Rolling process for preparing er50-6e welding wire steel with tensile strength not greater than 1360mpa and application thereof

Abstract

The present application belongs to the field of rolling technology, and relates to a rolling process for preparing ER50-6E welding wire steel with tensile strength not more than 1360MPa and application thereof. The billet is continuously fed, the time in the furnace is not less than 110 minutes, the heating temperature is 1100-1150 DEG C, the soaking temperature is 1170-1220 DEG C, the rough rolling temperature is 1070-1120 DEG C, the finish rolling temperature is not less than 960 DEG C, the water volume of finish rolling cooling water is reduced to increase the finish rolling outlet temperature to not less than 1050 DEG C, the wire feeding temperature is 920-950 DEG C, the heat preservation cover is fully closed, the roller speed is slow, and the cover outlet temperature is controlled below 650 DEG C. The hot-rolled wire rod has tensile strength not more than 500MPa, yield strength not more than 310MPa, and yield strength ratio not more than 0.63, and is suitable for drawing 0.8mm welding wire from the Φ6.5mm wire rod, the welding wire has tensile strength not more than 1360MPa, and has good wire feeding performance.

Description

Technical Field

[0001] This invention relates to the field of rolling technology, and specifically to a rolling process for ER50-6E gas-shielded welding wire steel wire rod, that is, a rolling process for drawing fine wire welding wire steel wire rod. Background Technology

[0002] With the continuous development of welding technology, the demand for ER50-6E gas shielded welding wire has increased significantly. CO2 gas shielded welding and CO2+Ar mixed gas shielded welding are welding methods vigorously promoted by my country's welding industry, primarily using ER50-6 solid core welding wire. This welding wire not only has good arc stability and high welding performance, but also features stable arc, high deposition efficiency, less spatter, beautiful weld formation, strong resistance to oxidation and corrosion, low porosity sensitivity of weld metal, and convenient operation. Furthermore, the annealing process can be omitted during the wire processing, reducing manufacturing costs. It is widely used in various fields such as petrochemicals, pressure vessels, power, automobiles, shipbuilding, and power plants.

[0003] Currently, the specifications of ER50-6 welding wire steel used in domestic CO2 gas shielded welding and CO2+Ar mixed gas shielded welding are Φ0.8mm~Φ1.2mm, generally produced by drawing from Φ5.5mm wire rod, and related patents also all involve drawing welding wire from Φ5.5mm wire rod. In recent years, in order to reduce costs, welding wire steel has begun to be produced by drawing from Φ6.5mm wire rod, but it has only been able to draw welding wire from Φ1.0mm~Φ1.2mm.

[0004] In previous ER50-6E wire rod patents, conventional rolling of the wire rod employed controlled rolling, with three modes: two-phase controlled rolling, non-recrystallized controlled rolling, and recrystallized controlled rolling. Two-phase controlled rolling is performed in the ferrite and austenite two-phase region at very low temperatures; non-recrystallized controlled rolling is performed in the Ar3–950℃ range; and recrystallized controlled rolling is performed in the 950–1000℃ range. The purpose of all three controlled rolling modes is to refine the austenite grains, causing the C-curve to shift to the left, allowing austenite to transform into ferrite as early as possible, thereby controlling the tensile strength of the wire rod within a suitable range.

[0005] All three controlled rolling modes require controlling the initial rolling temperature, which is primarily controlled by the heating process. Higher heating temperatures and longer heating times result in larger austenite sizes in the high-temperature billet. Therefore, to ultimately refine the austenite grain size, all three controlled rolling modes require the initial rolling temperature to be relatively low; thorough heating of the billet is sufficient. Thus, the initial rolling temperature is generally controlled between 960 and 1050℃. Due to the low initial rolling temperature, the roughing, intermediate rolling, and pre-finishing rolling processes are essentially in a recrystallization-type controlled rolling process, resulting in some austenite grain refinement. The main control point for all three controlled rolling modes is in the finishing mill, as the entire rolling line only has cooling water tanks before and after the finishing mill. The finishing mill has 10 stands, with a final rolling speed exceeding 100 m / s. The rolling deformation heat is high, and the material temperature rises rapidly. Therefore, the cooling water volume inside the finishing mill is very large to control the exit temperature of each stand, thereby controlling the exit temperature of the finishing mill. The ER50-6E wire rod patent generally requires an entry temperature of 900-950℃ for the finishing mill. The entry temperature for the finishing mill is a non-recrystallization type controlled rolling temperature. However, due to the rapid temperature rise of the material during the rolling process, most of the rolling process is within the recrystallization type controlled rolling temperature range. That is, the 10 stands inside the finishing mill are mainly controlled rolling modes based on recrystallization type controlled rolling.

