CN101683685A - A production technology of micro-alloyed wide and thick continuous casting slab - Google Patents

Abstract

The invention provides a micro-alloyed wide-thick continuous casting slab production technology, aiming at micro-alloyed steel grades, controlling the content of Als, P and S, adopting relatively large current electromagnetic stirring, controlling the superheat of the tundish and the taper of the crystallizer, increasing the Increase the amount of cooling water on the narrow side, increase the number of foot rolls, adopt a higher casting speed and implement a weak cooling process to produce cast slabs with wide and thick sections. Thereby improving the purity of the steel, controlling the central segregation of the slab, improving the thermoplasticity of the steel, increasing the ratio of equiaxed grains by more than 25%, reducing the belly by 50% to 80%, and greatly reducing the internal defects of the slab. The qualified rate of flaw detection is increased by 6 to 10 percentage points, various surface cracks are basically eliminated, and the qualified rate of casting slab surface quality reaches 99.4%. At the same time, the continuous casting output is correspondingly increased, which provides successful experience for the continuous mass production of medium-high carbon micro-alloyed high-strength wide-thick continuous casting slabs, and has high promotion and application value.

Description

A production technology of micro-alloyed wide and thick continuous casting slab

technical field

The invention belongs to the technical field of steelmaking and continuous casting, and in particular relates to a technical method for producing wide and thick continuous casting slabs by adopting medium-high carbon micro-alloying treatment steel grades.

Background technique

In recent years, the market demand for large-scale Nb, V, Ti micro-alloyed high-performance low-alloy wide-thick plates has been increasing, especially in the European market. Therefore, major domestic iron and steel enterprises are competing to add continuous casting wide-thick slab production lines, and qualified manufacturers are also scrambling to produce this kind of micro-alloyed high-performance low-alloy wide-thick slab. However, during the production process, it was discovered that these iron and steel complexes that have been mainly producing thick slabs of ordinary carbon steel, once the steel type is changed to low-alloy wide and thick slabs, if they want to produce slabs with qualified internal and external quality and high yield There are still many problems to be solved urgently in wide and thick slabs microalloyed with Nb, V and Ti.

Among them, the most prominent problem is that the quality pass rate of the produced microalloyed wide and thick slab is too low, which leads to the high production cost of the cast slab. In addition to the internal cracks in some slabs, which caused the unqualified flaw detection of the steel plate after rolling, the most serious problem is that the surface quality of the slab is not up to standard, and there are a large number of various surface cracks, such as corner cracks, surface transverse cracks, etc., resulting in The surface quality is substandard. If it is serious, it will be scrapped due to surface cracks, and if it is light, it must be cleaned or peeled off, which increases the workload of mechanical or flame cleaning and increases the expense. In addition, there is also the problem of excessive bulging on the side of the slab. Generally, the bulging is 10-15mm, which is also one of the reasons for the internal cracks (triangle cracks, corner cracks, etc.) in the slab.

Studies have shown that the main reason for the occurrence of various cracks is the alloying elements added during the microalloying process. In addition to adding a certain amount of Nb, V, and Ti alloys in the microalloying treatment, it is generally required that the Mn content in the steel reaches 1.3-1.9%. The main purpose of increasing the Mn content and adding Nb, V, and Ti alloys is to improve The strength of the cast slab and even the rolled material meets the requirements of low alloy and high strength. However, while the strength is increased, the thermoplasticity of the slab is also reduced accordingly. The casting slab needs to undergo continuous bending and straightening deformation during the continuous casting process, which is acceptable for low-carbon steel with good thermoplasticity and toughness, but for medium-high carbon steel with high carbon content after micro-alloying treatment, it is bound to be During the bending and straightening process, the surface cast shell is cracked, or cracks are formed due to stress during the cooling process.

After searching, no reports on the production technology of similar products and relevant data records on the production of microalloyed wide and thick continuous casting slabs were found.

Contents of the invention

The purpose of the present invention is to solve the above problems and the causes, and adopt the method of combining the control of smelting components with the control of continuous casting process and the improvement of continuous casting equipment, so as to realize the continuous mass production of qualified medium-high carbon micro-alloyed high-strength wide-thick specification continuous castings. cast slab.

For this reason, the technical solution provided by the present invention is:

A micro-alloyed wide-thick continuous casting slab production technology adopts the measures of controlling the smelting composition, controlling the continuous casting process, and improving equipment to produce 280-310×1800-2000mm wide-thick section casting slabs. Its specific process and control method are:

1. Use Nb, V, Ti micro-alloyed steels, and control Als≤0.008%.

2. P<0.015% and S<0.005% in the control steel.

3. The electromagnetic stirring scheme with a large current at the solidification end of the slab is adopted, so that the double electromagnetic stirring current in the secondary cooling section can reach 1000-1200A.

4. Control the superheat of the tundish at 10-20°C.

5. Control the taper of the crystallizer, and the control range is 9.3 to 9.8;

6. The cooling water on the narrow side of the slab is increased by 10-15% compared with the normal amount, and the control range is 9-10Nm ³ /h;

7. Increase crystallizer foot rolls and use 5 to 6 pairs of foot rolls for production;

8. Higher casting speed is adopted, and the casting speed is controlled within the range of 0.9-1.1m/min;

9. The weak cooling process is implemented, and the cooling intensity is controlled at 0.75-0.9Nm ³ /t.

The preferred continuous casting process parameters are:

The double electron stirring current is 1000A.

