JP2525786B2 - Method for producing steel with ultrafine grain structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention refines crystal grains by precipitating carbides, nitrides or carbonitrides in steel to obtain an ultrafine grain structure. The present invention relates to a method for manufacturing steel having high hardness and toughness.

(Prior Art) Refining the crystal grains of an alloy improves not only the strength but also the toughness, and is therefore an extremely important method for improving the mechanical properties.

Conventionally, about this crystal grain refining method (1); a method of straining an alloy by cold or warm working and further heating at a recrystallization temperature to refine the alloy, (2); movement of crystal grain boundaries In order to make it harder to do so, a method of precipitating the second phase in the alloy matrix and combining it with the recrystallization method (1) to refine the alloy is often used.

(Problems to be Solved by the Invention) In the method (1), since the crystal grain size depends on the strain amount and the recrystallization temperature, it is necessary to control the conditions, and when using at high temperature, the fine grain The crystal grains also grow and become grainy.

In the above method (2), the crystal grains of the matrix are generally proportional to the size of the precipitate of the second phase and inversely proportional to the amount of the precipitate, so that the second phase must be uniformly, finely and in large quantities. In order to uniformly precipitate the second phase, it is necessary to first perform a solution treatment to dissolve the second phase in the matrix and a treatment to precipitate it thereafter. If an attempt is made to disperse a large amount of the precipitation amount, a large amount of second phase will be generated during solidification in the normal melting and casting method, and it will be difficult to dissolve this by the solution heat treatment. There is a limit to increasing the amount of precipitation.

Therefore, it was extremely difficult to uniformly refine both the matrix crystal grains and the second phase by this method.

(Means for Solving Problems) An object of the present invention is to provide a steel and a manufacturing method thereof capable of eliminating and improving the above-mentioned various problems of the prior art. The above object can be achieved by providing a steel having an ultrafine grain structure described in the range and a method for producing the steel. That is, the present invention, 1.Al 0.01 ~ 30.0%, Ti 0.01 ~ 30.0%, V 0.01 ~ 30.0%, C
r 0.01 to 30.0%, Mo 0.01 to 30.0%, W 0.01 to 30.0%, Nb
0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.0%, Hf 0.
Steel containing 1 or 2 or more selected from 01 to 10.0%, the balance being Fe and unavoidable impurities, is strained by warm or cold working, and then carburized,
A method for producing a steel having an ultrafine grain structure, characterized by uniformly and finely precipitating carbides, nitrides or carbonitrides by nitriding or carbonitriding, and at the same time, 2.Al 0.01- 30.0%, Ti 0.01 to 30.0%, V 0.01 to 30.0%, C
r 0.01 to less than 11.0%, Mo 0.01 to 30.0%, W 0.01 to 30.0%,
Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.0%, Hf
A steel containing at least one of 0.01 to 10.0% and a balance of Fe and unavoidable impurities with the balance being carburized, nitrided or carbonitrided to uniformly and finely carburize, nitride or carbonitride. After depositing on
A method for producing a steel having an ultrafine grain structure, characterized by annealing and recrystallizing after applying strain by warm or cold working, 3.Al 0.01-30.0%, Ti 0.01-30.0% , V 0.01 to 30.0%, C
r 0.01 to 30.0%, Mo 0.01 to 30.0%, W 0.01 to 30.0%, Nb
0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.0%, Hf 0.
One or more selected from 01 to 10.0%, with the balance being Fe and inevitable impurities 0.5
Carbide, nitriding or carbonitriding method is used to uniformly and finely deposit carbides, nitrides or carbonitrides on ~ 2.0mm thick plate steel, and then hot work is performed by stacking multiple plate steels. After performing joining, further applying strain by warm or cold working, annealing and recrystallization,
A method for producing a steel having an ultrafine grain structure characterized by having a thickness of 5 mm or more, 4.Al 0.01 to less than 11.0%, Ti 0.01 to 30.0%, V 0.01 to 30.0
%, Cr 0.01 to 30.0%, Mo 0.01 to 30.0%, W 0.01 to 30.0%,
Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.0%, Hf
A steel containing at least one of 0.01 to 10.0% and two or more of which are balance Fe and unavoidable impurities, and uniformly and finely carburize, nitride or carbonitride by carburizing, nitriding or carbonitriding methods. After depositing on
Furthermore, after applying strain by warm or cold working, a material of high hardness having an ultrafine grain structure, obtained by annealing and recrystallizing, is superposed on a metal / alloy plate of another material. The present invention relates to a method for producing a steel having an ultrafine grain structure, which is a composite material by performing hot working and joining.

