JP2002294325A - Method for producing wear resistant and impact resistant low alloy steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the hardenability of thick low alloy steel in particular. SOLUTION: In the method for producing low alloy steel containing alloy elements such as Ni, Cr and Mo individually or in combination, in the final stage of dissolution refining, 0.01 to 0.1% Al and 0.05 to 0.20% Zr are simultaneously added, and the steel is forcedly subjected to deoxidation and denitrification to improve its hardenability. Zr is not used for directly increasing its hardness by the formation of carbide, but, the componential ranges of the additional elements are limited so as to improve its hardenability by the cleaning and refining of the structure, and great importance has been attached to the action of Zr which is allowed to enter into solid solution in ferrite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of low-alloy steels, especially low-alloy steels having improved wear resistance and impact resistance.

[0002]

2. Description of the Related Art Low-alloy steel is produced by adding a small amount of Mn, N
It is a material containing i, Cr, Mo, etc., and is widely used mainly as a main component of steel for machine structural use. Its composition is JIS or AS.
It is standardized to TM and is the most common general-purpose material.
For example, JIS G5111SCrM and G4105
The SCM material or the like is a typical Cr-Mo alloy steel. However, as standard products of steel for machine structural use, for example, SCM4
35 materials (in terms of% by weight, C: 0.33 to 0.38, Si:
0.15 to 0.35, Mn: 0.60 to 0.85, C
r: 0.90 to 1.20, Mo: 0.50 to 0.35)
Then, even if the toughness is satisfactory, the hardness is HB269-3.
31 or more, even if ordinary structural steel is sufficient, for example, crushing of debris, coal, ore, and end-of-life vehicles such as ore processing machinery, waste treatment and dredging machinery Members that face severe abrasion effects cannot withstand their services at all and must be renewed quickly.

In order to cope with such wear members, it is necessary to employ a special wear-resistant material. However, metal wear is roughly classified into sliding wear and partial wear, and the present invention is particularly concerned with sliding wear. In addition, C and carbide forming elements Cr and Mo are added, and S is added to strengthen ferrite.
It is common to increase the hardness by increasing i and Mn to increase the hardness as a whole, and the prior art discloses a proposal focusing on this aim.

The prior art according to Japanese Patent Publication No. 48-34650 discloses C: 0.30 to 0.40, Si: 1.30 to 1.
70, Mn: 0.80 to 1.20, Ni: 2.0 to 3.
0, Cr: 0.80 to 1.20, Mo: 0.40 to 0.
60 (% by weight) and a small amount of V, Zr, Ce, and La to reduce microinclusions and microshrinkage pores by refining the macro grain size, to prevent nitrogen embrittlement, and to increase toughness. It is said that the above-mentioned component range was specified. As a result, V,
Comparing the mechanical properties of the example containing Zr, Ce, and La and the comparative example having almost the same components but not containing these trace components, the tensile force is at substantially the same level, but the elongation, drawing, and Charpy It is stated that the impact value is improved by about twice, and that the toughness is clearly enhanced. The hardness H
V indicates 525 and 590, two examples, which greatly exceed the JIS SC46 of 125 and the JIS SCA3 of 215, suggesting a difference in wear resistance. However, the difference due to special rare earth elements such as La and Ce Did not touch.

[0005]

It has been a long development to balance the toughness and hardness of low alloy steels that dominate structural steel, especially Ni-Cr, Ni-Cr-Mo or Cr-Mo low alloy steels. History is a long-lived challenge, and there is no almighty material to date. However, in the above-mentioned prior art, the gist is to increase the toughness by adding a rare earth element, in particular, a misch metal of Ce or La to reduce, refine, and inactivate the impurity element. It is well known that, besides being expensive, the reaction is very violent and the effect of the addition of the molten metal is rapidly lost over time. Therefore, if the time for pouring successively into a large number of molds is prolonged, there will be a significant difference in the operation and effect between the first and last mold castings. Is likely to occur.

