Method for controlling strip segregation, rolling layering and center crack of medium and high manganese steel

Abstract

The invention belongs to the technical field of medium-high manganese steel production, and particularly relates to a method for controlling strip segregation, rolling layering and center cracks of medium-high manganese steel, and in the continuous casting process of the medium-high manganese steel, casting blank segregation is reduced through precise low-superheat-degree continuous casting and a long-distance or multi-section secondary cooling electromagnetic stirring technology; high-temperature heating is adopted in the casting blank heating process before rolling, so that casting blank segregation is further reduced; during rolling, low-temperature multi-pass rough rolling is adopted, the center strength of an intermediate billet is enhanced, the rolling resilience force is reduced, and the phenomena of center cracks and rolling layering occurring in the rolling process are restrained. Through the cooperation of the continuous casting process, the heating process and the rolling process, the phenomena of strip segregation, rolling layering and center cracks in the medium-high manganese steel rolled material are well controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of medium-high manganese steel production, and specifically provides a method for controlling band segregation, rolling delamination, and center cracks in medium-high manganese steel. Background Art

[0002] Medium-high manganese steel is often used as wear-resistant steel, automotive steel, steel for low-temperature containers, non-magnetic steel, etc., and has a wide range of applications. However, in the production process, the production of medium-high manganese steel is difficult. For example, the control of its segregation, especially band segregation control, as well as the delamination in rolled products and the center crack problems during rolling seriously affect the quality, yield rate, and smooth production of medium-high manganese steel.

[0003] Although a certain degree of segregation control can be achieved through continuous casting superheat control, secondary cooling electromagnetic stirring, etc. during production, due to the high manganese content in medium-high manganese steel, the existing calculation errors of liquidus and solidus temperatures are relatively large, and the control of casting superheat during continuous casting production is not precise; at the same time, the current continuous casting machines are not designed specifically for continuous casting of medium-high manganese steel. Some continuous casting machines do not have electromagnetic stirring in the secondary cooling section, or have electromagnetic stirring but the length of the electromagnetic stirring is short. In the continuous casting production of medium-high manganese steel, the length of the liquid core is large and the columnar crystals of the billet are well-developed. Without secondary cooling electromagnetic stirring or with short electromagnetic stirring, the control of billet segregation is very limited.

[0004] At the same time, due to reasons such as severe segregation and low solidus temperature in medium-high manganese steel, it is also difficult to improve the segregation of rolled products and control the center cracks during the rolling process by using traditional billet heating and rolling processes. It is necessary to adopt heating and rolling process technologies suitable for the composition and solidification characteristics of medium-high manganese steel to well solve the problems of band segregation, rolling delamination, and center cracks in medium-high manganese steel. Summary of the Invention

[0005] To solve the problems existing in this technology, the main purpose of the present invention is to propose a method for controlling band segregation, rolling delamination, and center cracks in medium-high manganese steel.

[0006] According to one aspect of the present invention, the present invention provides the following technical solution:

[0007] A method for controlling band segregation, rolling delamination, and center cracks in medium-high manganese steel, which reduces the billet segregation through precise low-superheat continuous casting and long-distance or multi-segment secondary cooling electromagnetic stirring processes during the continuous casting of medium-high manganese steel; further reduces the billet segregation by using high-temperature heating during the billet heating process before rolling; and adopts low-temperature multi-pass rough rolling during rolling to enhance the center strength of the intermediate billet, reduce the rolling springback force, and inhibit the center crack and rolling delamination phenomena that occur during the rolling process.

[0008] The beneficial effects of the present invention are as follows:

[0009] The present invention provides a method for controlling banded segregation, rolling delamination and central cracks in medium-high manganese steel. During the continuous casting process of medium-high manganese steel, the segregation of the billet is reduced by precise low superheat continuous casting and long-distance or multi-segment secondary cooling electromagnetic stirring processes; during the heating process of the billet before rolling, high-temperature heating is used to further reduce the segregation of the billet; during rolling, low-temperature multi-pass rough rolling is adopted to enhance the central strength of the intermediate billet, reduce the rolling springback force, and suppress the central cracks and rolling delamination phenomena that occur during the rolling process. Through the coordination of the above continuous casting process, heating and rolling processes, good control of banded segregation, rolling delamination and central cracks in medium-high manganese steel rolled products is achieved. Detailed implementation manners

[0010] The technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0011] To solve the technical problems in the prior art, the present invention provides a method for controlling banded segregation, rolling delamination and central cracks in medium-high manganese steel.

[0012] According to one aspect of the present invention, the following technical solutions are provided:

[0013] A method for controlling banded segregation, rolling delamination and central cracks in medium-high manganese steel. During the continuous casting process of medium-high manganese steel, the segregation of the billet is reduced by precise low superheat continuous casting and long-distance or multi-segment secondary cooling electromagnetic stirring processes; during the heating process of the billet before rolling, high-temperature heating is used to further reduce the segregation of the billet; during rolling, low-temperature multi-pass rough rolling is adopted to enhance the central strength of the intermediate billet, reduce the rolling springback force, and suppress the central cracks and rolling delamination phenomena that occur during the rolling process.

