Search

CN-121972618-A - Method for carrying out on-line heating on surface layer and subcutaneous of large-section casting blank

CN121972618ACN 121972618 ACN121972618 ACN 121972618ACN-121972618-A

Abstract

The application belongs to the technical field of continuous casting, and particularly relates to a method for carrying out on-line heating on the surface layer and the skin of a large-section casting blank, which comprises the following steps: heating devices are arranged in front of straightening rollers, among the straightening rollers and among supporting rollers in front of the straightening rollers of the large-section casting blank continuous casting machine to heat the surface layer of the large-section casting blank and the area within 20mm below the skin, so that the temperature of the surface layer of the large-section casting blank and the area within 20mm below the skin is between the lower limit of the temperature range of the thermoplastic temperature range of the casting steel grade to 1250 ℃ before and during the straightening process of the straightening rollers, and the area shrinkage rate of the surface layer of the large-section casting blank and the area within 20mm below the skin is more than or equal to 0.4. According to the application, the temperature of the surface layer and the subcutaneous region of the casting blank within 20mm before and during the straightening process of the straightening roller is controlled, so that the surface layer and the subcutaneous plasticity of the large-section casting blank are improved, defects generated in the straightening process of the casting blank are obviously inhibited, and the surface quality and the yield of the casting blank are improved.

Inventors

  • LIU JIANHUA

Assignees

  • 北京科技大学

Dates

Publication Date
20260505
Application Date
20260128

Claims (10)

