Production method of high carbon steel wire rod and high carbon steel wire rod

Abstract

The present invention discloses a production method of a high-carbon steel wire rod and a high-carbon steel wire rod. The method adopts a process of heating-descaling-rough rolling-intermediate rolling-pre-finishing rolling-finishing rolling-spinning-Styelmor cooling: the rough rolling start temperature is 1060-1090°C; the rough and intermediate rolling mill adopts water cooling to make the roller surface temperature 30-70°C, and the temperature of the corner of the rolled piece 1000-1080°C; the first two stages of finishing rolling are water-cooled, the water pressure is 0.40-0.60MPa, and the water flow rate is 800-1000L / min and 400-500L / min respectively; the inlet of the finishing mill is 940-970°C, the outlet is below 1040°C, the water cooling guide is 0.32-0.42MPa and 120-150L / min; the water pressure of the three stages after finishing rolling is 0.42-0.48MPa, and the water flow rate adopts a high-low-high scheme; the spinning temperature is 910-950°C. The obtained wire rod has uniform structure and reduced cementite and martensite.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel production and manufacturing, and specifically relates to a production method of high-carbon steel wire rod, and also relates to a high-carbon steel wire rod prepared based on the production method. Background Art

[0002] High-carbon steel wire prepared by cold-drawing high-carbon steel wire rod is the highest-strength steel material known. High-carbon steel wire is widely used in many industries of the national economy, such as various types of wire ropes, bridge cables, galvanized steel wire, and tire frame materials, and occupies an important position in the industry.

[0003] Due to the high strength and multi-pass drawing characteristics of high carbon steel wire rod, very high requirements are placed on the uniformity of the structure, and the generation of grain boundary cementite and martensite should be avoided as much as possible. The existing technology solves this problem mainly through the following ways: 1) Control the parameters such as superheat, secondary cooling water, electromagnetic stirring, and light reduction in the continuous casting process to reduce the segregation of the continuous casting billet, thereby reducing the martensite grain boundary cementite caused by segregation; 2) Perform high-temperature diffusion on the continuous casting billet to eliminate the impact of segregation on the structure; 3) Optimize the post-rolling air cooling process, increase the cooling rate in the early stage of phase transformation, and reduce the cooling rate in the later stage of phase transformation to reduce or eliminate grain boundary cementite and martensite; 4) Perform salt bath and other heat treatments on the wire rod to further uniformize the structure. It is worth affirming that the existing technology has a good effect on improving the uniformity of organizational performance and reducing the impact of abnormal structure.

[0004] However, for water cooling, an essential part of hot rolling technology, current technology and research only focus on how to control temperature to reduce temperature differences, but ignore the impact of water cooling control on wire rod microstructure performance. There is no public technology to provide guidance on how to improve wire rod microstructure uniformity and reduce abnormal microstructures such as grain boundary cementite and martensite through water cooling control. Summary of the Invention

[0005] The object of the present invention is to provide a production method of high carbon steel wire rod, and also relates to a high carbon steel wire rod prepared based on the production method.

[0006] To achieve the above object, one embodiment provides a method for producing high carbon steel wire rod, wherein a billet having a mass percentage of carbon ≥ 0.70% is prepared into wire rod according to a process of heating in a heating furnace - high-pressure water descaling - roughing rolling - intermediate rolling - pre-finishing rolling - finishing rolling - spinning - Stelmor cooling, wherein:

[0007] The water pressure in the high-pressure water descaling process is 10-15 MPa;

[0008] The starting rolling temperature of the rough rolling process is 1060-1090°C;

[0009] The rolls of the roughing mill and the intermediate mill are water-cooled, the roll surface temperature is controlled at 30-70°C, and the corner temperature of the rolled piece is 1000-1080°C;

[0010] Two-stage water cooling is carried out between the pre-finishing mill and the finishing mill, with the water pressure controlled at 0.40-0.60 MPa and the water flow rate at 800-1000 L / min and 400-500 L / min respectively;

[0011] The inlet temperature of the finishing mill is 940-970°C, and the outlet temperature is below 1040°C. The water pressure of the water-cooled guide in the finishing mill is controlled at 0.32-0.42 MPa, and the water flow rate is 120-150 L / min.

