Method for improving yield of steel wire rods for welding wires

Abstract

The invention relates to a method for increasing the yield of a steel wire rod for a welding wire. The method comprises the working procedures of heating, temperature-controlled rolling and slow cooling which are carried out in sequence. Wherein the heating procedure comprises the step that a steel billet is subjected to sectional type heating, the temperature of a preheating section ranges from 700 DEG C to 800 DEG C, the temperature of a first heating section ranges from 760 DEG C to 840 DEG C, the temperature of a second heating section ranges from 890 DEG C to 970 DEG C, and the temperature of a soaking section ranges from 1000 DEG C to 1040 DEG C; the air-fuel ratio of the heating furnace is 0.7-1.0; the temperature-controlled rolling procedure comprises the steps that the steel billets obtained in the heating procedure are descaled through high-pressure water and then rolled into wire rods, then water cooling and spinning are conducted, and the descaling water pressure is larger than or equal to 22 Mpa; the initial rolling temperature is 950-990 DEG C, and the inlet temperature of a finishing mill is 900-950 DEG C; the spinning temperature is 940-960 DEG C; the slow cooling procedure comprises the steps that the steel wire rod obtained in the temperature control rolling procedure is slowly cooled on a Stelmor line and then enters a heat preservation vestibule for slow cooling, the temperature of entering the heat preservation vestibule ranges from 700 DEG C to 740 DEG C, the temperature of leaving the heat preservation vestibule is smaller than or equal to 300 DEG C, the heat preservation time of the heat preservation vestibule is larger than or equal to 120 min, and the produced steel wire rod for the welding wire is excellent in performance and high in yield.

Description

Technical Field

[0001] The invention relates to the field of iron and steel metallurgical production, and in particular to a method for improving the yield rate of steel wire rods for welding wires. Background Art

[0002] At present, the main varieties of 5.5mm steel wire rod products are welding wire products. Since the organizational state of the non-cooling part of the product head is not conducive to the drawing production of the downstream process of the product, the non-cooling part of the product head needs to be cut off in the finishing stage. According to sampling and testing, the non-cooling part of the product head needs to be cut off for at least 40 turns. Such a large number of cuts not only seriously affects the yield rate of the product, but also increases the work intensity of the workers who cut the head and tail on site.

[0003] In addition, when measuring the size of the finished product of 5.5mm welding wire steel, smaller sizes are often measured around 40 turns of the head. The smaller size is only 5.23mm. The smaller size may affect the use of the welding wire, so the smaller size can only be sheared. Shearing more than 40 turns of the head seriously affects the yield rate of 5.5mm welding wire. Therefore, it is necessary to study the problem of smaller head size and eliminate the smaller head size.

[0004] The problem of head drawing of 5.5mm steel wire rod mainly considers the tension between the pre-finishing rolling and finishing rolling mills. Therefore, the problem of head drawing mainly focuses on the tension adjustment between the pre-finishing rolling and finishing rolling mills, thereby determining the direction of research. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the yield rate of steel wire rod for welding wire, so that the quality and performance of the prepared steel wire rod for welding wire can be optimized.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for improving the yield rate of steel wire rod for welding wire, comprising a heating process, a temperature-controlled rolling process and a slow cooling process performed in sequence to obtain the steel wire rod for welding wire;

[0008] The heating process includes heating the steel billet in sections, with the preheating section temperature being 700-800°C, the first heating section temperature being 760-840°C, the second heating section temperature being 890-970°C, and the soaking section temperature being 1000-1040°C; the air-fuel ratio of the heating furnace being 0.7-1.0;

[0009] The temperature-controlled rolling process comprises: descaling the steel billet obtained in the heating process with high-pressure water, rolling it into a wire rod, and then cooling it with water for spinning, wherein the descaling water pressure is ≥ 22Mpa; the starting rolling temperature is 950-990°C, the finishing mill inlet temperature is 900-950°C; the spinning temperature is 940-960°C;

[0010] The slow cooling process includes: keeping the wire rod obtained in the temperature-controlled rolling process warm and slow cooling on a Stelmor slow cooling line; wherein, the temperature entering the insulation corridor is 700-740°C, the temperature exiting the insulation corridor is ≤300°C, and the insulation time in the insulation corridor is ≥120min.

