Method for improving defect detection inconsistency of head blank

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a method for improving flaw detection incompatibility of a head blank. Comprising the following steps that (1) large-tonnage casting is conducted, specifically, the casting tonnage of a tundish is increased to 38 tons in a high-temperature rapid casting mode; (2) after the large ladle is cast, the ladle filler sand is taken away in time; (3) adding a covering agent in a delayed manner: adding the covering agent when the tonnage of the tundish reaches 35 tons; (4) water gap insertion depth: dynamically adjusting the insertion depth of the submersed water gap; (5) constant-liquid-level pouring of the crystallizer is conducted, and the starting time of the automatic variable slag line is controlled after the first blank stage is finished; and (6) dynamically matching section width: matching a water gap inclination angle according to the section width change of the casting blank. According to the large-tonnage casting technology, the cognitive limit of the industry on the safe tonnage is broken through, the condition that inclusions fully float upwards is created, the cleanliness of molten steel is improved, and the problem that flaw detection of a first blank is not matched is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel smelting, and particularly relates to a method for improving the non-compliance of head billet flaw detection. Background Art

[0002] With the increasing maturity of the technology in the steel industry, steel users have higher and higher requirements for products. For example, in the use of bridges, buildings, pipelines, wind power, large-scale construction machinery, etc., product defects may lead to various problems such as fractures and collapses, posing great safety risks. Especially when facing downstream customers such as pipeline networks, customers' requirements are even more stringent. Therefore, each steel enterprise has stricter control over product quality. However, for head and tail cast billets, quality control is very difficult, especially in terms of internal quality control, and only flaw detection after rolling can be relied on for inspection. Therefore, the vast majority of steel enterprises will directly reject the head and tail billets to prevent quality abnormalities or quality objections after delivery. This not only increases additional production costs but also may lead to delays in production plans and deliveries. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for improving the non-compliance of head billet flaw detection to solve the problems existing in the prior art.

[0004] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0005] A method for improving the non-compliance of head billet flaw detection includes the following steps:

[0006] (1) Pouring with a large-tonnage ladle: Raising the pouring tonnage of the tundish to 38 tons through high-temperature and fast-pouring methods;

[0007] (2) After pouring from the large ladle, promptly remove the drainage sand;

[0008] (3) Delaying the addition of the covering agent: Adding the covering agent when the tundish tonnage reaches 35 tons;

[0009] (4) Inserting the submerged nozzle deeply: Dynamically adjusting the insertion depth of the submerged nozzle;

[0010] (5) Pouring with a constant liquid level in the mold, and controlling the starting time of the automatic variable slag line after the end of the head billet stage;

[0011] (6) Dynamically matching the section width: Matching the nozzle inclination angle according to the change in the section width of the cast billet.

[0012] Further, the overflow capacity of the tundish is 50 tons.

[0013] Further, the specific method for fast pouring at high temperature in step (1) is as follows: the tundish baking temperature is increased to 1300 °C, the temperature of the first ladle of molten steel is increased to a superheat of 45 °C, the starting speed is increased to 0.25 m / min, the starting time is reduced to 60 s, and the ramp rate is increased to 0.15 m / min 2 , and the tundish is quickly poured at a large tonnage in a way of rapid automatic speed increase.

[0014] Further, the dynamic adjustment method for the submerged nozzle insertion depth in step (4) is as follows:

[0015] For large-section production with a size above 2000 mm, the insertion depth is controlled at 180 mm;

[0016] For small-section production with a size below 2000 mm, the insertion depth is controlled at 150 mm.

[0017] Further, the method for dynamically matching the section width in step (6) is as follows: for production with a width below 2000 mm, a submerged nozzle with a small inclination angle of 15° is used; for production with a width above 2000 mm, a submerged nozzle with a large inclination angle of 20° is used.

[0018] The present invention has the following beneficial effects:

[0019] 1. The large-tonnage pouring technology of the present invention breaks through the cognitive limit of the "safe tonnage" in the industry, creates conditions for inclusions to fully float, improves the cleanliness of molten steel, and improves the problem of non-conforming head billet flaw detection.

[0020] 2. By timely removing the drainage sand and delaying the addition of the covering agent, the pollution of molten steel is avoided, the purity of molten steel is further improved, and thus the problem of non-conforming head billet flaw detection is improved.

[0021] 3. By dynamically adjusting the insertion depth of the submerged nozzle and matching the nozzle inclination angle according to the change of the slab section width, the floating of inclusions can be promoted and the activity of the mold flow field can be improved.

