JPS583929A - Manufacture of steel wire rod - Google Patents

Abstract

PURPOSE:To prevenet the breaking of a steel wire rod in a drawing stage by manufacturing a rough steel wire rod by hot rolling and by regulating the remp. and cooling rate of the rod after passing through the final rolls. CONSTITUTION:A steel contg. 0.4-1.5wt% C, 0.1-0.4wt% Si and 0.1-1.5wt% Mn as basic components or contg. further 1 or >=2 kinds of elements selected from Cu, Ni, Cr, Mo, W, Co, Al, V, Nb, Ti, Zr and B is hot rolled to a rough steel wire rod, and by regulating the temp. and cooling rate of the rod after passing through the final rolls, a metallic structure contg. <=90% by area in total of ferrite and pearlite at ordinary temp. is provided. The rod is then spheroidized at 750 deg.C for 6hr to enhance the toughness, and the occurrence of breaking due to surface cracks during drawing is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a steel wire rod with excellent breakage resistance during wire drawing.

There are many types of steel wire rods, ranging from low carbon steel wire rods to medium and high carbon steel wire rods, and even alloy steel wire rods. It is manufactured by rolling and then annealing it into a spheroid.

Then, this steel wire rod is usually drawn into a steel wire by a wire drawing process. However, in the above wire drawing process,
Minute surface flaws that occur during hot rolling or during the transportation of wire rods can lead to breakage, and the occurrence of such breakage significantly reduces the efficiency of the wire drawing process. Conventionally, countermeasures against the above-mentioned surface flaws have been taken, such as inspecting the entire length using inspection methods such as eddy current flaw detection, and removing surface flaws using surface solvents, surface peeling, etc. However, it is difficult to completely remove minute surface flaws. In addition, if such measures are taken, steel wire manufacturing costs will be reduced because wire drawing operations will have to be temporarily interrupted when surface flaws are discovered, and yields will decrease due to surface solvents. It had the problem of rising. Therefore, there has been a desire to develop a steel wire rod that is less prone to breakage during wire drawing even if the degree of surface flaws is the same. Few methods have been proposed to reduce the occurrence of wire breakage during wire drawing in the presence of flaws.

Therefore, the present inventors focused on reducing the occurrence of breakage during wire drawing by increasing the toughness of the steel wire rod, and as a result of various experimental studies, the toughness of this type of steel wire rod is as follows.
It was confirmed that the evaluation could be made by measuring the fracture deflection by the press notch bending test as shown in Figures 1 and 2, and further experiments were carried out with the aim of developing a steel wire rod with a larger fracture deflection. It was completed. In addition, in Fig. 1 and Fig. 2,
1 is a test piece, 2 is a suppressor, 6 is a support, and 4 is a notch formed in the test piece 1.

This invention was made by paying attention to the conventional problems mentioned above.As mentioned above, a steel wire rod with a larger breaking deflection was developed, and this steel wire rod was drawn into a steel wire. The purpose is to reduce the occurrence of breakage during the process.

This invention provides C: 0.4 to 1.5if, 5l-0,
When manufacturing a steel wire rod by hot rolling using steel with a basic composition of 1 to 0.4 weight %, Mn: 0.1 to 1.5 weight %, and further containing appropriate alloy components according to demand. ,
By adjusting the temperature and cooling rate of the steel wire material after passing through the final roll in the hot rolling (at this time, if necessary, the steel wire material after passing through the final roll may be heated to a transformation temperature of 7.
By reheating to 1J or more and adjusting the temperature and cooling rate, the metal structure of the steel wire material at room temperature is adjusted so that the total area ratio of ferrite + pearlite is 90J or less, and then spherical It is unique in that it is made to resemble a bowl of rice from the northern capital.

The steel wire rod according to the present invention contains C: 0.4 to 1.5% by weight.
, 81: 0.1-0.4 weight, Mn: 0.1
The basic composition is ~1.5wt%, and further contains appropriate alloying elements as necessary, such as ordinary carbon steel wire rods (hard steel wire rods, spring steel wire rods, carbon steel wire rods for cold heading). etc.) and alloy steel wire rods (including spring steel wire rods, heat-resistant steel wire rods, iron-chromium heating wire rods, etc.).

Among the above chemical components, if the content of C is less than 0.4% by weight, the necessary strength as a steel wire cannot be expected;
．． If the content exceeds 5% by weight, a large amount of reticular cementite will be produced and the toughness will be significantly impaired, so the content was set at 0.4 to 1.5% by weight.

Further, in order to sufficiently deoxidize and obtain defect-free steel in steel manufacturing operations, it is necessary to contain Si in an amount of 0.01% by weight or more. However, even if it exceeds 0.004% by weight, the deoxidizing effect reaches a saturated state, so the Si content for the purpose of deoxidizing is set to 0.1 to 0.4% by weight as a basic component of steel.

