Controlled rolling and controlled cooling method for steel with low yield ratio and low welding crack sensitivity

Abstract

The invention relates to a controlled rolling and cooling method for low-yield ratio low welding crack-sensitivity steel. The steel comprises the compositions of, by weight, less than or equal to 0.10% of C, 0.30-0.50% of Si, 1.2-1.8% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.010-0.050% of Nb, 0.01-0.03% of Ti, less than or equal to 0.30% of Cr, 0.02-0.06% of Alt, less than or equal to 0.0005% of B, and the balance Fe and unavoidable impurity elements, wherein C*Nb is equal to 0.18-0.22ppm, and Pcm is less than or equal to 0.20%. A steel plate comprises 45-55% of ferrite, 40-50% of bainite, and a small amount of pearlite, and the yield ratio of the steel plate is less than or equal to 0.85%. The steel plate produced by the controlled rolling and coolingmethod has low cost and high production efficiency and the plate shape is easy to control.

Description

technical field

[0001] The invention belongs to the field of low alloy steel, in particular to a controlled rolling and cooling method for steel with low yield ratio and low welding crack sensitivity. Background technique

[0002] For low-alloy steel, the mixed structure of ferrite + pearlite or bainite is a common way to obtain low yield ratio. Usually, the yield strength mainly depends on the yield strength of ferrite, while the tensile strength follows the law of mixture. Therefore, obtaining a certain amount of pearlite with sufficient carbon content or obtaining bainite with sufficient strength is the key to ensure a low yield ratio. Relevant literature shows that in the strengthening mechanism of iron and steel materials, the role of displacement solid solution strengthening in improving tensile strength is slightly greater than that of improving yield strength, while dislocation strengthening and fine grain strengthening are mainly to significantly improve yield stren...

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