KR101650318B1 - Nitriding method of stainless steel - Google Patents
Nitriding method of stainless steel Download PDFInfo
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- KR101650318B1 KR101650318B1 KR1020150040534A KR20150040534A KR101650318B1 KR 101650318 B1 KR101650318 B1 KR 101650318B1 KR 1020150040534 A KR1020150040534 A KR 1020150040534A KR 20150040534 A KR20150040534 A KR 20150040534A KR 101650318 B1 KR101650318 B1 KR 101650318B1
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/40—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions
- C23C8/42—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions only one element being applied
- C23C8/48—Nitriding
- C23C8/50—Nitriding of ferrous surfaces
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Abstract
The present invention relates to a nitriding method by a salt bath in which a nitrided hard layer is formed on the surface of a stainless steel in which a passive film is formed in the atmosphere, comprising the steps of: preparing a salt bath containing nitrate; Maintaining the bath at a constant temperature; Immersing the stainless steel in the salt bath;
Maintaining the immersed state; And pickling the stainless steel from the bath and pickling the stainless steel.
Description
The present invention relates to a surface nitriding method of a stainless steel by a salt bath, and more particularly, to a method of nitriding a surface of a stainless steel by a salt bath, And a nitriding method in which the passivation film is removed and the nitriding is performed in parallel.
It is already known that chromium (Cr) contained in a stainless steel forms a chromium oxide (Cr 2 O 3 ) passivation layer on the surface, and thus has good corrosion resistance. The use of stainless steel is widely used in various chemical and industrial structural applications to meet various corrosion resistance. However, in order to use in a severe environment, it is required to improve abrasion resistance, mechanical properties, and hardness.
Dual surface hardening can be achieved by physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel dip coating, electroplating and electrochemical nitriding, shot peening, have.
The physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel dip coating and the like require a different production method for mass production since the production speed is slow, The shot peening method is disadvantageous in that the surface of the shot peening is roughened after the treatment, which is disadvantageous in appearance decoration.
Carburizing, a typical surface hardening method, is a process of diffusing carbon atoms into stainless steel to form a hard carburizing layer on the surface. Carburizing is generally carried out at 700 ° C or higher.
At this time, chromium carbide precipitates to increase the surface hardness, but chromium atoms which improve the corrosion resistance are consumed to form chromium-carbide, causing a Cr-depleted zone having a low chromium content in the adjacent region, It forms a galvanic cell and adversely affects the corrosion resistance.
As the nitriding method of stainless steel, there is a method by gas. The application temperature range of the gas nitriding is nitriding at a relatively high temperature range of 1000-1200 ° C or 600-900 ° C depending on the type of stainless steel. Also, the gas nitriding has a disadvantage of nitriding for a long time (1-30 hours) even though the application temperature is high.
As a method for improving the hardness and improving the corrosion resistance and the abrasion resistance of a steel material in the past, a method of diffusing nitrogen into the steel material and simultaneously forming an iron-nitrogen compound on the surface of the steel material is disclosed in Japanese Patent Application Laid- cyan, and CN) based salts has been disclosed.
However, this method of carburizing carburizing reduces the amount of nitrogen that is consumed to form a compound with iron on the surface of the steel and diffuses into the steel, thereby improving the hardness, strength and corrosion resistance of the surface. However, There is a limit that can not be sufficiently improved. Therefore, the steel material thus formed is used for tools, engine parts, and the like, and there is a limit to be used for exterior parts of automobiles.
In addition, the cyanide salt has a cyanide ion present in the salt bath. The cyanide ion is classified as a poison, so that the reprocessing cost for prevention of pollution must be added, and the sedimentation in the cyanide- Since the treatment is a carbo-nitriding method in which carbon and nitrogen simultaneously penetrate the steel material, the hardness of the surface of the steel after nitriding is greatly improved, but the synergistic effect of tensile strength is insignificant and the thickness to be nitrided is also thin.
However, such a nitriding method has a limitation in that only a steel material having a low carbon content is targeted.
It is an object of the present invention to provide a method of enhancing strength by a nitriding method by a salt bath in a surface strengthening method of stainless steel.
Another object of the present invention is to provide a method for solving the problem by nitriding a passive film formed on the surface of a stainless steel by immersion in a bath without removing the passive film before immersion in a salt bath.