[0022] 4. By pouring the molten steel at a constant level in the mold and controlling the starting time of the automatic variable slag line, the fluctuation of the mold liquid level is reduced, the floating of inclusions is promoted, and the qualified rate of head billet flaw detection is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a screenshot of the control parameter setting interface during large-tonnage pouring of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] A method for improving the non - compliance of head billet flaw detection, comprising the following steps:

[0026] (1) Pouring with a large tonnage: The overflow capacity of the tundish is 50 tons. The pouring tonnage of the tundish is increased to 38 tons by means of high - temperature and fast pouring. The specific method of high - temperature and fast pouring is as follows: The baking temperature of the tundish is increased to 1300 °C, the temperature of the first ladle of molten steel is increased to a superheat of 45 °C, and as Figure 1 shown, the starting speed is increased to 0.25 m / min, the starting time is reduced to 60 s, and the ramp rate is increased to 0.15 m / min 2 , and the large - tonnage rapid pouring of the tundish is carried out in the way of rapid automatic speed increase.

[0027] In the iron and steel industry, in order to avoid pouring failure, low - tonnage pouring (such as 15 tons) is generally adopted, resulting in insufficient floating time of inclusions. By increasing the baking temperature of the tundish and the temperature of the molten steel when it enters the machine, the pouring tonnage is increased from 15 tons to 38 tons (the liquid level is about 700 mm), breaking through the cognitive limit of the "safe tonnage" in the industry and creating conditions for the full floating of inclusions.

[0028] The principle is as follows: By increasing the pouring tonnage of the molten steel in the tundish, the higher the tonnage, the more conducive it is to the floating of inclusions. After the ladle (big ladle) starts pouring, the molten steel enters the tundish. The temperature of the tundish is much lower than that of the molten steel, which is a rapid heat - absorption process for the working layers such as the bottom and lining of the tundish. The tundish will quickly absorb the heat of the molten steel, resulting in a rapid decrease in the temperature of the molten steel. Seriously, the temperature of the molten steel entering the tundish will drop below the solid - phase line temperature, leading to accidents such as rapid solidification of the molten steel and unsuccessful pouring. Therefore, in most cases, major iron and steel enterprises will set a relatively low pouring tonnage of the tundish to prevent the tundish from quickly absorbing the heat of the molten steel and causing the rapid solidification of the molten steel. However, low - tonnage pouring will result in insufficient floating time for inclusions in the molten steel, causing inclusions to enter the mold after the tundish starts pouring, and ultimately resulting in a relatively high inclusion content inside the cast billet, affecting the flaw - detection quality of the head billet.

[0029] Since the higher the pouring tonnage of the tundish, the more heat the working layers such as the bottom and lining of the tundish will absorb from the molten steel, how to increase the pouring tonnage of the tundish and still prevent the temperature of the molten steel from dropping below the solid - phase line temperature after the tundish quickly absorbs heat is the difficulty of this technology. The present invention mainly realizes the purpose of large - tonnage pouring on the premise of ensuring the pouring success rate by increasing the baking temperature of the tundish, increasing the superheat of the molten steel, rapid pouring of the mold, etc., thereby improving the problem of non - compliance of head billet flaw detection.

[0030] (2) After the big ladle starts pouring, promptly remove the drainage sand.

[0031] If drainage sand is mixed into molten steel, it will become a large foreign inclusion, resulting in non-compliant flaw detection. Taking away the drainage sand within 3 seconds after the ladle is poured can prevent the drainage sand from being drawn into or dissolved by the molten steel, thus reducing the number of inclusions. Experimental verification: the mixing rate of drainage sand is reduced from 8% to 0.5%, thereby improving the cleanliness of the molten steel and avoiding secondary oxidation caused by contact with the molten steel.

[0032] (3) Delayed addition of covering agent: Add covering agent when the tundish tonnage reaches 35 tons;

[0033] In the prior art, the covering agent is added when the tonnage of the molten steel reaches 15 tons. After it is improved to 35 tons, the covering agent entering the molten steel has a certain floating space and the melting rate of the covering agent is increased, thereby reducing the pollution of the molten steel by the covering agent and further improving the purity of the molten steel.

[0034] (4) Water inlet insertion depth: Dynamically adjust the insertion depth of the submerged water inlet.

[0035] The dynamic adjustment method of the water nozzle insertion depth is:

[0036] The insertion depth of large-section production above 2000mm is controlled at 180mm;

[0037] When producing small sections below 2000mm, the insertion depth is controlled at 150mm.

