CN115216587B - Method for improving composition and structure uniformity of large-scale cast steel ingot of high-carbon chromium bearing steel and high-carbon chromium bearing steel - Google Patents

Abstract

The invention discloses a method for improving the composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel and the high-carbon chromium bearing steel, which sequentially comprises the following steps: (1) smelting; (2) LF+RH refining, and adding rare earth elements at the end of refining; (3) die casting: molding to obtain an F20T steel ingot with the section diameter of 1140-1230 mm; (4) high temperature homogenization: homogenizing at 1250-1270deg.C for 29-31 hr; (5) forging cogging: upsetting and drawing to obtain an intermediate blank; (6) high-temperature diffusion of intermediate blanks: heating the intermediate blank, and preserving heat after thorough firing; (7) forging into a material: forging the intermediate blank into a bar with the diameter of 400-600 mm; and (8) softening and annealing. The invention adopts the addition of rare earth elements into steel and the high-temperature homogenization treatment of the F20T large steel ingot, the structure and the component uniformity of the F20T large steel ingot are both better improved, and the cost is low.

Description

Method for improving composition and structure uniformity of large-scale cast steel ingot of high-carbon chromium bearing steel and high-carbon chromium bearing steel

Technical Field

The invention relates to a method for improving the uniformity of forging components and carbide structures of a large-scale cast steel ingot of high-carbon chromium bearing steel and the high-carbon chromium bearing steel, belonging to the field of special steel smelting and processing.

Background

Along with the rapid development of high-end equipment in China and the adjustment of a national energy structure, the high-end bearing applied to the fields of railways, heavy-load equipment, wind power main shafts and large shield machines is more and more required, and along with the enlargement of equipment, the size of the used bearing is also more and more larger, the sizes of the wind power main shafts and the outer rings of the shield machine bearings reach more than 1 meter, and the high-end equipment bearings have higher requirements on the composition and the organization uniformity.

The size of the raw materials used for the large-size bearing is also larger and larger, the smelting production of the bearing steel at present has two modes of continuous casting and die casting, the smelting of the large-size bearing steel bar is more produced by die casting, and the size of the die cast steel ingot is correspondingly increased along with the size increase of the bearing steel bar.

As the cross-sectional diameter size of the ingot increases, the solidification speed of molten steel from the outer surface to the core of the ingot is smaller, segregation is more serious, and the composition and the tissue uniformity of the forged product are poorer.

At present, the specification of a die casting 5T (with the section diameter of 605 mm) forged product is below 350mm, the uniformity of components and tissues meets the technical requirements, while large-specification high-carbon bearing steel with the specification of more than 400mm-600mm is forged and produced by a large steel ingot with larger section diameter, for example, F20T steel ingot (with the section diameter of 1185 mm) is cast by a large die to produce high-carbon bearing steel with the specification of more than 400mm-600mm, but the section diameter of the F20T steel ingot is too large, the segregation problem exists after molten steel solidification, and the serious component and tissue non-uniformity problem exists after the forged product. Therefore, the composition and carbide structure uniformity of the F20T (cross-sectional dimension up to 1185 mm) ingot forging stock cannot fully meet the technical requirements.

Therefore, the problem of uniformity of components and structures must be solved for high carbon bearing steel produced from large steel ingots above F20T (with cross-sectional dimensions up to 1185 mm).

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for improving the uniformity of the components and the structure of a large-scale die casting steel ingot of high-carbon chromium bearing steel and the high-carbon chromium bearing steel, and the problems of non-uniformity of the components and the carbide structure of the high-carbon bearing steel forged by an F20T steel ingot are improved by controlling the casting temperature of the large-scale die casting, adding rare earth elements to refine and solidify the structure, further optimizing the high-temperature homogenizing heating system and the forging deformation system of the steel ingot.

In order to achieve the above object, the following technical scheme is adopted.

A method for improving the composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel sequentially comprises the following steps:

(1) Smelting: smelting molten iron and scrap steel in an electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the crude molten steel obtained by smelting, and adding rare earth elements at the end of refining;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot with the section diameter of 1140-1230 mm;

(4) High temperature homogenization: homogenizing the steel ingot at a high temperature, wherein the homogenization temperature is 1250-1270 ℃ (1260+/-10 ℃), and the homogenization heat preservation time is 29-31h (30+/-1 h);

(5) Forging and cogging: upsetting and drawing the steel ingot homogenized at the high temperature in the step (4) to obtain an intermediate blank;

(6) High-temperature diffusion of the intermediate blank: heating the intermediate blank obtained in the step (5), and preserving heat after thorough firing;

(7) Forging into a material: forging the intermediate billet obtained in the step (6) into a bar with the diameter of 400-600 mm;

(8) Softening and annealing: and (3) annealing the bar in the step (7).

