NL2035289A

NL2035289A - Decarburization and nitriding process for oriented silicon steel with high magnetic induction

Info

Publication number: NL2035289A
Application number: NL2035289A
Authority: NL
Inventors: Fan Lifeng; Zhu Tiannan; Yue Erbin
Original assignee: Univ Inner Mongolia Technology
Priority date: 2022-10-26
Filing date: 2023-07-06
Publication date: 2024-05-14
Also published as: CN115584380A

Abstract

The invention discloses a decarburization and nitriding process for oriented silicon steel with high magnetic induction, which belongs to the technical field of oriented silicon steel manufacturing. In the invention, the annealing furnace 5 is used for decarburization and nitriding, and the annealing furnace is divided into preheating section, decarburization section, nitriding section and cooling section in turn; the process of decarburization first and then nitriding is adopted, and the carbon is firstly removed below 0.0015% in low temperature and wet atmosphere; then, high-temperature and short-time nitriding is 10 carried out in dry atmosphere. The invention can stably remove carbon below 0.0015%, control the nitriding amount at 200~220 ppm, control the average grain size of the primary recrystallization at 15~20 um, and control the deviation angle of goss grains at 5~8°. The invention is helpful to solve the problem of unstable magnetic properties caused by large fluctuation of 15 nitriding amount range.

Description

DECARBURIZATION AND NITRIDING PROCESS FOR ORIENTED

SILICON STEEL WITH HIGH MAGNETIC INDUCTION

TECHNICAL FIELD

The invention relates to the technical field of oriented silicon steel manufacturing, in particular to a decarburization and nitriding process for oriented silicon steel with high magnetic induction.

BACKGROUND

Oriented silicon steel is widely used in the production of transformer core because of its excellent magnetization in the rolling direction. In the current technology, in the decarburization annealing and nitriding process of oriented silicon steel, there are many technological conditions that affect the final performance of the product, especially the magnetic properties are unstable due to the large fluctuation of nitriding amount, and how to optimize the decarburization and nitriding process and improve the product performance has attracted more and more attention in the industry.

After searching, the Chinese patent application number: 2016110164685, and the invention name is a decarburization and nitriding annealing method for producing low temperature and high magnetic induction oriented silicon steel, the application includes the following steps: smelt; heat the casting blank after continuous casting; carry out conventional hot rolling and normalized annealing, then, carry out the cold rolling to the thickness of finished products; decarbonize and anneal after conventional alkali washing; carry out nitriding annealing; detect of P1.3/50 value of steel plate on-line, and calculate its revised value according to the formula; according to the content of AN after decarburization and nitriding, it is judged whether the relationship is satisfied simultaneously; and carry out the post-process conventionally. By adjusting decarburization annealing and nitriding annealing, the P1.3/50 value of steel coil material and nitriding amount AN are within a defined reasonable range at the same time, so that the magnetic properties of the products with a thickness of less than 0.30 mm can reach 1.92 T or more.

Another embodiment is Chinese patent application number: 2018106146768, and the invention name is a production method for nitriding and annealing the oriented silicon steel with high magnetic induction and its products. The production method of this application is as follows: carry out medium temperature nitriding, nitriding temperature is 800~850°C, which is consistent with decarbonization temperature, nitriding time is 10~50 s, nitriding medium is ammonia, flow rate is 5-6 mh, the pressure is 25-30 kpa, and nitrogen-hydrogen mixed protective gas is introduced into the furnace. The technological standard range of nitriding value is 150-210 ppm; the application is used to produce the finished products of low temperature and high magnetic induction oriented silicon steel with iron loss value of 0.90- 0.90-0.95 W/kg. To sum up, the decarbonization and nitriding process of oriented silicon steel has been widely disclosed, and its research and development ideas and technical purposes are different, and new research and development paths are constantly being explored in the industry.

