JPH04254526A - Manufacture of high carbon steel wire excellent in wire drawability - Google Patents

Abstract

PURPOSE:To obtain a high carbon steel having excellent wire drawability as hot-rolled by subjecting a steel constituted of a specified compsn. to hot rolling and thereafter executing cooling under specified conditions. CONSTITUTION:A steel contg. 0.9 to 1.3% C, 0.1 to 2.0% Si, 0.2 to 1.3% Mn, 0.1 to 1.8% Cr and the balance Fe with inevitable impurities is hot rolled, (1) is thereafter rapidly cooled to the temp. range from the Tc to the Tc-100 deg.C, is successively cooled in the temp. range till the completion of the pearlite transformation at <=8 deg.C/sec cooling rate, (2) is rapidly cooled to the temp. range from the Tc to the Tc-150 deg.C and is thereafter successively held till the completion of the pearlite transformation; where Tc( deg.C)=821-122.5[C%]+ 6.8[Si%]-25.3[Mn%]-5.6[Cr%].

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides excellent wire drawability for PC steel wires, rope steel wires, tire reinforcing steel wires, bearing steel wires, etc. as hot-rolled without heat treatment. ．．
The present invention relates to a method for producing a high carbon steel wire containing 9 to 1.3% C.

0002

[Prior Art and Problems] In order to reduce weight and improve fatigue properties, demands for higher strength of hard steel wire rods such as PC steel wires, steel wires for ropes, steel wires for tire reinforcement, and piano wire rods are increasing. ing. In order to increase the strength of such a steel wire, it is effective to increase the C content and add Cr as a component approach. This is because increasing C increases the amount of strong cementite,
This is also because Cr has the effect of narrowing the cementite spacing, which is a factor controlling the strength of the pearlite structure.

On the other hand, when C exceeds about 0.8%, the eutectoid C concentration becomes higher than that, and thus pro-eutectoid cementite, which deteriorates wire drawability, is likely to occur in the cooling process after hot rolling. Further, since Cr has the effect of shifting the eutectoid C concentration to the lower carbon side, in a steel wire having a eutectoid C concentration or higher, the amount of pro-eutectoid cementite increases as the amount of Cr increases. The pro-eutectoid cementite that precipitates at the austenite grain boundaries is not only harmful to the drawability of hot-rolled wire rods, but also requires a longer austenitizing treatment time to dissolve the coarse pro-eutectoid cementite during the intermediate or final patenting treatment. This lengthens the time and reduces productivity. For this reason, practical hard steel wire rods or piano wire rods naturally have limits on their C and Cr contents, and there is a limit to their ability to increase their strength.

Furthermore, for the above-mentioned reasons, high carbon chromium bearing steel specified in JIS G 4805 contains coarse pro-eutectoid cementite at austenite grain boundaries that deteriorates wire drawability and cold workability when hot rolled. is precipitated. Therefore, at present, it is necessary to perform spheroidizing annealing, which is costly and low in productivity, before wire drawing, so high-carbon chromium bearing steel that suppresses the formation of pro-eutectoid cementite and has excellent wire drawability as hot-rolled. line is requested.

[0005] Conventional knowledge for reducing pro-eutectoid cementite in high carbon steel wires containing Cr includes, for example, "Materials and Processes" Vol. 2.No. 6 (1989) of 1772
As described on pages 1-1775, low-temperature rolling and accelerated cooling are known to be effective. This is a technical idea of increasing the grain boundary area by making austenite grains finer by low-temperature rolling, thereby finely dispersing pro-eutectoid cementite, and suppressing the growth of pro-eutectoid cementite due to accelerated cooling.

[0006] However, low-temperature rolling has problems in that surface flaws in the hot-rolled wire rod increase and the durability of the hot-roll rolls decreases. Furthermore, although accelerated cooling is effective for steel bars with large wire diameters and slow cooling rates, in the case of wire rods with small diameters, bainite and martensitic structures are likely to occur, which deteriorate wire drawability, and the strength of the rolled material is also high. As a result, there is a limit to the application of low-temperature rolling and accelerated cooling techniques to steel wire rods, as the wire drawability deteriorates.

