CN104392107A - Method for predicting initial crack of continuous casting slab upon force analysis - Google Patents

Abstract

The invention discloses a method for predicting an initial crack of a continuous casting slab upon force analysis. The method comprises the following steps: determining an initial solidified slab shell load in the vertical throwing direction of a meniscus in a vibration crystallizer; determining mechanical parameters of an initial solidified slab shell, wherein the mechanical parameters comprise the bending moment of a simply supported beam, the inertia moment of the cross section of the simply supported beam and bending stress of the cross section of the simply supported beam; determining the steel grade high-temperature critical breaking strength; predicting the initial crack of the continuous casting slab; if the value of the bending stress of the cross section of the simply supported beam is greater than the obtained steel grade high-temperature critical breaking strength, showing that the initial solidified slab shell load in the vertical throwing direction breaks the strength of the initial solidified slab shell, and the initial crack is generated in the initial solidified slab shell on the meniscus of the current continuous casting slab, and if not, no initial crack is generated in the initial solidified slab shell on the meniscus of the current continuous casting slab. According to the method disclosed by the invention, the vibration effect of the crystallizer is converted into the bending stress borne by the slab shell, and therefore a new idea is provided for analyzing the formation of the crack in the slab shell, and preliminary judgment is conveniently and effectively made on the possibility of the formation of the initial crack of the continuous casting slab.

Description

A kind of method based on force analysis prediction continuous casting billet initial crack

Technical field

The invention belongs to Ferrous Metallurgy casting process Quality Control Technology field, particularly a kind of method based on force analysis prediction continuous casting billet initial crack.

Background technology

Cracks In Continuous Cast Billets is the major defect affecting steel products final mass, not only increases follow-up cleaning process, reduces recovery rate of iron, strand and stocking also may be caused to scrap, and even causes bleed-out accident.Continuous casting vibrating crystallizer menisci initial solidification region is the cradle of the series of defect such as base shell shake line, and the mechanical force of the complexity that initial set base shell bears is one of factor of bringing out initial crack formation.By understanding fully that the stress of base shell in vibrating crystallizer process of setting can judge the possibility that crackle is formed, such as base shell meets with stresses and exceedes this temperature threshold intensity and then likely can produce initial crack, and these initial cracks can further expand in the operations such as follow-up throwing, aligning and rolling, finally form product defects.Therefore, probe into crystallizer initial set base shell mechanical state, and propose evaluation method, reduction base shell shake line is produced and has important practical significance.

At present, initial set base shell to crack in the research of mechanism only qualitative elaboration base shell protected slag road pressure because of mechanical vibration, the combined action of ferrostatic pressure and friction force etc., the disturbing influence of the changes such as slag road pressure to molten steel meniscus is have studied as document " dynamic pressure of Soft Contact Electromagnetic C. C mold flux channel " and " under high pulling rate continuous casting billet Mechanism of Oscillation Mark Formation and oscillation parameter optimization ", when base shell used load reduces, the stability of initial solidification process is improved, meniscus disturbance behavior weakens, casting billet surface oscillation mark alleviates, the occurrence probability also corresponding reduction of the defects such as base shell shake line.In casting process, the vibration behavior of crystallizer prevent base shell from boning and while improving cc billet surface quality also to the process of setting important of base shell, and existing correlative study does not take into full account that the vibration behavior of crystallizer is to the effect of base shell initial crack.Owing to there is complicated heat-power effect in crystallizer, could detect after the generation of base shell quality problems can only terminate completing cooled and solidified process and learn.Therefore, how to introduce the vibration behavior of crystallizer and in conjunction with meniscus initial set base shell reality, analyze the formation possibility of base shell shake line, taking corresponding reasonable instrument and supplies reduce and prevent the generation of this class behavior from just seeming particularly important in advance.Judge base shell shake line formation Water demand its stressedly whether reach Critical fracture condition, simple qualitative analysis truly can not reflect the mechanical state of base shell, and existing research still lack a kind of effectively, the determination methods that formed of base shell shake line easily.

