JP3090280B2 - Steel for hot press tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for a hot press tool, and more particularly to a steel having a higher transformation point, a resistance to sintering cracking, a thermal shock resistance,
With regard to tool steel with excellent high-temperature strength and fracture toughness, the hot slab after continuous casting is strongly pressed in the width direction, and is repeatedly subjected to rolling down using a working tool (hereinafter referred to as anvil), from the tip of the slab to the rear. Widely used for anvils and the like in continuous width presses developed to reduce the width to the end according to the size of the billet.

[0002]

2. Description of the Related Art Hot die steels used for press dies, forging dies, and the like, as well as steels for cutting tools, impact-resistant tools, and steels for cold dies, have JIS G4404 alloy tool steel standards. Conventionally, as an anvil for continuous press, mainly S
KD6 has been used. However, these conventional mold steels show sufficient resistance to normal hot working, but are insufficiently suitable for uses such as anvils for continuous width pressing.

[0003] In other words, anvils for continuous width pressing are large and 1
It is continuously used under the width pressure of a hot slab of 200 ° C. or more, and the surface of the anvil reaches up to 850 ° C. while heating and cooling are repeated in each width reduction cycle. In the hot die steel of SKD6 described above, Because the transformation points (A _C1 , A _C3 ) are low, and the slab contact surface is inadequate due to insufficient cracking resistance and thermal shock resistance, the slab contact surface has many cracks, and the chipping rate is high. The cycle was short, and there was a disadvantage that the press productivity was reduced. For this reason, the applicant of the present invention has disclosed in
68846 proposed an advantageous mold steel, but the above-mentioned problems were not sufficiently solved.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a steel for a hot press tool adapted to use under severe conditions in a continuous width press or the like.

[0005]

Means for Solving the Problems and Actions The subject of the present invention is as follows. That is, by weight ratio, C:
0.08 to 0.16%, Si: 0.80 to 1.20%,
Mn: 0.10 to 0.60%, Cr: 7.00 to 9.0
0%, Mo: 0.50 to 1.50%, W: 0.50
1.50%, V: 0.10 to 0.60%, N: 0.030
0 to 0.1000%, REM: 0.0005 to 0.07
And 0.10% to 0.100% of one or two selected from Nb and Ti, and
Satisfies 15% or less, and the balance is Fe
And hot press tool steel, which comprises unavoidable impurities. Serial Cr + 4Mo + 1.5W + 5Nb + 11V + 6Ti + 6
Si-40C-2Mn-30N (% by weight)

Conventionally, since the SKD6 used has a high C content, the transformation point (A _C1 = 810 ° C., A _C3 = 880 ° C.)
Is lower than the maximum temperature of 850 ° C on the surface of the anvil such as a continuous width press, and the insufficiency of fire cracking resistance and thermal shock resistance. There was a problem that progress was easy. Therefore, in order to prolong the life of the anvil, it is important to raise the transformation points (A _C1 , A _C3 ) and to improve the resistance to fire cracking and thermal shock, which reduce the amount of C. Can be achieved by: However, when the amount of C is reduced, the high-temperature strength becomes insufficient. Therefore, in order to improve the high-temperature strength, the amount of Cr is increased, and one of Nb and Ti is selected.
Species or two species.

Furthermore, when reducing the amount of C δ- ferrite is likely to generate, from the high-temperature strength and toughness is remarkably lowered when δ- ferrite amount is more than 10%, Cr eq = Cr + 4Mo + 1.5W + 5Nb + 11V +
6Ti + 6Si-40C-2Mn-30N (% by weight) must be 15% or less to prevent the appearance of δ-ferrite. For that purpose, it is effective to substitute Mo for W and to contain N.

In the present invention, the transformation point (Ac ₁ , Ac ₃ ) is raised to a higher temperature by lowering the C content, optimizing the Cr content, and containing Nb and Ti. To improve on δ
- the formation of ferrite, by substituting a part of Mo to W, N-containing
The content was suppressed by setting the content higher, and the high temperature strength and toughness were further improved. In addition, there is a problem that sulfide precipitates at the crystal grain boundary of the slab contact surface during use as an anvil and the thermal shock resistance is reduced. To improve this, a rare-earth element REM is included. Specifically, a parameter [S] = S− (32/140) REM (× 1) indicating a fixed S amount
0 ^4% by weight) achieving sulfide precipitation prevention of the grain boundaries by the 20 following further improved thermal shock resistance.