[0007] As described above, in the current state of the art, no sufficient method has been found for improving the wire drawability of a high carbon steel wire containing Cr as hot rolled.

[0008]

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned actual situation, and it is an object of the present invention to solve the problem of wire drawing that occurs during the cooling process after rolling when hot rolling a high carbon steel wire containing Cr. The object of the present invention is to provide a method for manufacturing a high carbon steel wire that prevents the formation of pro-eutectoid cementite that is harmful to workability and has extremely excellent wire drawability as hot rolled.

[0009]

[Means and effects for solving the problem] The present inventors have discovered that Cr
As a result of detailed analysis of the precipitation behavior of pro-eutectoid cementite after hot rolling in a high carbon steel wire containing 0.9% C or more, it was found that the cooling start temperature after hot rolling is found that it had the greatest impact. Therefore, in order to prevent the precipitation of pro-eutectoid cementite, the limit temperature (T) after hot rolling at which pro-eutectoid cementite does not precipitate is
As a result of intensive studies on the effects of alloying elements on c) and the effects of cooling patterns after the critical temperature on the transformation structure, we found that if the critical temperature determined by the steel material composition and the subsequent cooling pattern are optimally selected, low-temperature rolling can be achieved. The present invention was made based on the completely new knowledge that it is possible to completely prevent the formation of pro-eutectoid cementite even without it, and to produce a high carbon steel wire with extremely good wire drawability.

The present invention has been made based on the above findings, and its gist is that C:0
．． 9-1.3%, Si: 0.1-2.0%, Mn: 0.
After hot rolling a steel containing 2 to 1.3% Cr, 0.1 to 1.8% Cr, and the remainder consisting of Fe and unavoidable impurities, Tc
After rapid cooling to a temperature range from Tc to 100°C, the temperature range is then cooled at a cooling rate of 8°C/second or less until pearlite transformation is completed, or after hot rolling, from Tc to T
The present invention provides a method for producing a high carbon steel wire with excellent wire drawability, which comprises rapidly cooling the wire to a temperature range of c-150° C. and then holding the wire until pearlite transformation is completed.

[0011] Here, Tc is the limit temperature at which pro-eutectoid cementite does not precipitate, and can be expressed by the following formula, which varies depending on the C, Si, Mn, and Cr contents (wt%). Tc (℃) = 821-122.5 [C%] + 6.8 [S
i%]-25.3[Mn%]-5.6[Cr%] The present invention will be explained in detail below.

[0012] First, the reason for limiting the composition of high carbon steel, which is the object of the present invention and has good wire drawability as hot-rolled, will be described. C: In the case of hard steel wire rods and piano wire rods, C is an essential element to increase the strength of the final wire-drawn material. Furthermore, in high carbon bearing steel wires, it is necessary to increase the amount of carbides in order to increase fatigue life, and in this respect, C is an essential element. C
If C is less than 0.9%, the above-mentioned effect of C cannot be fully expected. On the other hand, if it exceeds 1.3%, it becomes difficult to completely prevent the precipitation of pro-eutectoid cementite in the cooling process after hot rolling. Therefore, it was limited to a range of 0.9 to 1.3%.

Si: Si is effective for deoxidizing steel, and has the effect of suppressing the precipitation of pro-eutectoid cementite even with the same amount of carbon. Furthermore, Si not only has the effect of increasing the ferrite strength in pearlite, but also has the effect of increasing the ferrite strength in pearlite.
It is an extremely effective element, as it has the effect of reducing the strength loss that occurs during high-temperature bluing treatment after wire drawing, such as in steel wire, but if it is less than 0.1%, the above effect cannot be achieved. SiO exceeding 2.0% is harmful to wire drawability.
2-based inclusions are likely to occur, so 0.1 to 2.0
% range.

Mn: Mn is not only necessary for deoxidation and desulfurization, but is also an effective element for improving the hardenability of steel and increasing its strength, but if it is less than 0.2%, the above effects will not be achieved. is not obtained. On the other hand, if it exceeds 1.3%, the above effects will be saturated, and in addition, bainite and martensite, which are harmful to wire drawability, will be likely to be generated during the cooling process after hot rolling, and if retained after rolling, pearlite transformation will occur. Since it takes a long time to finish, it was limited to a range of 0.2 to 1.3%.

