JP4379804B2 - High nitrogen austenitic stainless steel - Google Patents

Description

  The present invention relates to a high nitrogen austenitic stainless steel.

JP-A-10-183303

  As steel having high corrosion resistance and excellent workability, austenitic stainless steels such as SUS304 and SUS316 are frequently used. In particular, as a material that has excellent corrosion resistance and strength is required at the same time, steel types such as SUS316, which is an austenitic stainless steel, and SUS329, which is a duplex stainless steel, are generally used. In applications where further corrosion resistance is required, SUS836L (also referred to as superaustenitic stainless steel) in which the amount of Ni and Mo is greatly increased is used.

  However, although the austenitic stainless steel is excellent in corrosion resistance, it has a limit of use against local corrosion, and there is a high need for further strengthening. Further, since a large amount of expensive Ni or Mo is used, a cheaper material is demanded. Therefore, in recent years, as a stainless steel having higher strength and corrosion resistance than that of austenitic stainless steel, the concentration of nitrogen, which is an interstitial solid solution element, is significantly higher than that of ordinary stainless steel. High-nitrogen austenitic stainless steel that has been stabilized is attracting attention. Such high nitrogen austenitic stainless steels have already been used in a wide variety of applications such as air shafts, ball bearings, bearings, plastic molds, etc., but as disclosed in Patent Document 1, they are used as biomaterials. Is also expected. That is, Ni, which is added in a considerable amount in general austenitic stainless steel, is positioned as one of the elements that are undesirable for the human body and can cause Ni allergy in the field of biomaterials. Nitrogen austenitic stainless steel uses nitrogen as a main austenite phase stabilizing element, and therefore has the advantage that most of Ni can be reduced and the hardness and corrosion resistance can be maintained at the same level or higher.

  However, a relatively large amount of Mn is added to the austenitic stainless steel of Patent Document 1 in order to increase the amount of nitrogen solid solution (in the claims, the Mn content range is widely set to 2 to 26% by mass). However, the Mn content of the steel compositions disclosed in the examples is as high as 11% by mass and 12% by mass). In such a high nitrogen austenitic stainless steel, if such a high Mn composition is adopted, the corrosion resistance may be deteriorated and the strength may be insufficient.

  The subject of this invention is providing the high nitrogen austenitic stainless steel which was excellent in both corrosion resistance and intensity | strength compared with the past, although Ni content rate is low.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the high nitrogen austenitic stainless steel of the present invention is
Cr: 24.0 mass% or more and 35.0 mass% or less;
Mo: 0.05 mass% or more and 8.0 mass% or less;
Mn: 0.2% by mass or more and 10.0% by mass or less;
Cu: 0.01% by mass or more and 4.0% by mass or less;
N: 0.8% by mass or more and 1.5% by mass or less
C content is 0.20 mass% or less, Si content is 2.0 mass% or less, P content is 0.03 mass% or less, S content is 0.05 mass% or less, Ni The content is 0.5 mass% or less, the Al content is 0.03 mass% or less, the O content is 0.020 mass% or less , the balance is Fe and inevitable impurities ,
When the Cr content is WCr (mass%), the Mo content is WMo (mass%), the N content is WN (mass%), and the Mn content is WMn (mass%),
η≡ (WCr + 3.3WMo + 16WN) / WMn
The content of Cr, Mo, N, and Mn is adjusted so that the composition parameter η represented by

  According to the high nitrogen austenitic stainless steel of the present invention, a large amount of N (nitrogen) is dissolved while regulating the Ni content, and the composition of essential elements composed of Cr, Mo, N, and Mn is further defined. By optimizing in a specific range, strength and corrosion resistance can be balanced at a high level. As a result, despite the low Ni content, it is possible to realize a high nitrogen austenitic stainless steel that is superior in both corrosion resistance and strength. For example, in a solution treatment state, for example, SUS836L, which is a super austenitic stainless steel, is used. It is not impossible to achieve both comparable corrosion resistance and higher strength than SUS329J4L, which is a duplex stainless steel.

