Method for reducing red rust on surface of high-silicon high-strength steel

Abstract

The invention discloses a method for reducing red rust on the surface of high-silicon and high-strength steel. The method comprises the step of optimizing chemical components and a hot rolling process of the high-silicon and high-strength steel. The high-silicon high-strength steel plate comprises the following chemical components in percentage by weight: 0.15 to 0.30 percent of [C], 1.40 to 2.50 percent of [Si], 1.80 to 2.20 percent of [Mn], 0.05 to 0.20 percent of [P], less than or equal to 0.005 percent of [S], 0.04 to 0.06 percent of [Nb] and [Ti], less than or equal to 0.005 percent of [Ni] and the balance of Fe and inevitable impurity elements in steel. According to the method, new equipment is not added, the surface red rust of a hot-rolled finished product can be effectively improved by adjusting components and a hot rolling process, and the surface quality of finished strip steel is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled strip steel production, and in particular relates to a method for reducing red rust on the surface of high-silicon high-strength steel. Background Art

[0002] When designing the composition of high-strength steel, a certain amount of Si element is added to enhance the strength and hardenability of the steel; however, as the Si content increases, especially when it is higher than 0.5% (such as DP, QP, TRIP steel, etc.), red rust defects are very likely to occur on the surface of the hot-rolled strip. Because at high temperatures, the Si element will form a fayalite phase (Fe2SiO4) between the strip matrix and the iron oxide skin, and after solidification, it will form an anchor-like morphology that pins and wraps the FeO. The pinned FeO is difficult to be completely removed in the subsequent descaling process. The residual FeO is broken during the subsequent hot rolling process and comes into contact with oxygen in the air, eventually forming a reddish-brown Fe2O3, such as Figure 1 As shown, it directly affects the surface quality of hot-rolled products.

[0003] At present, the formation mechanism of red rust defects on the hot-rolled surface and the influence of silicon on the growth characteristics of iron oxide scale have been studied sufficiently, and the conclusions have been unanimously recognized by the academic community. However, effective control measures suitable for large-scale industrial implementation have not been found, which greatly limits the production of high-surface grade, high-silicon and high-strength steel plates.

[0004] Patent application with publication number CN103920729A discloses a method for removing red rust defects of high-silicon high-strength automobile plates. This method requires the addition of a curtain descaling device and an iron chain. The iron chain produces friction and collision on the surface of the strip, which may have an adverse effect on the surface of the strip and increase the equipment cost.

[0005] Patent application with publication number CN116251841A discloses a method for reducing red rust on the surface of 800Mpa grade high silicon ultra-high strength steel, which controls the soaking temperature at 1250-1290°C and the furnace temperature at 1240-1280°C; the heating temperature can ensure the liquid phase state of the fayalite phase, but in the high temperature zone, the intrusion of the fayalite phase into the matrix is ​​more intense, so the formation of fayalite phase anchor points cannot be suppressed, and therefore the removal effect of the fayalite phase is difficult to ensure. Summary of the invention

[0006] The present invention aims to provide a method for reducing red rust on the surface of high-silicon high-strength steel, which can effectively improve the red rust on the surface of hot-rolled finished products and improve the surface quality of finished strip steel.

[0007] To achieve the above purpose, the technical solution of the present invention is as follows: A method for reducing red rust on the surface of high-silicon high-strength steel comprises optimizing the chemical composition and hot rolling process of the high-silicon high-strength steel; the chemical composition of the high-silicon high-strength steel plate is as follows by weight percentage: [C]: 0.15-0.30%, [Si]: 1.40-2.50%, [Mn]: 1.80-2.20%, [P]: 0.05-0.20%, [S]≤0.005%, [Nb]+[Ti]: 0.04-0.06%, [Ni]≤0.005%, and the rest are Fe and inevitable impurity elements in steel.

