JP4806722B2 - Metal salt bath nitriding method and metal produced by the method - Google Patents

Description

  The present invention relates to a metal salt bath nitriding method and a metal produced by the method, and more particularly, a pure iron or steel salt bath nitriding method using a non-cyanide salt and a pure produced by the method. Related to iron or steel.

  Generally, steel materials (steel) used as materials for machine parts are widely used because they satisfy the strength required for parts. Most of the mechanical parts are required to have strong and durable quality. For this reason, the steel material is heat-treated in the first step to give strength, resistance, durability and the like. Some mechanical parts exposed to a poor external environment are also subjected to a surface treatment by heat treatment in order to improve the corrosion resistance of the surface.

As one of surface treatment methods for the corrosion resistance of such machine parts, a method of nitriding the surface of the machine parts is known. Nitriding methods include gas nitriding using only NH ₃ gas, salt bath nitriding using a salt bath such as KCNO, and gas softening using a mixture of NH ₃ gas and endothermic gas (RX gas). There are known a nitriding method, an ion nitriding method in which a mixed gas of N ₂ and H ₂ is put in plasma and processed.

  In general, such a nitriding method has the main purpose of improving the wear resistance, fatigue strength, etc. of the steel material to be processed, but the surface of the nitriding machine part is resistant to corrosion. It can also be used where it is resistant.

  Furthermore, in the case of the salt bath nitriding method, the properties or melting points of the inorganic salts that melt into it can be freely adjusted, and a stable range of processing temperatures can be obtained, and the steel surface is not eroded. It is widely applied to many machine parts such as In particular, salt baths have excellent thermal conductivity, cracking properties, ease of atmosphere control, etc., have lower equipment costs compared to other heat treatments, are easy to operate, and have a heating rate in the atmosphere. 4 times faster than this, especially suitable for heat treatment of high-speed steel sensitive to crystal growth. When the treated product is taken out into the atmosphere, a salt bath adheres to the surface and forms a film. It has the advantage of helping to cut off and preventing surface oxidation, clean the surface after processing, and suitable for heat treatment of small quantities of various parts.

  In such a salt bath nitriding method, a cyan salt is generally used, whereby cyanide ions are present in the bath. The cyanide ions are classified as poisonous and deleterious substances, and at present, environmental problems have become severe, and considerable costs and labor are required for pollution prevention measures, which causes an increase in treatment costs such as wastewater and exhaust gas. ing.

  In addition, nitriding treatment in molten salt containing cyanide significantly improves the surface hardness after nitriding treatment of carbonitriding material in which carbon and nitrogen penetrate at the same time, but increases tensile strength. The conventional salt bath nitriding method using a cyan salt has a problem that the nitriding thickness is thin and its application fields such as a mold and a gear are extremely limited.

  In order to solve the above-mentioned problems, an object of the present invention is to provide a method of nitriding a metal using a non-cyanide salt and a metal produced by the method.

  Another object of the present invention is to provide a salt bath nitriding method capable of nitriding to the inside of the metal and a metal produced by the method.

  Still another object of the present invention is to provide a salt bath nitriding method and a metal produced by the method, which can increase the hardness and tensile strength of the metal to be processed compared to before the salt bath nitriding treatment. By the way.

  Still another object of the present invention is to provide a metal salt bath nitriding method capable of maximizing the nitriding depth and a metal produced by the method.

The metal salt bath nitriding method according to the present invention includes a step of adding at least one of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO _{2 into} a salt bath, and melting the salt to maintain a constant temperature. And nitriding the metal in the salt bath.

Another salt bath nitriding method of the metal according to the present invention includes any one of KNO ₃ or KNO ₂ and at least one of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO _{2 in} the salt bath. Adding a mixed salt; melting the salt to maintain a constant temperature; and nitriding a metal in the salt bath.

  At this time, the constant temperature is preferably in the range of 400 ° C. to 700 ° C., and the immersion time is preferably in the range of 1 minute to 24 hours.

Still another salt bath nitriding method of the metal according to the present invention includes the step of putting KNO ₃ salt in the salt bath, the step of melting the salt and maintaining it at 400 ° C. or more and 620 ° C. or less, and 8 hours in the salt bath. Less than nitriding the metal.

Still another salt bath nitriding method of the metal according to the present invention comprises the steps of placing KNO ₃ salt in the salt bath, melting the salt to maintain it above 620 ° C. and below 640 ° C., and 1 hour in the salt bath. Less than nitriding the metal.

