CN113957340A

CN113957340A - Control method for medium-carbon high-manganese vanadium-containing alloy structure round steel material structure

Info

Publication number: CN113957340A
Application number: CN202111197060.3A
Authority: CN
Inventors: 邓向阳; 李仕超; 谢有; 沈艳; 林俊
Original assignee: Zenith Steel Group Co Ltd; Changzhou Zenith Special Steel Co Ltd
Current assignee: Zhongtian Iron And Steel Group Huai'an New Materials Co ltd; Zenith Steel Group Co Ltd; Changzhou Zenith Special Steel Co Ltd
Priority date: 2021-10-14
Filing date: 2021-10-14
Publication date: 2022-01-21
Anticipated expiration: 2041-10-14
Also published as: CN113957340B; WO2023060877A1

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a control method of a medium-carbon high-manganese vanadium-containing alloy structure round steel material structure. In the continuous casting process, low superheat degree and slow pulling speed are adopted for pouring, a pulse magnetic oscillation solidification homogenization technology is adopted, meanwhile, large electromagnetic stirring current is adopted for stirring and crushing dendritic crystals, the nucleation cores of the dendritic crystals are increased, equiaxed crystal regions are enlarged, and columnar crystal regions are reduced, so that the segregation of a casting blank is reduced, wherein the electromagnetic stirring current of a crystallizer is 350A; terminal electromagnetic stirring current 450A. The rolling process adopts a high-temperature long-time diffusion heating process and a controlled rolling and cooling process. The produced medium-carbon high-manganese vanadium-containing alloy structural round steel material has uniform structure, and the area ratio of a heat affected zone (abnormal structure) after friction welding processing of a user is reduced to be within 5 percent, thereby reaching the international advanced level.

Description

Control method for medium-carbon high-manganese vanadium-containing alloy structure round steel material structure

Technical Field

The invention belongs to the technical field of metallurgy, particularly relates to a control method for the structure of medium-carbon high-manganese vanadium-containing alloy structural round steel materials, and particularly relates to a continuous casting and rolling process for reducing the structure of medium-carbon high-manganese vanadium-containing alloy structural round steel materials.

Background

The medium-carbon high-manganese vanadium-containing alloy structural steel is widely applied to the fields of engineering machinery, automobile part manufacturing and the like due to excellent processing and mechanical properties, but the steel has the characteristic of being very easy to have abnormal structures such as a belt shape, a center segregation belt and the like, and finally influences the service performance of the material.

After smelting and pouring, most of metal materials are processed by pressure to form the section. However, in the processed material, a structure in which pearlite and ferrite are distributed in a band shape along the deformation direction, that is, a band-shaped structure is easily obtained, and in general carbon steel and structural alloy steel, a band-shaped structure refers to a structure form in which ferrite bands and pearlite bands formed in the rolling direction are stacked on each other. The existence of the banded structure can make the mechanical property of the metal be anisotropic, greatly reduce the plasticity and the toughness of the steel, and the direction along the banded structure is obviously superior to the vertical direction. The pressure working is liable to crack from the boundary. For parts needing subsequent heat treatment, the belt-shaped structure is light, so that the thermal deformation is too large, the stress concentration is caused by the heavy part, even cracks are generated, and the service life of the material is seriously shortened.

The microsegregation of the alloy element is the main reason for forming the ferrite-pearlite band, and the microsegregation is caused by the selective crystallization of the alloy element in the process of solidifying molten steel, and in high manganese steel, the concentration of the manganese element between dendrites is higher and the concentration of the manganese element in dendrites is lower due to the selective crystallization of the element. Manganese is an austenite stabilizing element and can reduce the transformation temperature of Ar3, so the transformation temperature of Ar3 in a high manganese area (between dendrites) is lower than that of a low manganese area (within dendrites), ferrite preferentially nucleates in the dendrites along with the reduction of the temperature, the solubility of carbon elements in the ferrite is far lower than that in austenite, carbon is gathered between the dendrites, after rolling, a pearlite band is formed in an original intercrystalline area, and the ferrite band in the dendrites and the pearlite band formed between the dendrites are overlapped and staggered to form a band-shaped structure and generate a wider pearlite and even martensite abnormal segregation band in the core.

Therefore, how to reduce the problems of the banded structure and the abnormal core segregation zone of the medium-carbon high-manganese steel and improve the service performance of the material becomes a great difficulty in the industry.

Disclosure of Invention

The invention aims to provide a production process for reducing the micro segregation and the banded structure and the core segregation zone of medium-carbon high-manganese vanadium-containing alloy structural round steel, and effectively improve the comprehensive mechanical property of the material.

