JPH03151445A - Steel rod or wire for prestressed concrete with improved welding workability - Google Patents

Abstract

PURPOSE:To enhance the welding workability and the quality of welds by allowing a component of steel wire, which is rapidly cooled after giving a bending strain under specific percentage, to contain such components as C, Si, Mn, Mo in respective specified wt.%, and permitting decrease in the Si content to correspond to increase in the Mo content. CONSTITUTION:A steel rod or wire is subjected to rapid heating and cooling while it is running continuously, and this quenching of the material is made. Then a bending strain of 2% or less is given in the condition being heated quickly to the specified tempering temp., and thereafter rapid cooling is made. The steel rod or wire contains such components in wt.% as 0.10-0.40 C, 0.15-2.0 Mn, 0.6-2.0 Mn, 0.08-0.35 Mo, and the rest is Fe plus inevitable impurities. Therein decrease in the Si content is made corresponding to increase in the Mo content.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a W! The object of the present invention is to improve the welding workability of bars or steel wires (hereinafter referred to as PC steel bars/wires).

(Prior Art) As a method of manufacturing PC steel rods and wires, there are cases where heat treatment is used as a means to increase the strength of the raw material steel rods and wires.
As shown in No. 3), there is a well-known method in which a raw steel rod or wire is caused to burn out by rapid heating and cooling while running continuously, and then rapidly heated and rapidly cooled to a predetermined tempering temperature.

However, one of the applicants of this application has proceeded with development in order to obtain preferable characteristics that exceed the above-mentioned patented invention, and has filed a patent application for the results. The invention is disclosed as JP-A-58-157921 (hereinafter referred to as the prior invention), and the gist of the invention is that the added basic component is C:0.10"0.60.S in weight%.
i: 0.15-2.0. Mn: 0.6-2.0
A process in which the raw material steel rod/wire is run continuously while being rapidly heated and cooled to cause a slight bending strain (2% or less) and then rapidly cooled. The object is to obtain a product that is excellent in delayed fracture properties and mechanical properties, especially -like elongation and high temperature relaxation value.

The structure of the prior invention is significantly different from the structure of the patented invention mentioned above. For example, as is clear from the comparison of the chemical components of the two materials shown in Table 1 below, in the prior invention, the amount of added Si is different from that of the patented invention. 1) The prior invention involves a step of adding minute marks under the tempering heating temperature, which is not included in the patented invention; these two points reduce the doffing effect.

In addition, both chemical components in the same table are 9.2 mm JIS 0.
It is for type D (130/145) in 3109,
The patented invention is currently manufactured and commercially available by the present applicant, and the prior invention is based on Table 7 disclosed as Experimental Example 3 in the above-mentioned publication.

Table Weight % (Problems with the prior art) By the way, both the PC steel rods and wires according to the above-mentioned patent invention and the PC steel rods and wires according to the prior invention, the intersections with the auxiliary reinforcements are determined using a reinforcing bar cage knitting machine. In most cases, it is welded and organized into a reinforcing cage and used as a component of prestressed concrete members.

Therefore, it is customary to weld the intersections of the PGI1 rods/wires and the auxiliary bars when forming the above-mentioned reinforcing bar cage by spot welding by applying a welding current to the intersections. In the case of PC steel rods and wires related to the patented invention, it is difficult for current to flow, so the set voltage to obtain sufficient adhesive strength at the welded part is set approximately 50% higher than in the case of PCI rods and wires related to the patented invention. It was necessary to set the welding voltage value.

Businesses that organize reinforcing bar cages are constantly dealing with both PC steel bars and wires related to patented inventions and prior inventions, and the voltage settings must be changed frequently. It was desired.

(Objective of the Invention) The present invention has been made to solve the above-mentioned problems of the PCM rod and wire according to the prior invention, and includes the delayed fracture characteristics and mechanical properties of the PC8I rod and wire according to the prior invention, In particular, we have further improved the excellent points of -like elongation and high temperature relaxation value.

The purpose of the present invention is to provide a steel rod or steel wire for prestressed concrete with improved welding workability.