Summary of the invention

For prior art Problems existing, the invention provides a kind of method based on force analysis prediction continuous casting billet initial crack.

Technical scheme of the present invention is:

Based on a method for force analysis prediction continuous casting billet initial crack, comprise the following steps:

Step 1: in casting process, determines the initial set base shell load in the vertical throwing direction of vibrating crystallizer menisci, comprises the slag road pressure that ferrostatic pressure and mold oscillation cause;

Step 2: according to the initial set base shell load determination initial set base shell material mechanics parameter in vertical throwing direction, comprise free beam moment of flexure, free beam xsect moment of inertia, free beam cross-section bending stress;

Step 3: determine steel grade high temperature Critical fracture intensity;

Step 4: by free beam cross sectional curve stress value compared with the steel grade high temperature Critical fracture intensity obtained, carry out the prediction of continuous casting billet initial crack: if free beam cross sectional curve stress value is greater than the steel grade high temperature Critical fracture intensity obtained, then the initial set base shell load in vertical throwing direction breaks through himself intensity, current continuous casting billet meniscus initial set base shell produces initial crack, otherwise current continuous casting billet meniscus initial set base shell does not produce initial crack.

Determination initial set base shell material mechanics parameter described in step 2, concrete steps are as follows:

Step 2.1: determine free beam moment of flexure;

In conjunction with actual crystallizer meniscus initial set base shell, set up free beam mechanical model to initial set base shell, calculate moment of flexure suffered by free beam, formula is as follows:

$M\left(x\right)=F_{A}x-{\∫}_0^{x}q\left(x\right)\mathrm{bdx}(x-x_R)$

In formula, M (x) is free beam x point xsect moment of flexure, Nm; x _rfor force action line position; B is meniscus initial set base shell width, i.e. free beam cross-sectional width, m;

Step 2.2: according to free beam cross-sectional width and free beam cross-sectional height determination free beam xsect moment of inertia;

Step 2.3: according to free beam moment of flexure and free beam xsect moment of inertia determination free beam cross-section bending stress.

Described step 3 is the composition information determination steel grade high temperature Critical fracture intensity according to steel grade.

Beneficial effect:

The present invention proposes a kind of computing method tentatively passing judgment on mild carbon steel continuous casting billet initial crack formation possibility based on force analysis, namely simplifying meniscus place initial set base shell based on theory of mechanics of materials is free beam, determine base shell stress state by bending in mold oscillation process, and contrast with its high temperature Critical fracture intensity level, to reach accurately, effectively to analyze the object of base shell mechanical state.

The present invention tentatively judges by stress analysis the method that mild carbon steel continuous casting billet initial crack produces based on a kind of of theory of mechanics of materials proposition, mold oscillation effect is converted into bending stress suffered by base shell, formed provide new thinking for analyzing base shell shake line, convenient, effectively preliminary judgement is made to the possibility that continuous casting billet initial crack is formed.

Accompanying drawing explanation

Fig. 1 is that the crystallizer of the specific embodiment of the invention simplifies geometric model schematic diagram;

Fig. 2 is the method flow diagram based on force analysis prediction continuous casting billet initial crack of the specific embodiment of the invention;

Fig. 3 is the meniscus mold flux channel pressure history of the specific embodiment of the invention;

Fig. 4 is the continuous cast mold meniscus initial set base shell free beam model schematic of the specific embodiment of the invention;

Fig. 5 is the initial set base shell stress changing curve by bending of the specific embodiment of the invention;

Fig. 6 is mild carbon steel ([C]=0.04%) the high temperature Critical fracture intensity temperature variation graph of a relation of the embodiment of the present invention 1;

Fig. 7 is medium carbon steel ([C]=0.358%) the high temperature Critical fracture intensity temperature variation graph of a relation of the embodiment of the present invention 2;

Fig. 8 is high-carbon steel ([C]=0.701%) the high temperature Critical fracture intensity temperature variation graph of a relation of the embodiment of the present invention 3.

