Ultrahigh-strength high-carbon steel wire rod and preparation method thereof

Abstract

The invention discloses an ultrahigh-strength high-carbon steel wire rod and a preparation method thereof. The ultrahigh-strength high-carbon steel wire rod comprises the following components in percentage by mass: 0.89%-0.93% of C, 0.10%-0.20% of Si, 0.25%-0.40% of Mn, less than or equal to 0.015% of P, 0.0055%-0.017% of S, 0.0015%-0.0045% of N, 0.0008%-0.0025% of As, 0.1%-0.3% of Cr, 0.0002%-0.0008% of Ca, 0.0010%-0.0040% of Mo, 0.0010%-0.0030% of total oxygen, 0.0001%-0.0005% of Als and the balance of iron and inevitable impurities. The precipitation level of network cementite of the produced wire rod is smaller than or equal to grade 1, the thickness of the network cementite is smaller than or equal to 500 nm, and the thickness standard deviation is smaller than or equal to 50 nm.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more specifically, to an ultra-high strength high carbon steel wire rod and a preparation method thereof. Background Art

[0002] Ultra-high strength high carbon steel wire rod is widely used in the fields of steel cord and wire rope. For ultra-high strength high carbon steel wire rod, the network cementite in the wire rod structure is a brittle structure. The presence of cementite destroys the continuous and uniform deformation ability of the matrix, which is easy to cause stress concentration during drawing and plying, resulting in wire breakage. At the same time, if there is a network cementite structure in the core of the wire rod, the internal quality defects of the produced steel wire cannot be discovered in time and used in the project, which will bring serious safety hazards to the bearing capacity of the project. Therefore, in order to prevent the wire rod from breaking due to excessively coarse cementite, it is necessary to strictly control the network cementite in the structure of ultra-high strength high carbon steel wire rod.

[0003] In order to control the precipitation problem of network cementite, technicians have conducted a lot of research. For example, application number 202110722840.9 discloses a method for eliminating network cementite of hypereutectoid steel wire rod, comprising: uncoiling a hypereutectoid steel wire rod with network cementite, the diameter of the wire rod is ≥10mm and the network cementite rating is ≤3.5, or the diameter of the wire rod is <10mm and the network cementite rating is ≤4; then introducing it into a heating furnace and keeping it in the uniform temperature section of the heating furnace for more than 4min and less than 10min, and the temperature T of the uniform temperature section is maintained at 100-150°C above the Accm of the wire rod; transferring the wire rod from the heating furnace to a salt bath tank adjacent to the heating furnace, and performing a salt bath for 30-120s, and the temperature T of the molten salt in the salt bath tank is maintained at 80-120°C below the Ar1 of the wire rod; after the wire rod leaves the salt bath tank, it is naturally air-cooled to room temperature to obtain a wire rod with five network cementite. This patent focuses on the method for controlling the network cementite of the wire rod. The method mainly uses a salt bath process to control the network cementite of the wire rod, but the process is relatively costly.

[0004] Therefore, in the current situation of fierce market competition, it is of great positive significance to study how to economically solve the problem of controlling the network cementite of ultra-high strength high carbon steel wire rods, so as to meet the application needs of customers in the market of extremely high strength wire steel. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and to provide an ultra-high strength high carbon steel wire rod and a preparation method and application thereof. Through the production process of "converter smelting + LF refining + continuous casting + continuous rolling + heating + rolling + cooling" combined with low-cost alloy design, the ultra-high strength high carbon steel wire rod produced has a network cementite precipitation level ≤1, a network cementite thickness ≤500nm, and a thickness standard deviation ≤50nm.

[0006] Meet users' requirements for drawing performance of ultra-high strength high carbon steel wire rod.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] An ultra-high strength high carbon steel wire rod comprises the following components in mass percentage: C: 0.89%-0.93%, Si: 0.10%-0.20%, Mn: 0.25%-0.40%, P≤0.015%, S: 0.0055%-0.017%, N: 0.0015%-0.0045%, As: 0.0008%-0.0025%, Cr: 0.1%-0.3%, Ca: 0.0002%-0.0008%, Mo: 0.0010%-0.0040%, total oxygen: 0.0010%-0.0030%, Als: 0.0001%-0.0005%, and the balance is iron and inevitable impurities.

