JPS5839737A - Manufacture of high tensile wire rod - Google Patents

Abstract

PURPOSE:To make a descaling stage and a hardening stage unnecessary by hot rolling a steel contg. specified amounts of C, Si, Mn, Cr, B and Ti and/or Al to form a wire rod, converting the structure of the rod into martensite, and drawing the rod through roller dies without carrying out descaling. CONSTITUTION:A steel consisting of, by weight, 0.1-0.4% C, 0.05-1.5% Si, 0.7-2.5% Mn, 0.1-1.5% Cr, 0.0002-0.005% B, 0.005-0.05% Ti and/or 0.007- 0.05% Al and the balance Fe with inevitable impurities is hot rolled to form a wire rod. The structure of the rod is converted into martensite by controlled cooling from <=700 deg.C after the hot rolling, and the rod is drawn through roller dies without carrying out descaling. The drawn rod may be deformed or further tempered and subjected to temp. adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-tensile steel bars or steel wires (hereinafter collectively referred to as wire rods). Here, the high tensile strength wire rod is mainly used as a PC steel rod, and includes both wire rods that have been subjected to deformation processing and those that have not been subjected to deformation processing.

For example, JXSO-310's 5BPR/10//3!
The production of high-strength PC steel bars of f or 5BPD /30//4tj class is generally carried out by the following procedure. That is, hot-rolled wire rods are pickled or mechanically descaled, then coated with lime or treated with a chemical coating to give them lubricity, and then drawn into wire, and then shaped into different shapes if necessary. , and finally heat treatment of quenching and tempering is performed using a separate fin.

The biggest problem with this method is hot rolling → descaling → wire drawing (
→ irregular shape processing) and heat treatment of quenching and tempering are performed on separate lines.

This is because heat treatment requires a long time and cannot be carried out in a continuous line, but it goes without saying that such separation of lines leads to a decrease in productivity. Furthermore, there is a problem with the descaling process. Descaling is an indispensable process from the viewpoint of ensuring the quality of the wire and preventing dye damage during wire drawing, and is generally carried out by pickling or mechanical descaling using a roll bender. There are problems with waste liquid treatment, and mechanical treatment is undeniably disadvantageous in terms of equipment.

An object of the present invention is to greatly simplify the wire manufacturing process by eliminating the need for descaling prior to wire drawing and quenching after wire drawing.

As mentioned above, the scale of normal hot-rolled wire rods will become an obstacle in the subsequent wire drawing process if it is not removed. If we make it into a material with good rolling properties,
The descaling process can be omitted. On the other hand, one possible way to simplify the heat treatment process is to use the heat retained after hot rolling to transform the wire rod into martensite in advance, thereby eliminating the need for the quenching process that is normally performed after wire drawing. .

For this reason, the present inventors have conducted various experiments and research on methods for suppressing the formation of hot-rolling scale as much as possible and obtaining martensite at the post-hot-rolling stage. In addition to improving hardenability, by directly adjusting cooling from a temperature of 700℃ or less in the cooling process after hot rolling, a wire rod that is reliably martensitized can be obtained, and at the same time, scale generation is extremely effective. We found that this was suppressed by

That is, the present invention provides Co, to~θ110%, S
1θOj −/, j 0%, Mn 0.70−! ,
j O%, Cr O, / 0- /, j 0%, BO
,0002-0.0030%, and TiO,00j
O-0, Oj 0% and At O, 007-0, Oj O
Steel containing Type 501 or Type 2, with the balance being Fe and unavoidable impurities is made into a hot-rolled wire rod, and after hot-rolling, it is cooled at a temperature of 700°C or less to become martensite, and then descaled. The gist of the present invention is a method for producing a wire rod, which is characterized by drawing the wire using a roller dynu.

Needless to say, cooling at a critical cooling rate or higher is required for martensite formation. Normally, when blast-cooling a loop coil developed on a conveyor using the Stelmore method, the cooling start temperature is too high, and untransformed aunutenite remains and remains, passing through the conveyor and forming a coil in the converging device. Therefore, the cooling rate becomes less than the critical cooling rate, resulting in the formation of a bainite structure.

