CN105583382A - Method for suppressing casting blank inclusion segregation by means of pulse current - Google Patents

Abstract

The invention provides a method for suppressing casting blank inclusion segregation by means of pulse current, and relates to the technical field of steelmaking continuous casting production. The method specifically comprises the steps that the pulse current with the frequency ranging from 1 Hz to 105 Hz and the current intensity ranging from 1.0 A.m<-2> to 105 A.m<-2> is applied between every two opposite clamping rollers behind a crystallizer for continuous casting, and therefore the nucleation rate and nucleation speed of fine sulfide and carbide formed by sulfur, carbon and other elements prone to segregation in the solidification process are increased, and casting blank segregation is suppressed. The method has the beneficial effects that the treatment cost is low, operation is easy and convenient, and the effect of suppressing casting blank segregation is remarkable.

Description

A method of suppressing segregation of inclusions in slab by using pulse current

technical field

The invention relates to the technical field of steelmaking and continuous casting production. More specifically, it relates to a method for suppressing segregation of inclusions in slab by using pulse current.

Background technique

Due to the significant difference in the solubility of carbon, sulfur and other elements in the solid/liquid two phases of steel, segregation easily occurs during the solidification process of molten steel, which seriously affects the mechanical properties, fatigue properties and corrosion resistance of steel. One of the reasons why grades of steel still need to be imported. Therefore, eliminating or reducing the harm of segregation of harmful elements in the solidification process has always been an important research topic for metallurgists, and it is one of the important directions to improve the quality of steel products and promote the upgrading of my country's steel industry.

So far, researchers have researched and developed many methods to reduce the harm of element segregation in the solidification process, among which the effect is more obvious is the electromagnetic stirring technology and the soft reduction technology developed in the 1970s. An important means of continuous casting slab quality. Through the combination of laboratory numerical simulation and on-site industrial experiments, the researchers found that appropriate electromagnetic stirring and soft reduction technology can strengthen the flow and heat transfer of the solid/liquid interface during solidification, and reduce the segregation in the center of the slab to form sulfuration. The danger of large inclusions. However, the forced convection caused by electromagnetic stirring will inevitably produce a wide range of fluctuations in solute composition, which may intensify the segregation of sulfides in the slab.

Ozbayrakta et al. found that low superheat casting can increase the nucleation rate of inclusions and improve segregation. Subsequent studies have shown that low superheat pouring can promote the nucleation and precipitation of sulfide in the solid/liquid two-phase region and expand the equiaxed crystal region, thereby significantly reducing the segregation and internal defects of the slab. However, this technology reduces the fluidity of molten steel, the inclusions are not easy to float up and remove, and it is easy to form large particle inclusions to reduce the quality of the slab.

Therefore, trying to find a more effective way to reduce slab segregation during solidification.

Contents of the invention

The present invention proposes a method of applying a pulse current during the solidification process of the slab to reduce the segregation of the slab, by applying a pulse current between the paired and mutually insulated pinch rods on the continuous casting machine , increase the nucleation rate and nucleation speed of fine sulfides and carbides formed by segregation elements such as sulfur and carbon during solidification, and achieve the miniaturization and uniform distribution of inclusions, so as to prevent slab segregation. The invention belongs to a method for suppressing slab segregation with low cost and simple operation.

The method included in the present invention includes applying a pulse current between pairs of pinch rods that are opposite to each other and insulated from each other after the crystallizer on the continuous casting machine, wherein:

(A) The position where the pulse current is applied: along the line of the slab after it comes out of the mold;

(B) Impulse current application method: 2-50 pairs of clamping rods corresponding to each other and insulated from each other at the rear of the mold on the continuous casting machine, including the clamping rods facing each other and insulated from each other on the dynamic pressing equipment;

(C) Pulse current waveform: including square wave and sawtooth wave;

(D) Pulse current mode: including positive and negative pulses, positive and negative interval pulses, positive and negative proportional pulses, positive pulses or negative pulses;

(E) Pulse current density: 1A·m ^-2 ~ 105A·cm ^-2 , the current density between different pairs of pincers can be the same or different, and can be dynamically determined according to the billet;

(F) Pulse frequency: 1-105Hz, determined according to steel type and continuous casting parameters;

(G) Processing time: It can be the whole solidification process of the slab, or pulse current processing can be applied in sections, which is determined according to the steel type and continuous casting parameters.

