A method for improving the iron oxide scale on weathering steel

Abstract

This invention discloses a method for improving the iron oxide scale on weathering steel. The weathering steel is Q450NQR1 high weathering steel plate: slab exit temperature 1220-1230℃, heating section temperature 1240-1320℃, soaking section temperature 1220-1290℃, pre-rolling heat preservation heating section temperature 1190-1260℃, soaking section temperature 1200-1240℃, controlled coal ratio 1.7-1.9 in the upper part of the preheating section, 1.6-1.8 in the lower part of the preheating section, 2.0-2.2 in the upper part of the heating section, 1.9-2.1 in the lower part of the heating section, 1.6-1.8 in the upper part of the soaking section, and 1.5-1.7 in the lower part of the soaking section. The purpose of this invention is to reduce the amount of iron oxide scale generated in the slab furnace, and at the same time reduce the probability of molten Fe2SiO4 (2FeO·SiO2) penetrating into the iron oxide scale and the pores of the steel matrix, thereby promoting the peeling off of the iron oxide scale, improving the surface quality of the product and its excellent mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling technology, and particularly relates to a method for improving the iron oxide scale on weathering steel. Background Technology

[0002] During the heating process, the furnace gas contains a large amount of oxidizing gases such as CO2, H2O, and excess O2, causing oxidation on the surface of the steel to form furnace-grown iron oxide scale. Generally, this scale can be completely removed by high-pressure water descaling. However, high-weather-resistant slabs, such as Q450NQR1, often exhibit incomplete descaling after furnace removal, with a descaling pass rate of only about 80%. Furnace-grown iron oxide scale remains on the slab surface in localized or large areas. If this scale is not completely removed before rolling, it will be pressed into the strip surface during rolling, resulting in a defective quality issue. This defect can severely impact the mechanical properties of the product, degrade the rolling condition, and even lead to scrap steel or damage to the main rolling line equipment. Summary of the Invention

[0003] The purpose of this invention is to provide a method for improving the iron oxide scale of weathering steel. This method optimizes the slab heating time, tapping temperature, and furnace temperature in the heating and soaking zones, thereby reducing the amount of iron oxide scale generated in the slab and reducing the probability of molten Fe2SiO4 (2FeO·SiO2) penetrating into the iron oxide scale and steel matrix pores. This promotes the peeling off of the iron oxide scale, improves the surface quality of the product, and enhances its mechanical properties.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention discloses a method for improving the iron oxide scale on weathering steel, wherein the weathering steel is Q450NQR1 high weathering steel plate, and its preparation process includes: The slab exit temperature is controlled at 1220-1230℃, the heating section temperature at 1240-1320℃, and the soaking section temperature at 1220-1290℃. The preheating and holding temperature for rolling is 1190-1260℃, and the soaking section temperature is 1200-1240℃. The soaking section holding time is 0.8-1.2h, and the waiting time for rolling is 10-30min. The coal ratio is controlled at 1.7-1.9 in the upper part of the preheating section, 1.6-1.8 in the lower part of the preheating section, 2.0-2.2 in the upper part of the heating section, 1.9-2.1 in the lower part of the heating section, 1.6-1.8 in the upper part of the soaking section, and 1.5-1.7 in the lower part of the soaking section.

[0005] Furthermore, any high weathering steel to be rolled that has been kept at a constant temperature in the soaking zone of the heating furnace for more than 1 hour will be returned to the furnace for further processing.

[0006] Furthermore, the chemical composition of the weathering steel by weight percentage is: C≤0.10%, Si 0.3-0.5%, Mn≤1.00%, P≤0.02%, S≤0.01%, Cu≤0.4%, Cr≤0.6%, Ni≤0.35%, Ti≤0.08%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition of the weathering steel by weight percentage is: C 0.10%, Si 0.31%, Mn 0.9%, P 0.0173%, S 0.015%, Cu 0.35%, Cr 0.5%, Ni 0.22%, Ti 0.03%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the chemical composition of the weathering steel by weight percentage is: C 0.09%, Si 0.35%, Mn 0.8%, P 0.0107%, S 0.009%, Cu 0.29%, Cr 0.45%, Ni 0.27%, Ti 0.05%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the chemical composition of the weathering steel by weight percentage is: C 0.10%, Si 0.41%, Mn 0.9%, P 0.0111%, S 0.012%, Cu 0.32%, Cr 0.48%, Ni 0.3%, Ti 0.05%, with the balance being Fe and unavoidable impurities.

[0010] Furthermore, the chemical composition of the weathering steel by weight percentage is: C 0.09%, Si 0.37%, Mn 0.9%, P 0.0090%, S 0.011%, Cu 0.35%, Cr 0.55%, Ni 0.25%, Ti 0.04%, with the balance being Fe and unavoidable impurities.

[0011] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The Q450NQR1 high weathering steel plate of the present invention reduces the amount of iron oxide scale generated in the slab by optimizing the slab heating time, tapping temperature and furnace temperature in the heating and soaking sections. At the same time, it reduces the probability of molten Fe2SiO4 (2FeO·SiO2) penetrating into the iron oxide scale and steel matrix pores, thereby promoting the peeling off of iron oxide scale, improving the surface quality of the product and its excellent mechanical properties. Detailed Implementation

[0012] The method for improving the iron oxide scale on weathering steel according to the present invention will be described in further detail below.

