JP2864960B2 - Wear-resistant steel with excellent workability and weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasion-resistant steel excellent in workability and weldability, and is subject to severe abrasion such as transportation of slurry-like substances such as industrial machines, mining-related equipment, ore slurry, and coal slurry. Abrasion-resistant steel suitable for use in parts.

[0002]

2. Description of the Related Art Generally, the wear resistance of steel is improved by increasing its surface hardness. For this reason, the conventional wear-resistant steel is C
And steel containing a large amount of alloying elements. Such wear-resistant steel has the drawback that workability is inferior due to its high hardness, and that weldability is inferior because the carbon equivalent is necessarily high.

In order to solve this problem, the following techniques have been disclosed for steel sheets. One of them is a method of producing wear-resistant steel by quenching after hot rolling using steel having a relatively low carbon equivalent.
4127, JP-A-57-89426, JP-A-61-76
615. However, all of them improve the wear resistance by hardening the hardness, but do not improve the wear resistance by forming a metal structure having excellent wear resistance as in the present invention. . Therefore, an unnecessarily high hardness is required as compared with the present invention, and the efficiency for obtaining abrasion resistance is low, and there still remain problems such as a fear of cracking during welding.

Further, using a composite steel sheet in which a high hardness steel sheet and a low hardness steel sheet are superposed, the wear resistance is secured by the high hardness steel sheet located on the surface, and the weldability is located inside. Japanese Unexamined Patent Publication (Kokai) No. 3-227233 discloses a composite steel plate for abrasion resistance which is imparted to a steel plate having low hardness. However, since the thickness of the hardened steel sheet as the hardened layer in the composite steel sheet is small, there is a problem that the steel sheet cannot be used for a long time in an environment where the hardened layer becomes thin due to wear.

On the other hand, a method for producing a wear-resistant steel pipe using austenitic or duplex stainless steel excellent in workability and weldability is disclosed in JP-A-51-13361.
However, these have a problem that they need to contain a large amount of expensive Ni and Cr, resulting in high cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel which is excellent in weldability and workability, is inexpensive and has excellent wear resistance.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted research on the composition of carbon steel, which is less expensive than stainless steel, based on the composition and heat treatment conditions. It has been found that steel dispersed in the ground structure has better wear resistance than expected from the relationship between hardness and wear resistance of conventional steel.

Further, it has been found that it is not necessary to contain a large amount of alloying elements as in conventional steel in order to obtain this structure. The present invention has been made based on such findings, and is as follows.

That is, in the first invention, C: 0.05% by weight.
-0.20%, Al: 0.02-2.00%, Mn:
A wear-resistant steel containing 0.50-2.50%, the balance being Fe and unavoidable impurities, containing martensite in the ground structure and having an area fraction of martensite of 5% or more and 50% or less. It is.

In the second invention, C: 0.05-0.
20%, Al: 0.02-2.00%, Mn: 0.50
-2.50%, and Si: 0.50-2.0
0%, Cu: 0.05-1.00%, Ni: 0.05-
2.00%, Cr: 0.05-2.00%, Mo: 0.
005-1.00%, Nb: 0.005-0.10%,
V: 0.005-0.10%, Ti: 0.005-0.
10%, B: Steel containing at least one of 0.0003-0.0020% and the balance being Fe and unavoidable impurities, containing martensite in the ground structure, and having a martensite area fraction of 5%. It is a wear-resistant steel that is not less than 50%.

According to a third invention, the martensite contains at least one of a martensite single phase and an island martensite, and the area fraction of the martensite is an area fraction of the martensite single phase and the island martensite. The wear-resistant steel according to any one of claims 1 to 3, which is a total.

