CN115846405A

CN115846405A - Method for preparing high-strength steel with low surface white line defects and high-strength steel

Info

Publication number: CN115846405A
Application number: CN202211667337.9A
Authority: CN
Inventors: 王畅; 于洋; 王林; 倪有金; 付光; 张亮亮; 高小丽; 王泽鹏; 李高峰; 颜晨曦; 刘李斌; 李金保; 武巧玲; 焦会立
Original assignee: Shougang Group Co Ltd; Beijing Shougang Co Ltd
Current assignee: Shougang Group Co Ltd; Beijing Shougang Co Ltd
Priority date: 2022-12-23
Filing date: 2022-12-23
Publication date: 2023-03-28

Abstract

The application relates to the technical field of steel rolling, in particular to a method for preparing high-strength steel with low surface white line defects and the high-strength steel; the method comprises the following steps: heating, roller preheating and continuous rolling are carried out on the casting blank to obtain strip steel; cold rolling the strip steel, and then annealing and leveling to obtain high-strength steel with low surface white line defects; wherein the continuous rolling is carried out by adopting an infinite chilled roll; the roller preheating comprises the step of preheating the infinite chilled roller by using a hot roller material, wherein the preheating end point temperature is not more than 880 ℃; the graphite spheroidization grade of the infinite chilled roll is more than or equal to grade 2; the high-strength steel comprises the following chemical components: c, si, mn, P, S, al, B, nb, ti; the preheating temperature of the infinite chilled roll and the graphite spheroidization grade of the infinite chilled roll in the rolling stage are controlled, so that the thickness of an oxide film and the surface oxide film of the infinite chilled roll are ensured to be difficult to fall off, and the generation of surface white line defects caused by the falling off of the oxide film is avoided.

Description

Method for preparing high-strength steel with low surface white line defects and high-strength steel

Technical Field

The application relates to the technical field of steel rolling, in particular to a method for preparing high-strength steel with low-surface white line defects and the high-strength steel.

Background

Modern automobiles, especially high-grade and luxury saloon cars, have very important surface brightness, beauty and good painting performance in the quality requirements of the automobile plates, especially the high-grade and luxury saloon cars require clean and flawless steel plate surfaces, and the outer plates all require cold-rolled plates with O5 grade and flatness higher than 5I; in the production process of the steel plate, the steel strip can contact hundreds of pairs of rollers, rolling, trimming shears, transverse shearing shears and the like, and the final steel plate product does not allow any scratch, impression and spot marks, but actually, the generation of the surface defects of the plate strip runs through all processes from smelting, continuous casting to hot rolling, cold rolling, annealing, flattening and packaging, so that short linear iron sheet defects frequently occur when the high-strength IF steel is used for producing an automobile outer plate; however, the defects exist on the surface of the steel plate only in cold rolling through field back inspection, and no obvious corresponding defects exist in the hot rolling process.

Although the feedback of the current reports of the iron sheet pressing defects is closely related to the use of the roller, most research and solutions aim at high-speed steel type press rollers, but aim at non-high-speed steel rollers, especially infinite chilled rollers, and the occurrence of the defects cannot be effectively reduced at present, so that how to provide a preparation method for reducing the white line defects on the surface of high-strength steel to reduce the white line defects on the surface of the high-strength steel after the infinite chilled rollers are cold-rolled is a technical problem which needs to be solved at present.

Disclosure of Invention

The application provides a method for preparing high-strength steel with low surface white line defects and high-strength steel, and aims to solve the technical problem that in the prior art, the surface white line defects of an infinite chilled roll after cold rolling are difficult to reduce in the preparation process of the high-strength steel.

In a first aspect, the present application provides a method of producing a high strength steel with low surface white line type defects, the method comprising:

heating, roller preheating and continuous rolling are carried out on the casting blank to obtain strip steel;

cold rolling the strip steel, and then annealing and flattening to obtain high-strength steel with low surface white line defects;

wherein the continuous rolling is carried out by adopting an infinite chilled roll;

the roller preheating comprises the step of preheating the infinite chilled roller by using a hot roller material, wherein the preheating end point temperature is not more than 880 ℃;

the graphite spheroidization grade of the infinite chilled roller is more than or equal to grade 2.

Optionally, the number of the ironing roller materials is more than or equal to 10.

Optionally, the number of the continuously rolled casting blanks is less than or equal to 15.

Optionally, the continuous rolling further comprises adding wear-resistant particles for continuous rolling, wherein the diameter of the wear-resistant particles is less than 5 μm.

Optionally, the chemical composition of the wear-resistant particles satisfies:

[V]/[Nb]＝0.5～1.5:1，

wherein [ V ] is the content of V in the wear-resistant particles, and [ Nb ] is the content of Nb in the wear-resistant particles.

Optionally, the continuous rolling comprises rough rolling, rough rolling descaling, finish rolling descaling and finish rolling, and the descaling water pressure of the rough rolling descaling and the finish rolling descaling is 18 MPa-22 MPa.

Optionally, the inlet temperature of the finish rolling is 1000-1040 ℃, and the finish rolling temperature of the finish rolling is 880-900 ℃.

Optionally, the cooling water pressure between two adjacent stands of the finish rolling is 8MPa to 10MPa, and the cooling water input mass ratio between two adjacent stands of the finish rolling is 0.5 to 0.8.

Optionally, the soaking temperature for heating is 1180-1200 ℃, the heating time is 140-160 min, and the lambda value for heating is 0.8-0.9.