Embodiment

Below in conjunction with drawings and Examples, specific embodiment of the invention is elaborated.

Present embodiment gets free beam length l, and Ji Zha road length is 0.008m; Ignore flux film thickness, meniscus initial set base shell width is 0.2m; Crystallizer physical dimension schematic diagram as shown in Figure 1, L=1200mm, b=200mm, H=700mm.

Based on a method for force analysis prediction continuous casting billet initial crack, as shown in Figure 2, comprise the following steps:

Step 1: in casting process, determines the initial set base shell load in the vertical throwing direction of vibrating crystallizer menisci, comprises the slag road pressure that ferrostatic pressure and mold oscillation cause;

q＝p _s+p _f

In formula, q is load suffered by the base shell of vertical throwing direction, Pa; p _sfor ferrostatic pressure, Pa; p _ffor slag road pressure, Pa;

The defining method (as document " under high pulling rate continuous casting billet Mechanism of Oscillation Mark Formation and oscillation parameter optimization ") of existing slag road pressure and ferrostatic pressure; Fig. 3 is the situation of change of mold oscillation typical time Dian Zha road pressure with distance under meniscus.Present embodiment selective freezing device vibrates positive slippage section produces peak suction c moment point due to maximum speed of related movement and analyzes.Now, slag road pressure is identical with ferrostatic pressure direction, and initial set base shell bearing load reaches maximum.

Step 2: according to the initial set base shell load determination initial set base shell material mechanics parameter in vertical throwing direction, comprise free beam moment of flexure, free beam xsect moment of inertia, free beam cross-section bending stress;

Step 2.1: determine free beam moment of flexure;

Due to covering slag consumption cyclical variation in mold oscillation slag road, and slag road pressure is comparatively remarkable to the effect of initial set base shell.So, as in Tu4Dui Zha road length range, initial set base shell sets up free beam model, and by carrying out the position of integral operation determination force action line to used load on free beam:

$x_R=\frac{{\∫}_0^{x}q\left(x\right)\mathrm{xdx}}{{\∫}_0^{x}q\left(x\right)\mathrm{dx}}$

In formula, x _rfor force action line position, m;

Present embodiment, on the basis determining force action line position, calculates A strong point place reacting force:

$F_A=\frac{l-x_R}{l}{\∫}_0^{l}q\left(x\right)\mathrm{bdx}$

In formula, F _afor free beam A holds strong point place reacting force, N; L is free beam length, m; B is meniscus initial set base shell width, i.e. free beam cross-sectional width, m;

According to load force action line position and in conjunction with strong point place reacting force, calculate free beam moment of flexure, formula is as follows:

$M\left(x\right)=F_{A}x-{\∫}_0^{x}q\left(x\right)\mathrm{bdx}(x-x_R)$

In formula, M (x) is free beam x point xsect moment of flexure, Nm; x _rfor force action line position, namely set the non-uniformly distributed load of 0-x section initial set base shell as one make a concerted effort time, this force action in the position of free beam, m; B is meniscus initial set base shell width, i.e. free beam cross-sectional width, m;

Step 2.2: according to free beam cross-sectional width and free beam cross-sectional height determination free beam xsect moment of inertia;

Definition free beam xsect is standard rectangular, and calculate its moment of inertia, formula is as follows:

$I=\frac{{\mathrm{bd}}^3}{12}$

In formula, I is square-section moment of inertia, m ⁴; D is free beam square-section height, i.e. meniscus initial set shell thickness, m;

Crystallizer meniscus initial set shell thickness is very little, about 1-2mm, and present embodiment is got meniscus initial set shell thickness 1.6mm and calculated.

Step 2.3: according to free beam moment of flexure and free beam xsect moment of inertia determination free beam cross-section bending stress.