[0012] Three-stage water cooling is carried out between the finishing mill and the laying head. The water pressure is controlled at 0.42-0.48 MPa, and the water flow rate is 900-1100 L / min, 620-920 L / min, and 900-1100 L / min, respectively. The water flow rate of the middle section is smaller than that of the two sections before and after.

[0013] The spinning temperature is 910-950℃;

[0014] On the Stelmor cooling line, starting from the first fan, 6 to 14 fans are turned on and the air volume of the fans turned on is controlled to 100%.

[0015] Preferably, when water cooling the rolls of the roughing mill and the intermediate rolling mill, the water temperature is controlled to be ≤25° C. and the water pressure is controlled to be 0.20-0.40 MPa.

[0016] Preferably, in the high-pressure water descaling process, the removal rate of iron oxide scale on the surface of the blank is ≥98%.

[0017] Preferably, in the "water cooling of the rolls of the roughing mill and the intermediate rolling mill, and the control of the roll surface temperature at 30-70°C", the roll surface temperature of the first three rolling mills in the roughing mill and the intermediate rolling mill is controlled at 50-70°C, and the roll surface temperature of the remaining rolling mills is controlled at 30-50°C.

[0018] Preferably, the prepared wire rod has a diameter of ≤7 mm, and:

[0019] The water flow rates of the two stages of water cooling between the pre-finishing mill and the finishing mill are 800-850 L / min and 480-500 L / min respectively;

[0020] The water flow rate of the water-cooled guide in the finishing mill is 120-130 L / min;

[0021] The water flow rates of the three stages of water cooling between the finishing mill and the laying head are 900-1000 L / min, 620-720 L / min, and 900-1000 L / min, respectively.

[0022] Preferably, the prepared wire rod has a diameter of 7 to 14 mm, and:

[0023] The water flow rates of the two stages of water cooling between the pre-finishing mill and the finishing mill are 850-1000 L / min and 400-480 L / min respectively;

[0024] The water flow rate of the water-cooled guide in the finishing mill is 130-150 L / min;

[0025] The water flow rates of the three stages of water cooling between the finishing mill and the laying head are 950-1100 L / min, 720-920 L / min, and 950-1100 L / min, respectively.

[0026] Preferably, between the finishing mill and the laying head, the core-surface temperature difference of the rolled piece when leaving the third water cooling section is ≥150°C.

[0027] To achieve the above object, one embodiment provides a high carbon steel wire rod prepared by the above production method, wherein the grain boundary cementite detection rate of the wire rod is ≤5%, and the martensite detection rate is ≤5%.

[0028] Preferably, the diameter of the wire rod is ≤10 mm, the grain boundary cementite is ≤level 1 and the detection rate is ≤3%, and the martensite is ≤level 1 and the detection rate is ≤2%.

[0029] Preferably, the diameter of the wire rod is 10-14 mm, the grain boundary cementite thereof is ≤ level 2 and the detection rate is ≤5%, and the martensite is ≤ level 1 and the detection rate is ≤5%.

[0030] Compared with the prior art, the beneficial effect of the present invention lies in: by designing water cooling in the rolling process, including water cooling of the rolls in rough rolling and intermediate rolling, water cooling between pre-finishing rolling and finishing rolling, water cooling in the finishing mill and water cooling after rolling, etc., not only the effective control of key temperatures in rolling is achieved, but also the idea of ​​regulating the wire rod structure by water cooling during the rolling process is innovatively proposed, and the uniformity of the wire rod structure is improved and the detection probability and level of grain boundary cementite and martensite are reduced with a simple water cooling scheme without the need for additional processes such as high-temperature diffusion of the continuous casting billet, air cooling and then salt bath heat treatment. In particular, the improvement effect on the structural uniformity is more significant for continuous casting billets with higher segregation levels; and on the basis of the above-mentioned effects, the common phenomenon of water cooling causing production accidents such as steel piling is not caused. That is, the water cooling scheme can also ensure the smooth progress of production and does not cause equipment instability. DETAILED DESCRIPTION

[0031] One embodiment of the present invention provides a method for producing high-carbon steel wire rod. In this method, a billet is prepared into wire rod according to a process consisting of heating in a heating furnace, descaling in high-pressure water, rolling, and Stelmor cooling. Furthermore, one embodiment provides wire rod produced using this production method.

