阅读说明：本技术 一种减少热连轧65Mn带钢晶界氧化的生产方法 (Production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel ) 是由 任俊威 张吉富 丛志宇 李江委 苏小利 刘金超 王杰 王存 刘旺臣 于 2021-09-14 设计创作，主要内容包括：本发明涉及一种减少热连轧65Mn带钢晶界氧化的生产方法,冶炼65Mn钢,钢中成分P≤0.02％,S≤0.01％；连铸浇注选用保护渣CaO与SiO-(2)之比在0.1～1.0,结晶器液渣层厚度不低于10mm；控制钢水过热度范围15～25℃；连铸板坯下线保温坑或集中堆垛摆放处理,不超过8小时,入炉温度不小于400℃；加热炉采用弱氧化性或还原性气氛,各段加热温度控制；粗轧温度控制在1030～1060℃,精轧温度控制在840～900℃,卷取温度不超过730℃,在轧制板坯搬运过程中,不允许等钢或摆动降温；层流冷却采用前冷方式,侧喷吹扫,带钢表面不带水。本发明大幅度减少在生产过程中产生晶界氧化缺陷的几率,减轻晶界氧化严重程度,提高生产65Mn带钢的质量水平,满足用户的加工性能要求。(The invention relates to a production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel, which is used for smelting 65Mn steel, wherein the P content in the steel is less than or equal to 0.02 percent, and the S content in the steel is less than or equal to 0.01 percent; casting powder CaO and SiO for continuous casting 2 The ratio of the thickness of the liquid slag layer to the thickness of the liquid slag layer is 0.1-1.0, and the thickness of the liquid slag layer of the crystallizer is not less than 10 mm; controlling the superheat degree range of the molten steel to be 15-25 ℃; continuous casting plate blank off-line heat preservation pit or centralized stacking placement treatmentThe charging temperature is not less than 400 ℃ within 8 hours; the heating furnace adopts weak oxidizing or reducing atmosphere, and the heating temperature of each section is controlled; the rough rolling temperature is controlled to be 1030-1060 ℃, the finish rolling temperature is controlled to be 840-900 ℃, the coiling temperature is not more than 730 ℃, and steel waiting or swinging temperature reduction is not allowed in the conveying process of the rolled plate blank; the laminar cooling adopts a front cooling mode and side spraying purging, and the surface of the strip steel does not carry water. The method greatly reduces the probability of generating crystal boundary oxidation defects in the production process, lightens the severity of crystal boundary oxidation, improves the quality level of 65Mn strip steel production, and meets the processing performance requirements of users.)

1. A production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel is characterized by comprising the following specific steps:

1) smelting 65Mn steel, wherein the P content in the steel is less than or equal to 0.02 percent, and the S content in the steel is less than or equal to 0.01 percent;

2) selection of continuous castingCaO and SiO of covering slag₂The ratio of the thickness of the liquid slag layer to the thickness of the liquid slag layer is 0.1-1.0, and the thickness of the liquid slag layer of the crystallizer is not less than 10 mm;

3) controlling the superheat degree range of the molten steel to be 15-25 ℃;

4) placing and processing the continuous casting plate blank off-line heat preservation pits or centralized stacks for no more than 8 hours at the charging temperature of no less than 400 ℃;

5) the heating furnace adopts weak oxidizing or reducing atmosphere, and the heating temperature of each section is controlled as follows: the upper and lower temperatures of the first heating section are 1150-1200 ℃, the upper temperature of the second heating section is 1280-1330 ℃, the lower temperature of the second heating section is 1250-1300 ℃, the upper temperature of the soaking section is 1220-1280 ℃, the lower temperature of the soaking section is 1200-1260 ℃, and the tapping temperature is 1220-1250 ℃; the heating time of the second heating section and the soaking section is not more than 100 minutes, and the total in-furnace time is not more than 300 minutes;

6) controlling the temperature of hot continuous rolling: the rough rolling temperature is controlled to be 1030-1060 ℃, the finish rolling temperature is controlled to be 840-900 ℃, and the coiling temperature is not more than 730 ℃.

7) The laminar cooling adopts a front cooling mode and side spraying purging, and the surface of the strip steel does not carry water.

