Control method for tire cord steel segregation

Abstract

The invention relates to the technical field of tire cord steel, and provides a tire cord steel segregation control method which comprises the steps of molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, spinning and heat treatment which are conducted in sequence, and tire cord steel is composed of, by weight, 0.80%-0.85% of C, 0.15%-0.30% of Si, 0.10%-0.55% of Mn, 0.13%-0.25% of V, 0.12%-0.22% of Sn, smaller than or equal to 0.008% of P, smaller than or equal to 0.005% of S, 0.01%-0.05% of Cu, 0.001%-0.05% of Ni, 0.02%-0.05% of Cr, 0.001%-0.005% of Al, smaller than or equal to 0.005% of N and the balance iron and inevitable impurities. According to the technical scheme, the problem that in the related technology, the tire cord steel segregation control effect is poor is solved.

Description

Technical Field

[0001] The invention relates to the technical field of cord steel, and in particular to a method for controlling segregation of cord steel. Background Art

[0002] Cord steel is mainly used for the skeleton of tire radial reinforcement. It has the characteristics of high strength and good toughness. It is one of the products with extremely high requirements and the most difficult production among wire products. Cord steel is prone to segregation during the production process. Cord steel segregation refers to the phenomenon of uneven distribution of chemical composition and organization in steel, mainly including carbon segregation and segregation of other alloy elements. Cord steel segregation has a significant impact on the performance and quality of steel. If the segregation degree of cord steel billet is too high, it will have an adverse effect on the organization control of the rolling process, and at the same time, the steel inclusions will be unevenly distributed, and wire breakage is prone to occur during the processing. At the same time, center segregation reduces the wire drawing limit and ductility of cord steel, especially significantly reduces toughness, affecting the drawing performance of cord steel. Therefore, cord steel segregation must be controlled in the production of cord steel. However, it is difficult to control the segregation of cord steel. The traditional means of controlling segregation are low superheat casting, gas mist cooling, crystallizer electromagnetic stirring, end electric stirring, and light pressure technology, but the control effect is not ideal. Therefore, proposing a control method for cord steel segregation can reasonably and effectively reduce the cord steel segregation problem, which is a technical problem that urgently needs to be solved. Summary of the invention

[0003] The invention provides a method for controlling segregation of cord steel, which solves the problem of poor control effect of segregation of cord steel in the related art.

[0004] The technical solution of the present invention is as follows: The present invention provides a method for controlling segregation of cord steel, comprising sequentially performing molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, wire laying and heat treatment, wherein the cord steel is composed of the following components in weight percentage: C 0.80%~0.85%, Si 0.15%~0.30%, Mn 0.10%~0.55%, V 0.13%~0.25%, Sn 0.12%~0.22%, P≤0.008%, S≤0.005%, Cu 0.01%~0.05%, Ni 0.001%~0.05%, Cr 0.02%~0.05%, Al0.001%~0.005%, N≤0.005%, and the rest are iron and its inevitable impurities.

[0005] As a further technical solution, the weight ratio of the sum of the weights of V and Sn to that of Mn is 1:0.5~1.

[0006] In the present invention, when the weight ratio of V and Sn to Mn is 1:0.5-1, the control effect of cord steel segregation can be further improved.

[0007] As a further technical solution, the weight ratio of V to Sn is 1:1.

[0008] As a further technical solution, the heat treatment includes a first stage heat treatment, a second stage heat treatment and a third stage heat treatment.

[0009] In the present invention, the heat treatment process is a segmented heat treatment process. By optimizing the heat treatment process and rationally regulating and optimizing the heat treatment temperature, the diffusion of the component elements of the cord steel and the transformation of the organizational structure can be further promoted to obtain a cord steel with a more uniform composition.

[0010] As a further technical solution, during the first stage of heat treatment, the temperature is 350~450°C, the holding time is 60~100 minutes, and the material is cooled to room temperature after holding; during the second stage of heat treatment, the temperature is 650~750°C, the holding time is 40~60 minutes, and the material is cooled to room temperature after holding; during the third stage of heat treatment, the temperature is 400~500°C, the holding time is 50~80 minutes, and the material is cooled to room temperature after holding.

[0011] As a further technical solution, during the first stage heat treatment and the third stage heat treatment, the cooling rate is independently 8-12°C / min; during the second stage heat treatment, the cooling rate is 20-25°C / min.