The purpose of the invention is mainly realized by the following technical scheme:

a control method for medium-carbon high-manganese vanadium-containing alloy structural round steel material tissue comprises the following steps of component optimization and adjustment, continuous casting production, heating by a heating furnace and rolling:

(1) when the contents of fine crystal elements such as vanadium, titanium, aluminum and the like and easily segregated elements such as Mn, P and S in steel are more, ferrite-pearlite strip-shaped structures are easy to appear in corresponding rolled and forged materials, and large pearlite and even martensite abnormal segregation zones appear in the core, so that on the premise that the material strength meets the standard requirement, the contents of Mn and V are reduced by 10%, the content of aluminum is reduced by 30%, meanwhile, P is adjusted from the original content of less than or equal to 0.015% to the content of P of less than or equal to 0.013%, the content of S is adjusted from the original content of less than or equal to 0.010% to the content of S of less than or equal to 0.005%, and the grain size of the material is reduced from the original 7-8 level to the 6-7 level.

The medium-carbon high-manganese vanadium-containing alloy structural round steel comprises the following elements in percentage by mass: 0.39-0.46% of C, 0.25-0.45% of Si, 0.90-1.1% of Mn, less than or equal to 0.013% of P, less than or equal to 0.005% of S, less than or equal to 0.20% of Ni, 0.10-0.25% of Cr, 0.014-0.025% of Al, 0.07-0.11% of V, less than or equal to 0.20% of Cu, less than or equal to 0.05% of Mo, and the balance of Fe and inevitable impurities.

(2) The superheat degree of molten steel is strictly controlled to be 15-30 ℃, and the phenomenon that a large temperature gradient occurs in the casting blank solidification process due to high-temperature pouring is prevented, so that serious dendritic crystal segregation is generated, and a segregation band structure occurs in the subsequent rolling extension process.

(3) The dendritic crystal segregation can be effectively controlled by reasonably inhibiting the development of columnar crystals, expanding the proportion of equiaxed crystal regions and reducing the secondary dendritic crystal spacing in the continuous casting process, and the related process measures are as follows: controlling the continuous casting drawing speed, adopting slow drawing speed for pouring, and setting the drawing speed to be 0.60-0.68 m/min (the target drawing speed is 0.65 m/min); controlling the secondary cooling water ratio, adopting weak cooling, controlling the water ratio to be 0.18L/Kg, and setting the secondary cooling water ratio as 35%: 40%: 25 percent.

(4) The continuous casting production process adopts some auxiliary technical means: the electromagnetic stirring intensity of a crystallizer is improved to the maximum extent (wherein, the electromagnetic stirring current of the crystallizer is 350 +/-5A, the frequency is 2 +/-0.2 Hz, the electromagnetic stirring current of the tail end is 450 +/-5A, the frequency is 6 +/-0.2 Hz) on the premise of ensuring that a white bright band (negative segregation) does not appear in the macrostructure of a casting blank), the dendritic crystal is stirred by utilizing the electromagnetic force, the nucleation core of the dendritic crystal is increased, the equiaxed crystal area is enlarged, and the voltage parameter of the solidification homogenization technology is set to be 100V by adopting a Pulse Magnetic Oscillation (PMO) solidification homogenization technology, so that heterogeneous nucleation is promoted, and the solidification structure is refined. The method can achieve the purpose of reducing the microsegregation of the material.

(5) The high-temperature long-time diffusion heating process is adopted, so that Mn, C, S, P and other easily segregated elements are diffused, the strip-shaped tissues are prevented from appearing in the rolling process, and the specific heating process parameters are as follows: heating the first section at 900-1050 ℃; heating the second stage at 1255-1280 ℃; the temperature of the soaking section is 1255-1280 ℃; the initial rolling temperature is 1160-1190 ℃; the tapping rhythm is 240-300S; the total heating time is 420-550 min; the time of the high-temperature section is more than or equal to 180min, and meanwhile, the air-fuel ratio in the heating furnace is controlled to be 0.40-0.75 in order to prevent the material from being decarburized and exceeding the standard caused by long-time heating at high temperature.

(6) The controlled rolling and controlled cooling process is adopted to realize low-temperature rolling, prevent rolling in a two-phase region and carry out forced cooling after rolling, thereby preventing pearlite and ferrite strips and core segregation strips from occurring, and the specific controlled rolling and controlled cooling process parameters are as follows: the temperature of the round steel entering KOCKS is 850 +/-15 ℃, the temperature of the steel throwing is 750 +/-15 ℃, and the control is mainly realized by opening No. 1 to No. 7 water tanks, adjusting the water quantity and adjusting the rolling speed.