In a second aspect, the present application further provides a high-strength steel prepared by the method of the first aspect, wherein the high-strength steel comprises the following chemical components by mass fraction: 0.0015 to 0.004 percent of C, 0.05 to 0.12 percent of Si, 0.3 to 0.5 percent of Mn, 0.03 to 0.05 percent of P, 0.01 to 0.02 percent of S, 0.03 to 0.05 percent of Al, 0.0004 to 0.0008 percent of B, 0.025 to 0.035 percent of Nb, 0.035 to 0.045 percent of Ti, and the balance of Fe and inevitable impurities.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:

according to the method for preparing the high-strength steel with the low surface white line defects, the preheating temperature of the infinite chilled roll in the rolling stage and the graphite spheroidization grade of the infinite chilled roll are controlled, the oxidation film thickness of the infinite chilled roll is increased due to the fact that the infinite chilled roll is oxidized at an accelerated speed at a temperature higher than 1080 ℃, the oxidation film on the infinite chilled roll is easy to fall off in the subsequent cold rolling stage and is pressed into a steel plate to form the surface white line defects, therefore, the temperature requirement of a casting blank in the rolling process is comprehensively considered, the use temperature of the infinite chilled roll is controlled to be below 880 ℃, the thickness of the oxidation film of the infinite chilled roll is guaranteed, the graphite spheroidization grade of the infinite chilled roll is controlled, the graphite in the roll mainly plays a lubricating role, the peeling defect of the roll body surface can be relieved, the thermal shock on the roll surface can be relieved, the spheroidization grade of the graphite of the infinite chilled roll is controlled on the premise that the use temperature of the infinite chilled roll is guaranteed, the surface oxidation film of the infinite chilled roll is difficult to fall off, the surface white line defects caused by the falling of the oxidation film are avoided, and the surface white line defects of the steel plate after the infinite chilled roll is guaranteed only to have fewer surface white line defects.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.

Fig. 1 is a schematic flow chart of a method provided in an embodiment of the present application;

FIG. 2 is a schematic view of a macro topography of a surface white line defect provided by an embodiment of the present application;

FIG. 3 is a schematic view of the micro-topography of a surface white line defect according to an embodiment of the present application;

FIG. 4 is an enlarged schematic view of the micro-topography of a surface white line defect provided by an embodiment of the present application;

FIG. 5 is a graph showing the result of the spectrum analysis of the scab-like body in the surface white line defect according to the embodiment of the present disclosure;

FIG. 6 is an enlarged view of the analysis results of the C element of the scar-like scar-body interface electron probe in the surface white line defect provided in the embodiment of the present application;

fig. 7 is a diagram illustrating a result of analyzing C element of a scab-like scab body interface electron probe in a surface white line defect according to an embodiment of the present application;

FIG. 8 is a diagram illustrating the results of O element analysis of the scar-like body interface electron probe in the surface white line defect according to the embodiment of the present disclosure;

FIG. 9 is a graph showing the results of Si analysis of the scar-like body interface electron probe in the surface white line defect provided in the embodiment of the present application;

fig. 10 is a diagram illustrating a result of analyzing Cr element in a scar-like scar-body interface electron probe in a surface white line defect according to an embodiment of the present application;

FIG. 11 is a diagram illustrating the results of analyzing Ni elements in the scar-like scar-body interface electron probe in the surface white line defects according to the embodiment of the present disclosure;

fig. 12 is a diagram illustrating an energy spectrum analysis result of a scab-like, in-vivo, blocky white and bright metal in a surface white line defect provided in an embodiment of the present application;

FIG. 13 is a graph illustrating an oxidation weight gain curve for an indefinite chilled roll according to an embodiment of the present disclosure;

FIG. 14 is a graph showing the results of the oxidation of graphite in an infinitely variable chilled roll under the heating condition of 800 deg.C according to the present embodiment;

FIG. 15 is a schematic view of a problem graphite in the structure of an indefinite chilled roll according to an embodiment of the present application;

fig. 16 is a schematic view of a state of a problem wear-resistant particle of an indefinite chilled roll according to an embodiment of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the protection scope of the present application.

The inventive thinking of the application is that: at present, domestic manufacturers analyze the defects of the expression white lines, and the method specifically comprises the following steps:

(1) The small white strip defects generated on the surface of the pickling plate are distributed on the surface of the strip steel along the length direction in a full-length mode, the defects are in a fine strip shape, the surface is rough and has hand feeling, and the small white strip defects are analyzed to be in a corresponding relation with the meteor-shaped stripping of the M part of the surface of the high-speed steel roller of the front frame;

(2) When 2.0mm export materials are produced, the surface of hot rolled strip steel in a finish rolling area has pit-shaped iron scale defects in batches, and the defects can not be removed after pickling, thus forming a large amount of improvement judgment. The analysis shows that the iron scale is high in density at the initial stage of formation and distributed in a pockmark shape with the high-speed steel roller, the degree of the iron scale is gradually reduced along with the continuation of the rolling process, and finally the iron scale is in a belt shape.

