CN113714476A

CN113714476A - Process method for improving surface quality of small square billet

Info

Publication number: CN113714476A
Application number: CN202111000659.3A
Authority: CN
Inventors: 杨俊�; 周文浩; 迟云广; 叶明在; 巨银军; 曾凡政; 陈波涛; 杨碑; 左建林
Original assignee: Hunan Valin Xiangtan Iron and Steel Co Ltd
Current assignee: Hunan Valin Xiangtan Iron and Steel Co Ltd
Priority date: 2021-08-30
Filing date: 2021-08-30
Publication date: 2021-11-30
Anticipated expiration: 2041-08-30
Also published as: CN113714476B

Abstract

The invention relates to a process method for improving the surface quality of a small square billet, belonging to the technical field of steel smelting process control. The crystallizer copper tube of a billet continuous casting machine with 150 multiplied by 150 square is changed into a round angle of R12 from an original round angle of R8, the outer diameter of the crystallizer copper tube is changed into phi 60mm from original phi 80mm under the condition that the inner diameter of an invasive water gap is not changed, meanwhile, the covering slag is changed into high-aluminum low-fluorine covering slag from original covering slag, the continuous casting cooling adopts weak cooling control, and the surface quality of a casting blank is obviously improved compared with the surface quality of the original process.

Description

Process method for improving surface quality of small square billet

Technical Field

The invention belongs to the technical field of steel smelting, and particularly relates to design of functional materials of a small square billet casting machine with a 150 x 150 square cross section, control of relevant process parameters and the like.

Background

With the economic society entering the high-quality development stage, various industries put higher requirements on the used steel materials, and the surface quality of the steel materials is required to be zero. Aiming at the high requirements of users on the surface quality of steel products, at present, all steel enterprises basically solve the surface defects of casting blanks by grinding the casting blanks, but the grinding metal loss is large, the efficiency is low, the cost is high, and the grinding capacity is limited, so that all the casting blanks cannot be ground. Therefore, in order to improve the surface quality of steel products, it is necessary to solve the problem of surface defects of a cast slab, which is closely related to the accuracy of continuous casting equipment, continuous casting process parameters, and the like.

Disclosure of Invention

The invention aims to optimally design a copper pipe, a submerged nozzle, casting powder and the like of a billet crystallizer according to the reason of forming surface defects of a 150 multiplied by 150 billet, and simultaneously optimize a cooling process of continuous casting aiming at the characteristics of the copper pipe, the submerged nozzle and the casting powder so as to improve the surface quality of a casting blank.

A process method for improving the surface quality of a billet comprises the following process steps:

(1) four fillet radiuses of a crystallizer copper pipe of a 150X 150 small square billet continuous casting machine are made into R12;

(2) when the inner diameter of the submerged nozzle is phi 32mm, the outer diameter is made to be phi 60 mm;

(3) high-aluminum low-fluorine mold flux is adopted, the alkalinity of the high-aluminum low-fluorine mold flux is R = 0.6-1.3, and Al₂O₃=7%~11%，F^-=0% -1%, the thickness of the covering slag in the liquid slag layer of the crystallizer is 7-10 mm;

(4) controlling the superheat degree of molten steel to be 20-30 ℃, the pulling speed to be 2.2-2.6 m/min, the water flow rate of the crystallizer to be 1800-2000L/min and the temperature difference of inlet and outlet water to be 6-9 ℃ during cooling of the crystallizer; the unit pulling speed set values of the water flow of each area of the secondary cooling water are respectively 45L/min, 65L/min and 40L/min, and the specific water amount of the secondary cooling water is 0.7-0.9L/kg.

The invention has the beneficial effects that: the invention is developed aiming at surface defects of corner cracks, slag channels, deep vibration marks and the like of a small square billet, four round corners of a crystallizer copper pipe of a small square billet continuous casting machine with the square of 150 multiplied by 150 are optimized, the outer diameter of the crystallizer copper pipe is reduced under the condition that the inner diameter of an invasive water gap is not changed, and the contact area between molten steel and protective slag in the crystallizer is enlarged; meanwhile, new covering slag is developed, and the cooling process of continuous casting is optimized according to the changes of a copper pipe, an invasive water gap, covering slag and the like of a continuous casting crystallizer, so that the surface quality is obviously improved.

Drawings

FIG. 1 is a surface quality diagram of a casting blank after shot blasting of the casting blank according to the process of the invention.

FIG. 2 is a diagram showing the surface quality of a cast blank after shot blasting of the cast blank in the prior art.

FIG. 3 is a surface quality chart of an acid-washed cast slab according to the process of the present invention (example 2).

