CN109022663B

CN109022663B - Method for refining 890 QL-grade arm support steel

Info

Publication number: CN109022663B
Application number: CN201810757359.1A
Authority: CN
Inventors: 张玉亭; 丛军; 刘宪民; 李林
Original assignee: Shigang Jingcheng Equipment Development And Manufacturing Co ltd
Current assignee: Shigang Jingcheng Equipment Development And Manufacturing Co ltd
Priority date: 2018-07-11
Filing date: 2018-07-11
Publication date: 2020-05-15
Anticipated expiration: 2038-07-11
Also published as: CN109022663A

Abstract

The invention discloses a method for smelting 890 QL-grade arm support steel, which comprises the working procedures of converter smelting, LF refining and VD vacuum treatment, wherein the working procedure of the converter smelting comprises the following steps: the total content of Pb, Sn, As, Sb and Bi in the furnace charging is less than or equal to 0.035%, and the total content of Sn, Sb and As is less than or equal to 0.020%; p in converter tapping is less than or equal to 0.010%, and steel core aluminum is added into molten steel according to 1.0-2.5 kg/t in the tapping process; the LF refining process comprises the following steps: LF in-place component target Al is 0.020% -0.040%; 1.0-3.5 kg/t steel of ferrosilicon powder or silicon carbide powder and 0.3-0.5 kg/t steel of aluminum particles are adopted for diffusion deoxidation; the VD vacuum treatment process comprises the following steps: after the vacuum treatment is finished, feeding an aluminum wire according to 0.030-0.040%, feeding a pure calcium wire according to 0.01-0.03 kg/t steel after feeding aluminum and soft blowing for 3-6 minutes, and adding a covering agent according to 1.0-3.0 kg/t; the soft blowing time is more than or equal to 15 minutes. The method has the advantages that various inclusions in the steel are fewer, finer and uniformly distributed, the shape is more reasonable, the content of harmful elements is lower, the gas content is less, and the molten steel is cleaner; the structure of the steel is more uniform, and further the mechanical properties of the steel are more uniform.

Description

Method for refining 890 QL-grade arm support steel

Technical Field

The invention relates to a steelmaking method, in particular to a method for refining 890 QL-grade cantilever crane steel.

Background

890QL high-strength tube blank is mainly used for manufacturing crawler cranes and is a key component for bearing, transferring and lifting heavy objects by the crawler cranes. The seamless pipe for the high-strength crane boom requires light dead weight, and has higher requirements on material lightness, toughness, welding performance and the like.

890 QL-grade arm frame tube blanks are developed by domestic well-known steel companies firstly, but the low-temperature toughness index is not ideal and cannot meet the requirements of customers. 890QL arm support pipe steel is required to have high strength and low-temperature toughness at the same time, and is suitable for safe and efficient operation in high and cold areas. The existence of H, O, N gas, inclusions, P, As, Sn, Pb, Sb, Bi and other harmful elements in the steel can greatly weaken the continuity and ductility of the steel matrix performance and weaken the grain boundary bonding force. At normal temperature, the influence on the toughness of the steel is not obvious, but when the temperature is gradually reduced, the toughness of the steel is reduced, and the steel becomes brittle gradually. These substances are inevitably present in the steel, and therefore, it is a decisive factor to design and control the contents of gases, inclusions, harmful elements and other elements so as to significantly improve the cleanliness of the steel.

Disclosure of Invention

The invention aims to provide a method for refining 890 QL-grade arm support steel, which can effectively improve the cleanliness of the steel.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the method comprises the working procedures of converter smelting, LF refining and VD vacuum treatment, wherein the working procedure of the converter smelting comprises the following steps: the total content of Pb, Sn, As, Sb and Bi in the furnace charging is less than or equal to 0.035%, and the total content of Sn, Sb and As is less than or equal to 0.020%; p in converter tapping is less than or equal to 0.010%, and steel core aluminum is added into molten steel according to 1.0-2.5 kg/t in the tapping process;