In the method, as a preferred embodiment, the high-carbon chromium bearing steel prepared by the method comprises the following chemical components in percentage by mass: c:0.90% -0.96%; si 0.40-0.60%; mn 0.80-1.10%; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr:1.80% -2.05%; mo:0.50% -0.60%; al:0.015% -0.050%; ca is less than or equal to 0.001 percent (Ca is less than or equal to 10 ppm); less than or equal to 0.0012 percent of O (less than or equal to 12ppm of O), 0.001 to 0.01 percent of rare earth, and the balance of Fe and unavoidable impurities; preferably, the rare earth is 0.002-0.008% (e.g., 0.003%, 0.004%, 0.005%, 0.006%, 0.007%).

In the above method, as a preferred embodiment, the final refining stage refers to before pit formation of the LF furnace or/and after RH vacuum; preferably, the rare earth element is: one or both of La and Ce, preferably Ce.

The rare earth element is added before pit forming of the LF furnace or after RH vacuum, the temperature of the molten steel is adjusted to be in place, the molten steel is well deoxidized, the rare earth alloy is prevented from being oxidized and burnt, and the rare earth alloy element can enter the molten steel.

In the invention, rare earth elements are added into the steel, the molten steel is purified and modified by the rare earth elements to improve carbide segregation of the steel ingot with large cross section size, the chemical affinity of rare earth and impurities such as oxygen, sulfur and the like in the molten steel is large, and the rare earth steel additive can be used as a strong deoxidizer and desulfurizing agent of the molten steel to play a role in purification; oxides, sulfides or oxysulfides generated by the reaction of the rare earth with oxygen and sulfur in the molten steel can partially remain in the molten steel and become inclusions in the steel. Because of the high melting point of the inclusions, the inclusions can be used as heterogeneous nucleation centers during molten steel solidification, and play a role in refining the solidification structure of steel and improving carbide segregation.

In the above method, as a preferred embodiment, the conditions for adding the rare earth element before pit forming of the LF furnace are as follows: the refining final slag is white slag, and the retention time of the white slag is more than 15min.

The rare earth element is added into refined steel liquid under the condition of adding the rare earth element, at the moment, the temperature of the molten steel component is adjusted to be in place, the molten steel is well deoxidized, the rare earth alloy is prevented from being oxidized and burnt, and the rare earth alloy element can enter the molten steel. If the rare earth alloy is not added under the condition, the oxidation burning loss of the rare earth alloy is large, the effective rare earth alloy elements which can enter the molten steel are few and low, and the effect is poor.

In the above method, as a preferred embodiment, the rare earth element is added in an amount of 0.14 to 0.23 Kg/ton of steel (e.g., 0.15 Kg/ton of steel, 0.16 Kg/ton of steel, 0.18 Kg/ton of steel, 0.20 Kg/ton of steel, 0.21 Kg/ton of steel, 0.22 Kg/ton of steel).

In the above method, as a preferred embodiment, in the lf+rh refining step, soft argon blowing is performed after RH vacuum (after RH breaking), the total soft argon blowing time is controlled to be 30-50min (e.g., 35min, 40min, 45 min), the slag surface is not red, and the slag surface is slightly fluctuated, so that the molten steel is prevented from being exposed; preferably, when rare earth elements are added after RH vacuum is applied, the time of soft argon blowing before rare earth elements are added is 10 to 20min (e.g., 12min, 15min, 18 min), and the time of soft argon blowing after rare earth elements are added is 20 to 30min (e.g., 22min, 25min, 28 min).

The purpose of soft argon blowing is to collide with each other, focus and grow up fine inclusions in molten steel and then float up again under the stirring action of low-flow argon, so that the fine inclusions are finally adsorbed and removed by slag.

The total soft blowing time is controlled to be 30-50min, so that the method is beneficial to the mutual collision and focusing growth of the fine inclusions in the molten steel until the fine inclusions float upwards. When the total soft blowing time exceeds the upper time limit of the invention, the temperature of molten steel is reduced too much due to the too long soft blowing time, which is unfavorable for die casting.

In the above method, as a preferred embodiment, in the molding step, a nozzle of 50mm diameter is used for casting.

In the above method, as a preferred embodiment, the casting step is carried out at a pit-forming casting temperature of 1488-1493 ℃ (e.g., 1489 ℃, 1490 ℃, 1491 ℃, 1492 ℃)

In the die casting step, when the casting temperature is too high (exceeds 1493 ℃), the severity of the segregation of the components of the steel ingot obtained by die casting is increased, so that the pit-forming casting temperature is controlled to be 1488-1493 ℃, the segregation degree of the components of the steel ingot can be reduced, and the uniformity of the components and carbide tissues after the steel ingot is forged into a material is ensured.

In the above method, as a preferred embodiment, in the die casting step, the ingot mold is filled with argon during die casting, the whole argon seal is used for protecting the casting, secondary oxidation is forbidden, the casting time of the ingot body is 840 seconds to 1250 seconds (for example, 850 seconds, 900 seconds, 950 seconds, 1100 seconds, 1150 seconds, 1200 seconds and 1240 seconds), and the casting time of the cap opening is equal to or more than 320 seconds (for example, 350 seconds, 400 seconds and 450 seconds).

