阅读说明：本技术 一种提高大规格高碳铬钼轴承钢超声探伤合格率的轧制方法 (Rolling method for improving ultrasonic flaw detection qualification rate of large-size high-carbon chromium-molybdenum bearing steel ) 是由 王凌云 高坤 吴剑 周敦世 邓小利 周杰 王曙 卢荣凤 于 2021-07-26 设计创作，主要内容包括：本发明公开了一种提高大规格高碳铬钼轴承钢超声探伤合格率的轧制方法,以铸锭为原料,包括：加热工序、轧制工序和退火工序,其中：所述加热工序中,将所述铸锭装炉后进行加热处理,其中,装炉温度为≤850℃,加热处理的保温温度为1240-1260℃；所述轧制工序中,将加热后的铸锭进行轧制,包括初轧和连轧,其中,初轧中,开轧温度不低于980℃,共25道次,其中15～25道次中分布4个单道次大压下,单道次的压下量不低于70mm,所述轧制通过一火次完成。本发明通过优化加热和轧制工艺,可有效改善大规格比如D≥180mm的高碳铬钼轴承钢心部质量,提高超声探伤合格率。(The invention discloses a rolling method for improving the ultrasonic flaw detection qualification rate of large-size high-carbon chromium molybdenum bearing steel, which takes ingot as a raw material and comprises the following steps: a heating step, a rolling step and an annealing step, wherein: in the heating procedure, the ingot is loaded into a furnace and then is subjected to heating treatment, wherein the charging temperature is less than or equal to 850 ℃, and the heat preservation temperature of the heating treatment is 1240-1260 ℃; in the rolling procedure, the heated cast ingot is rolled, and the rolling procedure comprises initial rolling and continuous rolling, wherein in the initial rolling, the rolling temperature is not lower than 980 ℃, the rolling is performed for 25 passes, 4 single-pass high reduction is distributed in 15-25 passes, the reduction of the single pass is not lower than 70mm, and the rolling is completed by one fire. By optimizing the heating and rolling process, the invention can effectively improve the quality of the high-carbon chromium molybdenum bearing steel core with large specification, such as D being more than or equal to 180mm, and improve the ultrasonic flaw detection qualification rate.)

1. A rolling method for improving the ultrasonic flaw detection qualification rate of large-size high-carbon chromium-molybdenum bearing steel is characterized in that an ingot is used as a raw material, and the rolling method comprises the following steps: a heating step, a rolling step and an annealing step, wherein:

in the heating procedure, the ingot is loaded into a furnace and then is subjected to heating treatment, wherein the charging temperature is less than or equal to 850 ℃, and the heat preservation temperature of the heating treatment is 1240-1260 ℃;

in the rolling procedure, the heated cast ingot is rolled, and the rolling procedure comprises initial rolling and continuous rolling, wherein in the initial rolling, the rolling temperature is not lower than 980 ℃, the rolling is performed for 25 passes, 4 single-pass high reduction is distributed in 15-25 passes, the reduction of the single pass is not lower than 70mm, and the rolling is completed by one fire.

2. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel as claimed in claim 1, wherein the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel produced by the rolling method is more than 95%.

3. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel according to claim 1, characterized in that in the heating procedure, the ingot is firstly subjected to rewarming treatment after being charged and then subjected to heating treatment, wherein the rewarming time is not less than 1 h;

preferably, the rewarming time is 60-90 min.

4. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel according to claim 3, wherein in the heating process, the heating treatment comprises: heating the furnace temperature of the heating furnace to a heat preservation temperature and preserving the heat, wherein the temperature is raised to 880-920 ℃ at a speed of below 50 ℃/h;

preferably, the temperature is increased to 900 ℃ at the speed of 30-50 ℃/h;

more preferably, the temperature is kept for 10-10.5h at the temperature of 1250-1260 ℃.

5. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium-molybdenum bearing steel as claimed in any one of claims 1 to 4, wherein in the annealing procedure, the annealing heat preservation temperature is 790-810 ℃;

preferably, the annealing holding time is 5.5-7 h.

6. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel according to claim 5, wherein in the annealing procedure, the temperature rise rate of raising the temperature to the annealing heat preservation temperature is 50-70 ℃/h.

7. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel as claimed in claim 6, wherein in the annealing procedure, the steel is cooled to below 410 ℃, preferably to 380-410 ℃ after annealing and heat preservation and then is taken out of the furnace;

preferably, the cooling rate is 20-40 ℃/h;

more preferably, in the annealing step: heating to 800 ℃ at a heating rate of 60 ℃/h, preserving heat for 6h, and reducing the temperature to 400 ℃ at a cooling rate of 30 ℃/h for discharging.

8. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel according to claim 1, wherein the diameter of the large-specification high-carbon chromium molybdenum bearing steel is not less than 180 mm;

preferably, the diameter of the large-specification high-carbon chromium molybdenum bearing steel is 180-240 mm.

9. The rolling method for improving the ultrasonic flaw detection yield of large-specification high-carbon chromium molybdenum bearing steel according to claim 1, wherein the ingot is a die ingot of not more than 5 tons.

10. The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium-molybdenum bearing steel according to any one of claims 1 to 9, wherein the large-size high-carbon chromium-molybdenum bearing steel comprises the following components in percentage by mass: 0.9 to 1.05 percent of C, 0.2 to 0.4 percent of Si, 0.6 to 0.8 percent of Mn, 0.2 to 0.5 percent of Mo, 1.65 to 1.95 percent of Cr, less than or equal to 0.025 percent of P, less than or equal to 0.3 percent of Cu, less than or equal to 0.25 percent of Ni, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of S, less than or equal to 0.002 percent of Pb, and the balance of iron and inevitable impurities.

Technical Field

The invention belongs to the technical field of special steel production and processing in the metallurgical industry, and particularly relates to a rolling production method for improving the ultrasonic flaw detection qualification rate of large-size high-carbon chromium molybdenum bearing steel. By optimizing the heating and rolling process, the invention can effectively improve the quality of the high-carbon chromium molybdenum bearing steel core with large specification, such as D being more than or equal to 180mm, and improve the ultrasonic flaw detection qualification rate.

Background

The production of high-carbon chromium bearing steel by adopting an external refining method has been carried out in China for more than forty years, and along with the improvement of equipment and process level, the purity of the steel has been greatly improved, which is shown in that the total oxygen content is obviously reduced by T.0 and large-particle inclusions are obviously reduced. Although the existing national standard GB/T18254-2016 for high-carbon chromium bearing steel has definite regulations on the content of non-metallic inclusions and oxygen, the requirements of critical bearing steel load, long service life and high reliability cannot be met even if the highest-level special-grade steel has the requirements on purity, such as total oxygen content T.0 being less than or equal to 6ppm and brittle DS type inclusion particles being less than 27 microns.

At present, the rolling production method of the quality of the large-specification high-carbon chromium molybdenum bearing steel core part comprises two processes of one-step rolling and two-step rolling.

The large-specification high-carbon chromium molybdenum bearing steel produced by the process has lower flaw detection qualification rate after being formed, the requirement is that the flaw detection qualification rate is only about 70%, which not only increases the production cost, but also affects the delivery of contracts.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide the rolling method for improving the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium-molybdenum bearing steel, which promotes the welding of a central shrinkage cavity, effectively improves the core quality of the large-specification steel and enables the flaw detection qualification rate of the large-specification high-carbon chromium-molybdenum bearing steel to reach more than 95% by optimizing the charging temperature, the heating speed, the heat preservation temperature and the rolling process.

In order to achieve the purpose, the invention adopts the following technical scheme:

a rolling method for improving the ultrasonic flaw detection qualification rate of large-size high-carbon chromium-molybdenum bearing steel takes an ingot as a raw material and comprises the following steps: heating, rolling and annealing processes, wherein:

in the heating procedure, the ingot is loaded into a furnace and then is subjected to heating treatment, wherein the charging temperature is less than or equal to 850 ℃, and the heat preservation temperature of the heating treatment is 1240-1260 ℃;

in the above rolling method, as a preferred embodiment: in the rolling procedure, the heated cast ingot is rolled, and the rolling procedure comprises initial rolling and continuous rolling, wherein in the initial rolling, the rolling temperature is not lower than 980 ℃, the rolling is performed for 25 passes, 4 single-pass high reduction is distributed in 15-25 passes, the reduction of the single pass is not lower than 70mm, and the rolling is completed by one fire.

In the above rolling method, as a preferred embodiment: the ultrasonic flaw detection qualification rate of the large-specification high-carbon chromium molybdenum bearing steel produced by the rolling method is more than 95 percent.