SUMMARY

1. Technical problems to be solved in the invention

The purpose of the present invention is to solve the problems in the current technology that the nitriding amount fluctuates widely after decarburization and nitriding of oriented silicon steel, and the grain size of primary recrystallization is large, which is not conducive to secondary recrystallization. It is intended to provide a decarburization and nitriding process for oriented silicon steel with high magnetic induction, which can stably remove carbon below 0.0015%, control the nitriding amount at 200-220 ppm, control the average grain size of primary recrystallization at 15-20 um, and control the deviation angle of goss grains at 5~8°. 2. Technical scheme

In order to achieve the above purpose, the technical scheme provided by the invention is as follows:

A decarburization and nitriding process for oriented silicon steel with high magnetic induction in the invention comprises preheating, decarburization, nitriding and cooling. Specially, the annealing furnace is used for decarburization and nitriding. Correspondingly, the annealing furnace is divided into preheating section, decarburization section, nitriding section and cooling section in turn. In the invention, the process of decarburization first and then nitriding is adopted, and the carbon is firstly removed below 0.0015% in low temperature and wet atmosphere; then, high-temperature and short-time nitriding is carried out in dry atmosphere, the nitriding amount is 200-220 ppm, the primary recrystallization grain size is 15~20 um, and the deviation angle of goss grain is 5~8°

Furthermore, the incoming material thickness of strip steel is less than or equal to 0.23 mm.

Furthermore, the preheating section is heated by flame, and the strip steel is rapidly heated from room temperature to 830~840°C, the heating rate is 100~120°C/s, and the furnace pressure is controlled at 10~15 Pa.

Furthermore, the decarburization section is heated by a resistance band, and the temperature is stably controlled at 810~820°C, the H20 dew point is controlled at 10~15°C, the furnace pressure is controlled at 15-20 Pa, and the strip steel traveling time in the decarburization section is controlled at 90-120 s.

Furthermore, the decarbonization section is protected by hydrogen and oxygen, the content of Hz is 15~25% and the content of O2 is 400-500 ppm.

Furthermore, the nitriding section is heated by resistance band, the temperature is controlled at 900~920°C, the furnace pressure is controlled at 20-25 Pa, and the nitriding is carried out by ammonia decomposition, the ammonia flow rate is 100-130 m?/h, and the strip steel traveling time in the nitriding section is controlled at 50-60 s.

Furthermore, a closed furnace throat is adopted between the decarbonization section and the nitriding section, and the atmosphere does not interfere with each other.

Furthermore, the cooling section is divided into precooling section and rapid cooling section, and the precooling section is air-cooled to 550~500°C; the rapid cooling section is cooled by aerial fog, cooled to room temperature, and squeezed by squeezing roller.

In the invention, the N content of oriented silicon steel determines the amount of inhibitor AIN, and the larger the nitriding amount range, the more unstable the AIN amount is, and it is difficult to adjust it through high- temperature annealing, resulting in large fluctuations in magnetic properties, and even the abnormally grown goss texture cannot be obtained. The process of decarbonization and nitriding is unstable, and the nitriding amount is wide, so it can't be controlled in the future. No matter whether the nitriding amount is small or large, as long as the stability is high and the nitriding amount is stable, it can be remedied by adjusting the high-temperature annealing process. However, the nitriding amount fluctuates widely, exceeding 30 ppm, which leads to uneven distribution of AIN along the thickness and width of the plate. At this time, it cannot be remedied by adjusting the process. Stable nitriding amount is the premise of obtaining stable magnetic properties. The magnetic properties of oriented silicon steel fluctuate greatly, which is a direct manifestation of the instability of inhibitors. There is a phenomenon that the production process is divided into small rolls, because the magnetic properties are uneven, and the rolls can only be divided according to the magnetic properties, resulting in a large number of rolls and increasing the workload. The stability of nitriding process is the core process that restricts the oriented silicon steel with high magnetic induction. The invention is helpful to solve the technical problem of unstable magnetic properties caused by large fluctuation of nitriding amount range.