  1. 1. The method for carrying out on-line heating on the surface layer and the skin of the large-section casting blank is characterized by comprising the following steps: Heating devices are arranged in front of straightening rollers, among the straightening rollers and among supporting rollers in front of the straightening rollers of the large-section casting blank continuous casting machine, and the surface layer and the area within 20mm below the skin of the large-section casting blank are heated, so that the temperature of the surface layer and the area within 20mm below the skin of the large-section casting blank is between the lower limit of the temperature range of the thermoplastic temperature of the cast steel grade to 1250 ℃ before and during the straightening process of the straightening rollers, the area reduction of the surface layer and the area within 20mm below the skin of the large-section casting blank is more than or equal to 0.4, and the large-section casting blank is one of a plate blank with the thickness of more than or equal to 220mm, a round blank with the diameter of more than or equal to 600mm, a rectangular blank with the thickness of more than or equal to 250mm and a special blank with the thickness of more than or equal to 350 mm.
  2. 2. The method for heating the surface layer and the skin of the large-section casting blank on line is characterized by comprising the specific heating modes of installing lasers in front of straightening rollers, among the straightening rollers and among supporting rollers in front of the straightening rollers of a large-section casting blank continuous casting machine, irradiating the large-section casting blank, controlling laser spots to cover heating areas of the surface layer of the large-section casting blank, precisely heating the surface layer of the large-section casting blank, conducting heat conduction to the skin of the large-section casting blank, and improving the temperature of the area below the skin of the large-section casting blank by 20 mm.
  3. 3. The method for carrying out on-line heating on the surface layer and the subcutaneous layer of the large-section casting blank according to claim 2, wherein laser of a laser is perpendicular to the surface layer of the large-section casting blank or keeps a certain angle with the surface layer of the large-section casting blank, the laser outlet of the laser is 20mm-5m away from the surface layer of the large-section casting blank, the rated power of the laser is more than 5kW, laser spots generated by the laser are rectangular, long-strip, elliptic or near-elliptic spots parallel to the central shafts of a supporting roller and a straightening roller of the continuous casting machine or are round, elliptic or rectangular spots covered at corners of the casting blank, and the power density of the spots is 10-300W/cm 2 .
  4. 4. The method for carrying out on-line heating on the surface layer and the skin of a large-section casting blank according to claim 2 is characterized in that according to the temperature distribution of the surface layer of the large-section casting blank before a straightening roller during continuous casting, a laser irradiation spot heating area and heating power are set, the area of the large-section casting blank which is higher in straightening tensile stress strain and lower in temperature than a thermoplastic temperature area of cast steel is preferentially selected for heating, 1 set or more sets of lasers are arranged between a supporting roller before the straightening roller of a continuous casting machine, between the supporting roller and a straightening roller of a 1 st straightening frame or between part of straightening rollers, and the temperature of the surface layer of the heated casting blank area and the temperature of the area within 20mm below the skin are heated to a thermoplastic temperature area of cast steel before straightening through reasonable arrangement of the number and positions of the lasers, and the temperature of the area within 20mm below the skin is ensured to be always in the thermoplastic temperature area, and when the thickness of the casting blank or the diameter of a round blank is larger, or the straightening tensile stress and the stretching strain of the surface layer of the large-section casting blank are larger, the heating depth of the large-section casting blank needs to be larger.
  5. 5. The method for carrying out on-line heating on the surface layer and the subcutaneous layer of the large-section casting blank according to claim 2 is characterized in that the power density of the light spots is controlled by controlling the working current or the working power of a laser, the higher the working current or the power of the laser is, the higher the power density of the laser is, the faster the surface layer of the large-section casting blank heats up, the higher the pulling speed of the large-section casting blank is, and the larger the quantity of casting blanks of which the surface layer of the large-section casting blank needs to be heated up is, so that the required laser power density is higher.
  6. 6. The method for carrying out on-line heating on the surface layer and the skin of the large-section casting blank is characterized in that the energy density of a homogenized light spot is reasonably designed through the internal light path of a laser, so that the uniform heating and the flat heating of a light spot coverage area are realized, the heating rate of the casting blank in the heating area is less than or equal to 80 ℃ per second, and the specific mode of the homogenized light spot is that the laser is collimated and shaped through the reasonable design of the internal light path of the laser by using a laser collimating shaper, so that the light spot with the uniformly distributed energy density is generated, the energy transition area of 10% -85% of the edge of the light spot is less than or equal to 1.0mm, and the length of the light spot area from the edge of the light spot to the energy density of less than 85% of the center of the light spot is controlled to be less than or equal to 1.0mm, so that the uniform heating and the flat heating of the light spot coverage area are realized.
  7. 7. The method for carrying out on-line heating on the surface layer and the skin of the large-section casting blank according to claim 2 is characterized in that the heating depth of the large-section casting blank skin is the heating depth of laser light to the large-section casting blank skin through the large-section casting blank surface layer, the casting blank is heated for a plurality of times in stages by increasing the size of a laser spot along the drawing speed direction of the casting blank or arranging a plurality of lasers before straightening, the conduction of laser energy to the inside of the casting blank is promoted on the basis of guaranteeing the flat heating of the surface layer casting blank, the larger the continuous casting drawing speed is, the larger the straightening stress strain born by the casting blank is, the length of the laser spot along the drawing speed direction is required to be increased, so as to increase the heating depth of the casting blank skin, the heating depth of the casting blank skin can be calculated through a numerical simulation or/and experimental detection method, and the relation between the laser heating power density, the length of the laser spot along the drawing speed direction and the steel type continuous casting speed and the surface layer temperature is obtained through a numerical regression method, and the on-line adjustment of the laser spot size and the power density is realized by applying the relation.
  8. 8. The method for carrying out on-line heating on the surface layer and the subcutaneous layer of the large-section casting blank according to claim 2 is characterized in that a laser is adopted to generate laser with the wavelength in the range of 780nm-11000nm to heat the surface layer of the casting blank which is being produced and operated, and the casting blank continuously moves along the direction of drawing the blank in the continuous casting production, so that continuous and stable scanning of a casting blank light spot in a casting blank heating area is realized, and the heating of the casting blank heating area is realized.
  9. 9. The method for on-line heating of the surface layer and the skin of the large-section casting blank according to claim 2, wherein the laser position, the laser irradiation angle and the irradiation laser spot size are reasonably set, and the direct irradiation of laser to a supporting roller and a straightening roller of a continuous casting machine is avoided.
  10. 10. The method for on-line heating of the surface and the subcutaneous of a large-section casting blank according to claim 2, wherein a shielding cover is arranged around the laser to ensure that the laser is in a good temperature environment, and the temperature is less than 80 ℃.

