JPH0436420A - Production of high tensile strength wire - Google Patents

Abstract

PURPOSE:To produce a high tensile strength wire with high productivity by hot-rolling a steel having a specific composition in which V content is specified, carrying out direct patenting treatment, descaling, and roller die drawing, and then performing warm straightening by means of continuous line. CONSTITUTION:A steel having a composition containing, by weight ratio, 0.70-0.85% C, 0.12-0.32% Si, 0.60-1.00% Mn, and 0.05-O.20% V is hot-rolled, and the resulting wire rod of about 800-950 deg.C is subjected to Stelmor direct patenting treatment by means of air blast at about 7-25 deg.C/sec cooling rate. This wire rod is descaled by a mechanical descaling method and wiredrawn by a roller die drawing method, and the resulting wire is subjected to warm straightening by means of continuous line. By this method, the high tensile strength wire having >= about 160kgf/mm<2> can be obtained while improving producitivity and reducing costs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing high-tensile wire rods (including steel bars), and for example, high-strength P wire rods used in prestressed concrete.
The present invention relates to a method for manufacturing high-tensile wire rods such as C steel wire at low cost and with high productivity.

Conventional technology For example, high-strength PC steel wire 5WPDI used in JIS G-3536 prestressed concrete is manufactured by the following procedure.

That is, after hot-rolled wire is subjected to lead patenting treatment off-line to obtain a specified strength, it is descaled by pickling, lubricated, and wire-drawn using a hole die. Accordingly, it is processed into a different shape and further subjected to bluing treatment to remove residual strain to obtain predetermined characteristics (see JP-A-58-197216, etc.).

Problems to be Solved by the Invention However, the conventional manufacturing method described above has the following problems.

■ Off-line lead patenting treatment is required, resulting in a significant cost increase.

■ Productivity is poor because offline lead patenting, descaling by pickling, cold wire drawing, and bluing are performed in separate processes.

■ The bluing process does not provide the good level of adhesive relaxation properties that are particularly required in the final product.

This invention was made to solve these problems, and aims to propose a method for manufacturing high-quality, high-tensile wire rods at low cost without performing offline lead patenting treatment and bluing treatment. It is something.

Means for Solving the Problems The inventor first studied various ways to omit the offline lead patenting process, and found that in order to omit the offline lead patenting process, it was necessary to apply the same level of offline lead patenting treatment at the wire rod rolling stage. It was found that it is necessary to obtain a strength higher than that, and that this is possible by adjusting the composition of the steel. In particular, it has been found that ■ greatly contributes to improving patentability.

That is, C is 0.70-0.85wt% and Si is 0.70-0.85wt%.
12-0.32wt%, Mn 0.60-1.00wt
%, Vo, 05-0, and 20wt%, respectively, and performed Stelmore direct patenting to obtain 120% of the lead obtained by conventional offline lead patenting.
It has been found that strength equivalent to or higher than the kgf/mm level can be obtained.

This invention was made based on the above findings, and the weight ratio is 0.70 to 0.85% of C and 0.12 to 0.32% of Si.
, Mn 0.60-1.00%, V 0.05-0
．． After hot rolling steel containing 20%, directly patenting it to obtain a wire rod with a tensile strength of 120 kgf/mm2 or more,
Subsequently, the wire is descaled and subjected to roller die wire drawing to have a tensile strength of 160 kgf/mm'' or more, and then warm straightened.

Note that the descaling may be performed by either a pickling method or a mechanical descaling method, but the mechanical descaling method is preferable in consideration of continuous secondary processing. Also,
Irregular shape processing is performed as necessary.

Effect The reasons for limiting the steel components in this invention are as follows.

C: 0.70-0.85wt% C is the main component that gives steel the necessary strength, but 0.70 to 0.85 wt%
If it is less than 0 wt%, it is difficult to secure the required strength, while if it exceeds 0.85 wt%, network-like cementite is formed during the cooling process of wire rolling, resulting in brittleness.
0.70 to 0.0, since cold wire drawability is significantly reduced.
It was set to 85 wt%.

Si: 0.12-0.32wt%Si is an effective component as a deoxidizing agent, but in this invention, it is
02 piano wire rod specified component range 0,12-0.32w
It was set as t%.

Mn: 0.60-1.00wt%Mn is a component that contributes to improving patentability and is an effective component for improving strength, but if it is less than 0.60wt%, this effect cannot be obtained, and on the other hand If it exceeds 1.00 wt%, a martensitic structure will occur during the cooling process during wire rolling, making it brittle and making cold wire drawing difficult.
It was set as wt%.

V: 0.05-0.20wt% (2) is the most important component in the composition of the present invention, and is a component that contributes to improving patentability.
If the content is less than 0.05 wt%, the effect cannot be obtained; on the other hand, if the content is less than 0.20
If it exceeds wt%, the strength will further increase, but this is not necessary in this invention, and the upper limit is set to 0.2 in consideration of economic efficiency.
It was set to 0 wt%.