[0008] Furthermore, the hot rolling process of the high-silicon high-strength steel of the present invention comprises the following steps: (1) The slab is heated in a heating furnace; (2) After the slab is taken out of the furnace, it is successively descaled after the furnace, rolled by the roughing mill, and descaled in the subsequent passes; (3) Finish rolling to remove scale, and then rolling the slab into the final required size through the finishing mill; (4) The finished strip after finish rolling is laminar cooled and coiled into a coil.

[0009] Furthermore, in the hot rolling method of the present invention, the heating in the heating furnace in step (1) has the following characteristics: the soaking temperature is 1130-1170°C, the furnace discharge temperature is 1120-1160°C, and the slab is in the furnace for ≤300 min.

[0010] Furthermore, in the hot rolling method of the present invention, the descaling pressure of the post-furnace descaling and pass descaling in step (2) and the finish rolling descaling in step (3) is 20-30 MPa. A larger descaling pressure is conducive to improving the descaling effect.

[0011] Furthermore, in the hot rolling method of the present invention, the inlet temperature of the finishing rolling in step (3) is 950-980°C, the final rolling temperature is 870-910°C, and no inter-stand cooling water is added.

[0012] Furthermore, in the hot rolling method of the present invention, the laminar cooling in step (4) adopts front-stage cooling, and the coiling temperature after cooling is 650-690°C.

[0013] The high-silicon high-strength steel obtained by the method of the present invention has a tensile strength of 700-850MPa and a surface iron oxide scale thickness of 3-8um.

[0014] The design ideas of the technical solution of the present invention are as follows: The present invention adopts a composition design of 0.05-0.20% phosphorus element. By adding a certain amount of phosphorus element, the solid-liquid conversion temperature of the fayalite phase (Fe2SiO4) is reduced, so that the difficulty of removing the fayalite phase (Fe2SiO4) is reduced; at the same time, the lower heating temperature reduces the activity of the fayalite phase (Fe2SiO4) invading the matrix, thereby reducing the probability of forming an anchor point. In addition, since the Ni element easily increases the tortuosity of the interface between the matrix and the iron oxide scale, the difficulty of removing the fayalite phase (Fe2SiO4) is increased, so the Ni element content is controlled to be ≤0.005%.

[0015] The present invention adopts a low-temperature short-time heating system, which reduces the total generation amount of the fayalite phase (Fe2SiO4) and the probability of forming anchor points.

[0016] The finishing rolling start temperature of the present invention is low, and the final rolling temperature is high, so the overall rolling temperature is low, the rolling time is short, the thickness of the iron oxide scale and the amount of FeO generated are reduced, and at the same time, a certain proportion of Fe3O4 phase is generated in the finishing rolling stage, which reduces the contact probability of the FeO phase and the diffused O2, thereby reducing the generation probability of red rust. No cooling water is added between the racks, which can prevent the iron oxide scale from being easily broken during rolling.

[0017] The beneficial effects of adopting the above technical solution are: 1) The method of the present invention does not require the purchase of new equipment. By adjusting the composition and hot rolling process, the red rust on the surface of the hot-rolled finished product can be effectively improved, thereby improving the surface quality of the finished strip steel.

[0018] 2) The method of the present invention adopts a high-phosphorus composition design. Since phosphorus can improve the strength of steel through solid solution strengthening and precipitation strengthening, the amount of alloy elements added in the present invention is relatively small compared with steels of the same strength level, thereby saving manufacturing costs.

[0019] 3) The method of the present invention adopts a low-temperature short-time heating system, which saves manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the red rust defect morphology on the surface of high-silicon high-strength steel in the prior art.

[0021] Figure 2 It is a schematic diagram of the red rust defect morphology on the surface of high-silicon high-strength steel obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the 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.

[0023] The chemical composition of the high-silicon high-strength steel in each embodiment is shown in Table 1.

[0024] Table 1 Chemical composition of steel plates in various examples (%)

[0025] The balance in Table 1 is Fe and unavoidable impurity elements in steel.

[0026] The hot rolling process of high-silicon high-strength steel in each embodiment includes the following steps: (1) The slab is heated in a heating furnace: the soaking temperature is 1130-1170℃, the furnace exit temperature is 1120-1160℃, and the slab time in the furnace is ≤300min.

