CN106636858B - A kind of method for producing high anti-corrosion high-nitrogen super austenitic stainless steel - Google Patents

Abstract

The present invention proposes a kind of method of high nitrogen steel technical field of smelting using the high anti-corrosion high-nitrogen super austenitic stainless steel of vaccum sensitive stove bottom blowing nitrogen production, it includes step：Dispensing simultaneously calculates smelting pressure；Charging；Be powered heating after being evacuated within 5Pa；Nitrogen is passed through after melting down to smelting pressure, bottom blowing nitrogen alloying；Sequentially add nitro-alloy, deoxidier and desulfurizing agent；Inflated with nitrogen to 0.08~0.095MPa, 1460~1530 DEG C of control molten steel temperature is cast.The method of the present invention is using bottom blowing nitrogen and adds efficient, the inexpensive nitrogen pick-up mode of nitro-alloy, match rational deoxidization desulfuration technique, the casting pressure and degree of superheat, for exploitation nitrogen content is higher and controllable precise, low segregation, pore-free, high cleanliness, excellent performance high anti-corrosion high-nitrogen super austenitic stainless steel technical guarantee is provided.

Description

A method for producing high corrosion resistance and high nitrogen super austenitic stainless steel

technical field

The invention relates to the field of high-nitrogen steel smelting, in particular to a method for producing high-corrosion-resistant high-nitrogen super austenitic stainless steel by blowing nitrogen at the bottom of a vacuum induction furnace.

Background technique

Nitrogen is added to stainless steel as a strong interstitial element. Through the synergistic effect with other alloying elements (chromium, molybdenum, etc.), it can not only effectively improve the strength, toughness, creep ability and wear resistance of the steel, but also significantly improve the corrosion resistance of the steel. It has been widely used in a series of steels such as austenitic stainless steel and duplex stainless steel. According to the different nitrogen content, nitrogen-containing austenitic stainless steel can be divided into nitrogen control type (nitrogen content 0.05% ~ 0.10%), medium nitrogen type (nitrogen content 0.10% ~ 0.40%) and high nitrogen type (nitrogen content 0.40% %above). High corrosion resistance and high nitrogen super austenitic stainless steel contains high chromium, molybdenum, nickel and nitrogen, has high strength and toughness, and its yield strength is about 50-100% higher than that of ordinary austenitic stainless steel; in high concentration chloride ion medium, seawater, In extremely harsh service environments such as low-speed erosion, it has excellent resistance to localized corrosion such as uniform corrosion and pitting corrosion and stress corrosion resistance. Some typical varieties are comparable to nickel-based corrosion-resistant alloys such as C276 and titanium alloys with excellent corrosion resistance, and have significant cost advantages. They are widely used in petrochemical, environmental protection (flue gas desulfurization, waste incineration, etc.), seawater Desalination and other extremely harsh service environments.

For high-nitrogen super austenitic stainless steel with high nitrogen content, the precise control of nitrogen alloying mode and nitrogen is very important in its preparation process. The commonly used methods for increasing nitrogen in molten steel mainly include: adding nitrided alloys (such as high-purity chromium nitride, manganese nitride, etc.) to molten steel, using nitrogen for nitrogen alloying or a combination of the two methods. Although the method of adding nitrogen alloy to increase nitrogen is simple and easy to operate, due to the high nitrogen content, the reaction is violent during the addition process, and the phenomenon of "splashing" occurs in serious cases, and the nitrogen content in the steel is not easy to control. In addition, the nitrided alloy is expensive, and the cost of increasing nitrogen by simply relying on the nitrided alloy is relatively high. Therefore, the use of cheap nitrogen instead of manganese nitride or high-purity chromium nitride for nitrogen alloying has attracted much attention. However, the nitrogen alloying method of nitriding the surface of molten steel by filling nitrogen in the smelting container has a slow reaction rate and a long period of nitrogen increase. soon. Nitrogen is blown into molten steel from the vent plug at the bottom of the smelting equipment for nitrogen alloying. The dispersed nitrogen bubbles can greatly improve the kinetic conditions of nitrogen alloying, increase the gas-liquid contact area, and promote the rapid increase of nitrogen in molten steel. Therefore, the method of nitrogen alloying by bottom blowing nitrogen provides a low-cost and high-efficiency way for the smelting of high-nitrogen stainless steel.

