JPS5839738A - 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 wire rod contg. specified amounts of C, Si, Mn, Cr, B and Ti and/ or Al while cooling it to a specified temp. between a group of intermediate rolling mills and a group of finish rolling mills, quenching the rod after the finish rolling to convert the structure into supercooled austenite, converting the austenite into martensite, and drawing the rod. CONSTITUTION:A steel wire rod 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. At this time, the rod is cooled to 750-900 deg.C between a group of intermediate rolling mills and a group of finish rolling mills. After the finish rolling, the rod is quenched to <=700 deg.C to convert the structure into austenite. The austenite is then converted into martensite by controlled cooling, and the rod is drawn through roller dies without carrying out descaling.

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).

For example, 5BPRIIO/135 of JISG-3109
The production of high-strength PC steel bars of 5BPD130/145 grade is generally carried out by the following procedure. That is, hot-rolled wire rods are pickled or mechanically descaled, then lime coated or chemically coated to give them lubricity, and wire drawn, and then deformed if necessary. Finally, heat treatment for quenching and tempering is performed on a separate line, which goes through the above steps.

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.

Since the heat treatment requires a long time, it is impossible to carry out the heat treatment in one continuous line, but needless to say, such separation of lines leads to a decrease in productivity. Furthermore, there is also a problem with the descaling process. Descaling is a process that cannot be omitted in order to ensure the quality of the wire rod and prevent damage to the die during wire drawing.
Alternatively, it is carried out by mechanical descaling using a roll bender, etc., but pickling treatment has the problem of waste liquid disposal, while mechanical treatment also has undeniable disadvantages in terms of equipment.

The purpose of the present invention is to provide a method for producing high-quality high-tensile wire rods efficiently and at low cost on one continuous line by omitting the descaling process prior to wire drawing and the quenching process after wire drawing. It is something. 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.

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. In addition, one possible means of simplifying the heat treatment process is to use the heat retained after hot rolling to transform the flux into martensite in advance, thereby eliminating the need for the quenching process that is normally performed after wire drawing. .

From this point of view, 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 in the cooling process after hot-rolling.
In order to improve the hardenability of the raw material steel, the steel is cooled to a predetermined temperature above the transformation point after exiting the intermediate rolling mill during hot rolling, and after finish rolling, it is rapidly cooled to form austenite, and then adjusted cooling is performed. It has been found that the formation of hot rolling scale can be effectively suppressed and, at the same time, complete martensite can be ensured.

That is, in the present invention, C0110-0.40%, Si0.
05-1.50%, Mn 0.70-2.50%, C
r O, 10-1.50%, B O, 0002-0.
0050% and TiO,0050-0,050%
ToAj! A steel wire rod containing one or both of 0.007 to 0.050%, with the remainder consisting of Fe and unavoidable impurities, is hot rolled. It is cooled to 900°C, and after finishing rolling, it is rapidly cooled to a temperature of 700°C or less to form a suitably cooled austenite state, and further modified to become martensite by controlled cooling.
The gist of the present invention is a method for producing a high-tensile wire rod, which is characterized in that the wire is then drawn using a roller die without descaling.

Needless to say, cooling below the critical cooling rate is required for martensite formation. Normally, when blast-cooling a loose coil developed on a conveyor using the Stelmor method, the cooling start temperature is too high, and untransformed austenite passes through the conveyor while remaining, forming a coil in the concentrator. becomes below 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 amount of scale increases as the material is cooled at a slower rate from a higher temperature. In order to draw wire without descaling, it is necessary to generate a thin and highly rollable FeO-based scale. Cooling must be performed promptly from the cooling start temperature. In the above-mentioned Stelmore method, since the high temperature is generally cooled slowly and slowly by blast cooling, a large amount of scale production is unavoidable.