[0038] Dynamically adjusting the insertion depth of the submerged nozzle can promote the floating of inclusions. After the tundish is poured, the molten steel enters the crystallizer. Generally, in order to prevent low-temperature accidents caused by heat absorption of refractory materials, the insertion depth of the submerged nozzle will be controlled at a shallow depth. Under the coordination of large-tonnage pouring and the increase of the baking temperature of the submerged nozzle, low-temperature accidents can be effectively reduced. At this time, the insertion depth of the submerged nozzle is dynamically adjusted according to the principle of matching the cross section, which can improve the activity of the crystallizer flow field. The emergence time is long during the production of large cross-sections. Deeper insertion can effectively increase the floating time of inclusions and reduce the problem of non-conformity of the first billet flaw detection. Therefore, the nozzle insertion depth is controlled to 180mm during the production of large cross-sections above 2000mm; the emergence time is short during the production of small cross-sections. A shallower insertion depth can effectively increase the activity of the crystallizer flow field and improve the floating ability of inclusions. Therefore, the nozzle insertion depth is controlled to 150mm during the production of small cross-sections below 2000mm.

[0039] (5) Constant liquid level pouring in the crystallizer reduces the fluctuation of the liquid level in the crystallizer and promotes the floating of inclusions. In order to ensure the qualified rate of flaw detection of the first billet, the start time of the automatic slag changing line is controlled after the end of the first billet stage, that is, the automatic slag changing line time of the tundish is delayed to after the length of the first billet, thereby reducing the liquid level fluctuation caused by the automatic slag changing line, promoting the floating of inclusions, and improving the qualified rate of flaw detection of the first billet.

[0040] (6) Dynamically match the cross-sectional width: Match the nozzle inclination angle according to the change of the slab cross-sectional width.

[0041] The method for dynamically matching the cross-sectional width is as follows: When producing with a width below 2000 mm, use a nozzle with a small inclination angle of 15°. When producing with a width above 2000 mm, use a nozzle with a large inclination angle of 20°.

[0042] Develop submerged nozzles with different inclination angles for different cross-sections to promote the floating of inclusions. To increase the production capacity of the continuous casting machine, general steel enterprises have developed the function of online width adjustment of the slab. Especially for the single-strand slab continuous casting machine, the cross-sectional adjustment range is relatively large. For example, the maximum change in the cross-sectional range of the single-strand slab continuous casting machine reaches 1.25 meters. Therefore, one nozzle inclination angle cannot meet the large cross-sectional changes. It is necessary to develop more than two nozzle inclination angles for dynamic matching adjustment according to different cross-sections. For example, develop two nozzle inclination angles of 15° and 20°. When producing with a width below 2000 mm, use a nozzle with a small inclination angle of 15°. When producing with a width above 2000 mm, use a nozzle with a large inclination angle of 20°. This can effectively ensure the stability of the mold flow field under different cross-sectional conditions, effectively promote the floating of inclusions, and improve the problem of unqualified inspection of the first slab.

[0043] In summary, the present invention can increase the inspection qualification rate from 70% to 96%.

[0044] The above embodiments are only used to describe the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various variations and improvements made by those of ordinary skill in the art to the technical solution of the present invention should fall within the protection scope of the present invention.

[0045] The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A method for improving the non-conformity of head blank flaw detection, characterized in that: The following steps are involved: (1) Large-tonnage pouring: The tundish pouring tonnage is increased to 38 tons through high-temperature rapid pouring; (2) After pouring the large bag, remove the drainage sand in time; (3) Delayed addition of covering agent: Add covering agent when the tundish tonnage reaches 35 tons; (4) Nozzle insertion depth: Dynamically adjust the insertion depth of the immersion nozzle; (5) The crystallizer is poured at a constant liquid level, and the start time of the automatic slag changing line is controlled after the first billet stage is completed; (6) Dynamically match the section width: match the water inlet angle according to the change of the section width of the ingot.

2. The method for improving the non-conformity of head blank flaw detection according to claim 1, characterized in that: The overflow capacity of the tundish is 50 tons.

3. The method for improving the non-conformity of head blank flaw detection according to claim 1, characterized in that: The specific method of high-temperature rapid pouring in step (1) is as follows: the tundish baking temperature is increased to 1300°C, the temperature of the first furnace molten steel is increased to 45°C superheat, the starting speed is increased to 0.25m / min, the starting time is reduced to 60s, and the climbing rate is increased to 0.15m / min 2 , and quickly start pouring large tonnage in the tundish in a fast and automatic speed-up manner.

4. The method for improving the non-conformity of head blank flaw detection according to claim 1, characterized in that: The dynamic adjustment method of the water inlet insertion depth in step (4) is: The insertion depth of large-section production above 2000mm is controlled at 180mm; When producing small sections below 2000mm, the insertion depth is controlled at 150mm.

5. The method for improving the non-conformity of head blank flaw detection according to claim 1, characterized in that: The method for dynamically matching the cross-sectional width in step (6) is as follows: when producing with a width below 2000 mm, a small-angle water inlet of 15° is used; when producing with a width above 2000 mm, a large-angle water inlet of 20° is used.

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