Small-scale production of high-nitrogen stainless steel by vacuum induction furnace bottom-blowing nitrogen alloying has the advantages of simple smelting process, high efficiency and low cost, especially for high-corrosion-resistant high-nitrogen super austenitic stainless steel with high added value and small batch demand. More market flexibility. However, in the production process of high-corrosion-resistant and high-nitrogen super austenitic stainless steel, reasonable matching of nitrogen alloying process, precise control of nitrogen content in molten steel, reasonable control of superheat and pressure during casting, and reasonable deoxidation and desulfurization methods, Both are very important to obtain high-nitrogen super austenitic stainless steel with high nitrogen content, precise controllability, low segregation, no porosity, high purity and high performance.

Contents of the invention

Based on the problems existing in the prior art, the object of the present invention is to provide a method for producing high corrosion resistance and high nitrogen super austenitic stainless steel by blowing nitrogen gas at the bottom of a vacuum induction furnace. The manufacturing cost is low, and the nitrogen content of the stainless steel is high and accurate. Controllable, low segregation, no porosity, high purity, excellent performance.

In order to achieve the purpose of the present invention, a method of using nitrogen blowing at the bottom of a vacuum induction furnace to produce high corrosion resistance and high nitrogen super austenitic stainless steel of the present invention comprises the following steps:

S1. Charging: put industrial pure iron, metal chromium, metal molybdenum, metal nickel, electrolytic copper, metal manganese, and industrial silicon into the crucible of the induction furnace, and put high-purity chromium nitride, electrolytic aluminum, nickel-magnesium alloy and rare earth placed in the feeding bin;

S2. Furnace charge melting: vacuumize the induction furnace to below 5Pa, and turn on the electricity to heat up until the charge in the induction furnace is completely melted;

S3. Nitrogen alloying: After the charge in the vacuum induction furnace is melted, nitrogen is introduced to the smelting pressure p, and the melting temperature is maintained at 1500-1560°C by controlling the power, and nitrogen is introduced into the furnace from the ventilation plug at the bottom of the furnace for bottom blowing and stirring For smelting, the nitrogen flow rate of bottom blowing is 0.05~0.20Nm ³ /h, and the bottom blowing time is 15~25min; among them, the smelting pressure p is calculated according to the following formula:

M＝0.13[%N]+0.118[%C]+0.043[%Si]+0.011[%Ni]+3.5×10 ^-5 [%Ni] ²

-0.024[%Mn]+3.2×10 ^-5 [%Mn] ² -0.01[%Mo]+7.9×10 ^-5 [%Mo] ²

-0.048[%Cr]+3.5×10 ^-4 [%Cr] ²

In the formula: p is the smelting pressure, p ^θ is the standard atmospheric pressure, and T is the smelting temperature;

The actual addition weight percentage (wt%) _N1 of nitrogen in the smelting raw material is calculated according to the following formula:

(wt%) _N1 = (0.1～0.2) (wt%) _N

In the formula, (wt%) _N represents the actual weight percentage of nitrogen added in the smelting raw material, and (wt%) _N represents the weight percentage of nitrogen in the target composition of high corrosion-resistant high-nitrogen super austenitic stainless steel;

S4. Deoxidation and desulfurization: After stopping the nitrogen blowing at the bottom, add high-purity chromium nitride to the furnace for further nitrogen alloying, and then sequentially add electrolytic aluminum, nickel-magnesium alloys, and rare earths for deep deoxidation and deep desulfurization; among them, high-purity nitrogen The weight percentage of chromium in chromium ≥ 85%, the weight percentage of nitrogen ≥ 10%, the addition amount of electrolytic aluminum is 0.6-0.8kg/t, the addition amount of nickel-magnesium alloy containing 20% magnesium is 0.8-1.2kg/t, the addition amount of rare earth 0.5～1kg/t;

S5. Casting: Fill the vacuum induction furnace with nitrogen to a casting pressure of 0.08-0.095MPa, control the temperature of the molten steel at 1460-1530°C for casting; after the casting is completed, cool down, break the vacuum and take out the ingot.

Preferably, the composition of the target austenitic stainless steel for smelting is: C: ≤0.02%, Si: ≤0.5%, Mn: 2.0-4.0%, Cr: 24.0-25.0%, Ni: 21.0-23.0%, Mo: 7.0-8.0%, Cu: 0.3-0.6%, N: 0.45-0.55%, S: ≤0.005%, P: ≤0.03%, Fe: balance.

