CN104962829A - Twin-roll continuous cast low-carbon microalloyed steel containing acicular ferrite and manufacturing method of low-carbon microalloyed steel - Google Patents

Abstract

The invention belongs to the field of low-carbon microalloy steel production, and in particular relates to twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite and a production method thereof. The present invention smelts molten steel according to a certain composition. The molten steel flows through the tundish into a cavity formed by two counter-rotating crystallization rollers and side sealing plates of a twin-roll continuous casting machine to form a molten pool. The superheated degree of molten steel on the upper surface of the molten pool is 10~50℃, through the gap between the two crystallization rollers, it is solidified and exported to form a 1~6mm thick low-carbon micro-alloy steel thin strip, and then cooled to 500~700℃ at a cooling rate of 5~30℃/s , and finally coiled by a coiler to obtain a low-carbon micro-alloy steel coil with a width of 100-2000mm, and the volume fraction of acicular ferrite in the low-carbon micro-alloy steel coil is 3-15%. The invention saves the thick slab continuous casting, rough rolling, hot continuous rolling and other processes in the traditional production process of low-carbon microalloy steel, significantly reduces production cost, energy consumption and pollutant discharge, and is a short-process manufacturing technology.

Description

A kind of twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite and its manufacturing method

technical field

The invention belongs to the field of low-carbon microalloy steel production, and in particular relates to twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite and a production method thereof.

Background technique

The low-carbon microalloyed steel mainly composed of acicular ferrite has excellent comprehensive mechanical properties. It is widely used in pipeline steel and large heat input welding steel. Compared with the traditional pipeline steel with ferrite-pearlite structure, the pipeline steel with acicular ferrite structure not only satisfies high strength and toughness, but also has good low-temperature toughness and low ductile-brittle transition temperature, thus greatly It improves the service life of pipeline steel and becomes a major development trend of modern high-performance pipeline steel. In terms of large input energy welding, when there is a large amount of acicular ferrite structure, the weld metal has high strength and good low-temperature impact toughness, and can effectively prevent crack propagation at the same time. Therefore, the acicular ferrite structure is favored by steels for high heat input welding. The reasons for the good strength and toughness of acicular ferrite steel are as follows: 1. The acicular ferrite laths are interlocked and closely arranged, the lath spacing is small, and there are high-density movable dislocations in the laths, which are easy to To achieve multi-slip, there are fine carbides in the lath, which can improve the strength and toughness of the material; 2. During the formation of acicular ferrite, a fine and diffuse M-A island structure will be formed, which can pin the grain boundary. Moreover, the retained austenite in the M-A island structure is a favorable toughness phase, which can reduce the stress at the crack tip and consume part of the expansion work, thereby improving the strength and toughness of the material.

The acicular ferrite structure refers to the mixed structure of acicular ferrite mainly acicular ferrite, a small amount of polygonal ferrite and trace bainite. Acicular ferrite has a body-centered cubic structure, which is a thermodynamically non-equilibrium structure. Its transformation temperature is slightly higher than the bainite transformation temperature range, and it is a non-equiaxed ferrite transformed by a mixture of shear and diffusion. . Its biggest feature is that there is no obvious original austenite grain boundary network, thus avoiding the brittleness caused by the precipitation or inclusion segregation in the large-angle grain boundary.

Acicular ferrite belongs to heterogeneous nucleation, which is nucleated on the fine, irregularly arranged non-metallic inclusions in the austenite grain, and grows in the shape of diffraction, and its shape is intersecting. Non-metallic inclusions can induce the nucleation of acicular ferrite, and without the presence of inclusions, acicular ferrite will not form. But not all fine and diffuse inclusions have the effect of inducing the nucleation of intragranular acicular ferrite. It has been proved that inclusions such as MnS, Ti ₂ O ₃ , TiO, TiN, and CuS can promote the nucleation of acicular ferrite. Among them, the nucleation of acicular ferrite on TiO and Ti ₂ O ₃ oxides has been confirmed to be the most effective acicular ferrite nucleating agent. According to the current experimental analysis, the mechanism of Ti ₂ O ₃ to promote the nucleation of IGF is mainly the Mn-poor region mechanism and the strain-induced mechanism. Since Ti ₂ O ₃ is rich in cation vacancies, the Mn element in the nearby matrix is absorbed into or around Ti ₂ O ₃ through the diffusion of cation vacancies, which is equivalent to consuming a part of the Mn element in the austenite matrix to make The stability of austenite decreases, and it is easy to decompose and transform to ferrite under certain conditions.

