JPS6021327A - Production of wire rod permitting quick spheroidization - Google Patents

Abstract

PURPOSE:To produce a wire rod which permits quick spheroidization in finish rolling of a steel wire rod by rolling the wire rod with the 1st finishing mill then cooling quickly the wire rod to a specific temp. and cooling the steel to cause transformation while said steel is kept applied with specific plastic strain with the 2nd finishing mill. CONSTITUTION:A steel wire rod is rolled with the 1st finishing mill and is then quickly cooled to a temp. range of 500-850 deg.C in the stage of forming the steel wire rod to a rod material by hot rough rolling and intermediate rolling then subjecting the same to finish rolling. The rolled steel is then applied with plastic deformation in a 20-80% range with the 2nd finishing mill and while the plastic strain is maintained, the steel is cooled to cause transformation so that fine pearlite, bentonite or martensite exists mixedly in the finely dispersed proeutectoid ferrite. The wire rod permitting easy spheroidization in the succeeding stage is thus obtd. The wire rod has the component compsn. consisting of 0.10- 0.70% C, 0.10-1.50% Si, 0.30-1.80% Mn and the balance Fe and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an fRa method for α-wire resistant material by hot rolling,
Specifically, by controlling the process of hot rolling steel wire rods, we manufacture hot rolled materials that can be quickly and effectively subjected to spheroidizing heat treatment, which is performed prior to the next cold working process. Regarding the method, the 0'/A wire rod after hot rolling,
Most of the material is subjected to cold processing such as drawing, cutting, machining, and forging, but conventional hot rolled materials generally lack the deformability to withstand these cold processings and Because of the high resistance, the hot-rolled material cannot be subjected to cold working.

In other words, after drawing a wire of 20 inches or more to a hot-rolled material, a spheroidizing heat treatment that requires a processing time of over 20 hours is applied to improve the performance of the hot-rolled material. Subjected to cold processing. However, performing these additional processing and heat treatments has the problem of wasting a large amount of thermal energy and processing time, and furthermore, scale loss is unavoidable.

Various proposals have been made to address these problems.

For example, the method disclosed in JP-A No. 47-8508 passes through the transformation region immediately after hot rolling, and is sufficient to suppress the formation of austenite crystal grains and the formation of pro-eutectoid ferrite. A method for obtaining a hot-rolled material having a +fi & fine pearlite, bainite or martensitic structure by cooling at a high speed, and for processing alloy steel, following the step of forming fine austenite particles after hot rolling, marten This is a method of obtaining a hot-rolled material by applying forced ventilation to promote the formation of sites, and then subjecting it to a spherical ratio treatment. In short, these methods simply utilize the austenite grain size after hot rolling to obtain a structure that actively transforms at low temperatures, such as a fine pearlite, bainite, or martensitic structure that is free of pro-eutectoid ferrite. However, these methods do not sufficiently reduce the austenite grain size, so they are not effective in shortening the spheroidization processing time, and the strength obtained after the spheroidization processing is lower than that of conventional wire drawing processing. It has disadvantages such as higher strength than that obtained after spheroidization treatment and high deformation resistance during cold working.

In addition, a proposal similar to this proposal was made in JP-A-51-9.
2719. It is a method for obtaining a hot-rolled material having an intermediate structure by rapidly cooling the alloy flN to a temperature within a humidity range of 550°C to M [1 point] after hot rolling.
Next, a spheroidization process is performed. However, this method also aims only at obtaining a simple bainite structure, and it is extremely difficult to obtain a single bainite structure under the disclosed conditions, and the strength obtained after spheroidization is also poor. However, there are drawbacks such as higher strength than that obtained after wire drawing as in the past.

Therefore, the present inventors proposed various proposals including the above-mentioned various proposals.
In the spherical f-ratio processing performed with
In order to obtain a hot-rolled material that can promote Wj in ν and also has a low strength after spherical ratio treatment, it was found that the plastic strain caused by "gap" rolling was reduced during cooling. Key points 1Jji
Various sets obtained by effectively utilizing behavior 4
I came to the conclusion that there is a relationship between R1f and spheroidization,
4.11 to 1u (as a result of the investigation, the hot 711 strain was maintained: 4: The structure changed to mapperite, beinite, and martensite shows that the formation of pro-eutectoid 7 erite is (゛) Regardless of G, the speed of Europeanization is fast<, T:
It has been found that this is effective for f< shape ratios and can also lower the strength after spherical (Is treatment).

