CN105950951A - Method for improving segregation of solute carbon in billet by adding rare earth element - Google Patents

Abstract

The invention discloses a method for improving segregation of solute carbon in billet by adding a rare earth element. According to the method, in the refining process or casting process of steel making, elemental cerium or a cerium compound is added to molten steel to serve as a segregation improving agent; and for the difficulty existing in the current macrosegregation control technology and the problems about high operating cost and the like, start with the balance distribution coefficient of the solute carbon in the steel, by adding trace amounts of rare earth cerium, the balance distribution coefficient of the solute carbon in a solidification system is increased, and consequently the purpose of essentially improving solute carbon segregation is achieved.

Description

A kind of by add rare earth element improve the method for solute carbon segregation in steel billet

Technical field

The invention belongs to field of metallurgy, particularly relate to process of setting Decreasing Segregation field of casting, be specifically related to one The method of solute carbon segregation in steel billet is improved by adding rare earth element.

Background technology

Currently, China's steel production capacity relative saturation, within 2013, crude steel yield has reached 7.7 hundred million tons, accounts for whole world total output 49.1%.The excessive size of capacity brings huge pressure to aspects such as China's energy, resource and environmental conservation.Conventional steel The development of the rough formula of ironworker's industry should change to quality and efficiency, and this meets the developing direction of China's steel and iron industry later.Along with Downstream industry transition and upgrade, user is more and more higher to the prescription of steel, and the defect how improving strand seems the heaviest Want.Gross segregation, particularly center segregation are the internal soundness defects that strand (containing molding and ingot casting) is main, show that strand is horizontal On section, chemical constituents analysis is uneven, and this is the biggest on steel performance impact.

Due to solute different solubility in solid phase and liquid phase, steel is caused to select a point crystallization to be generationization in process of setting Learn the reason of component segregation.Gross segregation once produces, and is difficult to be eliminated by techniques such as subsequent heat treatment, can leave over always In final products, the biggest to properties of product infringement.Steel is as a kind of common Fe-C alloy, and its solute carbon belongs to easy segregation unit Element, when controlling steel solute segregation, the segregation of solute carbon should consider by emphasis.The method improving continuous casting solute gross segregation at present Mainly have following several: the skills such as soft reduction technique, solidification end electromagnetic agitation, Optimizing Process Parameters (such as the degree of superheat, pulling rate etc.) Art.Then, these methods have the limitation of self in actual applications.

Soft reduction technique is that ad-hoc location applies certain reduction ratio, the liquid phase of soluterich is squeezed away from strand The heart, thus reach seam and improve the purpose of center segregation of casting blank.The use of slighter compress can be obviously improved the center deviation of continuous casting billet Analysis.But, what slighter compress there is also such as solidification end position and pattern in actual applications precisely determines that difficulty, operating mode adapt to Property strong (steel grade C content and the cooldown rate impact on pressure region), casting machine precision (opening degree, fan-shaped section Fructus Musae beam radian Deng) technical barrier such as dependency is high, occur the most in actual applications implementing phenomenon that the segregation of slighter compress rear center increases the weight of (due to The deviation of roll gap causes).

Solidification end electromagnetic agitation can improve the mobility of residue liquid phase, makes the residue liquid phase of solute evenly, It is significantly expanded isometry crystalline region, thus plays the effect improving continuous casting center segregation.Research shows that solidification end electromagnetic agitation is permissible Significantly improve center segregation.But, in actual application, the effect of electromagnetic agitation and mixing position and mixing parametric (such as size of current, frequency) is directly related, and mixing position and parameter are also relevant with steel grade and casting condition, and this also can give real Border application brings certain puzzlement.If mixing position and parameter are improper, end electromagnetic agitation can not alleviate strand Center segregation, the most even can cause strand to produce other defect, as made due to stirring intensity excessive (stir current is the biggest) Become flowing unreasonable, ultimately result in the generation of " white band ".Additionally, the effect of end electromagnetic agitation also has with continuous casting two cold situation Close, if two cold the most unreasonable (as too fast in some Local cooling), will electromagnetic agitation effect fluctuate acutely, can not be fine Improvement continuous casting center segregation.Problems above brings certain difficulty all can to the actual application of end electromagnetic agitation.

