JP2008303413A - High nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high nitrogen stainless steel powder for solidification molding which is free of Ni or reduced in Ni, and is excellent in corrosion resistance, and to provide a method for producing the high nitrogen stainless steel powder. <P>SOLUTION: The high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance is obtained by absorbing nitrogen into alloy powder comprising, by mass, 0 to 5.0% Ni and 10.0 to 40.0% Cr and incorporating ≥0.5% N therein, and in which the maximum size of CrN at the inside of the powder is 3 μm. Also, the high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance is obtained by absorbing nitrogen into alloy powder comprising 0.1 to 15.0% Mn and 0.1 to 20.0% Mo, and further comprising 0.1 to 10.0% Cu, 0.3 to 2.0% Si and ≤0.2% C in addition to the above componential composition and incorporating ≥0.5% N therein, and in which the maximum size of CrN at the inside of the powder is 3 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Ni-free, Ni-saving high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance and a method for producing the same.

  Conventionally, in producing stainless steel, Ni is an important alloying element for imparting corrosion resistance to stainless steel, and has been added in a large amount, but on the other hand, it is an extremely expensive alloying element and has a large price fluctuation. Therefore, it has been desired to reduce the amount of addition as much as possible. Moreover, Ni allergy is a problem in applications that come into contact with the human body, such as medical implants, ornaments, and tableware, and Ni-free or Ni reduction is desired.

  On the other hand, as described above, nitrogen is an element that contributes to stabilization of austenite, corrosion resistance, strength, and toughness, and attention has been paid to Ni replacement with stainless steel and higher performance. Various methods such as pressure melting method, solid phase absorption method, powder sintering method and mechanical alloying method have been proposed for the production of high nitrogen stainless steel, all of which are industrial in terms of cost and productivity. There are many problems in application to production, and a manufacturing method of high nitrogen stainless steel having low cost and stable performance is desired.

  Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 2005-2431 (Patent Document 1), as a method for producing high nitrogen stainless steel, nitrogen gas is blown into the molten steel, and nitriding is performed to dissolve the high nitrogen stainless steel. As disclosed in Japanese Patent Laid-Open No. 11-246828 (Patent Document 2), a gas atomized stainless steel is filled in a mild steel capsule, nitrided under reduced pressure, and then hot bar extruded by a hot extrusion method. A method of solidifying and forming a steel pipe or plate material has been proposed.

  Further, as a pressure melting method, for example, as disclosed in JP-A-2006-524252 (Patent Document 3), Cr: 15 to 35%, Mo: 0.05 to 8%, Mn: 0.2 Ni-less high-nitrogen austenitic stainless steels that are regulated to 10%, Cu: 0.01-4%, and N: 0.8-1.5% have been proposed. Further, as disclosed in JP 2007-51368 A (Patent Document 4), as pressure ESR, Cr: 14 to 30%, Mo: 1 to 10%, Mn: 0 to 1.5%, N: Ni-less high nitrogen stainless steel restricted to 1.0 to 2.0% has been proposed.

Further, as a powder sintering method under a nitrogen atmosphere, as disclosed in, for example, Japanese Patent Laid-Open No. 2-57661 (Patent Document 5), the powder is sintered in a nitrogen gas atmosphere, and a high nitrogen stainless steel is obtained. A manufacturing method has been proposed.
JP 2005-2431 A JP-A-11-246828 JP 2006-52452 A JP 2007-51368 A JP-A-2-57661

  Patent document 1 mentioned above adds nitrogen directly to molten steel, and can manufacture steel nitrogen steel comparatively easily. However, since nitrogen is added without processing, there is a problem that 0.5% (5000 ppm) or more, which is the subject of the present invention, is difficult. In addition, the powder-canning-nitriding method shown in Patent Document 2 and the powder sintering method in a nitrogen atmosphere shown in Patent Document 5 can produce high nitrogen steel relatively easily, but nitriding at a high temperature. There is a problem in that powders are easily sintered during processing, it is difficult to obtain a uniform nitrogen distribution, and it is difficult to produce a large product.

  Further, the pressure melting method shown in Patent Document 3 and the pressure ESR method shown in Patent Document 4 can add nitrogen directly to the molten steel, as in Reference Document 1, and can be manufactured even if it is relatively large. However, special melting equipment such as a pressure induction furnace and a pressure ESR is required, and high nitrogen steel has a problem that it is difficult to process and form steel ingots from steel ingots because work hardening is remarkable.