  When pure iron is nitrided using the salt bath according to the present invention, it can be nitrided from the surface of pure iron to the inside of 0.1 mm to 3.0 mm.

  When pure iron is nitrided using the salt bath according to the present invention, it can be nitrided from the steel surface to the inside of 0.1 mm to 3.0 mm.

  In the present invention, the steel is any one of extremely low carbon steel, low carbon steel, medium carbon steel, high carbon steel, and alloy steel.

  The ultra low carbon steel nitrided according to the present invention has a surface hardness of more than 120 Hv and not more than 450 Hv, the low carbon steel has a surface hardness of more than 200 Hv and not more than 410 Hv, the medium carbon steel has a surface hardness of more than 130 Hv and not more than 420 Hv, and the high carbon steel has The surface hardness is more than 150 Hv and less than 400 Hv, the alloy steel has a surface hardness of more than 200 Hv and less than 410 Hv, and the steel nitrided according to the present invention has a surface hardness improved to a maximum of 420 Hv. The surface hardness is also improved.

On the other hand, the tensile strength of the ultra low carbon steel nitrided by the present invention is 35 kg / mm ² exceeding 110 kg / mm ² or less, and the low carbon steel is tensile strength of 45 kg / mm ² exceeding 110 kg / mm ² or less. Has a tensile strength of over 45 kg / mm ^{2 and} 100 kg / mm ² or less, high carbon steel has a tensile strength of over 60 kg / mm ^{2 and} 95 kg / mm ² or less, and alloy steel has a tensile strength of 55 kg / mm ^{2 and} over 110 kg / mm ² There is a merit of increasing to ² or less, and pure iron also has a merit that the tensile strength is increased by the nitriding method of the present invention.

  Therefore, the salt bath nitriding method according to the present invention is applicable to pure iron and has a carbon content of 0.0001 wt. % Or more and 0.13 wt. %, An extremely low carbon steel with a carbon content of 0.13 wt. % To 0.2 wt. % Low carbon steel with a carbon content of 0.21 wt. % Or more 0.51 wt. % Carbon steel with a carbon content of 0.51 wt. % To 2.0 wt. % Or less of carbon steel such as high carbon steel or chromium content of 0.1 wt. % To 1.5 wt. % Steel and molybdenum content of 0.05 wt. % To 0.5 wt. % Steel, nickel content of 0.1 wt. % To 10 wt. % Steel and manganese content of 0.1 wt. % To 2.0 wt. % Steel, boron content is 0.001 wt. % To 0.1 wt. % Steel and titanium content of 0.001 wt. % To 0.1 wt. % Steel, the vanadium content is 0.05 wt. % To 0.15 wt. % Steel, niobium content of 0.005 wt. % To 0.1 wt. % Steel and aluminum content of 0.005 wt. % To 0.1 wt. % Steel is also applicable. Further, the salt bath nitriding method according to the present invention is applicable to alloy steels including at least two or more of the aforementioned steels.

The present invention relates to a non-cyanide salt such as sodium nitrate (NaNO ₃ ), sodium nitrite (NaNO ₂ ), calcium nitrate (Ca (NO ₃ ) ₂ ), and compounds using these in a salt bath nitriding method for steel. By using, environmental pollution problems can be solved and processing costs can be reduced.

  The present invention has the advantage that the nitriding depth of the metal can be increased to 2 to 6 times that of the prior art, and the inside of the metal can be nitrided, thereby expanding the field of application.

  The present invention improves the hardness and tensile strength of metals and is applied not only to the surface hardening of steel but also to the bulk hardening of the material itself, and it is light weight and high that requires improved wear resistance, wear resistance, corrosion resistance and fatigue life. It can be applied to various fields such as strong automotive parts and various structural materials.

  Hereinafter, the present invention will be described in more detail as follows.

The present invention uses a conventional cyanide, that is, a carbonitriding process in which nitrogen and carbon permeate into a metal at the same time using a cyanide, that is, KCN, NaCN, etc. containing cyanide as a molten salt. A non-cyan molten salt that is not a nitriding method using a system, more specifically, a nitrogen decomposition principle using NaNO ₃ , NaNO ₂ , Ca (NO ₃ ) ₂ and a mixture thereof as a molten salt is used.