In other words, as a result of investigating the effects of the rolling temperature range and rolling reduction on the ball ゛IKits old shortening ratio, etc., After quenching the strip material rolled with the +lt5' fij hot rolling machine to a temperature above the Is point and below 850"C, a plastic strain of 20 modulus or more is subsequently applied, and the plastic strain is maintained. The tissue that has been cooled and transformed is
As mentioned above, it has been found that this process is extremely effective, as it facilitates spheroidization in the next step.

To explain this point in more detail, first, the austenite crystal grains that have been rolled and refined in the easy recrystallization region are immediately rapidly cooled and then turned into supercooled austenite or metastable austenite at temperatures above the MS point and below 850°C. rear,
A plastic strain of 20% or more is applied and immediately cooled while retaining the plastic strain to obtain a transformed structure while retaining the plastic strain.

Based on this knowledge, the present invention has materialized the above-mentioned manufacturing process by considering the arrangement of actual rolling equipment, workability, etc., and the gist thereof is to When final rolling is performed after hot rough rolling and intermediate rolling into strips, the first finishing mill is used to roll the strips, which are then rapidly cooled to a temperature of 500°C to 850°C, and then the second finishing mill is used to roll 20 strips. A plastic strain of 80 cm or less is applied, and the plastic strain is maintained while being cooled and transformed to form a set of fine pearlite, bainite, or martensite mixed with finely dispersed pro-eutectoid 7°ite. A method for producing a wire rod capable of rapid spherical ratio, characterized in that it obtains.

Hereinafter, the present invention will be described in detail using examples. First, the reason why each condition is regulated as described above in the present invention is as follows.

The equipment for carrying out the manufacturing method of the present invention needs to be arranged in such a way that a cooling process is performed before the final finishing mill. By the way, in the case of wire rod rolling, conventional rough rolling mills, first and second
If a rolling mill row consisting of an intermediate rolling mill and a finishing rolling mill is used, and the cooling process is simply placed before the finishing rolling mill, the rolling reduction Ijt up to the intermediate rolling mill will inevitably be limited. Naturally, the amount of reduction shared between the two increases, and as a result, the finishing temperature rises. On the other hand, in the case of a wire rod finish rolling mill, as the productivity increases, the allowable rolling load decreases, and rolling at a low temperature of 850° C. or lower is no longer possible under such a low rolling load.

Therefore, with the conventional arrangement of rolling mills in which a cooling step is placed before the finishing mill, it is not possible to roll large unit weight fills at high speed according to the present invention. Therefore, in the present invention, a finishing rolling mill is separately installed at a position following the cooling line installed at the rear of the normal finishing rolling mill, and the former is used as the first finishing rolling mill, and the latter is used as the second finishing rolling mill. This makes it possible to easily perform high-speed rolling at rolling temperatures above the MS point and below 850°C.Moreover, in order to create such a rolling mill row, it is necessary to simply add a second finishing mill to the conventional one. The rolling temperature before the second finish rolling, that is, the quenching temperature after rolling with the first finish rolling mill, is 500°C, which corresponds to the Ms point.
As mentioned above, the temperature should be 850°C or less.If the temperature exceeds 850°C, the temperature will easily rise to over 900°C by rolling, and the release of strain after rolling will proceed rapidly, making it difficult to utilize strain for transformation behavior. Further, when rolling at a temperature lower than 500°C, the rolling load becomes too large to be practical, and not only is it not very effective in shortening the spheroidization time.

The reduction ratio in the second finish rolling is 20 inches or more and 80 inches or less. Regarding this point, the present inventors conducted the following tests. Made of 50M435H, 600℃, 800℃
, the rolling reduction was varied over a wide range at each rolling humidity of 900°C.
Finish rolling was performed, and after rolling, the material was cooled at a cooling rate of 2 to 5 DEG C./S to obtain a hot rolled material, which was then subjected to a spheroidization treatment and the time required for spheroidization was investigated. The results are shown in FIG. The spheroidization time is expressed as a ratio of 1 when the rolling temperature is 800°C and the rolling ratio is 1.
The time from 70° C. to air cooling (A(E)) was defined as the riverization time.

As can be seen from the figure, when the downstream rate is less than 20 cm, ]°
No significant shortening of the time period was observed.

On the other hand, when the reduction rate exceeds 80 inches, the finishing temperature is 1-,
, because of IJl, the effect of shortening the spheroidization time does not increase, and on the contrary, the effectiveness decreases by one person.