the LF refining process comprises the following steps: LF in-place component target Al is 0.020% -0.040%; 1.0-3.5 kg/t steel of ferrosilicon powder or silicon carbide powder and 0.3-0.5 kg/t steel of aluminum particles are adopted for diffusion deoxidation;

the VD vacuum treatment process comprises the following steps: after the vacuum treatment is finished, feeding an aluminum wire according to 0.030-0.040%, feeding a pure calcium wire according to 0.01-0.03 kg/t steel after feeding aluminum and soft blowing for 3-6 minutes, and adding a covering agent according to 1.0-3.0 kg/t; the soft blowing time is more than or equal to 15 minutes.

In the LF refining process, the time for keeping the white slag in the furnace at the reducing atmosphere and with low current is more than or equal to 20 minutes.

In the VD vacuum treatment process, the holding time of 67Pa and below is more than or equal to 15 minutes.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the invention controls five harmful elements of Pb, Sn, As, Sb and Bi in the steel at a lower level by reasonably designing the proportion of furnace charge, thereby improving the high-temperature performance of the steel, reducing the high-temperature brittleness of the steel and enhancing the strength and toughness of the steel. The low-temperature impact property of the steel is effectively improved by controlling the content of P; the deoxidation capability of the white slag is improved by controlling the aluminum content, and the continuous diffusion deoxidation is carried out, so that the O content in the steel is effectively reduced, and the performance of the steel is improved. The invention reduces the gas content in the steel by VD high vacuum, controls certain aluminum content, refines the crystal grains, prevents the growth of the subsequent heating crystal grains and improves the ductility of the material.

According to the invention, through controlling the development of the raw material formula and controlling the development of the smelting process, various impurities in the steel are fewer, finer, uniformly distributed, more reasonable in form, lower in harmful element content and less in gas content, so that the molten steel is cleaner; the structure of the steel is more uniform, and further the mechanical property of the steel is more uniform; the low-temperature performance is obviously improved, and the comprehensive performance is effectively improved.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments.

The method for refining the 890 QL-grade arm support steel comprises the working procedures of converter smelting, LF refining, VD vacuum treatment and continuous casting, and the processes of the working procedures are as follows:

(1) a converter smelting process: the five harmful elements of Pb, Sn, As, Sb and Bi in the steel have low melting points, and when the content exceeds a certain limit, the high-temperature performance of the steel can be obviously reduced, the high-temperature brittleness of the steel is increased, the strength and the toughness of the steel are reduced, and the steel becomes brittle; they tend to co-grow in one piece, cause severe segregation, rarely exist alone and thus have a greater destructive effect on the steel. The method reasonably designs the proportion of the furnace charge, the total content of Pb, Sn, As, Sb and Bi in the furnace charge is less than or equal to 0.035wt%, and the total content of Sn is less than or equal to 0.020wt%, Sb is less than or equal to 0.020wt%, and As is less than or equal to 0.020 wt%. P causes steel to generate cold brittleness and reduces low-temperature impact performance, P in the steel discharged from the converter is less than or equal to 0.010wt%, and steel core aluminum is added into the steel according to 1.0-2.5 kg/t molten steel in the steel discharging process.

(2) An LF refining procedure: the target Al of the LF in-place component is 0.020-0.040%, the white slag conversion time of the steel slag can be effectively controlled, the slag forming speed is increased, and the deoxidizing capacity of the white slag is improved. Carrying out diffusion deoxidation on 1.0-3.5 kg/t molten steel and 0.3-0.5 kg/t molten steel of silicon powder or silicon carbide powder in the in-place refining process; continuous diffusion deoxidation is carried out, and the reducing atmosphere is ensured; the deoxidation in the slag is sufficient, and the transfer removal of the oxygen at the interface of the steel slag is promoted. Keeping the reducing atmosphere in the furnace, and keeping the white slag at a small current (35-38 KA) for more than or equal to 20 minutes; the white slag time is long enough, and the more inclusions the white slag can sufficiently adsorb.