Twin-roll continuous casting technology is a green and environmentally friendly new process technology with short process, low energy consumption, low investment and low cost. As the cutting-edge technology of thin strip steel production in the world today, twin-roll continuous casting technology can omit production processes such as thick slab continuous casting, heating and hot rolling, and directly produce thin strips with a thickness of 1-6mm from liquid steel. However, the initial structure of the thin strip produced by twin-roll continuous casting is relatively coarse, and its strength and toughness are poor. In addition, due to the thin initial gauge and insufficient subsequent processing deformation, it is difficult to greatly refine the grains, and the mechanical properties of the steel are not satisfactory. Therefore, how to refine the initial structure of the thin strip has become a key problem to be solved urgently in the production of strip steel by twin-roll continuous casting.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite and its manufacturing method, with the purpose of solving the problem of complex traditional production process of low-carbon microalloy steel Problems such as excessive energy consumption, large environmental load, etc., and refining the initial solidification structure of twin-roll continuous casting low-carbon microalloy steel, effectively improving the strength and toughness of the strip.

The twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite according to the present invention has the following chemical composition in terms of mass percentage: C 0.02-0.08%, Si 0.1-0.5%, Mn 0.1-0.5%, S 0.002-0.01 %, P 0.01~0.15%, sol-Al (acid soluble aluminum) 0.002~0.03%, Cu <0.5%, Cr <1.0%, Ni <0.2%, O 0.002~0.01%, Ti 0.005~0.2%, balance It is Fe; the volume fraction of acicular ferrite in its metallographic structure is 3~15%.

Its manufacturing method is carried out according to the following steps:

(1) According to chemical composition: C 0.02~0.08%, Si 0.1~0.5%, Mn 0.1~0.5%, S 0.002~0.01%, P 0.01~0.15%, sol-Al 0.002~0.03%, Cu <0.5%, Cr <1.0%, Ni <0.2%, O 0.002~0.01%, Ti 0.005~0.2%, and the balance is Fe for smelting molten steel. The molten steel in the ladle flows into the two counter-rotating double-roll continuous casting machines through the tundish. A molten pool is formed in the cavity formed by the crystallization roller and the side sealing plate. The superheat of the molten steel on the upper surface of the molten pool is 10~50°C. The molten steel is solidified and exported through the gap between the two crystallization rollers, and the export speed is 20~80m /min, forming a thin strip of low carbon micro-alloyed steel with a thickness of 1~6mm;

(2) The low-carbon micro-alloy steel strip is cooled to 500-700 °C by the cooling system at a cooling rate of 5-30 °C/s, and finally coiled by a coiler to obtain a low-carbon micro-alloy steel coil with a width of 100-2000 mm , the volume fraction of acicular ferrite in low carbon microalloyed steel sheet coils is 3~15%.

Compared with prior art, feature and beneficial effect of the present invention are:

The invention saves the thick slab continuous casting, rough rolling, hot continuous rolling and other processes in the traditional production process of low-carbon microalloy steel, significantly reduces production cost, energy consumption and pollutant discharge, and is a short-process manufacturing technology.

In the invention, a large amount of Ti, Al, Si and Mn composite oxides are formed during the solidification process of molten steel, and these composite oxides can be used as nucleation cores of fine acicular ferrite during the cooling process. The low-carbon microalloy thin strip produced by this technology contains acicular ferrite structure with a volume fraction of 3%~15%, and the comprehensive mechanical properties of low-carbon microalloy steel sheet can be effectively improved by using acicular ferrite.

In the present invention, in order to prevent the formation of coarse columnar grain structure due to the occurrence of preferential growth, and to obtain a large amount of Ti, Al, Si, Mn composite oxides required for the nucleation of fine acicular ferrite, the upper surface of the molten pool The superheat of molten steel should be controlled at 10~50℃; in order to provide the supercooling conditions required for the nucleation of acicular ferrite with Ti, Al, Si and Mn composite oxides as the core, the cooling after the thin strip is taken out of the crystallization roll The rate should be controlled at 5~30°C/s; in order to provide the temperature conditions required for the growth of acicular ferrite, the coiling temperature should be controlled at 500~700°C.