[0014] Preferably, the manganese content of the medium-high manganese steel is 8-30 wt%. Specifically, the manganese content of the medium-high manganese steel can be, for example, any one of 8 wt%, 9 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt% or the range between any two of them.

[0015] Preferably, the precise low superheat continuous casting is specifically: during the continuous casting process, the molten steel temperature in the tundish is controlled to be T L +(10-20) °C, where T L is the liquidus temperature of the medium-high manganese steel, in °C.

[0016] Preferably, the liquidus temperature T of the medium-high manganese steel LPrecisely measured by thermal analysis methods or calculated by the following methods:

[0017] (1) When the Si content of medium-high manganese steel < 0.23 wt%,

[0018] T L = 1537 - 55.3[%C] - 18.7[%Si] + (-3.76 - 0.86[%C])[%Mn];

[0019] (2) When the Si content of medium-high manganese steel ≥ 0.23 wt%,

[0020] T L = 1537 - 55.3[%C] - 16.9[%Si] - 7.92[%Si] 2 + 2.17[%Si] 3 + (-3.76 - 0.86[%C])[%

[0021] Mn];

[0022] Among them, [%C], [%Si], [%Mn] are the mass percentage contents of carbon, silicon, and manganese in medium-high manganese steel, respectively, wt%.

[0023] Preferably, the long-distance secondary cooling electromagnetic stirring is specifically: the length of the secondary cooling electromagnetic stirring device is 2.0 - 10.0 m. Specifically, the length of the secondary cooling electromagnetic stirring device can be any one or the range between any two of, for example, 2.0 m, 3.0 m, 4.0 m, 5.0 m, 6.0 m, 7.0 m, 8.0 m, 9.0 m, 10.0 m.

[0024] Preferably, the multi-segment secondary cooling electromagnetic stirring is specifically: 2 - 4 electromagnetic stirring devices with a length of 1.0 - 2.5 m are used and arranged in sequence from front to back in the secondary cooling section.

[0025] Preferably, the high-temperature heating during the heating process of the slab before rolling is specifically: the high-temperature heating temperature is 1180°C - T1, and the heating time is 1.0 - 2.5 h; among them, T1 is the solidus temperature of medium-high manganese steel - 40°C, and the solidus temperature of medium-high manganese steel is precisely measured by thermal analysis methods.

[0026] Preferably, the low-temperature multi-pass rough rolling is specifically: the rolling temperature is 850°C - T2, where T2 is the solidus temperature of medium-high manganese steel - 100°C, and the solidus temperature of medium-high manganese steel is precisely measured by thermal analysis methods; the rough rolling is carried out with 5 - 9 passes, and the reduction rate per pass ≤ 16%.

[0027] Preferably, the head of the medium-high manganese steel ingot is pre-rolled with a small reduction rate during each rough rolling, that is, the head of the ingot is first rolled at 20 to 50 mm with a small reduction rate (a reduction rate of 3 to 10%), and then the ingot is withdrawn, and then the ingot is rolled in this pass with a preset reduction rate; the operation realizes more passes of small reduction rate rolling on the head of the ingot.

[0028] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0029] Example 1

[0030] A domestic steel plant produces Mn13 steel, the steel composition (mass percentage) is: 0.95% C, 0.44% Si, 12.67% Mn, 0.001% S, 0.01% P, 0.02% Al, the balance is iron and inevitable impurities. The continuous casting production casting temperature is controlled at 1450℃, without secondary cooling electromagnetic stirring; the rolling heating temperature is 1250℃, the high temperature is maintained for 2h, and the rough rolling temperature is controlled at 1050~1100℃; a large number of central cracks appear during the rolling process, and the yield rate is 10%.

[0031] By adopting the method of controlling the banded segregation, rolling delamination and center crack of medium-high manganese steel of the present invention, the liquidus temperature is calculated to be 1417°C, so the temperature of the tundish steel liquid is 1430-1435°C during continuous casting; at the same time, a 5.0m long second cooling electromagnetic stirring device is added in the continuous casting second cooling zone for stirring; the solidus temperature of medium-high manganese steel is measured to be 1252°C by thermal analysis, so the heating temperature of the billet before rolling is 1210°C, and the heating is 2h; the rough rolling temperature is 950-1000°C, the rough rolling is 7 passes, and the cumulative reduction rate is 70%. No center cracks appear during the rolling process, no delamination is found in the plate, and the banded structure rating is 1.0.

