relative crack coefficient of each test material, and it is clear that the inventive material has better heat check resistance than the comparative material and the conventional material. Also, among the invention materials, RE
Those containing at least one of M, Mg, and Ca (test materials Nos. 11, 12, and 13) have more excellent heat check resistance.

Further, in order to evaluate the erosion resistance characteristics of each test material, a erosion test was performed using a self-made tester. While rotating the test material in the molten Al-Mg alloy, 6
Hold at 50 ° C. for up to 100 hours. The amount of erosion was determined from the change in weight before and after the test, and the amount of erosion per unit area per unit time and the erosion rate constant were determined. The erosion rate constant of each test material with respect to the erosion rate constant of SKD61 steel (test material No. 19) as a conventional material was defined as a relative erosion rate coefficient. That is, the smaller the relative erosion rate coefficient, the better the erosion resistance characteristics. FIG. 3 shows the relative erosion rate coefficient for each test material, and it is clear that the inventive material has better erosion resistance characteristics than the conventional material. In particular, Σ is 18
% Or more of the inventive materials show very good erosion characteristics,
It was found to have a relative erosion rate coefficient almost equivalent to that of pure Co measured separately. The test material No. It is clear from FIGS. 1 and 2 that the comparative material No. 14 has the same erosion characteristics as the inventive material, but the softening resistance at high temperature and the heat check resistance are inferior to the inventive material.

As an example of actual production, the invention material 1 (composition alloy corresponding to test material No. 7) and invention material 2 (test material N
o. 11), comparative material (test material No. 14)
Structural members for a magnesium alloy injection molding machine were manufactured using a conventional alloy (composition alloy equivalent to test material No. 19) and a conventional material (composition alloy corresponding to test material No. 19). Vacuum induction melting of specified materials (VI
M) and then melted in an electroslag remelting furnace (E
SR) to produce an ingot having a diameter of 260 mm. After performing a uniform diffusion process to each ingot, it was forged, finished into a round bar having a diameter of 200 mm, and subjected to an annealing process.
Then, after quenching at 1050 ° C.,
Tempering treatment was performed at 0 ° C., and machining was performed to a predetermined shape.

By applying the parts manufactured in this way, injection molding of a magnesium alloy was actually performed. FIG. 4 shows the life of each material. It is clear that the invention material has a significantly longer life than the comparative material and the conventional material.

[0035]

As is apparent from the above description, according to the present invention, a hot work tool steel having more excellent softening resistance, heat check resistance, and erosion resistance at high temperatures than SKD61 steel can be provided. Therefore, when it is used for a casting mold and a structural member for a casting machine, a mold and a structural member for an injection molding machine, and a hot forging die, the life can be remarkably prolonged, which is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 ΔHR of each test material obtained from the hardness measurement results
It is a graph which shows C (the difference of the hardness of the test piece at the time of air-cooling after holding at 700 degreeC for 100 hours and the hardness of as-quenched).

FIG. 2 is a graph showing the relative crack coefficient of each test material (total crack length of each test material relative to the total crack length of SKD61 steel) obtained from the results of the heat check test.

FIG. 3 is a graph showing the relative erosion rate coefficient of each test material (the erosion rate constant of each test material relative to the erosion rate constant of SKD61 steel) obtained from the results of the erosion test.

FIG. 4 is a graph showing the service life of a structural member for a magnesium injection machine manufactured using each material, obtained from the results of using the actual machine.

Claims (6)

[Claims] C. 0.10 to 0.50% by weight,
Si: 0.5% or less, Mn: 1.5% or less, Ni: 1.
5% or less, Cr: 3.0-13.0%, Mo: 0-3.
0%, W: 1.0 to 8.0%, V: 0.01 to 1.0
%, Nb: 0.01 to 1.0%, Co: 1.0 to 10.
0%, B: 0.003-0.04%, N: 0.005-
A hot work tool steel containing 0.05%, with the balance being Fe and unavoidable impurities. 2. The composition further comprises, by weight percent, REM:
0.001-0.05%, Mg: 0.001-0.05
%, And at least one of Ca: 0.001 to 0.05%. 3. The total of the Co content and the W content is 5.0.
% Or higher, the hot work tool steel according to claim 1 or 2. 4. The ratio of B content to N content, B / N is in the range of 0.2 to 1.0, and the sum of B content and N content, B + N is 0.05. % Or less, the hot work tool steel according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the total amount of all the alloying elements except Fe is 15.0% or more.
4. The hot work tool steel according to any one of 4. 6. A casting mold and a structural member for a casting machine, a mold and a structural member for an injection molding machine, comprising the hot tool steel according to claim 1. High temperature components such as forging dies and extrusion dies