In the above method, as a preferred embodiment, in the high-temperature homogenizing step, the steel ingot is heated at a heating rate of 60 to 100 ℃/h until a homogenizing temperature is reached.

In the invention, the high-temperature homogenization of the large steel ingot is carried out, the homogenization temperature is increased from the conventional temperature 1220+/-10 ℃ to 1260+/-10 ℃, the heat preservation time is increased from the conventional temperature 15-18h to 30+/-1 h, the heat preservation temperature after thorough firing is 1260+/-10 ℃, the target is set at 1255 ℃ and the heat preservation time is 30+/-1 h, so that the carbide dilution and diffusion effects of the large steel ingot are further improved.

The high-temperature homogenization of the invention focuses on heating and homogenizing the steel ingot after the die casting of the refined molten steel, and the conventional electroslag remelting focuses on carrying out electroslag remelting again on the steel ingot after the die casting of the refined molten steel. Compared with the electroslag remelting process in the conventional technology, the high-temperature homogenization method provided by the invention has the advantages that one electroslag smelting process is omitted, and the process cost is low. In addition, only one steel ingot can be smelted and cast at one time by electroslag remelting, the smelting time of a large ingot type electroslag ingot is up to more than 20 hours, and the efficiency is low.

In the above method, as a preferred embodiment, in the forging cogging step, the steel ingot homogenized at high temperature in the step (4) is upsetted and drawn once, and an intermediate billet is obtained by forging, preferably, the intermediate billet is a 720mm square billet; still preferably, in the forging cogging step, the initial forging temperature is not less than 950 ℃ (e.g., 960 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃), and the final forging temperature is not less than 800 ℃ (e.g., 820 ℃,850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃).

In the above method, as a preferred embodiment, the intermediate blank is subjected to the high-temperature diffusion step, and then is subjected to heat preservation at a heat preservation temperature of 1220-1240 ℃ (1230.+ -. 10 ℃, e.g., 1225 ℃, 1230 ℃ and 1235 ℃) for 14-16 hours (15.+ -. 1 hour, e.g., 14.5 hours, 15 hours and 15.5 hours).

In the above method, as a preferred embodiment, in the forging forming step, the intermediate billet obtained in the step (6) is upset-drawn once and forged into a bar with a diameter of 400-600mm (for example, 450mm, 500mm, 550 m); preferably, in the forging forming step, the initial forging temperature is equal to or higher than 950 ℃ (e.g., 960 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃), and the final forging temperature is equal to or higher than 800 ℃ (e.g., 820 ℃,850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃).

In the above method, as a preferable embodiment, the softening annealing step is performed at 780-800℃in total (e.g., 785 ℃, 790 ℃, 795 ℃, 798 ℃) for a holding time of 4h/100mm or more (e.g., 5h/100mm, 6h/100mm, 7h/100 mm). Here, the holding time is related to the cross-sectional diameter of the forging material; when the section diameter of the forging material is 100mm, the heat preservation time in the softening annealing step is more than or equal to 4 hours; when the section diameter of the forging material is 200mm, the heat preservation time in the softening annealing step is more than or equal to 8h.

In the invention, the bar material forged into the bar material is softened and annealed to eliminate the stress of the bar material and prevent the steel material from cracking, so that the performance of the annealed steel ingot bar material meets the technical requirements.

The invention also provides the high-carbon chromium bearing steel prepared by the method for improving the uniformity of the forging material components and the structure of the large-scale casting steel ingot of the high-carbon chromium bearing steel, which comprises the following chemical components in percentage by mass: c:0.90% -0.96%; si 0.40-0.60%; mn 0.80-1.10%; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr:1.80% -2.05%; mo:0.50% -0.60%; al:0.015% -0.050%; ca is less than or equal to 0.001 percent (Ca is less than or equal to 10 ppm); less than or equal to 0.0012 percent of O (less than or equal to 12ppm of O), 0.001 to 0.01 percent of rare earth, and the balance of Fe and unavoidable impurities; preferably, the rare earth is 0.002-0.008% (e.g., 0.003%, 0.004%, 0.005%, 0.006%, 0.007%).

In the invention, the technical characteristics can be combined with each other to form a new technical scheme under the condition of no conflict.

For the prior art, the invention has the following beneficial technical effects:

(1) The invention adopts the addition of rare earth elements into steel and the high-temperature homogenization treatment of the F20T large steel ingot, and the structure and the component uniformity of the F20T large steel ingot are both better improved, for example, the width and the density of the banded structure of the F20T large steel ingot are loosely and sparsely distributed; the uniformity of chemical components is improved, and the carbon segregation index is more towards 1;

(2) The invention adopts electric furnace die casting non-electroslag remelting smelting, and has lower cost.

Drawings

Fig. 1 is a diagram showing a band structure at 1/2 radius of an annealed F20T ingot forging in example 1 of the present invention.