In addition, the smaller the grain size of primary recrystallization, the greater the driving force of secondary recrystallization. However, in order to better pursue the nitriding amount in the current process, most of them ignore the control of the grain size of primary recrystallization, or even get out of control, which also leads to magnetic instability. This is why some processes have a nitriding amount of more than 300 ppm, but their magnetic properties are average. Therefore, it is necessary to control the grain size of primary recrystallization while ensuring the nitriding amount in the decarbonization and nitriding process.

The invention adopts the process of decarbonization first and then 5 nitriding, and cooperates with the process control of each process. First, decarbonization is carried out at low temperature and wet atmosphere, and the carbon is removed to below 0.0015%. Because of the low temperature, the primary grain is fine; then the high-temperature and short-time nitriding is carried out in dry atmosphere, high temperature is beneficial to the increase of nitriding amount, and the grain growth is not obvious because of the short time; because the quality of decarburization in the previous stage is good, the temperature, time and flow rate in the nitriding stage are effectively controlled, there is no atmosphere interference, the nitriding amount is stable and the fluctuation range is small. The preheating section is heated by flame, which has fast heating rate, high nucleation rate and fine primary grains; in addition, the rapid heating rate is helpful to the nucleation and recrystallization of {111} grains and obtain more favorable textures. In the cooling stage, air cooling is carried out to 550~500°C and then water cooling is carried out to room temperature, and the air cooling speed is slow, so as to avoid increasing the stress of steel strip by direct water cooling; adopting air cooling first and then water cooling not only improves the cooling speed but also reduces the stress.

By adopting the design idea of the invention, the corresponding effect can be obtained by further adjusting the temperature or the running time of each section for the incoming materials with the thickness exceeding 0.23 mm. 3. Beneficial effects

Compared with the current technology, the technical scheme provided by the invention has the following beneficial effects: (1) The invention adopts the process of decarbonization first and then nitriding. First, decarbonization is carried out at low temperature and wet atmosphere, the primary grain is fine and the carbon is removed to below

0.0015%; Then the high-temperature and short-time nitriding is carried out in dry atmosphere, high temperature is beneficial to the increase of nitriding amount, and the grain growth is not obvious because of the short time; because the quality of decarburization in the previous stage is good, the temperature, time and flow rate in the nitriding stage are effectively controlled, there is no atmosphere interference, the nitriding amount is stable and the fluctuation range is small. The nitriding amount is controlled at 200~220 ppm. (2) In the invention, the preheating section is heated by flame, the faster the heating rate, the higher the nucleation rate, and the primary grain is fine; in addition, the rapid heating rate is helpful to the nucleation and recrystallization of {110} grains and obtain more favorable textures; however, the heating rate is too fast, and the orientation of the retained {110} goss grains is inaccurate, which leads to the increase of the deviation angle of the finished product; in the invention, the heating rate is strictly controlled at 100~120°C/s, when it is lower than 100°C/s, and the nucleation rate is slightly lower; when it is above 120°C/s, the orientation of goss crystal nucleus is not accurate; 100~120°C/s ensures that the nucleation rate and the deviation angle of goss crystal nucleus are in the best matching range. (3) The temperature of the preheating section is slightly higher than that of the decarburization section, and the temperature of the preheating section is high and the temperature rises quickly to obtain more nucleation points, the temperature of the decarburization section is low to inhibit the rapid growth of crystal nucleus formed in the previous section, so as to obtain fine primary recrystallization grains with the size of 15~20 um to provide sufficient driving force for secondary recrystallization.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is a schematic diagram of the metallographic structure of the strip steel obtained in Embodiment 1;

Fig. 2 is a schematic diagram of the metallographic structure of the strip steel obtained in Embodiment 2;

Fig. 3 is a schematic diagram of the metallographic structure of the strip steel obtained in Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

In order to further understand the content of the present invention, the present invention will be described in detail with the attached figures.

In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner" and "outer" are based on the orientation or positional relationship shown in the attached figures, and are only for the convenience of describing the present invention and simplifying the description, and they do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

The invention will be further described with embodiments.