[0012] During heat treatment, the cooling rate has a significant effect on the composition uniformity and structural stability of the cord steel. Strict and reasonable control of the cooling rate can further improve the control effect of cord steel segregation. In the present invention, when the cooling rates of the first stage heat treatment and the third stage heat treatment are independently 8-12°C / min, and the cooling rate of the second stage heat treatment is 20-25°C / min, the control effect of cord steel segregation can be further improved by reasonably regulating the cooling rates of the three stages heat treatment.

[0013] As a further technical solution, during the continuous casting, pure water cooling is adopted, and the water flow rate during the pure water cooling is 120~130cm 3 / h.

[0014] As a further technical solution, the rolling includes heating treatment, soaking treatment and start rolling; During the heating treatment, the temperature is 990-1010°C and the time is 2-2.5h; During the soaking treatment, the temperature is 1090-1110°C and the time is 3.5-4h; During the rolling, the temperature is 990-1010°C.

[0015] As a further technical solution, after the converter smelting, the weight percentage of P is ≤0.006%, and the weight percentage of S is ≤0.003%.

[0016] As a further technical solution, during the LF furnace refining, the refining slag is made of CaO-SiO 2 Binary slag system, the final slag basicity is 0.95~1.10.

[0017] The working principle and beneficial effects of the present invention are: Among them, the cord steel contains V, Sn and Mn elements. By reasonably adjusting the content ratio of the three, the uniformity of the cord steel composition and the stability of the internal structure are ensured, so that the control effect of cord steel segregation is optimized, reducing the problem of cord steel breakage caused by segregation, and ultimately improving the qualified rate of cord steel products. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1 A method for controlling segregation of cord steel comprises sequentially performing molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, wire laying and heat treatment, wherein the cord steel is composed of the following components in weight percentage: C 0.80%, Si 0.15%, Mn 0.10%, V 0.13%, Sn 0.12%, P 0.008%, S 0.005%, Cu 0.01%, Ni 0.001%, Cr 0.02%, Al 0.001%, N 0.005%, and the rest are iron and its inevitable impurities.

[0020] After converter smelting, the weight percentage of P is 0.003%, and the weight percentage of S is 0.002%; During LF furnace refining, the refining slag is CaO-SiO 2 Binary slag system, the final slag basicity is 0.95; During continuous casting, 120cm 3 / h water flow rate to cool with pure water to obtain the cord steel ingot; The cord steel ingot is heated in a heating section at 990° C. for 2.5 hours, and then in a soaking section at 1090° C. for 4 hours, and then rolled at 990° C. to obtain a rolled cord steel ingot; The rolled cord steel ingot is subjected to the first heat treatment at 350°C, kept at this temperature for 100 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the second heat treatment is carried out at 650°C, kept at this temperature for 60 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the third heat treatment is carried out at 400°C, kept at this temperature for 80 minutes, and then cooled to room temperature at a cooling rate of 6°C / min, thereby completing the heat treatment process to obtain the cord steel.

[0021] Example 2 A method for controlling segregation of cord steel comprises sequentially performing molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, wire laying and heat treatment, wherein the cord steel is composed of the following components in weight percentage: C 0.83%, Si 0.20%, Mn 0.34%, V 0.13%, Sn 0.13%, P 0.008%, S 0.005%, Cu 0.03%, Ni 0.01%, Cr 0.03%, Al 0.003%, N 0.003%, and the rest are iron and its inevitable impurities.

[0022] After converter smelting, the weight percentage of P is 0.006%, and the weight percentage of S is 0.003%; During LF furnace refining, the refining slag is CaO-SiO 2 Binary slag system, the final slag basicity is 1.00; During continuous casting, 125cm 3 / h water flow rate to cool with pure water to obtain the cord steel ingot; The cord steel ingot is heated in a heating section at 1000° C. for 2.5 hours, and then is soaked in a soaking section at 1100° C. for 3.5 hours, and then rolled at 1000° C. to obtain a rolled cord steel ingot; The rolled cord steel ingot is subjected to the first heat treatment at 400°C, kept at this temperature for 80 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the second heat treatment is carried out at 700°C, kept at this temperature for 50 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the third heat treatment is carried out at 450°C, kept at this temperature for 65 minutes, and then cooled to room temperature at a cooling rate of 6°C / min, thereby completing the heat treatment process to obtain the cord steel.