Hereinafter, the reasons for limiting the composition of each element in the high nitrogen austenitic stainless steel of the present invention will be described.
(1) Cr: 24.0 mass% or more and 35.0 mass% or less Cr functions to remarkably increase the N solubility in the molten metal, greatly contributes to improvement of corrosion resistance and strength, and generates nitrogen blowholes. It is also effective for suppression. When the Cr content is less than 15.0% by mass, the solubility of N in the molten metal becomes insufficient, and it becomes difficult to ensure corrosion resistance and strength, and nitrogen blowholes are likely to occur. On the other hand, if the Cr content exceeds 35.0 mass%, Cr is a ferrite-forming element, leading to destabilization of the austenite phase, and it may not be possible to keep the material nonmagnetic. In addition, a σ phase that causes deterioration of toughness is likely to precipitate. The Cr content is desirably 24.0 mass% or more and 32.0 mass% or less, and more desirably 25.0 mass% or more and 30.0 mass% or less.

(2) Mo: 0.05% by mass or more and 8.0% by mass or less Mo, like Cr, works to remarkably increase the N solubility in the molten metal, but exhibits a greater effect of improving corrosion resistance in a smaller amount than Cr. In addition, the effect of improving the strength by solid solution strengthening can be obtained. However, if the amount of Mo added is less than 0.05% by mass, the effect is poor, and if added over 8.0% by mass, the induction of nitrogen blowholes and the austenite phase become unstable. Ensuring is also difficult. In addition, the tough ductility is reduced due to the formation of the embrittled phase, which is also harmful during hot working. In addition, there is a problem that undissolved Cr nitride is increased during solution treatment, and the corrosion resistance is remarkably lowered. The amount of Mo added is more preferably 0.05% by mass or more and less than 5.0% by mass, and further preferably 0.10% by mass or more and less than 2.5% by mass.

(3) Mn: 0.2% by mass or more and 10.0% by mass or less Mn is an austenite-forming element that contributes to stabilization of the austenite phase and lowers the solid solution temperature of Cr nitride described later. Further, since the N solubility in the molten metal is remarkably increased, it is effective for improving the strength and suppressing the generation of nitrogen blowholes. It is also effective as a deoxidizing and desulfurizing element. If the Mn content is less than 0.2% by mass, the solubility of N in the molten metal becomes insufficient, and sufficient strength cannot be secured, and nitrogen blowholes are likely to occur. On the other hand, when Mn addition amount exceeds 10.0 mass%, it will lead to deterioration of corrosion resistance. The Mn content is more preferably 0.2% by mass or more and 6.0% by mass or less, and further preferably 0.2% by mass or more and 2.0% by mass or less.

(4) Cu: 0.01% by mass or more and 2.0% by mass or less Cu is an austenite-forming element and contributes to stabilization of the austenite phase and to improvement of corrosion resistance. However, if the addition amount is less than 0.01% by mass, the effect is poor, and the addition exceeding 2.0% by mass causes a problem that the hot workability is lowered. Moreover, the residual amount of the undissolved Cr nitride after the solution treatment is increased, and conversely, the corrosion resistance is deteriorated. The amount of Cu added is more preferably 0.02% by mass or more and 1.8% by mass or less, and further preferably 0.05% by mass or more and 1.5% by mass or less.

(5) N: 0.8 mass% or more and 1.5 mass% or less Basic addition that is an interstitial solid solution element for the austenite phase and contributes effectively to all of the improvement in strength, stabilization of the austenite phase and improvement in corrosion resistance. It is an element. When the N addition amount exceeds 1.5 mass%, nitrogen blowholes are easily generated, and after solution treatment, undissolved Cr nitride and other transition metal nitrides (for example, Ti, Nb, which will be described later) A large amount of nitride such as V) remains in the steel, leading to a problem that the corrosion resistance is remarkably lowered. The amount of N added is more preferably 0.8% by mass or more and 1.4% by mass or less.

(6) Fe: 50% by mass or more Fe is a main component of steel (that is, 50% by mass or more), and basically includes the above five essential additive elements, optional elements and inevitable impurities described below. It constitutes the remainder. However, as long as the effects of the present invention described above are not impaired, the inclusion of subcomponents not particularly described in the present specification is not excluded.

