Method for controlling the surface scale of a ni-containing steel sheet

Abstract

The application discloses a surface scale control method for a Ni-containing steel plate and belongs to the technical field of steel plate production. The control method comprises a billet heating process and a rolling process. The first heating section temperature is 850-1050 DEG C, the second heating section temperature is 1150-1230 DEG C, the third heating section temperature is 1200-1230 DEG C, and the soaking section temperature is 1200-1240 DEG C. The amount of the oxide scale generated in the heating process of the billet is small, the adhesion between the scale and the base material is small, and the scale is easy to remove. The rolling method makes the descaling effect of the steel plate better, and the steel plate with better surface quality is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel plate production, and particularly relates to a surface oxide scale control method for a Ni-containing steel plate. BACKGROUND

[0002] Ni element can improve the strength of steel, ensure good plasticity and toughness, and has high corrosion resistance and heat resistance, so the Ni-containing steel is widely used in precision instruments and special equipment.

[0003] Ni element is easily oxidized to form a dense, stable and not easy to fall off oxide. In production, it is difficult to remove such oxides, and if not properly controlled, the oxide scale will be pressed into the surface of the steel plate, forming scale, pitting, pressure pit and even cracking, which seriously affects the appearance quality of the steel plate.

[0004] The Ni-containing steel plates produced by major steel plants all have the problems of thick surface oxide scale and large area, which easily causes plan off. In order to ensure the smoothness of the surface of the steel plate, the oxide scale often needs to be ground. During the grinding process, due to the large thickness of the oxide scale, the thickness of the steel plate body is thinned, which does not meet the order requirements and causes plan off or waste products. The Ni-containing steel has a large grinding amount during production, which increases the surface grinding cost, and the steel plate thickness is thinned beyond the tolerance range specified in the standard or agreement, causing plan off or waste products, and the steel plate needs to be recharged, increasing the production cost. SUMMARY

[0005] The application discloses a surface oxide scale control method for a Ni-containing steel plate. The control method effectively reduces the oxide scale on the surface of the steel plate through reasonable heating and rolling process control, so that the appearance quality of the Ni-containing steel is good, the grinding amount of the steel plate is reduced, and the plan off and waste products are reduced, the production cycle is obviously shortened, the production cost is reduced, and the market competitiveness of the Ni-containing steel is greatly improved.

[0006] To solve the above technical problems, the technical scheme adopted by the application is as follows: a surface oxide scale control method for a Ni-containing steel plate, the control method comprises a billet heating process and a rolling process; the first heating section temperature of the billet heating process is 850-1050 DEG C, the second heating section temperature is 1150-1230 DEG C, the third heating section temperature is 1200-1230 DEG C, and the soaking section temperature is 1200-1240 DEG C.

[0007] The effective heating time of the first heating section, the second heating section and the third heating section of the billet heating process is greater than or equal to 2 min / cm, and the effective heating time of the soaking section is greater than or equal to 1.5 min / cm.

[0008] The air-fuel ratio of the billet heating process is 0.6-0.8, and the residual oxygen content is less than or equal to 3%.

[0009] The rolling process of the application, the first and second pass rough rolling reduction is 20-30mm, using the upper and lower water descaling at the same time; the third pass reduction is 20-30mm, air cooling 1-2min for temperature recovery, and no water descaling; the fourth pass reduction is 20-30mm, using the upper water descaling after the machine and the lower water descaling before the machine; the fifth pass reduction is 20-30mm, using the upper water descaling before the machine and the lower water descaling after the machine; the subsequent rolling passes all use the upper water descaling before the machine and the lower water descaling after the machine, and the water descaling is interval. The application uses the upper water descaling before the machine and the lower water descaling after the machine, through the single upper or lower descaling, the temperature difference of the upper and lower surfaces of the billet is intensified, so as to change the deformation of the upper and lower surfaces of the steel plate, and the buckling head phenomenon in the rolling process of the steel plate is suppressed.