2. The production method for reducing the grain boundary oxidation of the hot continuous rolling 65Mn strip steel as claimed in claim 1, wherein the atmosphere in the step 5) with the air-fuel ratio of 1.7-1.8 is a weakly oxidizing atmosphere, and the atmosphere with the air-fuel ratio of 1.8 (excluding 1.8) -1.9 is a reducing atmosphere.

3. The production method for reducing the grain boundary oxidation of the hot continuous rolled 65Mn steel strip according to claim 1, wherein in the step 7), steel waiting or swinging temperature reduction is not allowed during the transportation of the rolling slab.

Technical Field

The invention relates to the field of metallurgical hot rolled plate strip steel, in particular to a production method for reducing grain boundary oxidation of hot continuous rolled 65Mn strip steel.

Background

The 65Mn steel belongs to high-carbon cutting tool steel, can be produced by a conventional hot rolling continuous rolling unit, is widely applied to industries such as downstream saw blades, springs, vehicle parts and the like, and often generates the conditions of processing fracture and the like in the subsequent use process, thereby causing the quality complaint of users. Metallographic detection shows that the grain boundary oxidation cracks existing on the surface of the strip steel raw material are one of the main causes of subsequent processing cracks or fatigue failure. The oxidation of the grain boundary is an oxidation process which preferentially occurs along the metal grain boundary in a high-temperature environment, and the oxide generated along the grain boundary destroys the continuity of the material, affects the strength of a final finished product and causes the expansion and cracking of an oxidation crack source along the grain boundary in the processing process.

The surface oxidation phenomenon occurs in the heating and high-temperature rolling processes of a hot rolling heating furnace, oxygen atoms diffuse faster along the grain boundary than in the interior of the grains, grain boundary oxidation cracks exist on the surface of strip steel in metallographic examination, and the common length is 10-50 mu m.

65Mn grain boundary oxidation generally occurs in heat treatment processes, but grain boundary oxidation defects in 65Mn hot rolling processes are of less concern in the industry.

Disclosure of Invention

The invention aims to solve the technical problem of providing a production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel, and solving the defect of reducing grain boundary oxidation on the surface of the strip steel when the hot continuous rolling line is used for producing the 65Mn strip steel.

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

a production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel comprises the following specific steps:

1) smelting 65Mn steel, wherein the P content in the steel is less than or equal to 0.02 percent, and the S content in the steel is less than or equal to 0.01 percent;

2) casting powder CaO and SiO for continuous casting₂The ratio of the thickness of the liquid slag layer to the thickness of the liquid slag layer is 0.1-1.0, and the thickness of the liquid slag layer of the crystallizer is not less than 10 mm;

3) controlling the superheat degree range of the molten steel to be 15-25 ℃;

4) placing and processing the continuous casting plate blank off-line heat preservation pits or centralized stacks for no more than 8 hours at the charging temperature of no less than 400 ℃;

5) the heating furnace adopts weak oxidizing or reducing atmosphere, and the heating temperature of each section is controlled as follows: the upper and lower temperatures of the first heating section are 1150-1200 ℃, the upper temperature of the second heating section is 1280-1330 ℃, the lower temperature of the second heating section is 1250-1300 ℃, the upper temperature of the soaking section is 1220-1280 ℃, the lower temperature of the soaking section is 1200-1260 ℃, and the tapping temperature is 1220-1250 ℃; the heating time of the second heating section and the soaking section is not more than 100 minutes, and the total in-furnace time is not more than 300 minutes;

6) controlling the temperature of hot continuous rolling: the rough rolling temperature is controlled to be 1030-1060 ℃, the finish rolling temperature is controlled to be 840-900 ℃, the coiling temperature is not more than 730 ℃, and steel waiting or swinging temperature reduction is not allowed in the conveying process of the rolled plate blank;

7) the laminar cooling adopts a front cooling mode and side spraying purging, and the surface of the strip steel does not carry water.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, by researching the relevant influence factors of grain boundary oxidation in the hot rolling process and adopting the approach of optimizing the steelmaking continuous rolling process, the optimization control of the composition design, the internal quality, the hot rolling heating process and the rolling temperature of the continuous casting billet can greatly reduce the probability of producing the grain boundary oxidation defect in the production process, reduce the severity of the grain boundary oxidation, improve the quality level of producing the 65Mn strip steel and meet the processing performance requirements of users.