The superheat of the tundish is controlled at 15°C.

The cooling water on the narrow side of the slab is increased by 10% compared with the normal cooling water.

The casting speed is controlled at 1.0m/min.

The cooling intensity is controlled at 0.80Nm ³ /t.

The crystallizer taper is 9.5.

Crystallizer foot rolls increased from 3 pairs to 5 pairs.

Owing to taking above-mentioned measures, the present invention has obtained following beneficial effect:

One is to improve the purity of the steel and the internal quality of the slab, effectively control the central segregation of the slab, improve the thermoplasticity of the steel during bending and straightening, make the segregation below B0.5, and increase the ratio of equiaxed grains by 25%. above. The second is to greatly reduce the number and specifications of the bulging belly, so that the produced bulging belly is significantly reduced, and its size is reduced from the original 10-15mm to 0-5mm. The third is that the internal defects of the rolled steel plate are reduced, the pass rate of flaw detection is increased, and the average pass rate of flaw detection is increased by an average of six to ten percentage points. Fourth, various surface cracks are basically eliminated, and the pass rate of the surface quality of the slab is increased from 50% to 99.4%. At the same time, due to the use of a higher casting speed than usual for other steel types, the continuous casting output has also been increased accordingly. Thus, it provides successful experience for high-efficiency, high-quality, continuous mass production of medium-high carbon micro-alloyed high-strength wide-thick specification continuous casting slabs, and has high promotion and application value.

Detailed ways

Taking the continuous casting slab whose production specification is 300×1950 mm as an example, the present invention will be described in detail below.

The present invention is characterized by treating both symptoms and root causes, combining control of smelting components with control of continuous casting process and improvement of continuous casting equipment to produce qualified medium-high-carbon micro-alloyed high-strength wide-thick section billets. Its specific process parameters and control process are:

For slabs with a wide and thick section of 300×1950mm, Nb, V, and Ti microalloying treatments are carried out during the smelting process, and Als≤0.005% is strictly controlled to reduce the AlN content in the steel to reduce the probability of cracks on the surface of the slab.

Reduce the content of harmful elements in steel, control P<0.015%, S<0.005%, so as to effectively prevent the central segregation and internal cracks of the slab.

The electromagnetic stirring scheme with a large current at the end of the solidification of the slab is adopted, and the double electromagnetic stirring current in the secondary cooling section reaches 1000A, which improves the internal quality of the slab.

Control the superheat of the tundish to 15°C, and increase the ratio of equiaxed grains inside the slab.

Control the taper of the crystallizer to 9.5; increase the cooling water on the narrow side by 10% compared with the normal amount, and control it at 9.3Nm ³ /h; to control and reduce the belly.

The bulge and internal cracks are further controlled by increasing the foot rolls of the crystallizer, and the number of foot rolls is increased to 5 pairs, which can effectively prevent internal cracking of the steel plate after rolling and improve the qualified rate of steel plate flaw detection.

High casting speed is adopted, and the casting speed is controlled at 1.0m/min; the weak cooling process is implemented, and the cooling intensity is controlled at 0.8Nm ³ /t, so that the transverse cracks and corner cracks on the surface of the casting billet can be controlled.

By controlling and organizing smelting and continuous casting production according to the above-mentioned process method, qualified continuous casting slabs with medium-high carbon microalloying wide and thick sections can be produced efficiently and with high quality.

Claims (8)

1, a kind of production technology of microalloying wide and thick continous casting slab is characterized in that, takes to control and smelts composition and the measure of controlling continuous casting process, improving equipment and combine, and produces the generous section casting blank of 280～310 * 1800～2000mm; Its concrete technology and control method are:

1), adopts Nb, V, Ti microalloying steel grade, control Als≤0.008%;

2), control P＜0.015% in the steel, S＜0.005%;

3), adopt the electromagnetic agitation scheme of the big electric current of casting blank solidification end, make the two electromagnetic agitation electric currents of secondary cooling section all reach 1000～1200A;

4), the bag degree of superheat is 10～20 ℃ in the control;

5), crystallization control device tapering, control range is 9.3～9.8;

6), strand leptoprosopy cooling water increases 10～15% than normal amount, control range is 9～10Nm ³/ h;

7), increase crystallizer foot roll, adopt 5～6 pairs of sufficient roller productions;

8), adopt higher casting speed, pulling rate to be controlled in 0.9～1.1m/min scope;

9), carry out weak cold technology, intensity of cooling is controlled at 0.75～0.9Nm ³/ t.

2, the thick strand production technology of microalloying according to claim 1 is characterized in that, described pair of electromagnetic agitation electric current is 1000A.

3, the thick strand production technology of microalloying according to claim 1 is characterized in that, the middle bag degree of superheat is controlled at 15 ℃.

4, the thick strand production technology of microalloying according to claim 1 is characterized in that, strand leptoprosopy cooling water increases 10% than normal amount.

5, the thick strand production technology of microalloying according to claim 1 is characterized in that described casting speed is controlled at 1.0m/min.

6, the thick strand production technology of microalloying according to claim 1 is characterized in that described intensity of cooling is controlled at 0.8Nm ³/ t.

7, the thick strand production technology of microalloying according to claim 1 is characterized in that, described crystallizer foot roll is 5 pairs.

8, the thick strand production technology of microalloying according to claim 1 is characterized in that, described conical degree of crystallizer is 9.5.