[0009] The present invention also discloses a method for preparing the ultra-high strength high carbon steel wire rod as described above, comprising the following steps: converter smelting, LF refining, continuous casting, continuous rolling, heating, wire rod rolling and wire rod cooling;

[0010] In the LF refining, the molten steel discharged from the converter is put into the LF furnace for refining treatment. The refining temperature of the LF furnace is 1500° C. to 1550° C., and the refining time is 40 min to 55 min.

[0011] In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast, and the superheat of the continuous casting tundish is ≤25°C; the electromagnetic stirring current intensity of the continuous casting crystallizer is 400A-600A, and the frequency is 1Hz-4Hz; intermittent electromagnetic stirring is adopted, the continuous stirring time is 10s-30s, and the ratio of the interval time to the continuous stirring time is 0.40-0.55, to obtain a continuously cast ingot;

[0012] In the continuous rolling, the continuous casting billet off the line in the continuous casting process is continuously rolled, the total heating time of the continuous casting billet is 3.5h-4.5h, the soaking section temperature is 1200°C-1260°C, the soaking section time is 40min-60min; the continuous casting billet starting rolling temperature is 950°C-1000°C, and the final rolling temperature is 800°C-850°C;

[0013] During the heating, the steel billet after continuous rolling is heated in a heating furnace, the temperature of the soaking section is 1050°C to 1155°C, the soaking time is 60min to 80min, the temperature difference between the surface and the core of the continuous rolling billet is ≤40°C, and the temperature difference between the head and the tail of the continuous rolling billet is ≤50°C;

[0014] In the wire rod rolling, the steel billet after continuous rolling is subjected to high-pressure water descaling treatment, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling and double module rolling in sequence;

[0015] During the wire rod cooling, the wire rod after spinning is cooled at a cooling rate of 10°C / s to 20°C / s to obtain the ultra-high strength high carbon steel wire rod.

[0016] Implementing the embodiments of the present invention will have the following beneficial effects:

[0017] (1) The present invention can effectively improve the quality of ultra-high strength high carbon steel wire rods. Through the production process of "converter smelting + LF refining + continuous casting + continuous rolling + heating + rolling + cooling" combined with low-cost alloy design, the organization of the wire rods can be optimized, and ultra-high strength high carbon steel wire rods that meet high strength requirements, reduce the generation of network cementite and have good drawing properties can be produced.

[0018] (2) The ultra-high strength high carbon steel wire rod produced by the production method provided by the present invention has excellent drawing performance, with a network cementite precipitation level of ≤1, a network cementite thickness of ≤500nm, and a thickness standard deviation of ≤50nm. This helps to reduce the wire breakage rate during drawing, improve drawing production efficiency, meet users' requirements for wire rod drawing performance, and wire rod production of steel wire can effectively avoid wire breakage during the drawing process, significantly improving the market competitiveness of the product.

[0019] (3) The process of the present invention is based on conventional production equipment and has the characteristics of process applicability and strong controllability, and does not require additional investment. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0021] 1. Chemical composition and mechanical properties

[0022] The invention discloses an ultra-high strength high carbon steel wire rod, comprising the following components in mass percentage: C: 0.89%-0.93%, Si: 0.10%-0.20%, Mn: 0.25%-0.40%, P≤0.015%, S: 0.0055%-0.017%, N: 0.0015%-0.0045%, As: 0.0008%-0.0025%, Cr: 0.1%-0.3%, Ca: 0.0002%-0.0008%, Mo: 0.0010%-0.0040%, total oxygen: 0.0010%-0.0030%, Als: 0.0001%-0.0005%, and the balance is iron and inevitable impurities.

[0023] Specifically, the mechanism of action of each alloy component in the wire rod of the present invention is as follows:

[0024] If the carbon content in the wire is too low, it cannot meet the strength requirements of users when drawing the steel wire. If the carbon content is too high, the strength of the wire rod and the steel wire will exceed the standard requirements. Therefore, the carbon content in the present invention is controlled at 0.89% to 0.93%.