[0023] Example 3 A method for controlling segregation of cord steel comprises sequentially performing molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, wire laying and heat treatment, wherein the cord steel is composed of the following components in weight percentage: C 0.85%, Si 0.30%, Mn 0.55%, V 0.25%, Sn 0.22%, P 0.008%, S 0.005%, Cu 0.05%, Ni 0.05%, Cr 0.05%, Al 0.005%, N 0.005%, and the rest are iron and its inevitable impurities.

[0024] After converter smelting, the weight percentage of P is 0.006%, and the weight percentage of S is 0.003%; During LF furnace refining, the refining slag is CaO-SiO 2 Binary slag system, the final slag basicity is 1.10; During continuous casting, 130cm 3 / h water flow rate to cool with pure water to obtain the cord steel ingot; The cord steel ingot is heated in a heating section at 1010° C. for 2 hours, and is soaked in a soaking section at 1110° C. for 3.5 hours, and then rolled at 1010° C. to obtain a rolled cord steel ingot; The rolled cord steel ingot is subjected to the first heat treatment at 450°C, kept at this temperature for 60 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the second heat treatment is carried out at 750°C, kept at this temperature for 40 minutes, and then cooled to room temperature at a cooling rate of 6°C / min; the third heat treatment is carried out at 500°C, kept at this temperature for 50 minutes, and then cooled to room temperature at a cooling rate of 6°C / min, thereby completing the heat treatment process and obtaining the cord steel.

[0025] Example 4 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the weight percentage of Mn is 0.16%, the weight percentage of V is 0.22%, and the weight percentage of Sn is 0.22%.

[0026] Example 5 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the weight percentage of Mn is 0.20%, the weight percentage of V is 0.20%, and the weight percentage of Sn is 0.20%.

[0027] Example 6 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the weight percentage of Mn is 0.30%, the weight percentage of V is 0.15%, and the weight percentage of Sn is 0.15%.

[0028] Example 7 The only difference between this embodiment and embodiment 6 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 12°C / min, the cooling rate of the second stage heat treatment is 16°C / min, and the cooling rate of the third stage heat treatment is 12°C / min.

[0029] Example 8 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 12°C / min, the cooling rate of the second stage heat treatment is 30°C / min, and the cooling rate of the third stage heat treatment is 12°C / min.

[0030] Example 9 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 6°C / min, the cooling rate of the second stage heat treatment is 25°C / min, and the cooling rate of the third stage heat treatment is 6°C / min.

[0031] Example 10 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 16°C / min, the cooling rate of the second stage heat treatment is 25°C / min, and the cooling rate of the third stage heat treatment is 16°C / min.

[0032] Embodiment 11 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 6°C / min, the cooling rate of the second stage heat treatment is 16°C / min, and the cooling rate of the third stage heat treatment is 6°C / min.

[0033] Example 12 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 16°C / min, the cooling rate of the second stage heat treatment is 30°C / min, and the cooling rate of the third stage heat treatment is 16°C / min.

[0034] Embodiment 13 The only difference between this embodiment and embodiment 7 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 8°C / min, the cooling rate of the second stage heat treatment is 20°C / min, and the cooling rate of the third stage heat treatment is 8°C / min.

[0035] Embodiment 14 The only difference between this embodiment and embodiment 6 is that in this embodiment, when performing the heat treatment process, the cooling rate of the first stage heat treatment is 12°C / min, the cooling rate of the second stage heat treatment is 25°C / min, and the cooling rate of the third stage heat treatment is 12°C / min.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that in this comparative example, Mn is not added, and the weight percentages of V and Sn added are 0.18% and 0.17%, respectively.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that in this comparative example, V is not added, the weight percentage of Mn added is 0.10%, and the weight percentage of Sn added is 0.25%.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that in this comparative example, Sn is not added, the weight percentage of Mn added is 0.10%, and the weight percentage of V added is 0.25%.

[0039] Comparative Example 4 The only difference between this comparative example and Example 1 is that in this comparative example, Mn, V and Sn are not added.

