Production method for improving yield ratio and bore expansion of 1000MPa-level high-strength steel

A production method and technology of high-strength steel, applied in furnaces, heat treatment equipment, heat treatment furnaces, etc., can solve problems such as difficulty in achieving complete austenitization of strip steel, difficulty in achieving yield strength, and low yield ratio

Active Publication Date: 2013-09-11
SHOUGANG CORPORATION
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

The introduction of martensite for phase strengthening has a significant effect on improving the tensile strength, so the dual-phase steel mainly composed of ferrite and martensite has been widely studied and applied, but this type of steel has an extremely low yield ratio, which is important to ensure In the case of a tensile strength of 1000MPa, it is difficult to achieve a yield strength of more than 800MPa. For some parts with small stamping deformation, it is difficult to achieve high stiffness in use
Although the yield strength can be significantly improved by flattening and pre-yielding after annealing, its basic structure has not been changed, and the material is prone to early cracking during the flanging or hole expansion process of free boundary condition processing
Although the above problems can be solved by using martensitic steel, the stable heating temperature of the extensive continuous annealing production line in China is generally less than 850°C, which makes it difficult to achieve complete austenitization of the strip steel, and the subsequent cooling without water quenching ensures the martensitic structure complete transformation

Method used

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  • Production method for improving yield ratio and bore expansion of 1000MPa-level high-strength steel
  • Production method for improving yield ratio and bore expansion of 1000MPa-level high-strength steel
  • Production method for improving yield ratio and bore expansion of 1000MPa-level high-strength steel

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Experimental program
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Effect test

Embodiment 1

[0057] The composition should meet: 0.15≤C≤0.25; 1.0≤Si≤2.0; 1.5≤Mn≤2.5; P≤0.015%; S≤0.015%; Alt≥0.015%; N≤0.005%; the balance is Fe and unavoidable impurities The steel is smelted through desulfurization, converter blowing, RH vacuum refining, continuous casting, hot rolling, coiling and other processes. Among them, the heating temperature of the continuous casting slab is 1300 ° C, the heat preservation is 3 hours, the final rolling temperature is 920 ° C, and the coiling temperature is 680 ° C. °C to obtain a hot-rolled sheet with a thickness of 4.5 mm. Then cold-rolled to obtain a cold-rolled sheet thickness of 2.0mm. Finally, the cold-rolled steel sheet was continuously annealed in a continuous annealing production line of radiation heating and jet cooling. See Table 2 for the relevant process parameters of annealing.

[0058] Table 2

[0059]

[0060]

[0061] see image 3 , The metallographic microstructure of the 1000MPa grade high-strength steel obtained in th...

Embodiment 2

[0063] The composition should meet: 0.15≤C≤0.25; 1.0≤Si≤2.0; 1.5≤Mn≤2.5; P≤0.015%; S≤0.015%; Alt≥0.015%; N≤0.005%; the balance is Fe and unavoidable impurities The steel is smelted through desulfurization, converter blowing, RH vacuum refining, continuous casting, hot rolling, coiling and other processes. Among them, the heating temperature of the continuous casting slab is 1300 ° C, the heat preservation is 3 hours, the final rolling temperature is 920 ° C, and the coiling temperature is 680 ° C. °C to obtain a hot-rolled sheet with a thickness of 4.5 mm. Then cold-rolled to obtain a cold-rolled sheet thickness of 2.0mm. Finally, the cold-rolled steel sheet was continuously annealed in a continuous annealing production line of radiant heating and jet cooling. See Table 3 for the relevant process parameters of annealing.

[0064] table 3

[0065]

[0066]

[0067] The metallographic microstructure of the 1000 MPa grade high-strength steel obtained in the embodiment of t...

Embodiment 3

[0069] The composition should meet: 0.15≤C≤0.25; 1.0≤Si≤2.0; 1.5≤Mn≤2.5; P≤0.015%; S≤0.015%; Alt≥0.015%; N≤0.005%; the balance is Fe and unavoidable impurities The steel is smelted through desulfurization, converter blowing, RH vacuum refining, continuous casting, hot rolling, coiling and other processes. Among them, the heating temperature of the continuous casting slab is 1300 ° C, the heat preservation is 3 hours, the final rolling temperature is 920 ° C, and the coiling temperature is 680 ° C. °C to obtain a hot-rolled sheet with a thickness of 4.5 mm. Then cold-rolled to obtain a cold-rolled sheet thickness of 2.0 mm. Finally, the cold-rolled steel sheet was continuously annealed in a continuous annealing production line of radiant heating and jet cooling. See Table 4 for relevant annealing process parameters.

[0070] Table 4

[0071]

[0072]

[0073] The metallographic microstructure of the 1000 MPa grade high-strength steel obtained in the embodiment of the pre...

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Abstract

The invention provides a method for improving a yield ratio and bore expansion of 1000MPa-level high-strength steel. The production method, which utilizes the existing 1000 MPa-level double-phase steel cold-rolled base material, comprises the following steps of: adopting a two-phase region heating mode and a three-stage cooling mode to obtain polygonal ferrite with the area fraction of 35-45%, lath upper bainite with the area fraction of 30-40% and martensite tissue with the area fraction of 10-25% in a metallographic figure; and using the lath upper bainite with the tissue type as a middle buffer phase of the ferrite and the martensite to buffer phase interface early-stage cracking caused by hardness difference of the ferrite and the martensite during a local flanging process. According to the production method for improving the yield ratio and bore expansion of the 1000MPa-level high-strength steel provided by the invention, the mechanical performances of the obtained 1000MPa-level high-strength steel are as follows: the tensile strength is bigger than 1000MPa, the yield ratio is 0.7-0.9, elongation at 80 scale distance is bigger than 10%, and the bore expansion rate is bigger than 50%.

Description

technical field [0001] The invention belongs to the technical field of iron and steel smelting and processing, in particular to a production method for improving the yield ratio and hole expandability of 1000MPa high-strength steel. Background technique [0002] To obtain 1000MPa cold-rolled continuous annealed ultra-high-strength steel with high yield strength, it is difficult to meet the strength requirements if only considering the mixed structure of ferrite and rigid pearlite, represented by low-alloy high-strength steel with Nb addition, the yield strength is greater than 500MPa, When the tensile strength level reaches above 600 MPa, the elongation rate deteriorates significantly. The introduction of martensite for phase strengthening has a significant effect on improving the tensile strength, so the dual-phase steel mainly composed of ferrite and martensite has been widely studied and applied, but this type of steel has an extremely low yield ratio, which is important ...

Claims

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Application Information

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IPC IPC(8): C21D9/573C21D1/26C21D11/00C22C38/06
Inventor 邝霜姜英花朱国森蒋光锐刘光明王海全刘广会尉冬刘华赛王彦超
Owner SHOUGANG CORPORATION
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