(7) η: 5 or more η is WCr (mass%) for the Cr content, WMo (mass%) for the Mo, WN (mass%) for the N content, and WMn (Mn content for the Mn content). Mass%)
η≡ (WCr + 3.3WMo + 16WN) / WMn
It is a composition parameter represented by. Among the additive elements involved in η, N, Cr, and Mo serve to improve the corrosion resistance, while Mn is an essential element that increases the amount of N solid solution, but the corrosion resistance works in the direction of deterioration. The molecule of η is obtained by quantifying the corrosion resistance improvement effect of Mo and N in terms of Cr equivalent, and N, Cr and Mo all contribute to the improvement of corrosion resistance, but the corrosion resistance improvement effect of N is Cr As many as 16 times. In order to dramatically increase the amount of N solid solution in the austenite phase, it is indispensable to add Mn after all. However, if too much Mn is added, the amount of N solid solution in the austenite phase increases, but Mn itself Since it acts on the corrosion resistance deterioration, it is an image in which the increase in corrosion resistance due to the increased N is partially eroded by the addition of Mn. Therefore, the η value in which the contribution of N, Cr and Mo to the corrosion resistance is reflected in the denominator and the contribution to the corrosion resistance degradation due to Mn in the numerator is effective for comprehensively predicting the corrosion resistance of the steel finally obtained. Parameter.

  And when this inventor examined in detail, by adjusting the addition amount balance of N, Cr, Mo, and Mn so that said (eta) may be 5 or more, the corrosion-resistant improvement effect is remarkably optimized, for example, super It has been found that corrosion resistance equivalent to or better than SUS836L, which is an austenitic stainless steel, can be secured.

Hereinafter, the reason for limiting the composition of trace elements (positively added elements and impurity elements) will be described.
(8) C: 0.20% by mass or less C is an interstitial solid solution element with respect to Fe and contributes to the improvement of strength, and is also effective in suppressing the formation of nitrogen blowholes as an austenite forming element. However, addition exceeding 0.20% by mass decreases the solubility of N and decreases the amount of Cr in the austenite phase due to the formation of Cr carbide, leading to deterioration in corrosion resistance. C is an optional element, but 0.005% by mass or more is desirably added in order to make the effect of positive addition remarkable. The content of C is desirably 0.005% by mass or more and 0.15% by mass or less, and more desirably 0.01% by mass or more and 0.10% by mass or less.

(9) Si: 2.0 mass% or less Although Si is effective as a deoxidizing element, Al, which is a stronger deoxidizing agent than Si in general steel, has high temperature strength and toughness in high nitrogen steel. As a main deoxidizing agent, it is desirable to use Si together with the essential element Mn because it causes generation of AlN that causes a significant decrease. The deoxidation effect by Si becomes remarkable when addition of 0.01 mass% or more is performed. On the other hand, when the amount of Si added exceeds 2.0% by mass, defects such as cracking are likely to occur during hot working, and the toughness of the steel also decreases. The amount of Si added is desirably 0.01% by mass or more and 1.0% by mass or less, and more desirably 0.01% by mass or more and 0.5% by mass or less.

(10) P: 0.03 mass% or less P is one of harmful impurities. If it exceeds 0.03% by mass, hot workability deteriorates and toughness deteriorates due to a decrease in grain boundary strength. It is better that P is not contained as much as possible, and the lower limit is appropriately set in consideration of cost.

(11) S: 0.05% by mass or less S is one of harmful impurities, and when it exceeds 0.05% by mass, hot workability is reduced and corrosion resistance is easily deteriorated due to the formation of MnS. It is better that S is not contained as much as possible, and a lower limit is appropriately set in consideration of cost. Desirably, it is good to set it as 0.01 mass% or less.

(12) Ni: 0.5% by mass or less Ni is actively added and suppressed in the present invention in order to reduce the cost of materials and avoid the effects of Ni allergy when applied to the human body. The Ni content should be as low as possible. However, since an excessive reduction leads to an increase in cost, the content is allowed up to 0.5% by mass. The Ni content is desirably 0.3% by mass or less, more preferably 0.1% by mass or less.

(13) Al: 0.03% by mass or less As described above, Al is effective as a deoxidizer, but in high nitrogen steel, if the Al content becomes even a little excessive, the generation of AlN proceeds and the corrosion resistance is remarkable. Incurs a decline. Accordingly, in the present invention, this is avoided, and from the viewpoint of increasing the N solid solution amount in the austenite phase as much as possible, the Al content is set to 0.03% by mass or less. The Al content is desirably 0.025% by mass or less, and more desirably 0.020% by mass or less.