Embodiment 1

In the decarburization and nitriding process for oriented silicon steel with high magnetic induction of the present embodiment, the incoming material thickness is 0.23 mm, the preheating section is heated to 840°C, the heating rate is 120°C/S, and the furnace pressure is 10 Pa; the temperature of decarbonization section is 810°C, the dew point of H20 is controlled at 10°C, the furnace pressure is controlled at 20 Pa, and the strip steel passing time is 90 s; the content of Hz in the atmosphere is 25%, and the content of O2 is 400 ppm. The furnace pressure in nitriding section is controlled at 20 Pa, the ammonia flow rate is 100 mh, the temperature is controlled at 900°C, and the strip steel passing time is 60 s; the precooling section is air-cooled to 550°C; then it is cooled to room temperature by water mist and squeezed dry.

The carbon content of that final decarburized annealing plate is 0.0015%, nitriding amount is 200 ppm, the grain size of the primary recrystallization is controlled at 15 um, and the deviation angle of goss grains is 7°. The metallographic structure of the obtained strip steel is shown in Fig. 1.

Embodiment 2

In the decarburization and nitriding process for oriented silicon steel with high magnetic induction of the present embodiment, the incoming material thickness is 0.20 mm, the preheating section is heated to 830°C, the heating rate is 100°C/S, and the furnace pressure is 15 Pa; the temperature of decarbonization section is 820°C, the dew point of H20 is controlled at 15°C, the furnace pressure is controlled at 20 Pa, and the strip steel passing time is 120 s; the content of Hz in the atmosphere is 15%, and the content of O2 is 500 ppm. The furnace pressure in nitriding section is controlled at 25 Pa, the ammonia flow rate is 130 m?h, the temperature is controlled at 920°C, and the strip steel passing time is 50 s; the precooling section is air-cooled to 500°C; then it is cooled to room temperature by water mist and squeezed dry.

The carbon content of that final decarburized annealing plate is 0.0011%, nitriding amount is 200 ppm, the grain size of the primary recrystallization is controlled at 20 pm, and the deviation angle of goss grains is 5°. The metallographic structure of the obtained strip steel is shown in Fig. 2.

Embodiment 3

In the decarburization and nitriding process for oriented silicon steel with high magnetic induction of the present embodiment, the incoming material thickness is 0.21 mm, the preheating section is heated to 835°C, the heating rate is 100°C/S, and the furnace pressure is 15 Pa; the temperature of decarbonization section is 820°C, the dew point of H20 is controlled at 15°C, the furnace pressure is controlled at 15 Pa, and the strip steel passing time is 105 s; the content of Hz in the atmosphere is 20%, and the content of O2 is 450 ppm. The furnace pressure in nitriding section is controlled at 25 Pa, the ammonia flow rate is 130 mh, the temperature is controlled at 900°C, and the strip steel passing time is 55 s; the precooling section is air-cooled to 540°C; then it is cooled to room temperature by water mist and squeezed dry.

The carbon content of that final decarburized annealing plate is 0.0013%,

nitriding amount is 210 ppm, the grain size of the primary recrystallization is controlled at 19 um, and the deviation angle of goss grains is 6°.

Embodiment 4

In the decarburization and nitriding process for oriented silicon steel with high magnetic induction of the present embodiment, the incoming material thickness is 0.20 mm, the preheating section is heated to 840°C, the heating rate is 120°C/S, and the furnace pressure is 12 Pa; the temperature of decarbonization section is 815°C, the dew point of H20 is controlled at 12°C, the furnace pressure is controlled at 18 Pa, and the strip steel passing time is 105 s; the content of Hz in the atmosphere is 20%, and the content of O2 is 400 ppm. The furnace pressure in nitriding section is controlled at 22 Pa, the ammonia flow rate is 120 m?h, the temperature is controlled at 910°C, and the strip steel passing time is 56 s; the precooling section is air-cooled to 520°C; then it is cooled to room temperature by water mist and squeezed dry.