Next, the reasons for limiting the composition ranges of the respective components in the present invention will be described. C: C is necessary for improving hardenability and maintaining strength after quenching and tempering. In addition, it combines with Cr, Mo, W and V to form carbides, and improves wear resistance and tempering softening resistance. In order to raise the transformation points (A _C1 , A _C3 ) to a higher temperature and to improve the quenching resistance and the thermal shock resistance, it is desirable to reduce the C content, but the C content is 0.08%.
If it is less than 10%, the strength is insufficient due to the balance with other components, and if it exceeds 0.16%, excellent toughness cannot be obtained.
Amounts ranged from 0.08 to 0.16%.

[0010] Si: Si is the maintenance of oxidation resistance and transformation point (A
_C1 , A _C3 ) has the effect of maintaining a high temperature, but if it is less than 0.80%, it is difficult to maintain the A _C1 transformation point at 850 ° C. or more, while if it exceeds 1.20%, the appearance of δ-ferrite Since the suppression becomes difficult, the range is set to 0.80 to 1.20%. Mn: Mn is necessary for improving hardenability and preventing the appearance of δ-ferrite. However, if the Mn content is less than 0.10%, the effect is poor. On the other hand, if it exceeds 0.60%, the transformation points (A _C1 , A _C3 ) are lowered, so the range is 0.10 to 0.60%. .

Cr: Cr forms carbonitrides and disperses in the matrix to improve wear resistance. In addition, a part of the alloy forms a solid solution, improves hardenability, increases high-temperature strength, further improves high-temperature oxidation resistance, and is effective for increasing the _AC1 transformation point and decreasing the thermal expansion coefficient at high temperatures. As a component, if the Cr content is less than 7.00%, the effect is poor.
If it exceeds 0%, the appearance of δ-ferrite cannot be suppressed, so the range was 7.00 to 9.00%. Note that δ-blow
In order to prevent the appearance of site, the Cr equivalent shown below
It is necessary to limit it to 5% or less. Serial Cr equivalent = Cr + 4Mo + 1.5W + 5Nb + 11V +
6Ti + 6Si-40C-2Mn-30N (% by weight)

Mo: Mo forms a solid solution in the matrix to improve hardenability and combines with C to form a hard carbide, and is dispersed in the matrix to improve abrasion resistance. And has the effect of increasing high temperature strength, but 0.50%
If it is less than 1.5%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 1.50%, the toughness is reduced. W: W forms a solid solution in the matrix to improve hardenability and
Forms hard carbides which disperse in the matrix to improve wear resistance and increase tempering softening resistance and high temperature strength. W has the same effect as Mo, and plays a role in preventing the formation of δ-ferrite by substituting a part of Mo for W. However, if it is less than 0.50%, the effect is not sufficient, whereas 1. If it exceeds 50%, the toughness deteriorates.
The range was 1.50%.

V: V has the effect of precipitating fine carbonitrides, increasing tempering softening resistance and high-temperature strength, and increasing the transformation point. However, if it is less than 0.10%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.60%, coarse carbides are formed and the toughness is reduced, so the range is 0.10 to 0.60%. N: N is added to improve the high-temperature strength and prevent the formation of δ-ferrite. However, if it is less than 0.0300%, its effect is small, and if it exceeds 0.1000%, the toughness is remarkably deteriorated. The range was 1000%.

REM: A rare earth element (REM) containing La and Ce as main components has the effect of fixing S and preventing sulfide from precipitating at crystal grain boundaries. Although it has the effect of improving thermal shock resistance, it does not require a large amount of inclusion, and if it exceeds 0.0700%, inclusions increase. Therefore, the upper limit is 0.0700%, and the lower limit is a parameter indicating a fixed amount of S. 0.0005% from the viewpoint of controlling [S].

