阅读说明：本技术 一种改善中碳合金钢铸坯偏析的开坯方法 (Cogging method for improving segregation of medium carbon alloy steel casting blank ) 是由 陈继林 杨成 孔令波 杨栋 马洪磊 刘维 薛正国 霍立伟 徐立刚 张旭 郑建 于 2020-11-06 设计创作，主要内容包括：本发明一种改善中碳合金钢铸坯偏析的开坯方法,包括开坯加热、开坯轧制工序,其特征在于,所述开坯加热工序,采用蓄热式加热炉分三段进行加热,从加热炉入口到出口依次为一加热段、二加热段、均热段,一加热段加热温度850～950℃,二加热段加热温度1050～1150℃,均热段加热温度1150～1250℃。本发明获得的小铸坯,中心偏析从2.5级降至1.0级以下,正常轧制的成品晶粒度可均匀控制在8级以上。(The cogging method for improving the medium carbon alloy steel casting blank segregation comprises the steps of cogging heating and cogging rolling and is characterized in that a heat accumulating type heating furnace is adopted for heating in three sections, a heating section and a soaking section are sequentially arranged from an inlet to an outlet of the heating furnace, the heating temperature of the heating section is 850-950 ℃, the heating temperature of the heating section is 1050-1150 ℃, and the heating temperature of the soaking section is 1150-1250 ℃. The center segregation of the small casting blank obtained by the invention is reduced from 2.5 grade to below 1.0 grade, and the grain size of the finished product which is normally rolled can be uniformly controlled to be above 8 grade.)

1. A cogging method for improving medium carbon alloy steel casting blank segregation comprises cogging heating and cogging rolling procedures and is characterized in that a heat accumulating type heating furnace is adopted to perform heating in three sections, a first heating section, a second heating section and a soaking section are sequentially arranged from an inlet to an outlet of the heating furnace, the heating temperature of the first heating section is 850-950 ℃, the heating temperature of the second heating section is 1050-1150 ℃, and the heating temperature of the soaking section is 1150-1250 ℃.

2. The cogging method for improving the casting blank segregation of the medium carbon alloy steel according to claim 1, wherein in the cogging rolling procedure, the large billet is rolled into the small billet, nine times of rolling are adopted, the rolling reduction of 50-60mm is adopted in the first four times, the rolling reduction of 20-30mm is adopted in the middle four times, and the rolling reduction of 10-20mm is adopted in the last time.

3. The cogging method for improving the casting blank segregation of the medium carbon alloy steel according to claim 1, characterized in that in the cogging heating process, the total heating time is 5-6 hours, and the holding time of the billet at the temperature of more than or equal to 1150 ℃ is 1.5-2 hours.

4. A cogging method for improving medium carbon alloy steel billet segregation in accordance with claim 3, characterized in that the residual oxygen content of the heating furnace is controlled to be below 4%.

5. A cogging method for improving segregation of medium carbon alloy steel billets as claimed in any one of claims 1 to 4, characterized in that the cross-sectional size of the bloom is 280 x 280mm to 325 x 325mm, and the cross-sectional size of the billet is 120 x 120mm to 180 x 180 mm.

Technical Field

The invention belongs to the technical field of steel material production, and particularly relates to a cogging method for improving medium carbon alloy steel casting blank segregation.

Background

The medium carbon alloy steel wire comprises alloy cold forging steel, spring steel and the like, and is mainly used for manufacturing key parts such as automobile high-strength bolts, sleeves, special-shaped parts, suspension springs and the like. In recent years, China has achieved outstanding performance in the aspects of preparation and replacement import of steel for automobile parts, but the production technology and application of the high-quality steel for automobile parts have a large gap compared with the foreign advanced countries, and the gap mainly shows in the aspects of production technology maturity and quality stability control of high-quality steel wires for automobile parts in China, such as the cracking rate in the material forming process, the fatigue life of high-strength bolts and springs and the like. The product can not meet the requirements of high fatigue, large deformation, low fluctuation, low cost and customization in the application process, wherein the material structure uniformity and stability are main factors influencing the performances of fatigue and the like, the most important factor for medium carbon alloy steel is the casting blank segregation problem, green development helps to promote curve overtaking of new energy automobiles, the high quality development of Chinese steel is vital, and the key performance needs to be improved urgently.