In terms of casting parameters improves segregation, usually come with low overheat casting (the beneficially formation of Center Equiaxial Crystal) Improve the center segregation of continuous casting billet.But, in actual production process, in order to ensure the direct motion of continuous casting, it is necessary to ensure molten steel tool There is certain degree of superheat.Additionally, it is generally acknowledged that relatively reasonable stable pulling rate can also improve the center segregation of strand, but in reality During border produces, pulling rate is often (disturbance of pulling rate causes the change of Interdendritic Liquid Flow, thus affects center segregation) fluctuated, this Also in terms of pulling rate, improved center segregation brought certain difficulty.

As can be seen here, it is badly in need of a kind of simple to operate, obvious method of effect of exploitation and improves steel process of setting solute carbon Segregation.

Summary of the invention

For deficiencies of the prior art, the present invention provides a kind of and improves in steel billet molten by interpolation rare earth element The method of matter carbon segregation, the method has simple to operate, solute carbon segregation and improves the advantages such as effect is notable, it is possible to be effectively improved Product quality.

To achieve these goals, the technical solution used in the present invention is as follows:

A kind of by add rare earth element improve the method for solute carbon segregation in steel billet, it is characterised in that steel-making essence In refining process or casting cycle, in molten steel, add cerium simple substance or cerium compound as segregation improving agent.

Further, the quality that described segregation improving agent contains Ce elements is the molten steel gross mass after adding segregation improving agent 0.02%～0.10%.

Further, the quality that described segregation improving agent contains Ce elements is the molten steel gross mass after adding segregation improving agent 0.04%～0.06%.

Further, the addition method for determination of amount of described segregation improving agent comprises the following steps:

1) setting up thermodynamical model: in Fe-C-Ce ternary system, the equilibrium distribution coefficient formula of solute carbon is:

$k_C^0=\frac{{\mathrm{\ω}}_C^S}{{\mathrm{\ω}}_C^L}$

Wherein,AndIt is respectively solid phase side, freezing interface and the concentration of liquid phase side solute carbon；As Fe-C-Ce tri- System of unit is when reaching thermodynamical equilibrium, and in system, solute carbon chemical potential in solid phase and liquid phase is equal, i.e. has a below equation:

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_C^L$

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_{C,0}^S+{\mathrm{RTlna}}_C^S$

${\mathrm{\μ}}_C^L={\mathrm{\μ}}_{C,0}^L+{\mathrm{RTlna}}_C^L$

Wherein,WithRepresent when Fe-C-Ce ternary system reaches thermodynamical equilibrium solute carbon respectively in solid phase and liquid phase In chemical potential；Represent the thermodynamic standard state of solute carbon in solid phase；Represent the thermodynamic standard state of solute carbon in liquid phase；R Represent ideal gas constant；T represents thermodynamic temperature；Represent the activity of solute carbon in solid phase；Represent solute carbon in liquid phase Activity；

By introducing solute interaction coefficient, activity coefficient γ_CComputing formula be:

${\mathrm{\γ}}_C={\mathrm{ln\γ}}_C^0+{\mathrm{\ϵ}}_C^C{\mathrm{\ω}}_C+{\mathrm{\ϵ}}_C^{Ce}{\mathrm{\ω}}_{Ce}$

Wherein,AndIt is respectively carbon self-acting coefficient, cerium to carbon function coefficient；Represent in solutions in the limit of extreme dilution molten The activity coefficient of matter carbon；

The above-mentioned formula of simultaneous, obtains the thermodynamical model formula of solute Carbon balance partition coefficient in Fe-C-Ce ternary system:

$k_C^0=\frac{{\mathrm{\γ}}_C^{0,L}}{{\mathrm{\γ}}_C^{o,S}}\exp \[\frac{{\mathrm{\μ}}_{C,o}^L-{\mathrm{\μ}}_{C,o}^S}{RT}+({\mathrm{\ϵ}}_C^{C,L}{\mathrm{\ω}}_i^L-{\mathrm{\ϵ}}_C^{C,S}{\mathrm{\ω}}_C^S)+({\mathrm{\ϵ}}_C^{Ce,L}{\mathrm{\ω}}_{Ce}^L-{\mathrm{\ϵ}}_C^{Ce,S}{\mathrm{\ω}}_{Ce}^S)\];$

2) equilibrium distribution coefficient variation diagram with cerium addition is drawn: set the content of different solute carbon, according to step 1) In the Fe-C-Ce ternary system obtained, the thermodynamical model formula of solute Carbon balance partition coefficient draws corresponding solute carbon content Equilibrium distribution coefficient is with the variation diagram of cerium addition；

3) determine the addition of segregation improving agent: according to content and the step 2 of the solute carbon of steel billet to be produced) draw flat Weighing apparatus partition coefficient determines the addition of segregation improving agent with the variation diagram of cerium addition.

Further, described equilibrium distribution coefficient is the solute carbon average mark under the whole solidification path of Fe-C-Ce ternary system Distribution coefficient.

Ferrous alloy process of setting, solute is toward liquid phase diffusion enrichment, and liquid phase solute concentration raises, this solute redistribution Result is the immediate cause that solidifying segregation produces.And the difficulty or ease of solute segregation and degree with the equilibrium distribution coefficient of solute direct phase Closing, solute balance partition coefficient the least (more deviation in other words), the easiest segregation of this solute, segregation degree also tends to the biggest. Steel is a kind of common Fe-C alloy, and its carbon content has material impact to tissue and the performance of steel.Carbon is a kind of easily segregation unit Element, process of setting causes some local concentration of carbon to increase due to segregation, it is likely that require at a distance of relatively big, directly with steel grade carbon content Have influence on tissue and the performance of steel.Therefore, solute carbon segregation in steel how is controlled significant to improving steel product quality.For Gross segregation at present controls the problems such as difficulty and the operation cost height of technology existence, and the present invention provides a kind of simple possible, easily The method of solute carbon gross segregation in steel is improved in realize.The method equilibrium distribution coefficient of solute carbon from steel is set about, logical Cross interpolation trace rare-earth cerium, make the equilibrium distribution coefficient of solute carbon in coagulation system improve, reach inherently to improve with this molten The purpose of matter carbon segregation.

Compared with prior art, there is advantages that

1, the present invention sets about from the basic parameter carbon solute distribution coefficient changing carbon segregation, it is provided that one can be from Substantially improve the method for solute carbon segregation in steel, can accurately adjust the distribution of solute carbon, farthest avoid solute The segregation of carbon, improves product quality.

2, owing to only needing the cerium adding trace in steel just can reach to improve the purpose of carbon segregation in steel, it is not necessary to its The technique of his auxiliary, whole process is simple, it is easy to accomplish.

3, the amount of this method interpolation cerium is the least, and without additionally purchasing main equipment, operation cost is low.

Accompanying drawing explanation

Fig. 1 be in Fe-0.1%C-x%Ce system solute carbon mean equilibrium partition coefficient with the variation diagram of cerium content；

Fig. 2 be in Fe-0.25%C-x%Ce system solute carbon mean equilibrium partition coefficient with the variation diagram of cerium content.

Detailed description of the invention

Below in conjunction with specific embodiment, the present invention is described in further detail.

Embodiment

Solute balance partition coefficient is to characterize solute segregation difficulty or ease and the key parameter of segregation degree, solute in process of setting Equilibrium distribution coefficient is the least, and in process of setting, solute segregation is the most serious.The present invention is based on this, by adding cerium the most really Determine the broiler diets of cerium to improve the equilibrium distribution coefficient of solute carbon in steel, reach to improve the purpose of solute carbon segregation in steel. The present invention, as a example by two kinds of systems of Fe-0.1%C-x%Ce Yu Fe-0.25%C-x%Ce, determines suitable cerium addition, in reality In application process, add suitable cerium content and just can reach and improve the purpose of carbon segregation in steel.