[0011] Furthermore, the chemical elements of the applicable steel wire rod for welding wire are calculated in mass percentage as follows: C: 0.06-0.08%; Si: 0.81-0.87%; Mn: 1.41-1.47%; P≤0.023%; S: 0.008-0.015%; Al≤0.010%; Ca≤0.0010%, Ti≤0.10%; Cr≤0.10%, and the balance is Fe and unavoidable impurities.

[0012] Furthermore, in the heating step, the heating time is 90 to 100 minutes.

[0013] In the heating process, the steel billets are spaced apart from each other and enter a heating furnace with a progressive beam step adjustment range of 230 to 300 mm. When the steel billet specification is a 150*150 mm square billet, the number of steel billets in the heating furnace is 79≤≤86; when the steel billet specification is a 180*180 mm square billet, the number of steel billets in the heating furnace is 67≤≤85.

[0014] In the temperature-controlled rolling process, the speed drop compensation coefficient is 1 to 1.030, the speed drop compensation time is 0 to 150 ms, and the side looper starting height is 150 to 175 mm.

[0015] Furthermore, in the slow cooling process, the inlet roller speed of the Stelmore slow cooling line is 0.152-0.168 m / s, and the outlet roller speed is 0.238-0.262 m / s.

[0016] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0017] The present invention breaks the inherent parameter settings by adjusting the process parameters set in the production process of steel wire rod for welding wire, designs the production process in the heating process and the temperature-controlled rolling process, reduces the oxidation loss of the wire during heating and the length of the non-cooling section of the head, and improves the minimum size of the wire head, thereby improving the same-circle structure stability of the steel wire rod, meeting the drawing requirements and greatly improving the yield rate. DETAILED DESCRIPTION

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

[0019] The present invention provides a method for improving the yield rate of steel wire rod for welding wire, comprising a heating process, a temperature-controlled rolling process and a slow cooling process in sequence, thereby obtaining a steel wire rod for welding wire. The chemical elements of the steel wire rod for welding wire suitable for the above-mentioned improvement method are as follows by mass percentage: C: 0.06-0.08%; Si: 0.81-0.87%; Mn: 1.41-1.47%; P≤0.023%; S: 0.008-0.015%; Al≤0.010%; Ca≤0.0010%, Ti≤0.10%; Cr≤0.10%, and the balance is Fe and unavoidable impurities.

[0020] In the present invention, by limiting the content of carbon element, the eutectoid ferrite in the steel wire rod for welding wire can be effectively reduced, and the content of acicular ferrite can be increased, thereby improving the strength and hardness of the weld metal. Si element and Mn element are the main deoxidizing elements and strengthening elements in the steel wire rod for welding wire, playing a role of solid solution strengthening, thereby improving the strength of the weld.

[0021] As impurity elements in the steel wire rod for welding wire, S and P elements, if their content is too high, will easily cause component segregation at the end of the solidification of molten steel, which is not conducive to the drawing of the wire rod and the low-temperature thermal properties of welding. However, adding an appropriate amount of S and P elements to the steel wire rod for welding wire can improve the cutting performance of the steel. While adding Al elements as deoxidizing elements, an appropriate amount of Al is also beneficial to improving the impact absorption energy of the weld metal. In addition, the addition of Cr elements can increase the hardenability of steel and has a secondary hardening effect, thereby improving the hardness and wear resistance of steel without making the steel brittle.

[0022] Specifically, each of the above steps is described in detail below.

[0023] (1) Heating process

[0024] The steel billet is heated by a walking-beam heating furnace, the center distance between the inlet and outlet rollers of the heating furnace is 20,000 mm, and a segmented heating method is adopted in the present invention, the preheating section temperature is 700-800°C, the first heating section temperature is 760-840°C, the second heating section temperature is 890-970°C, the equalizing section temperature is 1000-1040°C, and the heating time is 90-100 min.

[0025] Generally speaking, the optimal spacing of steel billets is between 0.3 and 0.7 times the billet thickness, which can maximize the production efficiency of the heating furnace. The steel billets in the embodiment of the present invention are selected to be 150mm or 180mm thick. For 150*150mm square billets, the optimal spacing should be 45-105mm, but at the same time, considering the furnace bottom strength and the stepping mechanical design capability and the adjustment range of the step distance of the stepping beam of this heating furnace is 230-300mm, so when the square billet with a specification of 150*150mm is heated in the walking heating furnace described in the present invention, the optimal spacing range is 80-105mm; similarly, when the square billet with a specification of 180*180mm is heated in the walking heating furnace described in the present invention, the optimal spacing range is 54-120mm.