In the salt bath nitriding method of a metal according to the present invention, at least one salt of NaNO ₃ , NaNO ₂ and Ca (NO ₃ ) ₂ is put in a salt bath, and then the salt is melted to 400 ° C. to Maintain a constant temperature in the 700 ° C. range. Thereafter, the metal to be treated is immersed in the salt bath for a predetermined time, for example, 1 minute to 24 hours, and is nitrided.

At this time, generation of nitrogen by decomposition of the salt in NaNO ₃ , NaNO _2, Ca (NO ₃ ) _2, etc., which are the non-cyan molten salt of the present invention, is represented by the following reaction formulas 1 and 2. Occur.

The following reaction formula 1 shows a nitrogen generation reaction in a molten salt bath of NaNO ₃ and NaNO ₂ .

(Chemical formula 1)
NaNO ₃ → NaNO ₂ + 1 / 2O ₂
2NaNO ₂ → Na ₂ O + NO ₂ + NO
2NaNO ₂ + 2NO → 2NaNO ₃ + N ₂

The following reaction formula 2 shows a nitrogen generation reaction of a molten salt bath of Ca (NO ₃ ) ₂ .

(Chemical formula 2)
Ca (NO ₃ ) ₂ → CaO + 2NO ₂ + 1 / 2O ₂
2NO ₂ → 2O ₂ + N ₂

  Among the metals nitrided by the salt bath nitriding method according to the present invention, carbon steel (very low carbon steel, low carbon steel, medium carbon steel, high carbon steel), alloy steel and pure iron are as shown in Table 1. Further, the nitrided depth is 0.1 mm to 3.0 mm from the surface, which is about 2 to 6 times the depth nitrided by the conventional nitriding method. This means that the surface is not diffused only at the surface part of the sample but affects the inside of the specimen. At this time, the nitrided metal also has an increased surface hardness and tensile strength. Has a value. The references according to Table 1 below are as follows.

[1] B. Finnem, Bad und Gasnitrieren. Vol. 18, Betriebsbuecher Carl-Hausner-Verlag, Muenchen (1965)
[2] Tufftride Information 15. DEGUSSA Durfeerit Abteilung
[3] H. Eiraku, K. Shinkawa, Y. Yoneyama, and M. Higashi, “Characteristics of Palsonite (Low temperature salt bath nitriding),” JSHT Conf. , No. 1, 49-50 (1998)
[4] E.E. A. Mattision, K. Frisk, and A. Melander, “Microstructure evolution during the combination hardening process of nitriding and induction hardening,” in: 5ASM-HTSE Europe (2002), pp. 209-219
[5] W.H. Junyi, P.A. Lin and Z. Hul, “Effect of rare earth on ionic nitriding process,” in: 1st Conf. Heat Trearment of Materials, May (1998), pp. 57-61
[6] S.E. Kondo, Y. Izawa, O. Nakano, S .; Uchida, and M. Onoda, “Influence of white layer produced by gas nitriding on fatigue strength of compressive spring,” J. JSHT, 36 (1), 34-40 (1996)
[7] J. et al. Georges, “TC plasma nitriding,” in: 12th IFHTSE Melbourne, Australia (2000), p. 229; Heat treatment Met. , No. 2, 33-37 (2001)
[8] T.M. Bell, Y. Sun, K. Mao, and P. Buchhagen, “Modeling plasma nitriding,” Advanced Mater. Pro. , No. 8, 40Y-40BB (1996)
[9] T. Bell, Y. Sun, Z. Lin, and M. Yan, “Rare earth surface engineering,” Heat Treatment Mat. , 27 (1), 12-13 (2000)

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First embodiment

In the first embodiment of the present invention, steel is nitrided using NaNO ₃ as a molten salt.

  The types of steels nitrided are extremely low carbon steel, low carbon steel, medium carbon steel, high carbon steel, and alloy steel.

The ultra low carbon steel, low carbon steel, medium carbon steel, high carbon steel and alloy steel are immersed in a NaNO ₃ molten salt bath and then subjected to nitriding treatment at a temperature of 500 ° C. for 2 hours.

  The hardness change and tensile strength change as a result of the immersion are as shown in Table 2 below, and the surface hardness measurement is a result of measurement by applying a load of 1 kg with a Vickers hardness machine.

  In the case of the extremely low carbon steel nitrided through the molten salt bath nitriding method of the first embodiment, the surface hardness is increased by 119% and the tensile strength is increased by 47%. In the case of the low carbon steel, the surface hardness is 47%. Increase and the tensile strength increases by 19%.