Because medium carbon alloy steel is mainly used for the service environment with the strength of more than 1000MPa, the requirement on fatigue life is strict, most of the medium carbon alloy steel depends on import, the main factor influencing the fatigue life is segregation, and domestic patents on reducing the segregation of casting blanks are rarely reported at present: the Chinese patent with the application number of 201210174384.X discloses a method for reducing the frame-shaped segregation of Cr and Mo steel rolled materials, which mainly controls the electromagnetic stirring intensity, the frequency, the total water quantity, the specific water quantity, the overheating and the pulling speed of a secondary cooling area, reduces the frame-shaped segregation by rolling, but has higher cost and low efficiency, and can not completely eliminate the problems of central segregation and the like. The chinese patent application No. 201911233884.4 discloses that "a process method for controlling central carbon segregation of a bearing steel casting blank" promotes the floating of molten steel inclusions by controlling the temperature of a package in the continuous casting process, and adopts technical schemes such as a submerged nozzle and electromagnetic stirring, reduces inclusions in the casting blank, improves the isometric crystal rate of the casting blank center, reduces the carbon segregation index of the casting blank center, and only can not completely guarantee the casting blank segregation quality from the steelmaking continuous casting process, and multiple tests find that the central segregation still exists. Chinese patent application No. 201910299087.X discloses a method for improving the frame segregation of a bloom continuous casting slab, which comprises the steps of: the drawing speed, the electromagnetic stirring of the crystallizer, the secondary cooling electromagnetic stirring position and the like are used for improving the frame segregation of the bloom continuous casting billet, reducing the influence of the drawing speed on the production efficiency, increasing the cost and the production period and being incapable of effectively improving the segregation quality of the casting billet.

The above patents mainly increase the cost and production period by means of pulling speed, electromagnetic stirring and the like in the steel-making continuous casting process, and the segregation of the casting blank cannot be solved effectively to a large extent. How to control under the conventional continuous casting parameters of a steelmaking process, the existing production equipment does not separately carry out a diffusion annealing process by utilizing a billet two-fire forming process to effectively ensure the segregation quality of a casting blank, and the problem of supporting the high quality improvement of carbon alloy steel in China is to be solved urgently.

Disclosure of Invention

The invention aims to solve the technical problem of providing a cogging method for improving the casting blank segregation of medium carbon alloy steel, and eliminating the casting blank segregation problem of medium carbon alloy steel, particularly the center segregation of the casting blank.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a cogging method for improving medium carbon alloy steel casting blank segregation comprises cogging heating and cogging rolling procedures, wherein a heat accumulating type heating furnace is adopted to carry out heating in three sections, a first heating section, a second heating section and a soaking section are sequentially arranged from an inlet to an outlet of the heating furnace, the heating temperature of the first heating section is 850-950 ℃, the heating temperature of the second heating section is 1050-1150 ℃, and the heating temperature of the soaking section is 1150-1250 ℃.

The casting blank can be heated to the temperature of 100 ℃ and 200 ℃ lower than the solidus line for heat preservation for a certain time, so that the uniform diffusion of segregation elements is realized after the solid solution, the dendritic crystal segregation and the regional segregation generated in the solidification process of the casting blank are effectively eliminated, and the dispersion distribution of components is realized. In addition, considering the temperature of the second brittle zone of the medium carbon alloy steel (700-;

compared with the conventional process, the method adopts sectional heating, quickly avoids a brittle zone at the initial stage, realizes the dispersion and diffusion of segregation components at a lower uniform heating temperature, ensures original austenite grains, and avoids mixed grains.

Further, in the cogging rolling procedure, the large square billet is rolled into a small square billet, nine times of rolling are adopted, the rolling reduction of 50-60mm is adopted in the first four times, the rolling reduction of 20-30mm is adopted in the middle four times, and the rolling reduction of 10-20mm is adopted in the last time.

