Method for producing low-alloy and large-size square steel by continuously casting and continuously rolling

Abstract

The invention provides a method for producing low-alloy and large-size square steel by continuously casting and continuously rolling. The process flow is as follows: molten iron pretreatment, converter smelting, refining, continuously casting, heating, continuously rolling and slow-cooling; the converter tapping temperature is 1640-1670 DEG C; after the LF refining is performed to the molten steel, the refining is performed in a VD or RH refining device for 20-40 minutes, the small flow soft argon blowing is performed to the molten steel during the late period of refining for 5 or more minutes, and the molten steel temperature is controlled between 1540 DEG C and 1570 DEG C after the refining is finished; the superheat degree of the tundish molten steel is controlled within 25 DEG C, the casting speed is 0.5-0.9 m / min, the width and the length of the cross section of the casting billet are respectively 280-320 mm and 380-420 mm; and the charging temperature of the casting billet is 700-800 DEG C, the tapping temperature is 1050-1180 DEG C and the total time of heating is 3 hours or more; the initial rolling temperature is 1050-1160 DEG C, the finishing temperature is 850 DEG C or higher, and the length and the width of the square steel are both 130-160 mm; and the stacking for slow-cooling is performed by using the waste heat of the square steel. The invention reduces the central porosity and the central cracks inside the steel casting billet and eases the influence of the residual stress in the steel billet to the internal structure of the square steel in the temperature reduction process, thereby reducing the central cracks in the process of continuously rolling the square steel and improving the qualification rate of flaw detection.

Description

technical field [0001] The invention relates to a method for producing low-alloy large-size square steel, in particular to a method for producing low-alloy large-size square steel by using a continuous casting and rolling bar process flow. Background technique [0002] The traditional production method of low-alloy large-size square steel is: electric furnace or converter steelmaking → refining → die casting or continuous casting → heating → rolling → slow cooling (or annealing) → inspection and cleaning → packaging and storage. [0003] The technological process adopted by a steel factory in Liaoning is: molten iron pretreatment → converter smelting → AHF+LF (or RH) refining → die casting → rolling → slow cooling → inspection and cleaning → packaging and storage. [0004] The technological process adopted by a steel factory in Shanghai is: electric furnace smelting→LF+RH refining→die casting→rolling→slow cooling→annealing→inspection and cleaning→packing and storage. [000...

AI Technical Summary

Problems solved by technology

[0007] The purpose of the present invention is to provide a method for continuous casting and rolling to produce low-alloy large-size square steel, so as to solve the problem that the existing continuous casting and rolling production of low-alloy large-size square steel is unqualified or has a low pass rate after high-level flaw detection