Description of drawings

Fig. 1 is the concrete process schematic diagram of the present invention;

Among them: 1: ladle; 2: tundish; 3: twin-roll continuous casting machine crystal roll; 4: melting pool; 5: low-carbon microalloy steel strip; 6: cooling system; 7: coiler; 8: low Carbon Microalloyed Steel Sheet Coil.

Fig. 2 is the metallographic structure diagram of the low-carbon microalloyed steel that the embodiment of the present invention 1 obtains;

Fig. 3 is the metallographic structure diagram of the low-carbon microalloyed steel that the embodiment of the present invention 2 obtains;

Fig. 4 is the metallographic structure diagram of the low-carbon microalloyed steel that the embodiment of the present invention 3 obtains;

Among them: the dotted circle is the acicular ferrite structure;

FIG. 5 is a metallographic structure diagram of the low-carbon microalloyed steel obtained in Comparative Example 1.

Detailed ways

Process of the present invention is as shown in Figure 1.

Firstly, the molten steel is smelted. The molten steel in the ladle 1 flows through the tundish 2 into the cavity composed of two counter-rotating twin-roll continuous casting machine crystallization rolls 3 and side sealing plates to form a molten pool 4. The molten steel on the upper surface of the molten pool 4 The superheat degree is 10~50℃, the molten steel is solidified and exported through the gap between two crystallization rollers 3, and the export speed is 20~80m/min, forming a thin strip 5 of low carbon microalloy steel with a thickness of 1~6mm. The strip 5 is cooled to 500-700°C by the cooling system 6 at a cooling rate of 5-30°C/s, and finally coiled by the coiler 7 to obtain a low-carbon microalloy steel coil 8 with a width of 100-2000mm.

The volume fraction of acicular ferrite in the low-carbon microalloyed steel obtained in the embodiment of the present invention is calculated according to the area of acicular ferrite in the metallographic structure diagram.

Example 1

The chemical composition of the low-carbon microalloyed steel in the examples is shown in Table 1.

(1) The molten steel is smelted according to the composition in Table 1. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rolls 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4 , the degree of superheat of the molten steel on the upper surface of the molten pool 4 is 10°C, and the molten steel is solidified through the gap between two crystallization rollers 3 and exported at a speed of 20/min to form a 1mm thick low-carbon micro-alloyed steel strip 5 ;

(2) The low-carbon micro-alloy steel strip 5 is cooled to 500 °C by the cooling system 6 at a cooling rate of 5 °C/s, and finally coiled by the coiler 7 to obtain a low-carbon micro-alloy steel coil 8 with a width of 100 mm. The volume fraction of acicular ferrite in the carbon microalloy steel sheet coil is 5%, and its metallographic structure is shown in Figure 2.

Example 2

The chemical composition of the low-carbon microalloyed steel in the examples is shown in Table 2.

(1) The molten steel is smelted according to the composition in Table 2. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rolls 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4 , the degree of superheat of the molten steel on the upper surface of the molten pool 4 is 20°C, and the molten steel is solidified through the gap between the two crystallization rollers 3 and exported at a speed of 45m/min to form a 3mm thick low-carbon micro-alloyed steel strip 5 ;

(2) The low-carbon micro-alloy steel strip 5 is cooled to 600 °C by the cooling system 6 at a cooling rate of 20 °C/s, and finally coiled by the coiler 7 to obtain a low-carbon micro-alloy steel coil 8 with a width of 800 mm. The volume fraction of acicular ferrite in the carbon microalloy steel sheet coil is 15%, and its metallographic structure is shown in Figure 3.

Example 3

The chemical composition of the low-carbon microalloyed steel in the examples is shown in Table 3.

(1) The molten steel is smelted according to the composition in Table 3. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rollers 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4 , the degree of superheat of the molten steel on the upper surface of the molten pool 4 is 50°C, and the molten steel is solidified through the gap between the two crystallization rollers 3 and exported at a speed of 80 m/min to form a 6 mm thick low-carbon micro-alloyed steel strip 5 ;

(2) The low-carbon micro-alloy steel strip 5 is cooled to 700 °C by the cooling system 6 at a cooling rate of 30 °C/s, and finally coiled by the coiler 7 to obtain a low-carbon micro-alloy steel coil 8 with a width of 2000 mm. The volume fraction of acicular ferrite in the carbon microalloy steel sheet coil is 9%, and its metallographic structure is shown in Fig. 4.