[0012]

The reasons for limiting the present invention will be described below. (1) Martensite area fraction of 5% or more and 50% or less Martensite is a metal structure composed of Fe and C having a body-centered tetragonal structure, which is extremely effective in improving wear resistance. If the content is 5% or more in the ground structure of the invention steel, the wear resistance is remarkably improved even if the hardness is the same as that of martensite of less than 5%. However, if the area fraction is less than 5%, there is no great effect on the improvement of wear resistance. On the other hand, if the area fraction is more than 50%, inconveniences such as cracking and welding cannot be obtained at the time of processing although the wear resistance is excellent. Therefore, the area fraction of martensite is 5% or more and 50% or more.
% Or less. Here, the ground structure of the steel of the present invention generally has a ferrite-pearlite or ferrite-bainite structure, and since soft ferrite is present, workability and weldability are good.

In the process of forming martensite, the structure of steel is once austenite, and the steel is rapidly cooled to partially transform austenite into martensite. When observing the martensitic portion in detail, there are two forms. One of them is a single phase of martensite, but another is martensite and a part that cannot be converted to martensite and remains as austenite (referred to as retained austenite) to form an island-like structure. It is a form. The island-like martensite is defined as an island-like structure in which martensite and retained austenite are finely mixed as described above, and is included in the category of martensite, but is different from a martensite single phase. The martensite for improving abrasion resistance may be a martensite single phase or an island martensite.
Therefore, the martensite is at least one of the martensite single phase and the island martensite.

The area fraction of martensite is 5% or more and 50% or more.
% Is not particularly limited, but there is a method in which the hot-rolled steel is heated to a ferrite-austenite two-phase region temperature between Ac3 and Ac1 of the steel and then rapidly cooled.

The reasons for limiting the range of components for obtaining wear-resistant steel containing martensite and having excellent workability and weldability will be described below. (2) C: 0.05-0.20% Since C increases the area fraction of martensite for improving abrasion resistance, the content of C is essential. Content is 0.
If it is less than 05%, this effect is small, so the lower limit of the content is set to 0.05%. If the content exceeds 0.20%, the weldability deteriorates, so the upper limit of the content is set to 0.20%.

(3) Mn: 0.50-2.50% Since Mn is effective in increasing the amount of retained austenite and martensite, the content of Mn is essential. If the content is less than 0.50%, this effect is small, and if it exceeds 2.50%, the weldability deteriorates, so the content is 0.50-2.
50% (4) Al: 0.02-2.00% One of the features of the present invention is that the Al content is 0.02-2.00%, which is higher than the conventional wear-resistant steel. It is. In other words, the required amount of martensite, whose wear resistance is improved by increasing the Al content, is generated. As a result, although the hardness is lower than that of conventional wear-resistant steel, the same wear resistance is obtained. It has the effect of exhibiting wear properties.

When the Al content is 0.02% or more, a sufficient amount of martensite is formed to exhibit good wear resistance, but when the Al content is less than 0.02%, the wear resistance is reduced. Has no effect on Therefore, the lower limit of the Al content is 0.0
2%. On the other hand, if the content exceeds 2.00%, the hot ductility of the steel sheet and the weldability deteriorate, so the upper limit is set to 2.00%.

The above are essential components of the present invention. The reasons for limiting the content of the selected element and the range are as follows. (5) Si, Cu, Ni, Cr, Mo, Nb, V, T
i, B These are components effective for increasing the amount of martensite or improving the abrasion resistance by increasing the hardness of the ground structure. One or more of these are added within the following range. Is also good. The lower limit of the content is the minimum amount required to exhibit the above effects, and the upper limit is the upper limit at which the effect is exhibited without deteriorating the weldability. Si: 0.50 to 2.00% Cu: 0.05 to 1.00% Ni: 0.05 to 2.00% Cr: 0.05 to 2.00% Mo: 0.05 to 1.00% Nb: 0.005-0.10% V: 0.005-0.10% Ti: 0.005-0.10% B: 0.0003-0.002% P and S are inevitable impurities. In general, they are contained in the range of P: 0.03% or less and S: 0.03% or less, but these contents do not essentially affect the abrasion resistance. In the production of the steel of the present invention, the composition of the steel is adjusted to the range of the present invention, the steel sheet is formed by hot rolling, and then, for example, the heat treatment described above may be performed.