Fig. 2 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in example 1 of the present invention.

Fig. 3 is a diagram showing a band structure at 1/2 radius of the F20T ingot forging after annealing in comparative example 1 of the present invention.

Fig. 4 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in comparative example 1 of the present invention.

Fig. 5 is a diagram showing a band structure at 1/2 radius of the F20T ingot forging after annealing in example 2 of the present invention.

Fig. 6 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in example 2 of the present invention.

Fig. 7 is a diagram showing a band structure at 1/2 radius of the F20T ingot forging after annealing in comparative example 2 of the present invention.

Fig. 8 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in comparative example 2 of the present invention.

Fig. 9 is a diagram showing a band structure at 1/2 radius of the F20T ingot forging after annealing in example 3 of the present invention.

Fig. 10 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in example 3 of the present invention.

Fig. 11 is a diagram showing a band structure at 1/2 radius of the F20T ingot forging after annealing in comparative example 3 of the present invention.

Fig. 12 is a diagram showing a band structure at the center of the F20T ingot forging after annealing in comparative example 3 of the present invention.

Fig. 13 is a graph showing the distribution of segregation index of the entire cross section [ C ] of the large-sized forging of the high-carbon bearing steel at the riser end of the F20T ingot forging after annealing in example 1 and comparative example 1 of the present invention.

Fig. 14 is a graph showing the distribution of segregation index of the entire cross section [ C ] of the large-sized forging of the high-carbon bearing steel at the riser end of the F20T ingot forging after annealing in example 2 and comparative example 2 of the present invention.

Fig. 15 is a graph showing the distribution of segregation index of the entire cross section [ C ] of the large-sized forging of the high-carbon bearing steel at the riser end of the F20T ingot forging after annealing in example 3 and comparative example 3 of the present invention.

Detailed Description

The present invention will be described in detail below with reference to the drawings and examples of the present invention. The examples are provided by way of explanation of the invention and not limitation of the invention. Indeed, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used on another embodiment to yield still a further embodiment. Accordingly, it is intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and their equivalents.

The invention provides a method for improving the composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel, which adopts the following process flow: molten iron and scrap steel, a 70T electric arc furnace, LF and RH, die casting of F20T ingot, high-temperature homogenization (1260+/-10 ℃), forging cogging, high-temperature diffusion of intermediate billets, forging into 400-600mm circles, softening and annealing of forging materials, peeling, flaw detection (surface and interior), finishing, inspection, packaging and warehousing.

In the invention, because the forging material specification is large, the large steel ingot is directly forged into a material on 45MN rapid forging, the steel ingot is firstly subjected to upsetting treatment to obtain an intermediate blank, and then the intermediate blank is upsetted for a short time, and the material bar is forged into a material bar; wherein, the initial forging temperature is equal to or higher than 950 ℃ (for example, 960 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃), and the final forging temperature is equal to or higher than 800 ℃ (for example, 820 ℃,850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃).

In the following examples, procedures not described in detail may employ conventional techniques in the art.

Example 1

A method for improving the composition and structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel, wherein the chemical composition of the high-carbon chromium bearing steel is shown in table 1, the method comprises the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the molten steel obtained in the smelting step, and adding rare earth elements before pit forming (namely, before vacuum) of an LF furnace at the end of refining; in particular, the method comprises the steps of,

refining the crude molten steel obtained in the smelting step, wherein at the end of refining, the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is longer than 15min; before pit forming of an LF furnace, adding rare earth element Ce into molten steel according to 0.22 Kg/ton steel for one time when the temperature of the molten steel is stable, then pit forming to a vacuum position for RH vacuum treatment, and after the vacuum treatment, carrying out soft argon blowing, wherein the total soft argon blowing time is controlled to be 45 minutes, the slag surface is not exposed to red, and the slag surface is slightly fluctuated, so that the exposure of the molten steel is forbidden;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1493 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 900 seconds, the casting time of the cap opening is 360 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) High temperature homogenization: heating the steel ingot in a furnace, heating to 1255 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving the temperature of the thoroughly burned steel ingot at a preserving temperature of 1255+/-10 ℃ for 30 hours;

(5) Forging and cogging: upsetting and drawing the steel ingot homogenized at the high temperature in the step (3) once to obtain a 720mm square billet, namely an intermediate billet; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

(6) High temperature diffusion of the intermediate billet (i.e., high temperature homogenization of the intermediate billet): heating the intermediate blank obtained in the step (5) in a furnace, controlling the heating rate to be less than or equal to 100 ℃/h, heating the intermediate blank to 1230 ℃, and preserving heat for 15h at the heat preservation temperature of 1230+/-10 ℃ after thorough firing, so that the intermediate blank is diffused at high temperature, and the carbide dilution and diffusion effects of the large steel ingot are improved;

(7) Forging into a material: upsetting and drawing the intermediate blank obtained in the step (6) once, and forging the intermediate blank into a round forging material with the section diameter of 450 mm; wherein, the initial forging temperature is 1080 ℃, and the final forging temperature is 870 ℃;

and (3) then, carrying out softening annealing, peeling, flaw detection (surface + inner), finishing, inspection, packaging and warehousing on the round forging material obtained in the step (7) to obtain the finished high-carbon bearing steel.

