JPS60114517A - Production of steel wire rod which permits omission of soft annealing treatment - Google Patents

Abstract

PURPOSE:To produce a steel wire rod which has excellent cold rollability as hot rolled and eliminates the need for soft annealing in the stage of producing the steel wire rod by rolling a steel material by using a rolling mill, etc. constituted of specific disposition and limiting the conditions for rolling and cooling. CONSTITUTION:A billet contg. 0.10-0.90% C, 0.05-0.80% Si and 0.1-1.5% Mn or contg. further 1 or >=2 kinds among 0.1-1.5% Cr, 0.1-0.8% Mo, 0.1-1.5%Ni and 0.0002-0.005% B is worked by rough rolling and intermediate rolling to a rough wire rod. The rough wire rod is subjected to partial hot finishing at 1,200-850 deg.C with the 1st rolling mill to manufacture the semi-finished product of the steel wire rod. Such product is cooled in the temp. range of the Ms point of said steel -850 deg.C to maintain the structure at supercooled austenite and immediately thereafter the steel is finished to the wire rod of the final size at >=20% draft with the 2nd rolling mill disposed behind the above-mentioned mill. The finished wire rod is coiled and the coil is passed through a heat treating device and is thereby subjected to slow cooling and holding. The steel wire rod is thus produced without requiring the soft annealing stage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing steel wire rods, and in particular, to cold IJI+
] The present invention relates to a method for manufacturing a mechanical Ri7 hazardous steel wire rod using a direct softening treatment method that can omit the softening annealing treatment preceding step 2.

-ff is used for the tightening machine (1゛・'' used for automobile bolts, nuts, ronds, etc.) Carbon steel and alloy steel wires are hot-rolled and then subjected to softening annealing treatment. The hardness of the as-hot-rolled state is extremely IK.
< , If cutting, wire drawing, and cold hardening are performed as they are, tool life will be reduced, cutting efficiency will be reduced, IIJi? J, ¥i
This is because misalignment may occur. In addition, since it is hard, the processing load for J is extremely large, and it is not a scale that requires a large amount of power, but it causes a lot of wear and tear on expensive processing tools such as molds and dies, which is uneconomical. However, this softening annealing treatment requires high-temperature heating and long-term holding. therefore,
Implementation of this treatment not only requires expensive heat treatment equipment such as an IJII heat furnace, but also causes many losses in terms of negative sources such as scale + J' Vf and decarburization, energy, cost, and small quantity.

Therefore, US Pat. No. 3,231,432 and Japanese Unexamined Patent Publication No. 1983 disclose a method and apparatus for softening steel wire by utilizing heat retained during hot rolling to improve these losses. - (No. i 4416, JP-A-56-4
No. 1824, JP-A-56-41825, JP-A-56-
No. 84424, JP-A-56-84126, JP-A-56
-86619 and Japanese Unexamined Patent Publication No. 56-86620.

All of these disclose methods and equipment for controlling retained heat after high-speed wires (Oetsuma 14-: extension), and
This method is based on a method for uniformly and more advantageously realizing the cooling rate necessary for softening a steel wire after a specific hot rolling process. However, the performance after softening depends on the method of controlling the retained heat, and in this respect, the required performance has become stricter in recent years (for 12. It is becoming difficult to respond.

In general, during cold working, for example cold plating, low deformation resistance and high deformability are required. Deformation resistance can be solved by further promoting the softening process, but it is difficult to deal with the deformation resistance by simply making it soft.

This is because the deformability depends on the microstructure. That is, the finer the microstructure, the better the deformability. Therefore, in order to lower the deformation resistance and improve the deformability at the same time, the fineness of the microstructure should be adjusted to 1lal.
ia is essential.

Since the fineness of this structure is mainly controlled by the austenite grain size before transformation, control of the austenite grain size is most important. However, in the hot rolling of ordinary steel wire rods, dynamic recrystallization occurs because it is carried out at a high speed of 40 to 100 m/s and with a high area reduction ratio, so the austenite grain size is , S, A8~
] 0 and 113 are constant, making it difficult to control by rolling conditions). 7:C That is, as long as softening is promoted by controlling the degree of cooling after hot rolling, the fineness of the microstructure remains almost constant, and there is a limit to the shape of the shape that can be obtained. become. For this reason, wire rods that have been directly softened after hot working by the prior art have the disadvantage that they cannot withstand intense cold working and can only be used for very limited purposes. Therefore, customers need to use different materials depending on the degree of processing, and it is also necessary to install softening annealing treatment 1ii+ prior to cold working, which complicates the manufacturing process and is in an unfavorable situation in terms of management.

