A method for controlling cooling of a steel wire rod for welding

Abstract

The present application relates to high speed wire production technical field, disclose a kind of welding steel wire rod control cooling method, the method sequentially includes the following steps: using conventional method smelting molten steel and continuous casting bloom, casting blank heating, heated casting blank enters high speed wire rolling mill and is rolled into bright round wire rod, wire rod enters Stelmor air cooling line in the state of scattered roll flat after wire drawing, according to different environmental temperature and humidity, adjust wire drawing temperature, roller speed and the opening of heat preservation cover, design a kind of temperature fitting formula influencing cooling speed, according to formula, corrected environmental temperature Tg numerical value, design 5 temperature intervals, and 5 corresponding control cooling processes are set, wire rod is collected, by roller conveying to collecting station collection.The wire rod is obtained by the method more ferrite and pearlite, has good through circle mechanical property uniformity, meets the use requirement of customer, production efficiency is improved, and downstream user production cost is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of high-speed wire rod production technology, and in particular to a method for controlled cooling of steel wire rods used in welding. Background Technology

[0002] With the increasing efficiency of welding wire drawing plants, higher demands are being placed on the performance and quality of welding steel wire rods. Traditional controlled cooling methods for welding steel wire rods typically employ fixed cooling parameters, which cannot adapt to the impact of changes in ambient temperature and humidity on the cooling rate. This results in unstable microstructure in 50kg-grade welding steel wire rods, with a sudden increase in the martensite / bainite ratio, leading to unstable drawing processes for downstream customers. Therefore, developing a controlled cooling method for welding steel wire rods that can adjust to changes in temperature and humidity is of great significance for stabilizing the microstructure and overall mechanical fluctuations of welding steel wire rods. Summary of the Invention

[0003] To overcome the above deficiencies, this invention provides a controlled cooling method for steel wire rods used in welding. By monitoring the ambient temperature and humidity in real time, the cooling parameters are dynamically adjusted according to changes in temperature and humidity to ensure stable cooling effect, improve the quality of steel wire rods used in welding, and increase the efficiency of downstream drawing plants.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for controlled cooling of steel wire rod for welding, the method comprising the following steps in sequence:

[0005] 1. Steel is smelted and rectangular billets are continuously cast using conventional methods;

[0006] 2. Heat the billet to ensure it is thoroughly heated and fully austenitized, but control the austenite grains to avoid abnormal growth. The billet heating section temperature is 950-1020℃, and the heating time is 40-50 min. The soaking section temperature is 1050-1080℃, and the soaking time is 20-30 min. The total time in the furnace is 80-100 min. The initial rolling temperature is 1020±30℃.

[0007] 3. The heated billet is rolled into a bright round wire rod by a high-speed wire rod mill. During the high-temperature and high-speed rolling process, the diameter reduction rate of the billet exceeds 1800%, the austenite grains are severely deformed, and a large amount of deformation energy is accumulated. As the water tank cools during the rolling process, the austenite grains are very easy to recover and dynamically recrystallize. Accompanied by the abnormal growth of grains due to uneven cooling in some areas, the overall temperature of the rolling process is strictly controlled to be above Ac3.

[0008] 4. After wire drawing, the wire rod enters the Steyr air-cooling line in a loose, flat state. According to the C-curve of the welding steel wire rod, when the cooling rate is greater than A℃ / s, bainite will appear in the microstructure. Bainite is a hard phase that affects the customer's drawing process. To ensure that the cooling rate at each position of the wire rod is less than A℃ / s and tends to be consistent, so that the phase transformation is converted into ferrite and pearlite microstructure, the wire drawing temperature, roller speed and the opening of the heat insulation cover are adjusted according to different ambient temperature and humidity. A temperature fitting formula affecting the cooling rate is designed: Tg=T+Tu, where T is the ambient temperature, Tu is the relative humidity correction value, and Tg is the corrected temperature.

[0009]

[0010] Where: u represents ambient humidity, and ut The relative humidity is defined as the temperature when the air temperature is equal to that under calm, non-direct sunlight conditions.

[0011]

[0012] Since the wind speed in the production workshop is basically zero, the effect of wind speed on the corrected temperature is not considered.

[0013] Based on the above formula and the corrected ambient temperature Tg value, five temperature ranges were designed: below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. Five corresponding controlled cooling processes were also established, as detailed below:

[0014]

[0015]

[0016] There are a total of 22 heat insulation covers;

[0017] 5. Wire rod collection: The wire rod is conveyed by roller conveyor to the coil collection station for collection.