(Structure of the Invention) The basic gist of the present invention is as follows: (1) The manufacturing process involves rapid heating and cooling of a steel bar or 11 wires while continuously running them to a predetermined tempering temperature. (2) The steel rod or steel wire material composition is C: 0 in weight%.
．． 10-0.40. Si: 0.15-2. O
, Mn: 0°6~2.0. Mo: 0.08~
0.35, with the balance consisting of iron and unavoidable impurities, (3) and the above-mentioned decrease in Si content is made to correspond to increase in Mo content, (4) conditions for seeking particularly favorable effects. The content of Si and Mo in the above (3) is characterized by the following relationship in weight %: (S i ) −2 [Mo] <1.3.

(5) Furthermore, in addition to the additive components described in Summary (2) above, Ti: 0.01 to 0.05% and B: 0.0% by weight.
005 to 0.005%, and according to the above summary (3) and (4).

(Function of the Invention) The present invention reduces the amount of Si, which has been added in large amounts, by adding Mo to the raw material steel rods and wires, and further adding small amounts of Mo, Ti, and B.

By replacing Si with Si, it is possible to improve the current conductivity, thereby making it possible to obtain a good welding condition without intentionally increasing the applied voltage.While achieving a dramatic improvement in welding workability, it is possible to overcome the delay achieved by the previous invention. fracture properties and mechanical properties;
In particular, it has the effect of further improving its excellent -like elongation and high temperature relaxation value.

In other words, the present inventor took into consideration the fact that the reason why the PCw4 rod and wire according to the prior invention cannot obtain sufficient adhesion strength at the welded part unless the set voltage when energized is high is due to the high content of St. , while further improving the characteristics shown by the prior invention,
- We are striving to find additive components that can replace Si, which greatly contributes to the -like elongation and high-temperature relaxation properties.
As a result of repeated exploration and numerous experiments, it was discovered that Mo can serve as an almost satisfactory alternative additive component.

Various test examples conducted on the PCM rods and wires of the present invention will be disclosed below.

[Creation of specimen]

The present inventor has added chemical components such as the addition of Mo and the addition of T to Mo.
Each material steel wire to which i and B were added with weight and the amount of 3i was varied, and each material steel wire to which the amount of Si was varied without addition of Mo was doffed according to the gist of the present invention (11). This book corresponds to the JIS standard irregular-shaped seed material, which is subjected to the heat treatment process, that is, the process of rapid heating and rapid cooling to a specified tempering temperature, adding slight bending at that temperature, and then rapid cooling. A specimen according to the invention and a specimen according to the prior invention were prepared.

The chemical components added to each specimen are as shown in Table 2, the wire diameter of each specimen is 9.2 mm, and the amount of minute bending strain imparted following tempering heating is the same for all 0.2 mm. 9
It was 5%.

[Mechanical property test]

The mechanical properties obtained for each specimen are shown in Table 3 along with other test results.

From consideration of the table, it is confirmed that the product of the present invention has mechanical properties equivalent to the comparative product, that is, the prior invention product. Particularly noteworthy is that the product of the present invention with a slight bending strain of about 1% has less decrease in uniform elongation, and even though the Si content is 0.73% by weight, the comparative product with Si: 1.7% by weight class material It is to show the equivalent value.

Although data is omitted, it has been confirmed that even when a bending strain of 2% or less is applied, the uniform elongation of the product of the present invention shows little decrease.

[Delayed fracture test]

Next, a delayed fracture test conducted by the present inventor using the Rodin Ammon (50° C.) method will be described. The test was carried out on comparative product specimen No. 2.3.7 and invention product specimen No. 10.11.17 in Table 2, with the number of specimens n=5.

The test results were as shown in Table 4.

In the same table, if we compare and consider the present invention product specimen and the comparative product specimen with the same amount of Si, M.

It was confirmed that the addition of Ti+B was effective, and the addition of a small amount of Ti+B was also effective, providing excellent delayed fracture properties.

[High temperature relaxation test]

The inventor also conducted room temperature and high temperature relaxation tests on each specimen. The test results are listed in Table 3, and the correlation between the content of Mo and Si, which is a feature of the present invention, is shown in particular regarding the high-temperature relaxation value, which the present invention aims to maintain the characteristics of the prior invention. For clarity, the test results are shown as a graph in FIG.

In the figure, the horizontal axis represents the Si content (% by weight), the vertical axis represents the high temperature relaxation value (%), and the high temperature relaxation value of each specimen is plotted. In this case, specimens with almost the same content elements except Si are represented by the same symbols shown below as the same type system, and each trend curve A-D is shown as the same series in Figure 9 regardless of the presence or absence of Mo addition. I asked for it.

Note that the number in parentheses indicates the specimen number.