[0032] Below, each process of a preferred embodiment of the present invention is introduced in sequence.

[0033] (1) Heating process in heating furnace

[0034] The billet is heated in a heating furnace. The billet can be produced by steelmaking and billet continuous casting, and its cross-sectional dimensions can be 140 mm x 140 mm. The billet has a carbon content of ≥ 0.70% by weight, and the wire rod produced from the billet also has a carbon content of ≥ 0.70% by weight.

[0035] Preferably, in the heating process of the heating furnace, a three-stage heating method of a preheating section, a heating section and a soaking section can be adopted.

[0036] (2) High-pressure water descaling process

[0037] After the heated billet leaves the heating furnace, it is descaled using high-pressure water to remove the iron oxide scale on the billet surface. The descaling water pressure is controlled at 10-15 MPa.

[0038] Preferably, the scale removal rate on the surface of the blank is ≥98% by high-pressure water descaling.

[0039] (3) High-speed wire rolling process

[0040] The descaled billet is rolled into wire rod with a diameter of less than 14 mm. The rolling process is further divided into rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling and wire laying.

[0041] Specifically, the starting rolling temperature of the rough rolling process is 1060-1090°C.

[0042] The rolls of the roughing mill and intermediate mill are water-cooled, with the roll surface temperature controlled at 30-70°C and the corner temperature of the rolled piece at 1000-1080°C. For example, preferably, the water temperature is controlled to ≤25°C and the water pressure is controlled to 0.20-0.40 MPa to keep the roll surface temperature at 30-70°C. Further preferably, in all roughing mills and intermediate mills (6 roughing mills + 6 intermediate mills), the roll surface temperature of the first three mills is controlled at 50-70°C, and the roll surface temperature of the remaining mills (e.g., mills 4 to 12) is controlled at 30-50°C.

[0043] Two stages of water cooling are carried out between the pre-finishing mill and the finishing mill, the water pressure is controlled at 0.40-0.60 MPa, and the water flow rate is 800-1000 L / min and 400-500 L / min respectively.

[0044] The inlet temperature of the finishing mill is 940-970°C, and the outlet temperature is below 1040°C. The water pressure of the water-cooled guide in the finishing mill is controlled at 0.32-0.42 MPa, and the water flow rate is 120-150 L / min.

[0045] Three-stage water cooling is carried out between the finishing mill and the laying head, the water pressure is controlled at 0.42-0.48 MPa, the water flow rate is 900-1100 L / min, 620-920 L / min, and 900-1100 L / min, respectively, and the water flow rate of the middle section is smaller than that of the front and rear sections, that is, the three-stage water cooling adopts a high, low, and high water flow control scheme.

[0046] The spinning temperature is 910-950℃.

[0047] It is further preferred that the water cooling methods before and after the finishing rolling process are different according to the diameter specifications of the prepared wire rod. Specifically: in the first case, the diameter of the prepared wire rod is ≤7mm, the water flow rates of the two-stage water cooling between the pre-finishing mill and the finishing mill are 800-850L / min and 480-500L / min respectively, the water flow rate of the water cooling guide in the finishing mill is 120-130L / min, and the water flow rate of the three-stage water cooling between the finishing mill and the laying head is 900-1000L / min, 620-720L / min respectively. n, 900 ~ 1000L / min; in the second case, the diameter of the prepared wire rod is 7 ~ 14mm, the water flow rates of the two stages of water cooling between the pre-finishing rolling process and the finishing rolling process are 850 ~ 1000L / min and 400 ~ 480L / min, respectively, the water flow rate of the water-cooling guide in the finishing mill is 130 ~ 150L / min, and the water flow rates of the three stages of water cooling between the finishing rolling process and the spinning process are 950 ~ 1100L / min, 720 ~ 920L / min, and 950 ~ 1100L / min, respectively.