On the other hand, scale that is generally generated at high temperatures depends on the initial temperature and cooling rate of the material, and the more slowly the material is cooled from a high temperature, the more the amount of scale increases.

In order to draw wire without descaling, it is necessary to generate a thin FeO-based scale that is highly rollable.
In order to generate such a scale that can be directly drawn, cooling must be performed at a high rate from a low cooling start temperature. - In the Nutilmore method described above, the high temperature is generally cooled at a slow rate by blast cooling, and therefore a large amount of scale formation is unavoidable.

However, as a result of experiments and research by the present inventors, it was found that Ti and At, which are effective in improving hardenability and to maximize the effect of B, are added to the steel material, and the wire rod after hot rolling is temperature below 700℃ (70℃) by forced cooling such as water cooling.
If quenching is performed from θ to 5ooc (preferably in the range of However, it was found that only extremely thin wires that could be drawn were produced.

The wire rod obtained by carrying out the method of the present invention has a beautiful surface and has high commercial value, regardless of whether the wire rod has been subjected to deformation processing or not.

The reasons for limiting the steel components and manufacturing conditions in the present invention will be explained below.

First, regarding the steel components: C: A component that imparts the necessary strength and hardenability to steel. 0
．． / If it is less than 0%, it is difficult to secure the required strength, and if it exceeds the unbroken o, po%, the ductility and spot weldability required for a PC'WI rod cannot be obtained.

Si: Effective for improving hardenability and strength.

If O,OS% is less than this, no such effect can be expected, while if /, j exceeds 0%, ductility will deteriorate significantly.

Mn: A component that contributes to improving hardenability and is required to be present in an amount of 0.70% or more, but there is no point in containing more than 2.50%.

Cr: Effective in improving hardenability, the content is 0.10
~/, j 0% is appropriate.

B: This is an extremely effective component for improving hardenability when added in small amounts, and the appropriate content is O1θθ02 to O1θOjθ%.

Ti, A7: These are all essential components for protecting B from N and maximizing the hardenability improvement effect of B. In particular, T1 itself is effective in improving hardenability. One or two of these are added, but Ti is 0.00j
If the amount of At is not more than 0.0% and At is not more than 0.007%, B cannot be sufficiently protected from N.
i, Ti O, Oj O%, Ato, os
It is not necessary to contain more than 0%.

Next, regarding the manufacturing conditions, the reason why we limited the starting temperature of adjusted cooling after hot rolling to 700°C or less is because the cooling rate in adjusted cooling is set above the critical cooling rate and martensitic transformation occurs on the Nutilmore conveyor. This is because the temperature needs to be 700° C. or lower in order to completely complete the process, suppress scale formation as much as possible, and make the scale thin and have excellent rollability.

After conditioning and cooling, the martensitic wire rod is drawn with a roller die without going through the descaling process, but the reason we decided to use a roller dyne for wire drawing is that by using this roller die, the descaling process cannot be completed for the first time. This is because if you make it unnecessary, it becomes possible to do so. The roller die operates on the same principle as general rolling, and draws the wire by applying pressure to the wire using a combination of rolls (1-H). Incidentally, roller dies themselves are already known for drawing wire rods, but even if this die is used, hot-rolled wire rods manufactured in a normal process cannot be drawn without descaling to obtain high-quality wire rods. Needless to say, this is impossible.

A wire rod drawn to a predetermined diameter by a roller die is sent directly to a tempering process without being quenched, or is tempered after being straddled and shaped. High strength P
In the case of C steel bars, heat treatment of quenching and tempering is generally required, but in the method of the present invention, the wire rod has already been turned into martensitic by direct cooling, so the heat treatment after wire drawing or deformation processing is as follows: Just tempering is enough. If the steel bar is only martensited, the tensile strength ti, -pc steel bar will satisfy the predetermined values, but the yield point will be insufficient. Tempering treatment is performed to improve this yield point value. Tempering heating is preferably performed by high-frequency induction heating.

After tempering, the seven seats will be straightened if necessary.

The PC steel bar has the characteristics of straightness and luxation resistance (especially about l
♂Warm relaxation at 0°C is often required. Warm straightening is effective in imparting these characteristics. In the method of the present invention, warm straightening can be performed during the cooling process by utilizing the heat retained during tempering, which is advantageous in terms of energy saving.