The invention has the beneficial effects that: considering that medium-carbon high-manganese vanadium-containing alloy structural steel, a rolled material is easy to generate a pearlite segregation strip structure, and a large-area heat-affected zone (martensite strip) appears in a segregation strip area after friction welding by a user, so that the material becomes brittle and the service life of the material is influenced finally. The invention does the following work:

firstly, the chemical components (the content of Mn and V is reduced by 10 percent, the content of aluminum is reduced by 30 percent, meanwhile, the content of P is adjusted from the original content of less than or equal to 0.015 percent to the content of P of less than or equal to 0.013 percent, and the content of S is adjusted from the original content of less than or equal to 0.010 percent to the content of S of less than or equal to 0.005 percent) are optimally adjusted, so that the content of fine crystal elements such as V, Al and the like is reduced, and the phenomenon that the crystal grains are too fine and a strip-shaped tissue appears is prevented; on the other hand, the content of Mn element is properly reduced, and the content of harmful segregation-prone elements such as P, S and the like is reduced.

Secondly, the superheat degree of molten steel is reduced in the continuous casting production process; reducing the casting speed; electromagnetic stirring of a crystallizer and electromagnetic stirring of the tail end are adopted, and the electromagnetic stirring current parameters are optimally designed; the Pulse Magnetic Oscillation (PMO) solidification homogenization technology is adopted, and aims to crush dendritic crystals, improve the proportion of equiaxed crystals, refine a solidification structure and finally reduce casting blank segregation, thereby reducing the segregation of rolled materials and the level of a banded structure.

And thirdly, a high-temperature diffusion heating process is adopted in the rolling process, and the essence of the process is that segregation elements such as C, Mn, P, S and the like in a casting blank can be uniformly diffused through a long-time heat preservation process at high temperature, and a ferrite-pearlite banded structure and a core segregation zone can not be formed in the subsequent cooling and recrystallization processes.

And fourthly, rolling in a controlled rolling and controlled cooling process is adopted, rolling in a two-phase region is avoided, and cooling is performed after the rolling is strengthened through low-temperature rolling, so that the purpose of reducing the banded structure of the rolled material is achieved.

Through the efforts, the segregation of the material is effectively reduced, so that the core segregation bandwidth is effectively controlled, and the user service performance of the medium-carbon high-manganese vanadium-containing steel is improved.

Description of the drawings:

FIG. 1 is a photograph of a steel bar core segregation band structure before optimization (core pearlite segregation band width 676 μm);

FIG. 2 is a photograph showing the structure of the center segregation band of the round steel of example 1 (the center pearlite segregation band has a width of 82 μm);

FIG. 3 is a low-magnification photograph of round steel before optimization (with a black center with obvious carbon segregation in the center);

figure 4 is a low magnification photograph of the round steel of example 1 (no black core evident in the center).

Detailed Description

The present invention will be described in detail with reference to specific examples.

Example 1

The production of medium-carbon high-manganese vanadium-containing steel F40MnV (C0.41%, Si 0.31%, Mn 0.95%, P0.011%, S less than or equal to 0.003%, Ni 0.01%, Cr 0.15%, Al 0.018%, V0.08%, Cu 0.04%, Mo 0.005%) (specification phi 62mm) is taken as an example:

the production process flow comprises the following steps: 5-machine 5-flow arc continuous casting machine with 220mm by 260mm cross section, casting blank finishing, heating of a regenerative heating furnace, rolling of a continuous rolling unit, rolling of a KOCKS finishing rolling unit, cooling, off-line finishing, packaging and warehousing.

1. Continuous casting production:

pouring with low superheat degree, and controlling the superheat degree of molten steel to be 28 ℃; controlling the continuous casting drawing speed: 0.65 m/min; controlling the secondary cooling water ratio to be 0.18L/Kg, and setting the secondary cooling water ratio to be 35%: 40%: 25 percent; setting electromagnetic stirring parameters of a crystallizer: the current is 350A, and the frequency is 2 Hz; the electromagnetic stirring current at the tail end is 450A, and the frequency is 6 Hz; the voltage parameter of the solidification homogenization technology of Pulsed Magnetic Oscillation (PMO) is set to be 100V.