[0048] In addition, preferably, between the finishing mill and the laying head, the core-surface temperature difference of the rolled piece when leaving the third water cooling stage is ≥150°C.

[0049] (4) Stelmor cooling process

[0050] The wire rod rolled through the rolling process is cooled in a Stelmor cooling line. On the Stelmor cooling line, starting with the first fan, 6 to 14 fans are turned on and the air volume of the turned-on fans is controlled to be 100%.

[0051] In this way, after cooling in Stelmor, the wire rod can be coiled, inspected and put into storage.

[0052] The production method, by designing water cooling in the rolling process, including water cooling of the rolls in rough rolling and intermediate rolling, water cooling between pre-finishing rolling and finishing rolling, water cooling in the finishing mill and water cooling after rolling, not only achieves effective control of key temperatures in rolling, but also innovatively proposes the idea of ​​regulating the wire rod structure by water cooling during the rolling process, and achieves the improvement of the wire rod structure uniformity and the reduction of the detection probability and level of grain boundary cementite and martensite with a simple water cooling scheme without the need for additional processes such as high-temperature diffusion of the continuous casting billet and salt bath heat treatment after air cooling. In particular, the improvement effect on the structure uniformity is more significant for continuous casting billets with higher segregation levels. Moreover, based on the aforementioned effects, the common phenomenon of water cooling causing production accidents such as steel piling is not caused. That is, the water cooling scheme can also ensure the smooth progress of production and does not cause equipment instability.

[0053] As previously mentioned, in one embodiment, the wire rod produced by the production method has a grain boundary cementite detection rate of ≤5%, and a martensite detection rate of ≤5%. Furthermore, when the diameter of the produced wire rod is 10-14 mm, the grain boundary cementite is ≤ Grade 2 and has a detection rate of ≤5%, and the martensite is ≤ Grade 1 and has a detection rate of ≤5%. Furthermore, when the wire rod diameter is even smaller, such as when the wire rod diameter is ≤10 mm, the grain boundary cementite is ≤ Grade 1 and has a detection rate of ≤3%, and the martensite is ≤ Grade 1 and has a detection rate of ≤2%.

[0054] The technical solution of the present invention is further introduced below through Examples 1 and 2.

[0055] Example 1

[0056] This embodiment uses a continuous casting billet with a cross-sectional size of 140 mm × 140 mm to prepare a SWRH82B wire rod with a diameter of 6.5 mm. The process is as follows:

[0057] The blank is heated in a heating furnace in a three-stage heating mode of a preheating section at 910-960°C, a heating section at 1040-1090°C, and a soaking section at 1150-1190°C.

[0058] After leaving the heating furnace, the billet is descaled with high-pressure water. The descaling water pressure is controlled at 12MPa, and the removal rate of iron oxide scale on the billet surface reaches 98.8%.

[0059] The scale-removed billet enters the roughing mill, intermediate mill, pre-finishing mill and finishing mill in turn for rolling, and then leaves the laying head; the starting rolling temperature when entering the roughing mill is 1060-1080°C; the rollers of the 12 rolling mills, including the roughing mill and the intermediate mill, are water-cooled at a water temperature of 23°C and a water pressure of 0.28MPa. The surface temperature of the rollers of the first three rolling mills is controlled at 50-60°C, and the surface temperature of the rollers of the remaining 9 rolling mills is controlled at 30-40°C, while the corner temperature of the rolled piece is 1020°C±20°C; two water tanks are set between the pre-finishing mill and the finishing mill, and accordingly, the pre-finishing process and the finishing process are Two stages of water cooling are carried out between the mill and the finishing mill, with the water pressure controlled at 0.46 MPa and the water flow rates of 840 L / min and 490 L / min, respectively. The inlet temperature of the finishing mill is 940-950°C and the outlet temperature is below 1020°C. The water pressure of the water-cooled guide in the finishing mill is controlled at 0.33 MPa and the water flow rate is 126 L / min. Three stages of water cooling are carried out after the finishing mill, with the water pressure controlled at 0.45 MPa and the water flow rates of 960 L / min, 720 L / min and 960 L / min, respectively. The core-surface temperature difference of the rolled piece when it leaves the third stage of water cooling is 180°C. The spinning temperature is 910-930°C.

