JPH07243003A - Maraging steel excellent in heat check resistance - Google Patents

Abstract

PURPOSE:To obtain a maraging steel excellent in heat check resistance by specifying a composition consisting of C, Si, Mn, P, S, Ni, Cr, Mo, Co, Ti, Al, B, Zr, Ca, and Fe. CONSTITUTION:This steel is a maraging steel excellent in heat check resistance, having a composition consisting of, by weight, <=0.03% C, <=0.10% Si, <=0.10% Mn, <=0.010% P, <=0.010% S, 6.0-11.0% Ni, <=0.30% or 8.1-9.0% Cr, 4.0-9.0% Mo, 7.0-11.0% Co, 0.10-1.0% Ti, 0.05-0.15% Al, <=0.010% B, <=0.10% Zr, <=0.10% Ca, and the balance essentially Fe. This steel can, be hardened with reduced strain by performing aging treatment at a relatively low temp. of about 500 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maraging steel which has excellent heat check resistance and is suitable for use in die casting dies.

[0002]

2. Description of the Related Art Conventionally, hot work tool steel mainly containing 5% Cr and 1 to 1.5% Mo has been used as a steel material for die casting dies. When a die casting die is manufactured with this hot work tool steel, quenching and tempering are performed in the process to develop the required hardness and strength.

However, the quenching treatment is 1000 ° C.
Since it is a high-temperature treatment that exceeds, and since it involves martensitic transformation during quenching, large heat treatment distortion and deformation occur due to quenching and tempering.

For this reason, when a die casting die is manufactured from such hot work tool steel, it is necessary to perform roughing once before quenching and tempering and then finish it again after quenching and tempering. Needs to be processed twice,
Therefore, the number of processing steps is increased and the time required for manufacturing the mold is long, which is a serious problem.

On the other hand, application of maraging steel, which has high strength and is excellent in workability, which is mainly used as an aircraft material as a die material, has also been studied.

The maraging steel is a steel in which very low C, high Ni and various elements such as Co and Mo are added, has a martensite structure, is subjected to an aging treatment, and is hardened by precipitating an intermetallic compound. The aging temperature at that time is as low as around 500 ° C, and since there is no transformation during the aging treatment, distortion due to heat treatment is small, and therefore it is possible to manufacture the mold with one-time processing, and the processing time can be reduced. Have advantages.

[0007]

Conventionally, the maraging steel used for such a die contains at least 12% of Ni, which has heat check resistance, that is, rapid heating of the die surface. The resistance to cracks generated on the surface due to repeated thermal stress due to cooling is not sufficient.Therefore, when used as a mold, its life is significantly shorter than that of a mold made of conventional hot work steel. It was

[0008]

The invention of the present application has been made for the purpose of solving such a problem.
Thus, the invention of claim 1 uses maraging steel on a weight basis as C: ≤ 0.03% Si: ≤ 0.10% Mn: ≤ 0.10% P: ≤ 0.010% S: ≤ 0. 010% Ni: 6.0-11.0
% Cr: ≤ 0.30% Mo: 4.0-9.0
% Co: 7.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% The balance is characterized by having a structure consisting essentially of Fe.

According to the present invention, the Ni content is reduced to 6.0 to 11.0% as compared with the conventional maraging steel, and the amount of Mo and the balance of amounts of Ni, Co and Mo are optimized. That is the main point.

The present inventors have been pursuing the reason why the heat check resistance of maraging steel is low,
It was concluded that the main cause is the As point due to the high addition of Ni, that is, the low transformation start temperature for transforming martensite to austenite.

For example, in the case of a die casting mold, the mold surface temperature rises to a high temperature of about 650 ° C. However, N
In the case of maraging steel with i content of 12% or more, the As point is lower than the reached temperature of this mold surface, and therefore, the surface part of the mold is partially austenized and there are martensite phase and austenite phase. A state in which both phases are mixed appears.

Therefore, there is a difference in the coefficient of thermal expansion between austenite and martensite (austenite has a larger coefficient of thermal expansion than martensite). It was concluded that cracks are generated and grow at the interface between both phases by repetition, which is the main cause of lowering the heat check resistance.

Therefore, in the present invention, the Ni content is set as low as 6.0 to 11.0% with respect to the conventional maraging steel,
In response to this, the aging hardness was improved by optimizing the amount of Mo and the balance of the amounts of Ni, Co and Mo.
It was confirmed that a maraging steel having good heat check resistance when used as a die-casting die, and thus having a sufficient die life, was obtained.

Next, the reasons for limiting each component in the present invention will be described in detail. C: ≤0.03% When C exceeds 0.03%, the toughness of the steel deteriorates, and the age hardenability during aging treatment is impaired, so the upper limit is 0.03.
%.

Si: ≤0.10% If Si exceeds 0.10%, the toughness of the steel deteriorates, so the upper limit was made 0.10%.

Mn: ≤0.10% If Mn exceeds 0.10%, the toughness of the steel deteriorates, so the upper limit was made 0.10%.

P: ≤0.010% P exceeds 0.010% and impact resistance decreases, so the upper limit was made 0.010%.