[0040] The cord steels obtained by the cord steel segregation control methods of Examples 1 to 14 and Comparative Examples 1 to 4 were tested for center segregation index according to the method in YB / T 4413-2014 "Metallurgical Evaluation Method for Center Segregation of High Carbon Steel Wire Rods", and the results are shown in Table 1 below: Table 1 Central segregation index of Examples 1 to 14 and Comparative Examples 1 to 4

[0041] Compared with Comparative Examples 1 to 4, the central segregation index of Example 1 is significantly reduced, indicating that when the cord steel contains V, Sn and Mn elements, the three have a synergistic effect. By reasonably regulating the content ratio of the three, the uniformity of the cord steel composition and the stability of the internal structure are ensured, which can significantly improve the control effect of cord steel segregation and improve the qualified rate of cord steel products.

[0042] Compared with Examples 2 and 4, the central segregation index of Examples 5-6 is reduced, indicating that when the weight ratio of V and Sn to Mn is 1:0.5-1, the control effect of cord steel segregation can be further improved.

[0043] Compared with Examples 6, 11, and 12, the central segregation index of Examples 7 to 10 and Examples 13 to 14 is reduced, indicating that during heat treatment, the cooling rate has a significant effect on the composition uniformity and structural stability of the cord steel, and reasonable control of the cooling rate can further improve the control effect of cord steel segregation. Compared with Examples 7 to 10, the central segregation index of Examples 13 to 14 is reduced, indicating that when the cooling rates of the first stage heat treatment and the third stage heat treatment are independently 8 to 12°C / min, and the cooling rate of the second stage heat treatment is 20 to 25°C / min, the control effect of cord steel segregation can be further improved by reasonably regulating the cooling rates of the three stages of heat treatment.

[0044] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling cord steel segregation, characterized in that: The process comprises the following steps: molten iron pretreatment, converter smelting, LF furnace refining, continuous casting, rolling, wire laying and heat treatment, wherein the cord steel is composed of the following components in weight percentage: C 0.80%~0.85%, Si 0.15%~0.30%, Mn 0.10%~0.55%, V 0.13%~0.25%, Sn 0.12%~0.22%, P≤0.008%, S≤0.005%, Cu 0.01%~0.05%, Ni 0.001%~0.05%, Cr 0.02%~0.05%, Al 0.001%~0.005%, N≤0.005%, and the rest are iron and its inevitable impurities.

2. A method for controlling cord steel segregation according to claim 1, characterized in that: The weight ratio of the sum of the weights of the V and Sn to the weight ratio of the Mn is 1:0.5-1.

3. A method for controlling cord steel segregation according to claim 1, characterized in that: The heat treatment includes a first stage heat treatment, a second stage heat treatment and a third stage heat treatment.

4. A method for controlling cord steel segregation according to claim 3, characterized in that: During the first stage of heat treatment, the temperature is 350~450℃, the holding time is 60~100min, and the temperature is cooled to room temperature after holding; during the second stage of heat treatment, the temperature is 650~750℃, the holding time is 40~60min, and the temperature is cooled to room temperature after holding; during the third stage of heat treatment, the temperature is 400~500℃, the holding time is 50~80min, and the temperature is cooled to room temperature after holding.

5. A method for controlling cord steel segregation according to claim 4, characterized in that: During the first heat treatment and the third heat treatment, the cooling rate is independently 8-12°C / min; during the second heat treatment, the cooling rate is 20-25°C / min.

6. A method for controlling cord steel segregation according to claim 1, characterized in that: During the continuous casting, pure water cooling is adopted, and the water flow rate during the pure water cooling is 120-130 cm 3 / h.

7. A method for controlling cord steel segregation according to claim 1, characterized in that: The rolling process includes heating treatment, soaking treatment and start rolling; During the heating treatment, the temperature is 990-1010°C and the time is 2-2.5h; During the soaking treatment, the temperature is 1090-1110°C and the time is 3.5-4h; During the rolling, the temperature is 990-1010°C.

8. A method for controlling cord steel segregation according to claim 1, characterized in that: After the converter smelting, the weight percentage of P is ≤0.006%, and the weight percentage of S is ≤0.003%.

9. A method for controlling cord steel segregation according to claim 1, characterized in that: During the LF furnace refining, the refining slag adopts a CaO-SiO2 binary slag system, and the final slag basicity is 0.95-1.

10.

10. A method for controlling cord steel segregation according to claim 1, characterized in that: During the continuous casting, the superheat is 17-23°C.

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