Nb, Ti: Nb and Ti both have an effect of increasing tempering softening resistance and high-temperature strength, and have an effect of suppressing crystal grain coarsening during quenching at a higher temperature.
It is an important component for obtaining excellent high-temperature strength and toughness. N
When the content of Ti or Ti alone or in combination is more than 0.100%, carbides that hardly form a solid solution are formed and the toughness is reduced. On the other hand, if the content is less than 0.010%, the effect is hardly obtained. The range was 0.010 to 0.100%.
Note that P and S may contain 0.020% or less and 0.015% or less, respectively, as inevitable impurity components. The steel for a hot press tool of the present invention is manufactured by the following manufacturing process. Steelmaking → Forging → Heat treatment → Machining

[0016]

EXAMPLES Steels having the respective component compositions shown in Tables 1 to 5 were melted in a converter, ingoted, forged into a shape of 410 mm × 440 mm square, kept at 1040 to 1050 ° C. for 10 hours, and quenched by rapid cooling. After heat treatment of air-cooled tempering after holding, and holding at 670 to 700 ° C. for 10 hours, machined to a predetermined anvil,
It was subjected to an actual machine test. In addition, Cr equivalent shown in Tables 1-5,
The Mo equivalent and the parameter [S] were determined by the following equations. All are weight ratios. Cr equivalent = Cr + 4Mo + 1.5W + 5Nb + 11V +
6Ti + 6Si-40C-2Mn-30N (%) Mo equivalent = Mo + (1/2) W (%) Parameter [S] = S- (32/140) REM (× 1 )
0 ⁴ %)

[0017]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

The results obtained by examining the results of using anvils for each of the test steels thus obtained were selected and are shown in Tables 6 to 12 and FIG. 1, and the relationship between the C content and the transformation points (A _C1 and A _C3 ) is shown in FIG. FIG. 3 shows the strength and fracture toughness at each temperature.

[0019]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

In Comparative Examples 1 to 4, since the A _C1 transformation point is lower than the maximum temperature of the anvil surface of 850 ° C., the structure change and material change during use are liable to occur, and the fire cracking resistance and thermal shock resistance are insufficient. Therefore, in the forging of 1500 hot slabs, crack-like cracks with a crack depth of 30 to 50 mm were generated, and the chipping rate was 1
The figure was as high as 8 to 36%. On the other hand, in the steels Nos. 5 to 26 of the present invention, the A _C1 transformation point has an anvil surface temperature of 850.
C. and higher in slab cracking resistance, thermal shock resistance, high temperature strength and fracture toughness.
The condition of a crack depth of 10 mm or less is satisfied by zero forging, and the occurrence rate of cracks is also improved without any improvement.

[0021]

As is clear from the above-mentioned embodiments, the present invention limits the components of steel for hot press tools,
Increased transformation points (A _C1 , A _C3 ), which were previously inadequate, and improved quenching crack resistance, thermal shock resistance, high-temperature strength, and fracture toughness, making it suitable for hot slab continuous width pressing, etc. It has become possible to provide tools that have been used.

[Brief description of the drawings]

FIG. 1 is a diagram showing the crack depth and the occurrence rate of chipping flaws in the results of using anvils of test steel.

FIG. 2 is a diagram showing the relationship between the C content of a test steel and the A _C1 transformation point and the A _C3 transformation point.

FIG. 3 is a diagram showing strength and fracture toughness of a test steel at various temperatures from room temperature (20 ° C.) to 800 ° C.

Claims (1)

(57) [Claims] 1. C: 0.08 to 0.16 by weight ratio
%, Si: 0.80 to 1.20%, Mn: 0.10 to 0.10%
0.60%, Cr: 7.00 to 9.00%, Mo: 0.
50-1.50%, W: 0.50-1.50%, V:
0.10 to 0.60%, N: 0.0300 to 0.1000
%, REM: 0.0005 to 0.0700%, and one or two selected from Nb and Ti are 0.0%
Cr containing 10 to 0.100% and having the following composition:
A steel for a hot press tool, wherein an equivalent is less than 15% and the balance is Fe and inevitable impurities. Serial Cr + 4Mo + 1.5W + 5Nb + 11V + 6Ti + 6
Si-40C-2Mn-30N (% by weight)