A hot-rolled mill scale control method for a high-surface engineering machinery steel with a tensile strength of 960 MPa

Abstract

The application discloses a hot-rolled oxide scale control method for a high-surface 960MPa-grade engineering machinery steel with tensile strength, and belongs to the technical field of metallurgy. The method comprises the following steps: S1, proportioning components; S2, smelting and casting into a steel billet, the furnace time of the steel billet is 180-240 min, and the steel billet is heated to 1200-1300 DEG C and discharged; S3, rough rolling, obtaining an intermediate billet, and the rough rolling opening rolling temperature is 1150-1230 DEG C; S4, finish rolling, obtaining a finish-rolled plate strip, the finish rolling opening rolling temperature is 1000-1060 DEG C, and the final rolling temperature is 850-930 DEG C; S5, super-fast cooling and laminar cooling to 450-650 DEG C, and then coiling, the steel coil is ventilated and cooled to room temperature, and a high-surface 960MPa-grade engineering machinery steel with a volume fraction of eutectoid structure Fe and Fe3O4 in the oxide scale being less than 40% is obtained.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for controlling the iron oxide scale of hot-rolled engineering machinery steel with a tensile strength of 960MPa. Background Technology

[0002] Construction machinery steel is used to manufacture load-bearing engineering structures. It needs sufficient strength to prevent permanent deformation and damage during use. With the rapid development of the machinery industry, the application environment for construction machinery steel has become more complex, placing higher demands on its strength. Therefore, the development of high-strength construction machinery steel has become a current research hotspot.

[0003] To improve steel strength, reinforcing alloying elements such as Mn, Cr, and V are typically added. However, this complex composition, coupled with prolonged high-temperature heating for complete solution treatment, results in a complex oxide scale composition. Furthermore, the subsequent rolling process involves even higher temperatures, making it difficult to control the thickness of the oxide scale and the flatness of the oxide scale-matrix interface after rolling. Improper control can easily lead to surface defects on the steel plate. In the coiling and cooling process, controlling the oxidation cooling path also alters the microstructure of the surface oxide scale, affecting subsequent deep processing. Therefore, there is an urgent need to develop new hot-rolling technologies to achieve high-surface-quality production of 960MPa grade engineering machinery steel. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the iron oxide scale of hot-rolled steel with a tensile strength of 960MPa and high surface finish for engineering machinery, so as to solve the problem of high content of eutectic structure (Fe+Fe3O4) in the iron oxide scale on the surface of hot-rolled steel in the prior art.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0007] S1. The following components are formulated according to the following mass percentages: C: 0.10%–0.20%, Si: 0.15%–0.25%, Mn: 1.0%–2.0%, S: ≤0.015%, P: ≤0.025%, Als: 0.015%–0.045%, Cr: 0.20%–0.40%, V: 0.02%–0.03%, Nb: 0.01%–0.03%, Mo: 0.10%–0.70%, with the remainder being Fe and unavoidable impurities during smelting;

[0008] S2. The components in the proportion of S1 are smelted and cast into steel billets. The steel billets are in the furnace for 180 to 240 minutes and then heated to 1200 to 1300°C before being taken out of the furnace.

[0009] S3. Rough rolling is performed on the steel billet after it exits the furnace to obtain an intermediate billet. The rough rolling temperature is 1150~1230℃.

[0010] S4. The intermediate billet is finished rolled to obtain finished rolled strip. The initial rolling temperature is 1000-1060℃, the final rolling temperature is 850-930℃, and the rolling speed is 4-9m / s.

[0011] S5. The finished strip is first subjected to ultra-fast cooling to 810-880℃, then laminar cooling to 450-650℃, and then coiled to obtain a steel coil. After the steel coil is removed from the production line, it is ventilated and cooled to room temperature (25-30℃) to obtain 960MPa grade engineering machinery steel.

[0012] Furthermore, the thickness of the steel billet in S2 is 210–230 mm.

[0013] Furthermore, the thickness of the intermediate blank in S3 is 28–60 mm.

[0014] Furthermore, during the roughing and finishing rolling processes, descaling is performed using a descaling water pressure of 15–25 MPa.

[0015] Furthermore, the iron oxide scale thickness of the 960MPa grade engineering machinery steel plate is ≤12μm, the outermost Fe3O4 thickness is <4μm, and the volume fraction of Fe and Fe3O4 in the eutectoid structure is <40% in the iron oxide scale.

[0016] Furthermore, in S5, the cooling rate of ultra-fast cooling is 20–80 °C / s, the cooling rate of laminar flow cooling is 10–35 °C / s, and the cooling rate of ventilation cooling is 10–20 °C / h.