S: ≤0.010% If S exceeds 0.010%, the hot workability deteriorates, so the upper limit was made 0.010%.

Ni: 6.0 to 11.0% When the Ni content is less than 6.0%, the age hardenability is insufficient. On the other hand, if it exceeds 11.0%, the As point decreases, and as a result, the heat check resistance decreases. In addition, the cost becomes high. Therefore, in the present invention, the lower limit of Ni is 6.0% and the upper limit is 11.0%.

Cr: ≦ 0.30% When Cr exceeds 0.30%, it deteriorates toughness as an impurity. Therefore, the upper limit is set to 0.30%.

Mo: 4.0-9.0% When Mo is less than 4.0%, the age hardenability is insufficient, while
If it exceeds 9.0%, the Ms point decreases and the cost also increases. Therefore, in the present invention, the lower limit and the upper limit are 4.0, respectively.
% And 9.0%.

Co: 7.0-11.0% When Co is less than 7.0%, the age hardening property due to the combined effect with Mo is insufficient. Moreover, the As point is also lowered. On the other hand, 11.
If it exceeds 0%, the toughness deteriorates and the cost also increases.
Therefore, in the present invention, it is set to 7.0 to 11.0%.

Ti: 0.10 to 1.0% When Ti is less than 0.10%, the age hardenability is insufficient,
Also, the crystal grains become coarse. On the other hand, if it exceeds 1.0%, the amount of inclusions increases and the toughness deteriorates. Therefore, in the present invention, 0.1
It was set to 0 to 1.0%.

Al: 0.05 to 0.15% When Al is less than 0.05%, the age-hardenability is insufficient. On the other hand, if it exceeds 0.15%, the toughness deteriorates and ferrite is generated. Therefore, here, it is set to 0.05 to 0.15%.

B: ≤0.010% B has the function of preventing segregation at the crystal grain boundaries, which causes a decrease in strength. However, the effect is saturated at 0.010%, so the upper limit was made 0.010%.

Zr: ≦ 0.10% Zr fixes C and N, improves the toughness of the material, and prevents coarsening of crystal grains. However, the effect is saturated at 0.10%, so the upper limit was made 0.10%.

Ca: ≦ 0.10% Ca improves machinability, but if it exceeds 0.10%, the amount of non-metallic inclusions increases. Therefore, the upper limit was made 0.10%.

Next, the invention of claim 2 is based on the weight of maraging steel C: ≤ 0.03% Si: ≤ 0.10% Mn: ≤ 0.10% P: ≤ 0.010% S: ≤ 0.010% Ni: 6.0-11.0
% Cr: 8.1-9.0% Mo: 4.0-9.0
% Co: 7.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% The composition is characterized in that the balance consists essentially of Fe.

According to the present invention, in the maraging steel according to the first aspect of the present invention, Cr is contained in the range of 8.1 to 9.0%. In this way, Cr
When it is contained in the range of 9.0%, the oxidation resistance of the maraging steel is effectively improved, and as a result, the heat check resistance is improved. Therefore, when a die casting mold is made of this maraging steel, the mold life is improved.

In the present invention, the Cr content is 8.1.
If the content is less than 8.1%, the oxidation resistance cannot be sufficiently improved, and if it is more than 9.0%, a ferrite phase is generated and the heat check resistance is to degrade. Therefore, the content is regulated to 8.1 to 9.0%.

Next, the invention of claim 3 is based on the weight of maraging steel C: ≤ 0.03% Si: ≤ 0.10% Mn: ≤ 0.10% P: ≤ 0.010% S: ≤ 0.010% Ni: 9.0-11.0
% Cr: ≤ 0.30% Mo: 4.0-9.0
% Co: 9.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% The composition is characterized in that the balance consists essentially of Fe.

According to the present invention, the Ni content and the Co content in the maraging steel of the invention of claim 1 are 9.0 respectively.
-11.0% and 9.0-11.0% are specified as high, and by doing so, the characteristics of the maraging steel can be further improved.

In the present invention, Ni is 9.0 to 11.0.
% And Co are specified in the range of 9.0 to 11.0%, respectively, when Ni is less than 9.0%, it is difficult to obtain a sufficiently desirable age hardening property, and when Co is less than 9.0%. This is because it is difficult to obtain a sufficiently desirable age hardening property under the combined action with Mo. The reason for limiting the upper limit value is the same as in claim 1.

Next, the invention of claim 4 is based on the weight of maraging steel C: ≤ 0.03% Si: ≤ 0.10% Mn: ≤ 0.10% P: ≤ 0.010% S: ≤ 0.010% Ni: 6.0-8.0% Cr: 8.1-9.0% Mo: 7.0-9.0
% Co: 7.0 to 9.0% Ti: 0.10 to 1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% The composition is characterized in that the balance consists essentially of Fe.

According to the present invention, in the maraging steel according to the invention of claim 2, Ni: 6.0 to 8.0%, Cr: 8.1.
~ 9.0%, Mo: 7.0 to 9.0%, Co: 7.0
It is defined as 9.0%. That is, Ni, Cr, M
It is desirable that the contents of o and Co be the contents specified here, and the properties of the maraging steel can be further improved by containing Ni, Cr, Mo, and Co within this range.

