JP2000212700A - Die excellent in weldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce tool steel excellent in weldability and machinability without deteriorating its mechanical property such as toughness and wear resistance and to provide a die excellent in various characteristics to be required. SOLUTION: This die is produced by refining tool steel having a compsn. contg., by weight, 0.45 to <0.65% C, 0.1 to 2.1% Si, 0.1 to 1.2% Mn, 4.5 to 12.0% Cr, one or two kinds of Mo and W so as to satisfy (Mo+1): 1.5 to 3.5%, 0.05 to <0.5% V, and the balance Fe with inevitable impurities, in which eutectic value Z=[=8×(C%)+0.6×(Cr%)] is controlled to <=10.8 to the hardness of >=55 HRC and executing machining. Preferably, in the tool steel, the content of Cr is controlled to 4.5 to 9.0%, the contents of one or two kinds of Mo and W are controlled to (Mo+1/2W):1.5 to 2.5%, and 0.005 to 0.1% S, <=5.0% Ni and <=100 ppm Ca are controlled. Additionally, it is applied to quenching at 1000 to 1050 deg.C and tempering at >=500 deg.C to control its hardness to >=55 HRC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die for punching, bending, drawing or trimming a steel sheet used for automobiles, household appliances, agricultural equipment and the like.

[0002]

2. Description of the Related Art Automakers and the like have been reducing costs in various fields in order to overcome price competition and secure profits. The field extends to molds, and to reduce costs, shorten the manufacturing process of products formed by press dies, reduce the number of dies, and develop mold processing methods and tools. Various reduction measures have been implemented.

[0003] In such a mold, conventionally used mold materials, especially mold materials for cold working, contain a large amount of carbides for imparting wear resistance, and further have excellent hardenability and ensure toughness. Therefore, a material having a high Cr content is required, and for example, a high C-high Cr steel such as SKD11 which is an alloy tool steel according to JIS G4404 is used.

[0004]

However, in recent years, there has been a tendency to reduce the number of parts constituting a mold, to integrally mold, to complicate the shape, etc., and to obtain a shape by processing from a steel material such as the above-mentioned SKD11. Although it has excellent wear resistance, the volume to be processed is enormous, which causes an increase in manufacturing cost. On the other hand, attempts have been made to reduce the machining allowance by casting with a material component equivalent to SKD11. However, since it contains a large amount of carbide, there is a problem in toughness and the like. The situation is not yet reached.

[0005] Particularly, in a die used for punching, bending, drawing or trimming of a steel plate, cracks frequently occur in a die for forming a shape of a punched product which is three-dimensionally changed. As a result, demands for weld repairability and the like have increased. In other words, looking at the recent trends, it has been found that repairs can be made even if the start-up of the die machining process has been shortened and the shape has been modified by a design change, or if damage or cracks have occurred due to severe conditions during use of the die. Therefore, the weldability for reusability has become important.

[0006] As described above, tool steels conventionally applied to molds and the like each have advantages and disadvantages in mechanical properties recently required. Thus, the present invention is to provide a tool steel which can achieve tool steel excellent in weldability and machinability without reducing mechanical properties such as toughness and wear resistance, and can solve the above problems. .

[0007]

Means for Solving the Problems The present inventors consider the maintenance of basic mechanical properties such as toughness and wear resistance and consider the basic conditions required for improvement of weldability and machinability. Revised.

First, in such a mold material, at present, a component containing a large amount of hard brittle carbide is designed for the purpose of abrasion resistance, but a surface treatment technique has recently been used as a means for imparting abrasion resistance. Due to the development, it is no longer necessary to emphasize the wear resistance of the mold material itself as much as the current situation. Then, from the viewpoint of crack resistance, such a carbide is a factor that promotes crack propagation, so that it is necessary to reduce the amount to an appropriate amount.

As a result of these considerations, we have:
Even if the content of C, which is a basic component of tool steel, is reduced, good mechanical properties, in particular, the composition and composition of components sufficient to obtain hardness and toughness are found, and further, weldability, machinability, and surface treatment. They conceived a tool steel having excellent properties, and arrived at the mold of the present invention.

That is, according to the present invention, C: 0.
45 to less than 0.65%, Si: 0.1 to 2.1%, M
n: 0.1 to 1.2%, Cr: 4.5 to 12.0%, M
One or two kinds of o or W are (Mo + 1 / 2W):
1.5 to 3.5%, V: 0.05 to less than 0.5%, the balance being Fe and unavoidable impurities, and the eutectic value Z [= 8 × (C%) + 0.6 × (Cr%)] is 10.8
This is a mold produced by tempering the following tool steel to a hardness of 55 HRC or more and performing cutting.