  As a result of diligent development by the inventors to solve the above-mentioned problems, nitrogen contributes to the stabilization of the austenite phase, corrosion resistance, strength, and toughness. Therefore, expensive Ni-free or a small amount is added. For this purpose, a method for producing high nitrogen stainless steel in which sintering during nitriding is suppressed by low-temperature nitriding in a powder state and nitrogen is uniformly contained in each powder is provided.

The gist of the invention is that
(1) Nitrogen is absorbed in an alloy powder containing Ni: 0 to 5.0% and Cr: 10.0 to 40.0% by mass%, and 0.5% or more of N is contained, and the powder High nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized in that the maximum diameter of internal CrN is 3 μm or less.

  (2) Alloy containing Ni: 0 to 5.0%, Cr: 10.0 to 40.0%, Mn: 0.1 to 15.0%, Mo: 0.1 to 20.0% by mass A high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized in that nitrogen is absorbed into the powder to contain 0.5% or more of N, and the maximum diameter of CrN inside the powder is 3 μm or less.

  (3) In mass%, Ni: 0 to 5.0%, Cr: 10.0 to 40.0%, Mn: 0.1 to 15.0%, Mo: 0.1 to 20.0%, Cu : 0.1 to 10.0%, Si: 0.3 to 2.0%, C: Nitrogen is absorbed into an alloy powder containing 0.2% or less, and 0.5% or more of N is contained, A high nitrogen stainless steel powder for solidification molding with excellent corrosion resistance, characterized in that the maximum diameter of CrN inside the powder is 3 μm or less.

(4) It contains 0.5% or more of nitrogen and 0.2% or less of oxygen, and other than that, it has the component composition according to any one of (1) to (3), and has a size. A high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized by comprising a powder of 500 μm or less.
(5) A powder having a size of 500 μm or less having the component composition described in any one of (1) to (3) is nitrogen-containing by low-temperature nitriding at 200 to 600 ° C. A method for producing high nitrogen stainless steel powder for solidification molding with excellent corrosion resistance.

(6) A method for producing high nitrogen stainless steel obtained by solidifying and molding a powder containing nitrogen having the component composition according to any one of (1) to (4).
(7) After canning the powder containing nitrogen according to any one of (1) to (4), solidified and formed into a steel bar, a steel pipe, a plate material, and a clad material, 0.5% or more of nitrogen, It exists in the manufacturing method of the high nitrogen stainless steel characterized by containing 0.2% or less of oxygen.

  As described above, after the canned low-temperature nitrided powder in the powder state according to the present invention is heated to 1000 to 1300 ° C., it is solidified by HIP and hot extrusion to form a solid solution of CrN generated during nitriding treatment. High-nitrogen stainless steel with a uniform nitrogen content in the powder by promoting denitrification and suppressing denitrification makes it possible to reduce the cost of high-nitrogen stainless steel to various shapes such as steel pipes, plate materials, bar steel, and cladding An extremely excellent effect that can be produced is achieved.

Hereinafter, the reason for limitation of the component composition according to the present invention will be described in detail.
Ni: 0 to 5.0%
Ni is known as an important element in stabilizing the austenite phase and obtaining corrosion resistance. On the other hand, since it is an expensive element and known to have adverse effects on the human body such as Ni allergy, it is desired to reduce the amount of addition as much as possible while ensuring the necessary characteristics. In the present invention, Ni can be substituted by adding high nitrogen to the powder. Therefore, expensive Ni is added free or added in a small amount of 5.0% or less.

Cr: 10.0-40.0%
Cr is an important element for imparting corrosion resistance, and needs to be 10.0% or more to sufficiently obtain the effect. On the other hand, Cr is a ferrite-forming element, and excessive addition causes precipitation of the σ phase that causes a decrease in toughness and instability of the austenite phase, so the upper limit is made 40.0%. Preferably it is 15 to 30%.

Mn: 0.1 to 15.0%
Mn contributes to the stabilization of the austenite phase and has the effect of increasing the nitrogen solubility of the matrix, so the lower limit was made 0.1%. On the other hand, in addition to inhibiting the absorption of nitrogen by generating an oxide on the powder surface, non-metallic inclusions are formed and the corrosion resistance is lowered, so the upper limit was made 15.0%. Preferably it is 2.0 to 10.0%.

Mo: 0.1 to 20.0%
Mo contributes to the improvement of corrosion resistance, and the combined addition with N is highly effective. Moreover, since there exists an effect which increases the nitrogen solubility of a matrix, the minimum was made into 0.1%. On the other hand, when it exceeds 20.0%, an embrittled phase precipitates and the toughness is lowered. Preferably, the content is 2.0 to 15.0%.