  In the case of medium carbon steel nitrided through the molten salt bath nitriding method of the first embodiment, the surface hardness is increased by 32% and the tensile strength is increased by 18%, and in the case of high carbon steel, the surface hardness is increased by 28%. And the tensile strength is increased by 16%. In the case of alloy steel, the surface hardness is increased by 24% and the tensile strength is increased by 17%.

  That is, the steel nitrided through the molten salt bath nitriding method according to the first embodiment of the present invention has a surface hardness increased by 20% to 120% and a tensile strength increased by 15% to 50%.

  On the other hand, the difference in the increase in the surface hardness depending on the type of steel can be said to be a result of the diffusion difference of nitrogen due to the carbon content in the steel.

FIG. 1 shows the hardness (As) and nitriding treatment of non-nitriding steel after ultra low carbon steel was nitrided in a NaNO ₃ molten salt bath at 500 ° C. for 30 minutes, 1 hour, 2 hours and 5 hours, respectively. It is the graph which showed distribution with the hardness of the made steel in the thickness direction.

  As shown in FIG. 1, the nitriding depth of the steel increases as the nitriding time increases, but the hardness decreases as it enters from the surface of the steel. This is because the concentration of nitrogen decreases as it enters from the surface of the steel, and when the steel is nitrided for 5 hours by the nitriding method, it is nitrided from the steel surface to the inside of 0.6 mm. You can see that.

FIG. 2 shows the distribution of the surface hardness in the thickness direction of the nitrided steel after nitriding the low carbon steel in a NaNO ₃ molten salt bath at 680 ° C. for 3 hours, 6 hours, 12 hours and 24 hours, respectively. The hardness is Vickers hardness and is an experiment with a load of 3 kg.

  As shown in FIG. 2, even in the case of low carbon steel, the nitriding depth of steel increases as the nitriding time increases, and the steel is nitrided from the surface of the steel to the inside of 3.0 mm, which is 6 times the conventional steel. It turns out that it nitrides to the above thickness.

  Further, it can be seen that the surface hardness of the nitriding treatment thickness is 450 Hv, which is 4 times or more higher than the value (As) before the nitriding treatment.

  Therefore, when the nitriding method of the present invention is used, the nitriding depth of the steel can be improved to 2 to 6 times that of the conventional cyan salt bath nitriding method.

FIG. 3 shows nitriding treatment of ultra-low carbon steel in a NaNO ₃ molten salt bath at 500 ° C. and 600 ° C. for 3 hours, respectively, and hardness distributions before (As) and after nitriding of ultra-low carbon steel Is shown in the thickness direction, and the steel nitrided at a temperature of 600 ° C. is about three times deeper than the steel nitrided at a temperature of 500 ° C., and its hardness is also increased by about 100 Hv. It can be seen that the increase in the hardness of the steel increases as the nitriding temperature rises, and the penetration depth at which nitrogen penetrates from the surface to the inside of the steel also increases.

  Table 3 shows the change in the tensile strength of the steel by changing the treatment temperature by nitriding ultra low carbon steel for 3 hours in the temperature range of 450 ° C. to 600 ° C. using the salt bath nitriding method according to the first embodiment of the present invention. Is shown.

  As shown in Table 3, when the processing temperature is 450 ° C., the tensile strength increase rate is 5%, and as the processing temperature increases, the tensile strength of the steel also increases, and the processing temperature is 600 ° C. The tensile strength increase rate is 134%.

  That is, the steel nitriding treatment according to the first embodiment of the present invention can improve the hardness and tensile strength of the steel at the same time, and has an advantage that it can be applied to various fields such as various parts and structural materials.

Second embodiment

The second embodiment of the present invention nitrides steel using NaNO ₂ as the molten salt.

  The types of nitrided steel are extremely low carbon steel, low carbon steel, medium carbon steel, high carbon steel, and alloy steel, which are immersed for 2 hours at a temperature of 450 ° C.

  As a result of the immersion, the hardness change and tensile strength change of the steel are as shown in Table 4 below, and the surface hardness is measured by applying a load of 1 kg with a Vickers hardness machine.

  In the case of the ultra-low carbon steel nitrided through the molten salt bath nitriding method of the second embodiment, the surface hardness is increased by 54% and the tensile strength is increased by 21%. In the case of the low-carbon steel, the surface hardness is 32%. Increases the tensile strength by 15%.