[0025] Silicon is the main deoxidizing element in high carbon steel. Low silicon content will result in insufficient deoxidation of the molten steel. Silicon is a ferrite strengthening element. Too high silicon content will reduce the drawing performance of the wire rod. Therefore, the silicon content in the present invention is controlled to be 0.10% to 0.20%.

[0026] Manganese is an element that controls the strength and phase transformation characteristics of the wire rod. Manganese reduces the eutectoid transformation temperature of steel, causing the pearlite transformation of the wire rod to occur in the low temperature zone. Manganese is also an element that improves the strength of the wire rod. However, if the manganese content is too high, the work hardening of the wire rod is significant, which is not conducive to improving the cold working performance of the wire rod. Therefore, the manganese content in the present invention is controlled at 0.25% to 0.40%.

[0027] Phosphorus is a harmful element in steel, and the lower its content, the better. In the present invention, phosphorus is ≤ 0.015%.

[0028] Sulfur forms MnS with manganese in steel, which reduces the harm of other oxide and nitride inclusions in steel. However, its content should not be too high. Coarse MnS inclusions reduce the drawing performance of wire rod. Therefore, the sulfur content in the present invention is controlled at 0.0055% to 0.017%.

[0029] The nitrogen element significantly increases the work hardening of the wire rod during the drawing and torsion process, so the nitrogen content of the present invention is controlled at 0.0015% to 0.0045%.

[0030] Arsenic is easily enriched at the grain boundary of steel, reducing system energy and stabilizing austenite. However, too high arsenic content in steel will reduce the drawing performance of wire rod. In the present invention, the arsenic content is controlled at 0.0008% to 0.0025%.

[0031] Calcium has a deteriorating effect on the inclusion components in steel, forming Al2O3-CaO and CaS-MnS as well as composite inclusions, and the inclusions are relatively round and small in size. The calcium element control range of the patented invention is 0.0002% to 0.0008%.

[0032] Molybdenum has a solid solution strengthening effect on ferrite and also improves the stability of carbides, thus having a beneficial effect on improving the strength of steel. In the present invention, the molybdenum content is controlled at 0.0010% to 0.0040%.

[0033] Chromium can control the spacing between pearlite lamellae of wire rod, improve the tensile strength of wire rod, improve the plasticity and drawing performance of wire rod, and improve the corrosion resistance. Too high chromium content will cause significant work hardening during the wire rod drawing process. The chromium content of the patented invention is controlled at 0.1% to 0.3%.

[0034] Acid-soluble aluminum controls the composition of inclusions in steel to make it in the low melting point region. In the present invention, the acid-soluble aluminum is 0.0001% to 0.0005%. The role of oxygen in steel is similar to that of acid-soluble aluminum, and is controlled at 0.0010% to 0.0030%.

[0035] In a specific embodiment, the size of the wire rod pearlite spheroids is ≤23 μm; wherein the number of wire rod pearlite spheroids with a size of ≥15 μm accounts for 10% to 15%.

[0036] In a specific embodiment, the number of grains with a local orientation difference of ≥15° on both sides of the grain boundary in the wire rod structure accounts for 15% to 25%.

[0037] In a specific embodiment, the network cementite precipitation level of the wire rod is ≤1, the network cementite thickness is ≤500nm, and the thickness standard deviation is ≤50nm.

[0038] 2. Production technology

[0039] The present invention also discloses a method for preparing an ultra-high strength high carbon steel wire rod as in any embodiment of the present invention, comprising the following steps: converter smelting, LF refining, continuous casting, continuous rolling, heating, wire rod rolling and wire rod cooling.

[0040] Further, the method specifically includes the following steps:

[0041] S1. In converter smelting, scrap steel and molten iron are used as furnace charge, and the mass percentage of scrap steel in the furnace charge is 3% to 10%.