Another object of the present invention is to provide a method of nitriding at a relatively low temperature of 400 DEG C to 700 DEG C for a relatively short time of 30 minutes to 10 hours.
According to an aspect of the present invention, there is provided a nitriding method by a salt bath in which a nitrided hard layer is formed on a surface of a stainless steel having a passive film formed thereon, the nitriding method comprising the steps of: KNO 3 , KNO 2 , Ca (NO 3 ) 2 , NaNO 3, and NaNO 2 ; Maintaining the bath at a temperature of from 500 ° C to 650 ° C; Immersing the stainless steel in the salt bath; Maintaining the immersed state for not less than 2 hours but not more than 4 hours; And pickling the stainless steel from the bath and pickling.
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Another feature of the invention is the salt bath has been made in parts of KNO 3 and NaNO 3 50 parts by mass 50 parts by mass.
Another feature of the invention is to add a chloride of an NaCl or CaCl 2 in the salt bath.
Another aspect of the present invention is that the chloride content is more than 0 parts by mass and less than 20 parts by mass based on 100 parts by mass of the salt bath.
Another feature of the invention is the salt bath is composed of 100 parts by mass of KNO 3 and 1 part by mass to 7 parts by weight of NaCl.
Another aspect of the present invention is that the salt bath comprises 100 parts by mass of NaNO 3 and 1 part by mass to 7 parts by mass of NaCl.
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Another feature of the present invention is that the stainless steel is any one of ferritic stainless steel, Duplex (ferrite-austenite) stainless steel, and ferrite-martensitic stainless steel.
As described above, the present invention provides a surface strengthening method in which the hardness value and the tensile strength value are increased by the nitriding method of the stainless steel by the salt bath, but the elongation is not greatly reduced.
The present invention also provides a method of solving the environmental pollution problem and reducing the processing cost by employing nitrogen in the steel using a non-cyanide salt.
The present invention also provides a method for nitriding a passive film formed on the surface of a stainless steel by immersion in a bath without removing the passive film before immersing the bath in a salt bath.
The present invention also proposes a method of nitriding at a relatively low temperature of 400 DEG C to 700 DEG C for a relatively short time of from 30 minutes to 10 hours.
1 is a graph showing hardness measurement results of a duplex stainless steel according to a distance from a surface in a thickness direction of a duplex stainless steel according to a nitriding treatment time at 500 ° C in a KNO 3 + 2.4 mass part NaCl salt bath of 100 mass parts,
Figure 2 is the hardness measurement results of the 100 parts by mass of KNO 3 + 2.4 parts by weight of NaCl salt bath in a duplex stainless steel in the thickness direction of the nitriding time of 550 ℃ distance from the surface graph,
Figure 3 is a graph of the hardness measurement results of the distance from the surface in a duplex stainless steel in the thickness direction according to the nitriding treatment time at 650 ℃ in 100 parts by mass of KNO 3 salt bath,
FIG. 4 is a graph showing hardness measurement results according to the distance from the surface in the thickness direction of the duplex stainless steel according to the nitriding treatment time at 650 ° C in a KNO 3 + 4.8 parts by mass NaCl salt bath of 100 parts by mass,
5 is a hardness measurement result according to the distance from the surface in a duplex stainless steel in the thickness direction of the nitriding time in 592 ℃ in 100 parts by mass of NaNO 3 + 4.8 parts by weight of NaCl salt bath graph,
6 is a graph of the tensile test results according to the nitriding treatment time at 650 ° C in a 100 parts by mass KNO 3 salt bath,
7 is KNO 3 (50 parts by weight) + NaNO 3 (50 mass part) as a graph of the tensile test result of the nitriding time of 650 ℃ in the salt bath,
FIG. 8 is a graph of tensile test results according to the nitriding treatment time at 600 ° C in a NaNO 3 salt bath of 100 parts by mass,
9 is a graph of tensile test results with a nitriding treatment time of 650 ° C in a NaNO 3 salt bath of 100 parts by mass,
10 is a graph of tensile test results with nitriding time of 585 ° C in a KNO 3 + 2.4 parts by mass NaCl salt bath of 100 parts by mass,
11 is a graph of tensile test results with nitriding time of 592 ° C in a NaCl salt bath of 100 parts by mass of NaNO 3 + 4.8 parts by mass,
12 is a graph of the tensile test result of the nitriding time of 650 ℃ in 100 parts by mass of NaNO 3 + 4.8 parts by weight of NaCl salt bath,
13 is a scanning electron micrograph of a fractured section after tensile test of an initial specimen of a duplex stainless steel,
Figure 14 after a tensile test after nitriding at 650 ℃ in NaNO 3 100 weight parts of the
The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.
Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described more fully hereinafter with reference to the accompanying drawings, in which: FIG.
First, prepare the bath. The salt bath is not a salt of a conventional cyanide (CN), that is, a salt of KCN or NaCN containing cyanide, a salt of a non-cyanide salt, more specifically NaNO 3 , NaNO 2 , KNO 3 , KNO 2 , and Ca NO 3 ) 2 .
This salt bath is maintained at a constant temperature in the range of 400 ° C to 700 ° C.
NaNO 2 reacts as in
5NaNO 2 → 3NaNO 3 + N 2 + Na 2 O
2NaNO 2 → Na 2 O + NO + NO 2
When oxygen is present in the bath, NaNO 2 is oxidized, as shown in
2NaNO + 2 O 2 → 3 2NaNO
The NaNO 3 reacts as shown in
4NaNO 3 → 5O 2 + 2N 2 + 2Na 2 O
2NaNO 3 → Na 2 O + NO + NO 2
5KNO2 → 3KNO 3 + N 2 + K 2 O
2 KNO 2 - > K 2 O + NO + NO 2
2KNO2 + O 2 → 2KNO 3
4KNO 3 → 5O 2 + 2N 2 + 2K 2 O
2KNO 3 → K 2 O + NO + NO 2
Ca (NO 3 ) 2 - > CaO + 2NO 2 + 1 / 2O 2
2NO 2 ? 2O 2 + N 2
As such, and to the NO and the NO 2 generated in the salt bath, as is the NO and NO 2 will be described later to generate the active nitrogen N in accordance with the reaction of the iron causes the nitrogen is diffused into the stainless steel base material.
Since iron oxide is formed on the surface of the base material by reacting with oxygen and Fe, which is the base material of stainless steel, generated in the
The present invention adds a chloride in the iron bath to solve the problem caused by such iron oxide.
The chloride is preferably NaCl and / or CaCl 2 , but is not limited thereto.
The chloride serves to break down the iron oxide layer formed on the surface of the steel, thereby shortening the nitriding time and allowing the nitrogen to diffuse more deeply at the same time, thereby improving the tensile strength.
As described above, after the base material is treated in a salt bath at a temperature of 400 ° C to 700 ° C, it is rapidly pickled with an acid such as diluted hydrochloric acid or sulfuric acid.
When the base material treated in the molten salt bath is quenched in this manner, the structure of the nitrogen solid solution layer formed on the stainless steel can be made to be the same as that of the base material not containing nitrogen. In this case, it is possible to obtain an effect of preventing cracks and fractures due to the homogeneous structure of the solid solution layer and the base material.
When the base material which has been treated in the molten salt bath is allowed to stand at room temperature and then slowly cooled, the solid solution structure exhibits a nitrogen compound in the acicular structure unlike the base material. Therefore, in this case, it is difficult to obtain cracking and fracture-preventing effects due to the homogeneous structure as described above.
Also, when the base material treated in the molten bath is quenched, the tensile strength is improved as compared with the cold.
The present invention can be applied to the nitriding of all stainless steels. In particular, it is preferable that the content of carbon is 0.03 wt% or less (not including 0), such as ferritic stainless steel, duplex stainless steel, and ferrite-martensitic stainless steel. It is more effective for stainless steel having relatively low carbon content.
Next, specific embodiments of the present invention will be described. In the present invention, the following Duplex (dual phase) ferrite and Austenite phase stainless steels were commonly used in Examples 1 to 12.
Table 1 shows the components of the duplex (dual phase) stainless steel used in the embodiment of the present invention.
Duplex stainless steel is a type of steel that is made of austenitic stainless steel with higher Cr content and added with Mo. It is a steel type containing about 22-25% of chromium (Cr) and 2-3% of molybdenum (Mo).
This steel grade is a dual type of steel which is developed to overcome the disadvantages of conventional Austenite stainless steel which is sensitive to intergranular corrosion and stress corrosion cracking. It is a dual phase structure in which about 50% of austenite structure coexists on a ferrite base .