[0060] After the rolled piece leaves the laying head, it enters the Stelmor cooling line for cooling. On the Stelmor cooling line, the first 7 fans are turned on and the air volume of the fans is controlled to 100%;

[0061] As described above, the obtained wire rod was sheared head-to-tail and sampled for testing. The tensile strength was 1170-1200 MPa, the area reduction was 35-40%, and the metallographic structure was etched with nitric alcohol. Only one grade 1 grain boundary cementite was detected from 44 samples tested, i.e., the grain boundary cementite detection rate was 2.3%. No martensite was found, i.e., the martensite detection rate was 0. It can be seen that the wire rod prepared in this embodiment has excellent structural uniformity, and abnormal structures such as grain boundary cementite and martensite are significantly reduced.

[0062] Example 2

[0063] This embodiment uses a continuous casting billet with a cross-sectional size of 140 mm × 140 mm to prepare a SWRH87B wire rod with a diameter of 12.5 mm. The process is as follows:

[0064] The blank is heated in a heating furnace in a three-stage heating mode of a preheating section at 920-970°C, a heating section at 1050-1100°C, and a soaking section at 1160-1200°C.

[0065] After leaving the heating furnace, the billet is descaled with high-pressure water. The descaling water pressure is controlled at 15MPa, and the removal rate of iron oxide scale on the billet surface reaches 99%.

[0066] The scale-removed billet enters the roughing mill, intermediate mill, pre-finishing mill and finishing mill in turn for rolling, and then leaves the laying head; the starting rolling temperature when entering the roughing mill is 1070-1090°C; the rollers of the 12 rolling mills, including the roughing mill and intermediate mill, are water-cooled at a water temperature of 22°C and a water pressure of 0.35MPa. The surface temperature of the rollers of the first three rolling mills is controlled at 60-70°C, and the surface temperature of the rollers of the remaining 9 rolling mills is controlled at 30-40°C, while the corner temperature of the rolled piece is 1030°C±20°C; two water tanks are set between the pre-finishing mill and the finishing mill, and accordingly, the rollers are cooled between the pre-finishing mill and the finishing mill. Two-stage water cooling is carried out, with the water pressure controlled at 0.60 MPa and the water flow rates at 980 L / min and 420 L / min, respectively. The inlet temperature of the finishing mill is 960-970°C and the outlet temperature is below 1030°C. The water pressure of the water-cooled guide in the finishing mill is controlled at 0.42 MPa and the water flow rate is 145 L / min. After the finishing rolling process, three-stage water cooling is carried out, with the water pressure controlled at 0.45 MPa and the water flow rates at 1080 L / min, 810 L / min, and 1080 L / min, respectively. The core-surface temperature difference of the rolled piece when leaving the third water cooling stage is 220°C. The spinning temperature is 930-950°C.

[0067] After the rolled piece leaves the laying head, it enters the Stelmor cooling line for cooling. On the Stelmor cooling line, the front 14 fans are turned on and the air volume of the fans is controlled to 100%;

[0068] As described above, the obtained wire rod was sampled and tested after shearing at the head and tail. The tensile strength was 1230-1260 MPa, the area reduction was 30-38%, and the metallographic structure was etched with nital. Among the 50 tested samples, only one first-grade grain boundary cementite and one second-grade grain boundary cementite were detected, i.e., the grain boundary cementite detection rate was 4%. One first-grade martensite was detected, i.e., the martensite detection rate was 2%. It can be seen that the wire rod prepared in this embodiment has excellent structural uniformity, and abnormal structures such as grain boundary cementite and martensite are significantly reduced.