Compared with the prior art, the present invention has the outstanding advantages of:

(1) The vacuum induction furnace bottom blowing nitrogen alloying method is adopted to save costs, greatly improve the kinetic conditions of nitrogen alloying, and promote the rapid nitrogen addition of molten steel;

(2) After the end of nitrogen blowing at the bottom, the nitrogen content of molten steel is further increased by adding a nitride alloy, which is beneficial to obtain a target alloy with high nitrogen content and precision;

(3) Deep deoxidation and deep desulfurization are carried out by means of electrolytic aluminum, nickel-magnesium and rare earth composite addition, which is conducive to obtaining high-purity target alloys with low oxygen and sulfur content;

(4) Nitrogen filling operation before pouring and casting with low superheat are beneficial to obtain the target alloy with high nitrogen content, low segregation and no porosity.

Description of drawings

The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawings. in:

Fig. 1 shows a process flow diagram of a method for producing high corrosion resistance and high nitrogen super austenitic stainless steel according to the present invention.

Detailed ways

The technological principle of the present invention is that the smelting pressure is firstly calculated by using the nitrogen solubility model, and then gas-phase alloying is carried out by using bottom blowing nitrogen in a vacuum induction furnace. Since the target nitrogen content cannot be achieved by simply relying on bottom blowing nitrogen, after the end of bottom blowing nitrogen, add nitride alloy to further increase the nitrogen content in molten steel, optimize the deoxidation and desulfurization process, and reasonably match the casting pressure and superheating process parameters, so as to obtain high corrosion resistance and high nitrogen super austenitic stainless steel with high nitrogen content, precise controllability, low segregation, no porosity, high purity and excellent performance.

The specific implementation of the present invention will be described in detail below in conjunction with the process steps and specific examples of the accompanying drawing 1, but the specific implementation of the present invention is not limited to the following examples.

In the example of the present invention, the smelting equipment is a 500kg vacuum induction furnace, the ultimate vacuum is 0.1Pa, the power supply is 350kW, the frequency is 1000Hz, and the furnace capacity is 380kg. The smelted steel is high corrosion resistance and high nitrogen super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N

The main components of the smelting raw materials used in the examples given by the present invention are shown in Table 1.

Table 1 Main components of smelting raw materials/wt%

Calculation formula of smelting pressure p①:

M＝0.13[%N]+0.118[%C]+0.043[%Si]+0.011[%Ni]+3.5×10 ^-5 [%Ni] ²

-0.024[%Mn]+3.2×10 ^-5 [%Mn] ² -0.01[%Mo]+7.9×10 ^-5 [%Mo] ²

-0.048[%Cr]+3.5×10 ^-4 [%Cr] ²

In the formula: p is the smelting pressure, p ^θ is the standard atmospheric pressure, and T is the smelting temperature.

The actual weight percentage (wt%) of nitrogen added to the smelting raw material _N1 calculation formula ②:

(wt%) _N1 = (0.1～0.2) (wt%) _N

In the formula, (wt%) _N1 represents the actual weight percentage of nitrogen added in smelting raw materials, and (wt%) _N represents the weight percentage of nitrogen in the target composition of high corrosion resistance and high nitrogen super austenitic stainless steel.

Embodiment one

A 500kg vacuum induction furnace is used to smelt high-corrosion-resistant and high-nitrogen super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N, and its composition control range and control objectives are shown in Table 2.

Table 2 Super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N composition control range and control target (wt%)

Specific steps are as follows:

(1) Calculation of ingredients and smelting pressure

According to the target composition of the steel grade in Table 2 and the smelting temperature of about 1550°C, it is calculated according to formula ①: the smelting pressure p is 0.076MPa; calculated according to formula ②: the actual weight percentage of nitrogen added in the smelting raw material (wt%) _N1 is 0.046%; the calculated weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N is shown in Table 3. The amount of deoxidizer and desulfurizer added is 95g of electrolytic aluminum, 418g of nickel-magnesium alloy, and 228g of rare earth cerium.

Table 3 The weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N

(2) Charging: put industrial pure iron, metal chromium, metal molybdenum, metal nickel, electrolytic copper, metal manganese, and industrial silicon into the crucible of the induction furnace, and put high-purity chromium nitride, electrolytic aluminum, nickel-magnesium alloy and Rare earth is placed in the feeding bin.

(3) Furnace charge melting: vacuumize the induction furnace to 4.6Pa, and turn on the electricity to heat up until the charge in the induction furnace is completely melted.

(4) Nitrogen alloying and deoxidation and desulfurization: After the furnace material in the vacuum induction furnace is melted, nitrogen is introduced to the smelting pressure of 0.076MPa, and the melting temperature is maintained at 1550°C by controlling the power, and nitrogen is introduced into the furnace from the ventilation plug at the bottom of the furnace. Bottom blowing stirring smelting, bottom blowing nitrogen flow rate 0.08Nm ³ /h, bottom blowing time 18min. After stopping the nitrogen blowing at the bottom, add high-purity chromium nitride into the furnace for nitrogen alloying, and then add electrolytic aluminum, nickel-magnesium alloy, and rare earth in sequence for deep deoxidation and deep desulfurization.