[0026] Through further research, it is found that if the stepping distance is too large, the distance between the billets becomes larger, the heating surface of the billets increases, and the heat absorption is strong, which can make the billets heat up quickly. However, the faster the billet heats up, the longer the billet stays in the high temperature section, thereby increasing the oxidation and burning of the billets; if the stepping distance is too small, the distance between the billets becomes smaller, the heating surface is reduced, affecting the heat absorption of the billets and consuming more energy.

[0027] Under the premise of maximizing the production efficiency of the heating furnace without generating any improvement margin, when the billet specification is 150*150mm square billet, the number of steel billets in the heating furnace can be selected as any natural number between 79 and 86 (including both end values); when the billet specification is 180*180mm square billet, the number of steel billets in the heating furnace can be any natural number between 67 and 85 (including both end values).

[0028] Finally, through experimental research and comparison, it was found that when the number of steel billets with specifications of 150*150mm was 79 and 80 in the heating furnace, they entered the heating furnace in an interval manner for heating; when the number of steel billets with specifications of 180*180mm was 74, 75, and 76 in the heating furnace, they entered the heating furnace in an interval manner for heating. When the production efficiency of the heating furnace is fully utilized, the thickness of the oxide scale of the steel billets is the smallest. Compared with the steel billets arranged at other spacings, the thickness of the oxide scale is reduced by about 25% at most, the yield rate is increased by up to 0.26%, and the adjustment of the pitch of the steel billets by on-site operators during steel discharge is also reduced.

[0029] In addition, in the embodiment of the present invention, the air-fuel ratio of the heating furnace is set at 0.7 to 1.0. The control of the air-fuel ratio is a theoretical air-fuel ratio calculated by comprehensively calculating the relationship between the composition and content of the combustible gas in the blast furnace gas and the mixed combustion of oxygen, and the excess air coefficient for complete combustion of the combustible gas.

[0030] Usually, blast furnace gas contains 25%-30% carbon monoxide (CO), 1.5%-4% hydrogen (H2), 0.2%-0.5% methane (CH4), 10%-16% carbon dioxide (CO2), 55%-60% nitrogen (N2), 0.2%-0.4% oxygen (O2), and the rest are impurities and dust, among which the combustible gases are CO, H2, and CH4. The air excess coefficient for the complete combustion of combustible gas in a gas-type heating furnace is usually 1.1-1.3, which is the best. Exceeding this coefficient range will lead to excess air, which will easily lead to unreasonable atmosphere in the furnace and cause heat loss in the furnace, thereby increasing the generation of iron oxide, and then causing gas waste; below this coefficient range will lead to incomplete combustion of combustible gas, high CO content in flue gas, and increased gas consumption.

[0031] After analyzing and studying the composition and content of combustible gas in blast furnace gas (CO content is about 25%), and calculating through the combustion chemical equation and the complete combustion coefficient, it was finally concluded that when the air-fuel ratio is between 0.7 and 1.0, the heat loss in the furnace is less, the production of iron oxide is less, the yield rate is increased by about 0.1% compared to when the air-fuel ratio is 0.6, and the gas consumption is less.

[0032] (2) Temperature controlled rolling process

[0033] The steel billet obtained through the heating process is descaled by high-pressure water and rolled into wire rod. The descaling water pressure is ≥22Mpa to effectively remove the iron oxide scale on the surface of the steel billet and avoid the residual iron oxide scale from being pressed into the deep wire rod structure during the rolling process, thereby affecting the drawing of the welding wire.

[0034] When the steel billet is rolled after descaling, the starting rolling temperature is 950-990°C, and the inlet temperature of the finishing mill is 900-950°C. The plasticity of the rolled wire rod can be improved by low-temperature rolling.

[0035] After the final rolling, the wire rod is cooled by water before spinning, and the spinning temperature is 940-960℃, that is to say, water cooling is carried out between the rolling mill and the spinning machine. Three or more water cooling tanks are arranged between the rolling mill and the spinning machine in sequence. The opening of the water cooling tank is controlled by the three-way quick shut-off valve on the main line. After the quick shut-off valve receives the signal, the cooling water is distributed to the three branch pipes along the main line, and then enters the cooling nozzle of the water tank.