In one embodiment of the present application, there is provided a method of producing a high strength steel having low surface white line type defects, the method comprising:

s1, heating, roller preheating and continuous rolling are carried out on a casting blank to obtain a strip steel;

s2, cold rolling the strip steel, and then annealing and leveling to obtain high-strength steel with low-surface white line defects;

In the embodiment of the application, the positive effect of controlling the preheating end point temperature to be not more than 880 ℃ is that in the range of the end point temperature, the stable and compact oxide film can be formed on the surface of the infinite chilled roll, the thickness of the oxide film is ensured to be in a proper range, and the situation that the surface of the infinite chilled roll is cracked and falls off due to the fact that the temperature is too high and the thicker oxide film is formed on the surface of the infinite chilled roll is avoided.

The positive effect that the graphite spheroidization grade of the infinite chilled roll is more than or equal to grade 2 is that the graphite plays a role in lubricating the roll, so that the peeling defect of the surface of the roll body can be reduced, and the thermal shock on the surface of the roll can be relieved; when the graphite spheroidization grade does not meet grade 2 or above, the graphite spheroidization state on the surface of the roller is poor, the roller presents worm-shaped and sea urchin-shaped appearances, and the condition of hard and soft interphase cracking in the use process of the boundary position is caused.

In some optional embodiments, the number of the ironing roller materials is more than or equal to 10.

In the embodiment of the application, the quantity of the hot roller materials is controlled, so that the temperature of the surface of the infinite chilled roller can reach below 880 ℃, and the generation of the surface oxidation film layer of the infinite chilled roller can be more complete.

In some alternative embodiments, the number of continuously rolled billets is less than or equal to 15.

In the embodiment of the application, the positive effect of controlling the number of continuously rolled casting blanks to be less than or equal to 15 is that the thickness of the oxide film on the surface of the steel plate can be reduced in the range of the number of continuously rolled casting blanks; when the rolling quantity is greater than or less than the end value of the range, the adverse effect is that a compact oxide film is not formed on the surface of the roller when the rolling quantity is too low, the condition of uneven surface oxide scales is easy to occur in the rolling process, the oxide film on the surface of the roller grows too thick when the rolling quantity is too high, the condition of oxide film peeling is easy to occur in the rolling process, and the pressing-in defects of the roller scales are easy to cause.

In some alternative embodiments, the continuous rolling further comprises adding wear resistant particles to the continuous rolling, the wear resistant particles having a diameter < 5 μm.

In the embodiment of the application, the positive effect of controlling the diameter of the wear-resistant particles to be less than 5 microns is that in the diameter range, the material can be ensured to generate high-hardness and fine-dispersion-distributed carbide (M-C or M-N) during high-temperature crystallization, so that the surface of a steel plate is ensured to have no white line defect; when the diameter is larger than the end point of the range, the adverse effect is fatigue cracking caused by the difference between the hardness of the wear-resistant particles and the hardness of the body in the use process of the roller.

In some alternative embodiments, the chemical composition of the wear resistant particles satisfies:

[V]/[Nb]＝0.5～1.5:1，

In the embodiment of the application, the positive effect of [ V ]/[ Nb ] = 0.5-1.5 is that in the proportion range, the formation of refined and dispersedly distributed wear-resistant particles can be ensured; when the value of the proportion is larger than or smaller than the end value of the range, the wear-resistant particles are in a state of large block aggregation distribution or too little precipitation, and the rolling of the steel is influenced.

In some optional embodiments, the continuous rolling comprises rough rolling, rough rolling descaling, finish rolling descaling and finish rolling, and the descaling water pressure of the rough rolling descaling and the finish rolling descaling is 18 MPa-22 MPa.

In the embodiment of the application, the positive effects that the descaling water pressure for rough rolling descaling and finish rolling descaling is controlled to be 18 MPa-22 MPa are that the surface scale is effectively removed, and the scale is prevented from being pressed into a steel plate to form surface defects; when the value of the pressure is larger than or smaller than the end value of the range, the scale cannot be removed due to too low pressure, and the descaling pressure system is unstable due to too high pressure.

In some alternative embodiments, the entry temperature of the finish rolling is 1000 ℃ to 1040 ℃, and the finish rolling temperature of the finish rolling is 880 ℃ to 900 ℃.

In the embodiment of the application, the positive effect that the inlet temperature of finish rolling is 1000-1040 ℃ is beneficial to ensuring that the iron sheet structure in the finish rolling process is mainly FeO, the FeO content reaches over 95 percent, the iron sheet structure has better plastic deformation capability, and the problem of crushing and cracking in the rolling process is not easy to occur; when the temperature value is larger than or smaller than the end point value of the range, the adverse effect is that the FeO proportion is reduced and changed in the finish rolling process, and the problem of iron sheet crushing and cracking in the rolling process is easy to occur.

The positive effect of controlling the finish rolling temperature of finish rolling to be 880-900 ℃ is to avoid the steel grade from falling into a two-phase region for rolling; when the value of the temperature is larger than or smaller than the end value of the range, the adverse effect is that the temperature is too low, the temperature is easy to fall into a two-phase region for rolling, and the surface structure of the steel plate is easy to be abnormal; if the temperature is too high, the surface temperature of the strip steel rises, so that the surface temperature of a roller rises, and the oxide film is easy to break and crack due to too thick oxide film.

In some optional embodiments, the finish rolling has a steel throwing speed of 8m/s to 10m/s and the finish rolling has an inter-stand cooling water pressure of 8MPa to 10MPa.

In the embodiment of the application, the positive effect that the steel throwing speed of the finish rolling is 8-10 m/s is to ensure that the thickness of an oxide film in the finish rolling process is controlled to be lower; when the value of the steel throwing speed is larger than or smaller than the end point value of the range, the adverse effect is caused that the rolling stability is in risk due to overhigh speed, and the situations of deviation and rolling waste are easy to occur; and an over-thick iron sheet is formed in the process of finish rolling at too low speed, and the steel sheet is easy to crack and press in the rolling process.