[0019]

EXAMPLES Table 1 shows the chemical components of the test materials. Both the weldability and workability of the steels in Table 1 are considered to be equivalent to those used as general structural steels, and the price is also equivalent. Steel sheets were manufactured from the steels in Table 1 by hot rolling and subjected to various heat treatments and subjected to tests.

[0020]

[Table 1]

Tables 2 and 3 show the heat treatment method, the martensite area fraction, and the results of the abrasion resistance test of each steel subjected to the test. Table 2 shows the results of the steel of the present invention, and Table 3 shows the results of the comparative steel. FIG. 1 shows the relationship between the wear resistance test results, the hardness, and the martensite area fraction. As the abrasion resistance test, a rotation test of a test piece is performed in an environment in which water and silica sand are mixed, and a value obtained by dividing a loss on wear of each wear test piece by a loss on wear according to JIS SS400 (referred to as a wear rate ratio). ).
The smaller the wear amount ratio, the better the wear resistance.
FIG. 2 schematically shows the test apparatus, and FIG. 2A is a cross-sectional view thereof. The test tank 1 is filled with a mixed solution of water and silica sand. Abrasion test piece 3 is 150 mm from rotating shaft 2
Are installed at intervals, and wear occurs when rotating in a mixture of water and silica sand. (B) shows the dimensions of the abrasion test piece 3, which is 10 mm in diameter and 60 mm in length. Abrasion test pieces were obtained by cutting out round bars from the center of the thickness of the steel sheet.

[0022]

[Table 2]

[0023]

[Table 3]

From FIG. 1, it is apparent that the wear resistance is remarkably improved by containing 5% or more of martensite. That is, in the steel having the component composition of the steel of the present invention and having a martensite area fraction of 5% or more, good wear resistance is obtained with a wear amount ratio of 0.7 or less.

On the other hand, S-1, T-1, U-1, V-1, and W-1 among the steels not having the component composition of the steel of the present invention do not produce a sufficient amount of martensite, and as a result, the amount of wear The ratio is 0.
8 or more, indicating that the abrasion resistance is insufficient. Also,
When the martensite area fraction is less than 5% (steel C-3, C-4) due to inappropriate heat treatment conditions, etc., the composition of the steel of the present invention is insufficient in abrasion resistance. It turned out to be.

[0026]

As described above, according to the present invention, good wear resistance is exhibited by controlling the structure of steel, and a steel excellent in workability and weldability is accurately produced. This is an invention which can be industrially effective.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of steel hardness and martensite area fraction on wear resistance.

FIG. 2 is a diagram showing a cross section of a wear resistance evaluation test apparatus.

[Explanation of symbols]

 1 ··· Test tank 2 ··· Rotating shaft 3 ··· Abrasion test piece

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-271985 (JP, A) JP-A-6-17188 (JP, A) JP-A-5-148579 (JP, A) JP-A-63-1988 83225 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00-38/60

Claims (3)

(57) [Claims] (1) C: 0.05 to 0.20% by weight, M
n: 0.50-2.50%, Al: 0.02-2.00
%, With the balance being Fe and unavoidable impurities, containing martensite in the ground structure and having an area fraction of martensite of 5% or more and 50% or less and having excellent workability and weldability. . 2. C: 0.05-0.20% by weight%, M
n: 0.50-2.50%, Al: 0.02-2.00
%, Si: 0.50-2.00%, C
u: 0.05-1.00%, Ni: 0.05-2.00
%, Cr: 0.05-2.00%, Mo: 0.005-
1.00%, Nb: 0.005 to 0.10%, V: 0.
005-0.10%, Ti: 0.005-0.10%,
B: Steel containing at least one of 0.0003-0.0020% with the balance being Fe and unavoidable impurities, containing martensite in the ground structure and having an area fraction of martensite of 5% or more and 50% or less. Wear-resistant steel with excellent workability and weldability. 3. The martensite comprises at least one of a martensite single phase and an island martensite, and the area fraction of martensite is the sum of the area fraction of the martensite single phase and the island martensite. Abrasion-resistant steel according to any of 1 to 3.