(5) Casting: Fill the vacuum induction furnace with nitrogen to a casting pressure of 0.082MPa, and control the temperature at 1530°C for casting; after the casting is completed, cool and release the pressure, and take out the ingot.

The cast ingot has a dense structure without nitrogen pore defects, and its chemical composition is shown in Table 4.

Table 4 Chemical Composition of Finished Steel (wt%)

Embodiment two

A 500kg vacuum induction furnace is used to smelt high-corrosion-resistant and high-nitrogen super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N, and its composition control range and control objectives are shown in Table 5.

Table 5 Super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N composition control range and control target (wt%)

Specific steps are as follows:

(1) Calculation of ingredients and smelting pressure

According to the target composition of the steel grade in Table 5 and the smelting temperature of about 1530°C, it is calculated according to formula ①: the smelting pressure p is 0.085MPa; calculated according to formula ②: the actual weight percentage of nitrogen added in the smelting raw material (wt%) _N1 is 0.075%; the calculated weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N is shown in Table 6. The amount of deoxidizer and desulfurizer added is 131g of electrolytic aluminum, 380g of nickel-magnesium alloy, and 304g of rare earth cerium.

Table 6 The weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N

(2) Charging: put industrial pure iron, metal chromium, metal molybdenum, metal nickel, electrolytic copper, metal manganese, and industrial silicon into the crucible of the induction furnace, and put high-purity chromium nitride, electrolytic aluminum, nickel-magnesium alloy and Rare earth is placed in the feeding bin.

(3) Furnace charge melting: vacuumize the induction furnace to 3.5Pa, and turn on the electricity to heat up until the charge in the induction furnace is completely melted.

(4) Nitrogen alloying and deoxidation and desulfurization: After the furnace material in the vacuum induction furnace is melted, nitrogen is introduced to the smelting pressure of 0.085MPa, and the melting temperature is maintained at 1530°C by controlling the power, and nitrogen is introduced into the furnace from the ventilation plug at the bottom of the furnace. Bottom blowing stirring smelting, bottom blowing nitrogen flow rate 0.12Nm ³ /h, bottom blowing time 20min. After stopping the nitrogen blowing at the bottom, add high-purity chromium nitride into the furnace for nitrogen alloying, and then add electrolytic aluminum, nickel-magnesium alloy, and rare earth in sequence for deep deoxidation and deep desulfurization.

(5) Casting: Fill the vacuum induction furnace with nitrogen to a casting pressure of 0.09MPa, and control the temperature at 1510°C for casting; after the casting is completed, cool and release the pressure, and take out the ingot.

The cast ingot has a dense structure without nitrogen pore defects, and its chemical composition is shown in Table 7.

Table 7 Chemical Composition of Finished Steel (wt%)

Embodiment Three

A 500kg vacuum induction furnace is used to smelt high-corrosion-resistant and high-nitrogen super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N, and its composition control range and control objectives are shown in Table 8.

Table 8 Super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N composition control range and control target (wt%)

Specific steps are as follows:

(1) Calculation of ingredients and smelting pressure

According to the target composition of steel grades in Table 8 and the smelting temperature of about 1510°C, it is calculated according to formula ①: the smelting pressure p is 0.09MPa; calculated according to formula ②: the actual weight percentage of nitrogen added in the smelting raw material (wt%) _N1 is 0.108%; the calculated weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N is shown in Table 9. The amount of deoxidizer and desulfurizer added is 167g of electrolytic aluminum, 380g of nickel-magnesium alloy, and 380g of rare earth cerium.

Table 9 The weight of raw materials required for smelting a furnace of super austenitic stainless steel 24.5Cr22Ni7.3Mo0.5N

(2) Charging: put industrial pure iron, metal chromium, metal molybdenum, metal nickel, electrolytic copper, metal manganese, and industrial silicon into the crucible of the induction furnace, and put high-purity chromium nitride, electrolytic aluminum, nickel-magnesium alloy and Rare earth is placed in the feeding bin.

(3) Furnace charge melting: vacuumize the induction furnace to 1.2Pa, and turn on the electricity to heat up until the charge in the induction furnace is completely melted.

