A 20-roller cold rolling method for iron-chromium-aluminum alloy

Abstract

The invention relates to the field of cold rolling of iron-chromium-aluminum alloy by a 20-roll mill. A cold rolling method for an iron-chromium-aluminum alloy by a 20-roll mill comprises the following steps: the alloy is kept at 180°C in a heating furnace for 8-10 hours before rolling; during the first rolling, the alloy is rolled on a reel for 18 meters before rolling; the starting tension of the first rolling is 100-120KN; after the steel strip is rolled to about 100 meters and the state is stabilized, the tension is gradually increased to 160KN; constant pressure rolling is adopted for the second rolling, the rolling pressure is 200-450KN, and AFC is put into operation at the same time; after 3-5 rolling passes at constant pressure, AGC is put into operation in time according to the thickness fluctuation to adopt automatic rolling.

Description

Technical Field

[0001] The invention relates to the field of cold rolling of iron-chromium-aluminium alloy by a 20-roller mill. Background Art

[0002] Iron-chromium-aluminum alloy belongs to electrothermal engineering materials, containing Cr and Al elements of about 13%-27% and 3%-6% respectively. The grades include 1Cr13Al4, 0Cr21A16, 0Cr23A15 and OCr27A17Mo2, etc. It has the characteristics of high resistivity, small temperature coefficient of resistance, good oxidation resistance and high operating temperature.

[0003] Iron-chromium-aluminum alloy is generally made into ingots by melting method and processed into materials by pressure. Iron-chromium-aluminum alloy is a high-aluminum, high-chromium ferrite structure with high brittleness. Generally, the brittle-ductile transition temperature is 30-40℃, and the processing performance is poor. After long-term use at level 1 temperature, it is easy to become brittle due to grain growth. Iron-chromium-aluminum is particularly prone to fracture during rolling. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to provide a method for stably rolling an iron-chromium-aluminum alloy with a 20-roller reversible rolling mill.

[0005] The technical scheme adopted by the present invention is: a 20-roller cold rolling method for iron-chromium-aluminum alloy, heating and heat preservation before rolling, curling to avoid temperature uneven sections, starting with small tension, gradually increasing rolling tension during rolling, constant pressure rolling, and uniform acceleration, so as to achieve stable batch rolling, specifically: before rolling, the temperature is kept at 180°C in a heating furnace for 8-10 hours, in the first rolling, rolling is started after curling on the reel for 18 meters, the starting tension of the first pass is 100-120KN, and the tension is gradually increased to 160KN after rolling to about 100m and the state of the steel strip is stable, constant pressure rolling is adopted from the second pass, the rolling pressure is 200-450KN, and AFC is put into use at the same time, after 3-5 passes of constant pressure rolling, AGC is put into use in time according to the thickness fluctuation to adopt automatic rolling.

[0006] When increasing or decreasing the speed during the rolling process, turn off the automatic pressing down AGC and the automatic plate shape control AFC, and adopt a uniform speed increase and decrease.

[0007] Heating and insulation before rolling

[0008] Due to the high brittleness of Fe-Cr-Aluminum alloy, the probability of brittle fracture during rolling at room temperature is very high. Therefore, a one-stage constant temperature heating method is adopted before rolling, and the temperature is kept at 180℃ in the heating furnace for 8 hours. According to the experimental results, under this condition, the temperature of the whole coil can reach about 100℃, and the temperature of the steel strip during the unwinding process can also be guaranteed to be above 50℃. The temperature of the steel strip during the rolling process is basically 80℃, so the risk of strip breakage in the middle pass is very low, and the brittle fracture of the first pass is mainly controlled. Compared with the previous two-stage different temperature control, it ensures the heating efficiency and the uniformity of the heating temperature of the whole coil.

[0009] The first crimping avoids the brittle part

[0010] During the loading and uncoiling process, the temperature of the opened steel strip head drops sharply and is prone to brittle fracture below 40°C. Due to the high brittleness of iron-chromium-aluminum alloy, stable state is a prerequisite during the rolling process. According to the previous measures, whether the uncoiling process will have brittle fracture mainly depends on the temperature of the head of the steel coil after heating and the temperature uniformity. The probability of brittle fracture is about 40%. After uncoiling temperature measurement and statistical measurement values, the temperature of the head tends to be above 50°C after about 18 meters. Therefore, the optimized measure is to start rolling after the first pass is coiled on the reel for about 8 turns, so as to avoid the part with insufficient head temperature and uneven temperature.