TABLE 1 Main Components (wt%) of finished high carbon chromium bearing steels obtained in examples 1-3 and comparative examples 1-3

Element(s)	C	Si	Mn	P	S	Cr	Ni	Cu	Mo	Al	Ce
												Example 1	0.928	0.52	0.91	0.016	0.0020	1.94	0.05	0.050	0.52	0.022	0.0055
Example 2	0.932	0.54	0.91	0.014	0.0020	1.93	0.03	0.060	0.54	0.014	0.0050
												Example 3	0.925	0.52	0.91	0.016	0.0020	1.95	0.05	0.050	0.52	0.021	0.0052
Comparative example 1	0.913	0.54	0.91	0.012	0.0020	1.93	0.03	0.060	0.52	0.014	0
												Comparative example 2	0.905	0.51	0.89	0.015	0.0020	1.92	0.05	0.050	0.50	0.021	0
Comparative example 3	0.916	0.52	0.90	0.015	0.0020	1.94	0.05	0.050	0.53	0.022	0.0051

Comparative example 1

The comparative example provides a method for preparing a large-scale cast steel ingot of high-carbon chromium bearing steel, which is different from the method in the embodiment 1 in that rare earth elements are not added in the steel ingot, high-temperature homogenization is not carried out (namely, the conventional process is adopted for carrying out heating treatment, the heating temperature of the steel ingot is lower before forging), and the steel ingot is directly forged and drawn into a product in the forging process. Specifically, the chemical composition of the high carbon chromium bearing steel is shown in table 1, and the method comprises the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the crude molten steel obtained in the smelting step, wherein the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is longer than 15min; RH vacuum treatment is carried out after refining, soft argon blowing is carried out after the vacuum treatment, the total soft argon blowing time is controlled to be 45 minutes, the slag surface is not exposed to red, slight fluctuation is carried out, and the exposure of molten steel is forbidden;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1492 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 963 seconds, the casting time of the cap opening is 370 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) Heating steel ingot: heating the steel ingot in a furnace, heating to 1230 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving heat of the thoroughly burned steel ingot at a heat preservation temperature of 1230+/-10 ℃ for 28 hours;

(5) Forging into a material: directly forging and drawing the steel ingot heated in the step (4) into a round forging material with the diameter of 450 mm; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

and (3) then carrying out softening annealing, peeling, flaw detection (surface+inside), finishing, inspection, packaging and warehousing on the 450mm round forging material obtained in the step (5) to obtain the finished high-carbon bearing steel, wherein the specific steps are the same as the corresponding steps in the embodiment 1.

Example 2

A method for improving composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel, wherein the chemical composition of the high-carbon chromium bearing steel is shown in table 1, the method comprising the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the molten steel obtained in the smelting step, and adding rare earth elements after RH vacuum treatment is finished at the end of refining; in particular, the method comprises the steps of,

rare earth element addition conditions: the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is more than 15min;

rare earth element addition time: after RH vacuum treatment is finished;

rare earth element addition: adding the steel according to the weight of 0.15 Kg/ton of steel;

the rare earth element adding method comprises the following steps: after the vacuum treatment is finished, the mixture is added when the temperature is stable, and the mixture is added at one time.

Vacuum is complete and soft blowing time is reached: controlling the total soft blowing time to be 45min, soft blowing for 20min before adding the rare earth element, and soft blowing for 25min after adding the rare earth element; the slag surface is not exposed to red, slightly fluctuates, and molten steel is forbidden to be exposed;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1490 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 960 seconds, the casting time of the cap opening is 550 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) High temperature homogenization: heating the steel ingot in a furnace, heating to 1255 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving the temperature of the thoroughly burned steel ingot at 1255+/-10 ℃ for 30 hours;

(5) Forging and cogging: forging the steel ingot homogenized at high temperature in the step (3), and upsetting and drawing once to obtain a 720mm square billet, namely an intermediate billet; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

(6) High-temperature diffusion of the intermediate blank: heating the intermediate blank obtained in the step (5) in a furnace, controlling the heating rate to be less than or equal to 100 ℃/h, heating the intermediate blank to 1230+/-10 ℃, and carrying out heat preservation at the heat preservation temperature of 1230+/-10 ℃ for 15h after thorough firing, so that the intermediate blank is diffused at high temperature, and the carbide dilution and diffusion effects of the large steel ingot are improved;

(7) Forging into a material: upsetting and drawing the intermediate blank obtained in the step (6) once, and forging the intermediate blank into a round forging material with the diameter of 450 mm; wherein, the initial forging temperature is 1080 ℃, and the final forging temperature is 870 ℃;

and (3) then, carrying out softening annealing, peeling, flaw detection (surface + inner), finishing, inspection, packaging and warehousing on the round forging material obtained in the step (7) to obtain the finished high-carbon bearing steel.