2. Heating a casting blank:

heating the finished continuous casting square billet with the cross section of 220 mm-260 mm in a regenerative heating furnace, wherein the temperature of the heating section I is 980 ℃; heating to 1271 ℃ in the second stage; the temperature of the soaking section is 1272 ℃; the tapping rhythm is 280S; the total heating time is 515 min; the high temperature period is 236min, and the air-fuel ratio in the heating furnace is controlled to be 0.51 in order to prevent the material decarburization from exceeding the standard caused by long-time heating at high temperature.

3. Controlled rolling

Descaling the steel billet before rolling, controlling the rolling temperature to be 1172 ℃ by utilizing high-pressure water with the pressure of 18MPa, and controlling the temperature of the round steel entering KOCKS to be 855 ℃ by opening a water tank, adjusting the water quantity and adjusting the rolling speed.

4. Controlled cooling

The casting temperature 752 ℃ of the round steel is controlled by opening the No. 6-7 water tank and adjusting the water quantity.

Example 2

Continuous casting production: controlling the superheat degree of the molten steel to be 26 ℃.

Heating a casting blank: the temperature of the first section is 975 ℃; heating to 1267 ℃ in the second stage; the temperature of a soaking section is 1263 ℃; the tapping rhythm 270S; the total heating time is 510 min; the high temperature period is 237 min.

Controlling rolling: the rolling temperature is 1169 ℃, and the KOCKS temperature of the round steel is 845 ℃.

And (3) controlling cooling: the throwing temperature of the round steel is 745 ℃.

Example 3

Continuous casting production: the superheat degree of the molten steel is controlled to be 27 ℃.

Heating a casting blank: heating the first section to 997 ℃; heating to 1262 deg.c in stage II; the temperature of the soaking section is 1258 ℃; tapping rhythm 268S; total heating time 507 min; the high temperature period is 223 min.

Controlling rolling: the initial rolling temperature is 1175 ℃, and the temperature of the round steel entering KOCKS is 849 ℃.

And (3) controlling cooling: the casting temperature of the round steel is 747 ℃.

Example 4

Continuous casting production: controlling the superheat degree of the molten steel to be 28 ℃.

Heating a casting blank: heating the first section at a temperature of 983 ℃; heating to 1269 deg.c in stage II; the temperature of a soaking section is 1261 ℃; tapping rhythm 283S; the total heating time is 542 min; the high temperature period is 243 min.

Controlling rolling: the rolling temperature is 1165 ℃ and the KOCKS temperature of the round steel is 837 ℃.

And (3) controlling cooling: the casting temperature of the round steel is 740 ℃.

Example 5

Continuous casting production: controlling the superheat degree of the molten steel to be 29 DEG C

Heating a casting blank: heating the first section at 1021 ℃; heating to 1266 deg.c in stage II; the temperature of a soaking section is 1265 ℃; the tapping rhythm 264S; the total heating time is 499 min; the high temperature period is 225 min.

Controlling rolling: the initial rolling temperature was 1181 ℃ and the round bar entry temperature was 844 ℃.

And (3) controlling cooling: the casting temperature of the round steel is 754 ℃.

The processes are adopted to prepare one batch of round steel, and the total number of the round steel is 5.

Comparative example 1

Comparative example 1 is different from example 1 in that: the pouring with low superheat degree is not realized, the superheat degree is 38 ℃, and other operations are carried out in the same way as the embodiment.

Comparative example 2

Comparative example 2 differs from example 1 in that: the casting at the low drawing speed is not realized, the drawing speed is controlled to be 1.0m/min, and other operations are the same as the embodiment.

Comparative example 3

Comparative example 3 differs from example 1 in that: the continuous casting pouring process does not adopt large electromagnetic force for stirring, adopts weaker electromagnetic stirring, and controls the electromagnetic stirring parameters of the crystallizer: the current is 250 +/-5A, and the frequency is 2 +/-0.2 Hz; the electromagnetic stirring current at the end is 200 +/-5A, the frequency is 6 +/-0.2 Hz, and the other operations are the same as the embodiment.

Comparative example 4

Comparative example 4 is different from example 1 in that: a high-temperature diffusion heating process is not adopted, and the temperature of the heating stage II is controlled to be 1196 ℃; the temperature of the soaking section is 1202 ℃; the total heating time is 400 min; the time of the high temperature period is more than or equal to 100min, and other operations are the same as the embodiment.

Comparative example 5

Comparative example 5 differs from the examples in that: the rolling and cooling control process is not adopted, the temperature of the round steel entering KOCKS is controlled to be 885 ℃, the temperature of the steel throwing is controlled to be 835 ℃, and other operations are carried out in the same way as the embodiment.