Mn is an effective element for improving the hardenability of steel, as well as improving its strength and toughness, but the effect cannot be obtained if it is less than 0.1% by weight. Moreover, if it exceeds 1.5% by weight, there is a risk of uneven strength due to segregation during agglomeration, so the basic component of the steel is set at 0.1 to 1.5% by weight.

In addition to the basic ingredients, 81. Cu.

Ni, Cr Mo, W, (:o, A
t+V*Nb+Ti, Zr tB, etc. 1
A species or two or more species can also be included.

Among these, Si is an effective element for increasing the tempering softening resistance and flattening resistance of steel, and especially in the case of spring steel wire rods, Si should be contained in an amount exceeding the amount required for deoxidation. is desirable. However, if the content is too large, it becomes extremely brittle, so it is preferable to set the upper limit to 3 weight t%.

When Cu is contained in an appropriate amount, it increases the strength of the steel by precipitation hardening, but if it is too large, it significantly impairs hot workability, so the upper limit is preferably set to 0.5% by weight.

N1 is an element that helps improve the toughness of steel, but if it is too large, austenite will become unstable and yield strength will be insufficient, so the upper limit should be 3% by weight.

Cr is an effective element for increasing the hardenability and strength of steel, but too much Cr makes the steel brittle and impairs hot workability, so the upper limit is preferably 2% by weight.

Mo is an effective element for increasing the hardenability and strength of steel, but its effect reaches saturation when it exceeds 1.5% by weight, and if it is contained more than that, it will actually impair the hot workability of steel. , the upper limit is preferably 1.5% by weight.

W is an effective element for increasing the strength of steel, but too much W impairs hot workability, so the upper limit is set at 1.
The content is preferably 5% by weight.

Co is an effective element for increasing the temper softening resistance of steel, but if it exceeds 2% by weight, its effect reaches saturation, so the upper limit is preferably 2% by weight.

Furthermore, kt and V, Nb, Ti, Zr
is an effective element for promoting spheroidization in the spheroidizing annealing after rolling by refining crystal grains during the rolling process and refining pearlite produced by Ar3 transformation. At this time, if the At content is too large, large alumina-based inclusions will be formed, resulting in a decrease in fatigue strength, so it is preferable to set the upper limit to 0.033% by weight. Also, V, Nb.

'['t, When containing Zr, it is best to contain it within a range where the above-mentioned effects are saturated; therefore,
The upper limits of V, Nb, Ti, and Zr are each set to 0.1
% by weight, and preferably regulates V+Nb+Ti +Zr<0.3% by weight.

Next, when producing a steel wire rod by hot rolling using steel containing the above basic composition and appropriate additive elements as necessary, the temperature and cooling of the steel wire material after passing through the final roll in the hot rolling and the cooling By adjusting the speed, the metal structure of the steel wire material at room temperature was adjusted so that the total area ratio of ferrite and pearlite was 90% or less, and then spherical Hokuto annealing was performed. The metal structure of the wire material at room temperature is 90% or less of ferrite and pearlite in the area ratio Wall, and martensite,
If one or more of bainite and retained austenite is contained in a proportion of 10% or more, then the toughness of the steel wire rod can be significantly improved by performing spheroidizing annealing. It's for a reason. At this time, ferrite pearlite is 90% or more, martensite,
When the amount of one or more of bainite and retained austenite is 10 or less, the above-mentioned effect on improving the toughness is not seen much. In addition, by adjusting the m1f and cooling rate of the steel wire material after passing through the final roll during hot rolling, the metal structure of the steel wire material at room temperature can be changed to ferrite +
In order to reduce the pearlite to 90 cm or less, if necessary, the steel wire material after passing through the final roll may be reheated to a temperature higher than the Aca transformation temperature, and then the cooling rate may be adjusted. The toughness of steel wire can be significantly improved.

Next, examples will be described.

[Example 1] Steel having the chemical composition shown in Table 1 is melted in a high-frequency induction furnace and then formed into an ingot. After heating these steel ingots to the heating temperature also shown in Table 1, rolling is started, and then finish rolling is carried out. The temperature was set as shown in Table 1, and the temperature and cooling rate after the steel wire material passed through the final roll were adjusted so that the metal structure of each steel wire material at room temperature became as shown in Table 1. did. Next, the obtained steel wire material was heated at 750℃ for 6 hours.
A steel wire rod was manufactured by performing spheroidizing annealing under the following conditions.

Next, test pieces 1 shown in FIGS. 1 and 2 were cut out from each steel wire rod. The dimensions of test piece 1 at this time are the diameter (
I)) is 7 ura, length 100w+m, and θ of notch 4
=60°, H=0.2 wn XR=0.02 +
nm, and was set to L-8011III+, and a press notch bending test was conducted using the suppressor 2. The results are also shown in Table 1.

