Controlled cooling method for steel wire rod for welding

Abstract

The invention relates to the technical field of high-speed wire rod production, and discloses a control cooling method of a steel wire rod for welding, which sequentially comprises the following steps of: smelting molten steel and continuously casting a rectangular blank by adopting a conventional method, heating the casting blank, rolling the heated casting blank into a smooth round wire rod in a high-speed wire rod rolling mill, after spinning, a wire rod enters a Stetamol air cooling line in a scattered and tiled state, the spinning temperature, the roller speed and opening of a heat preservation cover are adjusted according to different environment temperatures and humidity, a temperature fitting formula influencing the cooling speed is designed, five temperature intervals are designed according to the formula and the corrected environment temperature Tg value, and the temperature fitting formula is matched with the temperature fitting formula. Five corresponding controlled cooling processes are correspondingly set, and the wire rods are collected and conveyed to a coil collecting station through a roller way to be collected. By means of the method, the wire rod obtains more ferrite and pearlite, the good through-ring mechanical property uniformity is achieved, the use requirements of customers are met, the production efficiency is improved, and the production cost of downstream users is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of high-speed wire production, and in particular to a method for controlling cooling of a steel wire rod for welding. Background Art

[0002] As the efficiency of wire drawing plants increases, higher requirements are placed on the performance and quality of welding steel wire rods. Traditional controlled cooling methods for welding steel wire rods usually use fixed cooling parameters, which cannot adapt to the impact of changes in ambient temperature and humidity on the cooling rate, resulting in unstable microstructure of 50kg-grade welding steel wire rods, and a sudden increase in the martensite / bainite ratio, leading to unstable drawing for downstream customers. Therefore, developing a controlled cooling method for welding steel wire rods that can adjust according to changes in temperature and humidity is of great significance for stabilizing the microstructure and through-loop mechanical fluctuations of welding steel wire rods. Summary of the invention

[0003] In order to make up for the above shortcomings, the present invention provides a method for controlling the cooling of steel wire rods for welding. By real-time monitoring of the ambient temperature and humidity, the cooling parameters are dynamically adjusted according to the changes in temperature and humidity to ensure the stability of the cooling effect and improve the quality of the steel wire rods for welding and the efficiency of the downstream drawing plant.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: a method for controlling cooling of a welding steel wire rod, the method comprising the following steps in sequence:

[0005] 1. Use conventional methods to smelt molten steel and continuously cast rectangular billets;

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

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

[0008] 4. After spinning, the wire rod enters the Steinmer air cooling line in a loose coil and 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 organization. Bainite is a hard phase that affects the customer's drawing. In order to ensure that the cooling rate of each position of the wire rod is less than A℃ / s and tends to be consistent, so that the phase transformation is transformed into ferrite and pearlite organizations, the spinning temperature, roller speed and opening of the insulation cover are adjusted according to different ambient temperature and humidity. A temperature fitting formula that affects the cooling rate is designed: Tg=T+Tu, T is the ambient temperature, Tu is the relative humidity correction value, and Tg is the corrected temperature;

[0009]

[0010] Where: u is the ambient humidity, and ut It is defined as the relative humidity when it is equal to the air temperature under calm wind and non-direct sunlight conditions;

[0011]

[0012] Since there is no wind speed in the production workshop, which is basically 0, the effect of wind speed on the corrected temperature is not considered;

[0013] According to the above formula, the corrected ambient temperature Tg value is used to design 5 temperature ranges, which are below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. 5 corresponding cooling control processes are set accordingly, as follows:

[0014]

[0015]

[0016] There are 22 thermal covers in total;

[0017] 5. The wire rods are collected and transported to the coiling station by rollers.