[0011] Low tension rolling

[0012] The yield strength of FeCrAl is about 600-800MPa. According to the characteristics of ordinary stainless steel, the starting tension of the first pass should be about 200-450KN. Due to the brittle characteristics of FeCrAl, excessive tension can easily break the steel strip. According to laboratory measurements, it is more reasonable to use about 50% of the conventional tension, set the starting tension to 100KN, and gradually increase the tension to 160KN after the steel strip is stable after rolling to about 100m. The second pass starts with the normal tension setting and AFC is put into use. Compared with the previous low tension rolling in each pass, the optimized measures can ensure the good plate shape of FeCrAl.

[0013] Constant pressure rolling

[0014] The premise of stable rolling of brittle materials is stable state. Since the annealing state and thickness fluctuation of the incoming materials are unknown, constant pressure rolling can ensure the stability of the rolling process. After several passes of constant pressure rolling, AGC is promptly put into automatic rolling according to the thickness fluctuation to ensure that there is no obvious fluctuation in the thickness of the finished product, which meets customer needs. The previous plan was mainly to prevent strip breakage, and the thickness could not be guaranteed.

[0015] Uniformly accelerated rolling

[0016] The rolling process needs to increase or decrease the speed at the head and tail. The automatic pressing down AGC and automatic plate shape control AFC will be turned off during the speed increase or decrease process. Since the stress state of the steel strip will fluctuate during the speed increase or decrease process, it is necessary to increase or decrease the speed evenly, and avoid sudden increase or decrease in speed to avoid brittle fracture caused by unstable state. Compared with the previous solution, the rolling efficiency is higher, and the hourly output can reach 20t / h, which is about 10t / h before.

[0017] The beneficial effects of the present invention are as follows: according to the brittle fracture characteristics of the steel type, its brittle-to-ductile transition temperature is studied, and then measures are taken (heating and heat preservation in the heating furnace) to ensure that the rolling temperature is above the brittle-to-ductile transition temperature (above 40°C). Through experimental measurement, the temperature of the head of the steel strip about 18 meters drops rapidly and cannot be guaranteed to be above 40°C. Therefore, measures are taken during the rolling process to avoid brittle fracture caused by mechanical deformation (curling the uncoiling cooling section onto the reel without rolling) and to avoid brittle fracture caused by unstable steel state (starting with small tension, constant pressure rolling, and uniform acceleration rolling).

[0018] 1. Before rolling iron, chromium and aluminum, they must be heated in the furnace to ensure that the temperature of the entire coil is above the brittle-ductile transition temperature during rolling;

[0019] 2. During the uncoiling and feeding process, the outer ring head cools down quickly. In order to ensure the temperature of the steel plate, the outer ring is completely rolled onto the reel without rolling to avoid brittle fracture;

[0020] 3. During the starting given tension process, the steel plate is prone to brittle fracture due to instantaneous force, so a small tension is used for starting;

[0021] 4. Since the annealing state of steel is unstable, including annealing temperature, thickness, etc., which can cause pressure fluctuations during the rolling process, constant pressure rolling is adopted to avoid brittle fracture caused by unstable state;

[0022] 5. During the rolling process, the speed should be increased or decreased evenly to avoid brittle fracture caused by sudden increases or decreases. DETAILED DESCRIPTION

[0023] Steel type: 0Cr21A16; Specification: 3.0mm rolled 1.0mm; Width: 1250mm.

[0024] The specific parameters are as follows:

[0025]

[0026] According to the material properties of iron-chromium-aluminum alloy and the equipment characteristics of the 20-roll mill, stable batch rolling is achieved by heating and keeping warm before rolling, curling to avoid temperature uneven sections, starting with small tension, gradually increasing the rolling tension during the rolling process, constant pressure rolling, and uniform acceleration.

[0027] Heating and insulation before rolling

[0028] Due to the high brittleness of Fe-Cr-Aluminum alloy, the probability of brittle fracture during rolling at room temperature is very high. Therefore, a one-stage constant temperature heating method is adopted before rolling, and the temperature is kept at 180℃ in the heating furnace for 8 hours. According to the experimental results, under this condition, the temperature of the whole coil can reach about 100℃, and the temperature of the steel strip during the unwinding process can also be guaranteed to be above 50℃. The temperature of the steel strip during the rolling process is basically 80℃, so the risk of strip breakage in the middle pass is very low, and the brittle fracture of the first pass is mainly controlled. Compared with the previous two-stage different temperature control, it ensures the heating efficiency and the uniformity of the heating temperature of the whole coil.