[0006] Patent CN202210065495.0 describes a rolling process for high-speed drawing of welding wire steel. The process controls the temperature at the entry point of the finishing mill to 920–960°C and the exit temperature to less than 1050°C. This is a typical controlled rolling mode where the 10 stands inside the finishing mill primarily employ recrystallization-type controlled rolling, with the main purpose of refining austenite grains. However, this patent does not specifically address the cooling water control within the finishing mill, and it does not investigate the mechanical properties or wire feeding performance of the welding wire produced from wire rod drawing.

[0007] The reason users do not use Φ6.5mm wire rod to produce Φ0.8mm welding wire is because the increased reduction in surface area during drawing increases the work hardening capacity, making Φ0.8mm welding wire more prone to breakage. This is especially true since the tensile strength of the welding wire is also very high, reaching approximately 1350–1420 MPa, resulting in high rigidity and severely impacting wire feeding performance. (According to welding wire manufacturers' experience, the wire feeding performance of Φ0.8mm welding wire decreases significantly once the tensile strength exceeds 1360 MPa.)

[0008] To date, there is no technical information on the research of drawing 0.8mm welding wire from 6.5mm wire rod, and there are no reports on how to achieve low work hardening performance by appropriately coarsening the austenite grains and pursuing a uniform and relatively coarse ferrite structure. Summary of the Invention

[0009] The purpose of this invention is to provide a rolling process for ER50-6E welding wire steel used for drawing fine wires. When Φ6.5mm wire rod produced by this process is drawn into Φ0.8mm welding wire, the work hardening is low, the tensile strength of the welding wire will not exceed 1360MPa, and the wire feeding performance is good.

[0010] To achieve the above objectives, the technical solution adopted by this invention is as follows: a rolling process for welding wire steel used for drawing fine wires, comprising furnace heating, roughing and intermediate rolling and pre-finishing mill rolling, finishing mill rolling, wire drawing, and cooling with a Steyrmore fan and insulation cover. The steps are as follows:

[0011] (1) After the continuous casting billet is heated and taken out of the furnace, it is descaled by high pressure water with a descaling pressure greater than 20MPa. After descaling, there is no iron oxide scale residue on the surface of the billet.

[0012] (2) During the rolling process, the temperature of the steel mill is controlled by the two water tanks in front of the finishing mill, and the temperature of the steel mill exit is controlled by the water volume of the finishing mill.

[0013] (3) The wire rod is coiled and the wire is evenly piled up. After passing through the finishing mill, the wire is controlled by 5 water tanks at the wire feeding stage.

[0014] (4) Close all insulation covers and fans in Steyrmo. The speed at the roller conveyor inlet section is 6 m / min, and the speed at the Steyrmo outlet section is 23 m / min. The temperature at the outlet of the cover should not exceed 650℃.

[0015] Furthermore, the chemical composition of the welding wire steel, by mass percentage, is as follows: C: 0.06–0.10, Si: 0.80–0.90, Mn: 1.40–1.51, P≤0.025, S≤0.025, Cr≤0.10, Ni≤0.10, Cu≤0.10, Al≤0.004, Ca≤0.001, with the remainder being iron and unavoidable impurities.

[0016] Furthermore, in step (1), the continuously cast billet is a rectangular billet of 142mm×166mm.

[0017] Furthermore, in step (1), during the continuous casting billet heating process, the heating temperature is 1100℃~1150℃, the soaking temperature is 1170℃~1220℃, the billet is continuously fed, and the time in the furnace is not less than 110 minutes.

