JP2506517B2 - Stainless steel fiber for concrete reinforcement - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength stainless steel fiber used for concrete reinforcement, and particularly at a low cost suitable for production by a melt extraction method (hereinafter referred to as ME method), which has strength, ductility and toughness. Regarding high stainless steel fiber.

[0002]

As is well known, concrete has excellent durability, compressive strength, rigidity, etc. However, on the other hand, its tensile strength and impact strength are low, and its energy absorption capacity is low, so it is physically fragile. It has a drawback. As a means for compensating for this drawback, fiber-reinforced concrete (hereinafter referred to as FRC) in which fibers are mixed and reinforced in concrete is known.

As the FRC fibers, in addition to steel fibers and glass fibers, carbon fibers and polymer fibers have recently been used. Among them, steel fiber has been used for the longest time because of its relatively low cost and excellent concrete reinforcing performance. Conventionally, thin plate shearing method, steel wire cutting method, steel material cutting method, steel material cutting method and the like have been conventionally known as methods for producing steel fibers for concrete reinforcement. Steel fibers have been manufactured. However, ordinary steel fibers are liable to rust, causing discoloration of concrete due to rusting, which impairs aesthetics, and corrosion of fibers deteriorates durability. Therefore, stainless steel fibers that do not have such difficulties have attracted attention, and examples of such steel types include AISI430, 431, and CB30.
Etc. have been used.

However, stainless steel fibers produced by cutting or cutting stainless steel plate materials and wire rods made of such steel types cannot avoid becoming expensive, and as a reinforcement for inexpensive concrete. Difficult to use. Therefore, the ME method, which is an inexpensive metal fiber manufacturing method, is adopted. While rotating a cylindrical drum with many protrusions on the outer peripheral surface, the protrusion end is brought into contact with the molten metal to scoop it, solidify it into a fiber on the edge of the protrusion, and separate it from the drum by centrifugal force. This is a method for producing metal fibers by squeezing.

[0005]

However, the conventional stainless steel fibers produced by the ME method using the above-mentioned conventional stainless steel types have the following problems, respectively, and the metal fibers for concrete reinforcement are as follows. As was not enough. That is, in the case of the stainless steel fiber made of AISI430, the tensile strength σ _B is 50 to 60 kgf / mm ²
However, the reinforcement performance is insufficient. In addition, since it is soft, it bends easily, and it is difficult to uniformly disperse it in concrete.

In the case of the stainless steel fiber made of AISI431, the tensile strength is sufficient, but the one not subjected to the heat treatment is brittle and cannot be used because it breaks when kneading with concrete. On the other hand, the heat-treated product increases the number of steps and costs more. Also, the Ni content is 1.
25-2.5 wt%, of which 1.5-2.5 wt%
However, it is difficult to manufacture them by the ME method.

In the case of stainless steel fiber made of CB30, the tensile strength σ _B is 60 to 80 kgf / mm ² , and the reinforcing performance of concrete is insufficient. Also, its carbon content is
Although it is 0.3 wt% or less, it is difficult to manufacture the high carbon product containing 0.3 wt%, which is the upper limit, by the ME method because the oxidation is severe. Therefore, the present invention has been made to solve the above-mentioned conventional problems, is a low-cost stainless fiber that can be manufactured by the ME method with a low manufacturing cost, is easily kneaded with concrete, and has a sufficient concrete reinforcing effect. It is an object of the present invention to provide a stainless steel fiber for concrete reinforcement, which is obtained.

[0008]

The present invention provides a stainless steel fiber produced by the melt extraction method, which comprises:
C is 0.03 to 0.2 wt%, Si is 1.5 wt% or less, and Mn is 1.0
wt% or less, Ni more than 2 to 5.0 wt%, Cr 17.0 to 20.0 wt
%, N is 0.01 to 0.30 wt%, other unavoidable impurities are contained, and the balance is Fe.

[0009]

The present invention uses the ME method, which has a low manufacturing cost, to inexpensively manufacture stainless steel fibers for concrete reinforcement. Further, the composition of the stainless alloy of the present invention is almost the same as the structure of the Schaeffler phase diagram, and a ferrite structure containing martensite , or martensite
It is a ferrite + austenite structure containing . As a result, M which is rapidly cooled from the molten state and cooled in the air
In addition to ensuring the oxidation resistance required for application of Method E, it can be dispersed with high strength (without bending or deformation during concrete kneading, and can give concrete a sufficient tensile strength. It is possible to obtain a stainless steel fiber having high ductility and high toughness (which does not break during concrete kneading and can sufficiently absorb even when an impact force is applied to FRC) and which is suitable for concrete reinforcement.