Cr: Cr is an effective element for refining the cementite spacing of pearlite, increasing strength, and improving the wire drawing hardening rate. In addition, in the case of bearing steel,
It is an extremely important element because it increases the hardenability during heat treatment and also increases the amount of carbide and carbide hardness. However, if it is less than 0.1%, the effect of the above action is small; on the other hand,
If it exceeds 1.8%, the cooling conditions after hot rolling to prevent the precipitation of pro-eutectoid cementite will be narrowed even with the same carbon content, and bainite and martensite will be more likely to occur.
．． It was limited to a range of 1 to 1.8%.

[0016] Other elements are not particularly limited, but if Mo and V are each 0.15% or less, they will not have a large effect on the precipitation behavior of pro-eutectoid cementite and will not deteriorate wire drawability, so they may be used as necessary. There is no problem in adding it. In addition, from the viewpoint of improving wire drawability, each of P and S is desirably within a range of 0.015% or less. Next, we will discuss the quenching temperature after hot rolling and the subsequent The reason for limiting the cooling conditions will be explained.

[0017] In the present invention, the cooling conditions for the steel wire after hot rolling are as follows: (1) after hot rolling, after rapid cooling to a temperature range from Tc to Tc - 100°C, the temperature range continues until pearlite transformation is completed; Cool at a cooling rate of 8°C/sec or less, or
(2) The formation of pro-eutectoid cementite can be completely prevented by any of the following methods: quenching to a temperature range from Tc to Tc-150°C and then holding it until pearlite transformation is completed, resulting in good wire drawability. It is possible to create a pearlite structure. Here, Tc is the limit temperature at which pro-eutectoid cementite does not occur during the cooling process after hot rolling, and the generation of pro-eutectoid cementite can be completely suppressed by forced cooling to a temperature below Tc after hot rolling. The limit temperature Tc changes depending on the Si, Mn, and Cr contents (wt%) in addition to the C content in the steel, and is expressed by the following formula.

[0018] Tc (°C) = 821-122.5 [C%]
+6.8 [Si%] -25.3 [Mn%] -5.6 [C
r%] The above formula was determined by performing multiple regression analysis on the results of extensive and detailed analysis of the influence of alloying elements on the precipitation temperature of pro-eutectoid cementite after hot rolling.

First, the reason why the temperature range after hot rolling is rapidly cooled to a temperature range from Tc to Tc-100°C until the end of pearlite transformation is limited to cooling at a cooling rate of 8°C/sec or less will be explained. The upper limit of the quenching temperature range of the hot-rolled wire rod was limited to Tc because it is necessary to keep it below the critical temperature at which pro-eutectoid cementite does not precipitate. On the other hand, the quenching temperature is T
If the temperature is less than c-100°C, bainite that deteriorates wire drawability is likely to occur in the subsequent cooling process, so the temperature was limited to a range from Tc to Tc-100°C. The cooling rate after rapid cooling from Tc to Tc-100°C is:
If the speed exceeds 8°C/sec, bainite and martensite, which are harmful to wire drawability, tend to occur, so the speed was limited to 8°C/sec or less. In addition, when rapidly cooling to a temperature range from Tc to Tc-100°C after hot rolling, the preferable cooling rate is 15°C/sec or more, and if the cooling rate is slow, pro-eutectoid cementite will precipitate, resulting in good wire drawing. Steel wire with workability cannot be obtained.

[0020] Next, the reason for the limitation that after hot rolling, the temperature is rapidly cooled to a temperature range from Tc to Tc-150°C and then maintained until the pearlite transformation is completed will be described. The upper limit of the holding temperature range was limited to Tc, which is the limit temperature at which pro-eutectoid cementite does not precipitate. On the other hand, if the holding temperature is less than Tc-150°C, bainite, which is harmful to wire drawability, is likely to occur, so the holding temperature range is set from Tc to Tc-150°C.
The temperature range was limited to 0°C. After hot rolling, the cooling rate during rapid cooling from the holding temperature Tc to the temperature range of Tc-150°C is preferably 15°C/second or more, as described above.