The positive effect that the cooling water pressure between the finish rolling frames is 8 MPa-10 MPa is to effectively reduce the surface temperature of the steel plate and inhibit the excessive growth of iron sheet; when the value of the cold water pressure is larger than or smaller than the end value of the range, the adverse effect is that the iron sheet on the surface of the steel plate cannot be effectively controlled due to too low water pressure, and the situation of unstable pressure occurs due to too high water pressure, and the situations of mixed crystals and the like caused by the surface structure of the steel plate and the mechanical property are possibly influenced.

In some optional embodiments, the finish-rolled intermediate slab has a thickness of 32mm to 38mm, the reduction ratio of the finish-rolled fourth stand is 30% or less, and the reduction ratio of the finish-rolled fifth stand is 20% or less.

In the embodiment of the application, the positive effect that the thickness of the finish-rolled intermediate billet is 32-38 mm is to transfer the rolling load, reduce the rolling load in the finish rolling process and avoid the condition that the compression ratio is too large and exceeds the deformation limit of FeO; when the thickness of the intermediate billet is larger than or smaller than the end point value of the range, the adverse effect is that a large amount of dislocation generation cannot be effectively completed in the finish rolling process if the thickness of the intermediate billet is too low, and the nucleation and fine grain effects are realized; if the thickness is too large, the situation that FeO cannot deform along with the matrix to cause cracking is easy to occur when the compression ratio in the finish rolling process is too large.

The rolling reduction rate of the finish rolling fourth frame is less than or equal to 30 percent, so that the stability of the roller oxide film is ensured; when the reduction ratio is larger or smaller than the end point value of the range, the adverse effect is that the compression deformation of the whole finish rolling process cannot be ensured if the reduction ratio is too low, and the peeling and crushing of the roller oxide film are easy to occur if the reduction ratio is too high.

The positive effect that the reduction rate of the finish rolling fifth frame is less than or equal to 20 percent is to ensure the stability of the roller oxidation film; when the value of the reduction rate is larger than or smaller than the end point value of the range, the adverse effect is too low, the compression deformation of the whole finish rolling process cannot be ensured, and the surface layer mixed crystal condition is easy to occur; if the temperature is too high, the oxide film of the roll is liable to peel and break.

In some optional embodiments, the cooling water pressure between two adjacent stands of the finish rolling is 8MPa to 10MPa, and the cooling water input mass ratio between two adjacent stands of the finish rolling is 0.5 to 0.8.

In the embodiment of the application, the positive effect that the cooling water pressure between two adjacent frames for finish rolling is 8-10 MPa is that the surface temperature of the steel plate is effectively reduced, and the excessive growth of iron scales is inhibited; when the value of the cold water pressure is larger than or smaller than the end value of the range, the adverse effect is that the iron sheet on the surface of the steel plate cannot be effectively controlled due to too low water pressure, and the situation of unstable pressure occurs due to too high water pressure, and the situations of mixed crystals and the like caused by the surface structure of the steel plate and the mechanical property are possibly influenced.

The active effect that the cooling water input mass ratio between two adjacent frames for finish rolling is 0.5-0.8 is to ensure the surface effect of the cooling steel plate and avoid the generation of a large amount of iron scale; when the value of the ratio is larger or smaller than the end value of the range, a large amount of scale is generated, resulting in scale indentation.

In some optional embodiments, the soaking temperature of the heating is 1180-1200 ℃, the heating time is 140-160 min, and the lambda value of the heating is 0.8-0.9.

In the embodiment of the application, the positive effect of controlling the soaking temperature of heating to 1180-1200 ℃ is that the stable state of the oxide film of the roller can be ensured in the temperature range; when the value of the temperature is larger than or smaller than the end value of the range, the adverse effect is that the temperature of the heating furnace is too high, the surface temperature is high due to heredity in the steel plate finish rolling process, the surface temperature of the roller is too high, the oxide film falling condition is easy to occur, the surface temperature of the steel plate is too low in the heating temperature finish rolling process, the rolling force is too large, the roller fatigue cracking and the oxide film falling problem are easy to occur, and meanwhile, the problem that the Nb-Ti precipitate separated out in the continuous casting process is not effectively redissolved can be caused.

The positive effect of controlling the heating time to be 140-160 min is that the stable state of the oxide film of the roller can be ensured within the temperature range; when the time value is larger than or smaller than the end value of the range, the adverse effect is caused by that the heating temperature is too low to cause the steel burning to be impermeable, the austenitizing is insufficient, and the performance fluctuation in the rolling process is obvious; the problems of iron sheet residue and press-in are caused by overhigh surface temperature and too thick iron sheet due to overhigh heating temperature.

The positive effect of controlling the lambda value of heating to be 0.8-0.9 is that the stable state of the oxide film of the roller can be ensured within the range of the lambda value; when the value of the lambda value is larger than or smaller than the end value of the range, the adverse effect is that a large amount of oxidation occurs in the heating process of the steel grade due to overhigh value, the fluctuation of the gas pressure in the furnace is large due to overlow value, and the oxidation atmosphere is difficult to control.