[0010] The rolling process of the application, when the black print is found in the rolling process, the billet is air cooled for temperature recovery, and after the black print is eliminated, the rolling continues. The "black print" is the color difference formed by the excessive temperature drop of the steel billet surface compared with other parts in the rolling process due to the viscosity of the iron oxide scale. When the local temperature difference of the steel billet surface exceeds 100℃, the low temperature part is black and is commonly known as "black print". The purpose of air cooling for temperature recovery is to homogenize the surface temperature of the billet; the temperature homogenization refers to reducing the temperature difference of the billet surface, and when the temperature difference is reduced to within 50℃, the color difference of the billet surface will be eliminated, that is, the black print is eliminated.

[0011] The control method of the application is suitable for the billet thickness of 200-330mm; the control method is suitable for the heating furnace of the empty gas double-accumulation type continuous furnace.

[0012] The Ni content in the Ni-containing steel plate of the application is 0.15-9%.

[0013] The Ni content in the Ni-containing steel plate of the application is 0.15%≤Ni≤0.4%, and the steel plate surface is free of iron oxide scale.

[0014] The Ni content in the Ni-containing steel plate of the application is 0.40%<Ni≤0.6%, the area of the iron oxide scale on the steel plate surface is ≤5%, and the thickness of the iron oxide scale is ≤0.2mm.

[0015] The Ni content in the Ni-containing steel plate of the application is 0.60%<Ni≤9%, the area of the iron oxide scale on the steel plate surface is ≤10%, and the thickness of the iron oxide scale is ≤0.35mm.

[0016] The "black print" of the present application is a large-viscosity oxide scale, and the temperature of the oxide scale is obviously lower than the temperature of the steel plate body. In the case of an increase in rolling reduction and a decrease in rolling temperature, the oxide scale and the steel plate body are deformed unevenly along the rolling direction, and a clear rolling slip tension is generated between the oxide scale attached to the surface of the steel plate and the steel plate body. The rolling slip tension causes the rupture of the oxide scale and the expansion to the steel plate body. The air cooling of the steel plate restores the temperature, reduces uneven deformation, and avoids crack expansion to the body.

[0017] The beneficial effects produced by the above technical solution are that the amount of oxide scale generated during the heating of the billet is small, the thickness of the scale on the surface of the billet is ≤3mm; the adhesion between the scale and the base material is small, the scale on the side and the lower surface of the billet has fallen off completely before the billet is transported to the descaling box, and the scale on the upper surface has obvious broken phenomenon, the residual area of the oxide scale of the billet after the descaling process is ≤10%, and there is no obvious blocky dark scale. The rolling method makes the descaling effect of the steel plate better, and the steel plate with better surface quality is obtained. DETAILED DESCRIPTION

[0018] The present application will be further described in detail below in combination with specific embodiments.

[0019] Embodiments 1-8

[0020] A surface oxide scale control method for a Ni-containing steel plate, comprising a billet heating and rolling process;

[0021] 1) The first heating section temperature is 850-1050℃, the second heating section temperature is 1150-1230℃, the third heating section temperature is 1200-1230℃, and the soaking section temperature is 1200-1240℃.

[0022] The effective heating time (in-furnace time) of the first heating section, the second heating section, and the third heating section is ≥2min / cm, and the effective heating time (in-furnace time) of the soaking section is ≥1.5min / cm.

[0023] The air-fuel ratio of the billet heating process is 0.6-0.8, the residual oxygen content is ≤3%, and the billet thickness is 200-330mm. The control parameters are shown in Table 1.

[0024] Table 1 Control parameters of the billet heating process in embodiments 1-8

[0025]

[0026] 2) Rolling process: descaling and rolling method: the height of the descaling box is adjusted to 200 / 250 / 300mm according to the billet thickness to ensure that the high-pressure water is at a 45° angle with the surface of the billet; the high-pressure descaling water pressure is ≥20Mpa. Odd passes are used in the rough rolling stage, and the rolling line is adjusted to +8~+12mm in advance; the total rolling passes in the rough rolling stage are 5-11 passes.

[0027] The first and second rough rolling pass reduction amount is 20-30mm, and the water is sprayed from above and below to remove scale; the third pass reduction amount is 20-30mm, and the steel is air-cooled for 1-2min for temperature recovery, and no water is sprayed to remove scale; the fourth pass reduction amount is 20-30mm, and the water is sprayed from above before the rolling mill and from below after the rolling mill; the fifth pass reduction amount is 20-30mm, and the water is sprayed from above before the rolling mill and from below after the rolling mill; and the water is sprayed from above before the rolling mill and from below after the rolling mill in subsequent rolling passes.