As direct patenting processing methods, Stelmore Batente Ink, Schlemann Cooling, etc. are known, but the present invention employs the Stelmore direct patenting method.

The Stelmore direct patenting method is a method in which the steel is hot-rolled and then cooled by air blast at a high temperature to transform the austenite into a fine pearlite structure.

This direct patenting method requires that the material temperature at the start of the blast,
Cooling rate etc. are important, and this direct patenting achieves the desired strength, that is, tensile strength of 120 kgf/mm'
In order to obtain the above, the material temperature at the start of the blast must be set to 800
It is desirable to set the temperature to ~950°C and the cooling rate to 7~b.

In other words, if the material temperature at the start of blasting is less than 800°C and the cooling rate is less than 7°C/S, the Stelmor cooling effect cannot be obtained, while if the material temperature exceeds 900°C, the austenite grain size becomes coarser and the ductility decreases. decreases and cannot withstand the next process of wire drawing.

Furthermore, if the cooling rate exceeds 25° C./S, a very brittle martensitic structure will occur, causing problems such as breakage.

The tensile strength obtained by direct patenting of Stelmore is about 120 kgf/mm, for example, JIS
Required strength 154 for 5WPD 17mm equivalent to G-3536
．． In order to obtain 6 kgf/mm2 or more, the strength before heating is 160 kgf, taking into account the decrease in strength during warm straightening.
/mm" or more. Therefore, in this invention, it is necessary to increase the strength by wire drawing, and by making the wire drawing degree 40% or more, the tensile strength is 160 kgf.
/mm” or more can be obtained.

In order to enable continuity of this secondary processing, it is desirable to use a mechanical descaling method as the descaling method and a roller die wire drawing method that does not require surface chemical coating treatment as the wire drawing method.

By the way, the most required properties for PC steel are linearity,
Regarding relaxation properties, autoclave curing has recently become mainstream for the purpose of shortening concrete curing time, and there is a demand for improvement in relaxation properties at temperatures around 180°C. Warm straightening is effective for imparting these characteristics.

Example Figure 1 is a manufacturing process diagram for carrying out the method of this invention.
(1) is the hot rolling process, (2) is the Stelmore direct patenting process, (3) is the mechanical descaling process, (4) is the roller die wire drawing process, (5) is the profile processing process, and (6) is the Each warm straightening process is shown.

Example 1 Six steel types A-F shown in Table 1 (A-E are steels of the present invention, F
(conventional steel) was rolled into a wire rod with a rolled product size of 9.5 mmφ, water-cooled to 900°C immediately after hot finish rolling, and rolled out on a Stelmore conveyor at a conveyor speed of 0.6 m/s.
The pearlite transformation was completed by cooling at a cooling rate of 10° C./S.

Table 2 shows the tensile properties after direct patenting in this example.

From Table 2, all the steels of the present invention have 120 kgf/mm.
While the above tensile strength was obtained, the tensile strength of conventional steel remained as low as 115 kgf/++++n''.

Next, the directly patented steel material of the present invention steels A-E was descaled with a roller of a repeated bending method, and cooled from 9.5 mmφ to 7.0 mmφ using a roller die (4 set tandem) at a processing speed of 90 m 7 minutes. (Wire drawing degree: 45.8%).

Furthermore, after performing cold processing (oval shape), it was heated to 400°C using a high-frequency heating device to perform warm straightening, and then placed in a spinner-type straightening machine installed approximately 5 meters from the exit side of the high-frequency heating device. The wire rod was straightened so that the bend was within 3 mm/1.5 m. The inlet temperature of the straightener was 390°C. The line speed from mechanical descaling to warm straightening was 90 m/min.

Table 3 shows the mechanical properties of the wire after warm straightening.

As is clear from Table 3, all the wire rods obtained by the method of the present invention have good mechanical properties and excellent relaxation properties, and it is clear that the off-line lead patenting treatment can be omitted.

Note that the glue relaxation value of the bluing treated material of RH82B is 15%.

As described in detail below, the method of the present invention can ensure good mechanical properties and excellent relaxation properties through direct patenting treatment, making it possible to omit offline lead patenting treatment. At the same time, by making it possible to adopt the low die wire drawing method, it is possible to make the production line continuous, which has the significant effect of improving the productivity of high-tensile wire rods and reducing costs. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a manufacturing process for carrying out the method of this invention. 1... Hot rolling process 2... Stelmore direct patenting process 3... Mechanical descaling process 4... Roller die wire drawing process 5... Deformation processing process 6... Warm straightening process

Claims (1)

[Claims] Weight ratio: C0.70-0.85%, Si0.12-0
．． 32%, Mn0.60-1.00%, V0.05-0
．． A high-tensile wire rod characterized in that after hot-rolling steel containing 20%, it is directly patented, subsequently descaled, and subjected to roller die wire drawing, and then warm straightened on a continuous line. manufacturing method.