Comparative example 1

The chemical composition of the low-carbon microalloyed steel in the comparative example is shown in Table 4.

The molten steel is smelted according to the composition in Table 4. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rollers 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4. 4. The degree of superheat of the molten steel on the upper surface is 65°C. The molten steel is solidified and exported through the gap between the two crystallization rollers 3 at a speed of 30m/min to form a thin low-carbon microalloy steel strip 5 with a thickness of 1mm. The thin strip 5 is cooled to 500°C at a cooling rate of 40°C/s by the cooling system 6, and finally coiled by the coiler 7 to obtain a 100mm-wide low-carbon microalloy steel coil 8, the metallographic structure of which is shown in Figure 5 , which does not contain ferrite.

Comparative example 2

The chemical composition of the low-carbon microalloyed steel in the comparative example is shown in Table 5.

The molten steel is smelted according to the composition in Table 5. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rollers 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4. 4. The degree of superheat of the molten steel on the upper surface is 20°C. The molten steel is solidified and exported through the gap between two crystallization rollers 3 at a speed of 55 m/min, forming a thin strip 5 of low-carbon micro-alloyed steel with a thickness of 3 mm. The thin strip 5 is cooled to 600°C at a cooling rate of 15°C/s by the cooling system 6, and finally coiled by the coiler 7 to obtain an 800mm-wide low-carbon microalloy steel coil 8, which does not contain ferrite.

Comparative example 3

The chemical composition of the low-carbon microalloyed steel in the comparative example is shown in Table 6.

The molten steel is smelted according to the composition in Table 6. The molten steel in the ladle 1 flows through the tundish 2 into the cavity formed by the two counter-rotating crystallization rollers 3 and the side sealing plates of the twin-roll continuous casting machine to form a molten pool 4. 4. The degree of superheat of the molten steel on the upper surface is 40°C. The molten steel is solidified through the gap between the two crystallization rollers 3 and exported at a speed of 80m/min to form a 5mm-thick low-carbon micro-alloyed steel strip 5. The thin strip 5 is cooled to 700°C at a cooling rate of 30°C/s by the cooling system 6, and finally coiled by the coiler 7 to obtain a 2000mm-wide low-carbon microalloy steel coil 8, which does not contain ferrite.

Claims (2)

1. A twin-roll continuous casting low-carbon microalloy steel containing acicular ferrite, characterized in that the chemical composition is: C 0.02~0.08%, Si 0.1~0.5%, Mn 0.1~0.5%, S 0.002~0.01%, P 0.01~0.15%, sol-Al 0.002~0.03%, Cu <0.5%, Cr <1.0%, Ni <0.2%, O 0.002~0.01%, Ti 0.005~0.2%, the balance is Fe ; The volume fraction of acicular ferrite in its metallographic structure is 3~15%. 2. the manufacture method of the twin-roll continuous casting low-carbon micro-alloyed steel containing acicular ferrite as claimed in claim 1, is characterized in that carrying out according to the following steps: (1) According to chemical composition: C 0.02~0.08%, Si 0.1~0.5%, Mn 0.1~0.5%, S 0.002~0.01%, P 0.01~0.15%, sol-Al 0.002~0.03%, Cu <0.5%, Cr <1.0%, Ni <0.2%, O 0.002~0.01%, Ti 0.005~0.2%, and the balance is Fe for smelting molten steel. The molten steel in the ladle flows into the two counter-rotating double-roll continuous casting machines through the tundish. A molten pool is formed in the cavity formed by the crystallization roller and the side sealing plate. The superheat of the molten steel on the upper surface of the molten pool is 10~50°C. The molten steel is solidified and exported through the gap between the two crystallization rollers, and the export speed is 20~80m /min, forming a thin strip of low carbon micro-alloyed steel with a thickness of 1~6mm; (2) The low-carbon micro-alloy steel strip is cooled to 500-700 °C by the cooling system at a cooling rate of 5-30 °C/s, and finally coiled by a coiler to obtain a low-carbon micro-alloy steel coil with a width of 100-2000 mm , the volume fraction of acicular ferrite in low carbon microalloyed steel sheet coils is 3~15%.