Due to the presence of austenite structure, it has better toughness than ferrite stainless steel and has a strength of about twice as much as that of austenitic stainless steel due to the presence of ferrite structure.
It has lower thermal expansion coefficient and higher thermal conductivity than austenitic stainless steel and is suitable as a tube material for heat exchangers.
≪ Example 1 >
The dough flux stainless steel was immersed in a salt bath in which 2.4 parts by mass of chloride NaCl was added to 100 parts by mass of nitrate KNO 3 while the salt bath was kept at 500 ° C, and the plate was immersed for 2 hours to 8 hours and pickled.
FIG. 1 shows the hardness (Hv) with respect to the depth from the surface when the nitriding temperature is maintained at 500 ° C. for 2, 4, 6 and 8 hours.
As can be seen from FIG. 1, according to the present invention, nitriding in a salt bath to which NaCl is partially added shows that there is no change in hardness and hardness is maintained even though the depth increases from the surface to 900 μm. This indicates that the optimum nitriding time is about 2 hours at 500 캜 nitrification temperature of a salt bath in which 2.4 mass part of chloride NaCl is added to 100 mass parts of nitrate KNO 3 .
≪ Example 2 >
The above-mentioned dough flux stainless steel was immersed in a salt bath in which 2.4 parts by mass of chloride NaCl was added to 100 parts by mass of nitrate KNO 3 , maintained at 550 ° C, and immersed for 2 hours to 8 hours, followed by pickling.
2 shows the hardness (Hv) with respect to the depth from the surface when the nitriding temperature is maintained at 550 DEG C for 2, 4, 6 and 8 hours.
As can be seen from FIG. 2, according to the present invention, nitriding in a NaCl-added salt bath shows no change in hardness and maintains hardness even though the depth increases from the surface to 900 μm. Also, it can be seen that there is no difference in the hardness increase even though the nitriding time is longer than 2 hours. This indicates that a salt bath in which 2.4 parts by mass of chloride NaCl was added to a salt bath of 100 parts by mass of KNO 3 at an annealing temperature of 550 ° C and an optimum nitriding time of about 2 hours.
≪ Example 3 >
3 shows the hardness (Hv) with respect to the depth from the surface when the nitriding temperature is maintained at 650 DEG C for 1, 4 and 8 hours.
As can be seen from FIG. 3, when the nitriding time of 2 to 4 hours was maintained while the salt bath of 100 parts by mass of KNO 3 was maintained at 650 ° C., the depth from the surface increased to 900 μm, , And the hardness is maintained. Also, it can be seen that there is no difference in the hardness increase even though the nitriding time is longer than 2 hours. This indicates that the salt bath of 100 parts by mass of KNO 3 is nitrided at 650 ° C and the optimum nitriding time is 2 to 4 hours.
<Example 4>
The dough flux stainless steel was immersed in a salt bath containing 4.8 parts by mass of chloride NaCl as 100 parts by mass of nitrate KNO 3 and held at 650 ° C, and then immersed for 2 hours to 8 hours and pickled.
4 shows the hardness (Hv) with respect to the depth from the surface when the nitriding temperature is maintained at 650 DEG C for 2, 4, 6 and 8 hours.
As can be seen from FIG. 4, according to the present invention, nitriding for 4 hours or more in a salt bath to which NaCl is partially added shows that hardness is increased and hardness is maintained even with increasing depth. This indicates that the salt bath of 100 parts by mass of KNO 3 is nitrided at 650 ° C and the optimum nitriding time is 2 to 4 hours.
≪ Example 5 >
The dough flux stainless steel was immersed in a salt bath containing 4.8 parts by mass of NaCl chloride and 100 parts by mass of NaNO 3, and maintained at 592 캜, and immersed for 1 hour to 8 hours, and pickled.
5 shows the hardness (Hv) with respect to the depth from the surface when the nitriding temperature is maintained at 650 DEG C for 1, 2, 4 and 8 hours.
As can be seen from FIG. 5, it can be seen that nitriding for 1 hour or more in a salt bath to which NaCl is partially added according to the present invention increases hardness and maintains hardness even with increasing depth. This indicates that the optimum nitriding time is from 1 hour to 4 hours at a nitriding temperature of 592 ° C in a salt bath to which 4.8 parts by mass of NaCl chloride is added to 100 parts by mass of the NaNO 3 nitrate.
