Low-chromium high-carbon steel wire rod and preparation method thereof

Abstract

The invention discloses a low-chromium high-carbon steel wire rod and a preparation method thereof. The wire rod comprises the following components in percentage by mass: 0.81%-0.85% of C, 0.12%-0.24% of Si, 0.40%-0.60% of Mn, less than or equal to 0.013% of P, 0.0020%-0.010% of S, 0.0025%-0.0040% of total oxygen, 0.0001%-0.0008% of Als, 0.0003%-0.0012% of Nb, 0.0006%-0.0013% of Mo, less than or equal to 0.01% of Cr and the balance of iron and inevitable impurities. The chromium content of the high-carbon steel wire rod is controlled to be less than or equal to 0.01% by controlling the reduction reaction of the chromium element and the interface process of the chemical reaction of the chromium element, so that the chromium content in the high-carbon steel wire rod meets the quality requirement of a user on the wire rod.

Description

Technical Field

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

[0002] High-carbon steel used for product processing has very strict requirements on the strength of the steel wire, and the fluctuation of the Cr content in the steel is a key factor affecting the strength of the steel wire made from the wire rod. Therefore, it is necessary to accurately control the chromium content in the wire rod to meet the user's strength requirements for high-carbon steel.

[0003] Chinese patent application number 2021109557561 discloses a method for controlling the chromium content according to AOD steel sample, which includes the following steps: (1) judging the slag removal conditions; (2) comparing the chromium content: taking a steel sample when the slag removal conditions are met, testing the carbon content and chromium content, and comparing the carbon and chromium content of the steel sample with the carbon and chromium content in the standardized steel sample carbon-chromium range table; (3) determining the comparison results and taking corresponding adjustment measures. In the standardized steel sample carbon-chromium content range table prepared by collecting a large number of typical furnace steel sample carbon content and chromium content data, the carbon content variation range and the chromium content variation range are controlled within 0.4%; by limiting the slag removal conditions to ensure that the steel is in good condition, the chromium content of the steel sample is compared with the chromium content of the standardized steel sample, and the chromium content of the steel sample is quickly determined whether the chromium content of the molten steel in the furnace is sufficient or exceeds the standard, and then timely adjustments are made according to the judgment results, so as to accurately control the chromium content of the steel. However, the patent introduces a method for controlling the chromium content by AOD. However, the control range of the chromium content in this solution is 13.0% to 15.0%, which does not meet the control requirements of the chromium content of high-carbon steel wire rods. At the same time, the chemical reaction of chromium is an interface process, and the control of chromium also needs to consider the interface reaction mechanism.

[0004] Therefore, how to accurately control the chromium content of high carbon steel wire rod is of great significance to the current production of high-strength steel wire. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a low-chromium high-carbon steel wire rod and a preparation method thereof. By controlling the reduction reaction of the chromium element and the reduction process of the chromium chemical reaction, the chromium content of the high-carbon steel wire rod is controlled to below 0.01%, so that the chromium content in the high-carbon steel meets the quality requirements of users for the wire rod.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A low-chromium high-carbon steel wire rod, the low-chromium high-carbon steel wire rod comprising the following components in percentage by mass:

[0008] C: 0.81%~0.85%, Si: 0.12%~0.24%, Mn: 0.40%~0.60%, P≤0.013%, S: 0.0020%~0.010%, total oxygen: 0.0025%~0.0040%, Als: 0.0001%~0.0008%, Nb: 0.0003%~0.0012%, Mo: 0.0006%~0.0013%, Cr≤0.01%, and the balance is iron and unavoidable impurities.

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

[0010] During the converter smelting, the temperature after the converter is 1570°C to 1610°C, and the oxygen activity of the molten steel after smelting is controlled at 70ppm to 200ppm;

[0011] In the LF refining, the sulfur content is controlled to be 0.0045% to 0.0145%, the oxygen activity is controlled to be 0.0030% to 0.0070%, and the refining temperature is 1420° C. to 1490° C.; the argon flow rate is controlled to be 50NL / min to 150NL / min during the refining process, and the liquid level fluctuation is ≤40mm;

[0012] In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast to obtain a continuously cast ingot;

[0013] During the continuous rolling, the continuous casting billet produced in the continuous casting process is sent into a heating furnace for heating;

[0014] In the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence;

[0015] During the wire rod cooling, the wire rod is cooled on an air-cooled roller after spinning.