However, as a result of experiments and research, the inventors of the present invention (1) added Ti5N to the material steel to fully bring out the effect of B, which is effective in improving hardenability, and (2) added Ti5N to the material steel to fully bring out the effect of B. When it comes out, it is first cooled to 50°C for 750 minutes,
■After finish rolling, it is rapidly cooled to 700"C or less (preferably in the range of 700 to 500C) to form appropriately cooled austenite. If controlled cooling is performed from there, it is possible to achieve relatively gentle blasting using the general Stelmor method equipment mentioned above. It was found that even by cooling, martensite could be reliably obtained before convergence, stable mechanical properties could be ensured, and at the same time the scale could be kept to an extremely thin wire that could be drawn.

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.

Regarding steel components, C: A component that gives steel the necessary strength and hardenability;
, ios, it is difficult to secure the required strength, and 0,
If it exceeds 40%, the ductility and spot weldability required for a PC steel bar cannot be obtained.

Si: Effective for improving hardenability and strength.

If it is less than 0.051, such an effect cannot be expected, while if it exceeds 1.50%, the ductility deteriorates significantly.

Mn: A component that contributes to improving hardenability, and is required to be present in an amount of 0.70% or more, but no improvement in the effect is observed even if the content exceeds 2.50%.

Cr: Effective for improving hardenability, content is 0.10
~1.50- is appropriate.

B: A component that is extremely effective in improving hardenability when added in small amounts, and an appropriate content is 0.0002 to 0.0050%.

It is a component that maximizes the effect of improving hardenability.
One or two types are added. In particular, Ti itself also contributes to improving hardenability. T1 is 0.0050
% or more, and N is 0. Oe If there are no more than 7, N to B
On the other hand, normal N-containing ht can sufficiently protect ri
o, oso%, AN There is no need to add more than 0.050%.

Next, regarding the manufacturing conditions, cooling is performed once between the intermediate rolling mill group and the finishing rolling mill group in the hot rolling process to eliminate variations in finishing rolling temperature due to variations in the heating temperature of the billet. The purpose is to suppress the finish rolling temperature to a low level, reduce the size of austenite grains during the next adjustment cooling, eliminate variations, improve ductility after martensitic transformation, and reduce variations in mechanical properties.

This cooling is done by controlling the cooling water according to the entrance temperature of the hot rolling mill or the initial rolling temperature, so that the temperature before finish rolling is 75.
The temperature is within the range of 6 to 900°C. If the cooling temperature is lower than 750°C, there is a danger that the surface temperature of the wire will fall below the transformation point, and if it exceeds 900°C, the austenite grains after rolling will recrystallize and grow, resulting in failure. It becomes uniform, and the ductility after martensitic transformation deteriorates, and the variation in mechanical properties increases.

After finishing rolling, the material is rapidly cooled to 700°C or less, but this is done to ensure that the cooling rate for the next adjustment cooling is at least the critical cooling rate to completely complete the martensitic transformation on the Stelmore conveyor. , and are essential to suppress the formation of scale so that the scale does not become an obstacle to wire drawing with a roller die.

The wire rod that has been turned into martensitic material through controlled cooling is drawn using a roller die without going through a descaling process.

The reason why a roller die is used for wire drawing is that the use of a roller die makes it possible to eliminate the need for a descaling process. The roller die draws the wire by applying pressure to the wire using a combination of V-H rolls, based on the same principle as general rolling. 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 processed into a different shape. High strength M
In the case of PC steel rods, 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 shape processing is as follows: Just tempering is enough 1
If only martensite is formed, the tensile strength will satisfy the predetermined value for the PC steel bar, 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, OPC steel bars undergo warm straightening if necessary.
Warm relaxation at C is often required. Warm straightening is effective in imparting these characteristics. In the method of the present invention, warm straightening can be carried out 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. Here, we will take the production of deformed PC steel bars as an example.

The five types of steels with the compositions shown in Table 1 are cooled before finish rolling during hot rolling, the material temperature at the finishing inlet is 830°C, the finish rolling is made into a wire rod of 7.5 fiφ, and then this is forced. It was rapidly cooled to 650'C by water cooling.