By adopting enough cogging reduction, the microscopic crystals of the casting blank slide through dislocation to break the mutual locking action among crystal branches, so that dispersed and isolated irregular shrinkage porosity formed in the solidification shrinkage process is welded in the cogging uniform reduction process, the internal porosity of the steel blank is eliminated, the casting blank uniformly remolds the isometric crystals and columnar crystals of the casting blank through uniform deformation of large reduction, and the segregation quality of the casting blank is greatly improved by the principle.

Further, in the cogging heating procedure, the total heating time is 5-6 hours, and the heat preservation time of the steel billet at the temperature of more than or equal to 1150 ℃ is 1.5-2 hours.

In order to avoid excessive growth of austenite grains in a casting blank, the heating temperature is reduced and the heat preservation time is shortened, so that the total heating time is designed to be 5-6 h, and the heat preservation time of the billet at the temperature of more than or equal to 1150 ℃ is designed to be 1.5-2 h.

Further, the residual oxygen content of the heating furnace is controlled to be below 4 percent.

Considering the influence of the heating process on the decarburization of the cast billet, the residual oxygen amount in the furnace is strictly controlled to avoid oxidation reaction, so that the residual oxygen amount in the heating furnace is controlled below 4 percent.

Preferably, the cross-sectional dimension of the bloom is 280 × 280mm to 325 × 325mm, and the cross-sectional dimension of the billet is 120 × 120mm to 180 × 180 mm.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

the center segregation of the small casting blank obtained by the invention is reduced from 2.5 grade to below 1.0 grade, and the grain size of the finished product which is normally rolled can be uniformly controlled to be above 8 grade. The invention can effectively improve the casting blank segregation and the structure uniformity of the medium carbon alloy steel, and the parts made of the medium carbon alloy steel can meet the requirements of uniform component distribution and structure state of raw materials under high-speed service no matter an engine or a suspension spring is in service.

Drawings

FIG. 1 is a photograph showing the macrostructure of a billet obtained by cogging the carbon alloy steel in example 1

FIG. 2 is a photograph showing the macrostructure of a billet obtained by cogging the carbon alloy steel in example 2

FIG. 3 is a photograph showing the macrostructure of a billet obtained by cogging the medium carbon alloy steel in example 3

FIG. 4 is a photograph showing the macrostructure of a billet obtained after cogging the carbon alloy steel in example 4

FIG. 5 is a photograph showing the macrostructure of a billet obtained after cogging the carbon alloy steel in example 5

FIG. 6 is a photograph showing the macrostructure of a billet obtained after cogging the medium carbon alloy steel in example 6

FIG. 7 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 1 by rolling

FIG. 8 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 2 by rolling

FIG. 9 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 3 by rolling

FIG. 10 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 4 by rolling

FIG. 11 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 5 by rolling

FIG. 12 is a photograph showing the grain size of a wire rod made of a carbon alloy steel in example 6.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to better illustrate the invention, the following examples are given by way of further illustration.

Example 1

Cogging a medium carbon alloy steel casting blank bloom, wherein the section size of the bloom is 280 x 325mm, the section size of a small billet is 160 x 160mm, the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step is that a heat accumulating type heating furnace is divided into three sections for heating, the heating temperature of the first heating section is 850 ℃, the heating temperature of the second heating section is 1050 ℃, the heating temperature of the soaking section is 1150 ℃, the total heating time is 6h, the heat preservation time of the steel billet in the temperature section which is more than or equal to 1150 ℃ is 2h, and the residual oxygen content of the heating furnace is 4%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine times of rolling, adopting 50mm of rolling reduction in the first four times, adopting 30mm of rolling reduction in the middle four times, and adopting 10mm of rolling reduction in the last time.

Example 2

Cogging a medium carbon alloy steel casting blank bloom, wherein the section size of the bloom is 280 x 325mm, the section size of a small bloom is 160 x 160mm, the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step is that a heat accumulating type heating furnace is divided into three sections for heating, the heating temperature of the first heating section is 950 ℃, the heating temperature of the second heating section is 1150 ℃, the heating temperature of the soaking section is 1250 ℃, the total heating time is 5h, the heat preservation time of the steel blank in the temperature section which is more than or equal to 1150 ℃ is 1.5h, and the residual oxygen content of the heating furnace is 3%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine times of rolling, adopting 60mm of rolling reduction in the first four times, adopting 20mm of rolling reduction in the middle four times, and adopting 20mm of rolling reduction in the last time.