[0018] Further, in step (2), the initial rolling temperature of the billet is controlled at 1070℃~1120℃; during the rolling process, the pre-finishing mill temperature is controlled at no less than 960℃; the temperature entering the finishing mill is controlled at no less than 960℃, the cooling water flow rate of the finishing mill is controlled at 30-40%, and the finishing mill outlet temperature is controlled at no less than 1050℃. Preferably, the temperature entering the finishing mill is controlled at 975℃~985℃; and the finishing mill outlet temperature is controlled at 1060~1073℃.

[0019] Furthermore, the spinning temperature in step (3) is 920–950°C.

[0020] Furthermore, in step (4), the speed of the roller conveyor from the 1st to the 8th section remains unchanged, the cooling time inside the cover is extended, and the speed of the roller conveyor from the 9th to the 11th section is increased by 5% step by step.

[0021] The beneficial effects of this invention are: the process controls the tensile strength of hot-rolled wire rod to not exceed 500MPa and the yield strength to not exceed 310MPa, it is suitable for drawing 0.8mm welding wire from Φ6.5mm wire rod, the tensile strength of the welding wire is not greater than 1360MPa, and it has good wire feeding performance.

[0022] This invention differs from the traditional technique of refining austenite grains through three controlled rolling modes. Instead, it aims to produce uniform, slightly coarse austenite grains in the wire rod before the ferrite phase transformation, thereby reducing the efficiency of dynamic and static recrystallization. After the transformation, it generates a uniform and relatively coarse ferrite structure, resulting in wire rod properties with low yield strength and low tensile strength, thus achieving the goal of low work hardening capacity. The billet must first be fully heated in the furnace to ensure a uniform and high temperature across its cross-section, allowing the austenite grains to grow appropriately and mitigating the grain refinement effect during roughing, intermediate rolling, and pre-finishing rolling. The temperature of the billet entering the final rolling mill (finishing mill, MINI mill, or sizing mill) is controlled above 960℃, and the cooling water volume is controlled to ensure that the hot steel is rolled above the recrystallization controlled rolling temperature for most of the time. The final rolling exit temperature is above 1050℃, meaning that recrystallization controlled rolling, which aims to refine austenite grains, is not carried out in the finishing rolling area. The goal is to make the austenite grains of the steel uniform and slightly coarser before the phase transformation. Considering the high hardenability of this steel grade and the small size of the wire rod, if the coiling temperature is too low, the undercooling of the wire rod will be very large, that is, the cooling rate will be very fast. When the wire rod transforms from austenite to ferrite, the ferrite crystals will be refined. In addition, the iron oxide scale of the wire rod needs to be controlled. Therefore, the coiling temperature is controlled at the upper limit temperature at which the iron oxide scale will not be pulverized, that is, relatively high temperature for entering the shroud, to continue to coarsen the austenite grains and prolong the transformation time in the ferrite region. In this way, the generated ferrite grains are relatively larger and the work hardening is relatively smaller. Detailed Implementation

[0023] The following is a production example of rolling a 142mm×166mm rectangular continuously cast billet of welding wire steel into a Φ6.5mm wire rod.

[0024] Further details are provided below with reference to the embodiments:

[0025] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0026] Example 1

[0027] The composition of the continuous casting billet for welding wire steel, by mass percentage (wt%), is C: 0.07, Si: 0.85, Mn: 1.51, P: 0.012, S: 0.012, Cr: 0.02, Ni: 0.01, Cu: 0.02, Al: 0.002, Ca: 0.0004, with the remainder being iron and unavoidable impurities.

[0028] The continuous casting billet is heated at 1120℃~1140℃, the soaking temperature is 1180℃~1210℃, the feeding is continuous, and the time in the furnace is 125 minutes. After the continuous casting billet is taken out of the furnace, it is descaled by high pressure water at a pressure of 25MPa. After descaling, there is no iron oxide scale residue on the surface of the billet.

[0029] The initial rolling temperature of the billet before entering the rolling mill is controlled at 1080℃~1110℃; the temperature of the billet entering the finishing mill is controlled at 975℃~985℃ during the rolling process; the cooling water flow rate of the finishing mill is controlled at 36%, and the outlet temperature of the finishing mill is controlled at 1060~1072℃.