Claims

1. A method for producing a high carbon steel wire rod, characterized in that: The billet with a mass percentage of C ≥ 0.70% is prepared into a wire rod according to the process of heating in a heating furnace - high-pressure water descaling - rough rolling - intermediate rolling - pre-finishing rolling - finishing rolling - spinning - Stelmor cooling, wherein: The water pressure in the high-pressure water descaling process is 10-15 MPa; The starting rolling temperature of the rough rolling process is 1060-1090°C; The rolls of the roughing mill and the intermediate mill are water-cooled, the roll surface temperature is controlled at 30-70°C, and the corner temperature of the rolled piece is 1000-1080°C; Two-stage water cooling is carried out between the pre-finishing mill and the finishing mill, the water pressure is controlled at 0.40-0.60 MPa, and the water flow rate is 800-1000 L / min and 400-500 L / min respectively; The inlet temperature of the finishing mill is 940-970°C, the outlet temperature is below 1040°C, the water pressure of the water-cooled guide in the finishing mill is controlled at 0.32-0.42MPa, and the water flow rate is 120-150L / min; Three-stage water cooling is carried out between the finishing mill and the laying head, the water pressure is controlled at 0.42-0.48 MPa, the water flow rate is 900-1100 L / min, 620-920 L / min, 900-1100 L / min, and the water flow rate of the middle stage is smaller than that of the front and rear stages; The spinning temperature is 910-950℃; On the Stelmore cooling line, starting from the first fan, 6 to 14 fans are turned on and the air volume of the fans turned on is controlled to 100%.

2. The method for producing high carbon steel wire rod according to claim 1, characterized in that: When water cooling the rolls of the roughing mill and the intermediate rolling mill, the water temperature is controlled to be ≤25°C and the water pressure is controlled to be 0.20~0.40MPa.

3. The method for producing high carbon steel wire rod according to claim 1, characterized in that: In the high-pressure water descaling process, the removal rate of iron oxide scale on the surface of the billet is ≥98%.

4. The method for producing high carbon steel wire rod according to claim 1, characterized in that: In the "water cooling of the rolls of the roughing mill and the intermediate rolling mill, and the roll surface temperature is controlled at 30-70°C", the roll surface temperature of the first three rolling mills among the roughing mill and the intermediate rolling mill is controlled at 50-70°C, and the roll surface temperature of the remaining rolling mills is controlled at 30-50°C.

5. The method for producing high carbon steel wire rod according to claim 1, characterized in that: The diameter of the prepared wire rod is ≤7mm, and: The water flow rates of the two stages of water cooling between the pre-finishing mill and the finishing mill are 800-850 L / min and 480-500 L / min respectively; The water flow rate of the water-cooled guide in the finishing mill is 120-130L / min; The water flow rates of the three-stage water cooling between the finishing mill and the spinning machine are 900-1000 L / min, 620-720 L / min, and 900-1000 L / min respectively.

6. The method for producing high carbon steel wire rod according to claim 1, characterized in that: The prepared wire rod has a diameter of 7 to 14 mm and: The water flow rates of the two stages of water cooling between the pre-finishing mill and the finishing mill are 850-1000 L / min and 400-480 L / min respectively; The water flow rate of the water-cooled guide in the finishing mill is 130-150L / min; The water flow rates of the three-stage water cooling between the finishing mill and the spinning machine are 950-1100 L / min, 720-920 L / min, and 950-1100 L / min, respectively.

7. The method for producing high carbon steel wire rod according to claim 1, characterized in that: Between the finishing mill and the spinning mill, the core-surface temperature difference of the rolled piece when leaving the third water cooling section is ≥150℃.

8. A high carbon steel wire rod, characterized in that: The wire rod is prepared by the production method according to any one of claims 1 to 7, wherein the grain boundary cementite detection rate of the wire rod is ≤5%, and the martensite detection rate is ≤5%.

9. The high carbon steel wire rod according to claim 8, characterized in that: The diameter of the wire rod is ≤10 mm, the grain boundary cementite thereof is ≤level 1 and the detection rate is ≤3%, and the martensite is ≤level 1 and the detection rate is ≤2%.

10. The high carbon steel wire rod according to claim 8, characterized in that: The diameter of the wire rod is 10-14 mm, the grain boundary cementite is ≤ level 2 and the detection rate is ≤5%, and the martensite is ≤ level 1 and the detection rate is ≤5%.