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CN-122013021-A - Method for improving low-temperature toughness of surface layer and core of 110 mm-thick EH47 steel plate

CN122013021ACN 122013021 ACN122013021 ACN 122013021ACN-122013021-A

Abstract

The invention belongs to the technical field of steel smelting, and relates to a method for improving the low-temperature toughness of a surface layer and a core of an EH47 steel plate with the thickness of 110 mm. The phase transformation temperature of Ar3 is improved to 735 ℃ or above by adjusting the chemical components of the steel plate, then the blank is rolled in an austenite single-phase region and an austenite plus ferrite two-phase region, the rolling temperature of the last two passes of the steel plate is controlled within the range of Ar3-10 to Ar3-20 ℃, the deformed ferrite, the equiaxial recrystallized ferrite and a small amount of refined pearlite clusters in the two-phase region are mainly used within 15mm of the surface layer of the finished steel plate, the impact energy of the surface layer and the core part of the steel plate at-50 ℃ is more than or equal to 180J, and the yield strength of the steel plate at 1/4 thickness is more than or equal to 470MPa.

Inventors

  • WANG HONGTAO
  • YAO JIANHUA
  • LUO DENG
  • LIU JIWEN
  • YANG JIANHUA
  • SHI SHUHUA
  • ZHANG QINGXUE
  • ZHOU GUANGJIE

Assignees

  • 湖南华菱湘潭钢铁有限公司

Dates

Publication Date
20260512
Application Date
20260206

Claims (5)

  1. 1. A method for improving the low-temperature toughness of the surface layer and the core part of an EH47 steel plate with the thickness of 110mm is characterized by comprising the following key process steps: heating the continuous casting billet with the section of 450 to 1180-1210 ℃ and keeping the total furnace time for 6-8 hours; A rolling step of rolling the blank to the thickness of the intermediate blank within 6 times of rough rolling by utilizing large reduction, wherein the rolling temperature of the first stage of finish rolling is 740-800 ℃, then the steel plate is heated in air for 50-60 s, the second stage of finish rolling is rolled for two times within the range of 715-725 ℃ of the surface temperature of the steel plate, and the final thickness of the steel plate is 110mm; And cooling the rolled steel plate to 330-400 ℃ in ultra-fast speed.
  2. 2. The method for improving the low-temperature toughness of the surface layer and the core of the 110mm thick EH47 steel plate according to claim 1, wherein the chemical components of the steel plate are C：0.04%～0.06%,Si≤0.3%,Mn：1.50%～1.70%,P≤0.009%,S≤0.0020%,Al：0.080%~0.12%,Cr: 0.02%-0.07%, Nb: 0.02%-0.04%,V: 0.010%-0.020%, Ti：0.011%～0.016%, Ni：0.5%～0.9%,Cu：0.15%～0.27%, weight percent of Fe or unavoidable impurities and trace elements, and the Ar3 transformation point temperature is 735 ℃ or above by adopting the formula Ar3 = 903-328C-102Mn +116 Nb-0.909V.
  3. 3. The method for improving the low-temperature toughness of the surface and the core of the 110mm thick EH47 steel sheet according to claim 2, wherein in the post-rolling cooling step, the cooling time is 80-90 s and the cooling rate is 3-6 ℃ per s.
  4. 4. A method for improving the surface and core low temperature toughness of a 110mm thick EH47 steel sheet according to claim 3, wherein the finished steel sheet is subjected to an austenite single phase region and an austenite+ferrite two phase region rolling, and the rolling temperature of the last two passes is in the range of Ar3-10 to Ar3-20 ℃.
  5. 5. The method for improving the low-temperature toughness of the surface layer and the core of the EH47 steel plate with the thickness of 110mm as claimed in claim 4, wherein the impact energy of the surface layer and the core of the steel plate at the temperature of 50 ℃ below zero is more than or equal to 180J, and the yield strength of the steel plate at the thickness of 1/4 is more than or equal to 470MPa.