  In the case of the medium carbon steel nitrided through the molten salt bath nitriding method of the second embodiment, the surface hardness is increased by 19% and the tensile strength is increased by 13%. In the case of the high carbon steel, the surface hardness is increased by 18%. And the tensile strength is increased by 12%.

  In the case of alloy steel, the surface hardness increases by 17% and the tensile strength increases by 14%.

  That is, the steel nitrided through the molten salt bath nitriding method according to the second embodiment of the present invention has an increased surface hardness of about 15% to 60% and a tensile strength of about 10% to 25%.

  Therefore, it can be seen that the molten salt bath nitriding method according to the second embodiment of the present invention also increases the surface hardness and tensile strength of the steel.

Third embodiment

The third embodiment of the present invention nitrides steel using KNO ₃ as the molten salt.

  The type of nitrided steel is IF (Interstitial-Free) steel, 0.003 wt% carbon (C), 1.23 wt% manganese (Mn), 0.037 wt% aluminum (Al), 0.027 wt% Titanium (Ti), 0.050 wt% IN (P), 0.002 wt% nitrogen (N) and 0.008 wt% sulfur (S).

The nitriding temperatures according to the third embodiment of the present invention are 560 ° C., 580 ° C., 600 ° C., 620 ° C. and 640 ° C., and the IF steel is immersed in a KNO ₃ molten salt bath according to temperature for nitriding.

FIG. 4 is a graph showing the surface hardness of IF steel nitrided with KNO ₃ molten salt at different temperatures.

  As shown in FIG. 4, as the time and temperature for nitriding increase under most temperature conditions, the surface hardness increases, and this increase in hardness is a solid solution strengthening phenomenon due to an increase in nitrogen concentration. However, the present invention is not necessarily limited to such a theory.

However, if the nitriding time using KNO ₃ molten salt at 620 ° C. exceeds 8 hours or the nitriding time using KNO ₃ molten salt at 640 ° C. exceeds 1 hour, the surface hardness is rather lowered. It can be seen that this is due to the formation of a nitride layer by crystal growth of IF steel.

  FIG. 5 is a graph showing the hardness distribution in the thickness direction for the IF steel nitrided according to the third embodiment of the present invention.

At this time, nitriding is performed with KNO ₃ molten salt at 560 ° C. for 16 hours, and KNO ₃ molten salt at 560 ° C., 580 ° C., 600 ° C., and 620 ° C. for 8 hours.

  Referring to FIG. 5, the hardness of IF steel decreases as it enters the interior from the surface. Such a decrease in hardness is considered to be due to a decrease in the nitrogen concentration toward the inside, and the thickness of the nitride layer is reduced to a thickness corresponding to 110% or more of the hardness before nitriding of the IF steel center. If defined, the thickness of the nitride layer formed under each condition is about 1.38 mm to 1.5 mm, and a nitride layer that is about 3 to 5 times thicker than the conventional nitride layer can be formed.

Fourth embodiment

The fourth embodiment of the present invention nitrides steel using Ca (NO ₃ ) ₂ as a molten salt.

  The type of steel nitrided in the fourth example is low carbon steel.

Since Ca (NO ₃ ) ₂ is strongly hygroscopic at room temperature and contains crystal water, it is desirable to use it after performing heat treatment for a certain period of time to evaporate the water.

In the fourth embodiment of the present invention, Ca (NO ₃ ) ₂ is heat-treated at 100 ° C. to 150 ° C. for 4 hours to evaporate water, and then heated at a temperature of 580 ° C. to heat Ca (NO ₃ ) _2. After forming the molten salt bath, the low carbon steel is immersed for 3 hours.

  FIG. 6 is a graph showing the surface hardness of the low carbon steel nitrided according to the fourth embodiment of the present invention.

  As shown in FIG. 6, the low carbon steel nitrided according to the fourth example is nitrided to a depth of 0.5 mm from the surface, and the surface hardness is higher than the surface hardness (As) before nitriding. It is improved about 2 times.

Example 5

The fifth embodiment of the present invention nitrides steel using a mixed salt of KNO ₃ and NaNO ₃ as a molten salt.

In the fifth embodiment, the low carbon steel is nitrided with the mixing ratio of KNO ₃ and NaNO ₃ being 1: 1, 8: 2, and 2: 8.