[0011] Preferably, the tool steel to be provided is contained in a
Cr: 4.5 to 9.0%, one or two of Mo and W are (Mo + 1 / 2W): 1.5 to 2.5%, or S: 0.005 to 0.1% %, Ni ≦ 5.
0%, Ca ≦ 100 ppm. And, in addition to these inventions, quenching at 1000 to 1050 ° C, 500
It is a mold made of tool steel that is applied to tempering at a temperature of ℃ or more and has a hardness of 55 HRC or more.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The feature of the present invention is that even if the content of C, which is a basic component constituting tool steel, is reduced, good mechanical properties, particularly, component composition and composition sufficient for obtaining hardness and toughness are obtained. The present inventors have found that a tool steel having excellent weldability, machinability, and surface treatment characteristics is further improved, thereby improving the characteristics of a mold to be manufactured.

[0013] That is, the tool steel provided for the mold of the present invention suppresses the content of C to ensure excellent weldability. When used in a mold, the tool steel has excellent toughness. Even if damage, cracks or wear occur inside, it can be easily reused by repairing by welding. And, in order to cope with the case where the wear resistance is insufficient due to the suppression of the C content, excellent surface treatment properties are also ensured.

In the present patent, excellent weldability or weldability means that JI which performs prescribed preheating and post-heating is used.
SZ 3158 indicates that no weld cracking is observed in the Y shape test. In performing welding, preheating and postheating are usually performed in order to prevent welding cracks at that time. Preheating is generally performed to prevent high-temperature cracking during welding, and post-heating is to prevent low-temperature cracking, and is particularly a kind of tempering that lowers the hardness of the weld heat affected zone.

[0015] Generally, a mold is welded to change its shape or to be repaired depending on the situation during its manufacture or use, but the alloy steel is used in a state where it is preheated to a high temperature to prevent cracking during welding. Is done. In particular, when Cr or the like is contained, 45
It is generally carried out after preheating to 0 to 550 ° C. or higher. In the present invention, even if the preheating temperature is lowered, specifically to 250 ° C., a Y shape test according to JIS Z 3158 is conducted. Tool steel with no weld cracking can be provided, and a mold with excellent weldability can be achieved. by this,
Workability related to welding is improved, and it is economical.

Next, in the case of high C, Cr steels, the post-heat after welding is also important, but by lowering the hardness of the heat affected zone, the heating temperature and time in post-heat can be reduced. In particular, to control the heat affected zone, it is effective to reduce the C content to less than 0.65% and the Cr content to 4.5% or more. This is effective for optimally adjusting the amounts of solid solution C and Cr.

Next, the surface treatment properties of the present invention will be described. The present invention sufficiently secures the surface treatment properties in order to cope with the case where the wear resistance is insufficient due to the suppression of the C content. The properties required for this are the hardenability, the amount of C dissolved in the austenitic structure at the surface treatment temperature such as the salt bath method and the CVD treatment, and the hardness of the base metal near the surface.

That is, the quenchability is given to enable application to any surface treatment apparatus, and mainly comprises C
It can be secured by maintaining the amount of r at 4.5% or more. At the same time, the content of Cr of 4.5% or more should be ensured for the purpose of preventing a kind of burning cracking phenomenon that occurs during cooling after the surface treatment of a complex shape.

The amount of C that forms a solid solution in the austenite structure at the surface treatment temperature depends on the MX type compound (T
iC, VC, etc.). That is, solid solution C
Is required to be supplied from the steel material in order to generate an MX-type compound by the surface treatment method, and the optimum amount depends on the amount of C dissolved in the martensite structure before holding at the surface treatment temperature. In order to adjust the amount of solid solution C, the mold of the present invention is to adjust the C content of the tool steel used for the production to 0.4%.
5% or more. Maintaining the hardness of the base material in the vicinity of the surface is an important factor for imparting peel resistance of a film formed by the surface treatment.

In addition, in manufacturing a mold from tool steel, one of means for reducing the cost is to improve the machinability of the tool steel. The tool steel provided in the present invention has excellent machinability after quenching and tempering in addition to its annealed state, and specifically, excellent machinability can be achieved even in a quenched and tempered state of 55 HRC or more. Therefore, the tool steel provided in the present invention is most suitable as a so-called pre-hardened steel for a die manufactured by performing a cutting process after tempering to a predetermined hardness. Based on these, the elements constituting the tool steel provided for the mold of the present invention and the reasons for limiting the contents thereof will be described.