[0036] Generally, the response time of the cut-off valve is less than 0.5s. Since the feedback time between the heat detection and the rolled piece entering the water tank directly affects the length of the non-cold section of the wire head, the feedback time is set to 1.9s in the present invention, thereby reducing the number of shearing circles of the product head from about 30 circles in normal times to 15-20 circles, which not only reduces the labor intensity of the on-site operators, but also can increase the product yield rate by about 0.3%.

[0037] In addition, when the rolling mill is running without load, there is a certain no-load speed. When there is a load, the speed of the rolling mill will decrease. Generally, the speed reduction when reaching a stable state is called speed drop. When the roller is subjected to a static load, the speed drop generated when reaching a stable state is called static speed drop. When the workpiece in the line is sent to the roller at a certain speed, the speed drop generated when the roller is subjected to the impact load of the workpiece is called dynamic speed drop.

[0038] Through the study of the speed drop compensation coefficient and the control parameters of the loop in the temperature-controlled rolling process, it is found that the larger the speed drop compensation coefficient is, the faster the speed of the finishing mill will be increased. When the speed of the finishing mill becomes faster, it is easy to cause the finishing mill and the pre-finishing mill to pull the steel when the head is bitten. The speed drop compensation coefficient during rolling is generally 1-1.030.

[0039] After research, it was found that when the speed drop compensation coefficient for producing welding wire steel in the present invention is 1.003, the head drawing phenomenon will not occur; the speed drop compensation time is the response time of the speed drop compensation, the longer the speed drop compensation time is, the longer the speed increase time of the finishing mill is, and the long speed increase time of the finishing mill will also cause the steel drawing time between the finishing mill and the pre-finishing rolling to become longer. During rolling, the speed drop compensation time is generally 0-150ms. After research, it was found that the speed drop compensation time is 100ms delay, which is similar to the bite stabilization delay, so the speed drop compensation delay is adjusted to 100ms.

[0040] In the present invention, since the lifting height of the side looper will affect the size uniformity of the steel wire rod, the lifting height adjustment of the side looper is the main adjustment method for adjusting the tension between the pre-finishing mill and the finishing mill. Whether the lifting height is reasonable is mainly reflected in the coefficient value of the looper after the looper is lifted. For example, if the lifting height of the side looper between the pre-finishing mill and the finishing mill in the rolling of 5.5mm welding wire steel is 165mm, in this case, the coefficient value of the looper will fluctuate between 0.998-1.003. This coefficient value of the looper proves that the tension between the pre-finishing mill and the finishing mill is relatively flat and there is no big problem. However, from the actual tracking situation, the looper is not stable during the rolling process. Therefore, the lifting height of the side looper is further studied, and it is found that when the lifting height of the side looper is adjusted to 171mm, it is the most stable. Increasing or reducing the height of the looper is unstable. At this lifting height, the wire rod in rolling has a great improvement in the effect on the head steel drawing due to the stability of its side looper.

[0041] (6) Slow Cooling Process

[0042] The wire rod obtained from the temperature-controlled rolling process is placed on the Stelmor slow cooling line for heat preservation and slow cooling. Specifically, the entrance roller speed of the slow cooling line is 0.152-0.168 m / s, and the exit roller speed is 0.238-0.262 m / s. During this period, the insulation cover and windshield are all closed. After the Stelmor slow cooling, the wire rod temperature is 730-770°C for coiling, and then enters the insulation corridor at 700-740°C for slow cooling for ≥120 minutes, and then exits the insulation corridor at a temperature of ≤300°C.

[0043] The specific implementation methods of the present invention are further introduced below by setting Examples 1 to 3 and Comparative Examples 1 to 3.

[0044] (I) Heating

[0045] The obtained steel billet is heated under temperature control in a walking beam gas heating furnace. The preheating section temperature, the first heating section temperature, the second heating section temperature, the soaking section temperature, the soaking section air-fuel ratio, the holding time, the stepping distance and the billet spacing of the three embodiments and the three comparative examples are shown in Table 1:

[0046] Table 1

[0047]

[0048]

[0049] (II) Temperature controlled rolling

[0050] The steel billet obtained in the heating process is descaled by high-pressure water and then rolled into a wire rod. The descaling water pressure, rolling start temperature, finishing mill inlet temperature, spinning temperature, speed drop compensation coefficient, speed drop compensation time and side looper starting height of the three embodiments and three comparative examples are shown in Table 2.

[0051] Table 2

[0052]

[0053] (III) Slow cooling

[0054] The wire rod obtained by the temperature-controlled rolling process is kept warm and slowly cooled on the Stelmor slow cooling line, and the heat preservation cover and the fan tuyere are all closed. In addition, the entrance roller speed and the exit roller speed on the Stelmor slow cooling line of the three embodiments and the three comparative examples are controlled as shown in Table 3.