[0021]

[Examples] The effects of the present invention will be explained in more detail below with reference to Examples. Example-1 Table 1 shows the chemical composition of the sample material, and Table 2 shows the cooling conditions etc. after finishing it to 5.5 mmφ by normal hot rolling. Test No. in both tables. 1, 3, 4, 5, 7, 9, 11, 13,
Nos. 15 and 17 are examples of the present invention, and the others are comparative examples. Using these wire rods, the structures of pro-eutectoid cementite, bainite, martensite, and pearlite were observed, and a wire drawability evaluation test was conducted. The wire drawing process was performed on a 5.5 mmφ hot rolled wire rod without heat treatment. Wire diameter (d) at which abnormal breakage (delamination) occurs in twisting test
mm), and the wire drawing process true strain at this time [
ε=2×ln(D/d), D=5.5 mm] and wire drawability was evaluated. The higher the wire drawing true strain ε, the better the wire drawability. These test results are also listed in Table 1.

As seen in the table, all of the examples of the present invention contain pro-eutectoid cementite, bainite, and
No martensite is generated, and as a result, wire drawability is extremely good. On the other hand, the comparative example No. In samples Nos. 2, 16, and 18, the quenching temperature after hot rolling was too high, so pro-eutectoid cementite precipitated during the subsequent cooling process, and as a result, the wire drawability was at a lower level than in the examples of the present invention. Also No. In No. 16, since the cooling rate was too fast, bainite and martensite, which are harmful to wire drawability, were generated.

Further, as a comparative example, No. In No. 10, bainite and martensite, which are harmful to wire drawability, were generated due to the cooling rate being too fast. In No. 12, since the quenching temperature after hot rolling was too low, bainite harmful to wire drawability was generated, and the wire drawability was not improved. Comparative example No. Nos. 6, 8, and 14 are all examples in which the wire drawability was not improved because the holding conditions after hot rolling were not optimal. That is, No. In Nos. 6 and 14, bainite was generated because the holding temperature was too low. In No. 8, pro-eutectoid cementite was generated because the holding temperature was too high, and the wire drawability was not improved.

[0024] Also, as a comparative example, No. Nos. 19 and 20 are examples in which the cooling conditions after hot rolling were optimal, but the steel material composition was inappropriate. That is, No. In No. 19, bainite was generated because the Mn content was too high. In No. 20, since the C content is too high, pro-eutectoid cementite is generated, which inhibits wire drawability.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

Effects of the Invention As is clear from the above examples, the present invention can produce high carbon steel containing 0.9 to 1.3% C by optimally selecting the steel material components and cooling conditions after hot rolling. The generation of pro-eutectoid cementite, bainite, and martensite, which are harmful to wire drawability, can be completely prevented, and as a result, it has become possible to manufacture high-carbon steel wire with excellent wire drawability. , the industrial effects are extremely remarkable.

Claims (1)

[Claims] Claim 1: In weight %, C: 0.9 to 1.3%, Si:
0.1-2.0%, Mn: 0.2-1.3%, Cr: 0
．． After hot rolling a steel containing 1 to 1.8% Fe and unavoidable impurities, it was rapidly cooled to a temperature range from Tc to Tc - 100°C, and then the temperature range was continued until pearlite transformation was completed. A method for producing a high carbon steel wire with excellent wire drawability, characterized by cooling at a cooling rate of 8° C./second or less. Tc (℃) = 821-122.5 [C%] + 6.8 [S
i%]-25.3[Mn%]-5.6[Cr%] [Claim 2] In weight%, C: 0.9 to 1.3%, Si: 0.1
~2.0%, Mn: 0.2~1.3%, Cr: 0.1~
1.8%, with the remainder consisting of Fe and unavoidable impurities. After hot rolling, the steel is rapidly cooled to a temperature range from Tc to Tc - 150°C, and then maintained until pearlite transformation is completed. A method for manufacturing high carbon steel wire with excellent wire drawability. Tc (℃) = 821-122.5 [C%] + 6.8 [S
i%]-25.3[Mn%]-5.6[Cr%]