CN-117625906-B - Preparation process of ultra-low carbon layered nano ferrite and bainite dual-phase steel

Abstract

The invention relates to the technical field of steel material preparation, in particular to a preparation process of ultra-low carbon layered nano ferrite and bainite dual-phase steel. The method comprises the steps of S1, carrying out room-temperature cold rolling on a hot-rolled ultra-low carbon steel sample, adjusting cold rolling parameters to enable original bainitic and ferrite tissues to be broken and elongated to obtain compact lamellar tissues, S2, rapidly heating the sample to the temperature close to that of a full austenitizing region AC 3 , preserving heat, and S3, rapidly cooling to room temperature to obtain a lamellar structure consisting of a non-recrystallization region and a recrystallization region, wherein the non-recrystallization region is deformed elongated ferrite in an original tissue, and the recrystallization region is nanoscale bainitic and ferrite. The invention adopts a simpler heat treatment process of cold rolling and annealing. The lamellar structure formed by recrystallized nano ferrite, bainite crystal grains and non-recrystallized ferrite coarse grains is obtained, and the lamellar structure has excellent properties of high strength and high plasticity.

Inventors

• LI JUN
• Cong Qianying
• LI MENGBO
• LI SHAOHONG
• BU HENGYONG

Assignees

• 昆明理工大学

Dates

Publication Date

20260505

Application Date

20231206

Claims (1)

1. 1. The preparation process of the ultra-low carbon layered nano ferrite and bainite dual-phase steel is characterized by comprising the following preparation steps: S1, cold rolling a hot-rolled ultra-low carbon steel sample at room temperature, adjusting cold rolling parameters to crush and elongate original bainitic and ferrite tissues to obtain a compact lamellar structure, wherein the rolling speed in S1 is 300-350mm/S, the rolling speed in multiple passes is one-way rolling, the rolling reduction in each pass is 0.05-0.2mm, and the total deformation is 70-90%; the hot rolled ultra low carbon steel sample adopted in S1 comprises, by weight, less than or equal to 0.1% of C, 0.2-0.6% of Si, 1.4-1.9% of Mn, less than or equal to 0.015% of P, less than or equal to 0.025% of S, less than or equal to 0.1% of Ti+V+Nb, 0.2-0.4% of Cr, 0.2-0.4% of Ni, 0.2-0.4% of Mo and 0.2-0.4% of Cu, and the balance of iron and other unavoidable impurity elements; S2, rapidly heating the sample to the temperature close to the temperature of the full austenitizing region AC 3 and preserving heat, wherein the temperature is rapidly raised to the temperature of the full austenitizing region AC 3 plus or minus 20 ℃ at the temperature rising rate of 50-300 ℃ per second in S2, and the preserving heat time is 40-120S; S3, rapidly cooling to room temperature to obtain a layered structure composed of a non-recrystallization region and a recrystallization region, wherein the non-recrystallization region is deformed and elongated ferrite in an original structure, the recrystallization region is nanoscale bainite and ferrite, and the temperature is rapidly reduced to the room temperature at a rate of 30-200 ℃ per second in S3.

Description

Preparation process of ultra-low carbon layered nano ferrite and bainite dual-phase steel Technical Field The invention relates to the technical field of steel material preparation, in particular to a preparation process of ultra-low carbon layered nano ferrite and bainite dual-phase steel. Background With the increasing progress of scientific technology, the petroleum pipeline is developed towards bearing high pressure and increasing the caliber of a pipeline, the comprehensive mechanical property of the pipe is required to be higher and higher, not only is the provision for yield strength and uniform elongation provided, but also the corresponding requirements for yield ratio and hardening index are provided. During long distance laying of petroleum pipelines, certain severe environments such as frozen earth zones, plate active zones, debris flows, seismic zones, etc. may be traversed. In order to prevent the pipeline from being broken when encountering large deformation and ensure the safe transportation of petroleum and natural gas, the steel needs to have the properties of high strength, high plasticity and low yield ratio. The ultralow-carbon steel with the carbon content less than or equal to 0.1 percent has excellent welding performance and reduces the sensitivity of cracks. In recent years, the environment is increasingly worse, and the performance requirements of the pipeline in the use process are difficult to be met by the existing steel materials. At present, for the improvement of the strength of ultra-low carbon steel, the most effective method is fine grain strengthening, and according to a Hall pecie formula, the grain size and the mechanical property are in inverse proportion. Through the large plastic deformation process, the internal crystal grains of the metal are elongated and broken, a large number of crystal defects are generated, the internal free energy is obviously improved, the recrystallization temperature is greatly reduced, and favorable conditions are created for the nanocrystalline. So that the nanocrystalline material has higher strength, but the inversion relation of strength and plasticity can not be broken through. The high-wave et al (Ultrastrong low-carbon nanosteel produced by heterostructure and interstitial mediated warm rolling.Sci.Adv.6,eaba8169,2020.) carries out simple industrial hot rolling at 300 ℃, the hot rolling thickness is reduced by 90 percent, and the massive super-strong low-carbon steel with the nano sheet structure with the average thickness of about 17.8nm is obtained, and has the high yield strength of the invasive record of 2.05GPa and the ultimate strength of 2.15 GPa. The method has the advantages of simple process, fully refining the structure and obtaining lamellar structure by a large deformation mode of warm rolling, and has the defect that the extensibility of the low-carbon steel is not considered. After large plastic cold deformation, the mechanical properties can be comprehensively improved through rapid annealing. Compared with the traditional annealing process, the rapid annealing can delay recrystallization and induce austenite to rapidly nucleate, and the grains are obviously refined in the subsequent austenite transformation process. Liu Shichun et al (Flash annealing enables 1GPa nanoprecipitate-strengthened"NANOHITEN"ferritic steels[J].Materials Science&Engineering,A.Structural Materials：Properties,Misrostructure and Processing,2022.) cold-rolled 84%, rapidly short-time annealed at the AC 1 point, the high-density stable nano-precipitates will act as effective barriers to prevent the growth of recrystallized ferrite and sub-temperature austenite on FA, so that ultra-low carbon steel builds a heterogeneous microstructure consisting of recrystallized ultra-fine ferrite grains and non-recrystallized ferrite, the mechanical properties reach a strength level of 1GPa, without significant loss of ductility. The method has good mechanical comprehensive performance, but the improvement of the overall performance is dependent on the difference between phases. However, it is also obvious that although the above method obtains higher yield and tensile strength, the indexes such as uniform elongation, yield ratio and the like cannot meet the requirement of large-caliber pipeline steel. Disclosure of Invention Aiming at the problems in the background technology, a preparation process of ultra-low carbon layered nano ferrite and bainite dual-phase steel is provided, and the preparation steps are as follows: S1, cold rolling a hot-rolled ultra-low carbon steel sample at room temperature, and adjusting cold rolling parameters to crush and elongate original bainitic and ferrite tissues to obtain a compact lamellar structure; s2, rapidly heating the sample to a temperature close to that of the AC 3 in the full austenitizing region, and preserving heat; s3, rapidly cooling to room temperature to obtain a layered structure composed of a non-recrystall