The conditions of the banded structures, the grain sizes and the macrostructures of examples 1 to 5 and comparative examples 1 to 5 of the present invention are compared as follows

Table 1:

table 1 shows the physical and chemical performance indexes of round steel and the comparison of the use conditions of users (if the user uses a friction welding process to process the material, if the width of the pearlite band at the center is large, a large-area heat affected zone, namely a large-area martensite abnormal structural zone, is easy to appear in the material after friction welding, so that the material becomes brittle, the plasticity and toughness become poor, and the service life of the material is finally influenced).

The results show that: by reasonable optimization design of components, parameters such as superheat degree, secondary cooling ratio water, drawing speed and the like are optimized in the continuous casting process, and large electromagnetic stirring current parameters are adopted; the rolling heating process adopts a high-temperature long-time heating process and a controlled rolling and controlled cooling process, so that the material structure detection index and the user final use performance of the medium-carbon high-manganese vanadium-containing alloy structural round steel reach the international advanced level.

The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified. The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all modifications of the above embodiments made according to the technical spirit of the present invention are included in the scope of the present invention.

Claims

1. A control method for medium-carbon high-manganese vanadium-containing alloy structural round steel material tissues is characterized by comprising the steps of continuous casting production, heating by a heating furnace and rolling, and the specific process steps are as follows:

(1) the superheat degree of molten steel is strictly controlled to be 15-30 ℃, so that the phenomenon that serious dendritic crystal segregation occurs due to large temperature gradient in the casting blank solidification process caused by high-temperature pouring and segregation band structure occurs in the subsequent rolling extension process is prevented;

(2) controlling the drawing speed to be 0.60-0.68 m/min in the continuous casting process; controlling the secondary cooling water ratio to be 0.18L/Kg, and setting the secondary cooling water ratio to be 35%: 40%: 25 percent;

(3) electromagnetic stirring of a crystallizer and electromagnetic stirring at the tail end are adopted, the electromagnetic stirring strength is enhanced, the electromagnetic stirring current is improved to the maximum extent on the premise that a white and bright band does not appear in the macrostructure of a casting blank, and heterogeneous nucleation is promoted by adopting a Pulsed Magnetic Oscillation (PMO) solidification homogenization technology;

(4) diffusing easy segregation elements such as C, S, P, Mn and the like by adopting a high-temperature long-time diffusion heating process, wherein the heating temperature of the first section is 900-1050 ℃, the heating temperature of the second section is 1255-1280 ℃, the temperature of the soaking section is 1255-1280 ℃, and the rolling temperature is 1160-1190 ℃; the steel tapping rhythm is 240-300S, the total heating time is 420-550 min, and the high-temperature period time is more than or equal to 180 min; simultaneously controlling the air-fuel ratio in the heating furnace to be 0.40-0.75;

(5) the controlled rolling and controlled cooling process realizes low-temperature rolling, and forced cooling is carried out after rolling, the temperature of the round steel entering the KOCKS is 850 +/-15 ℃, and the temperature of the steel throwing is 750 +/-15 ℃.

2. The method for controlling the structure of the medium-carbon high-manganese vanadium-containing alloy structural round steel material according to claim 1, characterized in that: and (3) the continuous casting drawing speed of the step (2) is 0.65 m/min.

3. The method for controlling the structure of the medium-carbon high-manganese vanadium-containing alloy structural round steel material according to claim 1, characterized in that: the electromagnetic stirring current of the crystallizer in the step (3) is 350 +/-5A, and the frequency is 2 +/-0.2 Hz; the electromagnetic stirring current at the tail end is 450 +/-5A, and the frequency is 6 +/-0.2 Hz.

4. The method for controlling the structure of the medium-carbon high-manganese vanadium-containing alloy structural round steel material according to claim 1, characterized in that: and (3) the pulse magnetic oscillation voltage is 100V.

5. The medium-carbon high-manganese vanadium-containing alloy structural round steel according to claim 1, which is characterized in that: the round steel material comprises the following elements in percentage by mass: 0.39-0.46% of C, 0.25-0.45% of Si, 0.90-1.1% of Mn, less than or equal to 0.013% of P, less than or equal to 0.005% of S, less than or equal to 0.20% of Ni, 0.10-0.25% of Cr, 0.014-0.025% of Al, 0.07-0.11% of V, less than or equal to 0.20% of Cu, less than or equal to 0.05% of Mo, and the balance of Fe and inevitable impurities.