≪ Example 6 >
The dough flux stainless steel was immersed in a salt bath of 100 parts by mass of nitrate KNO 3 while being maintained at 650 ° C, immersed for 1 hour to 8 hours, and pickled.
FIG. 6 is a graph showing a stress strain curve when the nitriding temperature is maintained at 650 ° C. for 1, 2, 4, 6 and 8 hours.
As can be seen from FIG. 6, when a salt bath of 100 parts by mass of KNO 3 was nitrided for 2 hours or more in a salt bath at 650 ° C. according to the present invention, the tensile strength increased and the elongation did not show any significant decrease. This indicates that the optimum nitriding time is about 2 hours at a nitriding temperature of 650 ° C in a salt bath of 100 parts by mass of the nitrate KNO 3 . This is consistent with the expected nitridation time through the hardness of Example 1.
≪ Example 7 >
The dough flux stainless steel was immersed in a salt bath of 50 parts by mass of
FIG. 7 is a graph showing a stress strain curve when the nitriding temperature is maintained at 650 DEG C for 2, 4, 6 and 7 hours.
As can be seen from FIG. 7, according to the present invention, when 50 parts by mass of
≪ Example 8 >
Nitrate NaNO 3 The dope flux stainless steel was immersed in a salt bath of 100 parts by mass while maintained at 600 ° C and immersed for 1 hour to 8 hours and pickled.
FIG. 8 is a graph showing a stress strain curve when the nitriding temperature is maintained at 600 ° C. for 1, 2, 4, 6 and 8 hours.
As can be seen from FIG. 8, when the salt bath of 100 parts by mass of NaNO 3 nitrate was nitrided for 1 hour or more in a salt bath at 600 ° C., the tensile strength was increased and the elongation was not decreased. This indicates that the optimum nitriding time is about 1 hour at 600 ° C nitriding temperature in a salt bath of 100 parts by mass of NaNO 3 nitrate.
≪ Example 9 >
The dough flux stainless steel was immersed in a salt bath of 100 parts by mass of NaNO 3 nitrate at a temperature of 650 ° C, and immersed for 2.5 hours to 10 hours, and pickled.
FIG. 9 is a graph showing a stress strain curve when held at the nitriding temperature of 650 DEG C for 1, 2, 4, 6 and 8 hours.
As can be seen from FIG. 9, when a salt bath of 100 parts by weight of NaNO 3 nitrate was nitrided for 2.5 hours or more in a salt bath at 650 ° C., the tensile strength increased and the elongation did not show any significant decrease. This indicates that the optimum nitriding time is about 2.5 hours at a nitriding temperature of 650 ° C in a salt bath of 100 parts by mass of the NaNO 3 nitrate.
≪ Example 10 >
The dough flux stainless steel was immersed in a salt bath containing 2.4 parts by mass of chloride NaCl as 100 parts by mass of nitrate KNO 3 and maintained at 585 캜, and immersed for 2 hours to 10 hours and pickled.
10 is a graph showing a stress strain curve when the nitriding temperature is maintained at 585 DEG C for 2, 4, 6, 8 and 10 hours.
As can be seen from FIG. 10, according to the present invention, when a salt bath prepared by adding 2.4 parts by weight of NaCl chloride to 100 parts by weight of nitrate KNO 3 was nitrided for 2 hours or more in a salt bath at 585 ° C, tensile strength increased and elongation did not show any significant decrease . This indicates that the optimum nitriding time is about 2 hours at a nitrification temperature of 585 ° C in a salt bath containing 2.4 parts by mass of chloride NaCl in 100 parts by mass of the nitrate KNO 3 .
≪ Example 11 >
The dough flux stainless steel was immersed in a salt bath containing 4.8 parts by mass of NaCl chloride and 100 parts by mass of NaNO 3, and maintained at 592 캜, followed by immersion for 2 hours to 8 hours, followed by pickling.
11 is a graph showing a stress strain curve when the nitriding temperature is maintained at 592 DEG C for 2, 4, 6 and 8 hours.