[0013] The steel component described in this invention is Q450NQR1 high weathering steel, and is manufactured according to the following steps: The slab exit temperature is controlled at 1220-1230℃, the heating section temperature at 1240-1320℃, and the soaking section temperature at 1220-1290℃. The preheating and holding temperature for rolling is 1190-1260℃, and the soaking section temperature is 1200-1240℃. The holding time in the soaking section is 0.8-1.2 hours, and the waiting time for rolling is 10-30 minutes. The coal ratio is controlled as follows: upper part of the preheating section 1.7-1.9, lower part of the preheating section 1.6-1.8, upper part of the heating section 2.0-2.2, lower part of the heating section 1.9-2.1, upper part of the soaking section 1.6-1.8, lower part of the soaking section 1.5-1.7. High weathering steel awaiting rolling in the soaking section of the heating furnace that is held for more than 1 hour will be returned to the furnace.

[0014] Table 1 shows the chemical composition and content of the steel grades in each embodiment; Table 2 shows the process parameters for each embodiment; Table 3 shows the mechanical property test results for each embodiment. Table 1 Chemical composition of each example (mass percentage / %) Example 1 0.10 0.31 0.9 0.0173 0.015 0.35 0.22 0.5 0.03 Example 2 0.09 0.35 0.8 0.0107 0.009 0.29 0.27 0.45 0.05 Example 3 0.10 0.41 0.9 0.0111 0.012 0.32 0.3 0.48 0.05 Example 4 0.09 0.37 0.9 0.0090 0.011 0.35 0.25 0．55 0.04 Table 2 Process parameters for each embodiment Example 1 10 1200 1190 1170 Example 2 15 1210 1250 1150 Example 3 20 1220 1200 1130 Example 4 30 1240 1230 1160 Table 3 Mechanical properties of each embodiment Example 1 491 583 28 Example 2 494 586 29 Example 3 486 573 28 Example 4 479 577 28 The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the iron oxide scale on weathering steel, characterized in that: The weathering steel is Q450NQR1 high weathering steel plate, and its preparation process includes: The slab exit temperature is controlled at 1220-1230℃, the heating section temperature at 1240-1320℃, and the soaking section temperature at 1220-1290℃. The preheating and holding temperature for rolling is 1190-1260℃, and the soaking section temperature is 1200-1240℃. The soaking section holding time is 0.8-1.2h, and the waiting time for rolling is 10-30min. The coal ratio is controlled at 1.7-1.9 in the upper part of the preheating section, 1.6-1.8 in the lower part of the preheating section, 2.0-2.2 in the upper part of the heating section, 1.9-2.1 in the lower part of the heating section, 1.6-1.8 in the upper part of the soaking section, and 1.5-1.7 in the lower part of the soaking section.

2. The method for improving the iron oxide scale on weathering steel according to claim 1, characterized in that: If the high weathering steel to be rolled in the soaking zone of the heating furnace is kept at a constant temperature for more than 1 hour, it will be completely recycled back into the furnace.

3. The method for improving the iron oxide scale on weathering steel according to claim 1, characterized in that: The chemical composition of the weathering steel by weight percentage is: C≤0.10%, Si 0.3-0.5%, Mn≤1.00%, P≤0.02%, S≤0.01%, Cu≤0.4%, Cr≤0.6%, Ni≤0.35%, Ti≤0.08%, with the balance being Fe and unavoidable impurities.

4. The method for improving the iron oxide scale on weathering steel according to claim 3, characterized in that: The chemical composition of the weathering steel by weight percentage is: C 0.10%, Si 0.31%, Mn 0.9%, P 0.0173%, S 0.015%, Cu 0.35%, Cr 0.5%, Ni 0.22%, Ti 0.03%, with the balance being Fe and unavoidable impurities.

5. The method for improving the iron oxide scale on weathering steel according to claim 3, characterized in that: The chemical composition of the weathering steel by weight percentage is: C 0.09%, Si 0.35%, Mn 0.8%, P 0.0107%, S 0.009%, Cu 0.29%, Cr 0.45%, Ni 0.27%, Ti 0.05%, with the balance being Fe and unavoidable impurities.

6. The method for improving the iron oxide scale on weathering steel according to claim 3, characterized in that: The chemical composition of the weathering steel by weight percentage is: C 0.10%, Si 0.41%, Mn 0.9%, P 0.0111%, S 0.012%, Cu 0.32%, Cr 0.48%, Ni 0.3%, Ti 0.05%, with the balance being Fe and unavoidable impurities.

7. The method for improving the iron oxide scale on weathering steel according to claim 3, characterized in that: The chemical composition of the weathering steel by weight percentage is: C 0.09%, Si 0.37%, Mn 0.9%, P 0.0090%, S 0.011%, Cu 0.35%, Cr 0.55%, Ni 0.25%, Ti 0.04%, with the balance being Fe and unavoidable impurities.

8. The method for improving the iron oxide scale on weathering steel according to claim 1, characterized in that: The holding time in the soaking zone of the hot furnace is 1 hour, and the waiting time for rolling is 20 minutes.