Example 3

Cogging a medium carbon alloy steel casting blank bloom, wherein the section size of the bloom is 280 x 325mm, the section size of a small bloom is 160 x 160mm, the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step is that a heat accumulating type heating furnace is divided into three sections for heating, the heating temperature of the first heating section is 900 ℃, the heating temperature of the second heating section is 1110 ℃, the heating temperature of the soaking section is 1200 ℃, the total heating time is 5.5h, the heat preservation time of the steel blank in the temperature section of more than or equal to 1150 ℃ is 1.5h, and the residual oxygen content of the heating furnace is 2%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine times of rolling, adopting 55mm of rolling reduction in the first four times, adopting 25mm of rolling reduction in the middle four times, and adopting 20mm of rolling reduction in the last time.

Example 4

Cogging a medium carbon alloy steel casting blank bloom, wherein the section size of the bloom is 280 x 325mm, the section size of a small bloom is 160 x 160mm, the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step is that a heat accumulating type heating furnace is divided into three sections for heating, the heating temperature of the first heating section is 920 ℃, the heating temperature of the second heating section is 1150 ℃, the heating temperature of the soaking section is 1180 ℃, the total heating time is 5.2h, the heat preservation time of the steel blank in the temperature section which is more than or equal to 1150 ℃ is 1.6h, and the residual oxygen content of the heating furnace is 1%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine-pass rolling, adopting the rolling reduction of 56mm in the first four passes, adopting the rolling reduction of 24mm in the middle four passes, and adopting the rolling reduction of 18mm in the last pass.

Example 5

Cogging a medium carbon alloy steel casting blank into a bloom with the section size of 280 x 280mm and the section size of a small billet of 120 x 120mm, wherein the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step comprises heating in three sections by a heat accumulating type heating furnace, the heating temperature of the first heating section is 871 ℃, the heating temperature of the second heating section is 1131 ℃, the heating temperature of the soaking section is 1167 ℃, the total heating time is 5.7h, the heat preservation time of the steel billet in the temperature section of more than or equal to 1150 ℃ is 1.3h, and the residual oxygen content of the heating furnace is 3.4%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine times of rolling, adopting 53mm of rolling reduction in the first four times, adopting 27mm of rolling reduction in the middle four times, and adopting 13mm of rolling reduction in the last time.

Example 6

Cogging a medium carbon alloy steel casting blank into a bloom, wherein the section size of the bloom is 325 multiplied by 325mm, the section size of a small billet is 180 multiplied by 180mm, the cogging process comprises the steps of cogging heating and cogging rolling, the cogging heating step comprises the steps of heating in three sections by a heat accumulating type heating furnace, the heating temperature of the first heating section is 891 ℃, the heating temperature of the second heating section is 1141 ℃, the heating temperature of the soaking section is 1231 ℃, the total heating time is 5.9h, the heat preservation time of the steel billet in the temperature section of more than or equal to 1150 ℃ is 1.8h, and the residual oxygen content of the heating furnace is 2.7%. And a cogging rolling procedure, namely rolling the large square billet into a small square billet, adopting nine times of rolling, adopting a rolling reduction of 58mm in the first four times, adopting a rolling reduction of 29mm in the middle four times, and adopting a rolling reduction of 16mm in the last time.

The billets obtained after cogging in examples 1 to 6 were pickled at a low power level according to the national test standards and then subjected to center segregation test, and the test results are shown in Table 1. FIGS. 1 to 6 are photographs of macrostructures of the pickled billets of examples 1 to 6. The billets obtained in examples 1 to 6 after cogging were rolled into wire rods, the structure grain size of the wire rods is shown in Table 1, and FIGS. 7 to 12 are photographs showing the structure grain size of the wire rods rolled from the billets in examples 1 to 6.

TABLE 1

Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.