Table 5 shows the surface hardness of the steel nitrided according to the fifth embodiment of the present invention. Various types of steel are immersed in a mixed salt in which the mixing ratio of KNO ₃ and NaNO ₃ is 1: 1, and then maintained at 650 ° C. for 12 hours or 24 hours.

  At this time, the measured hardness is Vickers hardness and is measured with a load of 3 kg.

As shown in Table 5, the steel nitrided with a mixed salt of KNO ₃ and NaNO ₃ exhibits a hardness improvement rate of 69% to 251% depending on the type.

In order to know the changes in the surface hardness and tensile strength of steel due to the time of nitriding performed using the mixed salt, various types are included in the 580 ° C. mixed salt in which the mixing ratio of KNO ₃ and NaNO ₃ is 1: 1. Immerse the steel.

  As a result, as disclosed in Table 6 below, in all steels, the hardness and tensile strength after nitriding increased, and the rate of increase in hardness and tensile strength also increased with time. I understand that.

  This shows that the surface hardness and tensile strength of the steel continuously increase as the nitriding time increases.

FIG. 7 is a graph showing changes in the surface hardness of steel depending on the type of salt bath. The type of salt bath used is KNO ₃ , a single salt of NaNO ₃ , and KNO ₃ and NaNO ₃ in a 1: The mixed salt mixed in 1 is nitrided at a temperature of 680 ° C. for 200 minutes.

  And the measurement of surface hardness measures hardness from the surface to the deep part using the Vickers hardness machine.

  As shown in FIG. 7, when mixed salt is used, the nitrided steel is nitrided to a depth of 1.5 mm from the surface, with a surface hardness of approximately 160 Hv, a single salt bath It shows a high hardness compared to steel nitriding using, and shows a hardness about three times higher than steel (As) before nitriding.

FIG. 8 shows the surface of the low carbon steel nitrided after nitriding the low carbon steel for 4 hours at 650 ° C. with the mixing ratio of the mixed salt of KNO ₃ and NaNO _{3 being} 8: 2 and 2: 8, respectively. It is the graph which showed hardness.

As shown in FIG. 8, even when the mixing ratio of KNO ₃ and NaNO ₃ is varied, the hardness of the surface is more than twice the steel (As) surface hardness before nitriding treatment. You can see that it rises.

  The terms and words used in the specification and claims are not to be interpreted in a general or limiting sense, and the inventor best describes the invention. Therefore, it should be based on the principle that the concept of terms can be appropriately defined and interpreted with the 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 only the most preferred embodiments of the present invention, and do not represent any technical ideas of the present invention. It should be understood that at the time, there can be various equivalents and variations that can be substituted for them.

It is a graph which shows the relationship between nitriding treatment time and the nitriding thickness of steel by 1st Example of this invention. It is a graph which shows the relationship between nitriding treatment time and the nitriding thickness of steel by 1st Example of this invention. It is a graph which shows the relationship between the nitriding process temperature and the nitriding thickness of steel by 1st Example of this invention. It is a graph which shows the relationship between nitriding treatment time and the nitriding thickness of steel by 3rd Example of this invention. It is a graph which shows the relationship between the nitriding temperature by the 3rd Example of this invention, and the nitriding thickness of steel. It is a graph which shows the relationship between the nitriding process temperature and the nitriding thickness of steel by 4th Example of this invention. It is a graph which shows the relationship between the kind of salt bath and the nitriding thickness of steel by 5th Example of this invention. It is a graph which shows the relationship between the mixing ratio of mixed salt and the nitriding thickness of steel by 5th Example of this invention.

Claims (35)