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

[0017] The present invention can effectively improve the quality of low-chromium high-carbon steel wire rod. Through the production process of "converter smelting + LF refining + continuous casting + continuous rolling + rolling + cooling" and the design of the components, the present invention reduces the chromium content in the steel by controlling the higher oxygen content in the converter smelting process, controls the Cr2O3 content of the top slag after the converter tapping to be ≤1%, and prevents the chromium in the top slag from being reduced into the steel to increase the chromium content of the molten steel; by using the characteristics of sulfur and oxygen as surface active elements, the chromium in the refined top slag is prevented from being reduced into the molten steel; by controlling the carbon content of the covering agent to be ≤1% and the Cr2O3 content to be ≤1% in the continuous casting and continuous rolling, the carbon in the covering agent is prevented from reducing the chromium element in the covering agent, and the chromium content of the molten steel is increased. The refining process is controlled to control the argon flow rate to 50-150NL / min, the liquid level fluctuation to be ≤40mm, and the crystallizer steel liquid level fluctuation to be ±3mm. Through the above measures, the reduction reaction of the chromium element is controlled, and the interface process of the chromium element chemical reaction is controlled, so that the chromium content of the high-carbon steel wire rod is controlled to be below 0.01%, meeting the quality requirements of the high-carbon steel wire rod. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0019] 1. Chemical composition and mechanical properties

[0020] The invention discloses a low-chromium high-carbon steel wire rod, which comprises the following components in mass percentage: C: 0.81%-0.85%, Si: 0.12%-0.24%, Mn: 0.40%-0.60%, P≤0.013%, S: 0.0020%-0.010%, total oxygen: 0.0025%-0.0040%, Als: 0.0001%-0.0008%, Nb: 0.0003%-0.0012%, Mo: 0.0006%-0.0013%, Cr≤0.01%, and the balance is iron and inevitable impurities.

[0021] Specifically, the mechanism of action of each alloy component in the wire rod of the present invention is as follows:

[0022] Too high a carbon content in the wire rod will cause the steel wire processed from the wire rod to exceed the strength requirement range; at the same time, a higher strength will increase the wire breakage rate during the steel wire preparation process, and increase the user's scrap rate. Too low a carbon content in the wire rod cannot meet the user's steel wire strength requirements. Therefore, the carbon content in the present invention is controlled at 0.81% to 0.85%.

[0023] Silicon increases the eutectoid transformation temperature of steel and makes the pearlite structure of the wire rod coarse, which is not conducive to the complex deformation of the steel wire processing process. Silicon is the main deoxidizing element in high carbon steel. If the silicon content in the steel is too high, coarse silicates and impurities will appear after the molten steel is deoxidized. If the silicon content is low, the molten steel will be insufficiently deoxidized, thereby reducing the deformation ability of the wire rod in the steel wire process. Therefore, the silicon content in the present invention is controlled at 0.12% to 0.24%.

[0024] Manganese is an element that improves the strength of wire rods, which helps ensure that the steel wire processed from wire rods meets the tensile strength requirements of users; manganese has the effect of reducing the eutectoid transformation temperature of steel, refining the pearlite structure of wire rods, and improving the deformation ability of wire rods for processing ropeway ropes. Therefore, the manganese content in the present invention is controlled at 0.40% to 0.60%.

[0025] Phosphorus reduces the deformation capacity of the wire rod during the steel wire processing, causing the steel wire to crack and break, so the phosphorus content in the present invention is ≤0.013%.

[0026] A higher sulfur content in the steel reduces the cold working performance of the wire rod. Since MnS inclusions have good deformation ability, a proper amount of sulfur in the steel can play a role in reducing the harm of spar inclusions, so the sulfur content in the present invention is controlled at 0.0020% to 0.010%.

[0027] When the oxygen content is low, the inclusions in the wire rod have poor deformation ability, which is not conducive to the processing of the steel wire; when the oxygen content in the wire rod is high, the inclusions in the steel are large in size and large in number, which easily leads to cracking and breaking of the steel wire during processing. The high oxygen content in the steel is conducive to inhibiting the chromium in the steel from being reduced to the steel. Therefore, the total oxygen content of the wire rod in the present invention is controlled at 0.0025% to 0.0040%.

[0028] When the acid-soluble aluminum content is high, larger Al2O3 inclusions will appear in the steel; when the acid-soluble aluminum content in the wire rod is too low, the melting point of the inclusions in the steel is high, and cracks are likely to occur between the inclusions and the matrix during processing, resulting in cracking and breakage during the steel wire processing. When the acid-soluble aluminum content in the steel is high, the chromium element in the steel is promoted to be reduced to the molten steel, increasing the chromium content of the molten steel. Therefore, the acid-soluble aluminum content of the present invention is controlled at 0.0001% to 0.0008%.