(14) O: 0.020% by mass or less In order to reduce the cleanliness of the steel and deteriorate the corrosion resistance when the O content is excessive, the content is restricted to 0.020% by mass or less. The O content is desirably 0.015% by mass or less, and more desirably 0.010% by mass or less.

Hereinafter, elements that can be further added to the high nitrogen austenitic stainless steel of the present invention will be described.
(15) W: 0.01% by mass or more and 1.0% by mass or less W contributes to improvement of corrosion resistance and contributes to improvement of strength as a solid solution strengthening element. If the amount added is less than 0.01% by mass, the effect is poor, and if it exceeds 1.0% by mass, as in the case of Mo, the toughness deteriorates due to the formation of an embrittled phase, which is also harmful during hot working. Invite. In addition, the undissolved Cr nitride during the solution treatment is increased and the corrosion resistance is remarkably lowered. The W content is desirably 0.05% by mass or more and 0.9% by mass or less, and more desirably 0.1% by mass or more and 0.8% by mass or less.

(16) Co: 0.01% by mass or more and 5.0% by mass or less Co contributes to improvement of corrosion resistance and strength. If the amount added is less than 0.01% by mass, the effect is poor, and if it exceeds 5.0% by mass, the cost increases, and the insoluble Cr nitride during solution treatment increases and the corrosion resistance decreases significantly. Invite. The Co content is desirably 0.05% by mass or more and 4.5% by mass or less, and more desirably 0.1% by mass or more and 4.0% by mass or less.
From the viewpoint of improving strength and corrosion resistance, W and Co can be added in the above range.

(17) Ti: 0.01% by mass to 0.5% by mass (18) Nb: 0.01% by mass to 0.5% by mass (19) V: 0.01% by mass to 1.0% by mass The following (20) Ta: 0.01% by mass or more and 0.5% by mass or less Ti, Nb, V and Ta all combine with C and N to precipitate carbide or carbonitride and contribute to the improvement of strength. At the same time, the pinning effect of the precipitates suppresses the growth of austenite crystal grains and contributes to the improvement of strength and toughness due to the refinement of crystal grains. When the addition amount is less than 0.01% by mass, the effect is poor, and when the addition exceeds the above upper limit value, harmful oxides or nitrides are formed in the steel, the corrosion resistance is remarkably lowered, and an effective solidity is added. The amount of dissolved N is reduced, and the strength tends to decrease. The Ti content is desirably 0.02% by mass or more and 0.4% by mass or less, and more desirably 0.03% by mass or more and 0.3% by mass or less. The Nb content is desirably 0.02 mass% or more and 0.4 mass% or less, and more desirably 0.03 mass% or more and 0.3 mass% or less. The V content is desirably 0.02% by mass or more and 0.9% by mass or less, and more desirably 0.03% by mass or more and 0.8% by mass or less. The Ta content is desirably 0.02 mass% or more and 0.4 mass% or less, and more desirably 0.03 mass% or more and 0.3 mass% or less.
Any one of Ti, Nb, V and Ta can be added, or two or more of them can be added in combination.

(21) B: 0.001% by mass or more and 0.01% by mass or less;
B is an element effective for improving the strength and hot workability. If it is less than 0.001% by mass, the effect is poor, and if it exceeds 0.01% by mass, the hot workability is adversely affected and the corrosion resistance is also deteriorated. The B content is desirably 0.001% by mass or more and 0.008% by mass or less, and more desirably 0.001% by mass or more and 0.005% by mass or less.

(22) Zr: 0.01 mass% or more and 0.50 mass% or less Zr is an additive element effective for strength improvement. If it is less than 0.01% by mass, the effect is poor, and if it exceeds 0.50% by mass, the toughness deteriorates. The Zr content is desirably 0.03% by mass or more and 0.40% by mass or less, and more desirably 0.05% by mass or more and 0.30% by mass or less.

