JP3003451B2 - 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 having excellent workability and weldability, and relates to a slurry-like material such as industrial machinery, mining-related equipment, ore slurry, coal slurry, and hard-wearing hard steel. The present invention relates to abrasion-resistant steel used for transporting materials.

[0002]

2. Description of the Related Art Generally, wear resistance is improved by increasing the surface hardness of a steel plate or the like. For this reason, a conventional wear-resistant steel plate is often manufactured by quenching a steel containing a large amount of alloying elements such as C. Such wear-resistant steel has disadvantages such as poor workability due to its high hardness, and inevitably high carbon equivalent and poor weldability.

In order to solve such a problem, a method of producing a wear-resistant steel by rolling and quenching a steel sheet having a relatively low carbon equivalent has been proposed in Japanese Patent Publication No. Sho 56-14.
No. 127, JP-A-57-89426, JP-A-61-7
No. 6615 is disclosed. Further, there has been developed a steel sheet in which only the surface hardness is increased by using a composite steel sheet so that workability and weldability of the steel are secured in a soft interior and wear resistance is secured in a hardened portion of a surface layer (Japanese Patent Application Laid-Open No. Hei 3 (1994)). -22723
No. 3).

A method for producing a wear-resistant steel pipe using austenitic or duplex stainless steel excellent in weldability and workability (Japanese Patent Laid-Open No. 51-13361) is disclosed. Manufacturing method (Japanese Unexamined Patent Publication No.
No. -290616) is also disclosed.

[0005]

However, steel manufactured by quenching is still inferior in workability, and in a composite steel sheet, the hardened layer is thin. There is a problem that it cannot be used for a long time. Further, stainless steel and clad steel pipes have problems such as being expensive. An object of the present invention is to appropriately produce a steel sheet having a relatively low carbon equivalent, that is, high workability and excellent weldability, and excellent wear resistance.

[0006]

SUMMARY OF THE INVENTION The present inventors have developed an abrasion-resistant steel plate having high workability and excellent weldability, that is, a wear-resistant steel pipe or a steel plate having relatively low hardness and low carbon equivalent. As a result of research and study on the steel composition and heat treatment conditions, as shown in Fig. 1, steel in which island martensite composed of martensite and retained austenite was dispersed in a ground structure such as ferrite and bainite was obtained. It has been found that a steel having better wear resistance than expected from the relationship between the hardness of the conventional steel and the wear resistance can be produced. It has also been found that it is not necessary to add 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 knowledge, and is as follows.

(1) In wt%, C: 0.10 to 0.20%, S
i: 0.50 to 2.00%, Mn: 0.50 to 2.50%, with the balance being Fe and unavoidable impurities, ferrite, bainite or ferrite and bainite
A wear-resistant steel excellent in workability and weldability, characterized in that the ground structure comprising a mixed structure of the above contains island-like martensite (composed of martensite and residual austenite) in an area fraction of 5% or more.

(2) In wt%, C: 0.10 to 0.20%, S
i: 0.50 to 2.00%, Mn: 0.50 to 2.50%, Cu: 0.05 to 1.00%, Ni: 0.05 to 2.00%, Cr: 0 .
0.5 to 0.5%, Mo: 0.05 to 0.5%, Nb: 0.005 to 0.10%, V: 0.5%
005 to 0.10%, Ti: 0.005 to 0.10%, B: 3 to 20 ppm, with the balance being Fe and unavoidable impurities. Ferrite, bainite or ferrite
5 by area fraction in ground structure consisting of mixed structure of
Abrasion-resistant steel excellent in workability and weldability, characterized in that it contains at least 10% of island martensite (composed of martensite and retained austenite).

[0009]

The present invention as described above will be further described. The steel according to the present invention is limited in the amount and composition of island martensite, and the reasons for the limitation are as follows.

FIG. 2 shows the relationship between the area fraction of the island martensite and the wear resistance. From FIGS. 1 and 2, when the amount of island martensite is less than 5%, there is no significant effect on the improvement of wear resistance, and
%, It can be seen that good wear resistance can be obtained. Therefore, the amount of island martensite is set to 5% or more.

[0011] manufacturing process of the steel for obtaining such tissue is not particularly limited, a hot rolled steel Ac ₁ to Ac
A method of reheating and cooling to a two-phase region of ferrite and austenite at _three temperatures, a hot rolling method and a heat treatment such that the structure of steel becomes upper bainite are preferable.

That is, when a ferrite-pearlite steel or bainite steel is heated to Ac ₁ to Ac ₃ , the structure becomes a mixed structure of ferrite (bainite) and austenite, and additional elements such as C and Mn diffuse from ferrite or bainite to austenite. Thus, the amount of added elements in austenite increases. When cooled from such a state, austenite at the time of heating remains austenite (retained austenite) even at room temperature or undergoes martensite transformation during cooling to form a mixed structure of ferrite or bainite and island-like martensite.

Further, since the additional element is concentrated in the austenite portion at the time of heating at the time of heating, a martensite or austenite structure can be sufficiently obtained at a cooling rate higher than air cooling, and the above-mentioned mixed structure can be obtained. Also, by making the structure of the steel of the present invention an upper bainite structure, the island-like martensite can be appropriately dispersed.

To explain the composition of the present invention, the steel used in the present invention is a low-carbon iron-based structural steel (for example, J
The composition is not limited as long as it is steel according to IS G 3101, 3106, 3115, etc., but it is preferable that C, Si, and Mn are contained in the range of Formula 1 as basic components.