Next, examples of the present invention will be described. Let's take the production of irregularly shaped PC steel bars as an example.

7. Five types of steel with the composition shown in Table 1 were hot rolled.
! It was made into a wire rod of ff$ and rapidly cooled to tso°C by forced water cooling. This is made into a ring shape using a laying cone.
It was spread out on a conveyor, and while being transferred at a speed of O1≠/sec, it was cooled in a controlled manner by blast air having a cooling capacity of about 1 Ot2/SeC. Conveyor length: lAOm.

Cooling time: /00 See.

For comparison, among the 14 types of 5f, ≠ steel types (A, B).

For D and E), cooling was performed under the same conditions as above except that the adjusted cooling start temperature was set to rso°C. Table 2 shows the mechanical properties and thickness of the wire after the above treatment.

These wire rods are cut into roller dies (,2
set, tandem), the machining speed is O”/min.
, 7 without lubrication. j tzf to 72 f tmj;
It was cold stretched. Table 53 shows the above wire drawing processing status.

*30 specimens used Table 3 In Table 2, the examples of the present invention (those with subscript 1) in which controlled cooling was performed after hot rolling according to the method of the present invention have very thin scale thicknesses of less than 1μ; As is clear from Table 3, all wires were successfully drawn using a roller die with the scale still attached. However, a comparative example (subscript 2) in which the adjusted cooling start temperature after hot rolling was higher than the range of the present invention
The case thickness of 7 cases was about 10 times that of the example of the present invention, and all of these cases suffered from seizure during wire drawing with a roller die.

The wire rod drawn by the above method of the present invention is subjected to cold processing into an irregular shape (oval shape), and then subjected to high frequency (2SOJJKH) processing.
The tempering process was carried out using the following methods.

A spinner type straightener is placed at the output side jm of the high frequency coil, and the bending of the wire is A n/1. ! Correction processing was carried out so that it was within rm. Inlet temperature of straightening machine q
It was 0°C. Processing from roller die wire drawing to warm straightening was carried out continuously on the same line, but the line speed was θ. Table 1 shows the Flj mechanical properties and other properties of the wire after warm straightening.

The value is l%.

As is clear from the above table, good mechanical properties and excellent relaxation properties are ensured by tempering and warm straightening the material which has been conditioned and cooled according to the method of the present invention.

As is clear from the above description, the method of the present invention eliminates the need for the descaling process and the quenching process in the manufacturing process of high-tensile wire rods. All processes can be carried out on one continuous line, and therefore, the present invention is significantly effective in improving the manufacturing efficiency and reducing costs of high-tensile wire rods used as PC steel bars.

Applicant: Sumitomo Metal Industries, Ltd. Continuation of page 1 0 shots by Hiroshi Nagai 1-3 Nishinagasu Hondori, Amagasaki City 0 shots Akira Ono Tetsu Lives at 5-15 Kitahama, Higashi-ku, Osaka. Within Yukinzoku Kogyo Co., Ltd. 0 shots Akira Katsutsugu Kajiyama Lives at 5-15 Kitahama, Higashi-ku, Osaka. Within Yukinzoku Kogyo Co., Ltd.

Claims (1)

[Claims] (1) CO, 10-0,100%, S'L O, 0
! =/, j 0%, Mn0.70-130%, CrO
,10~/,jO%,Bo,0002~117. o o
s o% and Ti O,00! 0-0.030%
A steel containing one or two types of O,007~o, oso% and the balance consisting of Fe and unavoidable impurities is made into a wire rod by hot rolling, and after hot rolling, it is heated at 700℃ from the following temperature. A method for producing a high-tensile wire rod, which is characterized in that it undergoes controlled cooling to become martensite, then descales, and then draws the wire with a roller die. (:l) A method for manufacturing a high-tensile wire rod according to claim 71, characterized in that after wire drawing, further deformation processing is performed. (3) After wire drawing, further deformation processing is performed followed by tempering and heating. Claim No. (1), characterized in that
The method for producing a high-tensile wire rod according to item (2) or item (2).