(23) Ca: 0.001% by mass to 0.01% by mass (24) Mg: 0.001% by mass to 0.01% by mass;
Ca and Mg are both additive elements effective for improving hot workability. Excessive addition deteriorates corrosion resistance, toughness, and hot workability. It is also effective from the viewpoint of improving machinability. In any case, if the amount is less than 0.001% by mass, the effect is poor, and if it exceeds 0.01% by mass, hot workability is adversely affected. The contents of Ca and Mg are desirably 0.001% by mass or more and 0.008% by mass or less, and more desirably 0.001% by mass or more and 0.005% by mass or less. Good.
B, Zr, Ca and Mg can be added alone or in combination of two or more thereof.

(25) Te: 0.005 mass% or more and 0.05 mass% or less (26) Se: 0.01 mass% or more and 0.20 mass% or less;
Te and Se are both additive elements effective for improving machinability. In any case, the effect is poor below the lower limit, and addition exceeding the upper limit is not preferable because corrosion resistance, toughness, and hot workability deteriorate. The Te content is desirably 0.01% by mass or more and 0.04% by mass or less. The Se content is desirably 0.02% by mass or more and 0.18% by mass or less, and more desirably 0.05% by mass or more and 0.15% by mass or less.

  The high nitrogen austenitic stainless steel of the present invention is preferably subjected to a solution treatment (for example, 0.1 hours to 2 hours) at 1100 ° C. or more and 1250 ° C. For example, by hot forging or rolling the steel of the present invention after melting so as to have the above composition, and further subjecting it to a solution treatment in the above temperature range, the precipitated Cr nitride can be re-dissolved. The structure can be made uniform and the corrosion resistance can be remarkably improved. According to the study of the present inventor, the Cr nitride has a diameter of 2 μm or more especially in the diameter (in this specification, the diameter of a circle having the same area as the nitride grains (hereinafter referred to as a circle-converted diameter)). If it remains, the effect on the corrosion resistance is increased. In order to ensure good corrosion resistance, it is naturally desirable that Cr-based nitrides having a diameter of 2 μm or more are not observed in the cross-sectional structure of steel. In this case, in any composition steel within the scope of the present invention, if the solution treatment temperature is within the range of 1100 ° C. to 1250 ° C., the Cr-based nitride having a diameter of 2 μm or more cannot necessarily be eliminated. However, as will be shown later in Examples, unless the optimum solution treatment temperature is selected within the above temperature range according to the steel composition, harmful Cr-based nitrides having a diameter of 2 μm or more cannot be sufficiently reduced. It is.

  And the steel of this invention can implement | achieve the high intensity | strength of 1000 Mpa or more by tensile strength by performing the said solution treatment to such an extent that Cr type nitride of diameter 2 micrometers or more is not observed.

  The high nitrogen austenitic stainless steel of the present invention can be made into a wire or plate. In this case, high strength can be achieved more remarkably by performing at least the final surface reduction of the wire or plate material by cold working such as cold drawing or cold rolling. Thereby, as shown in FIG. 1, in the case of the wire 100, when the structure is observed in the axial orthogonal cross section, and as shown in FIG. 2, in the case of the plate 150, in the cross section orthogonal to the rolling drawing direction. When observing the structure, no Cr-based nitride having a diameter of 2 μm or more is observed, and a wire or plate having an austenite matrix phase average crystal grain size (depending on the circle equivalent diameter) of 100 μm or less can be obtained. . By making the average crystal grain size of the austenite matrix phase into a fine structure, it is possible to obtain a wire material or plate material having very high strength and high corrosion resistance. The specific strength level can be 1500 MPa or more or 2000 MPa or more (the upper limit is not limited, but the strength can be improved up to, for example, 2500 MPa).

  The finally obtained crystal grain size of the wire or plate can be adjusted by the processing rate of cold working performed before the solution heat treatment (reduction ratio in the case of wire, reduction in the case of plate). When the average crystal grain size is 100 μm or more, the effect of improving the strength is not remarkable, and considering that recrystallization proceeds to some extent by the solution treatment in the above temperature range, the average crystal grain size is set to 2 μm or less in the process. Have difficulty. The refinement of the structure may be more prominent when one or more of Ti, Nb, V, and Ta, which are effective in suppressing crystal grain growth, are added in the aforementioned range.

  As described above, according to the high nitrogen austenitic stainless steel of the present invention, in a solution treatment state with almost no Ni, for example, the same level of corrosion resistance as SUS836L, which is a super austenitic stainless steel, and a duplex stainless steel Higher strength than some SUS329J4L can be achieved. Moreover, when it shape | molds to a wire and a board | plate material by the cold working after solution treatment, the high intensity | strength of 1500 Mpa or more (further 2000 Mpa or more) is realizable, for example.