(4) Nitrogen alloying and deoxidation and desulfurization: After the furnace material in the vacuum induction furnace is melted, nitrogen is introduced to the smelting pressure of 0.09MPa, and the melting temperature is maintained at 1510°C by controlling the power, and nitrogen is introduced into the furnace from the ventilation plug at the bottom of the furnace. Bottom blowing stirring smelting, bottom blowing nitrogen flow rate 0.18Nm ³ /h, bottom blowing time 21min. After stopping the nitrogen blowing at the bottom, add high-purity chromium nitride into the furnace for nitrogen alloying, and then add electrolytic aluminum, nickel-magnesium alloy, and rare earth in sequence for deep deoxidation and deep desulfurization.

(5) Casting: Fill the vacuum induction furnace with nitrogen to a casting pressure of 0.095MPa, and control the temperature to 1480°C for casting; after the casting is completed, cool and release the pressure, and take out the ingot.

The cast ingot has a dense structure without nitrogen pore defects, and its chemical composition is shown in Table 10.

Table 10 Chemical composition of finished steel (wt%)

The present invention proposes a more reasonable, efficient and economical nitrogen alloying method for the development of highly corrosion-resistant and high-nitrogen super Austrian Tensitic stainless steel provides technical support.

The present invention is not limited to the described embodiment, and those skilled in the art can still make some amendments or changes without departing from the spirit of the present invention, that is, within the disclosed scope, so the protection scope of the present invention is defined by the claims range prevails.

Claims (3)

1. a kind of method for producing high anti-corrosion high-nitrogen super austenitic stainless steel, the austenitic stainless steel steel grades are： C：≤0.02%、Si：≤0.5%、Mn：2.0~4.0%、Cr：24.0~25.0%、Ni：21.0~23.0%、Mo：7.0~8.0%、Cu： 0.3~0.6%、N：0.45~0.55%、S：≤0.005%、P：≤0.03%、Fe：Surplus；It is characterized in that, the method includes Following steps：

S1, charging：Ingot iron, crome metal, metal molybdenum, metallic nickel, cathode copper, manganese metal, industrial silicon are put into induction furnace In crucible, high purity silicon nitride chromium, electrolytic aluminium, nickel magnesium alloy and rare earth are placed in feeding chamber；

It is S2, load melting：Below 5Pa will be evacuated in induction furnace, and is powered and is warming up to furnace charge all fusings in induction furnace；

S3, nitrogen alloying：After furnace charge in vaccum sensitive stove is melting down, nitrogen is passed through to pressure p is smelted, by controlling power to maintain 1500 ~ 1560 DEG C of smelting temperature, is passed through nitrogen into stove from furnace bottom porous plug and carries out bottom blowing stirring melting, bottom blowing nitrogen flow 0.05~0.20Nm³/ h, 15 ~ 25min of bottom blowing time；Wherein, pressure p is smelted to calculate by following calculation formula：

In formula：P is smelting pressure,For standard atmospheric pressure, T is smelting temperature；

Nitrogen is actually added into percentage by weight (wt%) in raw materials for metallurgy_N1It is calculated as follows：

(wt%)_N1=（0.1~0.2）(wt%)_N

In formula, (wt%)_N1Represent that nitrogen is actually added into percentage by weight in raw materials for metallurgy, (wt%)_NRepresent high anti-corrosion high-nitrogen super The percentage by weight of nitrogen in austenitic stainless steel target component；

S4, deoxidization desulfuration：After stopping bottom blowing nitrogen, the further nitrogen alloying of high purity silicon nitride chromium progress, Ran Houyi are added into stove Secondary addition electrolytic aluminium, nickel magnesium alloy, rare earth carry out deep deoxidation and deep desulfurization process；

S5, casting：Be filled with into vaccum sensitive stove nitrogen to cast 0.08 ~ 0.095MPa of pressure, control molten steel temperature 1460 ~ 1530 DEG C are cast；After casting, cooling, vacuum breaker takes out ingot casting.

A kind of 2. method for producing high anti-corrosion high-nitrogen super austenitic stainless steel as claimed in claim 1, it is characterised in that In step S4, electrolytic aluminium additive amount is 0.6 ~ 0.8kg/t, and the nickel magnesium alloy additive amount containing magnesium 20% is 0.8 ~ 1.2kg/t, rare earth Additive amount is 0.5 ~ 1kg/t.

A kind of 3. method for producing high anti-corrosion high-nitrogen super austenitic stainless steel as claimed in claim 1, it is characterised in that In step S4, percentage by weight >=85% of chromium, percentage by weight >=10% of nitrogen in the high purity silicon nitride chromium.