[0032] Example 2

[0033] A domestic steel plant produces low-temperature high-manganese steel for liquefied natural gas storage and transportation tanks. The steel composition (mass percentage) is: 0.36% C, 0.22% Si, 26.0% Mn, 3.35% Cr, 0.40% Cu, 0.03% Al, and the balance is iron and inevitable impurities. The continuous casting production casting temperature is controlled at 1450℃, and secondary cooling electromagnetic stirring is used, but the secondary cooling electromagnetic stirring working distance is only 1.5m; the rolling heating temperature is 1200℃, the high temperature is maintained for 2h, and the rough rolling temperature is controlled at 1100-1150℃; a large number of central cracks appear during the rolling process, the yield rate is 50%, and the finished product banded structure rating is 2.5.

[0034] Using the method for controlling banded segregation, rolling delamination and center crack of medium-high manganese steel according to the present invention, the solid-liquid phase transition temperatures of this steel grade were measured by thermal analysis. The measured solidus temperature was 1342 °C and the liquidus temperature was 1400 °C. Therefore, the tundish pouring temperature during continuous casting was controlled at 1410 - 1420 °C; an electromagnetic stirrer was added after the original electromagnetic stirrer in the secondary cooling section of the continuous caster, and the total working length of the two electromagnetic stirrers became 3.0 m; the heating temperature of the billet before rolling was 1250 °C and it was held at a high temperature for 2 h; the rough rolling temperature was 1000 - 1050 °C, with 9 rough rolling passes and an accumulated reduction ratio of 80%. No center crack occurred during the rolling process, no rolling delamination was found in the rolled material, and the rating of the finished product's banded structure was 1.5 grade.

[0035] In the continuous casting process of medium-high manganese steel, the present invention reduces the billet segregation through precise low superheat continuous casting and long-distance or multi-segment secondary cooling electromagnetic stirring processes; during the heating process of the billet before rolling, high-temperature heating is adopted to further reduce the billet segregation; during rolling, low-temperature multi-pass rough rolling is adopted to enhance the center strength of the intermediate billet, reduce the rolling springback force, and inhibit the occurrence of center crack and rolling delamination during the rolling process.

[0036] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made using the content of the present invention's specification under the inventive concept of the present invention, or any direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for controlling banded segregation, rolling delamination and center cracking of medium and high manganese steel, characterized in that: During the continuous casting process of medium and high manganese steel, low superheat continuous casting and long-distance or multi-stage secondary cooling electromagnetic stirring process are used to reduce the segregation of the ingot; high-temperature heating is used during the heating process of the ingot before rolling to further reduce the segregation of the ingot; low-temperature multi-pass rough rolling is used during rolling to enhance the center strength of the intermediate ingot, reduce the rolling rebound force, and inhibit the center crack and rolling delamination phenomenon that occur during the rolling process.

2. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: The manganese content of medium-high manganese steel is 8-30wt%.

3. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: The specific low superheat continuous casting process is: the temperature of the molten steel in the tundish is controlled to be T L +(10~20)℃, where T L is the liquidus temperature of medium and high manganese steel, ℃.

4. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 3, characterized in that: Liquidus temperature T of medium and high manganese steel L Measured by thermal analysis method.

5. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 3, characterized in that: It is calculated by: (1) When the Si content of medium-high manganese steel is less than 0.23wt%, T L =1537-55.3[%C]-18.7[%Si]+(-3.76-0.86[%C])[%Mn]; (2) When the Si content of medium-high manganese steel is ≥0.23wt%, T L =1537-55.3[%C]-16.9[%Si]-7.92[%Si] 2 +2.17[%Si] 3 +(-3.76-0.86[%C])[% Mn]; Wherein, [%C], [%Si], and [%Mn] are the mass percentages of carbon, silicon, and manganese in medium and high manganese steel, respectively, in wt%.

6. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: The long-distance secondary cooling electromagnetic stirring is specifically as follows: the length of the secondary cooling electromagnetic stirring device is 2.0 to 10.0 m.

7. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: The multi-stage secondary cooling electromagnetic stirring is specifically: 2 to 4 electromagnetic stirring devices with a length of 1.0 to 2.5 m are used and arranged in sequence from front to back in the secondary cooling section.

8. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: High temperature heating is used in the heating process of the ingot before rolling: the high temperature heating temperature is 1180°C ~ T1, and the heating time is 1.0 ~ 2.5h; wherein T1 is the solidus temperature of medium and high manganese steel -40°C.

9. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: The low-temperature multi-pass rough rolling is specifically as follows: the rolling temperature is 850°C ~ T2, wherein T2 is the solidus temperature of medium and high manganese steel -100°C; the rough rolling is carried out in 5 to 9 passes, and the reduction rate of each pass is ≤16%.

10. The method for controlling band segregation, rolling delamination and center crack of medium and high manganese steel according to claim 1, characterized in that: During each rough rolling of the medium and high manganese steel ingot, the head of the ingot is pre-rolled with a small reduction rate, that is, the head of the ingot is first rolled down by 20 to 50 mm with a small reduction rate, and then exited, and then the ingot is rolled in this pass with a preset reduction rate.