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

[0019] Preferably, when the wire rod enters the insulation cover, the temperature of the edge is 780-800°C, the temperature of the middle is 750-770°C, the temperature of the wire rod before entering the cover is above the Ac1 line, and the residence time in the insulation cover is ≥500s. Since the 50kg-grade welding steel wire rod contains a certain amount of Mn element, which increases the stability of austenite and leads to a long incubation period, it is necessary to ensure that there is sufficient time for the microstructure phase change to occur. When leaving the cover, the temperature of the edge is above 630-600°C, and the temperature of the middle is 520-540°C, so as to ensure that the microstructure of the wire rod is completely transformed after leaving the cover.

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

[0021] According to the changes in temperature and humidity, the wire laying temperature, roller speed, opening of the insulation cover, etc. are adjusted in time to make the 50kg-grade welding steel wire rod obtain more ferrite and pearlite, have good uniformity of mechanical properties through the ring, and the wire breakage rate per ton of steel is controlled below 0.1 times, which meets the customer's usage requirements; the multi-pass drawing of 50kg-grade welding steel wire rod achieves a wire breakage rate of ≤0.1 times per ton of steel, which improves production efficiency and greatly reduces the production cost of downstream users. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of C curve in the embodiment. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0024] like Figure 1 As shown, this embodiment provides a method for controlling cooling of steel wire rods for welding, and the chemical composition of the 50 kg grade ER50-6E hot-rolled wire rods for welding wire is shown in Table 1.

[0025] Table 1 Chemical composition of 50kg grade welding steel wire rod / wt.%

[0026]

[0027] The production method comprises the following steps in sequence:

[0028] 1. Use conventional methods to smelt molten steel and continuously cast rectangular billets, the size of which is 180mm*240mm;

[0029] 2. Heat the ingot to ensure that the ingot is heated through and completely austenitized, but control the austenite grains to avoid abnormal growth. The temperature of the ingot heating section is 950-1020°C, the heating time is 40-50min, the temperature of the soaking section is 1050-1080°C, the soaking time is 20-30min, the total time in the furnace is 80-100min, the rolling temperature is 1020±30°C, and the rolling speed is 110m / s;

[0030] 3. The heated ingot enters the high-speed wire rolling mill and is rolled into a round wire. During the high-temperature and high-speed rolling process, the diameter reduction rate of the ingot exceeds 1800%, the austenite grains are severely deformed, and a large amount of deformation energy is accumulated. With the cooling of the water tank during the rolling process, the austenite grains are very likely to recover and dynamically recrystallize, accompanied by abnormal grain growth caused by uneven cooling in some areas. The rolling process temperature is strictly controlled to be above Ac3 as a whole. The Ac3 temperature of ER50-6E is 924°C. At this temperature, the organization is completely austenitized and no phase change occurs. Therefore, the finishing mill inlet temperature and the sizing inlet temperature during the rolling process of this embodiment are both 924°C;

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

[0032]

[0033] Where: u is the ambient humidity, and ut It is defined as the relative humidity when it is equal to the air temperature under calm wind and non-direct sunlight conditions;

[0034]

[0035] Since there is no wind speed in the production workshop, which is basically 0, the effect of wind speed on the corrected temperature is not considered;

[0036] According to the above formula, the corrected ambient temperature Tg value is used to design 5 temperature ranges, which are below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. Five corresponding cooling control processes are set accordingly, as shown in Table 2:

[0037] Table 2 Example rolling process and post-rolling controlled cooling parameters

[0038]

[0039]

[0040] There are 22 thermal covers in total;

[0041] When the wire rod enters the insulation cover, the temperature of the edge position is 780-800°C, the temperature of the middle position is 750-770°C, the temperature of the wire rod before entering the cover is above the Ac1 line (according to the C curve, the temperature of Ac1 is 731°C), and the residence time in the insulation cover is ≥500s. Since the 50kg-grade welding steel wire rod contains a certain amount of Mn element, the stability of austenite is increased, and the incubation period is long, it is necessary to ensure that there is sufficient time for the microstructure phase change to occur. When leaving the cover, the temperature of the edge position is above 630-600°C, and the temperature of the middle position is 520-540°C, so as to ensure that the microstructure of the wire rod is completely transformed after leaving the cover.