[0042] In S2 and LF refining, the molten steel discharged from the converter is put into the LF furnace for refining. The refining temperature of the LF furnace is 1500°C to 1550°C, and the refining time is 40min to 55min.

[0043] In a specific embodiment, during LF refining, argon stirring is performed during refining, and the argon stirring intensity is 300NL / min to 400NL / min; 18min to 22min before the end of LF refining, the argon flow rate is adjusted to 100NL / min to 250NL / min.

[0044] S3. During continuous casting, the molten steel treated by LF refining is continuously cast, and the superheat of the continuous casting tundish is ≤25°C; the electromagnetic stirring current intensity of the continuous casting crystallizer is 400A~600A, and the frequency is 1Hz~4Hz; intermittent electromagnetic stirring is adopted, the continuous stirring time is 10s~30s, and the ratio of the interval time to the continuous stirring time is 0.40~0.55, so as to obtain a continuously cast ingot.

[0045] S4. During continuous rolling, the continuous casting billet off the line in the continuous casting process is continuously rolled, the total heating time of the continuous casting billet is 3.5h~4.5h, the soaking section temperature is 1200℃~1260℃, the soaking section time is 40min~60min; the continuous casting billet starting rolling temperature is 950℃~1000℃, and the final rolling temperature is 800℃~850℃.

[0046] S5. During heating, the steel billet after continuous rolling is heated in a heating furnace, the temperature of the soaking section is 1050℃~1155℃, the soaking time is 60min~80min, the temperature difference between the surface and the core of the continuous rolling billet is ≤40℃, and the temperature difference between the head and the tail of the continuous rolling billet is ≤50℃.

[0047] S6. During the wire rod rolling, the steel billet after continuous rolling is descaled by high-pressure water, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling and double module rolling in sequence.

[0048] In a specific embodiment, the descaling pressure of the high-pressure water descaling treatment is 13MPa-16MPa; the pre-finishing rolling temperature of the wire rod is 900℃-950℃, and the cooling water flow rate of the pre-finishing rolling is 50m 3 / h~80m 3 / h; the temperature of finishing rolling is 900℃~930℃; the rolling temperature of rolled pieces out of the double module rolling mill is 880℃~900℃, and the cooling water flow rate out of the double module is 40m 3 / h~70m 3 / h, spinning temperature 860℃~880℃.

[0049] S6. During the wire rod cooling, the wire rod after spinning is cooled at a cooling rate of 10°C / s to 20°C / s to obtain an ultra-high strength high carbon steel wire rod.

[0050] Furthermore, the present invention also discloses a use of the ultra-high strength high carbon steel wire rod according to any embodiment of the present invention in the preparation of ultra-high strength steel wire.

[0051] In a specific embodiment, the diameter of the steel wire is 1.7 mm to 1.8 mm; the size of the pearlite nodules of the steel wire is 10 μm to 15 μm; the spacing between the pearlite lamellae of the steel wire is 0.07 μm to 0.075 μm; and the hardness difference of the cross section of the steel wire along the diameter direction is ≤30 HV.

[0052] The following are specific embodiments

[0053] Examples 1-6

[0054] The chemical composition, preparation process and performance parameters of the wire rods of Examples 1-6 of the present invention are shown in Table 1.

[0055] Table 1 Chemical composition, preparation process and performance parameters of wire rods of Examples 1-6

[0056]

[0057]

[0058]

[0059] According to the above results, the present invention controls the production process parameters of steel wire rods with a carbon content in the range of 0.89% to 0.93%, and reasonably designs the relevant parameters of the continuous casting, continuous rolling heating, rolling and cooling processes. The ultra-high strength and high carbon steel wire rods produced have excellent drawing performance, network cementite precipitation level ≤1 level, network cementite thickness ≤500nm, and thickness standard deviation ≤50nm, which helps to reduce the drawing breakage rate and improve the drawing production efficiency, meet the user's requirements for the drawing performance of the wire rod, and the production method is efficient and low-cost, and does not require a salt bath process.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An ultra-high strength high carbon steel wire rod, characterized in that: The following components are included in mass percentage: C: 0.89% ~ 0.93%, Si: 0.10% ~ 0.20%, Mn: 0.25% ~ 0.40%, P ≤ 0.015%, S: 0.0055% ~ 0.017%, N: 0.0015% ~ 0.0045%, As: 0.0008% ~ 0.0025%, Cr: 0.1% ~ 0.3%, Ca: 0.0002% ~ 0.0008%, Mo: 0.0010% ~ 0.0040%, total oxygen: 0.0010% ~ 0.0030%, Als: 0.0001% ~ 0.0005%, and the balance is iron and inevitable impurities.