Calculate free beam cross sectional curve stress according to fixed moment of flexure and moment of inertia, formula is as follows:

$\mathrm{\σ}=\frac{\mathrm{My}}{I}$

In formula, σ is free beam stress by bending, Nm ^-2; Y be xsect stress point to distance between center line, m;

The moment of inertia determined of moment of flexure step 2.1 determined and step 2.2 substitutes in bending stress formula, finally calculates base shell and bears bending stress and be:

$\mathrm{\σ}\left(x\right)=\frac{12y}{{\mathrm{bd}}^3}[x(1-\frac{{\∫}_0^{x}q\left(x\right)\mathrm{xdx}}{l{\∫}_0^{x}q\left(x\right)\mathrm{dx}}){\∫}_0^{l}q\left(x\right)\mathrm{bdx}-x{\∫}_0^{x}q\left(x\right)\mathrm{bdx}+{\∫}_0^{x}q\left(x\right)\mathrm{xbdx}$

In formula, σ is base shell bending stress, Nm ^-2; Y be xsect stress point to distance between center line, m;

The maximum stress in bend be subject to for cross section due to this method is discussed, and present embodiment defines xsect stress point at distance center line upper and lower two marginal point places farthest, namely ; Mold oscillation typical time point base shell bending stress with distance under meniscus situation of change as shown in Figure 5, wherein, vibration c moment point place base shell is by maximum stress in bend σ (x)=148.4kPa.

Step 3: according to the composition information determination steel grade high temperature Critical fracture intensity of steel grade;

Step 4: by free beam cross sectional curve stress value compared with the steel grade high temperature Critical fracture intensity obtained, carry out the prediction of continuous casting billet initial crack: if free beam cross sectional curve stress value is greater than the steel grade high temperature Critical fracture intensity obtained, then the initial set base shell load in vertical throwing direction breaks through himself intensity, current continuous casting billet meniscus initial set base shell produces initial crack, otherwise current continuous casting billet meniscus initial set base shell does not produce initial crack.

Embodiment 1

By mild carbon steel ([C]=0.04%) SSCT test figure, matching ejection shell is in the function changing relation formula of high-temperature region Critical fracture intensity and steel grade composition:

σ _max＝284.0686*[％C]+0.4863*[％Si]-1.8638*[％Mn]-63.0185*[％P]+115.7562*[％S]+2.9203*[％Al]-0.00805*T _int

In formula, T _intfor initial set base shell temperature, DEG C;

Get steel grade ([C] 0.04%, [Si] 0.1%, [Mn] 0.11%, [P] 0.013%, [S] 0.013%, [Al] 0.12%), liquidus temperature (1530.6 DEG C) and solidus temperature (1502.1 DEG C) is calculated according to steel grade composition, the solid phase fraction of setting meniscus solidification front is 0.9, then determine that meniscus initial solidification base shell temperature is 1506 DEG C.

Fig. 6 is the variation relation of this mild carbon steel ([C]=0.04%) high-temperature region Critical fracture intensity temperature.As seen from the figure, meniscus place initial set base shell bears maximum stress in bend and can reach 148.4kPa, and at this temperature, base shell Critical fracture intensity is only 119.1kPa.Now initial set base shell vertical throwing direction load force will break through himself intensity, and base shell initial crack starts to be formed.

Embodiment 2

By medium carbon steel ([C]=0.358%) SSCT test figure, matching ejection shell is in the function changing relation formula of high-temperature region Critical fracture intensity and steel grade composition:

σ _max＝81.149*[％C]-59.5764*[％Si]+135.887*[％Mn]-737.405*[％S]-1.0844*[％Al]-0.01922*T _int

In formula, T _intfor initial set base shell temperature, DEG C;

Get steel grade ([C] 0.358%, [Si] 0.15%, [Mn] 0.14%, [S] 0.015%, [Al] 0.015%), liquidus temperature (1505 DEG C) and solidus temperature (1414.5 DEG C) is calculated according to steel grade composition, the solid phase fraction of setting meniscus solidification front is 0.9, then determine that meniscus initial solidification base shell temperature is 1427 DEG C.