For example, apply positive and negative pulse currents between opposite rollers on the equipment under dynamic light pressure, the pulse frequency is 100Hz~104Hz, and the pulse current density is 1.0A·m ^-2 ~ 104A·m ^-2 .

Effect of the present invention is as follows:

(1) Simple and convenient operation: the present invention is suitable for continuous casting of various square slabs and slabs. It does not need to change or only slightly change the existing continuous casting method. The positive pole of the generator is connected, and the clamping rod on the other side is connected with the negative pole of the pulse current generator. The continuous casting slab coming out of the crystallizer is clamped between the same pair of clamping rods, and the pulse current is passed in for processing, so the process is simple, convenient and efficient. easy to accomplish.

(2) Low processing cost: Only pulse current needs to be applied during the solidification process of the existing slab, so only a small amount of electricity is required to meet the processing requirements. Compared with other methods, the power consumption is low, and other related costs are also very low. Therefore, while improving the quality of the slab, the increased cost is relatively low.

(3) Excellent effect of inhibiting segregation: After practical application, this method can almost achieve excellent effect of inhibiting segregation when treating slabs with different thicknesses. and uniform distribution, which significantly improves the internal quality of the continuous casting slab.

Description of drawings

Fig. 1 is a schematic diagram of a method for treating a slab with a pulse current.

Fig. 2 is an observation diagram of the microstructure of the cast slab solidified sample treated with pulse current.

detailed description

Example 1

After the mutual insulation treatment is carried out between the dynamic soft reduction clamp rollers of the existing continuous casting machine, the pulse current treatment is applied to the opposite clamp rollers of the dynamic soft reduction device. During the treatment process, the continuous casting operation was carried out according to the original operation mode of the steel plant, and the parameters of the pulse current treatment were: the current density of the first pair of clamp rods was 1.0A·m ^-2 , and the current density of the second pair of clamp rods was 10A·m ^{-2 2.} The current density between the third pair and the last ten pairs of pinches is 100A·m ^-2 , the pulse waveform is square wave, the pulse mode is positive and negative pulse, the pulse frequency is 100Hz, and the casting speed is 1600mm·min ^{- 1} , the billet width is 1600mm. Through the analysis, the cast slab treated with the pulse current has no segregation, which greatly improves the quality of the cast slab.

Using a metallographic microscope, a field emission scanning electron microscope (FE-SEM) and a transmission electron microscope (TEM), the solidified sample of the cast slab treated by pulse current was observed, and the observation results are shown in Fig. 2 . In Figure 2, the white circles are inclusions, and it can be seen from Figure 2 that the inclusions are small and diffusely distributed. Further energy spectrum analysis shows that these inclusions are mainly sulfide inclusions. Analysis of the entire strand showed that segregation of the strand was completely eliminated by pulsed current treatment.

As shown in Figure 2, transmission electron microscopy (TEM) analysis shows that a large number of nanoscale sulfide inclusions are formed in the metal matrix. Therefore, the pulse current can effectively promote the nucleation of inclusions such as sulfide during solidification, thereby greatly improving the solidification process. Reduce segregation.

Claims (2)

1. A method utilizing pulse current to suppress slab inclusion segregation, characterized in that the method comprises: A pulse current is applied between pairs of pinch rods on the continuous casting machine that are located behind the crystallizer and are insulated from each other, wherein: The position where the pulse current is applied: along the line of the slab after it comes out of the mold; Pulse current application method: 2-50 pairs of clamping rods facing and insulated from each other at the back of the mold on the continuous casting machine, including the clamping rods facing each other and insulated from each other on the dynamic reduction equipment; Pulse current waveform: including square wave and sawtooth wave; Pulse current mode: including positive and negative pulses, positive and negative interval pulses, positive and negative proportional pulses, positive pulses or negative pulses; Pulse current density: 1A·m ^-2 ~ 105A·cm ^-2 , the current density between each pair of clamping rods is the same or different; Pulse frequency: 1~105Hz; Processing time: for the entire solidification process of the slab, or apply pulse current processing in sections. 2. The method according to claim 1, characterized in that positive and negative pulse currents are applied between the opposite rollers on the equipment under dynamic light reduction, the pulse frequency is 100Hz～104Hz, and the pulse current density is 1.0A·m ^-2 ~104 A·m ⁻² .