2. The ultra-high strength high carbon steel wire rod according to claim 1, characterized in that: The size of wire rod pearlite spheroids is ≤23μm; among them, the number of wire rod pearlite spheroids with a size of ≥15μm accounts for 10% to 15%.

3. The ultra-high strength high carbon steel wire rod according to claim 1, characterized in that: The number of grains with local orientation difference ≥15° on both sides of the grain boundary in the wire rod structure accounts for 15% to 25%.

4. The ultra-high strength high carbon steel wire rod according to claim 1, characterized in that: The network cementite precipitation level of the wire rod is ≤1, the network cementite thickness is ≤500nm, and the thickness standard deviation is ≤50nm.

5. A method for preparing an ultra-high strength high carbon steel wire rod as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Converter smelting, LF refining, continuous casting, continuous rolling, heating, wire rod rolling and wire rod cooling; In the LF refining, the molten steel discharged from the converter is put into the LF furnace for refining treatment. The refining temperature of the LF furnace is 1500° C. to 1550° C., and the refining time is 40 min to 55 min. In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast, and the superheat of the continuous casting tundish is ≤25°C; the electromagnetic stirring current intensity of the continuous casting crystallizer is 400A-600A, and the frequency is 1Hz-4Hz; intermittent electromagnetic stirring is adopted, the continuous stirring time is 10s-30s, and the ratio of the interval time to the continuous stirring time is 0.40-0.55, to obtain a continuously cast ingot; In the continuous rolling, the continuous casting billet off the line in the continuous casting process is continuously rolled, the total heating time of the continuous casting billet is 3.5h-4.5h, the soaking section temperature is 1200°C-1260°C, the soaking section time is 40min-60min; the continuous casting billet starting rolling temperature is 950°C-1000°C, and the final rolling temperature is 800°C-850°C; During the heating, the steel billet after continuous rolling is heated in a heating furnace, the temperature of the soaking section is 1050°C to 1155°C, the soaking time is 60min to 80min, the temperature difference between the surface and the core of the continuous rolling billet is ≤40°C, and the temperature difference between the head and the tail of the continuous rolling billet is ≤50°C; In the wire rod rolling, the steel billet after continuous rolling is subjected to high-pressure water descaling treatment, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling and double module rolling in sequence; During the wire rod cooling, the wire rod after spinning is cooled at a cooling rate of 10°C / s to 20°C / s to obtain the ultra-high strength high carbon steel wire rod.

6. The preparation method according to claim 5, characterized in that: In the converter smelting, scrap steel and molten iron are used as furnace materials, and the mass percentage of the scrap steel in the furnace materials is 3% to 10%.

7. The preparation method according to claim 5, characterized in that: In the LF refining, argon stirring is performed during refining, and the argon stirring intensity is 300NL / min to 400NL / min; 18min to 22min before the end of LF refining, the argon flow rate is adjusted to 100NL / min to 250NL / min.

8. The preparation method according to claim 5, characterized in that: During the wire rod rolling, the descaling pressure of the high-pressure water descaling treatment is 13MPa-16MPa; the pre-finishing rolling temperature of the wire rod is 900°C-950°C, and the cooling water flow rate of the pre-finishing rolling is 50m 3 / h~80m 3 / h; the temperature of finishing rolling is 900℃~930℃; the rolling temperature of rolled pieces out of the double module rolling mill is 880℃~900℃, and the cooling water flow rate out of the double module is 40m 3 / h~70m 3 / h, spinning temperature 860℃~880℃.

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