Cu: 0.1 to 10.0%
Cu has the effect of stabilizing the austenite phase and improving the corrosion resistance, so its lower limit is made 0.1%. If the addition amount is large, the solidification moldability is remarkably lowered and the corrosion resistance is also lowered, so the upper limit was made 10.0%. Preferably it is 2.0 to 7.0%.

Si: 0.3-2.0%
Si is an effective element as a deoxidizing material, and the effect is obtained at 0.3% or more. On the other hand, if it exceeds 2.0%, the toughness is significantly reduced.
C: 0.2% or less C is an element that contributes to the improvement of strength. However, it forms a carbide with Cr and lowers the corrosion resistance, so the upper limit is made 0.2% or less.

N: 0.5% or more Nitrogen contributes to stabilization of the austenite phase, corrosion resistance, strength, and toughness. Ni substitution of 0.5% or more of nitrogen is required to obtain corrosion resistance, strength, and toughness improvement by nitrogen. The amount of nitrogen can be contained depending on the application and alloy components by adjusting the nitriding temperature, nitriding time, and nitrogen partial pressure.
O: 0.2% or less Oxygen contributes to improvement in strength and toughness of fine oxides. However, the amount of oxygen is 0.2% or less because the corrosion resistance decreases when the amount of oxides increases.

The maximum diameter of CrN is 3 μm or less N that cannot be dissolved in the matrix is combined with Cr to produce CrN. Fine CrN contributes to suppression of coarsening of crystal grains, but coarse CrN does not completely dissolve during hot solidification and solidification processes in which the matrix nitrogen solubility increases, and the remaining CrN reduces corrosion resistance. Therefore, the maximum diameter is 3 μm or less.

500 μm or less In order to incorporate nitrogen into the powder by low-temperature nitriding, the powder particle size is set to 500 μm or less. Desirably, it shall be 250 micrometers or less. The method and shape of the powder are not limited, but spherical gas atomized powder is preferable from the viewpoint of obtaining a uniform nitrogen distribution.

A temperature of 200 ° C. or higher is required to contain nitrogen in the low-temperature nitrided powder at 200 to 600 ° C. However, if the nitriding temperature is increased, coarse nitrides are likely to be generated, and powders are sintered and a uniform nitrided powder cannot be obtained. In order to suppress oxidation during the treatment, it is desirable to carry out the treatment under reduced pressure with the atmosphere in the furnace discharged.

Hereinafter, the present invention will be specifically described with reference to examples.
About the chemical component of each powder shown in Table 1, after dissolving 30 kg in the vacuum induction melting furnace, the powder obtained by the gas atomization method was obtained. In the initial powder stage, oxygen and nitrogen are unavoidable impurities. After classifying to 500 μm or less, disperse in a thickness of about 20 mm on a 100 × 100 mm tray, or after putting powder in a SC can of Φ100 mm × L200 mm, low-temperature nitriding with one side of the can open The powder was made to absorb nitrogen by (200 to 600 ° C., ammonia gas atmosphere). The nitrided powder was solidified by a method such as canning, HIP, or hot extrusion (1000 to 1300 ° C.) to obtain a high nitrogen stainless steel having a diameter of 10 to 60 mm. Then, CrN was made into solid solution by carrying out the solution heat treatment at 1100-1300 degreeC. The processing conditions and evaluation results are shown in Table 2.

  The oxygen and nitrogen values of the powder and molded product were analyzed by the inert gas dissolution method. Nitrogen that could not be dissolved in the matrix may be released into the atmosphere during hot working or solution treatment, but the amount is relatively small. The size of CrN was quantified with a scanning electron microscope 5000 times and 10 fields of view after polishing the specimen and etching it with dilute aqua regia. The corrosion test shown in Table 2 was soaked in a 10% NaCl solution at 25 ° C. for 1 week, and the superiority or inferiority was determined by the rusting state. Corrosion test results: ◎ → No rusting, ○ → Good, × → Rusting.

表２に示すように、Ｎｏ．１〜４、Ｎｏ．７〜９、Ｎｏ．１２、Ｎｏ．１４〜１９、Ｎｏ．２２〜２３は本発明例であり、Ｎｏ．５〜６、Ｎｏ．１０〜１１、１３、Ｎｏ．２０〜２１、Ｎｏ．２４〜２７は比較例である。

As shown in Table 2, no. 1-4, no. 7-9, no. 12, no. 14-19, no. Nos. 22 to 23 are examples of the present invention. 5-6, no. 10-11, 13, no. 20-21, no. 24-27 are comparative examples.