[0018] Preferably, the inlet temperature of the finishing mill and the inlet temperature of the sizing mill are both 924°C during the rolling process.

[0019] Preferably, when the wire rod enters the insulation cover, the temperature at the edge is 780-800℃, and the temperature at the middle is 750-770℃. The temperature of the wire rod before entering the cover is above the Ac1 line. The residence time inside the insulation cover is ≥500s. Since the 50kg grade welding steel wire rod contains a certain amount of Mn element, it increases the stability of austenite, but also results in a long incubation period. Sufficient time must be ensured for the phase transformation to occur. When exiting the cover, the temperature at the edge is above 630-600℃, and the temperature at the middle is 520-540℃, to ensure that the phase transformation is complete after the wire rod exits the cover.

[0020] The present invention has the following beneficial effects:

[0021] By adjusting the wire drawing temperature, roller speed, and opening of the insulation cover in a timely manner according to changes in temperature and humidity, the 50kg-grade welding steel wire rod obtains more ferrite and pearlite, has good uniformity of mechanical properties throughout the coil, and controls the wire breakage rate to below 0.1 times per ton of steel, meeting customer requirements. This achieves a wire breakage rate of ≤0.1 times per ton of steel for multi-pass drawing of 50kg-grade welding steel wire rod, improving production efficiency and significantly reducing production costs for downstream users. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of curve C in the embodiment. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown in the figure, this embodiment provides a method for controlled cooling of steel wire rod for welding. The chemical composition of the 50 kg class ER50-6E hot-rolled wire rod for welding wire is shown in Table 1.

[0025] Table 150kg Grade Welding Steel Wire Rod Chemical Composition / wt.%

[0026]

[0027] Its production method includes the following steps in sequence:

[0028] 1. Steel is smelted using conventional methods and rectangular billets are continuously cast. The dimensions of the continuously cast billets are 180mm*240mm.

[0029] 2. Heat the billet to ensure it is thoroughly heated and fully austenitized, but control the austenite grains to avoid abnormal growth. The billet heating section temperature is 950-1020℃, and the heating time is 40-50 min. The soaking section temperature is 1050-1080℃, and the soaking time is 20-30 min. The total time in the furnace is 80-100 min. The initial rolling temperature is 1020±30℃, and the rolling speed is 110 m / s.

[0030] 3. The heated billet is rolled into a bright round wire rod by a high-speed wire rod mill. During the high-temperature and high-speed rolling process, the diameter reduction rate of the billet exceeds 1800%, the austenite grains are severely deformed, and a large amount of deformation energy is accumulated. As the water tank cools during the rolling process, the austenite grains are very easy to recover and dynamically recrystallize. Accompanied by the abnormal growth of grains due to uneven cooling in some areas, the rolling process temperature is strictly controlled to be above Ac3. The Ac3 temperature of ER50-6E is 924℃. At this temperature, the microstructure is completely austenitized and no phase transformation begins. Therefore, in this embodiment, the entry temperature of the finishing mill and the entry temperature of the sizing mill are both 924℃ during the rolling process.

[0031] 4. After wire drawing, the wire rod enters the Steyr air-cooling line in a loose, flat state. According to the C-curve of ER50-6E 50kg welding steel wire rod, bainite will appear in the microstructure when the cooling rate is greater than 0.5℃ / s. Bainite is a hard phase that affects the customer's drawing process. To ensure that the cooling rate at all positions of the wire rod is less than 0.5℃ / s and tends to be consistent, so that the phase transformation is converted into ferrite and pearlite microstructure, the wire drawing temperature, roller speed and the opening of the heat insulation cover are adjusted according to different ambient temperature and humidity. A temperature fitting formula affecting the cooling rate is designed: Tg=T+Tu, where T is the ambient temperature, Tu is the relative humidity correction value, and Tg is the corrected temperature.

[0032]

[0033] Where: u represents ambient humidity, and ut The relative humidity is defined as the temperature when the air temperature is equal to that under calm, non-direct sunlight conditions.

[0034]

[0035] Since the wind speed in the production workshop is basically zero, the effect of wind speed on the corrected temperature is not considered.

[0036] Based on the above formula and the corrected ambient temperature Tg value, five temperature ranges were designed: below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. Five corresponding controlled cooling processes were also established, as detailed in Table 2.