[0029] Niobium can inhibit the grain growth of the steel billet during the heating process, thereby refining the pearlite structure of the wire rod and improving the deformation ability of the wire rod during the steel wire processing process. However, a higher niobium content leads to a higher niobium carbonitride content in the steel, and the wire rod is severely hardened during the steel wire processing process, which is easy to cause cracking and breaking of the steel wire. Therefore, the niobium content of the present invention is controlled at 0.0003% to 0.0012%.

[0030] 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 0.006% to 0.0013%.

[0031] The chromium element improves the hardenability of the wire rod, causing the strength of the steel wire to increase and the drawing performance to decrease. In the present invention, the molybdenum content is controlled to be ≤0.01%.

[0032] 2. Production technology

[0033] The present invention also discloses a method for preparing a low-chromium 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, wire rod rolling, and wire rod cooling.

[0034] Further, the method specifically includes the following steps:

[0035] S1. During converter smelting, the temperature after the converter is 1570℃~1610℃, and the oxygen activity of the liquid steel after smelting is controlled at 70ppm~200ppm; the higher oxygen content is used to reduce the chromium content in the steel.

[0036] In a specific embodiment, step S1 also includes: using scrap steel and molten iron as charge, the mass percentage of scrap steel in the charge is 5% to 15%; using slag as standard slag in the later stage of the converter tapping process, and the slag amount is ≤80kg; the Cr2O3 content of the top slag after the converter tapping is ≤1%, so as to prevent the chromium in the top slag from being reduced and entering the steel to increase the chromium content of the molten steel.

[0037] In S2 and LF refining, the sulfur content is controlled at 0.0045% to 0.0145%, the oxygen activity is controlled at 0.0030% to 0.0070%, and the refining temperature is 1420℃ to 1490℃; the characteristics of sulfur and oxygen as surface active elements are used to prevent the chromium in the top slag from being reduced and entering the molten steel. The argon flow rate is controlled at 50NL / min to 150NL / min during the refining process, and the liquid level fluctuation is ≤40mm.

[0038] S3. During continuous casting, the molten steel subjected to LF refining treatment is continuously cast to obtain a continuously cast ingot.

[0039] In a specific embodiment, the cross-sectional dimensions of the continuous casting billet are (260mm-300mm)×(360mm-400mm); the carbon content of the covering agent is ≤1%, the Cr2O3 content is ≤1%, and the liquid level of the molten steel in the crystallizer fluctuates by ±3mm. This prevents the carbon in the covering agent from reducing the chromium element in the covering agent and increasing the chromium content of the molten steel.

[0040] S4. During continuous rolling, the continuous casting billets produced in the continuous casting process are sent to a heating furnace for heating.

[0041] In a specific embodiment, the total time in the furnace is 2.5h to 3.5h; the temperature of the soaking section is 1200℃ to 1230℃, and the holding time is 50min to 80min; the final rolling temperature of the continuous rolling is 900℃ to 940℃; the cross-sectional size of the continuous rolling billet is (140mm to 180mm)×(140mm to 180mm).

[0042] S5. During the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then sequentially subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire drawing.

[0043] In a specific embodiment, during the wire rod rolling, the total furnace time of the steel billet is 100min-120min, the temperature of the soaking section is 1060℃-1120℃, and the insulation time of the steel billet soaking section is 40min-60min; after the steel billet is heated, it is subjected to high-pressure water descaling treatment, the descaling pressure is ≥14MPa, and the iron oxide scale coverage rate of the steel billet surface after high-pressure water descaling is ≤5%; after the steel billet is heated, it is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling, and then the wire rod spinning operation is performed; the pre-finishing rolling temperature of the wire rod is 940℃-960℃; the finishing rolling temperature is 920℃-940℃; the temperature of the double module is 910℃-930℃, and the rolling speed of the double module is 100m / s-120m / s; the wire rod spinning temperature is 910℃-930℃. The wire rod rolling specification is 8mm-10mm.

[0044] S6. During the wire rod cooling process, the wire rod is cooled on an air-cooled roller after spinning.

[0045] In a specific embodiment, during the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning, the cementite precipitation temperature of the wire rod is controlled to be 620°C ~ 670°C, the phase change time of the wire rod on the air-cooled line is 15s ~ 25s, the phase change supercooling is 80°C ~ 110°C, the temperature difference between the overlap point and the non-overlap point during the cooling process of the wire rod is ≤30°C, and the coiling temperature is 200°C ~ 300°C.