[0055] Table 3

[0056]

[0057] The specific data of the temperature entering the insulation corridor, the insulation time of the insulation corridor, and the temperature leaving the insulation corridor are shown in Table 4:

[0058] Table 4

[0059]

[0060] In the present invention, according to the production methods corresponding to the above three embodiments and three comparative examples, the finally prepared steel wire rod for welding wire was inspected, wherein the chemical composition and weight percentage of each finished product are shown in Table 5:

[0061] Table 5

[0062]

[0063] In addition, the organization, mechanical properties, scale penetration depth, mechanical stripping rate and aging time of the wire rod are shown in Table 6:

[0064] Table 6

[0065]

[0066] It can be seen from the above embodiments and comparative examples that the method for improving the yield rate of steel wire rod for welding wire provided in the present invention reduces the oxidation loss of wire rod during heating and the length of the non-cold section of the head by designing the heating and temperature-controlled rolling production process, so that the yield rate of wire rod is comprehensively improved by about 2.4%, and at the same time improves the minimum size of the wire rod head, improves the stability of the same coil structure of the steel wire rod, and meets the drawing requirements. The 5.5mm steel wire rod for welding wire produced by the improvement method of the present invention has a tensile strength of 502-530MPa and an elongation after fracture of ≥35%. The cross-sectional shrinkage rate is ≥80%, the uniformity of the mechanical properties of the same coil is good, the toughness is high, and the comprehensive performance is excellent.

[0067] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the yield rate of steel wire rod for welding wire, characterized in that: The method comprises a heating process, a temperature-controlled rolling process and a slow cooling process which are performed in sequence to obtain the steel wire rod for welding wire; The heating process includes heating the steel billet in sections, with the preheating section temperature being 700-800°C, the first heating section temperature being 760-840°C, the second heating section temperature being 890-970°C, and the soaking section temperature being 1000-1040°C; the air-fuel ratio of the heating furnace being 0.7-1; The temperature-controlled rolling process comprises: descaling the steel billet obtained in the heating process with high-pressure water, rolling it into a wire rod, and then cooling it with water to spin wire, wherein the descaling water pressure is ≥ 22Mpa; the starting rolling temperature is 950-990°C, the finishing mill inlet temperature is 900-950°C; the spinning temperature is 940-960°C; The slow cooling process includes: keeping the wire rod obtained in the temperature-controlled rolling process warm and slow cooling on a Stelmor slow cooling line; wherein, the temperature entering the insulation corridor is 700-740°C, the temperature exiting the insulation corridor is ≤300°C, and the insulation time in the insulation corridor is ≥120min.

2. A method for improving the yield rate of steel wire rod for welding wire according to claim 1, characterized in that: The chemical elements of the steel wire rod suitable for welding wire are as follows in mass percentage: C: 0.06~0.08%; Si: 0.81~0.87%; Mn: 1.41~1.47%; P≤0.023%; S: 0.008~0.015%; Al≤0.010%; Ca≤0.0010%, Ti≤0.10%; Cr≤0.10%, the balance is Fe and unavoidable impurities.

3. A method for improving the yield rate of steel wire rod for welding wire according to claim 1, characterized in that: In the heating process, the heating time is 90 to 100 minutes.

4. A method for improving the yield rate of steel wire rod for welding wire according to claim 1, characterized in that: In the heating process, the steel billets are spaced apart from each other and enter a heating furnace with a step adjustment range of a progressive beam of 230 to 300 mm. When the steel billet specification is a 150*150 mm square billet, the number of steel billets in the heating furnace is 79 ≤ ≤ 86; when the steel billet specification is a 180*180 mm square billet, the number of steel billets in the heating furnace is 67 ≤ ≤ 85.

5. The method for improving the yield rate of steel wire rod for welding wire according to claim 1, characterized in that: In the temperature-controlled rolling process, the speed drop compensation coefficient is 1-1.030, the speed drop compensation time is 0-150ms, and the side looper starting height is 150-175mm.

6. A method for improving the yield rate of steel wire rod for welding wire according to claim 1, characterized in that: In the slow cooling process, the inlet roller speed of the Stelmore slow cooling line is 0.152~0.168m / s, and the outlet roller speed is 0.238~0.262m / s.

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