In Table 1, when the metal structure of the steel wire material at room temperature after passing through the final roll is 100% ferrite + pearlite, as in sample material AI, the toughness of the steel wire material after spherical Hokuto annealing is is quite low, and the amount of deflection at break is also small. In addition, when the cooling rate of the steel wire material after passing through the final roll is slightly increased to reduce the sum of the haze ratio of ferrite + pearlite to about 95%, as in sample material A2, the amount of fracture deflection is also slightly increased. However, with this level of toughness, there is a sufficient risk that breakage will occur during wire drawing. On the other hand, as in specimens 53 to 6, the cooling rate of the steel wire rod after passing through the final roll is further increased so that the total area ratio of ferrite + pearlite is 90% or less, and martensite, If the total area ratio of one or more types of bainite and retained austenite is relatively increased, and then spherical Hokuto annealing is performed, the amount of deflection at break is considerably large, resulting in excellent toughness. Therefore, no breakage occurs during wire drawing. moreover,
When the steel contains an appropriate amount of Nb or V, the toughness of the steel wire can be further improved, and in the case of sample material A8, no breakage occurred in the press notch bending test in this example.

[Example 2] Steel having the chemical composition shown in Table 2 was melted in a high-frequency induction furnace and then formed into ingots. After heating these steel ingots to the heating temperature also shown in Table 2, rolling was started, and then finish rolling was carried out. The temperature was set as shown in Table 2, and the temperature and cooling rate were adjusted after the steel wire material passed the final goal, so that the metal structure of each steel wire material at room temperature became as shown in Table 2. I made it. Next, the obtained steel wire material was subjected to spherical drilling under the conditions of 750° C. for 6 hours to produce a steel wire rod.

Next, the same test piece 1 as in Example 1 was prepared from each steel wire.
A press notch bending test was conducted using the press notch bending test. The results are also shown in Table 2.

As shown in Table 2, almost the same results as in Example 1 were obtained for the spring steel wire containing about 2% Si by weight. In addition, experiments were also conducted on steel wire rods containing Cr and Bl, and similarly good results were obtained.

[Example 3] Steel having the chemical composition shown in Table 3 was melted in a high-frequency induction furnace and then formed into ingots. After heating these steel ingots to the heating temperature also shown in Table 3, rolling was started, and then finish rolling was carried out. After setting the temperature as shown in Table 3 and passing the steel wire material through the final roll, each steel wire material was heated to the re-extraction temperature IW also shown in Table 3, and the subsequent cooling rate IW was adjusted, The metal structure of each steel wire material at room temperature was made to be as shown in Table 3. Next, the obtained steel wire material was heated at 750°C for 6 hours.
A steel wire rod was manufactured by performing spherical cross-polishing under the conditions of r. Next, the same test piece 1 as in Example 1 was prepared from each steel wire and subjected to a press notch bending test. The results are also shown in Table 3.

As shown in Table 3, the steel wire material after passing through the final roll is
Even when the material was reheated to a temperature higher than 3 transformation temperature, almost the same results as in the above example could be obtained.

As explained above, according to this invention, C: 0
．． 4 to 1.5 weight, st: o, t to 0° 4% by weight
, Mn: When manufacturing a steel wire rod by hot rolling using a steel having a basic composition of O01 to 1.5% and further containing appropriate alloy components as necessary, the final roll passing in the hot rolling By adjusting the temperature and cooling rate of the subsequent steel wire material, at this time, if necessary, by reheating the steel wire material after passing through the final roll above the transformation temperature and adjusting the temperature and cooling rate. , the metal structure of the steel wire material at room temperature is ferrite +
Since the pearlite content is 90% or less, and then spherical Hokuto annealing is performed using the usual method, the toughness of the steel wire rod after spherical Hokuto annealing can be significantly increased, and the amount of fracture deflection of the steel wire rod can be significantly reduced. It has the very excellent effect of significantly reducing the occurrence of breakage during wire drawing by increasing the amount of breakage deflection.

[Brief explanation of drawings]

FIGS. 1 and 2 are an explanatory diagram showing the implementation status of the press notch bending test method used for evaluating the toughness of steel wire rods, and an enlarged explanatory diagram of the notch of the test piece. Patent applicant: Daido Steel Co., Ltd.

Claims (1)

[Claims] (1) C: 0.4-1.5iiiL%, St:
When manufacturing a steel wire rod by hot rolling using steel having a basic composition of 0.1 to 0.4% by weight, By adjusting the temperature and cooling rate of the subsequent steel wire material, the metal structure of the steel wire material at room temperature is adjusted so that the total area ratio of ferrite + pearlite is 90% or less,
A method for producing a steel wire rod, characterized in that a spheroidizing annealing process is performed thereafter.