[0046] The following are specific embodiments

[0047] Examples 1-6

[0048] 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.

[0049] Table 1 Chemical composition, preparation process and performance parameters of wire rods of Examples 1-6

[0050]

[0051]

[0052] According to the above results, the present invention has carried out a large number of systematic experimental studies from the aspects of converter smelting, LF refining, continuous casting, continuous rolling, wire rod rolling, wire rod cooling process design optimization, etc., and finally obtained an accurate preparation method of the chromium content of high carbon steel wire rod. By controlling the reduction reaction of chromium element, the chromium content of high carbon steel wire rod is controlled to below 0.01%, meeting the quality requirements of high carbon steel wire rod.

[0053] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it 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. A low chromium high carbon steel wire rod, characterized in that: The low chromium high carbon steel wire rod comprises the following components in percentage by mass: C: 0.81%~0.85%, Si: 0.12%~0.24%, Mn: 0.40%~0.60%, P≤0.013%, S: 0.0020%~0.010%, total oxygen: 0.0025%~0.0040%, Als: 0.0001%~0.0008%, Nb: 0.0003%~0.0012%, Mo: 0.0006%~0.0013%, Cr≤0.01%, and the balance is iron and unavoidable impurities.

2. A method for preparing a low-chromium high-carbon steel wire rod as claimed in claim 1, characterized in that: The following steps are involved: Converter smelting, LF refining, continuous casting, continuous rolling, wire rod rolling, wire rod cooling; In the converter smelting, the temperature after the converter is 1570°C to 1610°C, and the oxygen activity of the liquid steel after smelting is 70ppm to 200ppm; In the LF refining, the sulfur content is 0.0045% to 0.0145%, the oxygen activity is 0.0030% to 0.0070%, and the refining temperature is 1420° C. to 1490° C.; the argon flow rate is controlled to be 50NL / min to 150NL / min during the refining process, and the liquid level fluctuation is ≤40mm; In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast to obtain a continuously cast ingot; During the continuous rolling, the continuous casting billet produced in the continuous casting process is sent into a heating furnace for heating; In the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence; During the wire rod cooling, the wire rod is cooled on an air-cooled roller after spinning.

3. The preparation method according to claim 2, characterized in that: In the converter smelting, scrap steel and molten iron are used as furnace charge, and the mass percentage of scrap steel in the furnace charge is 5% to 15%; slag stopper is used as slag in the later stage of converter steel tapping, and the slag amount is ≤80kg; the Cr2O3 content of top slag after converter steel tapping is ≤1%.

4. The preparation method according to claim 2, characterized in that: In the continuous casting, the cross-sectional dimensions of the continuous casting billet are (260 mm to 300 mm)×(360 mm to 400 mm); the carbon content of the covering agent is ≤1%, and the Cr2O3 content is ≤1%; and the liquid level of the molten steel in the crystallizer fluctuates by ±3 mm.

5. The preparation method according to claim 2, characterized in that: During the continuous rolling, the total time in the furnace is 2.5h to 3.5h; the temperature of the soaking section is 1200°C to 1230°C, and the holding time is 50min to 80min; the final rolling temperature is 900°C to 940°C; and the cross-sectional size of the continuous rolling billet is (140mm to 180mm)×(140mm to 180mm).

6. The preparation method according to claim 2, characterized in that: During the wire rod rolling, the total furnace time of the steel billet is 100min-120min, the temperature of the soaking section is 1060℃-1120℃, and the insulation time of the steel billet soaking section is 40min-60min; after the steel billet is heated, it is subjected to high-pressure water descaling treatment, the descaling pressure is ≥14MPa, and the iron oxide scale coverage rate of the steel billet surface after high-pressure water descaling is ≤5%; after the steel billet is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling, the wire rod spinning operation is carried out.

7. The preparation method according to claim 6, characterized in that: The pre-finishing rolling temperature of the wire rod is 940℃~960℃; the finishing rolling temperature is 920℃~940℃; the entering double module temperature is 910℃~930℃, and the rolling speed out of the double module is 100m / s~120m / s; the wire rod spinning temperature is 910℃~930℃.

8. The preparation method according to claim 2, characterized in that: During the wire rod cooling, the wire rod is cooled on an air-cooled roller after spinning, the cementite precipitation temperature of the wire rod is controlled to be 620°C to 670°C, the phase change time of the wire rod on the air-cooled line is 15s to 25s, the phase change supercooling is 80 to 110°C, the temperature difference between the overlap point and the non-overlap point during the wire rod cooling process is ≤30°C, and the coiling temperature is 200°C to 300°C.

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