S of S1, S2, S3, and S4 in the figure is the first letter of english Stream of the Stream, S1 indicates the first Stream, S2 indicates the second Stream, S3 indicates the third Stream, and S4 indicates the fourth Stream.

FIG. 1 shows the surface quality of the first (S1) and fourth (S4) billets after shot blasting in the process test of the present application; FIG. 2 shows the surface quality of the second (S2) and third (S3) casting blanks after shot blasting in the prior art, and the surface defect of the casting blank comes out from a chalk coil; FIG. 3 shows the surface quality of the pickled slab in the process test of the present application.

Detailed Description

Example one

The trial production of the scheme for improving the surface quality of the casting blank is carried out on casting of a 4-machine 4-flow 150X 150 square billet 60Si2Mn in a steel mill, the test process is carried out on an S1 flow and an S4 flow, the S2 flow and the S3 flow of other times adopt the original processes, and the specific production process is as follows:

(1) the crystallizer copper tubes of the S1 flow crystallizer and the S4 flow crystallizer adopt an R12 chamfering crystallizer, and the S2 flow crystallizer and the S3 flow crystallizer adopt an R8 chamfering crystallizer;

(2) the submerged nozzles of the S1 flow and the S4 flow adopt improved nozzles, the outer diameter of the slag line part of the nozzle is phi 60mm, the inner diameter is 32mm, and the submerged nozzles of the original slag line part of the nozzle, the outer diameter of which is phi 80mm, are adopted for the S2 flow and the S3 flow;

(3) the S1 flow and S4 flow crystallizer casting powder adopts high-aluminum low-fluorine casting powder, the alkalinity R is 0.8, and Al₂O₃8% of F^-The thickness of the crystallizer liquid slag layer is 0.3 percent, the thickness of the crystallizer liquid slag layer is 8-9 mm, the S2 flow and S3 flow crystallizers adopt the original covering slag, and the thickness of the crystallizer liquid slag layer is 7.5-8.5 mm;

(4) the casting speed of the whole casting is 2.3m/min, the cooling water flow of the S1 flow crystallizer and the cooling water flow of the S4 flow crystallizer are 1850L/min, the water temperature difference is 7.2-7.8, the unit casting speed set values of the water flow of each area of the secondary cooling water are 45L/min, 65L/min and 40L/min respectively, the specific water amount is controlled according to 0.8L/kg, and the S2 flow and the S3 flow adopt the original cooling process.

Shot blasting inspection is carried out on the surface quality of the casting blank, no crack or other obvious defects are found in the casting blanks of the S1 flow and the S4 flow of the test process, and the defects of deep vibration marks, surface reconnection and the like exist in the casting blanks of the S2 flow and the S3 flow of the original process. The surface quality of the cast blank after shot blasting is shown in figure 1.

Example two

A scheme for improving the surface quality of a casting blank is tried on casting of a 4-machine 4-flow 150X 150 square billet 55SiCr in a steel plant, four flows of a casting machine S1 flow, a casting machine S2 flow, a casting machine S3 flow and a casting machine S4 flow are tested by adopting a test process, and the specific production process is as follows:

(1) the crystallizer copper pipes of four casting machines all adopt R12 chamfer crystallizers;

(2) the submerged nozzles are improved nozzles, the outer diameter of a nozzle slag line part is phi 60mm (original nozzle is 80 mm), and the inner diameter is phi 32mm and is kept unchanged;

(3) the crystallizer covering slag is high-aluminum low-fluorine covering slag with alkalinity R of 1.2 and Al₂O₃10.3% of F^-0.9 percent, and the thickness of the crystallizer liquid slag layer is 7-8 mm;

(4) the casting speed of the whole casting is 2.6m/min, the water flow of the crystallizer is 2000L/min, the water temperature difference is 7.7-8.1, the unit casting speed set values of the water flow of each zone of the secondary cooling water are 45L/min, 65L/min and 40L/min respectively, and the specific water amount is controlled according to 0.8L/kg (the original specific water amount is 1.1L/kg).

The surface quality of the casting blank is inspected by hot pickling, no cracks or other obvious defects are found, and the surface quality of the casting blank after pickling is shown in figure 3.

Claims

1. A process method for improving the surface quality of a billet is characterized by comprising the following process steps:

(3) high-aluminum low-fluorine mold flux is adopted, the alkalinity of the high-aluminum low-fluorine mold flux is R = 0.6-1.3, and Al₂O₃=7%~11%，

F^-=0% -1%, the thickness of the covering slag in the liquid slag layer of the crystallizer is 7-10 mm;