Description

Method for improving low-temperature toughness of surface layer and core of 110 mm-thick EH47 steel plate Technical Field The invention belongs to the technical field of steel smelting, and relates to a method for improving the low-temperature toughness of a surface layer and a core of an EH47 steel plate with the thickness of 110 mm. Background With the rapid development of global maritime engineering construction, the trend of upsizing of dominant equipment such as geophysical prospecting ships, semi-submersible platforms, drilling ships, floating Production Storage and Offloading (FPSO) and the like is obvious, and the thickness specification of required steel plates is obviously increased. In order to ensure the safety of structures, the requirements on the performance of the steel plates are more and more severe. From "only the properties of 1/4 thickness of the steel sheet" to "ensure the properties of 1/2 thickness of the steel sheet" to the present "and simultaneously ensure the properties of the surface layer and 1/2 thickness of the steel sheet". The document CN117403132A discloses a 420 MPa-level TMCP-state super-thick plate steel plate with good core impact toughness and a manufacturing method thereof, microalloy elements Nb, ti, al and the like are added by adopting a low-carbon equivalent design, the low-temperature toughness of 1/4 and 1/2 of the maximum thickness of a steel plate with 100mm is improved through a controlled rolling +DQ/ACC process, and the impact energy of the core part of the steel plate at-40 ℃ is more than or equal to 207J. The document CN113174534a discloses a large-thickness TMCP state FO460 ship plate steel plate and a manufacturing method thereof, which uses a heating temperature of 1100-1150 ℃ and a low finishing temperature of 700-730 ℃ and takes a ferrite and bainite dual-phase structure as a matrix, so that the 1/4 and 1/2 positions of the maximum thickness 100mm steel plate still keep toughness fracture at-80 ℃. And document CN105018838A, CN115838902a, only the low temperature toughness of 1/2 or 1/4 thickness of the ultra-thick steel plate is considered, and the low temperature toughness of both the surface layer and the core of the TMCP ultra-thick plate is not considered. The data fed back by the above documents show that lowering the finishing temperature in the non-recrystallized region of austenite is effective in improving the low temperature toughness of 1/4 and 1/2 thickness of extremely thick TMCP steel sheet. This is mainly because the production of a super-thick steel plate using a continuous casting billet is limited by insufficient rolling compression ratio, deformation and infiltration in the thickness direction, and gradual decrease in accelerated cooling after rolling, and the microstructure of the core roughening is a relatively weak place of the super-thick plate. The increase of the distortion state of the austenite grains in the core has become common in the industry because of the reduction of the finishing temperature to obtain a large rolling deformation resistance. At present, the finishing temperature of the TMCP extra-thick plate is basically close to the phase transition temperature of the steel plate Ar 3. The literature 100mm of high-crack-arresting-toughness steel plate tissue and performance research shows that the high-crack-arresting-toughness steel plate with the thickness of 100mm is developed in China through a unique NEU-Rolling control Rolling process, the low-temperature impact absorption energy of 1/4 and the core position of minus 60 ℃ is more than or equal to 370J, but the impact absorption energy of the steel plate surface layer under the same condition is only 21J at the lowest. The reason for this is mainly that when the rolling of the TMCP extra-thick plate is finished, the rolling temperature of the surface layer of the steel plate is reduced to the Ar3 transformation point, a large amount of ferrite transformation occurs before water cooling, and part of ferrite grains which grow abnormally deteriorate the uniformity of a microstructure, and finally poor low-temperature toughness is caused. The data of the document 'development of the production process of the high-strength ultra-wide super-thick steel plate for the container ship' show that coupling relaxation time and relaxation temperature of plum and the like are utilized to develop an EH40 crack-stopping steel plate with the thickness of 85mm, and the appearance of full-thickness toughened ferrite grains shows that the low-temperature impact behavior of the steel plate can be improved by properly controlling the size and the distribution of ferrite grains transformed from a two-phase region. However, the implementation of the relaxation technology requires defining accurate phase transition temperature points and residence time at different positions of the steel plate, the operability is poor, the implementation difficulty is high, and as the thickness of the