[0027] (2) After the slab is taken out of the furnace, it is sequentially subjected to post-furnace descaling, rough rolling mill rolling and pass descaling; the descaling pressure of the post-furnace descaling and pass descaling is 20-30 MPa.

[0028] (3) Finishing rolling and descaling, the descaling pressure is 20-30Mpa, and then the slab is rolled into the final required size through the finishing rolling unit; the finishing rolling inlet temperature is 950-980℃, the final rolling temperature is 870-910℃, and no inter-stand cooling water is added.

[0029] (4) The finished steel strip after finish rolling is cooled by laminar flow, coiled into coils, and then packaged and stored; the laminar flow cooling adopts front-stage cooling, and the coiling temperature after cooling is 650-690°C.

[0030] The main hot rolling process parameters of each embodiment are shown in Table 2.

[0031] Table 2 Main hot rolling process parameters of each embodiment

[0032] The tensile properties and iron oxide scale thickness of the high-silicon high-strength steel of each embodiment were tested, and the results are shown in Table 3. The iron oxide scale thickness is the thickness randomly measured under a scanning electron microscope with a magnification of 1000-2000 times and multiple fields of view.

[0033] Table 3 Tensile properties and iron oxide scale thickness of high silicon high strength steel in various examples

[0034] It can be seen from Table 3 that the tensile strength of the high-silicon high-strength steel obtained by the method of the present invention is 700-850 MPa; the thickness of the surface oxide scale is 3-8 um.

[0035] The red rust defect morphology on the surface of the high-silicon high-strength steel obtained in Example 1 of the present invention is as follows Figure 2 As shown by Figure 2 It can be seen that the red rust on its surface is distributed in dots, which is similar to Figure 1 The red rust in the form of large-area flakes is significantly improved. The morphology of the red rust defects on the surface of high-silicon high-strength steel obtained in the other embodiments is the same as that in the embodiment, and will not be shown one by one.

[0036] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for reducing red rust on the surface of high-silicon high-strength steel, characterized in that: The method comprises optimizing the chemical composition and hot rolling process of high-silicon high-strength steel; the chemical composition of the high-silicon high-strength steel plate is as follows by weight percentage: [C]: 0.15-0.30%, [Si]: 1.40-2.50%, [Mn]: 1.80-2.20%, [P]: 0.05-0.20%, [S]≤0.005%, [Nb]+[Ti]: 0.04-0.06%, [Ni]≤0.005%, and the rest are Fe and inevitable impurity elements in steel.

2. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 1, characterized in that: The hot rolling process of the high-silicon high-strength steel comprises the following steps: (1) The slab is heated in a heating furnace; (2) After the slab is taken out of the furnace, it is successively descaled after the furnace, rolled by the roughing mill, and descaled by the pass; (3) Finish rolling to remove scale, and then rolling the slab into the final required size through the finishing mill; (4) The finished strip after finish rolling is laminar cooled and coiled into a coil.

3. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 2, characterized in that: The heating in the heating furnace in step (2) is as follows: the soaking temperature is 1130-1170°C, the furnace discharge temperature is 1120-1160°C, and the slab time in the furnace is ≤300 min.

4. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 2, characterized in that: The descaling pressure of the post-furnace descaling and pass descaling in step (2) and the finish rolling descaling in step (3) is 20-30 MPa.

5. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 2, characterized in that: In step (3), the inlet temperature of the finishing rolling is 950-980°C, the final rolling temperature is 870-910°C, and no inter-stand cooling water is added.

6. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 2, characterized in that: The laminar cooling in step (4) adopts front-stage cooling, and the coiling temperature after cooling is 650-690°C.

7. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 1, characterized in that: The high-silicon high-strength steel obtained by the method has a tensile strength of 700-850 MPa.

8. The method for reducing red rust on the surface of high-silicon high-strength steel according to claim 1, characterized in that: The thickness of the iron oxide scale on the surface of the high-silicon high-strength steel obtained by the method is 3-8um.

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