Specifically use following steps:

(1) thermodynamical model is set up: in Fe-C-Ce ternary system, equilibrium distribution coefficient formula such as formula (1) institute of solute carbon Show:

$k_C^0=\frac{{\mathrm{\ω}}_C^S}{{\mathrm{\ω}}_C^L}---\left(1\right)$

Wherein,AndIt is respectively solid phase side, freezing interface and the concentration of liquid phase side solute carbon；As Fe-C-Ce tri- When system of unit reaches thermodynamical equilibrium, in system, solute carbon chemical potential in solid phase and liquid phase is equal, i.e. has:

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_C^L---\left(2\right)$

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_{C,0}^S+{\mathrm{RTlna}}_C^S---\left(3\right)$

${\mathrm{\μ}}_C^L={\mathrm{\μ}}_{C,0}^L+{\mathrm{RTlna}}_C^L---\left(4\right)$

Wherein,WithRepresent when Fe-C-Ce ternary system reaches thermodynamical equilibrium solute carbon respectively in solid phase and liquid phase In chemical potential；Represent the thermodynamic standard state of solute carbon in solid phase；Represent the thermodynamic standard state of solute carbon in liquid phase；R Represent ideal gas constant；T represents thermodynamic temperature；Represent the activity of solute carbon in solid phase；Represent solute carbon in liquid phase Activity；

By introducing solute interaction coefficient, activity coefficient can use formula (5) to calculate:

${\mathrm{\γ}}_C={\mathrm{ln\γ}}_C^0+{\mathrm{\ϵ}}_C^C{\mathrm{\ω}}_C+{\mathrm{\ϵ}}_C^{Ce}{\mathrm{\ω}}_{Ce}---\left(5\right)$

Wherein,AndIt is respectively carbon self-acting coefficient, cerium to carbon function coefficient；Represent in solutions in the limit of extreme dilution molten The activity coefficient of matter carbon；

The above-mentioned formula of simultaneous, obtains the thermodynamical model formula of solute Carbon balance partition coefficient in Fe-C-Ce ternary system:

$k_C^0=\frac{{\mathrm{\γ}}_C^{o,L}}{{\mathrm{\γ}}_C^{o,S}}\exp \[\frac{{\mathrm{\μ}}_{C,o}^L-{\mathrm{\μ}}_{C,o}^S}{RT}+({\mathrm{\ϵ}}_C^{C,L}{\mathrm{\ω}}_i^L-{\mathrm{\ϵ}}_C^{C,S}{\mathrm{\ω}}_C^S)+({\mathrm{\ϵ}}_C^{Ce,L}{\mathrm{\ω}}_{Ce}^L-{\mathrm{\ϵ}}_C^{Ce,S}{\mathrm{\ω}}_{Ce}^S)\]---\left(6\right)$

(2) drafting equilibrium distribution coefficient is with the variation diagram of cerium addition:

According to the thermodynamical model formula of solute Carbon balance partition coefficient in Fe-C-Ce ternary system, calculate peritectic steel carbon dense Under degree scope (Fe-0.1%C-x%Ce, corresponding with hypo-peritectic steel；Fe-0.25%C-x%Ce, peritectic steel is corresponding from crossing) different The impact on solute Carbon balance partition coefficient of the Ce addition.Wherein, the Ce content that every kind of system is different includes 0,0.01% respectively, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1% 11 kind of situation.Due to Solute balance partition coefficient varies with temperature, and for the more convenient contrast Ce addition impact on C equilibrium distribution coefficient, should round Under individual solidification path, solute carbon mean allocation coefficient compares.In Fe-0.1%C-x%Ce system, solute carbon mean equilibrium is divided Distribution coefficient with cerium content Changing Pattern as shown in Figure 1.Solute carbon mean equilibrium distribution system in Fe-0.25%C-x%Ce system Count the Changing Pattern with cerium content as shown in Figure 2.