[0030] After the wire rod is coiled and spun into yarn, it enters the Steyrmo roller conveyor for cooling, with a spinning temperature of 935–945°C.

[0031] The Steyrmo insulation cover is completely closed, the Steyrmo fans are completely shut down, the speed of the Steyrmo roller conveyor inlet section is 6 m / min, the speed of the roller conveyor remains constant from the inlet section to the 8th section to extend the cooling time inside the cover, the speed of the roller conveyor from the 9th to the 11th section is increased by 5% step by step, the speed of the Steyrmo outlet section is 23 m / min; the outlet temperature is 620℃~630℃.

[0032] Example 2

[0033] Based on Example 1, the continuous casting billet is heated at 1125℃~1135℃, the soaking temperature is 1180℃~1210℃, the feeding is continuous, and the time in the furnace is 130 minutes. After the continuous casting billet is taken out of the furnace, it is descaled by high pressure water at a pressure of 25MPa. After descaling, there is no iron oxide scale residue on the surface of the billet.

[0034] The initial rolling temperature of the billet before entering the rolling mill is controlled at 1080℃~1110℃; the temperature of the billet entering the finishing mill is controlled at 975℃~985℃ during the rolling process; the cooling water flow rate of the finishing mill is controlled at 36%, and the outlet temperature of the finishing mill is controlled at 1062~1073℃.

[0035] After the wire rod is coiled and spun into yarn, it enters the Steyrmo roller conveyor for cooling, with a spinning temperature of 935–945°C.

[0036] The Steyrmo insulation cover is completely closed, the Steyrmo fans are completely shut down, the speed of the Steyrmo roller conveyor inlet section is 6 m / min, the speed of the roller conveyor remains constant from the inlet section to the 8th section to extend the cooling time inside the cover, the speed of the roller conveyor from the 9th to the 11th section is increased by 5% step by step, the speed of the Steyrmo outlet section is 23 m / min; the outlet temperature is 620℃~630℃.

[0037] Example 3

[0038] Based on Example 1, the continuous casting billet is heated at 1130℃~1150℃, the soaking temperature is 1190℃~1220℃, the feeding is continuous, and the time in the furnace is 120 minutes. After the continuous casting billet is taken out of the furnace, it is descaled by high pressure water at a pressure of 25MPa. After descaling, there is no iron oxide scale residue on the surface of the billet.

[0039] The initial rolling temperature of the billet before entering the rolling mill is controlled at 1090℃~1120℃; the temperature of the billet entering the finishing mill is controlled at 975℃~985℃ during the rolling process; the cooling water flow rate of the finishing mill is controlled at 36%, and the outlet temperature of the finishing mill is controlled at 1060~1072℃.

[0040] After the wire rod is coiled and spun into yarn, it enters the Steyrmo roller conveyor for cooling, with a spinning temperature of 935–945°C.

[0041] The Steyrmo insulation cover is completely closed, the Steyrmo fans are completely shut down, the speed of the Steyrmo roller conveyor inlet section is 6 m / min, the speed of the roller conveyor remains constant from the inlet section to the 8th section to extend the cooling time inside the cover, the speed of the roller conveyor from the 9th to the 11th section increases by 5% step by step, the speed of the Steyrmo outlet section is 23 m / min; the outlet temperature is 620℃-630℃.

[0042] Comparative Example 1

[0043] Based on Example 1, the continuous feeding of billets and the furnace time of 120 minutes were adjusted to intermittent feeding of billets and the furnace time of 93 minutes; other parameters remained unchanged and were the same as in Example 1.

[0044] Comparative Example 2

[0045] Based on Example 1, the heating temperature of the continuous casting billet (1120℃~1140℃) and the soaking temperature (1180℃~1210℃) were adjusted to a heating temperature of 970℃~1040℃ and a soaking temperature of 1130℃~1180℃.