For this reason, there has been a long-awaited development of #i wire 1A that can withstand intense cold working and does not require softening annealing.

An object of the present invention is to solve the problems of the prior art described above and to provide a method for directly softening a steel wire that does not require softening annealing prior to cold working.

Therefore, as a result of repeated detailed research in order to achieve the above objective, the inventors of the present invention found that by using a borrowed equipment array in which steel materials are arranged at 1° and 11 fixed positions, and by limiting the rolling conditions and cooling conditions. It has been discovered that it is possible to advantageously produce a 4-wire steel sheet which does not require softening annealing and has excellent cold workability as it is hot I-rolled.

That is, the gist of the present invention is that 111.1g
(ii', and an example of a steel wire that has undergone intermediate rolling. 4) Partial hot finishing is performed at 1200 to 850°C in a rolling mill, and this rolled steel wire semi-finished product is then rolled at 850°C. It is cooled to a temperature of C or below and M8 point or above to maintain supercooled austenite, and then finished into a wire rod with product dimensions and shape at a reduction rate of 2G% or more in the @2 rolling mill located behind it. W that can omit the softening annealing process, which is characterized by winding it into a coil and passing the wound material through a heat treatment device.
4 line example jit! It's in the manufacturing method.

The method for manufacturing fjI4 wire will be described in detail below.

First, steel with a predetermined composition is melted to make a regular billet, and the long steel material that has undergone rough rolling and intermediate rolling is sent to the first rolling mill for 12
0 (partial hot finishing at 1 to 850" C.) This process results in 1.5 cases having the chemical composition of the present invention.
The austenite grains are refined by recrystallization, and as described below, a steel wire having excellent cold workability can be easily formed by cooling, using a H'S2 rolling mill, 1) rolling, and passing through a heat treatment device.

The austenite grains are recrystallized and refined by the first If rolling mill of the steel wire rod. Lowering the rolling temperature is effective in increasing this refinement, but due to the high speed and high area reduction rate, the current block mill type double rolling mill cannot perform rolling due to the heavy load. For this reason, it is necessary to roll at a temperature of 850'C or higher. Below 850'C, the deformation resistance of the rolled material becomes significant, and the temperature of the rolled material is maintained at 850'C or lower due to the temperature rise due to the heat of rolling. That is difficult.

Furthermore, in order to carry out the present invention advantageously, it is not preferable to use high-load rolling mills capable of low-temperature rolling as both the first rolling mill and the second rolling mill, as this would result in significant equipment costs. Therefore, as long as the first rolling mill is capable of rolling at 850° C. or higher, a conventionally used block mill for wire rods or the like may be used, eliminating equipment costs and providing great benefits. Note that the upper limit of rolling humidity in the first rolling mill is 1200″C.
The reason for this is that when this temperature is exceeded, austenite, which has been once refined by rolling, immediately becomes coarse.

Next, the rolled wire semi-finished product is subsequently rapidly cooled to 850"C to I4s point using a cooling device having a cooling capacity to maintain substantially supercooled austenite up to a temperature of M8 point or higher. This step is carried out in the second step. This is extremely important in increasing the effect of rolling in the rolling mill.In other words, the austenite grains in the wire rod that have gone through the first rolling mill have become sufficiently fine due to recrystallization, but if left as is, they will gradually become smaller over time. This causes grain growth, so rapid cooling is performed to prevent this.Also,
Dynamic recrystallization occurs in many cases during high-temperature, high-strain rolling such as hot rolling on the wire side, and each recrystallized grain has a high dislocation density and accumulates a large amount of working strain.

Since this strain rapidly attenuates after rolling, it is necessary to prevent release of strain as much as possible by rapid cooling in order to effectively utilize it in subsequent processes.

In copper, which is the object of the present invention, recrystallization coarsening and strain release are almost completely suppressed at temperatures below 850'C, so the upper temperature limit for rapid cooling is set at 850'C.

The lower limit temperature for rapid cooling was set to be above the Ms point because supercooled austenite transforms into martensite when it falls below the M8 point, making processing in the subsequent process impossible.

The above cooling can be achieved with a uniform and rapid cooling device such as a spray pipe. Therefore, it can be realized very easily and advantageously by improving the cooling capacity of the conventional water cooling device a and the like.

Next, the wire (e) having fine and uniform supercooled austenite that has gone through the above steps is rolled into a predetermined size and shape at a downstream rate of 20% or more in a second rolling mill located behind the cooling device 1N. The wire is finished.At this time, the number of stands used, the amount of reduction, and the cooling between the stands are adjusted so that the paper temperature does not exceed 1'F and 850C due to the accumulation of processing heat.

