High surface control method for thin-gauge Q345-grade steel for engineering mechanical structure

Abstract

The invention discloses a high surface control method for thin-gauge Q345-grade steel for engineering machinery structures, which relates to the technical field of steel production and comprises the following step: controlling the content of Si element to be less than or equal to 0.2%. According to the method, the Si component range and the heating process are controlled through optimization design, and the generation and pinning depth of a liquid latticed binary eutectic Fe2SiO4 / FeO are reduced from two angles of heat and dynamics, so that the scale structure of the carbon steel and the binding force of the scale structure and an iron matrix are changed, the pressing-in condition of the red scale is greatly reduced, and the service life of the carbon steel is prolonged. The problem of piebaldness on the steel plate surface is effectively solved, and steel plate surface quality is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a high surface control method for thin-gauge Q345 grade steel for engineering machinery structures. Background Art

[0002] High surface quality control of steel used in construction machinery structures is a key link to ensure the performance and life of the final product. This type of steel is usually used to manufacture mechanical equipment parts that withstand heavy loads and complex working conditions, such as excavators, bulldozers, cranes, etc. In order to meet the rapid development of the construction machinery market and the strict requirements on part performance, steel not only needs to have high toughness, good weldability and processability, but also excellent surface quality. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a high surface control method for thin-gauge Q345 grade steel for engineering machinery structures.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows: A method for controlling the high surface area of ​​thin-gauge Q345 grade steel for engineering machinery structure comprises: controlling the Si element content to be less than or equal to 0.2%.

[0005] As a preferred solution of the high surface control method of thin-gauge Q345 grade engineering machinery structure steel described in the present invention, it also includes: controlling the steel billet soaking temperature to be less than or equal to 1170°C.

[0006] As a preferred solution of the high surface control method of thin-gauge Q345 grade engineering machinery structure steel of the present invention, it also includes: Obtain the billet thickness and time in the furnace; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling.

[0007] As a preferred solution of the high surface control method of thin-gauge Q345 grade engineering machinery structure steel described in the present invention, the dephosphorization pressure of the dephosphorization process is greater than or equal to 18 MPa.

[0008] As a preferred solution of the high surface control method of thin-gauge Q345 grade engineering machinery structure steel described in the present invention, when the thickness of the steel billet is greater than 7 mm and less than or equal to 16 mm, the final rolling temperature is controlled to be 800-820°C.

[0009] The beneficial effects of the present invention are: The present invention controls the Si composition range and the heating process through optimized design, reduces the generation and pinning depth of the liquid grid-like binary eutectic Fe2SiO4 / FeO from both thermal and kinetic perspectives, thereby changing the scale structure of carbon steel and its bonding force with the iron matrix, thereby greatly reducing the indentation of red scale, effectively solving the problem of mottled surfaces on steel plates, and ensuring the surface quality of steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0011] Figure 1 It is a schematic diagram of the morphology of Fe2SiO4 / FeO at different heating temperatures under the same Si content composition conditions; Figure 2 Schematic diagram of the morphology of Fe2SiO4 / FeO with different Si components under the same heating temperature; Figure 3 Schematic diagram of the formation mechanism of red oxide scale in Si-containing steel. DETAILED DESCRIPTION

[0012] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation modes and in combination with the accompanying drawings.

[0013] The present application provides a method for controlling the high surface of thin-gauge Q345 grade engineering machinery structural steel, the method comprising the following steps: Step S101: Control the Si element content to be less than or equal to 0.2%.

[0014] Specifically, by studying the formation mechanism of iron oxide scale and its binary eutectic Fe2SiO4 / FeO and combining it with big data, the Si composition of all Q345-grade engineering machinery structural steel grades was optimized, and the upper limit of Si alloy composition was reduced to 0.2%.

[0015] Step S102: Control the steel billet soaking temperature to be less than or equal to 1170°C.

[0016] Step S103: Obtaining the thickness and the time in the furnace of the steel billet; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling.

[0017] See Table 1 for the above steps S102 and S103.