 Next, the present invention will be described in detail.

The present invention is intended to solve the above-mentioned problems. Carbide, nitriding or carbonitriding is performed on the steel containing the required amount of C and N in the end without carburizing, nitriding or carbonitriding to obtain carbides and nitrides. It is intended to provide a method for producing a steel having an ultrafine grain structure obtained by controlling the type, size, and precipitation amount of carbonitrides.

Concrete content: In order to refine the crystal grains of the matrix, it is necessary to disperse a large amount of a precipitation phase having a small grain size and difficult to grow. As a result of numerous experiments, the inventors of the present invention have found that the following types of carbides, nitrides, and carbonitrides are effective as precipitation phases that satisfy the above conditions. The present invention has been completed by newly discovering that a steel having a structure can be obtained.

MC type (M: Ti, Nb, V, Ta, Zr, Hf, W) MN type (M: Ti, Nb, V, Ta, Zr, Hf, Al) M (C, N) type … (M: Ti, Nb, V, Ta, Zr, Hf) M ₂ C type …… (M: Mo, W) M ₂ N type …… (M: Cr, Mo, W) M ₂₃ C ₆ type… … (M: Cr, Mo, W) M ₇ C ₃ type …… (M: Cr) M ₆ C type …… (M: Mo) On the other hand, these compounds have intrinsic solubility in matrix, When a solution having a concentration exceeding the solid solution limit is produced by the melting method, it precipitates as a huge precipitate during solidification, and the effect of refining the crystal grains of the steel is lost.

On the other hand, the method of the present invention is a method in which a steel whose C or N content in the matrix is less than the solid solubility limit is melted, and then carburized, nitrided or carbonitrided. Therefore, a large amount of precipitates that do not become huge precipitates can be dispersedly present.

As the above-mentioned carburizing, nitriding or carbonitriding method, any conventional method such as gas, solid, liquid or ion implantation method can be applied.

The present invention further provides, as a method for refining the crystal grains, by cold or warm working before carburizing, nitriding or carbonitriding processing, adding 5 to 95% of working strain to give a strain. Precipitate is finely and uniformly dispersed by carburizing, nitriding or carbonitriding, and at the same time, it is recrystallized to make it fine, or carburizing, nitriding or carbonitriding is performed to make the precipitate uniform and fine. After precipitating into the steel, cold or warm working adds 5 to 95% of work to give strain, and 500 to 1000
A method of refining by annealing and recrystallizing at ℃, when carrying out these methods, by changing the conditions of carburizing, nitriding or carbonitriding, such as temperature, time, atmosphere, etc. Since the content, and thus the amount of precipitates, can be varied, steels of various properties can be obtained, and the method of the present invention is applied to a wide range of applications.

The method described above is a method applied to relatively small shapes with a thickness of 5 mm or less, but in order to manufacture large shapes, carburizing, nitriding or carburizing into a thickness of 0.5 to 2 mm. By nitriding, stacking several or dozens of them, joining them by hot working, then applying strain by cold or warm working of 5 to 95%, then annealing and recrystallizing It can be manufactured by a method.

In addition, the steel having the ultrafine grain structure produced by the method of the present invention and other alloys are superposed, press-bonded by hot working, and then strained by cold or warm working of 5 to 95%. By annealing and recrystallizing at 500 to 1000 ° C, a composite material of high hardness material and soft material can be prepared.

Conventionally, there is a carburizing or nitriding method as a means for imparting hardness to the steel surface layer, but in the former case, C is infiltrated into the surface layer to increase the C content of that portion, and the surface layer is generally hardened by a general quenching method. It is a method of generating a hardened layer such as martensite, and in the latter case, by depositing a nitride on the surface layer,
This is a method of forming a precipitation hardened layer.

On the other hand, the steel having an ultrafine grain structure according to the present invention is different from the case where only a hard surface layer is formed, and various carbides are formed inside the steel structure by carburizing and nitriding the inside of the low C alloy steel. It is manufactured by a method of finely and uniformly forming nitrides and the like, which is fundamentally different from the existing carburized steel or nitrided steel.