The carbon content of that final decarburized annealing plate is 0.0014%, nitriding amount is 205 ppm, the grain size of the primary recrystallization is controlled at 18 um, and the deviation angle of goss grains is 8°.

Comparative Example 1

In the decarburization and nitriding process of oriented silicon steel of this Comparative Example, the incoming material thickness of strip steel is 0.20 mm, the temperature of preheating section is 750°C, and the furnace pressure is 15 Pa; the temperature of decarbonization section is 840°C, the dew point of H20 is controlled at 15°C, the furnace pressure is controlled at 20 Pa, and the H2 content is 15%. The furnace pressure in nitriding section is controlled at 25 Pa, the temperature is controlled at 980°C, the ammonia flow rate is 150 m?h, and the precooling section is air-cooled to 500°C; then it is cooled to room temperature with water and squeezed dry. The carbon content of that final decarburized annealing plate is 0.0013%, nitriding amount is 260 ppm, the grain size of the primary recrystallization is controlled at 30 um, the deviation angle of goss grains reaches 11°, and the grain uniformity iS poor.

The present invention and its embodiments have been described schematically above. This description is not restrictive, but only one of the embodiments of the present invention, and it is not actually limited to this.

Therefore, if the ordinary technicians in this field are inspired by it, and they donot deviate from the creative purpose of the invention, they will design the structural mode and embodiment similar to the technical scheme without creativity, which should all belong to the protection scope of the invention.

Claims

ConclusiesConclusions

1. Een ontkolings- en nitridingsproces voor georiénteerd siliciumstaal met hoge magnetische inductie, waarbij de gloeioven wordt gebruikt voor ontkoling en nitreren, en de gloeioven beurtelings is verdeeld in voorverwarmgedeelte, ontkolingsgedeelte, nitreergedeelte en koelgedeelte; het proces van eerst ontkolen en vervolgens nitreren wordt toegepast, en de koolstof wordt eerst verwijderd onder 0,0015% bij lage temperatuur en natte atmosfeer; vervolgens wordt nitreren bij hoge temperatuur en korte tijd uitgevoerd in een droge atmosfeer.1. A decarburization and nitriding process for high magnetic induction oriented silicon steel, in which the annealing furnace is used for decarburization and nitriding, and the annealing furnace is alternately divided into preheating section, decarburization section, nitriding section and cooling section; the process of first decarburization and then nitriding is adopted, and the carbon is first removed below 0.0015% at low temperature and wet atmosphere; then nitriding is carried out at high temperature and for a short time in a dry atmosphere.

2. Het ontkolings- en nitreringsproces voor georiënteerd siliciumstaal met hoge magnetische inductie volgens conclusie 1, waarbij het voorverwarmingsgedeelte wordt verwarmd door een vlam en het bandstaal snel wordt verwarmd van kamertemperatuur tot 830-840°C, de verwarmingssnelheid is 100-120°C/s, en de ovendruk wordt geregeld op 10- 15 Pa.2. The decarburization and nitriding process for high magnetic induction oriented silicon steel according to claim 1, wherein the preheating part is heated by a flame and the strip steel is quickly heated from room temperature to 830-840°C, the heating rate is 100-120°C/ s, and the furnace pressure is controlled at 10-15 Pa.

3. Het ontkolings- en nitreringsproces voor georiënteerd siliciumstaal met hoge magnetische inductie volgens conclusie 2, waarbij het ontkolingsgedeelte wordt verwarmd door een weerstandsband en de temperatuur stabiel wordt geregeld op 810-820°C, het H20-dauwpunt wordt geregeld bij 10-15°C wordt de ovendruk geregeld op 15-20 Pa, en wordt de looptijd van het bandstaal in de ontkolingssectie geregeld op 90-120s.3. The decarburization and nitriding process for high magnetic induction oriented silicon steel according to claim 2, wherein the decarburization part is heated by a resistance band and the temperature is stably controlled at 810-820°C, the H20 dew point is controlled at 10-15° C, the furnace pressure is controlled at 15-20 Pa, and the running time of the strip steel in the decarburization section is controlled at 90-120s.