C-◎-----Mo: 0.2%, Ti, B
Yes (12, 17, 20) From the same figure, the specimen series B containing Mo: 0.1% is S
Although the difference value decreases as the i content increases,
It is revealed that the high temperature relaxation value is definitely improved and a significant difference of more than 1% is shown at 5il1% or less. Specimen series C and D containing Mo: 0.2% and 0.3% showed more significant difference values when the Si content was small, and it was confirmed that there was a large improvement effect.

The figure also shows that the presence or absence of addition of Ti+B does not affect the high temperature relaxation value.

[Welded area adhesion force measurement test]

Furthermore, the present inventor conducted an experiment to investigate the adhesion force of the welded portion of each specimen.

Each specimen with a wire diameter of 9.2 mm and a wire diameter of 3. Weld the intersection with the 1mm auxiliary reinforcement at the same welding voltage: 1.45V, measure the welding current flowing through the weld, and measure the adhesion force of the weld using the JIS G 3551 r welded wire mesh weld point shear strength. Tested according to the following test method.

The experimental results are shown in Figure 2. The horizontal axis of the figure shows the Si content, and the lower side of the vertical axis shows the welding current value (A) flowing through the welded part.
The upper row shows the adhesion force (Kgf/mm2), and plots the measured current value and welding point shear strength test results for each specimen, and shows how the correlation between welding current value and adhesion force changes due to the present invention. We investigated whether The plotted values are the average values of n=10 specimens for each specimen, and the symbols in the figure indicate the type of each contained component specimen.

From Figure 2, it can be seen that in the comparison product specimen, the 2-type type, Si
When the content exceeds 1%, it gradually becomes difficult for welding current to flow through the welded area, and therefore the adhesion strength rapidly decreases. On the other hand, in the specimens containing Mo, the welding current flows much more easily in the Mutaip type specimens than in the comparative products, and therefore the adhesion is large. In particular, for specimen types ○ and ◎5△ containing Mo and Ti-B, the welding current value hardly changes until the Si content is around 1.75%, and compared to the case where only Mo is added, the welding current value is large. It has been shown that the adhesion force is significantly improved when it is included in

In parallel with the above test, the present inventor investigated the state of variation in adhesion depending on the presence or absence of addition of Ti and B.

A part of it is disclosed as FIG.

The figure shows specimens No. 18 and Ti containing approximately the same amounts of Si: 2% and Mo: 0.1%, but without the addition of Ti and B.

This shows a comparison of the investigation results for Specimen No. 19 with the addition of B, and it was confirmed that the addition of small amounts of Ti and B contributed to ensuring the stability of the adhesion force.

By the way, in the present invention, each added chemical component is set in the following range.

The product of the present invention obtains the strength necessary for pcJll rods and wires through heat treatment, and has a carbon content of 0.10, which provides flammability.
~0.40% by weight. If the C content is less than 0.10%, it is difficult to secure the required strength, and if it exceeds 0.40%, M
Even though o is added, a problem arises in terms of weldability. Further, in improving the flammability and micro-bending processing at the tempering heating temperature, Mn is set to 0.6 to 2.0% by weight as an element that resists mechanical properties, particularly --like elongation deterioration.

Furthermore, the present invention contains 0.15 to 2.0% by weight of Si, and M
o is 0.08 to 0.35% by weight. The feature of the present invention is the quantitative correlation between Si and Mo. That is, as stated in the overview of the above-mentioned prior invention, Si is
Although it is a component that significantly contributes to improving the high-temperature relaxation value by micro-bending under the tempering heating temperature, it is also an element that inhibits electrical conductivity. Therefore,
When welding under the same general constant voltage conditions as conventional PC steel rods and wires, by increasing the amount of Mo in response to decreasing the amount of Si, it is possible to obtain 1 conductivity while ensuring the specified high temperature relaxation value. to maintain the same adhesion force.

In this case, based on numerous test results, the content is between the two.

In particular, when the correlation of (S i) −2[Mo] <1.3% by weight is maintained, both of the above two effects can be completely obtained. This point is also proven from the test results disclosed above.

Therefore, there is no need for a high set welding voltage as in the case of the prior invention. In addition, even when giving priority to lowering the high-temperature relaxation value, while increasing the amount of added Si,
By adding Mo, even if the content exceeds 1.3% in the above relational expression, it is possible to improve current conductivity during welding and strengthen adhesion, and to maintain or improve delayed fracture characteristics.