Comparative example 2

The comparative example provides a preparation method of a large-scale die-cast steel ingot of high-carbon chromium bearing steel, wherein rare earth elements are not added in the steel ingot in the LF+RH refining step, and the round forging material with the diameter of 450mm is obtained by directly forging and drawing the steel ingot obtained by die casting after high-temperature homogenization. Specifically, the chemical composition of the high carbon chromium bearing steel is shown in table 1, and the method comprises the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the crude molten steel obtained in the smelting step (1), wherein the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is longer than 15min; RH vacuum treatment is carried out after refining, and soft blowing time is carried out after the vacuum treatment: the total soft blowing time is controlled for 35min, the slag surface is not exposed to red, the fluctuation is slight, and the exposure of molten steel is forbidden;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1495 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 1140 seconds, the casting time of the cap opening is 390 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) High temperature homogenization: heating the steel ingot in a furnace, heating to 1255 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving the temperature of the thoroughly burned steel ingot at 1255+/-10 ℃ for 30 hours;

(5) Forging and cogging: directly forging and drawing the steel ingot homogenized at the high temperature in the step (4) into a round forging material with the diameter of 450 mm; wherein, the initial forging temperature is 1080 ℃, and the final forging temperature is 870 ℃;

and (3) then, carrying out softening annealing, peeling, flaw detection (surface + inner), finishing, inspection, packaging and warehousing on the round forging material obtained in the step (5) to obtain the finished high-carbon bearing steel.

Example 3

A method for improving composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel, wherein the chemical composition of the high-carbon chromium bearing steel is shown in table 1, the method comprising the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the molten steel obtained in the smelting step, and adding rare earth elements after RH vacuum treatment is finished at the end of refining; in particular, the method comprises the steps of,

rare earth element addition conditions: the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is more than 15min;

rare earth element addition time: after RH vacuum treatment is finished;

rare earth element addition: adding the steel according to the ratio of 0.18 Kg/ton of steel;

the rare earth element adding method comprises the following steps: after the vacuum treatment is finished, the mixture is added when the temperature is stable, and the mixture is added at one time.

Vacuum is complete and soft blowing time is reached: controlling the total soft blowing time to 48min, soft blowing for 20min before adding rare earth elements, and soft blowing for 28min after adding; the slag surface is not exposed to red, slightly fluctuates, and molten steel is forbidden to be exposed;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1491 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 930 seconds, the casting time of the cap opening is 330 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) High temperature homogenization: heating the steel ingot in a furnace, heating to 1255 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving the temperature of the thoroughly burned steel ingot at 1255+/-10 ℃ for 30 hours;

(5) Forging and cogging: upsetting and drawing the steel ingot homogenized at the high temperature in the step (3) once to obtain a 720mm square billet, namely an intermediate billet; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

(6) High-temperature diffusion of the intermediate blank: heating the intermediate blank obtained in the step (5) in a furnace, controlling the heating rate to be less than or equal to 100 ℃/h, heating the intermediate blank to 1230+/-10 ℃, and carrying out heat preservation at the heat preservation temperature of 1230+/-10 ℃ for 15h after thorough firing, so that the intermediate blank is diffused at high temperature, and the carbide dilution and diffusion effects of the large steel ingot are improved;

(7) Forging into a material: upsetting and drawing the intermediate blank obtained in the step (6) once, and forging the intermediate blank into a round forging material with the diameter of 500 mm; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

and (3) then, carrying out softening annealing, peeling, flaw detection (surface + inner), finishing, inspection, packaging and warehousing on the round forging material obtained in the step (7) to obtain the finished high-carbon bearing steel.

Comparative example 3

The comparative example provides a method for preparing a large-scale cast steel ingot of high-carbon chromium bearing steel, rare earth elements are added at the end of refining, the cast steel ingot is not homogenized at high temperature, the high-carbon chromium bearing steel is obtained by adopting a conventional forging method, and specifically, the chemical compositions of the high-carbon chromium bearing steel are shown in table 1, and the method comprises the following steps:

(1) Smelting: smelting molten iron and scrap steel in a 70t electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the molten steel obtained in the smelting step, and adding rare earth elements at the end of refining; in particular, the method comprises the steps of,

rare earth element addition conditions: the refined molten steel is well deoxidized, the refined final slag is white slag, and the retention time of the white slag is more than 15min;

rare earth element addition time: after RH vacuum treatment is finished;

rare earth element addition: adding the steel according to the ratio of 0.18 Kg/ton of steel;

the rare earth element adding method comprises the following steps: after the vacuum treatment is finished, the mixture is added when the temperature is stable, and the mixture is added at one time.