Based on the same inventive concept, the embodiment of the application also provides the high-strength steel, which is prepared by the method, and the high-strength steel comprises the following chemical components in percentage by mass: 0.0015 to 0.004 percent of C, 0.05 to 0.12 percent of Si, 0.3 to 0.5 percent of Mn, 0.03 to 0.05 percent of P, 0.01 to 0.02 percent of S, 0.03 to 0.05 percent of Al, 0.0004 to 0.0008 percent of B, 0.025 to 0.035 percent of Nb, 0.035 to 0.045 percent of Ti, and the balance of Fe and inevitable impurities.

In the embodiment of the application, the positive effect that the mass fraction of C is 0.0015-0.004% is to ensure the formability, low yield strength, high uniform elongation and total elongation of the steel grade; when the value of the mass fraction is larger than or smaller than the end value of the range, the adverse effect is caused because the {111} component in the recrystallization texture is sharply reduced along with the increase of solid solution C, if the C element is controlled to be too low, the smelting cost in the process is increased, and the mechanical property of the steel can not be achieved through precipitation strengthening.

The positive effect that the mass fraction of Si is 0.05-0.12% is that the strength of the steel is ensured by solid solution strengthening; when the mass fraction is greater or less than the end point value of the range, the adverse effect will be that the intensity is too low or too high to meet the user's needs.

The positive effect that the mass fraction of Mn is 0.3-0.5% is that the strength of the steel is ensured by solid solution strengthening; when the value of the mass fraction is larger or smaller than the endpoint value of the range, the adverse effect is that the intensity is too low or too high to meet the user requirement.

The positive effect that the mass fraction of P is 0.03-0.05% is that the strength of the steel is greatly improved by the solid solution strengthening effect; when the mass fraction is larger than or smaller than the end point value of the range, the adverse effect is that the solid solution strengthening effect cannot be achieved due to too low mass fraction, and the brittle cracking of the steel plate is easily caused by P crystal boundary precipitation due to too high mass fraction.

The positive effect that the mass fraction of S is 0.01-0.02% is that sulfur is a harmful element in deep drawing steel, and is reduced as much as possible, so that a large amount of inclusions are easily generated and Ti \ Nb elements are consumed, and the precipitation strengthening effect cannot be achieved; when the mass fraction is larger or smaller than the end point of the range, the formation of a large amount of inclusions affects the deep drawability of the product, which is an adverse effect.

The Al with the mass fraction of 0.03-0.05 percent has the positive effects that the Al is added as a deoxidizer and mainly has the function of removing oxygen dissolved in molten steel during oxygen blowing smelting; when the mass fraction is larger or smaller than the end value of the range, the adverse effect is that the deoxidation cannot be effectively carried out due to too low mass fraction and the mechanical property of the product is affected due to too high mass fraction.

The positive effect that the mass fraction of B is 0.0004% -0.0008% is that the cold brittleness transformation temperature of IF steel can be obviously reduced, and because the element P is added into the steel, the element B can be segregated in the grain boundary, and the grain boundary segregation of the element P is inhibited; when the mass fraction is larger or smaller than the end value of the range, the adverse effect is that cost loss is caused by too high mass fraction, and the P element segregation inhibition effect cannot be achieved when the mass fraction is too low.

The positive effect that the mass fraction of Nb is 0.025-0.035% is precipitation strengthening effect, and the mechanical property of the steel is improved; when the value of the mass fraction is greater than or less than the endpoint value of the range, the adverse effect will be that the performance cannot meet the user's requirements.

The positive effect of Ti mass fraction of 0.035-0.045% is precipitation and fine grain strengthening effect, and the mechanical property of steel is improved; when the value of the mass fraction is greater than or less than the endpoint value of the range, the adverse effect will be that the performance cannot meet the user's requirements.

Example 1

By analyzing the defects shown in FIG. 2, the defects extend along the rolling direction, the width of the defects is about 0.2 mm-0.5 mm, the length of the defects is 2 mm-5 mm, the defects generally present the appearance characteristics of elongated white lines, the surface microscopic analysis is shown in FIGS. 3-12,

as shown in fig. 5, the in-vivo corresponding energy spectrum analysis of the scar, and the chemical component analysis of different spectrogram sites are shown in table 1:

TABLE 1

Spectrogram	O(％)	Si(％)	Cr(％)	Mn(％)	Fe(％)	Ni(％)	Mo(％)	Total (%)
									Spectrogram 1	3.37	1.26	4.12	0.83	89.61	0.83	-	100.00
Spectrogram 2	2.35	-	8.15	2.09	84.60	2.80	-	100.00
									Spectrogram 3	8.07	0.75	3.74	2.58	74.64	8.25	1.96	100.00
Spectrogram 4	4.31	1.71	1.22	1.15	83.53	8.08	-	100.00
									Spectrogram 5	4.64	0.91	3.18	1.57	84.16	5.53	-	100.00
Spectrogram 6	10.71	-	8.71	1.35	77.11	2.12	-	100.00
									Spectrogram 7	-	-	-	-	100.00	-	-	100.00
Spectrogram 8	-	-	-	-	100.00	-	-	100.00
									Spectrogram 9	-	-	-	-	100.00	-	-	100.00

As shown in fig. 12, for the energy spectrum analysis of the massive white and bright metal in the scar, the chemical component analysis of different spectrum sites is shown in table 2:

TABLE 2

The results show that: 1) The inside of the cold and hard coil defect has a scab-shaped broken shape, and more ferric oxide residues exist around a scab body; 2) After the surface is polished, the inside is analyzed and found to be in a scab-shaped string defect shape, the scar body is found to be a ferrite tissue after the tissue erosion, and the inside tissue is slightly fine; 3) The surface of most scar bodies captures Ni-Cr-Mo element residues at multiple positions and has a corresponding relation with the components of the F4-F6 roller of the finish rolling machine frame; 4) The scar body interface analysis shows that more cracks and oxidation round dots exist in the scar body, ni-Cr-Si alloy elements are adhered to the area corresponding to the scar body surface, and an oxidation phenomenon exists; 5) A large amount of Nb element residues can be captured on the surface of an individual scar, a bright white metal state is presented, the content can reach 8% -80%, and the Nb element residues are related to the falling of hard wear-resistant phases in the roller.