[0029] The first crimping avoids the brittle part

[0030] During the loading and uncoiling process, the temperature of the opened steel strip head drops sharply and is prone to brittle fracture below 40°C. Due to the high brittleness of iron-chromium-aluminum alloy, stable state is a prerequisite during the rolling process. According to the previous measures, whether the uncoiling process will have brittle fracture mainly depends on the temperature of the head of the steel coil after heating and the temperature uniformity. The probability of brittle fracture is about 40%. After uncoiling temperature measurement and statistical measurement values, the temperature of the head tends to be above 50°C after about 18 meters. Therefore, the optimized measure is to start rolling after the first pass is coiled on the reel for about 8 turns, so as to avoid the part with insufficient head temperature and uneven temperature.

[0031] Low tension rolling

[0032] The yield strength of FeCrAl is about 600-800MPa. According to the characteristics of ordinary stainless steel, the starting tension of the first pass should be about 200-450KN. Due to the brittle characteristics of FeCrAl, excessive tension can easily break the steel strip. According to laboratory measurements, it is more reasonable to use about 50% of the conventional tension, set the starting tension to 100KN, and gradually increase the tension to 160KN after the steel strip is stable after rolling to about 100m. The second pass starts with the normal tension setting and AFC is put into use. Compared with the previous low tension rolling in each pass, the optimized measures can ensure the good plate shape of FeCrAl.

[0033] Constant pressure rolling

[0034] The premise of stable rolling of brittle materials is stable state. Since the annealing state and thickness fluctuation of the incoming materials are unknown, constant pressure rolling can ensure the stability of the rolling process. After several passes of constant pressure rolling, AGC is promptly put into automatic rolling according to the thickness fluctuation to ensure that there is no obvious fluctuation in the thickness of the finished product, which meets customer needs. The previous plan was mainly to prevent strip breakage, and the thickness could not be guaranteed.

[0035] Uniformly accelerated rolling

[0036] The rolling process needs to increase or decrease the speed at the head and tail. The automatic pressing down AGC and automatic plate shape control AFC will be turned off during the speed increase or decrease process. Since the stress state of the steel strip will fluctuate during the speed increase or decrease process, it is necessary to increase or decrease the speed evenly, and avoid sudden increase or decrease in speed to avoid brittle fracture caused by unstable state. Compared with the previous solution, the rolling efficiency is higher, and the hourly output can reach 20t / h, which is about 10t / h before.

[0037] When rolling iron-chromium-aluminum according to the method of the present invention, the strip breakage rate is greatly reduced from the previous 40% to less than 3%.

[0038] The implementation of the present invention can roll Fe-Cr-Al alloy in batches, efficiently and stably;

[0039] The implementation of the present invention reduces the brittle fracture probability of the iron-chromium-aluminum alloy, and the brittle fracture probability is reduced from the previous 40% to less than 5%.

Claims

1. A 20-high mill cold rolling method for an iron-chromium-aluminum alloy, characterized in that: Stable batch rolling is achieved by heating and heat preservation before rolling, curling to avoid temperature uneven sections, starting with small tension, gradually increasing rolling tension during rolling, constant pressure rolling, and uniform acceleration. Specifically, before rolling, the strip is kept at 180℃ in a heating furnace for 8-10 hours. During the first rolling, the strip is curled on the reel for 18 meters before rolling. The starting tension of the first pass is 100-120KN. After rolling to about 100m and the state of the steel strip is stable, the tension is gradually increased to 160KN. Constant pressure rolling is adopted from the second pass, and the rolling pressure is 200-450KN. AFC is also put into operation. After 3-5 passes of constant pressure rolling, AGC is promptly put into operation for automatic rolling according to the thickness fluctuation.

2. The 20-high mill cold rolling method of an Fe-Cr-Al alloy according to claim 1, characterized in that: When increasing or decreasing the speed during the rolling process, turn off the automatic pressing down AGC and the automatic plate shape control AFC, and adopt a uniform speed increase and decrease.

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