  Comparative Example No. Since No. 5 has a large powder particle size and a low nitrogen content after solidification molding, the corrosion test evaluation result is poor. Comparative Example No. Since No. 6 has a high nitriding temperature, the amount of nitrogen after nitriding is large, the amount of nitrogen after solidification is large, and the CrN size is large, so the corrosion test evaluation result is bad. Comparative Example No. Since No. 10 has a large powder particle size, a low nitrogen content after solidification molding, and a low nitrogen content after solidification molding, the corrosion test evaluation result is poor. Comparative Example No. Since No. 11 has a low nitriding temperature, the amount of nitrogen after solidification molding is low, and the corrosion test evaluation result is poor.

  Comparative Example No. No. 13 has a large powder particle size, and since the amount of nitrogen after nitriding is low, the amount of nitrogen after solidification molding is low, resulting in poor corrosion test evaluation results. Comparative Example No. No. 20 has a low nitriding temperature and a low amount of nitrogen after nitriding, so that the amount of nitrogen after solidification is low and the corrosion test evaluation result is poor. Comparative Example No. Since No. 21 has a high nitriding temperature and a large CrN size, the corrosion test evaluation result is bad. Comparative Example No. No. 24 has a high nitriding temperature, a high amount of nitrogen after nitriding, a high amount of nitrogen after solidification molding, and a large CrN size, so that the corrosion test evaluation result is poor.

  Comparative Example No. No. 25 has a large powder particle size, a low amount of nitrogen after nitriding, and a low amount of nitrogen after solidification molding, so that the corrosion test evaluation result is poor. Comparative Example No. Since No. 26 is a steel whose Ni component composition of the initial powder is originally high, the corrosion test evaluation result is good. Comparative Example No. In No. 27, the Cr component composition of the initial powder is high and the CrN size is large, so the corrosion test evaluation result is bad. On the other hand, No. which is an example of the present invention. 1-4, no. 7-9, no. 12, no. 14-19, no. Since 22-22 satisfy | fills the conditions of this invention, it turns out that the corrosion test evaluation result is favorable.

As described above, after nitrogen is absorbed in the powder obtained by low temperature nitriding at 200 to 600 ° C. according to the present invention, solidification molding is performed by a method such as canning, HIP, hot extrusion, or HIP and hot extrusion. It is possible to obtain a high nitrogen stainless steel containing nitrogen uniformly by promoting solid solution of CrN and suppressing denitrification.



Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney Atsushi Shiina

Claims (7)

Nitrogen is absorbed in an alloy powder containing Ni: 0 to 5.0% and Cr: 10.0 to 40.0% by mass% to contain 0.5% or more of N, and CrN inside the powder A high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized by having a maximum diameter of 3 μm or less. Nitrogen in an alloy powder containing Ni: 0 to 5.0%, Cr: 10.0 to 40.0%, Mn: 0.1 to 15.0%, Mo: 0.1 to 20.0% by mass% Is a high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized in that 0.5% or more of N is absorbed and the maximum diameter of CrN inside the powder is 3 μm or less. In mass%, Ni: 0 to 5.0%, Cr: 10.0 to 40.0%, Mn: 0.1 to 15.0%, Mo: 0.1 to 20.0%, Cu: 0.00. Nitrogen is absorbed into an alloy powder containing 1 to 10.0%, Si: 0.3 to 2.0%, and C: 0.2% or less, and 0.5% or more of N is contained, and the inside of the powder A high nitrogen stainless steel powder for solidification molding excellent in corrosion resistance, characterized in that the maximum diameter of CrN is 3 μm or less. It contains 0.5% or more of nitrogen and 0.2% or less of oxygen, and other than that, it has the component composition according to any one of claims 1 to 3, and consists of a powder having a size of 500 μm or less. High nitrogen stainless steel powder for solidification molding with excellent corrosion resistance. Solidified molding excellent in corrosion resistance, characterized in that a powder having a component composition according to any one of claims 1 to 3 and having a size of 500 µm or less contains nitrogen by low-temperature nitriding at 200 to 600 ° C. Of manufacturing high nitrogen stainless steel powder for use. The manufacturing method of the high nitrogen stainless steel which solidified and formed the powder containing the nitrogen which has the component composition of any one of Claims 1-4. After canning the powder containing nitrogen according to any one of claims 1 to 4, it is solidified and formed into a steel bar, a steel pipe, a plate material, and a clad material, 0.5% or more of nitrogen, 0.2% or less A method for producing high nitrogen stainless steel, comprising oxygen.