Therefore, Mo needs to be added in an amount of at least 0.08%, and no effect is expected if it is less than 0.08%.

The reason why the upper limit of Mo was set at 0.35% is that the prerequisite of the present invention is that the heat treatment depends on a rapid heating method. There is no time for this, and even if the amount added is increased any further, there will be no effect.

Furthermore, the present invention provides Ti: 0.01 to 0.0 in addition to Mo.
5% by weight, B: 0.0005 to 0.005% by weight. If Ti is less than 0.01% by weight, it is not expected to contribute to improved delayed fracture properties, and if it exceeds 0.05% by weight, it will increase the inclusion rate, and B is 0.
．． 0.0005% by weight or more contributes to improving flammability, but 0.005% by weight or more contributes to improving flammability.
Even if the amount exceeds 0.005% by weight, no increase in effectiveness can be expected; however, by adding small amounts of Ti and B, the current value during welding can be increased and stabilized, thereby contributing to strengthening the adhesion and suppressing variations.

Although the above test examples were mainly disclosed for specimens with a wire diameter of 9.2 mm, the present inventor conducted similar tests on various wire diameter materials and obtained exactly the same effects as the disclosed examples. The effectiveness of the invention has been demonstrated.

(Effect of the invention) PC & II rods manufactured by the process according to the prior invention
By implementing the present invention as the wire material composition steel, when welding with auxiliary reinforcing bars, even if welded under the same general constant voltage conditions as for ordinary PCM rods and wires, the adhesion is exactly the same as that of ordinary PCwi rods and wires. It is possible to form reinforcing bars to ensure strength, and it is possible to obtain a product that further improves the delayed fracture characteristics and mechanical properties of the prior invention, particularly its excellent properties in -like elongation and high-temperature relaxation. This will contribute to improving the quality of prestressed concrete members while solving the problems of welding workability all at once.

Furthermore, even if the highest priority is to lower the high-temperature relaxation value, implementation of the present invention makes it possible to lower the high set welding voltage during welding that was required in the prior invention, and also makes it possible to reduce the high temperature setting that was achieved by the prior invention. Adhesion strength may be increased while further improving relaxation values.

As described above, the present invention has significant effects in improving welding workability, quality, and weld bond strength.

[Brief explanation of the drawing]

Figure 1 is a diagram summarizing the results of high-temperature relaxation tests conducted on each specimen, Figure 2 is a diagram showing the correlation between the welding current flowing through the weld and adhesion force for each specimen, and Figure 3 The figure is a diagram showing the state of variation in adhesive force related to the presence or absence of addition of Tt and B in the present invention. Table 2 *Ti: 0.02. B: 0.002 Table 1

Claims (1)

[Claims] 1) A steel rod or steel wire is burnt by rapid heating and cooling while running continuously, and is then rapidly heated to a predetermined tempering temperature, and a bending strain of 2% or less is applied. The steel rod or steel wire material components that are subsequently subjected to the quenching process are
C: 0.10-0.40. Si: 0.15 to 2.0,
Contains Mn: 0.6 to 2.0, Mo: 0.08 to 0.35, and the remainder consists of iron and unavoidable impurities, and the decrease in Si content corresponds to the increase in Mo content. A steel rod or wire for prestressed concrete with improved welding workability. 2) The content between Si and Mo is [Si]- in weight%
2. The steel rod or wire for prestressed concrete with improved welding workability according to claim 1, characterized in that the relationship is 2[Mo]<1.3. 3) The steel rod or steel wire is burnt out by rapid heating and cooling while running continuously, and then subjected to a process of rapidly heating to a predetermined tempering temperature, applying bending strain of 2% or less, and then rapidly cooling. The content of the steel rod or steel wire material is % by weight.
C: 0.10-0.40. Si: 0.15 to 2.0,
Based on Mn: 0.6 to 2.0, Mo: 0.08 to 0.35, furthermore Ti: 0.01 to 0.05% and B: 0.
0005 to 0.005%, with the remainder consisting of iron and unavoidable impurities, and the reduction in Si content corresponds to the increase in Mo content, which has improved welding workability. Steel rod or steel wire for prestressed concrete. 4) The content between Si and Mo is [Si]- in weight%
The steel rod or steel wire for prestressed concrete with improved welding workability according to claim 3, characterized in that the relationship is 2[Mo]<1.3.