Description

Method for carrying out on-line heating on surface layer and subcutaneous of large-section casting blank Technical Field The application relates to the technical field of continuous casting, in particular to a method for carrying out on-line heating on the surface layer and the skin of a large-section casting blank. Background With the development of continuous casting of thick slabs, large square billets, large round billets, large special-shaped billets and thick rectangular billets, the cross section size of the continuous casting billets is larger and larger, but the continuous casting drawing speed of the large-section billets is lower, the heat dissipation of the billets in continuous casting production is more serious, the surface temperature of part of the billets is lower when the billets enter a continuous casting straightening section, and in addition, the straightening stress of inner and outer arcs of the large-section continuous billets is larger, particularly the surface layer and the subcutaneous of the inner arc side are in higher tensile stress and tensile strain states, the defects of the surface layer and the subcutaneous of the billets are easily caused to be expanded into serious defects, or new surface layer and subcutaneous defects are generated, and serious quality problems of the billets are caused. The plasticity of the steel material has obvious high-temperature brittleness area, thermoplastic area and low-temperature brittleness area at high temperature. When the temperature of the steel is higher than about 1300 ℃, the steel is easy to crack when being stressed by a large deformation stress, the temperature interval is called a high-temperature brittle zone of the corresponding steel, when the temperature of the steel is lower than 800-900 ℃ and higher than 600-700 ℃, the plasticity of the steel is also very low, when being stressed by a large deformation stress, the steel is easy to crack, the temperature interval is called a low-temperature brittle zone of the corresponding steel, the plasticity of the steel is higher between the temperature of the low-temperature brittle zone and the temperature of the high-temperature brittle zone, and when the steel is stressed by a large deformation stress, the temperature interval is called a thermoplastic zone of the corresponding steel. In continuous casting production, in order to control the defects of the surface layer of a casting blank, the temperature of the casting blank in a straightening area is often required to be controlled in a thermoplastic area for casting steel, which is particularly important for continuous casting production of large-specification casting blanks, because the straightening stress strain of the surface layer and the subcutaneous area of the large-section casting blank is larger when the large-specification casting blanks are straightened. However, in actual production, because of the production of large-size casting blanks, the pulling speed is slower, when the casting blanks enter the straightening section of a continuous casting machine, the surface and subcutaneous temperatures of the casting blanks are always lower than the temperature of a thermoplastic region, the surface and subcutaneous plasticity of the casting blanks are lower, and huge straightening stress strain cannot be born. At present, the temperature of the surface layer of a casting blank before entering a straightening section is usually increased by technologies such as secondary cooling water optimization, semi-dry secondary cooling, high-speed continuous casting and the like in production, but the methods have limited effects in continuous casting production of large-size continuous casting blanks, and the problems of serious bulging of the casting blank, increased surface layer cracks and the like often occur. The device comprises a flame heater, an air supply device and a temperature measuring device, wherein the flame heater is composed of 4-8 flame ejectors which are respectively arranged at the corners of a casting blank, each flame ejector is independently adjustable and controllable, the air supply device is connected with the flame heater to provide heated fuel for the flame heater, and the temperature measuring device is arranged behind the flame heater, namely, behind the casting blank in the direction of drawing the casting blank. The method includes the steps of heating the corner of the casting blank through flame, adjusting the power of a flame heater according to the temperature measurement result of a temperature measuring device on the corner of the casting blank in the heating process, and increasing the flame heating power if the temperature of the corner is lower than T0, wherein T0 is the high temperature value of a third embrittlement zone of the material. However, the technology has a plurality of defects that 1) the energy of the flame is uneven, the heating area cannot be heated evenly and smoothly, the tem