[0028] During the rolling process, black marks are found, the steel is air-cooled for temperature recovery, and then the rolling is continued after the temperature is uniform (the surface temperature difference is less than 50℃), and the control parameters are shown in Table 2, the chemical composition of the Ni-containing steel plate and the billet thickness are shown in Table 3, and the results of the surface scale area and thickness of the steel plate are shown in Table 4.

[0029] Table 2 Rolling process control parameters of the steel billets in Examples 1-8

[0030]

[0031] Table 3 Chemical composition of the steel billets in Examples 1-8 (wt%)

[0032]

[0033] Table 4 Results of the surface scale area and thickness of the steel plates in Examples 1-8

[0034]

[0035] The residual scale amount on the surface of the steel plates in Examples 1-8 is less than or equal to 5%, and the obtained steel plates have no scale, pitting, and pressure pits, and all the quality inspections are qualified.

[0036] The above description is only the preferred examples of the present application, and cannot limit the scope of the present application. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples, or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application is within the scope of the present application.

Claims

1. A method for controlling the surface scale of a Ni-containing steel sheet, characterized by, The control method comprises a billet heating process and a rolling process. In the billet heating process, the first heating section temperature is 850-1050℃, the second heating section temperature is 1150-1230℃, the third heating section temperature is 1200-1230℃, and the soaking section temperature is 1200-1240℃. In the rolling process, the first and second passes of rough rolling have a reduction of 20-30mm, and the upper and lower sides are simultaneously sprayed with water to remove scales; the third pass has a reduction of 20-30mm, and the steel is allowed to stand for 1-2min for temperature recovery without water spraying; the fourth pass has a reduction of 20-30mm, and the upper side is sprayed with water after the rolling mill and before the next rolling mill; the fifth pass has a reduction of 20-30mm, and the upper side is sprayed with water before the rolling mill and after the next rolling mill; the subsequent passes are all sprayed with water before the rolling mill and after the next rolling mill, and the water spraying is performed at intervals; the rough rolling stage adopts even pass rolling, and the rolling line is adjusted to +8~+12mm in advance; the total rough rolling passes are 5-11 passes, and the number of even passes is between 5 and 11.

2. The method of controlling the surface scale of a Ni-containing steel sheet according to claim 1, characterized by, In the billet heating process, the effective heating time of the first heating section, the second heating section and the third heating section is ≥2min / cm, and the effective heating time of the soaking section is ≥1.5min / cm.

3. The method of controlling the surface scale of a Ni-containing steel sheet according to claim 1, characterized by, In the billet heating process, the air-fuel ratio is 0.6-0.8, and the residual oxygen content is ≤3%.

4. The method of controlling the surface scale of a Ni-containing steel sheet according to claim 1, characterized by, In the rolling process, black marks are found during rolling, the steel is allowed to stand for temperature recovery, and the steel billet surface temperature difference is less than 50℃, and the rolling is continued after the black marks are eliminated.

5. A method of controlling the scale on the surface of a Ni-containing steel sheet according to any one of claims 1 to 4, characterized by, The control method is suitable for steel billets with a thickness of 200-330mm.

6. A method of controlling the scale on the surface of a Ni-containing steel sheet according to any one of claims 1 to 4, characterized by, The Ni content in the Ni-containing steel plate is 0.15-9%.

7. A method of controlling the scale on the surface of a Ni-containing steel sheet according to any one of claims 1 to 4, characterized by, When the Ni content in the Ni-containing steel plate is 0.15%≤Ni≤0.4%, there is no iron oxide scale on the surface of the steel plate.

8. A method of controlling the scale on the surface of a Ni-containing steel sheet according to any one of claims 1 to 4, characterized by, When the Ni content in the Ni-containing steel plate is 0.40%<Ni≤0.6%, the area of the iron oxide scale on the surface of the steel plate is ≤5%, and the thickness of the iron oxide scale is ≤0.2mm.

9. A method of controlling the scale on the surface of a Ni-containing steel sheet according to any one of claims 1 to 4, characterized by, When the Ni content in the Ni-containing steel plate is 0.60%<Ni≤9%, the area of the iron oxide scale on the surface of the steel plate is ≤10%, and the thickness of the iron oxide scale is ≤0.35mm.

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