4. Het ontkolings- en nitreringsproces voor georiënteerd siliciumstaal met hoge magnetische inductie volgens conclusie 3, waarbij het ontkolingsgedeelte wordt beschermd door waterstof en zuurstof, het gehalte aan H2 15~25% is en het gehalte aan O2 400- is 500ppm.4. The decarburization and nitriding process for high magnetic induction oriented silicon steel according to claim 3, wherein the decarburization part is protected by hydrogen and oxygen, the content of H2 is 15~25% and the content of O2 is 400-500ppm.

5. Het ontkolings- en nitreerproces voor georiënteerd siliciumstaal met hoge magnetische inductie volgens conclusie 1, waarbij het nitreergedeelte wordt verwarmd door een weerstandsband, de temperatuur wordt geregeld op 900- 920°C, de ovendruk wordt geregeld op 20-25Pa, en het nitreren wordt uitgevoerd door ammoniakontleding, het ammoniakdebiet is 100-130 m3/uur en de looptijd van het bandstaal in de nitreersectie wordt geregeld op 50-605. The decarburization and nitriding process for high magnetic induction oriented silicon steel according to claim 1, wherein the nitriding part is heated by a resistance band, the temperature is controlled at 900-920°C, the furnace pressure is controlled at 20-25Pa, and the nitriding is carried out by ammonia decomposition, the ammonia flow rate is 100-130 m3/hour and the running time of the strip steel in the nitriding section is controlled at 50-60

S.S.

6. Werkwijze voor het ontkolen en nitreren van georiénteerd siliciumstaal met hoge magnetische inductie volgens conclusie 1, met het kenmerk, dat tussen het ontkolingsgedeelte en het nitreergedeelte een gesloten ovenhals wordt toegepast en de atmosfeer elkaar niet hindert.6. A method for decarburizing and nitriding oriented silicon steel with high magnetic induction according to claim 1, characterized in that a closed furnace neck is used between the decarburization section and the nitriding section and the atmosphere does not interfere with each other.

7. Het ontkolings- en nitreringsproces voor georiénteerd siliciumstaal met hoge magnetische inductie volgens conclusie 1, waarbij het koelgedeelte is verdeeld in een voorkoelgedeelte en een snelkoelgedeelte en het voorkoelgedeelte luchtgekoeld is tot 550-500°C; het snelle koelgedeelte wordt gekoeld door luchtmist, afgekoeld tot kamertemperatuur en geperst door een knijprol.The decarburization and nitriding process for high magnetic induction oriented silicon steel according to claim 1, wherein the cooling section is divided into a pre-cooling section and a rapid cooling section and the pre-cooling section is air-cooled to 550-500°C; the rapid cooling section is cooled by air mist, cooled to room temperature and squeezed by a pinch roller.

8. Ontkolings- en nitreerproces voor georiénteerd siliciumstaal met hoge magnetische inductie volgens een van de conclusies 1-7, waarbij de nitreerhoeveelheid van stripstaal 200-220ppm is en de primaire herkristallisatiekorrelgrootte 15-20 um is , de afwijkingshoek van gosskorrel is 5-8°, en koolstof wordt verwijderd onder 0,0015%.8. Decarburization and nitriding process for high magnetic induction oriented silicon steel according to any one of claims 1-7, wherein the nitriding amount of strip steel is 200-220ppm and the primary recrystallization grain size is 15-20 um, the deviation angle of goss grain is 5-8° , and carbon is removed below 0.0015%.

9. Werkwijze voor het ontkolen en nitreren van georiënteerd siliciumstaal met hoge magnetische inductie volgens een van de conclusies 1-7, waarbij de binnenkomende materiaaldikte van bandstaal kleiner is dan of gelijk is aan 0,23 mm.A method for decarburizing and nitriding oriented silicon steel with high magnetic induction according to any one of claims 1 to 7, wherein the incoming material thickness of strip steel is less than or equal to 0.23 mm.