[0015]

## EQU1 ## C: 0.10 to 0.20 wt% Si: 0.50 to 2.00 wt% Mn: 0.50 to 2.50 wt%

C: 0.10 to 0.20% C is an important element in order to secure an area fraction of the island-like martensite of 5% or more. When the amount of addition is less than 0.10% , this effect is not obtained. Since it is small, the lower limit of the addition amount is 0.10% .
If the amount exceeds 0.20%, the weldability deteriorates. Therefore, the upper limit of the amount is 0.20%.

Si: 0.50 to 2.00% When the amount of Si is reduced, a pearlite structure is easily formed, the amount of island martensite is reduced, and good wear resistance cannot be obtained. Therefore, the lower limit of the addition amount is set to 0.50%.
Further, an excessive addition causes a reduction in hot ductility of the steel sheet and a deterioration in weldability, so the upper limit is made 2.00%.

Mn: 0.50 to 2.50% Mn is particularly effective for increasing the amount of retained austenite, but if it is less than 0.50%, the effect is small.
Addition of more than 0% causes deterioration of weldability. Therefore, the lower limit of the addition amount is set to 0.50% and the upper limit is set to 2.50%.

The above are the essential components of the present invention. The addition amount of the selected element and the reason for the limitation are as follows. In other words, Cu, Ni, Cr, Mo,
Nb may be added in the following range. The lower limit of the addition amount in Equation 2 is the minimum necessary amount for exhibiting the above effect, and the upper limit thereof is the upper limit value for exhibiting the effect without deteriorating the weldability.

[0020]

## EQU2 ## Cu: 0.05 to 1.00% Ni: 0.05 to 2.00% Cr: 0.05 to 0.50% Mo: 0.05 to 0.50% Nb: 0.005 to 0.10%

V, Ti, and B may be added in the following ranges in order to increase the hardness of the ground structure portion and obtain more excellent wear resistance. The lower limit of the addition of Equation 3 is the lowest value that is effective in increasing the hardness, and the upper limit is the upper limit value that does not deteriorate the weldability and workability.

[0022]

V: 0.005 to 0.10 wt% Ti: 0.005 to 0.10 wt% B: 3 to 20 ppm

[0023]

EXAMPLES The composition of the test materials used by the present inventors is shown in Table 1 below. All the steels in Table 1 have a Ceq value of about 0.45 or less, and their weldability is generally less than 0.45. It is equivalent to that used as structural steel.

[0024]

[Table 1]

(Example 1) The manufacturing conditions and wear resistance of steel sheets for each steel in Table 1 are as shown in Table 2 below. The wear performance was evaluated in an environment in which water and silica sand were mixed. The test was performed by measuring the weight loss of a test piece in a test piece rotating type wear test in Example 1. The abrasion resistance in the table is a value obtained by dividing the abrasion loss of the test material by the abrasion loss of the SS400 test piece, and the smaller the value, the better the abrasion resistance. FIG. 3 shows an outline of the tester. The tester 1 is mounted at a distance of 150 mm from the rotating shaft 2 and rotated.

[0026]

[Table 2]

That is, the steel sheet obtained by heat-treating the invention steel under appropriate conditions has a wear resistance of not more than 0.7 at a hardness of Hv 300 or less. Further, even in the case of a steel not subjected to heat treatment, a steel in which the amount of island martensite exceeds 5% has good wear resistance. Even when the invention steel is used, the steel B-5 having a small amount of island martensite and the B- 3 and B-4 having a small amount of island martensite due to improper heat treatment conditions have an abrasion resistance of 0.7 or less. Is not obtained. In addition, steel R-1, S-1, T
If the inventive steel is not used as in the case of -1, U-1, and V-1 , even if the heat treatment of the present invention is performed, the amount of island martensite is small and good wear resistance cannot be obtained. As in U-2 , when the steel is not rolled and is not the steel of the present invention, even Hv230 shows a high value of 0.9 as the wear resistance.

[0028]

According to the present invention as described above, by controlling the composition and structure of the steel, a steel plate having good wear resistance and good workability and weldability can be obtained accurately. It is an invention which can be manufactured and has great industrial effects.

[Brief description of the drawings]

FIG. 1 is a chart showing the effects of hardness of steel and martensite islands on wear resistance.

FIG. 2 is a table showing the effect of the amount of island martensite on wear resistance.

FIG. 3 is a sectional explanatory view schematically showing a test apparatus used for evaluating wear characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test piece 2 Rotation axis 3 Disk 4 Container

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-157948 (JP, A) JP-A-60-152655 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 301 C22C 38/04

Claims (2)

(57) [Claims] (1) In wt%, C: 0.10 to 0.20%, Si: 0.2%
Steel containing 50 to 2.00%, Mn: 0.50 to 2.50%, the balance being Fe and unavoidable impurities. Ferrite, bainite or ferrite and bainite
A wear-resistant steel excellent in workability and weldability, characterized in that the ground structure comprising a mixed structure of the above contains island-like martensite (composed of martensite and residual austenite) in an area fraction of 5% or more. 2. In wt%, C: 0.10 to 0.20%, Si: 0.2%.
50 to 2.00%, Mn: 0.50 to 2.50%, Cu: 0.05 to 1.00%, Ni: 0.05 to 2.00%, Cr: 0.000%
0.5 to 0.5%, Mo: 0.05 to 0.5%, Nb: 0.005 to 0.10%, V: 0.5%
005 to 0.10%, Ti: 0.005 to 0.10%, B: 3 to 20 ppm, and the balance is Fe and unavoidable impurities. Ferrite, bainite or ferrite
5 by area fraction in ground structure consisting of mixed structure of
Abrasion-resistant steel excellent in workability and weldability, characterized in that it contains not less than 10% of island martensite (composed of martensite and retained austenite).