[0046] Comparative Example 3

[0047] Based on Example 1, replace "controlling the temperature of the finishing mill during rolling from 975℃ to 985℃" with "controlling the temperature of the finishing mill during rolling from 865℃ to 895℃"; replace "controlling the cooling water flow rate of the finishing mill at 36% and controlling the finishing mill outlet temperature at 1060℃ to 1072℃" with "controlling the cooling water flow rate of the finishing mill at 44% and controlling the finishing mill outlet temperature to not exceed 970℃"; other parameters remain unchanged and are the same as in Example 1.

[0048] In the embodiments and comparative examples of this invention, Φ6.5mm hot-rolled wire rods were directly drawn to 0.8mm after rust removal and sanding treatment. The properties of the hot-rolled wire rods and welding wires are shown in Table 1 below.

[0049] Table 1

[0050]

[0051] As can be seen from the data in the table above, the yield strength and yield strength ratio of the wire rod in the example are relatively small, and the tensile strength of the welding wire after drawing does not exceed 1360MPa, indicating good wire feeding performance. The yield strength and yield strength ratio of the wire rod in the comparative example are much higher than those in the example. Although the tensile strength of the comparative example 3 does not exceed 500MPa, its yield strength and yield strength ratio are not low. Therefore, the tensile strength of the welding wire after drawing exceeds the requirement of 1360MPa, indicating that the welding wire has high rigidity and poor wire feeding performance.

[0052] The above description, based on the preferred embodiments of the present invention, provides inspiration. Those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification but must be determined according to the claims.

Claims

1. A rolling process for preparing ER50-6E welding wire steel with a tensile strength not exceeding 1360 MPa, characterized in that: The steps include the following: (1) Heat the continuous casting billet to a heating temperature of 1100℃~1150℃ and a soaking temperature of 1170℃~1220℃. The continuous casting billet is continuously fed and the time in the furnace is not less than 110 minutes. After heating and exiting the furnace, high-pressure water descaling is performed. (2) During the rolling process, the temperature of the mill entering the finishing mill shall be controlled to be no less than 960℃ and the temperature of the mill exiting the finishing mill shall be controlled to be no less than 1050℃; (3) The wire rod is coiled and spun into strands at a temperature of 920-950℃; (4) Close all the insulation covers and fans in Steyrmore. The speed of the roller conveyor inlet section is 6 m / min and the speed of the Steyrmore outlet section is 23 m / min. The speed of the roller conveyor from section 1 to section 8 remains unchanged to extend the cooling time inside the cover. The speed of the roller conveyor from section 9 to section 11 is increased by 5% step by step. The temperature of the roller conveyor exiting the cover does not exceed 650℃ to obtain ER50-6E welding wire steel. The chemical composition of the ER50-6E welding wire steel, by mass percentage, is as follows: C: 0.06-0.10%, Si: 0.80-0.90%, Mn: 1.40-1.51%, P≤0.025%, S≤0.025%, Cr≤0.10%, Ni≤0.10%, Cu≤0.10%, Al≤0.004%, Ca≤0.001%, with the remainder being iron and unavoidable impurities.

2. The rolling process for preparing ER50-6E welding wire steel with a tensile strength of not more than 1360 MPa according to claim 1, characterized in that: In step (1), the high-pressure water descaling is performed at a pressure greater than 20 MPa, and no iron oxide scale remains on the surface of the continuous casting billet after descaling.

3. The rolling process for preparing ER50-6E welding wire steel with a tensile strength of not more than 1360 MPa according to claim 1, characterized in that: In step (2), during the rolling process, the temperature of the mill entering the mill is controlled by the two water tanks in front of the mill, and the opening of the cooling water volume of the mill is reduced to 30-40% to control the final rolling exit temperature to be no less than 1050℃.

4. The application of ER50-6E welding wire steel rolled according to any one of claims 1-3 in preparing welding wire with a tensile strength not exceeding 1360 MPa, characterized in that: Hot-rolled wire rod has a tensile strength not exceeding 500 MPa and a yield strength not exceeding 310 MPa. It is used for drawing 0.8 mm welding wire from Φ6.5 mm wire rod, and the tensile strength of the welding wire is not greater than 1360 MPa.

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