JPH06336658A - High strength and high toughness ni-co steel - Google Patents

Abstract

PURPOSE:To produce a high strength material excellent in toughness. CONSTITUTION:This Ni-Co steel consists of 0.15-0.25% C, 9-11% Ni, 1.5-3% Cr, 0.7-1.7% Mo, 9-11% Co, 0.05-0.1% V and the balance Fe with inevitable impurities and has such characteristics as excellent tensile strength, yield strength and toughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to 150 kg / mm ²
The present invention relates to a high-strength and high-toughness Ni-Co steel having super-grade high strength and excellent toughness.

[0002]

2. Description of the Related Art In recent years,
The properties required for materials are becoming more and more severe, and high toughness may be required even for high strength materials. Conventionally, various materials have been developed as high-strength materials, for example, Ni-Cr having a tensile strength of 150 kg / mm ^{2 or} more.
-Mo-V steel, 10Ni-14Co steel, etc. are known. However, although these materials have high strength, they do not have good toughness, and depending on the application, they have a drawback that they lack practicality due to their low toughness.

As a material of the same system, 9Ni-4
Co steel and 10Ni-8Co steel are known. The former of these materials has good toughness, but has low strength (particularly 0.2% proof stress), and is not suitable for applications requiring a strength of 150 kg / mm ^{2 or} more. Although the latter material is inferior in strength to 10Ni-14Co steel,
It has a strength of more than 50 kg / mm ² and has good toughness. However, it has a drawback of low yield strength, and in applications requiring high strength properties, it has a problem of lack of practicality due to poor balance of tensile strength and yield strength.

As described above, conventionally, a material having both high tensile strength and proof stress and excellent toughness has not been developed, and the appearance of a high strength and high toughness material excellent in all of these characteristics is desired. ing. The present invention has a basic object to solve the above problems, and an object thereof is to provide a Ni—Co steel having high strength and high toughness.

[0005]

That is, the high-strength and high-toughness Ni—Co steel of the present invention is C: 0.15 by weight%.
0.25%, Ni: 9-11%, Cr: 1.5-3%,
Mo: 0.7-1.7%, Co: 9-11%, V: 0.
It is characterized by containing 05 to 0.1% and the balance being Fe and inevitable impurities. A second aspect of the present invention is the inclusion of S in the unavoidable impurities of the high-strength and high-toughness Ni-Co steel.
i: 0.15% or less, Mn: 0.2% or less, P: 0.0
05% or less, S: 0.003% or less, O: 0.002%
It is characterized by the following restrictions.

[0006]

In other words, according to the invention of the present application, high values of both tensile strength and yield strength are obtained, and excellent toughness is obtained, and these characteristics are balanced. Next, the reason for limiting the chemical composition in the present invention will be described below. C: 0.15-0.25% C is added to improve the tensile strength. However, 0.
If it is less than 15%, the improvement in strength is insufficient and 0.2
If it exceeds 5%, the toughness decreases, so the above range is set.

Ni: 9-11% Ni increases the quenching strength of steel. Further, it has a role of assisting solid solution strengthening of Co. However, if the amount is increased too much, there is also an adverse effect that the yield strength decreases due to the influence of auslanite. Therefore, it is considered that the above range is appropriate to effectively maintain the strength. Cr: 1.5 to 3% This is an element that precipitates carbide along with Mo by aging treatment and causes secondary hardening. However, since the upper limit of the amount of C is fixed, the strength cannot be expected to increase even if added more than necessary. Therefore, in this case, the above range is considered appropriate.

Mo: 0.7 to 1.7% By aging treatment, carbide is precipitated together with Cr to cause secondary hardening. Similar to Cr, the upper limit of the amount of C is fixed, so addition of more than necessary promotes embrittlement. Therefore, in this case, the above range is considered appropriate. Co: 9 to 11% Co is added to improve the strength. However, if it is less than 9%, the strength is insufficient, and if it exceeds 11%, the toughness decreases, so the above range is set. V: 0.05 to 0.1% Effective for refining crystal grains. However, excessive addition adversely affects the hot forgeability and the like. Therefore, the above range is considered appropriate.

(Inevitable impurities) Si: 0.15% or less, Mn: 0.2% or less, P: 0.
005% or less S: 0.003% or less, O: 0.002% or less Since these impurities embrittle the material and lower the toughness, it is preferable that the content is as small as possible. However, due to manufacturing restrictions, the upper limit was set.

[0010]

Example A Ni-Co type 50 kg steel ingot having the composition shown in Table 1 was melted in a vacuum melting furnace (VIM). After subjecting the steel ingot to diffusion treatment (1200 ° C. × 20 hr), a forged (t30 mm × w130 mm × l−) test material was produced and heat treated. The heat treatment condition is 2 times quenching (925
C. × 2 hr water cooling + 830 ° C. × 2 hr water cooling) + aging treatment (510 ° C. to 550 ° C. water cooling).

The tensile strength, proof stress, elongation and Charpy impact energy at -40 ° C. of these test materials were measured, and the results are shown in Table 2. As you can see from the table,
The test materials of the examples have excellent properties in tensile strength, proof stress, and toughness, and satisfactory properties as high strength and high toughness materials are obtained. On the other hand, the test materials of Comparative Examples had a poor balance of tensile strength, proof stress, and toughness, and thus were inferior in any of the properties, and none of them had excellent properties. The test material 4 in the comparative example has a low Co content and low yield strength, the test material 5 has an excessive Co content and low Charpy impact energy, and the test material 6 has low yield strength and Charpy impact energy. Has been obtained.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

As described above, according to the high-strength and high-toughness Ni-Co steel of the present invention, C: 0.15 to 0.15% by weight.
0.25%, Ni: 9-11%, Cr: 1.5-3%,
Mo: 0.7-1.7%, Co: 9-11%, V: 0.
Since it contains 0.05 to 0.1% and the balance is Fe and unavoidable impurities, it has high tensile strength and proof stress, has excellent strength, and further has excellent toughness. A well-balanced high strength and high toughness material can be obtained.
Further, by controlling the contents of Si, Mn, P, S, and O in the unavoidable impurities, it becomes possible to further improve the toughness.

Claims (2)

[Claims] 1. C: 0.15 to 0.25% by weight,
Ni: 9-11%, Cr: 1.5-3%, Mo: 0.7
-1.7%, Co: 9-11%, V: 0.05-0.1
%, The balance being Fe and unavoidable impurities, the high strength and high toughness Ni-Co steel characterized by the above 2. Inevitable impurities: Si: 0.15% or less, Mn: 0.2% or less, P: 0.005% or less, S:
The high-strength and high-toughness Ni-Co according to claim 1, wherein the content is regulated to 0.003% or less and O: 0.002% or less.
steel