In the above rolling method, as a preferred embodiment: in the heating procedure, the ingot is firstly subjected to rewarming treatment after being charged, and then is subjected to heating treatment, wherein the rewarming time is not less than 1h, and preferably, the rewarming time is 60-90 min.

In the above rolling method, as a preferred embodiment: in the heating step, the heating process includes: raising the temperature of the heating furnace to a heat preservation temperature and preserving the temperature, wherein the temperature is raised to 880-920 ℃ at a speed of less than 50 ℃/h, and preferably raised to 900 ℃ at a speed of 30-50 ℃/h; more preferably, the temperature is kept for 10-10.5h at the temperature of 1250-1260 ℃.

In the above rolling method, as a preferred embodiment: in the annealing procedure, the annealing temperature is 790-810 ℃; further preferably, the annealing incubation time is 5.5-7 h.

In the above rolling method, as a preferred embodiment: in the annealing procedure, the heating rate of heating to the annealing heat preservation temperature is 50-70 ℃/h.

In the rolling method, as a preferred embodiment, in the annealing step, the annealing is performed after heat preservation, and then the steel sheet is cooled to 410 ℃ or lower, preferably 380-; further preferably, the cooling rate is 20-40 ℃/h; more preferably, the annealing process includes: heating to 800 ℃ at a heating rate of 60 ℃/h, preserving heat for 6h, and reducing the temperature to 400 ℃ at a cooling rate of 30 ℃/h for discharging.

In the above rolling method, as a preferred embodiment, the large-gauge high-carbon chromium molybdenum bearing steel has a diameter of not less than 180 mm;

preferably, the diameter of the large-specification high-carbon chromium molybdenum bearing steel is 180-240 mm.

In the above rolling method, as a preferable embodiment, the ingot is a die ingot of not more than 5 tons.

In the above rolling method, as a preferred embodiment: the large-size high-carbon chromium-molybdenum bearing steel comprises the following components in percentage by mass: 0.9 to 1.05 percent of C, 0.2 to 0.4 percent of Si, 0.6 to 0.8 percent of Mn, 0.2 to 0.5 percent of Mo, 1.65 to 1.95 percent of Cr, less than or equal to 0.025 percent of P, less than or equal to 0.3 percent of Cu, less than or equal to 0.25 percent of Ni, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of S, less than or equal to 0.002 percent of Pb, and the balance of iron and inevitable impurities.

The invention has the beneficial effects that: the rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel can effectively improve the core quality of the large-size high-carbon chromium molybdenum bearing steel with the D being more than or equal to 180mm by optimizing the heating and rolling processes, and improve the ultrasonic flaw detection qualification rate to enable the ultrasonic flaw detection qualification rate to reach more than 95%.

Detailed Description

The following examples further illustrate the present invention in detail, and the scope of the present invention includes, but is not limited to, the following examples.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel can effectively improve the core quality of the large-size (D is more than or equal to 180mm) high-carbon chromium molybdenum bearing steel and improve the ultrasonic flaw detection qualification rate by optimizing the heating and rolling processes, so that the ultrasonic flaw detection qualification rate reaches more than 95%.

In the specific embodiment of the invention, a rolling method for improving the ultrasonic flaw detection qualification rate of large-size high-carbon chromium-molybdenum bearing steel takes an ingot as a raw material, and comprises the following steps: the process comprises the following specific process flows of heating, rolling and annealing: mold ingot of not more than 5 tons → heating → rolling → annealing → ultrasonic flaw detection test.

Wherein in the heating step, the ingot is loaded into a furnace and then is subjected to heating treatment, the charging temperature of the heating treatment is less than or equal to 850 ℃ (for example, 850 ℃, 800 ℃ or 750 ℃), and the heat preservation temperature of the heating treatment is 1240 ℃ and 1260 ℃ (for example, 1240 ℃, 1250 ℃ or 1260 ℃). It should be noted that the lower the charging temperature is, the better the charging temperature is, and if the charging temperature is higher than 850 ℃, the temperature difference between the steel ingot and the furnace temperature is large, the temperature difference between the core and the surface of the steel ingot is too large, the stress in each direction of the steel ingot is increased, and the steel ingot is in risk of cracking, so the charging temperature is not higher than 850 ℃. In addition, the heat preservation temperature is properly increased, so that the subsequent heavy reduction process of the steel ingot can be easily executed, the higher the heating temperature of the steel ingot is, the more beneficial the execution of the heavy reduction process is, and the heat preservation temperature are complementary.