11, according to the present invention, when a salt bath prepared by adding 4.8 parts by mass of NaCl chloride to 100 parts by mass of NaNO 3 as a nitrate was nitrided for more than 2 hours at 592 ° C in a salt bath, the tensile strength increased and the elongation did not show any significant decrease . This indicates that the optimum nitriding time is about 2 hours at a nitriding temperature of 592 캜 in a salt bath in which 4.8 parts by mass of chloride NaCl is added to 100 parts by mass of the nitrate NaNO 3 .
≪ Example 12 >
Nitrate NaNO 3 was immersed in a salt bath containing 4.8 parts by mass of NaCl chloride and maintained at 650 ° C for 1 hour to 8 hours and pickled.
FIG. 12 is a graph showing a stress strain curve when the nitriding temperature is maintained at 650 ° C. for 1, 2, 4, 6 and 8 hours.
As shown in FIG. 12, according to the present invention, when a salt bath in which 4.8 parts by mass of NaCl chloride was added to 100 parts by mass of NaNO 3 as a nitrate was nitrided for more than 1 hour at 650 ° C in a salt bath, the tensile strength increased and the elongation did not show any significant decrease . This indicates that the optimum nitriding time is about 1 hour at a nitriding temperature of 650 ° C in a salt bath to which 4.8 parts by mass of NaCl chloride is added to 100 parts by mass of the NaNO 3 nitrate.
The results of Examples 1 to 12 described above show that the nitriding time is in the range of 1 to 4 hours in the nitriding temperature range of 500 to 650 ° C in all the salt baths and the optimum nitriding time is about 2 hours in the nitriding time Able to know.
It can be seen that the change in hardness and tensile strength is more prominent when nitriding is performed after addition of the chloride NaCl.
Figure 13 shows a scanning electron microscope (SEM) image of the fracture surface after tensile test before nitriding of the DUPLEX stainless steel. Failure of non-nitrided duplex stainless steel can confirm the appearance of ductile fracture.
Figure 14 shows a scanning electron micrograph of the fracture surface after tensile test after nitriding at 650 ° C for 6 hours in a NaNO 3 salt bath. It can be seen from this photograph that the ductile fracture can be confirmed by nitriding at 650 ° C for 6 hours in a NaNO 3 salt bath. This shows that the cross-sectional structure of the stainless steel after nitriding according to the present invention is the same as the cross- Therefore, the nitrided portion and the non-nitrided portion have a homogeneous structure, which can have the same physical properties and can prevent cracking or fracture.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.
Therefore, the embodiments disclosed in the present invention are not intended to limit the scope of the present invention but to limit the scope of the present invention.
The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.
Claims (15)
Preparing a salt bath comprising at least one nitrate selected from the group consisting of KNO 3 , KNO 2 , Ca (NO 3 ) 2 , NaNO 3 and NaNO 2 ;
Maintaining the bath at a temperature of from 500 ° C to 650 ° C;
Immersing the stainless steel in the salt bath;
Maintaining the immersed state for not less than 2 hours but not more than 4 hours; And
And removing the stainless steel from the bath and pickling the stainless steel.
Wherein the salt bath comprises KNO 3 and NaNO 3 .
The salt bath is 50 parts by mass of KNO 3 and NaNO 3 And 50 parts by mass of a nitriding agent.
Wherein a chloride of NaCl or CaCl 2 is added to the salt bath.
Wherein the amount of the chloride is more than 0 parts by mass and less than 20 parts by mass based on 100 parts by mass of the salt bath.
Wherein the salt bath nitriding method is characterized in that the stainless steel of 100 parts by mass of KNO 3 and 1 part by mass to 7 parts by weight of NaCl.
Wherein the salt bath comprises 100 parts by mass of NaNO 3 and 1 part by mass to 7 parts by mass of NaCl.
Wherein the stainless steel is a ferritic stainless steel.
Wherein the stainless steel is a dough flux (ferrite-austenite) stainless steel.
Wherein the stainless steel is ferritic-martensitic stainless steel.
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| CN109161840A (en) * | 2018-09-10 | 2019-01-08 | 义马丰达设备有限责任公司 | Prevent the two opposite methods and its valve member for moving back and forth the occlusion of stainless steel valve member |
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| CN109161840A (en) * | 2018-09-10 | 2019-01-08 | 义马丰达设备有限责任公司 | Prevent the two opposite methods and its valve member for moving back and forth the occlusion of stainless steel valve member |
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