[0042] 5. The wire rods are collected and transported to the coiling station by rollers.

[0043] In the traditional wire rod structure, the martensite and bainite structures have a high quenching ratio when the temperature changes greatly. During the drawing process, the ferrite and martensite / bainite will produce micro cracks due to uneven stress distribution, and then the drawing will break.

[0044] After adjusting the cooling process according to the ambient temperature after spinning, the martensite / bainite ratio is significantly reduced, the fluctuation of the tensile strength of the wire rod is reduced, and the shrinkage rate is relatively stable, and it is not easy to break during the drawing process. The specific situation is shown in Table 3.

[0045] Table 3 Comparison of the organizational properties of the wire rod of the embodiment and the wire rod of the traditional process

[0046]

[0047]

[0048] Finally, it should be noted that the above are only 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 aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

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

1. Use conventional methods to smelt molten steel and continuously cast rectangular billets; 2. Heat the ingot to ensure that it is heated through and completely austenitized, but control the austenite grains to avoid abnormal growth. The temperature of the ingot heating section is 950-1020℃, the heating time is 40-50min, the temperature of the soaking section is 1050-1080℃, the soaking time is 20-30min, the total time in the furnace is 80-100min, and the rolling temperature is 1020±30℃; 3. The heated ingot enters the high-speed wire rolling mill and is rolled into round wire. During the high-temperature and high-speed rolling process, the diameter reduction rate of the ingot exceeds 1800%, the austenite grains are severely deformed, and a large amount of deformation energy is accumulated. With the cooling of the water tank during the rolling process, the austenite grains are very likely to recover and dynamically recrystallize, accompanied by abnormal growth of grains due to uneven cooling in some parts. The overall temperature of the rolling process is strictly controlled to be above Ac3; 4. After spinning, the wire rod enters the Steinmer air cooling line in a loose coil and 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 organization. Bainite is a hard phase that affects the customer's drawing. In order to ensure that the cooling rate of each position of the wire rod is less than A℃ / s and tends to be consistent, so that the phase transformation is transformed into ferrite and pearlite organizations, the spinning temperature, roller speed and opening of the insulation cover are adjusted according to different ambient temperature and humidity. A temperature fitting formula that affects the cooling rate is designed: Tg=T+Tu, T is the ambient temperature, Tu is the relative humidity correction value, and Tg is the corrected temperature; Where: u is the ambient humidity, and u t It is defined as the relative humidity when it is equal to the air temperature under calm wind and non-direct sunlight conditions; Since there is no wind speed in the production workshop, which is basically 0, the effect of wind speed on the corrected temperature is not considered; According to the above formula, the corrected ambient temperature Tg value is used to design 5 temperature ranges, which are below -10℃, -10~0℃, 0~20℃, 20~40℃, and above 40℃. 5 corresponding cooling control processes are set accordingly, as follows: There are 22 thermal covers in total; 5. The wire rods are collected and transported to the coiling station by rollers.

2. The controlled cooling method for welding steel wire rod according to claim 1, characterized in that: During the rolling process, the finishing mill inlet temperature and the sizing mill inlet temperature were both 924°C.

3. The controlled cooling method for welding steel wire rod according to claim 1, characterized in that: When the wire rod enters the insulation cover, the temperature of the edge is 780-800°C, the temperature of the middle is 750-770°C, the temperature of the wire rod before entering the cover is above the Ac1 line, and the residence time in the insulation cover is ≥500s. Since the 50kg-grade welding steel wire rod contains a certain amount of Mn element, the stability of austenite is increased, and the incubation period is long, it is necessary to ensure that there is sufficient time for the microstructure phase change to occur. When leaving the cover, the temperature of the edge is above 630-600°C, and the temperature of the middle is 520-540°C, so as to ensure that the microstructure of the wire rod is completely transformed after leaving the cover.

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