[0017] Furthermore, the winding temperature in S5 is 450–650°C.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention provides a method for controlling the iron oxide scale of hot-rolled steel for high-surface engineering machinery with a tensile strength of 960MPa. By adjusting the coiling temperature and the post-coiling cooling regime, the phase ratio of the iron oxide scale is optimized, so that the volume fraction of eutectoid Fe3O4+FeO in the iron oxide scale is less than 40%, which facilitates subsequent surface treatment processes.

[0020] 2. By rationally controlling the process system and optimizing the process design of the rolling process, the thickness of the iron oxide scale was reduced. This reduced oxidation loss and resource waste while enhancing the high-temperature plasticity of the iron oxide scale, improving the coordinated deformation ability between the iron oxide scale on the strip surface and the steel substrate, ensuring the flatness of the oxidation interface, and improving the surface quality of the steel plate. Attached Figure Description

[0021] The present invention will now be further described with reference to the accompanying drawings.

[0022] Figure 1 This is a characterization image of the iron oxide scale cross-section of the 6mm specification engineering machinery steel plate with a tensile strength of 960MPa prepared in Example 1 of the present invention;

[0023] Figure 2 This is a characterization image of the iron oxide scale cross-section of an 8mm specification engineering machinery steel plate with a tensile strength of 960MPa prepared in Example 2 of the present invention;

[0024] Figure 3 This is a characterization diagram of the iron oxide scale cross-section of the 10mm specification engineering machinery steel plate with a tensile strength of 960MPa prepared in Example 3 of the present invention;

[0025] Figure 4 This is a characterization diagram of the iron oxide scale cross-section of the 12mm specification engineering machinery steel plate with a tensile strength of 960MPa prepared in Example 4 of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0028] S1. The following components are formulated according to the following mass percentages: C: 0.10%–0.20%, Si: 0.15%–0.25%, Mn: 1.0%–2.0%, S: ≤0.015%, P: ≤0.025%, Als: 0.015%–0.045%, Cr: 0.20%–0.40%, V: 0.02%–0.03%, Nb: 0.01%–0.03%, Mo: 0.10%–0.70%, with the remainder being Fe and unavoidable impurities during smelting;

[0029] S2. The components in the proportion of S1 are smelted and cast into steel billets with a thickness of 210-230mm. The steel billets are in the furnace for 180-240 minutes and then heated to 1200-1300℃ before being taken out of the furnace.

[0030] S3. Rough rolling is performed on the steel billet after it exits the furnace to obtain an intermediate billet with a thickness of 28-60 mm. The rough rolling temperature is 1150-1230℃.

[0031] S4. The intermediate billet is finished rolled to obtain finished strip. The initial rolling temperature of the finishing rolling is 1000-1060℃, the final rolling temperature is 850-930℃, and the rolling speed is 4-9m / s. During the roughing and finishing rolling processes, the heating furnace is used for descaling, and the descaling water pressure is 15-25MPa.

[0032] S5. The finished strip is first subjected to ultra-rapid cooling to 810-880℃, then laminar cooling to 450-650℃, and then coiled to obtain a steel coil. The ultra-rapid cooling rate is 20-80℃ / s, and the laminar cooling rate is 10-35℃ / s. After the steel coil is removed from the production line, it is ventilated and cooled to room temperature at a rate of 10-20℃ / h to obtain a high-surface-grade engineering machinery steel plate with a thickness of 5-12mm and a tensile strength of 960MPa.

[0033] The thickness of the iron oxide scale on the steel plate is ≤12μm, the thickness of the outermost Fe3O4 layer is <4μm, and the volume fraction of Fe and Fe3O4 in the eutectoid structure is <40% in the iron oxide scale.

[0034] Example 1

[0035] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0036] S1. The following components are formulated according to the following mass percentages: C: 0.13%, Si: 0.15%, Mn: 1.0%, S: 0.0055%, P: 0.025%, Als: 0.015%, Cr: 0.2%, V: 0.02%, Nb: 0.02%, Mo: 0.3%, with the remainder being Fe and unavoidable impurities during smelting;

[0037] S2. The components in the proportion of S1 are smelted and cast into steel billets with a thickness of 230mm. The steel billets are in the furnace for 240 minutes and then heated to 1270℃ before being taken out of the furnace.

[0038] S3. Rough rolling is performed on the steel billet after it exits the furnace. The initial rolling temperature is 1200℃, and the rolling is performed in 5 passes to obtain an intermediate billet with a thickness of 34mm.

[0039] S4. The intermediate billet is finished rolled to obtain a finished strip. The initial rolling temperature is 1050℃, the final rolling temperature is 920℃, the finishing rolling passes are 7, and the rolling speed of the F7 stand is 9m / s to obtain a 6mm thick finished strip. During the roughing and finishing rolling processes, descaling is carried out in the heating furnace. The descaling water pressure for both roughing and finishing descaling is 20MPa.

