High strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and method for manufacturing the same

A technology of cold-rolled steel plate and manufacturing method, which is applied in the field of high-yield-ratio high-strength cold-rolled steel plate and its manufacturing field, can solve problems such as poor weldability and dents, and achieve excellent yield ratio and hole expandability, and small material deviation Effect

Active Publication Date: 2016-06-15
POHANG IRON & STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

However, the steel sheet produced by the technique of Patent Document 2 may have poor weldability due to excessive addition of carbon, and may cause dents in the furnace due to excessive addition of silicon.

Method used

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  • High strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and method for manufacturing the same
  • High strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and method for manufacturing the same
  • High strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and method for manufacturing the same

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Experimental program
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Embodiment

[0074] Vacuum melting was performed on the slab with the composition in Table 1 below, reheating was carried out at a heating temperature of 1200° C. for one hour in a heating furnace, and then hot rolling and coiling were carried out according to the conditions in Table 2 below. Next, the coiled hot-rolled steel sheet was pickled and cold-rolled at a reduction ratio of 45%, thereby obtaining a cold-rolled steel sheet, and then subjected to continuous annealing, primary cooling, and secondary cooling according to the conditions in Table 2 below. Thereafter, overaging treatment was performed for 300 seconds at the secondary cooling termination temperature. At this time, the primary cooling rate was constant at 2°C / sec, the primary cooling termination temperature was constant at 650°C, and the secondary cooling rate was constant at 15°C / sec.

[0075] Next, the phase fraction, size and hardness of the microstructure of each produced cold-rolled steel sheet were measured, and the ...

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Abstract

The invention discloses a high strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and a method for manufacturing the same. The cold rolled steel sheet includes, by weight, 0.035-0.07% of C, less than 0.3% and greater than 0% of Si, 2.0-3.5% of Mn, 0.3-1.2% of Cr, 0.03-0.08% of Ti, 0.01-0.05% of Nb, 0.01-0.10% of Sol.Al, 0.0010-0.0050% of B, and the balance Fe and unavoidable impurities. In microstructure, the cold rolled steel sheet includes 90 area% of martensite, wherein the average grain diameter of the martensite is less than 3 [mu]m; the martensite includes tempered martensite and lath martensite; the average grain diameter of the lath martensite is less than 1 [mu]m; the area fraction of the lath martensite with the average grain diameter less than 1 [mu]m is less than 5%; and precipitate with the diameter less than 10 nm and 150 / [mu]m2 is included.

Description

technical field [0001] The present invention relates to a high-yield-ratio high-strength cold-rolled steel sheet excellent in hole expandability and a manufacturing method thereof. A high-yield-ratio high-strength cold-rolled steel sheet excellent in hole expandability for structural parts of automobiles, etc., and a method for producing the same. Background technique [0002] In recent years, with the strengthening of various environmental regulations and energy regulatory mechanisms, high-strength steel sheets for automobiles are required to improve fuel efficiency and durability of automobiles. In particular, with the spread of automobile impact safety regulations, high-strength steel plates are widely used for structural parts such as members, seat rails, and pillars in order to improve the impact resistance of the vehicle body. steel plate. This high-strength steel plate is designed to absorb the impact energy of a car, and is therefore characterized by a steel plate ...

Claims

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Application Information

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IPC IPC(8): C22C38/38C21D8/02
CPCC21D8/02C22C38/38
Inventor 韩成豪徐昌孝
Owner POHANG IRON & STEEL CO LTD
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