Drawings

FIG. 1 is a diagram showing a crystal phase without grain boundary oxide on the surface of example 1.

FIG. 2 is a diagram of the crystal phase without grain boundary oxidation on the surface of example 2.

FIG. 3 is a diagram of the crystal phase without grain boundary oxidation on the surface of example 3.

Detailed Description

The following further illustrates embodiments of the invention:

a production method for reducing grain boundary oxidation of hot continuous rolling 65Mn strip steel comprises the following specific steps:

1) the method has the advantages that the content range of components is controlled during smelting of 65Mn steel, the content of the parent oxygen is reduced, the design of phosphorus and sulfur elements is as low as possible, the content of P in the steel is less than or equal to 0.020%, and the content of S in the steel is less than or equal to 0.010%.

2) Casting powder CaO and SiO for continuous casting₂The ratio of the thickness of the liquid slag layer to the thickness of the liquid slag layer is 0.1-1.0, and the thickness of the liquid slag layer of the crystallizer is not less than 10 mm; the capability of absorbing impurities is increased, more impurity elements in the plate blank are avoided, and the purity of the steel is improved.

3) Controlling the superheat degree range of the molten steel to be 15-25 ℃ so as to be beneficial to inhibiting the generation of columnar crystals; the increase of the oxidation probability caused by multi-columnar crystal in the follow-up process is reduced.

4) Placing and processing the continuous casting plate blank off-line heat preservation pits or centralized stacks for no more than 8 hours at the charging temperature of no less than 400 ℃; avoiding the oxidation process caused by the secondary heating and temperature rising process of the heating furnace.

5) The heating furnace is a weakly oxidizing or reducing atmosphere, the atmosphere when the air-fuel ratio is 1.7-1.8 is a weakly oxidizing atmosphere, and the atmosphere when the air-fuel ratio is 1.8 (excluding 1.8) -1.9 is a reducing atmosphere.

Controlling the heating temperature of each section: the temperature of the upper part and the lower part of the first heating section is not more than 1150-1200 ℃, the temperature of the upper part of the second heating section is 1280-1330 ℃, the temperature of the lower part of the second heating section is 1250-1300 ℃, the temperature of the upper part of the soaking section is 1220-1280 ℃, the temperature of the lower part of the soaking section is 1200-1260 ℃, and the tapping temperature is 1220-1250 ℃; the heating time of the second heating section and the soaking section is not more than 100 minutes, and the total in-furnace time is not more than 300 minutes; high temperature overheating is avoided.

6) Controlling the temperature of hot continuous rolling: the rough rolling temperature is controlled to be 1030-1060 ℃, the finish rolling temperature is controlled to be 840-900 ℃, the coiling temperature is not more than 730 ℃, and steel waiting or swinging temperature reduction is not allowed in the conveying process of the rolled plate blank.

7) The laminar cooling adopts a front cooling mode and side spraying purging, and the surface of the strip steel does not carry water.

Example (b):

smelting 65Mn steel, and covering slag CaO/SiO₂Is 0.98. The steel contains C0.66%, Si 0.20%, Mn 0.93%, P0.015% and S0.001%.

The size of the continuously cast slab is 200 x 1250 x 12300 mm.

The atmosphere in the three sections of the walking beam furnace is weakly oxidizing atmosphere, the air-fuel ratio is set to be 1.9, and the temperature of furnace gas is shown in table 1.

Table 1:

heating section	Temperature of a heating section, DEG C	Temperature of the second heating section, DEG C	Temperature of soaking zone,. degree.C
				Upper part	1170	1310	1250
Lower part	1160	1280	1230

The heating in oven time is shown in table 2.

Table 2:

the rolling parameters are controlled as shown in Table 3.

Table 3:

by sampling and metallographic examination of the three coils of steel, a part of decarburized layer exists, but no surface grain boundary oxidation exists.

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 principles of the invention, and these modifications and variations also fall within the scope of the invention as defined in the appended claims. The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and their concepts should be equivalent or changed within the technical scope of the present invention.