[0040] S5. The precision-rolled strip is first subjected to ultra-rapid cooling to 830℃, and then laminar cooling to 550℃ before being coiled into a steel coil. The cooling rates of ultra-rapid cooling and laminar cooling are 75℃ / s and 25℃ / s, respectively. After the steel coil is removed from the production line, it is ventilated and cooled to room temperature at a cooling rate of 20℃ / h to obtain a high-performance engineering machinery steel plate with a thickness of 6mm and a tensile strength of 960MPa.

[0041] The iron oxide scale on a 6mm thick steel plate has a thickness of 5.90–6.90 μm, and its structure consists of 45% Fe3O4 and 5% eutectoid microstructure (Fe + Fe3O4). 4) Composed of 50% FeO, after hot rolling and cooling to room temperature, the cross-sectional morphology of the iron oxide scale is as follows: Figure 1 As shown.

[0042] Example 2

[0043] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0044] S1. The following components are formulated according to the following mass percentages: C: 0.16%, Si: 0.18%, Mn: 1.2%, S: 0.010%, P: 0.020%, Als: 0.025%, Cr: 0.3%, V: 0.025%, Nb: 0.015%, Mo: 0.35%, with the remainder being Fe and unavoidable impurities during smelting;

[0045] S2. The components in the proportion of S1 are smelted and cast into steel billets with a thickness of 230mm. The steel billets are in the furnace for 220 minutes and then heated to 1240℃ before being taken out of the furnace.

[0046] S3. The steel billet after exiting the furnace is rough rolled at an initial rolling temperature of 1170℃, and rolled in 5 passes to obtain an intermediate billet with a thickness of 38mm.

[0047] S4. The intermediate billet is finished rolled to obtain a finished strip. The initial rolling temperature is 1040℃, the final rolling temperature is 890℃, the finishing rolling passes are 7, and the rolling speed of the F7 stand is 7.5m / s to obtain an 8mm thick finished strip. Descaling is carried out in the heating furnace during roughing and finishing rolling. The descaling water pressure for both roughing and finishing descaling is 20MPa.

[0048] S5. The finished strip is first subjected to ultra-rapid cooling to 840℃, then laminar flow cooling to 580℃, and then coiled to obtain a steel coil. The cooling rates of ultra-rapid cooling and laminar flow cooling are 45℃ / s and 15℃ / s, respectively. After the steel coil is removed from the line, it is ventilated and cooled to room temperature at a cooling rate of 15℃ / h to obtain a high-performance engineering machinery steel plate with a thickness of 8mm and a tensile strength of 960MPa.

[0049] The iron oxide scale on the 8mm thick steel plate has a thickness of 6.40–7.3μm, and its structure consists of 45% Fe3O4 and 10% eutectoid (Fe+Fe3O4) microstructure. 4) Composed of 45% FeO, after hot rolling and cooling to room temperature, the cross-sectional morphology of the iron oxide scale is as follows: Figure 2 As shown.

[0050] Example 3

[0051] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0052] S1. The following components are formulated according to the following mass percentages: C: 0.18%, Si: 0.21%, Mn: 1.5%, S: 0.009%, P: 0.016%, Als: 0.030%, Cr: 0.25%, V: 0.02%, Nb: 0.018%, Mo: 0.45%, with the remainder being Fe and unavoidable impurities during smelting;

[0053] S2. The components in the proportion of S1 are smelted and cast into steel billets with a thickness of 230mm. The steel billets are in the furnace for 200min and heated to 1220℃ before being taken out of the furnace.

[0054] S3. The steel billet after exiting the furnace is rough rolled at an initial rolling temperature of 1160℃, and rolled in 5 passes to obtain an intermediate billet with a thickness of 42mm.

[0055] S4. The intermediate billet is finished rolled to obtain a finished strip. The initial rolling temperature is 1030℃, the final rolling temperature is 890℃, the finishing rolling passes are 7, and the rolling speed of the F7 stand is 6m / s to obtain a 10mm thick finished strip. Descaling is carried out in the heating furnace during roughing and finishing rolling. The descaling water pressure for both roughing and finishing is 20MPa.

[0056] S5. The precision-rolled strip is first subjected to ultra-rapid cooling to 830℃, and then laminar flow cooling to 590℃ before being coiled into a steel coil. The cooling rates of ultra-rapid cooling and laminar flow cooling are 40℃ / s and 15℃ / s, respectively. After the steel coil is removed from the production line, it is ventilated and cooled to room temperature at a cooling rate of 14℃ / h to obtain a high-surface-grade engineering machinery steel plate with a thickness of 10mm and a tensile strength of 960MPa.

[0057] The iron oxide scale on a 10mm thick steel plate has a thickness of 6.9–7.8 μm, and its structure consists of 42% Fe3O4 and 15% eutectoid microstructure (Fe + Fe3O4). 4) Composed of 43% FeO, after hot rolling and cooling to room temperature, the cross-sectional morphology of the iron oxide scale is as follows: Figure 3 As shown.