(3) VD vacuum treatment process: the VD high vacuum (67 Pa and below) is kept for more than or equal to 15 minutes, and the obvious exposure of the molten steel surface can be observed during the vacuum keeping period so as to ensure the vacuum degassing effect; the time for which the VD is kept under high vacuum determines the gas content in the steel, the longer the time, the lower the gas. Measuring temperature and sampling after the vacuum treatment is finished, feeding an aluminum wire according to the VD end point of 0.030-0.040% by considering residual aluminum, feeding a pure calcium wire according to 0.01-0.03 kg/t molten steel after feeding aluminum and soft blowing for 3-6 minutes, and adding a covering agent according to 1.0-3.0 kg/t molten steel to uniformly cover the whole slag surface; controlling a certain aluminum content can refine crystal grains, prevent the growth of the crystal grains after subsequent heating, and improve the ductility of the material. The soft blowing time is more than or equal to 15 minutes after the pure calcium wire is fed and the covering agent is added, so that the non-naked molten steel is ensured.

(4) And (3) continuous casting process: the steel ladle air brick adopts double air bricks, and continuous casting adopts constant drawing speed and is controlled according to the speed of 0.22-0.28 m/min; the target superheat degree of the tundish molten steel is 20-50 ℃.

(5) The high-strength 890QL steel produced by the method has mechanical properties meeting the requirements of steel and good low-temperature mechanical properties. The performance indexes of the 890QL steel produced by the method and the performance indexes of the 890QL steel produced by the conventional process are shown in Table 1.

Table 1: performance index of 890QL steel produced by the method and conventional process

Examples 1 to 6: the method for refining the 890 QL-grade arm support steel adopts the following specific process.

(1) The process comprises the following steps: specific process parameters for each of the procedures of examples 1-6 are shown in tables 2 and 3.

Table 2: technological process of converter smelting and LF refining process

In table 2, the harmful elements are the sum of the contents of five harmful elements of Pb, Sn, As, Sb and Bi in the steel.

Table 3: VD vacuum treatment and continuous casting process

The soft blow time after aluminum feeding in table 3 is the time after aluminum feeding, before feeding pure calcium wire and adding covering agent.

(2) Chemical components of steel: the chemical compositions of the cast slabs obtained in examples 1 to 6 are shown in Table 4.

Table 4: chemical composition (wt%)

(3) Mechanical properties: the mechanical properties of the cantilever crane steel finished product obtained by the casting blank obtained in the embodiment 1-6 through the subsequent conventional process are shown in 5.

Table 5: mechanical properties

Claims

1. The method for smelting 890 QL-grade arm support steel comprises the working procedures of converter smelting, LF refining, VD vacuum treatment and continuous casting, and is characterized in that the working procedure of the converter smelting is as follows: the total content of Pb, Sn, As, Sb and Bi in the furnace charging is less than or equal to 0.035%, and the total content of Sn, Sb and As is less than or equal to 0.020%; p in converter tapping is less than or equal to 0.010%, and steel core aluminum is added into molten steel according to 1.0-2.5 kg/t in the tapping process;

the VD vacuum treatment process comprises the following steps: after the vacuum treatment is finished, feeding an aluminum wire according to 0.030-0.040%, feeding a pure calcium wire according to 0.01-0.03 kg/t steel after feeding aluminum and soft blowing for 3-6 minutes, and adding a covering agent according to 1.0-3.0 kg/t; the soft blowing time is more than or equal to 15 minutes;

the continuous casting process comprises the following steps: the continuous casting is carried out at a constant drawing speed and is controlled at 0.22-0.28 m/min.

2. The method for refining 890 QL-grade boom steel according to claim 1, wherein: in the LF refining process, the time for keeping the white slag in the furnace at the reducing atmosphere and with small current is more than or equal to 20 minutes.

3. The method for refining 890 QL-grade boom steel according to claim 1 or 2, characterized by comprising: in the VD vacuum treatment step, the holding time of 67Pa or less is not less than 15 minutes.