C is necessary for improving hardenability and maintaining hardness after heat treatment. In order to ensure a hardness after heat treatment of 55 HRC or more to achieve abrasion resistance, and to secure a sufficient MX-type carbide film thickness in a surface treatment such as a CVD treatment or a salt bath method, 0.45% or more is required. Content is required. If it is less than 0.45%, quenching hardness is insufficient and sufficient strength cannot be secured, and it is difficult to form a film having a thickness of 3 μm or more by a salt bath method or a CVD method.

C combines with Cr, Mo, and V to form a carbide, and improves wear resistance and tempering softening resistance. If the amount of addition is excessive, the toughness is reduced, and 0.65%
If it becomes the above, weldability will be degraded. Further, the temperature range of the solid-liquid coexistence becomes large, which may cause the risk of casting defects, that is, increase the eutectic value Z. Therefore, the addition amount of C is 0.45 to 0.6.
It was less than 5%. Note that the eutectic value Z is an index for evaluating the likelihood of eutectic solidification, and Z = 8 × (C%) + 0.
Defined as 6 × (Cr%). (C%) and (C
r%) is the weight percent of C and Cr contained in the tool steel.

Si is contained for the purpose of improving the deoxidizing agent and castability.
% Or more is required. On the other hand, an excessive content causes the machinability and the weldability to be impaired, and the segregation of the matrix components also becomes severe. Therefore, the content of Si is 0.1
To 2.1%.

Mn is contained for improving hardenability.
If it is less than 0.1%, it is insufficient to stably obtain quench hardness. On the other hand, if the content is too large, the weldability is degraded, and further, like Si, the segregation of the matrix components becomes intense. However, Mn is also an economical element that can be replaced with expensive Cr, Mo, etc., and when the effects of Cr, Mo, etc. are sufficiently exhibited, Mn is used.
May be omitted.

Cr combines with C to form carbides, thereby improving wear resistance and increasing hardenability.
This has the effect of preventing a kind of burning cracking phenomenon that occurs during cooling after surface treatment of a complex-shaped object by a VD treatment, a salt bath method, or the like. However, if the content is too large, the toughness decreases due to an increase in Cr carbide. Further, similarly to the addition of C, the temperature range of solid-liquid coexistence becomes large, which causes the risk of casting defects (eutectic value Z) to increase. Therefore, the amount of Cr added is 4.5-12.
0%, and preferably 4.5 to 9.0%.

Mo and W improve hardenability. Further, it combines with C to form a hard carbide and improves wear resistance. Since the atomic weight of W is about twice that of Mo, Mo1
% Content has the same effect as the content of W2%, (M
o + ／ W) can show the effect.
In the present invention, one or two types of Mo and W can be contained, that is, the total content of Mo may be replaced with twice the content of W, and a part of Mo may be replaced with the corresponding W.
It may be used in place of the amount. Which component should be preferentially used in the (Mo + ／ W) amount may be determined in consideration of economic efficiency. If the amount of (Mo + 1 / 2W) is less than 1.5%, it is insufficient to secure hardness during high-temperature tempering. On the other hand, if the amount of addition is excessive, a massive eutectic carbide which deteriorates the fatigue properties is generated, so the content is set to 1.5 to 3.5%, preferably 1.5 to 2.5%.

V is effective in suppressing the growth of retained austenite due to quenching and ensuring toughness. To exhibit this effect, the content of V must be 0.05% or more. Conversely, an excessive content crystallizes a huge V-based carbide at the time of solidification and causes a decrease in weldability and toughness.
It was made to be less than 0.5 to 0.5%.

As described above, the eutectic value Z is an index for evaluating the likelihood of eutectic solidification. As the eutectic value Z increases, the solid-liquid coexistence temperature width increases. In the tool steel used for manufacturing the mold of the present invention, if the eutectic value Z is large, high-temperature cracking during welding and deterioration of toughness are concerned.

The tool steel used for the mold of the present invention is:
In accordance with other required effects, S,
Zr, Ca, Pb, Se, Te, Bi, In, Be, C
One or more of e may be contained. Among them, S is an element detestable in the field of welding and high-hardness steel as a representative of the embrittlement element. However, since it has a free-cutting effect, the toughness and weldability are improved by the purpose of improving machinability. Up to about 0.1% can be contained. In the present invention, the content is preferably 0.005 to 0.1%.