[0058] Example 4

[0059] A method for controlling iron oxide scale in hot-rolled engineering machinery steel with a tensile strength of 960 MPa includes the following steps:

[0060] S1. The following components are formulated according to the following mass percentages: C: 0.16%, Si: 0.18%, Mn: 1.6%, S: 0.008%, P: 0.012%, Als: 0.035%, Cr: 0.45%, V: 0.03%, Nb: 0.028%, Mo: 0.55%, with the remainder being Fe and unavoidable impurities during smelting;

[0061] S2. The components in the proportion of S1 are smelted and cast into steel billets with a thickness of 230mm. The steel billets are in the furnace for 190 minutes and then heated to 1210℃ before being taken out of the furnace.

[0062] S3. The steel billet after exiting the furnace is rough rolled at an initial rolling temperature of 1170℃, and rolled in 5 passes to obtain an intermediate billet with a thickness of 46mm.

[0063] S4. The intermediate billet is finished rolled to obtain a finished strip. The initial rolling temperature is 1015℃, the final rolling temperature is 860℃, the finishing rolling passes are 7, and the rolling speed of the F7 stand is 6m / s to obtain a 12mm thick finished strip. Descaling is carried out in the heating furnace during roughing and finishing rolling. The descaling water pressure for both roughing and finishing descaling is 20MPa.

[0064] S5. The precision-rolled strip is first subjected to ultra-rapid cooling to 810℃, and then laminar flow cooling to 600℃ before being coiled into a steel coil. The cooling rates of ultra-rapid cooling and laminar flow cooling are 25℃ / s and 12℃ / s, respectively. After the steel coil is removed from the production line, it is ventilated and cooled to room temperature at a cooling rate of 12℃ / h to obtain a high-surface-grade engineering machinery steel plate with a thickness of 12mm and a tensile strength of 960MPa.

[0065] The iron oxide scale on a 12mm thick steel plate has a thickness of 7.9–8.9 μm, and its structure consists of 40% Fe3O4 and 20% eutectoid (Fe+Fe3O4) microstructure. 4) Composed of 40% FeO, after hot rolling and cooling to room temperature, the cross-sectional morphology of the iron oxide scale is as follows: Figure 4 As shown.

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling hot-rolled mill scale of a high-surface engineering machine steel of a tensile strength grade of 960 MPa, characterized in that, It comprises the following steps: S1. The following components are proportioned according to mass percentage: C: 0.10%-0.20%, Si: 0.15%-0.25%, Mn: 1.0%-2.0%, S: ≤0.015%, P: ≤0.025%, Als: 0.015%-0.045%, Cr: 0.20%-0.40%, V: 0.02%-0.03%, Nb: 0.01%-0.03%, Mo: 0.10%-0.70%, and the rest is Fe and unavoidable impurities in smelting; S2. The components proportioned in S1 are smelted and cast into a steel billet, the billet is heated to 1200-1300℃ for 180-240min in the furnace and then discharged; S3. The discharged steel billet is roughed to obtain an intermediate billet, and the roughing temperature is 1150-1230℃; S4. The intermediate billet is finished to obtain a finished plate strip, and the finishing roughing temperature is 1000-1060℃ and the final rolling temperature is 850-930℃; S5. The finished plate strip is first cooled to 810-880℃ by ultrafast cooling, then cooled to 450-650℃ by laminar flow cooling, and then coiled to obtain a steel coil; after the steel coil is discharged, it is cooled to room temperature by ventilation cooling, and a 960MPa grade engineering machinery steel with an oxide scale thickness ≤12μm, an outermost layer Fe3O4 thickness <4μm, and a eutectoid structure volume fraction <40% in the oxide scale is obtained; The cooling rate of the ultrafast cooling in S5 is 20-80℃ / s, and the cooling rate of the laminar flow cooling is 10-35℃ / s; the cooling rate of the ventilation cooling in S5 is 10-20℃ / h; and the coiling temperature in S5 is 450-650℃.

2. The hot scale control method of a 960 MPa grade high surface engineering machinery steel against tensile strength according to claim 1, characterized in that, The thickness of the steel billet in S2 is 210-230mm.

3. The hot scale control method of a high surface engineering machinery steel with a tensile strength of 960 MPa according to claim 1, characterized in that, The thickness of the intermediate billet in S3 is 28-60mm.

4. The hot scale control method of a high surface engineering machinery steel with a tensile strength of 960 MPa according to claim 1, characterized in that, The rolling speed of the finishing in S4 is 4-9m / s.

5. The hot scale control method of a high surface engineering machinery steel with a tensile strength of 960 MPa according to claim 1, characterized in that, In the roughing and finishing processes, descaling is performed, and the descaling water pressure is 15-25MPa.

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