In addition, recently, for the purpose of refining the crystal grain size of high-speed steel, powdered high-speed steel has been developed by powderizing the molten steel in the atomized state and further sintering it under high temperature and high pressure. Compared with the product of the present invention, the grain size is still coarse (10 to 40 μm), the quality is not good, and the cost is high in view of the manufacturing process.

Next, the reason for limiting the component composition will be described. Ti,
V, Nb, Ta, Zr, Hf; All of these elements are MC, MN, M (C, N)
Type compounds and carbon / nitrides of these elements are very fine and stable, so they are difficult to grow and are particularly effective for grain refinement, but at least 0.01% for forming these compounds. % Or more is required.

On the other hand, if these elements are contained in a large amount, they form an intermetallic compound such as a sigma phase or a Lavas phase and embrittle the matrix. Therefore, for Ti, V, Nb, 30.0% or less, and for other elements Was 10.0% or less.

Although it is effective for forming Al; AlN and refining the crystal grains, it is necessary to contain at least 0.01% or more for this purpose. However, if it is contained in a large amount, a stable oxide is formed on the surface and it becomes difficult to nitrify, so the upper limit was made 30.0%.

Cr, Mo, W; these elements form M ₂ N type nitrides and various carbides, all of which are effective for grain refinement, but are elements that easily form a sigma phase or a Larvus phase. The upper limit was set to 30.0%.

 Next, the present invention will be described with reference to examples.

[Example 1] Various steels shown in Table 1 were melted, hot-forged and hot-rolled to form a plate having a thickness of 2 mm, and further cold-rolled to form a thin plate having a thickness of about 1 mm, which was carburized and nitrided. Treated. Further, as a comparative material, a steel to which C was added at the time of melting was melted, processed in the same manner, and heat-treated. As is apparent from Table 1, the material of the present invention has finer crystal grains than the conventional material by about half or less.

Although Si added to No. 5 material is not an element that forms carbides or nitrides, it has an effect of suppressing excessive carburization and formation of grain boundary carbides that deteriorate mechanical properties.

Fig. 1 shows a metallographic photograph of the carburizing treatment of No. 1 material after cold working, and Fig. 2 shows a metallographic photograph of No. 5 material when subjected to the same treatment. Further, FIG. 3 is a photograph of the metallographic structure after heat treatment of the comparative material No. 8 prepared by the melting method. As can be seen from comparison with FIG. 1, the crystal grains of the material of the present invention are finer than the conventional material. It is recognized that

In addition, Fig. 4 is a photograph of the metallographic structure of high speed steel produced by the powder method.
As is clear from comparison with Fig. 2 which is a structural photograph of the material,
Both the carbide and the crystal grains are finer in the material of the present invention than in the powder HSS.

Table 2 shows the mechanical properties of each material. As is clear from Table 2, the mechanical properties of the material of the present invention are remarkably improved as compared with the conventional material.

Example 2 The carburized No. 1 and No. 2 samples shown in Table 1 were further cold rolled for about 20% working and annealed at 850 ° C. for 1 hour.
As a result of recrystallization, the crystal grain sizes were 4.3 μm and 3.7, respectively.
It was possible to obtain steel having a very fine grain structure of μm. These sample Nos. Are 11 and 12, respectively, and the mechanical properties of each are shown in Table 3. In each case, the properties are further improved.

[Example 3] No. 21 and No. 22 in Table 4 are the invention materials No. 1 and No. 2 in Table 1.
20 pieces of 1mm thick carburized sample are piled up, press-forged to about 15mm by hot forging at about 1000 ℃, cold-rolled to 12mm, heated at 850 ℃ for 1 hour and oil-cooled at 180 ℃. The material annealed for a while, and No. 23 is a comparative material prepared by a conventional melting method for the component corresponding to No. 21.
From the measured values of the respective mechanical properties, it is recognized that the grain refinement according to the present invention significantly improved both strength and toughness.

Figures 5 and 6 show the shapes of the test pieces of No. 21 and No. 23 after the impact test, respectively, but clearly No. 2
It can be seen that one material has excellent impact resistance.