Placing at least one salt of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO _{2 in} a salt bath;
Melting the salt to maintain a constant temperature;
And nitriding the metal in the salt bath. Placing a mixed salt containing at least one of KNO ₃ and KNO ₂ and at least one of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO _{2 in} a salt bath;
Melting the salt to maintain a constant temperature;
And nitriding the metal in the salt bath.   The metal salt bath nitriding method according to claim 1 or 2, wherein the constant temperature is in a range of 400 ° C to 700 ° C.   3. The metal salt bath nitriding method according to claim 1, wherein an immersion time in the step of nitriding the metal is in a range of 1 minute to 24 hours. Putting KNO ₃ salt in a salt bath;
Melting the salt and maintaining it at 400 ° C. or higher and 620 ° C. or lower;
Nitriding the metal in the salt bath in less than 8 hours. Putting KNO ₃ salt in a salt bath;
Melting the salt and maintaining it above 620 ° C. and below 640 ° C .;
Nitriding the metal in the salt bath in less than 1 hour.   The metal salt bath nitriding method according to any one of claims 1, 2, 5, and 6, wherein the metal is pure iron or steel. In the metal nitrided in at least one salt bath among Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO ₂ ,
The metal is pure iron;
Pure iron nitrided from the surface of the pure iron to the inside of 0.1 mm to 3.0 mm. In a metal nitrided in a mixed salt bath containing at least one of KNO ₃ and KNO ₂ and at least one of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO ₂ ,
The metal is pure iron;
Pure iron nitrided from the surface of the pure iron to the inside of 0.1 mm to 3.0 mm. In the metal nitrided in at least one salt bath among Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO ₂ ,
The metal is steel;
A steel characterized in that it is nitrided from the surface of the steel to the inside of 0.1 mm to 3.0 mm. In a metal nitrided in a mixed salt bath containing at least one of KNO ₃ and KNO ₂ and at least one of Ca (NO ₃ ) ₂ , NaNO ₃ and NaNO ₂ ,
The metal is steel;
A steel characterized in that it is nitrided from the surface of the steel to the inside of 0.1 mm to 3.0 mm.   The steel according to claim 10 or 11, wherein the steel is any one of an extremely low carbon steel, a low carbon steel, a medium carbon steel, a high carbon steel, and an alloy steel.   The steel according to claim 12, wherein the ultra-low carbon steel has a surface hardness of more than 120Hv and not more than 450Hv.   The steel according to claim 12, wherein the low carbon steel has a surface hardness of more than 200Hv and not more than 410Hv.   The steel according to claim 12, wherein the medium carbon steel has a surface hardness of more than 130Hv and not more than 420Hv.   The steel according to claim 12, wherein the high carbon steel has a surface hardness of more than 150 Hv and not more than 400 Hv.   The steel according to claim 12, wherein the alloy steel has a surface hardness of more than 200Hv and not more than 410Hv. The ultra low carbon steel, steel of claim 13, the tensile strength is equal to or less than 35 kg / mm ² exceeding 110 kg / mm ^2. The low carbon steel, steel of claim 14 tensile strength equal to or less than 45 kg / mm ² exceeding 110 kg / mm ^2. Wherein the carbon steel, steel of claim 15, the tensile strength is equal to or less than 45 kg / mm ² exceeding 100 kg / mm ^2. The steel according to claim 16, wherein the high carbon steel has a tensile strength of more than 60 kg / mm ^{2 and not} more than 95 kg / mm ² . The steel according to claim 17, wherein the alloy steel has a tensile strength of 55 kg / mm ^{2 and} 110 kg / mm ² or less.   The chromium content of the steel is 0.1 wt. % To 1.5 wt. 23. Steel according to claim 22, characterized in that it is%.   The molybdenum content of the steel is 0.05 wt. % To 0.5 wt. 23. Steel according to claim 22, characterized in that it is%.   The nickel content of the steel is 0.1 wt. % To 10 wt. 23. Steel according to claim 22, characterized in that it is%.   The manganese content of the steel is 0.1 wt. % To 2.0 wt. 23. Steel according to claim 22, characterized in that it is%.   The boron content of the steel is 0.001 wt. % To 0.1 wt. 23. Steel according to claim 22, characterized in that it is%.   The titanium content of the steel is 0.001 wt. % To 0.1 wt. 23. Steel according to claim 22, characterized in that it is%.   The vanadium content of the steel is 0.05 wt. % To 0.15 wt. The steel according to claim 22, wherein the steel is%.   The niobium content of the steel is 0.005 wt. % To 0.1 wt. The steel according to claim 22, wherein the steel is%.   The aluminum content of the steel is 0.005 wt. % To 0.1 wt. 23. Steel according to claim 22, characterized in that it is%.   The carbon content of the ultra-low carbon steel is 0.0001 wt. % Or more and 0.13 wt. The steel according to claim 18, wherein the steel is less than%.   The carbon content of the low carbon steel is 0.13 wt. % To 0.2 wt. The steel according to claim 19, wherein the steel is less than%.   The carbon content of the medium carbon steel is 0.21 wt. % Or more 0.51 wt. 21. Steel according to claim 20, characterized in that it is less than%.   The carbon content of the high carbon steel is 0.51 wt. % To 2.0 wt. The steel according to claim 21, wherein the steel is not more than%.

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