Vacuum is complete and soft blowing time is reached: controlling the total soft blowing time to 46min, soft blowing for 22min before adding rare earth elements, and soft blowing for 24min after adding; the slag surface is not exposed to red, slightly fluctuates, and molten steel is forbidden to be exposed;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot; wherein the pit-lifting casting temperature is 1498 ℃; during die casting, the ingot mould is filled with argon, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 1140 seconds, the casting time of the cap opening is 450 seconds, and the casting nozzle size adopts a nozzle with the diameter of 50mm for casting;

(4) Heating steel ingot: heating the steel ingot in a furnace, heating to 1230 ℃ at a heating rate of less than or equal to 100 ℃/h, and preserving heat of the thoroughly burned steel ingot at a heat preservation temperature of 1230+/-10 ℃ for 28 hours;

(5) Forging into a material: directly forging and drawing the steel ingot heated in the step (4) into a round forging material with the diameter of 450 mm; wherein, the initial forging temperature is 1100 ℃, and the final forging temperature is 900 ℃;

and (3) then, carrying out softening annealing, peeling, flaw detection (surface + inner), finishing, inspection, packaging and warehousing on the round forging material obtained in the step (5) to obtain the finished high-carbon bearing steel.

F20T steel ingot Performance analysis

(1) Tissue uniformity

For the detection of the carbide banding structure of the riser site of the annealed F20T ingot forgings prepared in examples 1 to 3 and comparative examples 1 to 3 in the present invention, fig. 1 to 12 show the carbide banding structure diagrams of the riser site of the annealed F20T ingot forgings of examples and comparative examples of the present invention. Wherein, FIGS. 1, 5 and 9 show the 1/2 radius carbide structure diagram of the annealed F20T ingot forging material in examples 1 to 3 of the present invention, FIGS. 2, 6 and 10 show the center carbide diagram of the annealed F20T ingot forging material in examples 1 to 3 of the present invention, FIGS. 3, 7 and 11 show the 1/2 radius carbide structure diagram of the annealed F20T ingot forging material in comparative examples 1 to 3 of the present invention, and FIGS. 4, 8 and 12 show the center carbide diagram of the annealed F20T ingot forging material in comparative examples 1 to 3 of the present invention, respectively. For a detailed description, see the carbide ribbon structure of the annealed F20T ingot forging in table 2. Here, the carbide banding was evaluated according to the standard SEP 1520.

TABLE 2 carbide ribbon-like structure of F20T ingot forgings after annealing in examples 1-3 and comparative examples 1-3

As can be seen from fig. 1 to 12 and table 2, after the homogenization treatment of the steel ingot with rare earth and high temperature, the ribbon-shaped structure density of the F20T steel ingot forging material is loosely distributed in a sparse manner, and the ribbon-shaped width is very narrow. And F20T steel ingot forging without rare earth or high-temperature homogenization treatment has obviously wider, thicker and denser banded tissue width and density.

Therefore, the carbide ribbon structure uniformity of the high-carbon chromium bearing steel is obviously improved after the rare earth and large steel ingot are subjected to new high-temperature homogenization treatment.

(2) Uniformity of chemical composition

For the annealed F20T ingot forgings prepared in examples 1-3 and comparative examples 1-3 of the present invention, all-section carbon ([ C ]) segregation at the riser end was examined, and FIGS. 13-15 show all-section carbon segregation index diagrams at the riser end of the annealed F20T ingot forgings in examples 1-3 and comparative examples 1-3 of the present invention. The specific carbon segregation index is shown in table 3.

TABLE 3 full section carbon segregation index of F20T ingot forgings after annealing

Examples	Technical proposal	Carbon segregation index	Maximum carbon segregation index
				Example 1	Adding rare earth + high temperature homogenization	1.02-1.16	1.16
Example 2	Adding rare earth + high temperature homogenization	1.01-1.10	1.10
				Example 3	Adding rare earth + high temperature homogenization	1.01-1.16	1.16
Comparative example 1	No rare earth addition and no high temperature homogenization	0.91-1.36	1.36
				Comparative example 2	High temperature homogenization without addition of rare earth +	0.99-1.29	1.29
Comparative example 3	Rare earth addition and no high temperature homogenization	0.95-1.31	1.31

As shown in fig. 13-15 and table 3, after the F20T ingot is added with rare earth and homogenized at high temperature, the ingot is forged into a round forging, the C segregation index of the whole section corresponding to the riser end of the ingot forging is 1.01-1.16, and the maximum value at the center is 1.16, more approaching to 1. The F20T steel ingot is not added with rare earth or subjected to high-temperature homogenization treatment, and the C segregation index of the whole section of the dead head end of the corresponding steel ingot forging material is 0.91-1.36, and the maximum C segregation index is 1.36, and is greatly deviated from 1.

Therefore, the invention adds rare earth and steel ingot to carry out high-temperature homogenization treatment, the uniformity of chemical components is improved, and the carbon segregation index is more towards 1.

In summary, the invention adopts the addition of rare earth elements into steel and the high-temperature homogenization treatment of the F20T large-sized steel ingot, and the structure and the component uniformity of the F20T large-sized steel ingot forging material are both better improved.