(Effects of the Invention) As described above, the steel having the ultrafine grain structure according to the present invention has marked strength and toughness as compared with the conventional high-grade hard steel, and the manufacturing cost thereof is low, and the cutting tool will be used in the future. It is used for throw away chip materials, wire drawing dies materials, hard mold materials, various punch materials, liquid gas (liquefied oxygen, liquefied carbon dioxide, LPG, etc.) valve materials, and various clad materials.

Conventionally, hardened high alloy steel has been used as this kind of material, but as described above, the material of the present invention is significantly tougher and less expensive than these materials, and in the future,
It is used as a new metal material to replace high alloy steel,
The benefits to our domestic industry are enormous.

[Brief description of drawings]

FIG. 1 is a photograph of the metallographic structure of the invention No. 1 material which has been cold worked and then carburized, and FIG. 2 is the invention No. 5 material which has been cold worked and then carburized. 3 is a photograph of the metallographic structure of the comparative material No. 8 which has been heat-treated after cold working, and FIG. 4 is a metallographic photograph of the material of the comparative material No. 10 which has been heat treated. 5 is a front view showing the appearance of the test piece of the present invention No. 21 material after the impact test, and FIG. 6 is a front view showing the appearance of the test piece of the comparative material No. 23 material after the impact test. .

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location C23C 8/32 C23C 8/32 8/46 8/46 8/50 8/50 8/56 8/56 8 / 66 8/66 8/76 8/76 // C21D 8/00 8821-4K C21D 8/00 D (56) References JP-A-59-107028 (JP, A)

Claims (4)

(57) [Claims] 1. Al 0.01 to 30.0%, Ti 0.01 to 30.0%, V 0.01
~ 30.0%, Cr 0.01 ~ 30.0%, Mo 0.01 ~ 30.0%, W 0.01 ~ 3
0.0%, Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.
0%, Hf 0.01-10.0%, which contains one or more selected from the group consisting of Fe and unavoidable impurities in the balance, and after straining the steel by warm or cold working, carburizing, A method for producing a steel having an ultrafine grain structure, which comprises uniformly and finely precipitating carbides, nitrides or carbonitrides by nitriding or carbonitriding and simultaneously recrystallizing them. 2. Al 0.01 to 30.0%, Ti 0.01 to 30.0%, V 0.01
~ 30.0%, Cr 0.01 ~ 11.0%, Mo 0.01 ~ 30.0%, W 0.0
1 to 30.0%, Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01
-10.0%, Hf 0.01-10.0%, and any one or more of them selected from the group consisting of Fe and unavoidable impurities with the balance being carburized, nitrided or carbonitrided by carburizing, nitriding or carbonitriding A method for producing a steel having an ultrafine grain structure, which comprises uniformly and finely precipitating an object, applying strain by warm or cold working, and then annealing and recrystallizing. 3. Al 0.01 to 30.0%, Ti 0.01 to 30.0%, V 0.01
~ 30.0%, Cr 0.01 ~ 30.0%, Mo 0.01 ~ 30.0%, W 0.01 ~ 3
0.0%, Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01 to 10.
Carburizing, nitriding or carbonitriding method on 0.5 to 2.0 mm thick plate steel containing 1% or 2 or more selected from 0% and Hf 0.01 to 10.0% and the balance Fe and unavoidable impurities After uniformly and finely precipitating carbides, nitrides, or carbonitrides by stacking, a plurality of plate-shaped steels were superposed and hot-worked, and then strained by warm or cold working. A method for producing a steel having an ultrafine grain structure, characterized in that a steel having a thickness of 5 mm or more is obtained by subsequently annealing and recrystallizing. 4. Al 0.01 to less than 11.0%, Ti 0.01 to 30.0%, V
0.01 to 30.0%, Cr 0.01 to 30.0%, Mo 0.01 to 30.0%, W 0.0
1 to 30.0%, Nb 0.01 to 30.0%, Zr 0.01 to 10.0%, Ta 0.01
-10.0%, Hf 0.01-10.0%, and any one or more of them selected from the group consisting of Fe and unavoidable impurities with the balance being carburized, nitrided or carbonitrided by carburizing, nitriding or carbonitriding After precipitating the material uniformly and finely, further straining it by warm or cold working, and then annealing and recrystallizing it, a material of high hardness having an ultrafine grain structure, A method for producing a steel having an ultrafine grain structure, which is characterized in that a composite material is obtained by superposing it on a metal / alloy plate of the above material and performing hot working and joining.