[0018]

[0019] Table 1 See also Figure 1~Figure 3The above technical scheme controls the Si composition range and heating process through optimized design, reduces the formation and pinning depth of liquid grid-like binary eutectic Fe2SiO4 / FeO from the perspective of heat and dynamics, thereby changing the scale structure of carbon steel and its bonding force with the iron matrix. When the heating temperature is heated to 1170℃, the binary eutectic Fe2SiO4 / FeO melts from solid to liquid, thus forming a grid with higher adhesion, pinning the matrix and the FeO in the oxidation critical layer. In the subsequent rolling process, the FeO that is not completely cleared is crushed and pressed into the matrix along with Fe2SiO4 / FeO, and the crushed FeO is oxidized to form red Fe2O3. When it is higher than 1170℃, the higher the temperature and the longer the insulation time, the stronger the pinning ability. In terms of rolling technology, the steel composition, heating, rolling and descaling process are optimized under the conditions of ensuring the descaling overlap and impact force.

[0020] The following is further described by means of specific examples.

[0021] Example 1: This example uses a G1-Q355B steel billet with a thickness of 14 mm.

[0022] Composition design: The design range of Si content was optimized from 0.2%-0.3% to 0.07%-0.2%, and the actual Si content was 0.15%.

[0023] Blank size: 220×2065×2237mm; Order size: 14×2054×11700mm.

[0024] Heating method: Slab uniform heating temperature 1158℃, heating time 246 minutes.

[0025] Rolling and descaling methods: finishing rolling 7 passes, descaling in the 1st and 3rd passes of rough rolling, descaling in the 1st and 2nd passes of finishing rolling, final rolling temperature 813℃, rough rolling descaling pressure 19.25MPa, finishing rolling descaling pressure 19.12MPa.

[0026] Other processes: After the steel plate is rolled, it is cooled, straightened, slowly cooled on a cooling bed, sheared, and the finished product is put into storage. The steel plate is inspected before the finished product is put into storage. The surface quality of the steel plate is normal, without obvious dioxygen pressure. The shot blasting inspection shows that there are no spots on the surface of the steel plate. Compared with the previous design using 0.25% Si composition, the soaking temperature is 1190℃, the finishing rolling is 5 times, and the final rolling temperature is 840℃, the surface improvement effect is obvious.

[0027] A certain factory optimized the Si content of all engineering machinery steel grades, designed the flexible linkage between heating and rolling processes, and optimized and solidified the descaling process. The degrading rate of thin-gauge engineering machinery steel of 16mm and below was reduced from 2.24% to 0.29% due to the pressure-in of red iron oxide scale on the surface, which has a significant improvement effect, as shown in Table 2. At the same time, the finishing rolling can be reduced from 7 passes to 5 passes.

[0028]

[0029] Table 2 Therefore, the technical solution of the present application can significantly reduce the pressure of red iron oxide scale, effectively solve the problem of mottled steel plate surface, and ensure the surface quality of the steel plate.

[0030] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A method for controlling the high surface of thin-gauge Q345 grade engineering machinery structural steel, characterized in that: include: The Si element content is controlled to be less than or equal to 0.2%.

2. The high surface control method of thin-gauge Q345 grade engineering machinery structure steel according to claim 1 is characterized by: Also includes: Control the billet soaking temperature to be less than or equal to 1170℃.

3. The high surface control method of thin-gauge Q345 grade engineering machinery structure steel according to claim 1 is characterized by: Also includes: Obtain the billet thickness and time in the furnace; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than or equal to 6 mm and less than or equal to 7 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first finishing pass; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than 7 mm and less than 14 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the second pass of rough rolling and the first pass of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is less than or equal to 230 min, the billet finishing passes are controlled to be 5 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling; When the billet thickness is greater than or equal to 14 mm and less than or equal to 16 mm and the furnace time is greater than 230 min, the billet finishing passes are controlled to be 7 passes, and descaling is performed in the first and third passes of rough rolling and the first and second passes of finishing rolling.

4. The high surface control method of thin-gauge Q345 grade engineering machinery structure steel according to claim 3 is characterized by: The dephosphorization pressure of the dephosphorization process is greater than or equal to 18 MPa.

5. The high surface control method of thin-gauge Q345 grade engineering machinery structure steel according to claim 3 is characterized by: When the billet thickness is greater than 7 mm and less than or equal to 16 mm, the final rolling temperature is controlled to be 800~820℃.

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