Fig. 7 is the variation relation of this medium carbon steel ([C]=0.358%) high-temperature region Critical fracture intensity temperature.As seen from the figure, meniscus place initial set base shell bears maximum stress in bend and can reach 148.4kPa, and at this temperature, base shell Critical fracture intensity is 634.8kPa.Now initial set base shell vertical throwing direction load force can not break through himself intensity, and meniscus place base shell initial crack is not yet formed.

Embodiment 3

By high-carbon steel ([C]=0.701%) SSCT test figure, matching ejection shell is in the function changing relation formula of high-temperature region Critical fracture intensity and steel grade composition:

σ _max＝-25.613*[％C]-101.345*[％Si]+129.6665*[％Mn]+3246.755*[％P]+176.4084*[％S]+12.502*[％Al]-0.0114*T _int

In formula, T _intfor base shell surface temperature, DEG C;

Get steel grade ([C] 0.701%, [Si] 0.52%, [Mn] 0.32%, [P] 0.011%, [S] 0.012%, [Al] 0.56%) and calculate its liquidus temperature (1475 DEG C) and solidus temperature (1319 DEG C) according to steel grade composition, the solid phase fraction of setting meniscus solidification front is 0.9, then can determine that meniscus initial solidification base shell temperature is 1342 DEG C.

Fig. 8 is the variation relation of this high-carbon steel ([C]=0.701%) high-temperature region Critical fracture intensity temperature.As seen from the figure, meniscus place initial set base shell bears maximum stress in bend and can reach 148.4kPa, and at this temperature, base shell Critical fracture intensity is 372.9kPa.Now initial set base shell vertical throwing direction load force can not break through himself intensity, and meniscus base shell initial crack is not yet formed.

Claims (3)

1., based on a method for force analysis prediction continuous casting billet initial crack, it is characterized in that: comprise the following steps:

Step 1: in casting process, determines the initial set base shell load in the vertical throwing direction of vibrating crystallizer menisci, comprises the slag road pressure that ferrostatic pressure and mold oscillation cause;

Step 2: according to the initial set base shell load determination initial set base shell material mechanics parameter in vertical throwing direction, comprise free beam moment of flexure, free beam xsect moment of inertia, free beam cross-section bending stress;

Step 3: determine steel grade high temperature Critical fracture intensity;

Step 4: by free beam cross sectional curve stress value compared with the steel grade high temperature Critical fracture intensity obtained, carry out the prediction of continuous casting billet initial crack: if free beam cross sectional curve stress value is greater than the steel grade high temperature Critical fracture intensity obtained, then the initial set base shell load in vertical throwing direction breaks through himself intensity, current continuous casting billet meniscus initial set base shell produces initial crack, otherwise current continuous casting billet meniscus initial set base shell does not produce initial crack.

2. the method based on force analysis prediction continuous casting billet initial crack according to claim 1, it is characterized in that: the determination initial set base shell material mechanics parameter described in step 2, concrete steps are as follows:

Step 2.1: determine free beam moment of flexure;

In conjunction with actual crystallizer meniscus initial set base shell, set up free beam mechanical model to initial set base shell, calculate moment of flexure suffered by free beam, formula is as follows:

$M\left(x\right)=F_{A}x-{\∫}_0^{x}q\left(x\right)\mathrm{bdx}(x-x_R)$

In formula, M (x) is free beam x point xsect moment of flexure, Nm; x _rfor force action line position; B is meniscus initial set base shell width, i.e. free beam cross-sectional width, m;

Step 2.2: according to free beam cross-sectional width and free beam cross-sectional height determination free beam xsect moment of inertia;

Step 2.3: according to free beam moment of flexure and free beam xsect moment of inertia determination free beam cross-section bending stress.

3. the method based on force analysis prediction continuous casting billet initial crack according to claim 1, is characterized in that: described step 3 is the composition information determination steel grade high temperature Critical fracture intensity according to steel grade.