Analysis of oxidation characteristics: according to the temperature rise rate of 10 ℃/min and the oxidation weight gain curve shown in figure 13, the roller has better oxidation resistance at 1000 ℃, the whole oxidation weight gain is controlled within 0.25%, when the steel is heated to 1080 ℃ to generate an accelerated oxidation condition, the peak position of the oxidation weight gain rate is about 1130 ℃, the DTG can reach 0.2%/min, then the oxidation weight gain rate is slowed down, the oxidation weight gain rate of the steel increases along with the continuous temperature rise of 1200 ℃, the oxidation weight gain rate of the steel has an increasing trend, and the oxidation resistance of the roller is weakened along with the temperature rise, so the control idea is mainly to reduce the use temperature of the roller.

As shown in fig. 14, when the isothermal oxidation experiment at different temperatures is performed, it is found that, when the experiment is heated at 800 ℃ for 1 hour, a situation that graphite is significantly oxidized and thickened occurs in the oxidation process, and an inward oxidation situation exists inside the body, so that with the increase of the oxidation temperature, as the oxidation time is prolonged, different elements in the roller are selectively oxidized, and since the main element in the graphite is C, and the oxidation phenomenon is more likely to occur under the high-temperature condition of the C element, the roller oxide film is more likely to be stripped in the use process, and the stripped object is pressed into the substrate to form a surface white line defect.

Analyzing the tissue condition: as the graphite in the roller mainly plays a role in lubrication, the peeling defect of the surface of the roller body can be relieved, and the thermal shock on the surface of the roller can be relieved, but if the spheroidization state of the graphite on the surface of the roller is not good, as shown in figure 15, the graphite presents a worm-shaped or sea urchin-shaped appearance, and the appearance causes the situation of hard-soft interphase cracking in the use process of a boundary position.

At present, the improved ICDP roller is realized by adding V and Nb to a common ICDP roller to form wear-resistant particles so as to enhance the performance, and the wear-resistant particles are formed by adding special alloy elements (Nb, V, W and the like) into a nickel-chromium-molybdenum material so that the material is crystallized into high-hardness finely dispersed carbide (M-C or M-N) at a high temperature. As the content of Nb is increased, the wear-resistant particles are oversize to form massive distribution, but in order to ensure that wear-resistant particles with refined and dispersed distribution are formed, the mass fraction ratio of V to Nb is preferably 1: otherwise, the wear-resistant particles are likely to be precipitated too little or aggregated and distributed in large blocks.

Respectively controlling the smelting process and the rolling process of the high-strength steel according to the defect data and the tissue oxidation characteristic data to obtain a high-strength steel outer plate without surface white line defects; the specific idea is as follows:

according to the mass fraction, the chemical components of the steel grade in the high-strength steel smelting process are controlled as follows: 0.002% of C, 0.1% of Si, 0.4% of Mn, 0.04% of P, 0.01% of S, 0.04% of Al, 0.0006% of B, 0.03% of Nb, 0.04% of Ti, and the balance of Fe and inevitable impurities.

Before rolling the high-strength steel, 10 infinite chilled rolls need to be ironed and then rolled, the final rolling temperature of the ironed roll material before rolling the high-strength steel is 860 ℃, and the continuous rolling quantity of the ironed roll material before rolling the high-strength steel is 10

Controlling heating in the high-strength steel rolling process: controlling the soaking temperature of heating to 1180 ℃, the heating time of heating to 150min and the lambda value of heating to 0.9.

The dephosphorization process in the rolling process of the high-strength steel is controlled as follows: and the rough rolling is controlled to adopt three times of dephosphorization, the finish rolling inlet is controlled to adopt two times of dephosphorization, and the pressure of dephosphorization is controlled to be 22MPa.

Controlling a finish rolling stage in the high-strength steel rolling process: controlling the inlet temperature of finish rolling to be 1030 ℃, the finish rolling temperature of the finish rolling to be 890 ℃, the steel throwing speed of the finish rolling to be 9m/s, and the cooling water pressure between the racks of the finish rolling to be 9MPa.

The thickness of the intermediate billet in the finish rolling stage is controlled to be 36mm, the reduction ratio of the fourth stand for finish rolling is controlled to be 25%, and the reduction ratio of the fifth stand for finish rolling is controlled to be 15%.

Controlling the thermal fatigue characteristics in the rolling process of the high-strength steel: a fourth rack to a sixth rack for controlling finish rolling adopt new rollers to roll on the machine, and the first rack to the third rack adopt rollers with the roller surface level reaching 1 level; and controlling the cooling water consumption ratio between the first rack and the second rack of the finish rolling to be 0.8, controlling the cooling water consumption ratio between the second rack and the third rack of the finish rolling to be 0.6, and performing rolling lubrication in the rolling process.