In the prior art, the hardness which crucially determines the wear resistance is determined by JIS SC46 or SCA-JIS.
However, as mentioned above, the demands of the current consumers are at a much higher level of competition, and as a recent trend, especially the As the size of crushing equipment increases due to the tendency to increase the size of crushing equipment, such as the increase in scrap car treatment, the tendency to increase the size of wear-resistant members, such as the hammer of car shredder mills, is unavoidable. Comes to the surface. Even if the hardness of the test piece is appropriate for use, in the case of a thick cast product in which the distribution of crystal grains, inclusions, and segregation cannot be forcibly improved by hot or cold working, proceed to the inside of the product As the hardness rapidly decreases, the demand cannot be met.
There is a problem that unless the problem of so-called hardenability is discussed, it cannot be handled as a thick cast product.

[0007] The present invention, like the prior art, is a technique that seeks a balance between wear resistance and impact resistance. In particular, the present invention fulfills its mission as a more efficient wear-resistant material with a higher hardness than the conventional technique. Focusing on the improvement of hardenability, by suppressing the rate of decrease in hardness as it enters the surface from the surface of the black scale as much as possible, a method for producing a wear-resistant and impact-resistant low-alloy steel that effectively maintains wear resistance in both name and reality The purpose is to provide.

[0008]

According to the present invention, there is provided a method for producing a wear-resistant and impact-resistant low-alloy steel, which comprises alloying elements such as Ni, Cr and Mo, alone or in combination. 0.01-0.1% of A in the final stage of dissolving and scouring
The above problem was solved by simultaneously adding 0.05 to 0.20% of Zr together with 1 and forcibly deoxidizing and denitrifying to improve the hardenability.

The low alloy steel on which the present invention is based is made of a known N alloy.
i, Cr, Mo compounding materials such as JIS SNC, S
Materials corresponding to NCM, SCr, SCM, etc., or especially, Cr, Mo of carbide formation to enhance wear resistance
In order to strengthen ferrite, Si and Mn are also increased,
The base material is an alloy designed to increase the hardness by oil quenching and tempering to resist wear. The reason for limiting Al and Zr, which is a feature of the present invention, will be described. Al: 0.01 to 0.1% There is a maximum value near 0.05% as the deoxidizing effect. 0.0
If it is less than 1%, the deoxidizing effect is insufficient, but if it exceeds 0.1%, the amount of crystallization of giant Al ₂ O ₃ , which is extremely harmful to the toughness, increases, which is not preferable. Zr: 0.05-0.2% The effect of improving hardenability is strong when added in a small amount. It is a solid solution in ferrite and is the strongest denitrifying agent in practical materials, and has a large deoxidizing and desulfurizing action. It is effective for raising the crystal coarsening temperature and making austenite fine. This provides a significant cleaning action. On the other hand, the tendency of carbide formation is also maximum, and Z
rC and ZrN hinder the movement of the particles, hinder dislocations and refine the structure. 0.05% is necessary for improving the hardenability, but when added at 0.20% or more, the crystallization of carbides and nitrides of Zr becomes excessive and the toughness is rather lowered. Rather than directly increasing the hardness by forming carbides, the Zr of the present invention
It is significant to limit the component range aimed at improving the hardenability by cleaning and refining the structure, and it is characterized by emphasizing the action of Zr which forms a solid solution with ferrite.