The stainless steel fiber according to the present invention will be described in detail below, including the critical significance of its characteristic values. In order to obtain a low-cost stainless steel fiber for concrete reinforcement that is well balanced with the price of concrete, which is a very inexpensive material, it is necessary that the material of stainless steel itself is inexpensive and the manufacturing process is simple. Therefore, the stainless steel material of the present invention is preferably chromium-based stainless steel or low nickel content stainless steel. Further, it is desirable that the ME method can be used for the production, and that other steps such as heat treatment are not required. By the way, the following conditions are required as conditions for favorably producing stainless fibers by the ME method.

No large amount of slag is generated on the surface of the molten steel. This is because the slag on the surface of the molten steel interferes with the contact between the protrusions on the surface of the rotating drum and the molten metal, and the productivity of the fiber decreases. The fluidity of the molten steel is appropriate. The protrusion of the rotating drum scoops up an appropriate amount for dimensional accuracy,
This is to form fibers having a good shape and the like.

The composition has excellent oxidation resistance and can be produced in the atmosphere. This is because the surface of the high temperature fiber is susceptible to oxidation during production. Further, in order to use the produced stainless fiber for concrete reinforcement, it is required to have high strength, high ductility and high toughness. As a result of repeated research to provide inexpensive stainless steel fibers for concrete reinforcement having excellent properties capable of satisfying all such requirements, the inventors of the present invention have found that C: 0.03 to 0.2 wt%, Si: 1.5 wt% Below, Mn; 1.0
wt% or less, Ni; over 2 to 5.0 wt%, Cr; 17.0 to 20.0 wt
%, N; 0.01 to 0.30 wt% was found to be most suitable.

The critical significance of each component is as follows. C amount: 0.03 to 0.2 wt% Carbon is an element effective for obtaining a cheap and high-strength material, and it is necessary to contain 0.03 wt% or more, but the oxidation of the fiber surface is severe as the carbon amount increases. Therefore, it was found that the production of stainless fiber becomes impossible when added in a large amount. Therefore, the upper limit of the content is set to 0.2 wt%.

Si amount: 1.5 wt% or less Silicon is a ferrite-forming element, which is necessary as an element for adjusting the fluidity of molten steel and as a deoxidizing agent.
If a large amount of this is added, Ni, C, N
Since it is necessary to increase the austenite stabilizing elements such as, the upper limit of the content is set to 1.5 wt%.

Mn amount: 1.0 wt% or less Manganese is necessary as a deoxidizing agent, but if added in a large amount, the oxidation resistance deteriorates. Therefore, the upper limit of the content is 1.0 wt.
%. Ni content: over 2 to 5.0 wt% Nickel is an austenite stabilizing element, and is 2 wt%
A large amount of martensite was obtained. Strength, ductility, and toughness improve as Ni increases. However, at the same time, the oxidation resistance deteriorates and the scale of the fiber surface increases, so the upper limit of the content was made 5.0 wt%.

Cr content: 17.0 to 20.0 wt% Chromium is an important element for ensuring the corrosion resistance and oxidation resistance of stainless steel. More than 2 to 5.0 wt% Ni
When contained, a minimum of 17.0 wt% Cr is required to secure oxidation resistance capable of producing fibers by the ME method. on the other hand,
When the Cr content exceeds 20.0 wt%, it becomes difficult to increase the strength in terms of the metal structure because of the balance with the austenite stabilizing element.

N amount: 0.01 to 0.30 wt% Nitrogen is a strong austenite stabilizing element similar to carbon, and it is effective to increase the addition amount in order to obtain high strength fibers. However, in the case of high Cr, low C and low Ni, it is necessary to add at least 0.01 wt% N to obtain high strength fiber. On the other hand, if added in excess of 0.30 wt%, blowhole-like defects occur in the fiber, so the upper limit of the content was made 0.30 wt%.

The limitation of the amounts of the components of the present invention is to obtain a balance between austenite-forming elements and ferrite-forming elements and martensite during fiber production in order to obtain stainless steel fibers having high strength, high ductility and high toughness. It is determined as described above in consideration of the austenite stability that depends on the respective components. Furthermore, since it is necessary to limit the amount of scale generation on the fiber surface in order to utilize the ME method of producing metal fibers by rapidly cooling and solidifying molten steel in the atmosphere,
Elements such as C, Mn and Ni that promote oxidation and Cr and S
It is determined in consideration of the balance of the addition amount with an element such as i that prevents oxidation.

[0019]

EXAMPLES Examples of the present invention and comparative examples will be described below. Example 1 of stainless fiber according to the present invention
And ~ 11 Table 1 shows the chemical components of the Comparative Examples 12-15.

[0020]

[Table 1]

Each stainless fiber has a diameter of 0.4 mm and a length of 30 mm
Was manufactured by the ME method. That is, in each of Examples and Comparative Examples, stainless fibers were extracted from the surface of molten steel sealed with propane gas by the ME method using a water cooling drum. The fibers after being solidified and separated from the drum are cooled in the atmosphere, fall on the iron plate, and are further cooled. During this time, the fiber surfaces are subjected to oxidation, at the same time metal organizational circle
Tensile transformation occurs.