[0037] Table 2 Rolling process and post-rolling controlled cooling parameters of the embodiment

[0038]

[0039]

[0040] There are a total of 22 heat insulation covers;

[0041] When the wire rod enters the insulation cover, the temperature at the edge is 780-800℃, and the temperature at the middle is 750-770℃. Before entering the cover, the temperature of the wire rod is above the Ac1 line (according to the C curve, the temperature of Ac1 is 731℃). The residence time inside the insulation cover is ≥500s. Since the 50kg grade welding steel wire rod contains a certain amount of Mn element, it increases the stability of austenite, but also results in a long incubation period. Sufficient time must be ensured for the phase transformation to occur. When exiting the cover, the temperature at the edge is above 630-600℃, and the temperature at the middle is 520-540℃, to ensure that the phase transformation is complete after the wire rod exits the cover.

[0042] 5. Wire rod collection: The wire rod is conveyed by roller conveyor to the coil collection station for collection.

[0043] In traditional wire rod processing, the martensite and bainite structures are present. When the temperature changes significantly, the quenching ratio is relatively high. During the drawing process, the uneven stress distribution between ferrite and martensite / bainite can cause microcracks, leading to drawing fracture.

[0044] In the example, after the wire rod was drawn, the cooling process was adjusted according to the ambient temperature, resulting in a significant decrease in the martensite / bainite ratio. This reduced the fluctuation in the tensile strength of the wire rod throughout the coil, while also stabilizing the shrinkage rate, making it less prone to breakage during the drawing process. Specific details are shown in Table 3.

[0045] Table 3 Comparison of microstructure and properties of wire rod from the examples and wire rod produced by traditional processes.

[0046]

[0047]

[0048] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlled cooling of steel wire rod for welding, characterized in that, The method includes the following steps in sequence:

1. Steel is smelted and rectangular billets are continuously cast using conventional methods; 2. Heat the billet to ensure it is thoroughly heated and fully austenitized, but control the austenite grains to avoid abnormal growth. The billet heating section temperature is 950~1020℃, and the heating time is 40~50min. The soaking section temperature is 1050~1080℃, and the soaking time is 20~30min. The total time in the furnace is 80-100min. The initial rolling temperature is 1020±30℃.

3. The heated billet is rolled into a bright round wire rod by a high-speed wire rod mill. During the high-temperature and high-speed rolling process, the diameter reduction rate of the billet exceeds 1800%, the austenite grains are severely deformed, and a large amount of deformation energy is accumulated. As the water tank cools during the rolling process, the austenite grains are very easy to recover and dynamically recrystallize. Accompanied by the abnormal growth of grains due to uneven cooling in some areas, the overall temperature of the rolling process is strictly controlled to be above Ac3.

4. After wire drawing, the wire rod enters the Steyr air-cooling line in a loose, flat state. According to the C-curve of the welding steel wire rod, when the cooling rate is greater than 0.5℃ / s, bainite will appear in the microstructure. Bainite is a hard phase that affects the customer's drawing process. To ensure that the cooling rate at each position of the wire rod is less than 0.5℃ / s and tends to be consistent, so that the phase transformation is converted into ferrite and pearlite microstructure, the wire drawing temperature, roller speed and the opening of the heat insulation cover are adjusted according to different ambient temperature and humidity. A temperature fitting formula affecting the cooling rate is designed: Tg=T+Tu, where T is the ambient temperature, Tu is the relative humidity correction value, and Tg is the corrected temperature. ； Where: u represents ambient humidity, and The relative humidity is defined as the temperature when the air temperature is equal to that under calm, non-direct sunlight conditions. ； Since the wind speed in the production workshop is basically zero, the effect of wind speed on the corrected temperature is not considered. Based on the above formula and the corrected ambient temperature Tg value, five temperature ranges were designed: below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. Five corresponding controlled cooling processes were also established, as detailed below: ； There are a total of 22 heat insulation covers; 5. Wire rod collection: The wire rod is conveyed by roller conveyor to the coil collection station for collection.

2. The method for controlled cooling of welding steel wire rod according to claim 1, characterized in that: The inlet temperature of the finishing mill and the inlet temperature of the sizing mill during the rolling process are both 924℃.

3. The method for controlled cooling of welding steel wire rod according to claim 1, characterized in that: When the wire rod enters the insulation cover, the temperature at the edge is 780~800℃, and the temperature at the middle is 750~770℃. The temperature of the wire rod before entering the cover is above the Ac1 line. The residence time inside the insulation cover is ≥500s. Since the 50kg grade welding steel wire rod contains 1.5% Mn by mass, it increases the stability of austenite, but also results in a long incubation period. Sufficient time must be ensured for the phase transformation to occur. When exiting the cover, the temperature at the edge is above 630~600℃, and the temperature at the middle is 520~540℃ to ensure that the phase transformation is complete after the wire rod exits the cover.

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