This was spread out into a ring shape using a laying cone on a conveyor, and while being transported at a speed of 0.4 m/scc, it was controlled and cooled by blast air having a cooling capacity of about 10°C/scc. Conveyor length is 40m1 Cooling time is 100'C
/scc.

For comparison, four of the five steel types (A, aD, E)
The samples were cooled under the same conditions as above except that cooling was not performed during rolling and the adjusted cooling start temperatures after rolling were 850°C and 650°C. Table 2 shows the mechanical properties and scale thickness of the wire after the above treatment.

Table 1 Based on the present invention, the present invention f11 (subscript 1), which was subjected to water cooling during rolling and quenched after rolling to perform adjustment cooling, had small tensile strength and reduction of area.
The scale thickness is also extremely thin, but in the comparative example, water cooling was not performed during rolling, so the mechanical properties were more unstable than in the f91J of the present invention.
In addition, wire rods whose cooling temperature after rolling exceeds the range of the present invention (those with subscript 3) have particularly low tensile strength and scale thickness that is 4310 times that of the example of the present invention.Next, these wire rods are Using a roller die (2 sets/tandem) with the scale still attached, the machining speed was 90 my, participle lubrication, and cold rolling from 7.5 circle φ to 7.2811111 φ was carried out with subscript 2 of the present invention example and comparative example (after rolling). All wires with a cooling temperature within the range of the present invention were successfully drawn using a roller die with the scale still attached.

The well-drawn wire was cold-processed into an irregular shape (oval shape), and then tempered using high frequency (250 KW, 3 KH2) (450'C). Approximately 5 on the output side of the high frequency coil
Place the spinner type straightener at position m, and make sure the wire is bent 6.
Correction processing was performed so that the distance was within 1.1/1.5 m. The inlet temperature of the straightener was 440°C. The process from roller die wire drawing to warm straightening was carried out in one continuous line, and the line speed was 90 m/f+. The mechanical properties and other properties of the wire after warm straightening are shown in Table 4.

Table 4 * (1) Raise the temperature to 180°C in 4 hours and hold for 3 hours,
Cool slowly for 16 hours.

(2) The relaxation value of the 335 C quenched and tempered material is 16.0%.

The above table shows that cooling before finish rolling in hot rolling according to the present invention is effective in improving the properties of the material after martensite formation through refinement of the structure and stably obtaining martensite. I understand. In addition, by subjecting the wire manufactured according to the method of the present invention to tempering and full correction between I and IA,
It is clear that good mechanical properties and excellent relaxation properties are ensured.

As is clear from the above explanation, 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. can be placed on one continuous line, and therefore, the present invention has a remarkable effect on improving the manufacturing efficiency and reducing costs of high-tensile wire rods used as PC steel bars and the like.

Continuation of page 1 0 shots clear by Takuo Mizoguchi 1 Konibi-cho, Kokura Kita-ku, Kitakyushu City Sumitomo Metal Industries, Ltd. Kokura Steel Inside the office 0 shots: Shoji Nishimura 1 Konibi-cho, Kokura Kita-ku, Kitakyushu City Sumitomo Metal Industries, Ltd. Kokura Steel Inside the office 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 (3)

[Claims] (1) GO, 10-0640%, Si 0.05
~1.50%, Mrlo, 70~2.50%, Cr
0.10-1.50%, 86.0002-0.005
0% and TiO,0050~0.050% and Ag
A steel wire rod containing one or both of 0.007 to 0.050%, with the remainder consisting of Fe and unavoidable impurities, is hot rolled. It is cooled to 900°C, and after finish rolling, it is rapidly cooled to a temperature of 700°C or less to form a suitably cooled 1-stenite state, and then converted to martensite by controlled cooling, and then stretched with a roller die without descaling. Method 0 for producing high tensile strength wire rod characterized by wire (2) The method for manufacturing a high-tensile wire rod according to claim (1), characterized in that a deformation force R process is performed after wire drawing. (3) The method for producing a high-tensile wire rod according to item (1) or item (2), characterized in that tempering and warm straightening are performed after wire drawing or shaping.