The main role of rolling in this second rolling mill is to further process the fine and uniform supercooled austenite so that all the processing strain is accumulated in the form of deformation bands at the austenite grain boundaries and inside the grains. This essentially makes the austenite grains finer and provides lower deformation resistance and improved deformability necessary for cold working.

Direct softening treatment method using hot rolling heat heat +1 + J0:
.

After rolling, it is slowly cooled to form a soft ferrite/pearlite structure. Therefore, if the cooling rate during the transformation process is constant, the finer the austenite grains, the more
In addition, the accumulation (!1.L) in the austenite grains increases, the higher the transformation rate, and the faster the transformation rate and the formation of a microstructure. It is faster and the deformability is improved.

In the case of normal rolling, the austenite becomes ro crystal grains, and ferrite/pearlite nuclei are mainly generated at austenite grain boundaries, whereas in austenite grains subjected to rolling in the second rolling mill, recrystallized grains form. is further elongated and a deformation zone that becomes a transformation nucleus is introduced within the grain, so the number of ]-lite/pearlite nuclei increases significantly. In addition, since processing causes W fit of grain boundary energy and strain energy within grains, diffusion of carbon atoms Wi 1. which plays a dominant role in the growth process of ferrite and pearlite. tC increases rapidly, and softened ferrite and pearlite are rapidly formed.

As a result, when subjected to rolling in the second rolling mill, it easily becomes a fine ferrite/pearlite R-11 weave, giving it excellent cold workability.

In the present invention, the lower limit of the rolling reduction of the second rolling mill is set to 20%.
The reason for this limitation will be explained using the following example of actual pieces.

3450 and 50M435 steel billets at 1200°
The first rolling mill (10 stands, process mill) heats the rolled and intermediate rolled steel products to 1000°C to 900°C, and then heats the rolled and intermediate rolled steel products to 1000°C to 900°C. After passing the half-finished wire side product through a water-cooled spray pipe and rapidly cooling it to 700"C, it was continued to be heated to V-
H, 2nd rolling mill consisting of 2 stands G trowel 0-4.0%
After changing the downstream rate and finishing the wire rod with a product size of 9 rnsφ, it was bundled into a non-concentric coil using a winder and passed through a continuous slow cooling furnace at a cooling rate of 0.25"C/S. .The relationship between the cross-sectional shrinkage rate and the downstream rate in the second rolling mill at this time is shown in Figure 1.

As can be seen from FIG. 1, when the L-E reduction ratio is 20% or more, the cross-sectional shrinkage ratio increases rapidly, but when it is less than 20%, there is almost no effect. This is because the processing strain introduced into the austenite grains is too small, resulting in little accumulation of grain boundary energy and strain energy within the grains, and the introduction of deformation bands that become ferrite-pearlite transformation nuclei hardly occurs, resulting in substantial austenite grains. This is because the miniaturization effect is small.

Then, after passing through the second rolling mill, the coil has 51! After passing through a winding machine, the rolled material is passed through a heat treatment device to form a #;l material that does not require softening annealing treatment. In this case, the winding machine for bundling into a fill is a machine that bundles the rolled material having a predetermined size on the 21st IE rolling mill and facilitates subsequent processing, and an existing winding machine can be used. The heat treatment equipment ft performs either slow cooling, holding (-) or heating.
jl! This is to obtain a softened ferrite/pearlite structure, and can be achieved with commonly used continuous annealing furnaces.

As mentioned above, the method of the present invention has superior deformability and deformability (J) compared to the conventional method, and can advantageously produce wire rods that do not require softening annealing treatment and have a low resistance, without requiring large-scale modification of conventional equipment. Can be manufactured without reducing productivity.

Note that the composition of the steel wire examples targeted by the method of the present invention is not particularly limited;
It can be applied to ordinary wires such as Alloy 91 (OI), which are used as component yarns for various purposes.

However, the essential components for steel wire rods and the components added as necessary need to be adjusted according to various uses and product characteristics. The following is a rough guideline for this purpose.

C is an effective element for improving the hardenability of steel and easily increasing its strength, and is actively added, but if it is less than 0.10%, the effect will be small, while if it exceeds 0.90%, Hardenability increases excessively, cold workability deteriorates, and direct heat transfer treatment becomes difficult under the limited conditions of the present invention, so
It is desirable to set it in the range of %.

Si promotes deoxidation and increases strength, so it is an effective element like 0, but if it is less than 0.05%, its effect is small, and if it exceeds 0.80 fo, hardening will be significant.
Since it impairs cold workability, a range of 0.05 to 0.80% is desirable.

Mn has the effect of improving hardenability and increasing strength.