In the rolling procedure, the heated cast ingot is rolled, including initial rolling and continuous rolling, wherein in the initial rolling, the rolling temperature is not lower than 980 ℃, the rolling is performed for 25 times, 4 single-pass high reductions are distributed in 15-25 times, for example, 4 single-pass high reductions are distributed in 16, 20, 22 and 23, the reduction of the single pass is not lower than 70mm, preferably, the reduction of the single pass is in the range of 70-80mm, and the rolling is completed by one fire. In the invention, the single-pass high reduction sequence is relatively backward, and the high reduction is not distributed in continuous passes but distributed at intervals, so that the quality effect of the core part of the casting blank can be more effectively and more obviously improved.

The ultrasonic flaw detection qualification rate of the large-size high-carbon chromium-molybdenum bearing steel produced by the rolling method is more than 95 percent.

In the specific embodiment of the invention, in the heating procedure, the ingot is firstly subjected to rewarming treatment after being charged, and then is subjected to heating treatment, wherein the rewarming treatment is to place the ingot in a heating furnace for standing so as to reduce the temperature difference between the ingot and the furnace temperature, wherein the rewarming time is not less than 1h, and the rewarming operation has the effects of reducing the temperature difference between the steel temperature and the furnace temperature, reducing the temperature difference on the core surface of the steel ingot and avoiding the quality problems of direct cracking and the like caused by the large temperature difference between the steel temperature and the furnace temperature.

The purpose of rewarming is to reduce the temperature difference between the steel temperature and the furnace temperature and the temperature difference between the core and the surface of the steel ingot, so that the time is better, but the too long rewarming time can affect the turnover of the heating furnace and the waste of energy consumption, and preferably, the rewarming time is 60-90min (such as 60min, 65min, 70min, 75min, 80min, 85min or 90 min).

In an embodiment of the present invention, in the heating step, the heating process includes: heating the furnace temperature of the heating furnace to a holding temperature and holding the temperature, wherein the temperature is raised to 880-920 ℃ (such as 880 ℃, 890 ℃, 900 ℃, 910 ℃ or 920 ℃) at a speed of 50 ℃/h or less; the invention sets the heating speed below 50 ℃/h, can ensure that the current difference of flaw detection qualified rate is less than 0.5 percent, and has small difference. Preferably, the temperature is increased to 900 ℃ at the speed of 30-50 ℃/h (such as 30 ℃/h, 35 ℃/h, 40 ℃/h, 45 ℃/h or 50 ℃/h), the temperature increase speed of the section is controlled, and the temperature difference between the core part and the surface of the steel ingot is mainly reduced; then, the temperature is continuously increased to 1240-1260 ℃ (such as 1240 ℃, 1245 ℃, 1250 ℃, 1255 ℃ or 1260 ℃) and the temperature is preserved for 10 to 10.5 hours (such as 10 hours, 10.1 hours, 10.2 hours, 10.3 hours, 10.4 hours or 10.5 hours). It should be noted that the temperature can be freely raised above 900 ℃ without controlling the temperature raising speed.

In the specific embodiment of the invention, in the annealing step, the annealing heat preservation temperature is 790-810 ℃ (such as 790 ℃, 795 ℃, 800 ℃, 805 ℃ or 810 ℃), and the annealing heat preservation time is 5.5-7h (such as 5.5h, 6.0h, 6.5h or 7.0 h); and controlling the annealing heating rate to effectively reduce the temperature difference between the core part and the surface of the steel ingot, wherein optionally, the heating rate of heating to the annealing heat-preservation temperature is 50-70 ℃/h (such as 50 ℃/h, 55 ℃/h, 60 ℃/h, 65 ℃/h or 70 ℃/h).

The temperature of the core and the surface of the steel are consistent by controlling the cooling speed; and proper tapping temperature is selected, the tapping temperature is too high, the surface temperature is too fast, the temperature difference of the core surface of the variety with poor heat conductivity is large, stress is easy to generate, and the tapping temperature is low, so that the product quality is basically not influenced.

In an optional embodiment, in the annealing step, after the annealing heat preservation, the annealing heat preservation is performed, and then the annealing heat preservation is performed, the annealing temperature is cooled to below 410 ℃, preferably to 380-.

In an alternative embodiment, in the annealing step: heating to 800 ℃ at a heating rate of 60 ℃/h, preserving heat for 6h, and reducing the temperature to 400 ℃ at a cooling rate of 30 ℃/h for discharging.