[0010] In the present invention, the presence of Zr is an important point, but in order to exert its effect to the maximum, the addition means largely influences. When Zr alone or Fe-Zr is added as in the case of addition to a normal alloying element, the melting point of Zr is 1852, which is much higher than that of Fe.
Since it is ℃, it is extremely doubtful whether it will sufficiently dissolve in the molten metal and exert its own action. According to the present invention, Zr is added simultaneously with the final stage of forcible deoxidation by Al after almost adjusting the components of the molten metal and the scouring treatment to thereby add the melting points (for example, Al: 20% and Zr: 80%) It is required that the alloy be rapidly and completely melted into the molten metal together with the exothermic deoxidizing action of Al.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The following test was conducted to confirm the effect of improving the hardenability by Zr. Table 1 shows the two types of alloy components used to determine the superiority of hardenability. Table 2 shows the simple Al deoxidation according to the prior art and the synergistic deoxidizing and denitrifying agent of Al and Zr. When two types of deoxidizing and denitrifying systems adjusted to know the difference in penetration are combined with the two types of alloy components, a total of four types of test pieces can be prepared as shown in Table 3.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

The test piece was a thick test piece of 80 mmT assuming a car shredder mill. After melting, the test piece was adjusted to the target components shown in Table 1, heated to 1680 ° C., and then deoxidized and denitrified. Into a ladle sprayed on the bottom,
Promotes denitrification reaction. After casting, holding at 1000 ° C. × 3 hours, furnace cooling (heating rate is 50 ° C./Hr, 650 ° C. × 1 on the way)
annealing at 950 ° C. × 1
The material is adjusted through oil quenching with holding of Hr (heating rate 80 ° C / Hr, pulling up from the oil bath is 100 ° C or less), tempering with holding at 200 ° C x 6 hours, and cooling.

An 80 mm test piece is cut vertically from the center in the horizontal direction by an electric discharge machine, and the center cross section in this direction is measured for hardness in the horizontal direction, and the relationship between the distance from the surface of the black scale to the center and the hardness is measured. FIG. 1 is a plot.

FIG. 1A shows Cr: 1.32, Mo: 0.
Although the Cr-Mo steel was No. 40, the effect of improving the hardenability of Zr of the example was clearly superior at a depth of 20 mm from the surface of the black scale, but the inner side more than that of the comparative example of Al alone was The hardness is higher.

FIG. 2B is a diagram showing Cr: 1.17, Mo: 0.
79, Ni: 1.14% by weight of an NCM low alloy steel. This material shows the effect of adding Zr much more clearly than the component A. In the example of Zr addition, the hardness was higher than that of the comparative example in all the cross sections from the surface of the black scale to the inner center, and in particular, the HRC 54 near the surface almost maintained its hardness of 52 to 53 at the center. It has a high degree of uniformity which is ideal for wear resistant materials.

[0019]

As described above, the wear-resistant and impact-resistant low-alloy steel according to the present invention is different from the deoxidation of Al alone, regardless of the type of alloy material, although there is variation depending on the base component. In addition, the absolute value of the hardness near the surface of the black scale is high, and superior in initial wear resistance, and the quenching depth to the inside is large. In some cases, there is an example in which almost the same level of high hardness is almost maintained up to the center of the wall thickness, and there is an effect that the hardenability can be easily and easily improved. In addition, the hardness improvement is not brought about by hard carbide crystallization with high brittleness, but by the outstanding deoxidation and denitrification action of Zr, it is used for cleaning of molten metal, solidification process, grain refinement during heat treatment. Based on the amount added, the brittleness does not increase proportionately with the increase in hardness, making it an ideal material that balances abrasion resistance and impact resistance moderately. Greatly contributes to

[Brief description of the drawings]

1 (A) and 1 (B) are hardness-distance relation diagrams showing a difference between an example of the present invention and a comparative example.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Haruki Sumimoto, Kamo-cho, Soraku-gun, Kyoto Prefecture 25-figure Itaya-Kakiuchi F-term (reference) 4K013 BA08 BA11 EA18 EA19

Claims (1)

[Claims] 1. A method for producing a low-alloy steel containing alloy elements such as Ni, Cr and Mo, alone or in combination,
In the final stage of melting and refining, 0.05 to 0.20% Zr is added simultaneously with 0.01 to 0.1% Al, and the hardenability is improved by forcibly deoxidizing and denitrifying. A method for producing a low-impact, high-impact, low-alloy steel.