Controlling the structure condition of an infinite chilled roll in the rolling process of high-strength steel: controlling the graphite spheroidization grade in the infinite chilled roller to be more than or equal to grade 2.

Controlling the diameter of the wear-resistant particles to be 3 mu m;

controlling the wear-resistant particles to meet the following requirements: [ V ]/[ Nb ] =1, where [ V ] is the V content in the wear-resistant particles and [ Nb ] is the Nb content in the wear-resistant particles.

Example 2

Example 2 is compared to example 1, with example 2 differing from example 1 in that:

according to the mass fraction, the chemical components of the steel grade in the high-strength steel smelting process are controlled as follows: 0.0015 percent of C, 0.05 percent of Si, 0.3 percent of Mn, 0.03 percent of P, 0.01 percent of S, 0.03 percent of Al, 0.0004 percent of B, 0.025 percent of Nb, 0.035 percent of Ti, and the balance of Fe and inevitable impurities.

Controlling heating in the high-strength steel rolling process: controlling the soaking temperature of heating to 1180 ℃, controlling the heating time to 140min, and controlling the lambda value of the heating stage to be 0.8.

Controlling a dephosphorization process in the high-strength steel rolling process: and the rough rolling is controlled to adopt three times of dephosphorization, the finish rolling inlet is controlled to adopt two times of dephosphorization, and the pressure of dephosphorization is controlled to be 18MPa.

Controlling finish rolling in the high-strength steel rolling process: controlling the inlet temperature of finish rolling to be 1000 ℃, the finish rolling temperature of finish rolling to be 880 ℃, the steel throwing speed of finish rolling to be 8m/s, and the cooling water pressure between frames of finish rolling to be 8MPa.

The thickness of the intermediate billet in the finish rolling stage is controlled to be 32mm.

Controlling thermal fatigue characteristics in the high-strength steel rolling process comprises: and controlling the cooling water consumption ratio between the first rack and the second rack of the finish rolling to be 0.5, controlling the cooling water consumption ratio between the second rack and the third rack of the finish rolling to be 0.5, and performing rolling lubrication in the rolling process.

Example 3

Example 3 is compared to example 1, with example 3 differing from example 1 in that:

according to the mass fraction, the chemical components of the steel grade in the high-strength steel smelting process are controlled as follows: 0.004% of C, 0.12% of Si, 0.5% of Mn, 0.05% of P, 0.02% of S, 0.05% of Al, 0.0008% of B, 0.035% of Nb, 0.045% of Ti and the balance of Fe and inevitable impurities.

Controlling the heating during the rolling of the high-strength steel comprises: the soaking temperature of heating is controlled to be 1200 ℃, the heating time is controlled to be 160min, and the lambda value of heating is controlled to be 0.9.

Controlling a dephosphorization process in the high-strength steel rolling process: and the rough rolling is controlled to adopt three times of dephosphorization, the finish rolling inlet is controlled to adopt two times of dephosphorization, and the pressure of dephosphorization is controlled to be 22MPa.

Controlling finish rolling in the high-strength steel rolling process: controlling the inlet temperature of finish rolling to be 1040 ℃, the finish rolling temperature of finish rolling to be 900 ℃, the steel throwing speed of finish rolling to be 10m/s, and the cooling water pressure between the racks of finish rolling to be 10MPa.

The thickness of the finish-rolled intermediate billet is controlled to be 38mm.

Controlling the thermal fatigue characteristics in the rolling process of the high-strength steel: and controlling the proportion of the cooling water consumption between the first rack and the second rack in the finish rolling stage to be 0.8, and controlling the proportion of the cooling water consumption between the second rack and the third rack in the finish rolling stage to be 0.8.

Comparative example 1

Comparative example 1 and example 1 were compared, with comparative example 1 and example 1 differing in that:

according to the mass fraction, the chemical components of the steel grade in the high-strength steel smelting process are controlled as follows: 0.001% of C, 0.04% of Si, 0.2% of Mn, 0.02% of P, 0.008% of S, 0.02% of Al, 0.0003% of B, 0.020% of Nb, 0.030% of Ti, and the balance of Fe and inevitable impurities.

The heating stage in the process of controlling the rolling of the high-strength steel comprises the following steps: the soaking temperature in the heating stage is controlled to 1150 ℃, the heating time in the heating stage is controlled to 120min, and the lambda value in the heating stage is controlled to 0.7.

The dephosphorization process for controlling the high-strength steel rolling process comprises the following steps: and the rough rolling is controlled to adopt three times of dephosphorization, the finish rolling inlet is controlled to adopt two times of dephosphorization, and the pressure of dephosphorization is controlled to be 15MPa.

The finish rolling stage in the process of controlling the rolling of the high-strength steel comprises the following steps: controlling the inlet temperature of the finish rolling stage to be 800 ℃, the finish rolling temperature of the finish rolling stage to be 800 ℃, the steel throwing speed of the finish rolling stage to be 5m/s, and the cooling water pressure between racks of the finish rolling stage to be 5MPa.

The finish rolling stage in the process of controlling the high-strength steel to be rolled further comprises the following steps: the thickness of the intermediate billet in the finish rolling stage is controlled to be 25mm.

Controlling thermal fatigue characteristics in the high-strength steel rolling process comprises: and controlling the ratio of the cooling water consumption between the first rack and the second rack in the finish rolling stage to be 0.2, and controlling the ratio of the cooling water consumption between the second rack and the third rack in the finish rolling stage to be 0.3.

