High-strength steel plate and method for producing same

Abstract

Disclosed is a high-strength steel plate having superior bendability, weldability, and toughness, with yield strength of 885 MPa or greater and average absorbed energy value of 33 J / cm2 in impact tests at -40 DEG C, and a method for producing the same. The high-strength steel plate has a composition of 0.10 - 0.18% C, greater than 0.20% to 0.80% Si, 0.20 - 1.60% Mn, 0.10 - 0.60% Mo, 0.010% - 0.050% Nb, 0.005 - 0.030% Ti, 0.01 - 0.10% Al, 0.0003 - 0.0030% B, 0.012% or less P, 0.005% or less S, 0.0060% or less N, and 0.29% or less Pcm. The high-strength steel plate also has, on the steel plate surface, a Hv 250 or less softened layer with a thickness of 50 [mu]m or greater and exceeding 3% of the steel plate thickness. Furthermore, at a position 1 / 4 of the plate thickness from the surface, the average aspect ratios of former austenite particles in the L cross-section and T cross-section are both 1.6 or greater.

Description

technical field [0001] The present invention relates to a high-strength steel plate having a yield strength of 885 MPa or more and a plate thickness of 6 mm to 32 mm, which is excellent in bending workability, weldability, and toughness, and is used as a structural member of construction machinery and industrial machinery, and a manufacturing method thereof. Background technique [0002] Construction machines such as cranes and concrete pump trucks tend to be larger in size due to the increase in the height of buildings in recent years. In order to suppress the weight increase accompanying the increase in the size of construction machinery, the demand for reducing the weight of structural members is increasing, and the demand for high-strength steel with a yield strength of 885 MPa or more or a tensile strength of 950 MPa or more tends to increase further. When used as a cantilever material for a crane, etc., strict bending processing is often applied, such as 2.0t (bending ...

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Problems solved by technology

[0007] Patent Document 5 relates to steel with a tensile strength of 980 MPa in consideration of bending workability. However, the improvement of bending workability depends on the miniaturization of the crystal grain size. In order to make the crystal grain size fine and uniform, off-line reheating is required. Quenching, therefore low productivity, cannot adequately meet vigorous demand

In addition, the index of bending workability is only the elongation value, so it is not clear whether bending work can be performed at a severe bending radius of 2.0t

[0008] Patent Document 6 relates to a hot-rolled steel sheet with a tensile strength of 950 MPa or more in consideration of bending workability and weldability, but it is necessary to add a large amount of Ti, and it is considered that weldability decreases when it is used for a thick plate. Due to the decrease in toughness, Ni must be added, so there is also a problem with economy

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