The state of oxidation of the surface of the obtained stainless fiber was evaluated by visual inspection, and those with little oxidation and usable for concrete reinforcement were indicated by ◯, and those with a large amount of oxide scale that were unusable were indicated by x. The tensile strength of the stainless fiber was determined using a fiber tensile test device. The test conditions were such that the distance between chucks was 10 mm and the crosshead speed was 0.3 mm / min. The length of the test piece was set to 30 mm, the weight was measured, and the specific gravity was set to 7.8 constant.
The tensile strength (Kgf / mm ² ) was calculated from the measured value.

The bending test of the stainless fiber is conducted with a tip R0.5.
, The test piece fiber held straight between two bites with a blade angle of 60 °, the first time to the left, the second time to the right, 3
The number of times of bending, which was obtained by bending the right side to the left side again and fully to the right and left, was obtained, and the average value of 10 test pieces was evaluated. Fiber breaks and bends during FRC manufacturing are F
After the RC is manufactured, the concrete is washed with water in an uncured state to recover stainless fibers, and the broken and bent state of each fiber is observed. ○: No break, bent 10% or less ×: Bad (break) ●: Evaluated by showing as defective (bending).

The bending strength of stainless fiber was evaluated by measuring the bending strength of plain concrete containing no stainless fiber and FRC containing 1 vol% of stainless fiber, and determining the strength ratio of the FRC to the plain concrete. Table 1 shows the evaluation results for each item. According to the evaluation result of the oxidation state of the stainless fiber surface, the stainless fiber of the present invention having the Cr content of 17 wt% or more has a small oxide scale and the fiber shape is normal, but the Cr content is 17 wt% or less. In the comparative example with high carbon and high nickel, the oxidation was severe and some fibers had a curled shape.

Regarding the tensile strength of the fiber alone, Comparative Example 1
Except for 2 , the comparative examples showed generally larger values than those of the present invention, but the fibers of the present invention also have a minimum of 98 Kgf / mm ^{2 and about} 100 Kgf / mm ^2, which is no problem. On the other hand, in the bending test results, all other comparative examples except Comparative Example 12 were broken at 0 or once. The strength and ductility of the stainless steel fiber are closely related to the fiber performance for FRC, and the higher the strength of the fiber, the greater the reinforcing performance. However, it is clear from the results shown in Table 1 that the fiber that breaks in one bending in the bending test breaks due to the kneading with the concrete during FRC production, and the practical concrete reinforcement performance is small. . That is, it is understood that the stainless steel fiber for concrete reinforcement needs to have ductility that does not break during FRC production.

However, as shown in Comparative Example 12 , even if the ductility is sufficient (the bending test is frequent), if the tensile strength is low, the fibers will be bent during FRC production, and it will be difficult to uniformly disperse them in concrete. After all, the practical reinforcing effect is reduced. In addition, it was confirmed that among the fibers having a large amount of oxide scale, Comparative Example 15 had insufficient adhesion to concrete and had a small reinforcing effect.

From the results shown in Table 1 above, the stainless steel fiber for concrete reinforcement of this example has sufficient oxidation resistance during fiber production and is uniform without being broken or deformed during kneading with concrete. , Which can improve the bending strength of concrete by as much as 75 to 125%, and has no possibility of being rusted and spoiling the aesthetics of concrete or deteriorating its durability. It is clear to have.

The stainless steel fiber of the present invention can be applied in exactly the same manner for reinforcing mortar using cement as well as polymer concrete using polymer in addition to concrete.

[0029]

As described above, the stainless steel fiber for concrete reinforcement of the present invention has a C content of 0.03 to 0.
2 wt%, Si 1.5 wt% or less, Mn 1.0 wt% or less, Ni more than 2 to 5.0 wt%, Cr 17.0 to 20.
0 wt%, N is 0.01~0.30wt%, the balance comprises other unavoidable impurities the steel material having a composition consisting of Fe, ME
Has a structure containing martensite phase
Since it is intended to do , using simple processes and equipment,
A fibrous stainless alloy with high strength due to martensitic transformation, high ductility due to compounding components, high drossiness, and a shape with good concrete adhesion is also obtained, with special heat treatment and hardening treatment. It is possible to inexpensively provide concrete-reinforcing stainless steel fibers that can be easily kneaded with concrete and that have a sufficient concrete-reinforcing action without going through a process such as cutting.

Claims (1)

(57) [Claims] 1. C is 0.03 to 0.2 wt%, and Si is 1.
5 wt% or less, Mn is 1.0 wt% or less, and Ni is more than 2 to 5.
0 wt%, Cr 17.0 to 20.0 wt%, N 0.01
~ 0.30wt%, other unavoidable impurities and balance F
a stainless steel fiber made of e, which is produced by using the melt extraction method
A stainless steel fiber for concrete reinforcement, which has a structure including a site phase .