The diameter of the large-specification high-carbon chromium-molybdenum bearing steel is 180-240mm (such as 180mm, 190mm, 200mm, 210mm, 220mm, 230mm or 240 mm).

In the specific embodiment of the invention, according to mass percentage, the large-specification high-carbon chromium molybdenum bearing steel GCr18Mo comprises the following components: 0.9 to 1.05 percent of C, 0.2 to 0.4 percent of Si, 0.6 to 0.8 percent of Mn, 0.2 to 0.5 percent of Mo, 1.65 to 1.95 percent of Cr1, less than or equal to 0.025 percent of P, less than or equal to 0.3 percent of Cu, less than or equal to 0.25 percent of Ni, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of S and less than or equal to 0.002 percent of Pb.

The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel according to the invention is explained in detail by specific embodiments.

Example 1

The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel comprises the following steps of:

(1) a heating procedure: smelting 5 tons of GCr18Mo die cast ingots by adopting a 70 ton electric arc furnace, charging at 850 ℃, rewarming for 60min, heating by a central heat exchange soaking furnace, controlling the heating rate to be 50 ℃/h, heating to 900 ℃, continuing to heat to 1240 ℃, and keeping the temperature for 10 h;

(2) a rolling procedure: rolling by a reversible primary rolling mill with phi 850mm at 1100 ℃ for 25 passes, wherein 16, 20, 22 and 23 are subjected to single-pass high reduction of 4 times, the single-pass reduction is 70mm, rolling into a square blank with the diameter of 280mm, and forming into a round steel with the diameter of 230mm by a 750-pass rolling mill;

(3) and (3) annealing: annealing treatment is carried out by adopting a trolley type annealing furnace, the temperature is increased to 800 ℃ at the heating rate of 60 ℃/h, heat is preserved for 6h, and the temperature is reduced to 400 ℃ at the cooling rate of 30 ℃/h and then the product is discharged; and (5) carrying out ultrasonic flaw detection by adopting a GE ultrasonic flaw detector.

A plurality of round steel products with the diameter of 230mm and the specification of finished products prepared by the method of the embodiment 1 are tested, the core defects are qualified by flaw detection with the equivalent weight of less than or equal to phi 4mm, and the qualified rate of the finished product flaw detection is 98.13%.

Example 2

The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel comprises the following steps of:

(1) a heating procedure: smelting 5 tons of GCr18Mo die cast ingots by using a 70 ton electric arc furnace, wherein the charging temperature is 800 ℃, the rewarming time is not less than 1 hour, heating the ingots by using a central heat exchange soaking furnace, controlling the heating rate to be 40 ℃/h to be 900 ℃, continuing heating the ingots to be 1250 ℃, and keeping the temperature for 10.2 hours;

(2) a rolling procedure: rolling by a reversible primary rolling mill with phi 850mm at 1100 ℃ for 25 passes, wherein 16, 20, 22 and 23 are subjected to single-pass high reduction of 4 times, the single-pass reduction is 75mm, rolling into a square blank with the diameter of 280mm, and forming into a round steel with the diameter of 230mm by a 750-pass rolling mill;

(3) and (3) annealing: annealing treatment is carried out by adopting a trolley type annealing furnace, the temperature is increased to 800 ℃ at the heating rate of 60 ℃/h, heat is preserved for 6h, and the temperature is reduced to 400 ℃ at the cooling rate of 30 ℃/h and then the product is discharged; and (5) carrying out ultrasonic flaw detection by adopting a GE ultrasonic flaw detector.

A plurality of round billets with the diameter of 230mm prepared by the method of the embodiment 2 are tested, the core defects are qualified by flaw detection with the equivalent weight of less than or equal to phi 4mm, and the qualified rate of the flaw detection of the finished products is 98.33%.

Example 3

The rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel comprises the following steps of:

(1) heating: smelting 5 tons of GCr18Mo die cast ingots by adopting a 70 ton electric arc furnace, wherein the charging temperature is 750 ℃, the rewarming time is not less than 1 hour, heating the ingots by a central heat exchange soaking furnace, controlling the heating rate to be 35 ℃/h to be 900 ℃, continuing heating the ingots to be 1260 ℃, and keeping the temperature for 10 hours;

(2) a rolling procedure: rolling by a reversible primary rolling mill with phi 850mm at 1100 ℃ for 25 passes, wherein 16, 20, 22 and 23 are subjected to single-pass high reduction of 4 times, the single-pass reduction is 80mm, rolling into a square blank with the diameter of 280mm, and forming into a round steel with the diameter of 230mm by a 750-pass rolling mill;

(3) and (3) annealing: annealing treatment is carried out by adopting a trolley type annealing furnace, the temperature is increased to 800 ℃ at the heating rate of 60 ℃/h, heat is preserved for 6h, and the temperature is reduced to 400 ℃ at the cooling rate of 30 ℃/h and then the product is discharged; and (5) carrying out ultrasonic flaw detection by adopting a GE ultrasonic flaw detector.