Therefore, it is actively added, but if it is less than 0.1%, its effect is insufficient, and if it exceeds 1.8%, the hardenability becomes too high. A range of 0.1 to 1.8% is desirable because excellent cold workability can be obtained and the content is low.

Machine j
R is the basic component of steel for building, but O is added as necessary.
The objects of the present invention can be achieved equally or much better in a class containing one or more of the following r, Mo, Ni, and B at the same time.

Cr has the effect of improving hardenability and increasing strength, but if it is less than 0.1%, the effect is small;
If it exceeds 0.1 to 1.0, the hardenability will increase excessively and cold workability will deteriorate under the limited conditions of the present invention, so the range is set to 0.1 to 1.
It is desirable to set it to 5%.

MO has the effect of improving hardenability, but at 0.1t1
If it is less than 0.8%, the effect will be small, but if it exceeds 0.80%, hardening will be significant due to an increase in hardenability, impairing cold workability, so it is desirable to keep it in the range of 0.10 to 0.80%. .

Ni is an effective element for improving hardenability, but 0
．． If it is less than 1%, there is no effect, and if it exceeds 5%, the hardenability becomes too high and the cold workability is impaired.
It is desirable to keep it in the range of 1.5%.

B has the effect of increasing hardenability, but if it is less than 0j1002%, the effect is small, and if it is less than 0.005%, ductility is significantly inhibited and cracks occur during hot rolling. It is desirable that the content be in the range of .0002 to 0.005%.

(Example) Next, examples of the present invention will be described.

3450, SMr, 443,5Or440 and IS
The first rolling mill (stand 10 units, block mill)
The rolled wire rod semi-finished product was cooled in a water-cooled spray pipe and rapidly cooled to 7UO'C, followed by a second rolling process (!4) consisting of a V-H2 stand.
After finishing it into a 9 m length H with a rolling reduction rate of 30%, wind it up (at ・4, wind the coil in a circular shape between the valves, +1.2 ~
The sample was passed through a continuous annealing furnace at a cooling rate of 0.8''C/S.

On the other hand, as a comparative example, when producing 1 plJ of each of the above-mentioned drawings by the above-mentioned method, the second rolling mill was finished to a 9-square diameter portion in the first rolling mill without any rolling, and then water-cooled. After being passed through a spray pipe and rapidly cooled to 700'C, it is bundled into a non-concentric coil using a winding machine.
0.8 'C/S cold man 1? It was passed through a nakazuki slow cooling furnace at Jj degrees.

Their mechanical properties Tt are shown in Table 1.

Table 1 shows that the hardness and tensile strength of Inventive Example 1 (x 1 and Ib 8) were softened to the same extent as those of Comparative Examples IG 2 and A4, but the cross-sectional shrinkage rate was considerably higher. , the ductility is significantly improved.

In addition, the hardness and tensile strength of the side bending 5 and flat 7 of the present invention are low;
The softening progressed sufficiently and the cross-sectional shrinkage rate was high, both of which were superior to Comparative Examples A6 and A8.

As described above, by the second rolling (multi-rolling), it is possible to economically produce a 9゛1 wire rod, which is soft and has high ductility and does not require a softening annealing treatment, without impairing production efficiency.

As is clear from the detailed description above, according to the present invention, there is no need to perform softening annealing, which is accompanied by numerous problems, prior to cold working, and excellent cold workability can be achieved as hot rolled. The contribution made by this is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the rolling reduction in the second rolling mill used in the method of the present invention and the cross-sectional shrinkage rate during a tensile test. Patent applicant: Kawasaki Steel Co., Ltd. Representative patent attorney: Hide Sugimura H:,”5゜l H
', )・°, 1-

Claims (1)

[Claims] L 61 wire rod that has undergone rough rolling and intermediate rolling is partially hot-rolled at 1200 to 850°C in a first rolling mill,
This rolled 11f! iI'A semi-finished products were subsequently manufactured at 85
It is cooled to a temperature below 0°C and above the MS point to maintain it as supercooled austenite, and the second rolling mill located behind it finishes it to the line side of the product dimensions and shape at a reduction rate of 20% or more. , the winding example is wound into a coil, and the softening annealing process is omitted by passing the coiled example through the inside of the heat-treated casting. , 00.10~+1 , 90
%, Si 0.05-0.80%, MnO,1--1
, 5%, with the remainder consisting of PE and unavoidable impurities. .90%
, SiO, +15-0.80%, gnO,1-1,
, 5%, and further contains Oro, 1 to 1.5, MO0,
1-0.8%, N1-o, 1-1.5%, ) 30.00
02 to 0.005% σ] contains one or more I7j or two or more, and the remainder f'flKh' Fe and 'l'
Claim 1ir4 [Itt (method according to the first aspect).