  The high nitrogen austenitic stainless steel of the present invention can be processed into various shapes such as wire rod, bar steel, strip steel, plate material, pipe, forged product, die steel, etc., and is specifically suitable for the following uses. .

  For example, applications that should be considered for contact with living bodies include necklaces, earrings, rings and other decorative items that directly touch the human body, watch back covers, watch parts such as watch bands, eyeglass parts such as eyeglass frames, and door handles. Metal parts for furniture such as furniture and interior decoration, tableware and cooking utensils such as spoons, forks, ladle, metal parts for home appliances, dental materials such as interdental brushes, artificial roots or orthodontic wires, plates, bolts, nuts Medical devices such as springs, screws, wires, electrodes, artificial implants such as artificial bones and artificial joints, injection needles, knives, scalpels, scissors, forceps and surgical drills are suitable.

  It can also be applied to ordinary high-strength and high-corrosion resistant materials, such as bolts, nuts, cylinder liners, shafts, hubs, connectors, bearings, races, rails, gears, pins, screws, rolls, turbine blades, dies, dies, Drills, valves, valve seats, blades, nozzles, gaskets, rings, springs, beach environment members, industrial furnace members, chemical plant members, oil drilling members, oil refining plant members, waste incinerator members, steam turbine members, gas turbines Members, nuclear reactor members (for example, secondary cooling water piping members for pressurized water reactors), aircraft members, structural members for construction and civil engineering (for example, bridge members such as piers and fishing bridge members, high-voltage power poles and towers) Etc.), members for design and the like can be exemplified as suitable applications.

  Furthermore, as high-strength and high-corrosion-resistant materials that require non-magnetism, wires, meshes, biological implant electrodes for printed circuit board manufacturing parts such as springs, shafts, bearings, races, pins, dies, rails for precision electronic components, It is also effective for MRI parts, chemical manufacturing parts, hanger members, linear motor car members, semiconductor manufacturing equipment parts, tweezers, bearings, scissors, blades and the like.

Steels having the compositions shown in Tables 1 and 2 were melted in a pressurized atmosphere where the nitrogen partial pressure during melting was 50 atm or less by a high-frequency induction furnace capable of pressurizing in an atmosphere, and cast into a 50 kg steel ingot. A test piece was cut out from the bottom of the steel ingot, and the presence or absence of a nitrogen blowhole was visually confirmed. Subsequently, the steel ingot was homogeneously heated and then formed into a round bar having a diameter of 24 mm by hot forging. Thereafter, the round bar was subjected to a solution treatment in which it was kept at various temperatures of 1100 to 1300 ° C. for 1 hour and then cooled with water, and then the cross-sectional structure was observed with a scientific microscope (400 times magnification), and the diameter in terms of a circle Then, it was confirmed whether or not Cr-based nitride having a diameter of 2 μm or more was present, and the lowest temperature at which the presence of the Cr-based nitride was not recognized was determined as the solution treatment temperature. And the test piece was extract | collected from the steel processed at the determined solution treatment temperature, and the following measurements were performed (Comparative Examples 12-14 correspond to SUS836L, SUS329J4L, and SUS316). .
(1) Average crystal grain size Arbitrary 20 fields on the cross-sectional structure were observed with an optical microscope (100 times), and the average crystal grain size was measured according to JIS: G0551.
(2) Tensile strength Measured by a method based on JIS: Z2241.
(3) Pitting potential Measured by a method based on JIS: G0577.

  In Examples 5, 6, and 13, after the 50 kg steel ingot was homogenized and heated, it was subjected to solution treatment under the above-determined conditions after forming a φ12.5 wire by hot forging and hot rolling. Subsequently, cold drawing with a reduction in area of 50% and 70% was performed to obtain wire rods with a diameter of φ8.8 mm and φ6.8 mm. These wires were also measured for tensile strength and average crystal grain size by the same method as described above. Similarly, for Examples 5, 6, and 13, after homogenizing and heating a 50 kg steel ingot, a hot-forging and hot rolling to form a plate with a thickness of 5 mm, and then subjecting it to a solution treatment under the conditions determined above. Subsequently, cold rolling with a reduction ratio of 50% and 70% was performed to obtain a plate material having a thickness of 2.5 mm and a thickness of 1.5 mm. These plate materials were also measured for tensile strength and average crystal grain size by the same method as described above. The above results are shown in Tables 2 and 3.