A plurality of round billets with the diameter of 230mm and the core defects of phi 4mm prepared by the method of the embodiment 3 are tested, and the qualified rate of the flaw detection of the finished products is 98.25%.

Comparative examples 1 to 5

The rolling methods of comparative examples 1 to 5 are different from the heating process and part of the initial rolling process of example 1, the rest of the operations (including the reduction of the large reduction pass, and the reduction of other passes can be adjusted properly according to the specification of the rolled piece) are the same as those of example 1, and the heating process, the initial rolling process and the finished product flaw detection qualification rate corresponding to comparative examples 1 to 5 are shown in table 1.

TABLE 1 heating Process, blooming Process and flaw detection yields of the obtained products in comparative examples 1 to 5

As can be seen from Table 1, comparative example 1 changed the reduction operation of the blooming process, compared to example 1, example 1 was 4 single-pass high reduction, while comparative example 1 was only 2 single-pass high reduction, and comparative example 1 also changed the partial heating process, i.e., increased charging temperature (above 850 deg.C), reduced reheating time (less than 1h), and reduced holding temperature (below 1240 deg.C), as a result, the flaw detection yield of the product obtained in comparative example 1 was relatively low (71.2%).

Compared with the example 1, the rolling operation of the blooming process is changed in the comparative example 2, the reduction operation of the blooming process is 4 single-pass high-reduction in the example 1, the reduction operation of the blooming process is only 2 single-pass high-reduction in the comparative example 2, and the partial heating process is changed, namely, the charging temperature is increased (more than 850 ℃) and the holding temperature is reduced (less than 1240 ℃), so that the flaw detection yield of the finished product obtained in the comparative example 2 is slightly higher than that of the comparative example 1 (71.2%) but lower than that of the example 1 (98.13%).

Compared with the example 1, the rolling operation of the blooming process is changed in the comparative example 3, the rolling operation of the blooming process is changed, the rolling operation of the example 1 is 4 single-pass high-reduction, the rolling operation of the comparative example 3 is only 2 single-pass high-reduction, and the partial heating process is changed, namely, the temperature rise speed (more than 50 ℃/h) below 900 ℃ is increased, and the result shows that the flaw detection yield (78.3%) of the obtained material of the comparative example 3 is slightly higher than that (75.6%) of the comparative example 2 and is still lower than that (98.13%) of the example 1.

The rolling operation of the blooming step was changed in comparative example 4 as compared with example 1, and example 1 was 4 single-pass high-reduction, while comparative example 4 was only 2 single-pass high-reduction, and the partial heating step process was also changed, i.e., the holding temperature was lowered (less than 1240 ℃), and it was found from the results that the flaw detection yield of the product obtained in comparative example 4 (84.4%) was slightly higher than that of comparative example 3 (78.3%) but lower than that of example 1 (98.13%).

In comparative example 5, the reduction operation of the blooming process was not changed, but the partial heating process was changed, that is, the charging temperature was increased (more than 850 ℃ C.), the temperature increase rate of 900 ℃ or less (more than 50 ℃ C./h) was increased, and the holding temperature was decreased (less than 1240 ℃ C.) as compared with example 1, and the results showed that the flaw detection yield (85.6%) of the product obtained in comparative example 5 was slightly higher than that (84.4%) of comparative example 4 but lower than that (98.13%) of example 1.

In conclusion, the rolling method for improving the ultrasonic flaw detection qualification rate of the large-size high-carbon chromium molybdenum bearing steel can effectively improve the core quality of the large-size high-carbon chromium molybdenum bearing steel with the diameter of D being more than or equal to 180mm and improve the ultrasonic flaw detection qualification rate to reach more than 95% by simultaneously optimizing the heating and rolling processes, particularly optimizing the operating conditions of part of the initial rolling process and the heating process in the rolling process.

It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.