(3) the segregation improving agent (addition of Elements C e) is determined

1. Fe-0.1%C-x%Ce system

It will be seen from figure 1 that the mean allocation coefficient of solute carbon increases along with the increase of cerium addition in Fe-C system. The rate of change increased with cerium content from the mean allocation coefficient of solute carbon it can be seen that cerium addition is before 0.04%, solute The mean allocation coefficient of carbon increases rapidly with cerium addition, and increasing degree is big；After cerium addition reaches 0.06%, solute carbon Mean allocation coefficient increasing degree the most inconspicuous.Easy segregation element, simultaneously cerium is fallen within view of cerium itself Price is the highest, considering cost and improve two aspects of effect, it may be determined that Fe-0.1%C-x%Ce system is It is 0.04%～0.06% for suitable cerium addition scope.Especially, when in system, the addition of cerium is zero, solute carbon Mean equilibrium partition coefficient only has 0.157, and after system is added 0.06% cerium, the mean equilibrium partition coefficient of carbon in system Increase 0.234, increase 49%, it can be seen that improve effect obvious.

2. Fe-0.25%C-x%Ce system

Figure it is seen that in system Fe-0.25%C-x%Ce the mean allocation coefficient of carbon with cerium content change with System Fe-0.1%C-x%Ce is consistent, and the mean allocation coefficient of carbon increases with the increase of cerium content.From carbon mean allocation coefficient Change rate curve is it can be seen that the addition of cerium is before 0.03%, and the mean allocation coefficient of solute carbon is with the amplification of cerium content Very big, additionally, when cerium content increases to 0.04% from 0.03%, the equal partition coefficient that carbon is flat still has bigger amplification, therefore fits Preferably cerium addition lower limit still takes 0.04%；After cerium content reaches 0.06%, the mean allocation coefficient increasing degree of carbon is Tend to relaxing.Therefore, after considering and improving effect and operation cost, Fe-0.25%C-x%Ce system is determined equally The addition scope of optimum cerium is 0.04%～0.06%.Especially, when in system, the addition of cerium is zero, carbon average Partition coefficient is 0.215, and after system adds 0.06% cerium, the mean allocation coefficient of carbon increases to, 0.290, and increasing degree reaches To 35%, improve effect obvious.

To sum up, considering and improve effect and two aspects of operation cost, the present invention finally determines that cerium addition is the suitableeest Preferably in the range of 0.04%～0.06%.

(4) actual production is added cerium and improve carbon segregation

The addition determined by step (3), adds segregation improving agent in actual steelmaking process.

The present invention improves carbon segregation in steel by adding Trace Cerium, there is no the casting form (continuous casting or molding) of steel and wants Ask.Actual should during, the addition of cerium can add in refining process with the form of alloy, it is also possible at casting cycle Add.Only need to add to suitable cerium addition (0.04%～0.06%) and steel can improve the segregation of solute carbon in steel. After cast molding, the detection of chemico-analytic method can be used to add the improvement effect of product carbon segregation after cerium.

The present invention first should be for the Thermodynamic Calculating Model of Fe-C-Ce Establishing solute C equilibrium distribution coefficient, with this Calculate the change with Ce addition of the two kinds of system solute C partition coefficients of Fe-0.1%C-x%Ce Yu Fe-0.25%C-x%Ce, and Finally determine optimum cerium addition.

The above embodiment of the present invention is only for example of the present invention is described, and is not the enforcement to the present invention The restriction of mode.For those of ordinary skill in the field, can also be made other not on the basis of the above description Change and variation with form.Here cannot all of embodiment be given exhaustive.Every belong to technical scheme That is amplified out obviously changes or changes the row still in protection scope of the present invention.

Claims (5)

1. one kind is improved the method for solute carbon segregation in steel billet by adding rare earth element, it is characterised in that in the refine of steel-making In process or casting cycle, in molten steel, add cerium simple substance or cerium compound as segregation improving agent.