Next, regarding cooling after rolling from 500°C to 850°C with the second finishing mill, from the viewpoint of effectively utilizing plastic strain for transformation behavior, it is preferable to immediately adjust cooling after applying plastic strain. Even if the amount of strain partially recovers after strain is applied, if most of the strain remains↓, the effect of effective utilization will not be diminished.In addition, strains that can have an effective effect on metamorphosis behavior are: Whether the strain is immediately introduced by plastic working or the strain that remains after partial recovery, the degree of effect on transformation behavior is the same. On the other hand, even at a rolling temperature of 500°C or higher and 850°C or lower, dynamic recrystallization occurs as the reduction amount increases, and it is particularly likely to occur on the high temperature side of the temperature range, and if too much strain is applied, the temperature rises. becomes larger, and n after applying strain
11 By the time the cooling starts, the material temperature has increased, so the strain release rate increases.

Therefore, during cooling, it is preferable to take such phenomena into account and appropriately determine the conditions for adjusted cooling. In addition, since the necessary amount of strain used for transformation behavior and the rate of strain release after applying plastic strain depend on the component system of the material, the amount of reduction applied in the temperature range of 500°C to 850°C in the second finish rolling. Regarding the rolling reduction ratio, it is preferable to adjust it to an appropriate i;t fit depending on the component system, taking into consideration the above-mentioned phenomenon.

The structure of the pressure abrasive obtained in the present invention is as follows (4,
This is 41 different from the conventional method of kumibope.

1!1111. , cooling in general? (It is known that 11 hours hardens and creates a fine structure, but it is possible to shrink the +4-shaped 11 hours, but if it is cooled too rapidly by 1flG, the i11 of bainite or martensite
It has the disadvantage that it becomes a single or composite structure and its strength increases after forming into a 34< shape. On the other hand, as in the present invention, 500°C
I-118! 'i The plastic strain obtained by rolling and cooling at a temperature below 0°C (7) is the pro-eutectoid
Due to the formation of iZ11g, slight i1[1 pro-eutectoid ferrite is uniformly dispersed, and due to the generation of pro-eutectoid ferrite (3 etc. are concentrated, and residual A-stenite with plastic strain maintained) is transformed into fine pearlite and bainite, or a structure in which martensite is partially mixed, that is, finely dispersed pro-eutectoid ferrite and fine ^, 1.
11 exhibits a mixed structure of pearlite, bainite, or martensite. In such a structure, even if pro-eutectoid ferrite is formed, it is finely fractured, and furthermore, the transformed structure of fine pearlite, bainite, or martensite is affected by processing strain before transformation. Therefore, it is possible to shorten the spheroidization time in the spheroidization process,
At the same time, the strength after spheroidization can be reduced to the same level as the conventional material which is subjected to spheroidization after stretching.

The /6P4 wire rod targeted in the present invention includes what is usually called a bar-in-coil, and the composition of the steel wire rod is not particularly limited.
It can be applied to various component systems used as ordinary wire rod products such as low carbon net, Kanko carbon steel, alloy C1, and poron steel. The ingredients to be added need to be adjusted depending on the various uses and product characteristics.The following are some rough guidelines.

C is a component necessary to obtain strength and has a content of 0. It is desirable that the content exceeds 0.70.1%. On the other hand, if the content exceeds 0.70.1%, the formation of ferrite, which is the main focus of the present invention and is promoted by low-temperature rolling in the second finishing mill, is reduced. However, it is not easy to do so, and there are certain difficulties in implementing the present invention.

Sl is 1g1! It is used as a deoxidizing agent to produce a completely killed tone, and is also an effective ingredient for increasing strength.
It is 91 preferable to contain 0.10 or more.

+1. If it is less than the IO ratio, deoxidation may be insufficient and bubbles and non-gold 1.1↓ inclusions may easily occur. On the other hand, excessive addition of Sl leads to poor weldability and the formation of S x Og yarn inclusions that are harmful to fatigue resistance.
(< Therefore, it is desirable to set the upper limit of addition to 1.50%.

In is a necessary component when considering hardenability, and +
IK of 1.80~tso%! It is preferable to add it within the range. 0.31) If it is less than 4, the hardenability may be insufficient and the material may become unstable; Exceeding so% tends to induce quench cracking.

As mentioned above, G, Si, and Mn are 1#, which is necessary from the viewpoint of fitii material manufacturing and product characteristics, but in addition, Cr5
It may be desirable to add one or more of Ni, Mo, and B as necessary to improve product characteristics. The guidelines at that time are as follows.