  According to the results of Table 3, the steels of Examples 1 to 13 are extremely good in both the tensile strength after the solution heat treatment and the corrosion resistance indicated by the pitting potential, and SUS836L shown in Comparative Examples 12-14. It can be seen that a higher level of strength and corrosion resistance is realized than the well known austenitic stainless steels of SUS329J4L and SUS316. Moreover, according to the result of Table 4, it turns out that the ultra high strength of 2000 Mpa or more is realized in the steel of the present invention which is made into a wire or plate by cold working.

The figure which shows the definition of the crystal grain diameter of a wire. The figure which shows the definition of the crystal grain diameter of a board | plate material.

Explanation of symbols

100 Wire 150 Plate

Claims (10)

Cr: 24.0 mass% or more and 35.0 mass% or less;
Mo: 0.05 mass% or more and 8.0 mass% or less;
Mn: 0.2% by mass or more and 10.0% by mass or less;
Cu: 0.01% by mass or more and 4.0% by mass or less;
N: 0.8% by mass or more and 1.5% by mass or less
C content is 0.20 mass% or less, Si content is 2.0 mass% or less, P content is 0.03 mass% or less, S content is 0.05 mass% or less, Ni The content is 0.5 mass% or less, the Al content is 0.03 mass% or less, the O content is 0.020 mass% or less , the balance is Fe and inevitable impurities ,
When the Cr content is WCr (mass%), the Mo content is WMo (mass%), the N content is WN (mass%), and the Mn content is WMn (mass%),
η≡ (WCr + 3.3WMo + 16WN) / WMn
A high nitrogen austenitic stainless steel, wherein the content of Cr, Mo, N and Mn is adjusted so that the composition parameter η represented by W: 0.01% by mass or more and 1.0% by mass or less; and Co: 0.01% by mass or more and 5.0% by mass or less;
The high nitrogen austenitic stainless steel according to claim 1, which contains one or two of the following. Ti: 0.01% by mass or more and 0.5% by mass or less;
Nb: 0.01% by mass or more and 0.5% by mass or less;
V: 0.01% by mass or more and 1.0% by mass or less; and Ta: 0.01% by mass or more and 0.5% by mass or less;
The high nitrogen austenitic stainless steel according to claim 1 or 2, containing one or more of the following. B: 0.001 mass% or more and 0.01 mass% or less;
Zr: 0.01% by mass or more and 0.50% by mass or less;
Ca: 0.001% by mass or more and 0.01% by mass or less; and Mg: 0.001% by mass or more and 0.01% by mass or less;
The high nitrogen austenitic stainless steel according to any one of claims 1 to 3, comprising one or more of the following. Te: 0.005 mass% or more and 0.05 mass% or less; and Se: 0.01 mass% or more and 0.20 mass% or less;
The high nitrogen austenitic stainless steel according to any one of claims 1 to 4, comprising one or two of the following. 6. The Cr-based nitride having a diameter of 2 μm or more is not observed when the cross-sectional structure is observed after the solution treatment at 1100 ° C. or more and 1250 ° C. 6. High nitrogen austenitic stainless steel. The high nitrogen austenitic stainless steel according to claim 6, wherein the tensile strength after the solution treatment is 1000 MPa or more. When a wire is formed by cold working and the structure is observed in a cross section orthogonal to the axis, Cr-based nitride having a diameter of 2 μm or more is not observed, and the average crystal grain size of the austenite matrix phase is 100 μm or less. The high nitrogen austenitic stainless steel according to any one of claims 1 to 6. When a microstructure is observed in a cross-section that is made into a plate material by cold working and is orthogonal to the work drawing direction of the plate material, no Cr-based nitride having a diameter of 2 μm or more is observed, and the average crystal grain of the austenite matrix phase The high nitrogen austenitic stainless steel according to any one of claims 1 to 6, having a diameter of 100 µm or less. The high nitrogen austenitic stainless steel according to claim 8 or 9, wherein the tensile strength is 1500 MPa or more.

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