Specifically, in the invention of claim 2, Cr
Although the oxidation resistance is improved when the content of Cr is 8.1 to 9.0%, the high addition of Cr causes A of maraging steel to be increased.
The s point tends to decrease. Therefore, in the present invention, a high content of Cr and a low content of Ni are specified at the same time to prevent the As point from decreasing due to the addition of Cr. In addition, the contents of Mo and Co are appropriately set to achieve a good age hardening. I try to get sex.

Therefore, N in the invention of claim 4
The reasons for limiting the amounts of i, Cr, Mo, and Co added are as follows. Ni: 6.0 to 8.0% The lower limit is set to 6.0% for the same reason as described above, and the upper limit is set to 8.0% to lower the As point by adding Cr. The purpose is to prevent this by setting a lower Ni content.

Cr: 8.1 to 9.0% Cr is set to 8.1 to 9.0% for the same reason as described in claim 2.

Mo: 7.0-9.0% Co: 7.0-9.0% The main idea is to balance the amounts of Mo and Co depending on the addition of Ni and Cr, thereby improving the aging hardness. Is.

[0040]

EXAMPLES Examples of the present invention will be described in detail below. Table 1
A die-casting die was manufactured from the maraging steel having the chemical composition shown in Fig. 3 and a casting experiment was repeated using this die-casting die to examine the oxidation resistance, heat check resistance and die life. In addition, the As and Ms points were also obtained. The results are also shown in Table 2. Here, the heat check resistance is evaluated by a high-frequency heating heat check test, in which case a test piece of 15 mmφ and a wall thickness of 5 mm is 650 ° C.
X 4 seconds heating and water cooling 3 seconds cooling as 1 cycle, this is repeated 1000 times, the number of cracks generated,
I asked for the size.

The solution heat treatment (ST) and the aging treatment were carried out under the temperature conditions shown in Table 2. The hardness at that time is also shown in the table. Further, for the steel for hot tools of Comparative Steel 14 (SKD61), the values are shown when the quenching treatment and the tempering treatment are performed at the temperatures shown in the table (H: quenching,
T: tempered).

[0042]

[Table 1]

[0043]

[Table 2]

As can be seen from the results, in the case of the maraging steel of the present invention in which the Ni content is reduced and the balance of the Mo content and the Ni, Co, Mo content is optimized, or a predetermined amount of Cr is contained. It can be seen that in the case of the maraging steel of the present invention example, the heat check resistance and die life are improved as compared with the comparative example. Comparative Example 14 is SKD61, which is a quenched and tempered steel, and has good characteristics, but has a large quenching strain and has a problem in the working process.

[0045]

As described in detail above, according to the invention of claim 1, maraging steel having excellent heat check resistance can be obtained. This maraging steel is fully applicable to die casting dies. When a die-casting die is formed by using the maraging steel, the steps, time and cost required for producing the die can be reduced.

Further, according to the invention of claim 2, the oxidation resistance of the maraging steel is improved, and as a result, the heat check resistance is improved. Therefore, when a die casting mold is formed by using the maraging steel of the present invention, the effect of improving the life of the mold can be obtained.

According to the invention of claim 3, a maraging steel having more desirable characteristics can be obtained. Further, according to the invention of claim 4, the heat check resistance of the maraging steel is further improved based on the improvement of the oxidation resistance by the high addition of Cr, the setting of the low Ni content, and the optimization of the Mo and Co contents. The mold life can be extended.

Claims (4)

[Claims] 1. C: ≦ 0.03% Si: ≦ 0.10% Mn: ≦ 0.10% P: ≦ 0.010% S: ≦ 0.010% Ni: 6.0-11 by weight .0
% Cr: ≤ 0.30% Mo: 4.0-9.0
% Co: 7.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% Maraging steel excellent in heat check resistance consisting essentially of balance Fe . 2. C: ≦ 0.03% Si: ≦ 0.10% Mn: ≦ 0.10% P: ≦ 0.010% S: ≦ 0.010% Ni: 6.0-11 by weight .0
% Cr: 8.1-9.0% Mo: 4.0-9.0
% Co: 7.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% Maraging steel excellent in heat check resistance consisting essentially of balance Fe . 3. C: ≦ 0.03% Si: ≦ 0.10% Mn: ≦ 0.10% P: ≦ 0.010% S: ≦ 0.010% Ni: 9.0-11 by weight. .0
% Cr: ≤ 0.30% Mo: 4.0-9.0
% Co: 9.0-11.0% Ti: 0.10-1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% Maraging steel excellent in heat check resistance consisting essentially of balance Fe . 4. C: ≤0.03% Si: ≤0.10% Mn: ≤0.10% P: ≤0.010% S: ≤0.010% Ni: 6.0-8 by weight 0.0% Cr: 8.1 to 9.0% Mo: 7.0 to 9.0
% Co: 7.0 to 9.0% Ti: 0.10 to 1.
0% Al: 0.05 to 0.15% B: ≤ 0.010% Zr: ≤ 0.10% Ca: ≤ 0.10% Maraging steel excellent in heat check resistance consisting essentially of balance Fe .