Or is a component that improves hardenability, and is preferably added when the necessary properties cannot be obtained due to insufficient hardenability with additives such as Mn, or when it is desired to further improve ductility and toughness. When adding 0%, it is desirable to range from 0.1θ to 1.50%; if it is less than 0.10%, it will be difficult to achieve the above objective, and if it exceeds 1.50%, the manufacturing cost will increase. It is an effective component in contributing to hardenability and improving ductility and toughness, and is also effective in improving hot workability, so it is added when the necessary ductility and toughness cannot be obtained by adding Mn etc. It is desirable to do so. When added, G is preferably in the range of 0.20-1.50%, and o
If it is less than 3 o'ly, it will not be enough to meet the above purpose.
If the ratio exceeds 1.50%, the manufacturing cost will increase.

MO is a component that significantly improves hardenability, but is an expensive component. Therefore, it is preferable to add it only when the necessary product characteristics cannot be obtained by adding In etc. alone. A range of 0.10 to O,SO% is desirable. 0. lO staff member! Now, the above-mentioned objective has been fully achieved. OB is a component that significantly increases the hardenability at a very shallow depth, and is a component that significantly increases the hardenability when it exceeds 0.50%. It is an element that improves hardness. When added, it is preferably in the range of 0003% to 0.005%. 0. f) If it is less than 0.003%, the hardenability will be sufficiently improved 7! [Z, conversely, 0. O
If it exceeds 05φ, not only will the austenite crystal g:
Besides, it also has low ductility and toughness.
Ru. Naturally, the effect of B on hardenability is
(To make 111, add b'r% of Al or T1.
In addition, it is desirable to fix N1/)0 (Example) JIS Standard 84, which is a typical steel type
501, S Or 440 H and 50M440H (their component compositions are shown in Table 1), 200
After melting in a ton converter, it is subjected to RH degassing treatment and continuous casting to form a square plume of 300 x 350 mm, and after a billet processing stage, it is rolled into a plume of 7 to 12 m according to the rolling conditions shown in Table 1.
In addition to examining the rolling structure of the obtained wire rod, a strength test was conducted on the wire rod after the spheroidization treatment, and the spheroidization rate was also examined. The results are not shown in Table 1.0 As is clear from the table, in the case of the conventional method in which wire drawing is performed before spheroidizing treatment (A), it takes a long time to spheroidize, and When the hot-rolled material is directly subjected to short-time spheroidization treatment (B) without wire drawing, not only is the spheroidization insufficient, but also the strength is increased. In contrast, in the case of the method of the present invention, the hot-rolled material has a structure in which fine pro-eutectoid ferrite is mixed with fine pearlite, bainite, or martensite, and this is shortened without wire drawing. By only performing the time spheroidization process, the sphericity ratio was the same as that of the conventional method, and the strength after spheroidization was also the same.

In addition, in this example, medium carbon mechanical structural carbon steel and alloy steel are shown as a representative type 1, but as mentioned above, the method of the present invention is applicable to C content higher than that of eutectoid steel in which pro-eutectoid ferrite does not form. Needless to say, the present invention can be applied to wire rod steel types other than steel, and the same effects as the present embodiment can be achieved.

As is clear from the above description, according to the present invention, the hot-rolled material as it is can be subjected to the spheroidization treatment without being subjected to wire drawing as in the conventional method. It is possible to significantly shorten the time and obtain a steel wire with a low strength equivalent to the strength after spheroidization obtained in the conventional process, so it is possible to reduce the scale associated with conventional wire drawing processing. Significant effects can be expected, such as extremely reduced loss, spheroidization processing that can be carried out in a short time, and improved productivity in the next step of cold working.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the rolling reduction in the second finishing mill and the spheroidizing treatment time.

Claims (1)

[Scope of Claims] L: When finish rolling a steel wire rod after hot rough rolling and intermediate rolling to sell it, the temperature after rolling in the first finishing mill is 500°C or more and 850°C or less. Cool rapidly,
After that, a second finishing pressure (jli 4', ti) gives a plastic strain of 20 to 80 inches, and while maintaining that plastic strain, it is cooled and transformed to transform the finely dispersed pro-eutectoid ferrite into fine pearlite and bainite. Or a method for producing a wire rod capable of rapid spheroidization, characterized by obtaining a structure containing martensite.z W4 wire rod has OO, 10 to 0.70%, Sin, 1
1. The method according to claim 1, which has a composition comprising 0 to 1.50% of In, 0.30 to 1.80% of In, and the balance consisting of Fe and unavoidable impurities. 8. Steel wire rod is 0.10~0.70%, Si0.1
0-1.50%, MnO, 30-1.80%, and further contains Or 0.10-1.50%, NiO,2
0-1.50chi, MoO, 10-0.50chi and Bo,
2. The method according to claim 1, which has a composition comprising one or more of the following: 0008 to 0=005%, with the remainder consisting of Fe and unavoidable impurities.