Comparative example 2

Comparative example 2 is compared to example 1, with comparative example 2 differing from example 1 in that:

according to the mass fraction, the chemical components of the steel grade in the high-strength steel smelting process are controlled as follows: 0.005 percent of C, 0.15 percent of Si, 8 percent of Mn, 0.03 to 0.05 percent of P, 0.04 percent of S, 0.08 percent of Al, 0.0010 percent of B, 0.040 percent of Nb, 0.055 percent of Ti, and the balance of Fe and inevitable impurities.

Controlling heating in the high-strength steel rolling process: the soaking temperature of heating is controlled to 1250 ℃, the heating time is controlled to 180min, and the lambda value of heating is controlled to 0.95.

Controlling a dephosphorization process in the high-strength steel rolling process: and the rough rolling is controlled to adopt three times of dephosphorization, the finish rolling inlet is controlled to adopt two times of dephosphorization, and the pressure of dephosphorization is controlled to be 25MPa.

Controlling finish rolling in the high-strength steel rolling process: controlling the inlet temperature of finish rolling to be 1100 ℃, the finish rolling temperature of finish rolling to be 950 ℃, the steel throwing speed of finish rolling to be 15m/s, and the cooling water pressure between the racks of finish rolling to be 15MPa.

The thickness of the finish-rolled intermediate billet is controlled to be 40mm.

Controlling the thermal fatigue characteristics in the rolling process of the high-strength steel: and controlling the cooling water consumption ratio between the first rack and the second rack for finish rolling to be 0.9, and controlling the cooling water consumption ratio between the second rack and the third rack for finish rolling to be 0.9.

Related experiments:

the surface white line defect rates of the steel materials obtained in examples 1 to 3 and comparative examples 1 to 2 were counted, and the results are shown in Table 3.

TABLE 3

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Specific analysis of table 1:

from the data of examples 1-3, it can be seen that:

by adopting the method, the high-strength steel product with low surface white line defect rate can be effectively obtained by aiming at the chemical components and the rolling process in the smelting process of the high-strength steel.

From the data of comparative examples 1-2, it can be seen that:

if the parameters of the control process provided by the application are not adopted, the white line defects on the surface are increased, and the quality of the steel product is influenced.

One or more technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

(1) According to the method provided by the embodiment of the application, the surface white line defects are analyzed to determine the appearance and the microscopic characteristic data of the surface white line defects, and then the oxidation characteristics and the structure condition of the infinite chilled roll are analyzed, so that the chemical components of the steel in the smelting process and the process parameters in the rolling process can be determined, the surface white line defects are comprehensively controlled, and the high-strength steel outer plate without the surface white line defects is obtained.

(2) According to the method provided by the embodiment of the application, the relation between the generation mechanism of the surface white line defects and the relation between the finish rolling fourth machine frame and the finish rolling sixth machine frame is discovered through accurate analysis of the surface white line defects, so that a powerful basis is provided for improving the surface white line defects.

(3) The method provided by the embodiment of the application can effectively reduce the incidence rate of white line defects on the surface of the high-strength IF steel and improve the product quality.

(4) The method provided by the embodiment of the application has the advantages of simple overall process, strong applicability and obvious effect of reducing the surface white line defect rate.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrases "comprising a," "8230," "8230," or "comprising" does not exclude the presence of additional like elements in a process, method, article, or apparatus that comprises the element.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of producing high strength steel with low surface white line defects, the method comprising:

2. The preparation method of claim 1, wherein the number of the ironing roller materials is more than or equal to 10.

3. The method according to claim 1, wherein the number of continuously rolled slabs is 15 or less.

4. The method of claim 1, wherein the continuously rolling further comprises continuously rolling with the addition of wear resistant particles, the wear resistant particles having a diameter < 5 μm.

5. The preparation method according to claim 4, wherein the chemical composition of the wear-resistant particles satisfies the following conditions:

[V]/[Nb]＝0.5～1.5:1，

6. The production method according to claim 1, wherein the continuous rolling includes rough rolling, rough rolling descaling, finish rolling descaling, and finish rolling, and the descaling water pressure of the rough rolling descaling and the finish rolling descaling is 18MPa to 22MPa.

7. The production method according to claim 6, wherein an inlet temperature of the finish rolling is 1000 ℃ to 1040 ℃, and a finish rolling temperature of the finish rolling is 880 ℃ to 900 ℃.

8. The production method according to claim 6, wherein a cooling water pressure between adjacent two stands of the finish rolling is 8MPa to 10MPa, and a cooling water input mass ratio between adjacent two stands of the finish rolling is 0.5 to 0.8.

9. The preparation method according to claim 1, wherein the soaking temperature for heating is 1180-1200 ℃, the heating time is 140-160 min, and the lambda value for heating is 0.8-0.9.

10. A high-strength steel, characterized in that it has been produced by a method according to any one of claims 1 to 9, and that its chemical composition comprises, in mass fractions: 0.0015 to 0.004 percent of C, 0.05 to 0.12 percent of Si, 0.3 to 0.5 percent of Mn, 0.03 to 0.05 percent of P, 0.01 to 0.02 percent of S, 0.03 to 0.05 percent of Al, 0.0004 to 0.0008 percent of B, 0.025 to 0.035 percent of Nb, 0.035 to 0.045 percent of Ti, and the balance of Fe and inevitable impurities.