The most according to claim 1 by add rare earth element improve the method for solute carbon segregation in steel billet, its feature exists In 0.02% that, the quality that described segregation improving agent contains Ce elements is molten steel gross mass after adding segregation improving agent～ 0.10%.

The most according to claim 2 by add rare earth element improve the method for solute carbon segregation in steel billet, its feature exists In 0.04% that, the quality that described segregation improving agent contains Ce elements is molten steel gross mass after adding segregation improving agent～ 0.06%.

4. described improve the method for solute carbon segregation in steel billet by adding rare earth element according to claim 1-3 is arbitrary, its Being characterised by, the addition method for determination of amount of described segregation improving agent comprises the following steps:

1) setting up thermodynamical model: in Fe-C-Ce ternary system, the equilibrium distribution coefficient formula of solute carbon is:

$k_C^0=\frac{{\mathrm{\ω}}_C^S}{{\mathrm{\ω}}_C^L}$

Wherein,AndIt is respectively solid phase side, freezing interface and the concentration of liquid phase side solute carbon；When Fe-C-Ce ternary system When reaching thermodynamical equilibrium, in system, solute carbon chemical potential in solid phase and liquid phase is equal, i.e. has a below equation:

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_C^L$

${\mathrm{\μ}}_C^S={\mathrm{\μ}}_{C,0}^S+{\mathrm{RTln\α}}_C^S$

${\mathrm{\μ}}_C^L={\mathrm{\μ}}_{C,0}^L+{\mathrm{RTln\α}}_C^L$

Wherein,WithRepresent when Fe-C-Ce ternary system reaches thermodynamical equilibrium solute carbon respectively in solid phase and liquid phase Chemical potential；Represent the thermodynamic standard state of solute carbon in solid phase；Represent the thermodynamic standard state of solute carbon in liquid phase；R represents Ideal gas constant；T represents thermodynamic temperature；Represent the activity of solute carbon in solid phase；Represent the work of solute carbon in liquid phase Degree；

By introducing solute interaction coefficient, activity coefficient γ_CComputing formula be:

${\mathrm{\γ}}_C={\mathrm{ln\γ}}_C^0+{\mathrm{\ϵ}}_C^C{\mathrm{\ω}}_C+{\mathrm{\ϵ}}_C^{Ce}{\mathrm{\ω}}_{Ce}$

Wherein,AndIt is respectively carbon self-acting coefficient, cerium to carbon function coefficient；Represent solute carbon in solutions in the limit of extreme dilution Activity coefficient；

The above-mentioned formula of simultaneous, obtains the thermodynamical model formula of solute Carbon balance partition coefficient in Fe-C-Ce ternary system:

$k_C^0=\frac{{\mathrm{\γ}}_C^{o,L}}{{\mathrm{\γ}}_C^{o,S}}\exp \[\frac{{\mathrm{\μ}}_{C,o}^L-{\mathrm{\μ}}_{C,o}^S}{RT}+({\mathrm{\ϵ}}_C^{C,L}{\mathrm{\ω}}_i^L-{\mathrm{\ϵ}}_C^{C,S}{\mathrm{\ω}}_C^S)+({\mathrm{\ϵ}}_C^{Ce,L}{\mathrm{\ω}}_{Ce}^L-{\mathrm{\ϵ}}_C^{Ce,S}{\mathrm{\ω}}_{Ce}^S)\];$

2) equilibrium distribution coefficient variation diagram with cerium addition is drawn: set the content of different solute carbon, according to step 1) obtain Fe-C-Ce ternary system in solute Carbon balance partition coefficient thermodynamical model formula draw corresponding solute carbon content balance Partition coefficient is with the variation diagram of cerium addition；

3) addition of segregation improving agent is determined: according to content and the step 2 of the solute carbon of steel billet to be produced) balance drawn divides Distribution coefficient determines the addition of segregation improving agent with the variation diagram of cerium addition.

The most according to claim 4 by add rare earth element improve the method for solute carbon segregation in steel billet, its feature exists In, described equilibrium distribution coefficient is the solute carbon mean allocation coefficient under the whole solidification path of Fe-C-Ce ternary system.