Claims (13)

1. A method for improving the composition and structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel is characterized by sequentially comprising the following steps:

(1) Smelting: smelting molten iron and scrap steel in an electric arc furnace to obtain crude molten steel;

(2) LF+RH refining: refining the crude molten steel obtained by smelting, and adding rare earth elements at the end of refining; the final refining stage refers to before pit forming of the LF furnace or/and after RH vacuum; wherein, the conditions for adding the rare earth elements before pit forming of the LF furnace are as follows: the refining final slag is white slag, and the retention time of the white slag is more than 15min; when rare earth elements are added after RH vacuum is adopted, the soft argon blowing time before the rare earth elements are added is 10-20 min, and the soft argon blowing time after the rare earth elements are added is 20-30 min; the addition amount of rare earth elements is 0.14-0.23 Kg/ton of steel;

(3) And (3) die casting: casting the refined molten steel to obtain an F20T steel ingot with the section diameter of 1140-1230 mm; in the die casting step, the pit forming casting temperature is 1488-1493 ℃;

(4) High temperature homogenization: homogenizing the steel ingot at a high temperature, wherein the homogenization temperature is 1250-1270 ℃, and the homogenization heat preservation time is 29-31h;

(5) Forging and cogging: upsetting and drawing the steel ingot homogenized at the high temperature in the step (4) to obtain an intermediate blank; in the forging and cogging step, the initial forging temperature is more than or equal to 950 ℃, and the final forging temperature is more than or equal to 800 ℃;

(6) High-temperature diffusion of the intermediate blank: heating the intermediate blank obtained in the step (5), and carrying out heat preservation at a heat preservation temperature of 1220-1240 ℃ for 14-16h after the intermediate blank is thoroughly burned;

(7) Forging into a material: forging the intermediate billet obtained in the step (6) into a bar with the diameter of 400-600 mm; in the step of forging the finished product, the initial forging temperature is more than or equal to 950 ℃, and the final forging temperature is more than or equal to 800 ℃;

(8) Softening and annealing: annealing the rod in step (7);

the high-carbon chromium bearing steel prepared by the method comprises the following chemical components in percentage by mass: c:0.90% -0.96%; si 0.40-0.60%; mn 0.80-1.10%; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr:1.80% -2.05%; mo:0.50% -0.60%; al:0.015% -0.050%; ca is less than or equal to 0.001%; o is less than or equal to 0.0012%, rare earth is 0.001-0.01%, and the balance is Fe and unavoidable impurities.

2. The method for improving the composition and the structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1, wherein the rare earth is 0.002-0.008%.

3. The method for improving the composition and the structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1, wherein the rare earth elements are as follows: one or two of La and Ce.

4. A method of improving the composition and texture uniformity of a high carbon chromium bearing steel large die cast steel ingot according to claim 3, wherein the rare earth element is Ce.

5. The method for improving the composition and the structure uniformity of the large-scale cast steel ingot of the high-carbon chromium bearing steel according to any one of claims 1 to 4, wherein in the LF+RH refining step, soft argon blowing is carried out after RH vacuum, the total soft argon blowing time is controlled to be 30 to 50 minutes, the slag surface is not red, the fluctuation is slight, and the molten steel is forbidden to be exposed.

6. The method for improving the composition and structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1, wherein in the casting step, a nozzle with a diameter of 50mm is used for casting.

7. The method for improving the composition and the structure uniformity of a large-scale cast steel ingot of high-carbon chromium bearing steel according to claim 1 or 6, wherein in the die casting step, the ingot mold is filled with argon during die casting, the whole process of argon sealing protection casting is performed, secondary oxidation is forbidden, the casting time of the ingot body is 840-1250 seconds, and the casting time of a cap opening is more than or equal to 320 seconds.

8. The method for improving the composition and structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1, wherein in the high-temperature homogenizing step, the steel ingot is heated at a heating rate of 60-100 ℃/h until a homogenizing temperature is reached.

9. The method for improving the composition and the structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1, wherein in the step of forging and cogging, the steel ingot homogenized at high temperature in the step (4) is upset-drawn once, and a middle blank is obtained by forging.

10. The method for improving the composition and structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1 or 9, wherein the intermediate billet is a 720mm square billet.

11. The method for improving the composition and the structure uniformity of a large-scale cast steel ingot for high-carbon chromium bearing steel according to claim 1 or 9, wherein in the step of forging the steel, the intermediate billet obtained in the step (6) is upset-drawn once and forged into a bar with the diameter of 400-600 mm.

12. The method for improving the composition and the structure uniformity of the large-scale cast steel ingot of the high-carbon chromium bearing steel according to claim 1, wherein the total softening annealing step is 780-800 ℃, and the heat preservation time is more than or equal to 4h/100mm.

13. A high carbon chromium bearing steel prepared by the method for improving the composition and structure uniformity of a large-scale die casting steel ingot of the high carbon chromium bearing steel according to any one of claims 1 to 12.