Ni is an element whose toughness is improved by increasing the hardenability and the impact transition temperature. However, in the present alloy system, deterioration of weldability can be prevented by the effect of maintaining toughness particularly in a high C content region. It acts in the direction of expanding the surface treatment area that can be practically operated. However, the excessive Ni content has an upper limit of 5.0% or less due to manufacturing difficulties. To obtain the above effects, preferably at least 0.005%, more preferably,
0.01% or more.

[0031] Ca is an ideal free-cutting element without a decrease in mechanical properties or a change in structure. The mechanism for improving the free-cutting property is to lower the melting point of oxides, which are minutely dispersed in the steel, and to melt them by cutting heat to form a protective film on the cutting edge. However, at present, it is difficult to add a large amount because the vapor pressure is so high that it easily escapes from the molten steel. In view of the technical level, the upper limit is 100 ppm in the present invention. In addition, rare earths are 0.2% or less, preferably for the purpose of improving the machinability in the tool steel provided in the present invention,
A content of 0.1% or less is possible.

The tool steel provided for the present invention as described above, in addition to providing excellent weldability, can provide the conventional SKD11
Hardness of 55 HRC or more can be ensured even by quenching from 1000 to 1050 ° C., which is the same heat treatment condition as above, and tempering at 500 ° C. or more. In addition to achieving excellent machinability with a hardness of 55 HRC or more, it is also excellent in surface treatment properties such as a salt bath method and a CVD treatment. Further, when the tool steel of the present invention is used for a mold, flame quenching may be performed only on a necessary portion according to the required function, and the hardness may be adjusted in consideration of the number of manufacturing steps or required characteristics. What is necessary is just to select the heat treatment method for obtaining.

In the present invention, in order to further improve the present effect, it is effective to adjust the condition after quenching. That is, the content of C and Cr dissolved in the martensitic structure after quenching is C: 0.45 to 0.6% by weight,
r: 3.0 to 6.0% and to be, and is to less 1.5% _M 7 _{C 3} type primary carbides in a sectional structure in area%.

Adjusting the amounts of solid solution C and Cr in the martensite structure is effective for improving weldability. High C, C
In r steel, post-heat after welding is also important, and as described above, the post-heat heating temperature and time can be reduced by reducing the hardness of the weld heat-affected zone. It is effective to adjust the amounts of solid solution C and Cr in the martensite structure as a means for this purpose.
6% or less, and the amount of solid solution Cr should be 3.0% or more. Further, the amount of solid solution Cr is set to 6.0% or less, and in this case, it is effective in improving machinability.

As described above, the amount of Cr contained in the tool steel used in the present invention is set to 4.5% or more in improving hardenability, which leads to improvement in surface treatment. Preferably, it is effective to make the amount of solid solution Cr in the martensite structure 3.0% or more. Also,
The reason for securing the amount of solid solution C is, as described above, because it is necessary to supply from a steel material in order to generate the MX type compound by the surface treatment method, and also to maintain the hardness, It is preferable that the amount of dissolved C be 0.45% or more. In order to ensure good machinability, the primary carbide is preferably not more than 1.5 (area%) in its sectional structure. The amount of primary carbides can be reduced by heat treatment in addition to the chemical composition specified for the tool steel of the present invention.

[0036]

EXAMPLES Next, examples of the present invention will be described in detail, but the present invention is not limited to these examples. (Example 1) First, a material was melted using a 50 kg high frequency furnace, and an ingot having a chemical composition shown in Table 1 was prepared. The comparative material 1 is a material equivalent to SKD11. Next, hot rolling was performed so that the forging ratio was about 5, and after cooling, annealing was performed at 850 ° C. for 4 hours.

[0037]

[Table 1]

Next, the above-mentioned annealed material was JIS Z 3158
And then heated and maintained at 1025 ° C. using a vacuum heating furnace, followed by gas cooling and quenching with an inert gas.
Further, tempering was performed at 500 to 550 ° C. so that the target hardness of each test piece was HRC 55 or more. The test pieces manufactured in this manner were welded under the conditions shown in Table 2, and the weldability was evaluated. The comparative materials 4 to 10 are 50
Hardness of 55 HRC or more could not be obtained by tempering at 0 ° C. or more.

[0039]

[Table 2]

The weldability was evaluated based on the presence or absence of cracks after welding, and the results are shown in Table 3 together with the hardness by quenching and tempering heat treatment. In each case, no welding crack occurred in the material of the present invention.
Cracks occurred at 0 and 450 ° C.

[0041]

[Table 3]

Next, the above-mentioned annealed material was subjected to a JIS test for a tensile test.
A No. 4 test piece (diameter 14 mm) was used for a Charpy impact test in a 10 mm square, 55 mm long, 2 m notch depth at the center.
A test piece having a diameter of 10 mm and a radius of 10 mm was cut out in the rolling direction and subjected to evaluation of mechanical properties (tensile strength, Charpy impact value, bending stress). In the heat treatment, after heating to 1025 ° C. in a vacuum heating furnace, gas cooling quenching is performed with an inert gas, and further, 500 to 550 ° C. so that the target hardness becomes HRC 55 or more.
Tempering was performed. Table 4 shows the results.

[0043]

[Table 4]

As shown in Table 4, the materials 1 to 3 of the present invention were 55HRC
It can be seen that excellent toughness is achieved with the above hardness, and that the mechanical properties are excellent.

Example 2 Next, the machinability was evaluated. First, test materials in an annealed state having a hardness of 24 HRC or less were prepared from the materials shown in Table 1, and the machinability of the test pieces was evaluated using a square end mill. Table 5 shows the cutting test.
The conditions were as follows. From the results shown in Table 6, the material of the present invention 1
3 shows that the tool life is three times or more as long as that of the comparative material 1 corresponding to SKD11.

[0046]

[Table 5]

[0047]

[Table 6]

Next, test materials quenched and tempered to a hardness of 57 to 60 HRC using the materials shown in Table 1 under the heat treatment conditions of the present invention were produced, and the machinability of the test pieces was evaluated using a square end mill. The cutting conditions are shown in Table 7. From the test results shown in Table 8, it is understood that the inventive materials 1 to 3 can obtain a tool life 6 times or more as compared with the comparative material 1 corresponding to SKD11.

[0049]

[Table 7]

[0050]

[Table 8]

Example 3 Next, the effects of the preheating temperature before welding and the cooling time after welding on the weldability were investigated. In conducting the survey, the above-mentioned annealed material was
After heating and holding at 5 ° C, gas cooling and quenching was performed with an inert gas, and subsequently, tempered at 500 to 550 ° C to a predetermined hardness was used as a test material, and the post-heat after welding was 450 ° C for 1 hour. After the holding, it was cooled to room temperature over 3 hours or 7 hours. Table 9 shows the occurrence of cracks under these conditions, together with the adjusted hardness and the preheating temperature.

[0052]

[Table 9]

As can be seen from Table 9, cracks did not occur in the inventive materials 1 to 3 even when the cooling time was 3 hours, while cracks occurred in the comparative material even after a cooling time of 7 hours.

[0054]

As described above, according to the present invention, good mechanical properties, especially hardness and toughness can be ensured even when the content of C as a basic component is reduced, as compared with SKD11. It is possible to provide a steel material having excellent machinability and further excellent machinability. Further, the preheating temperature at the time of welding can be set lower, and even if the cooling time is shortened, cracks are less likely to occur and workability is excellent. In addition, since the excellent surface treatment property is also considered, the industrial value of the mold of the present invention is great.

Claims (6)

[Claims] C .: 0.45 to less than 0.65%, Si: 0.1 to 2.1%, Mn: 0.1 to 1.2% by weight.
%, Cr: 4.5 to 12.0%, one or two of Mo or W (Mo + 1 / 2W): 1.5 to 3.5%,
V: 0.05 to less than 0.5%, the balance being Fe and unavoidable impurities, eutectic value Z [= 8 × (C%)
+ 0.6 × (Cr%)] is a tool steel having excellent weldability, characterized by being prepared by tempering tool steel having a hardness of 10.8 or less to a hardness of 55 HRC or more and performing cutting. 2. The tool steel according to claim 1, wherein:
~ 9.0%, one or two of Mo or W
The mold having excellent weldability according to claim 1, wherein the ratio is + 1 / 2W): 1.5 to 2.5%. 3. The method according to claim 1, wherein the tool steel is S: 0.00 by weight%.
3. The composition according to claim 1, wherein the content is 5 to 0.1%.
A mold excellent in weldability described in 1. 4. The method according to claim 1, wherein the tool steel is Ni ≦ 5.0 by weight%.
%. The mold having excellent weldability according to claim 1, wherein 5. The tool steel according to claim 1, wherein the weight ratio is Ca ≦ 100.
The mold having excellent weldability according to any one of claims 1 to 4, wherein the amount is ppm. 6. The tool steel is used for quenching at 1000 to 1050 ° C., tempering at 500 ° C. or more, and 55 HR.
6. A hardness of at least C.
A mold excellent in weldability according to any one of the above.