US3910788A

US3910788A - Austenitic stainless steel

Info

Publication number: US3910788A
Application number: US461335A
Authority: US
Inventors: Tokio Fujioka; Kazuo Hoshino; Kenjiro Ito; Takashi Igawa
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1973-04-21
Filing date: 1974-04-16
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: JPS49130309A; JPS5129854B2; GB1419736A

Abstract

Austenitic stainless steel essentially consisting of 1.0-2.5 wt. percent Si, 1.5-5.0 wt. percent Mn, 1.0-4.0 wt. percent Cu, 6.09.0 wt. percent Ni, 15.0-19.0 wt. percent Cr, not more than 0.06 wt. percent C, nor more than 0.03 wt. percent N, and balance Fe and incidental impurities, in which the total content of C and N in the solid solution state is less than 0.04 wt. percent has excellent drawability and stretchability and is highly resistant to delayed cracking. Although the austenite phase of this steel is unstable to strain-induced martensitic transformation, the steel is highly resistant to delayed cracking. The said low content of C and N in the solid solution state is achieved by known decarbonization processes or by addition of a limited amount of Al and/or Ti to the melt.

Description

United States Patent Fujioka et al. 1 Oct. 7, 1975 15 1 AUSTENITIC STAINLESS STEEL 3.337.331 8/1967 Ljungberg 75/128 A x 1751 e Fuiioka; K2190 312231333 31133? Z11ZZ1".;111TJ.1-.......ji;.'.'i52/1535)? l Takashl lgawa, of 3,697,258 10/1972 Floreen 75/128 C i" Japan 3,795,507 3/1974 Allen 75/124 [73] Assignee: Nisshin Steel Co., Ltd., Tokyo.

Japa Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Arthur 1. Steiner 1221 Flled: 1974 Attorney, Agent. or Firm-Ladas. Parry, Von Gehr, [21] A L N 461,335 Goldsmith & Dcschamps 130 Foreign Application Priority Data 1 1 ABSTRACT Apr. 21, 1973 Japan 48-44656 Austenitic stainless steel essentially consisting of 1.0-2.5 wt. percent Si, 1.5-5.0 wt. percent Mn. [52] 1.1.8. Cl. 75/125; 75/124; 75/128 A; 1.0-4.0 wt. percent Cu, 6.0-9.0 wt. percent Ni.

75/128 C; 75/128 N; 75/128 T 15.0-19.0 wt. percent Cr, not more than 0.06 wt. per- 1 1 C C 38/02,C22C 38/06. cent Co not more than 0.03 wt. percent N. and bal- C22C 38/42 C22C 38/58 ance Fe and incidental impurities, in which the total [58] Field of Search 75/124, 125, 128 A, 128 C, content of C and N in the solid solution state is less 75/128 N, 128 T than 0.04 wt. percent has excellent drawability and stretchability and is highly resistant to delayed crack- [56] References Cited ing. Although the austenite phase of this steel is unsta- UNITED STATES PATENTS ble to strain-induced martensitic transformation, the 2 I50 901 3H939 Amess steel is highly resistant to delayed cracking. The said 3 5 10/1964 Lulawjm low content of C and N in the solid solution state is 3154412 0 19 Kasak achieved by known decarbonization processes or by 3,159,480 12/1964 Copson... addition of a limited amount of Al and/0r T1 to the 3,282,686 11/1966 Allen melt. 3,303,023 2/1967 Dulis et a1 75/128 6 Claims, 1 Drawing Figure AUSTENITIC STAINLESS STEEL BACKGROUND OF THE INVENTION with high elongation because of their high work hardening coefficient in addition to their excellent corrosion resistance properties, and therefore they are formed into desired shapes by deep drawing and are widely used in various technical fields.

As the steel species suitable for such cases, A151 301 0.15 percent C, l.00 percent Si, 2.00 percent Mn, 0.030 percent S, 0.045 percent P, 16-18 per cent Cr, 6-8 percent Ni), AISI 304 0.08 percent C, l .00 percent Si, 2.00 percent Mn, 0.030 percent S, 0.045 percent P, 18-20 percent Cr, 8-12 percent Ni), A151 305 0.12 percent C, l.00 percent Si, 2.00 percent Mn, 0.030 percent P, 0.045 percent S, 17-19 percent Cr, -13 percent Ni), etc. are known. (In this specification, all the percentages concerning steel composition are those by weight.)

From the view point of plastic deformation, AISI 301 is preferably used as the material for stretching, because when this steel is subjected to plastic deformation, strain-induced martensite is easily formed, which prevents local neckings and gives remarkable elongation to the material. However, if this steel undergoes drawing in which compression strain is given to the material and the material retains tension stress after drawing, delayed cracking occurs within a short period of time when the steel is simply allowed to stand in the at mosphere after drawing.

A151 304 is somewhat less sensitive to delayed cracking and the incubation time before occurrence of delayed cracking is longer. But when this steel is subjected to severe deep drawing, still delayed cracking often happens. Therefore, even A181 304 has to be annealed many times in the course of drawing forming in order to avoid the delayed cracking when it is shaped by severe drawing. Such annealing treatment not only adds to the manufacturing cost, but coarsens the crystal grains and thus deteriorates the surface of finished products or causes precipitation of chromium carbide which may locally impair corrosion resistance of finished products if the annealing conditions are not strictly controlled.

AISI 305 is more stable against strain-induced martenistic transformation and less sensitive to delayed cracking. However, A131 305 is inferior in stretchability and deep drawability because of its lower Work hardening coefficient. The lower work hardening coefficient is due to high Ni content of the steel, which means that the material is expensive, too.

Concerning the mechanism of occurrence of delayed cracking after drawing forming in these materials, F. W. Schaller et al. presented a theory (Sheet Metal Industries, Oct. 621 1972)). According to them, delayed cracking is caused by the strain-induced martensite which is more sensitive to occluded hydrogen, therefore the material in which its austenite phase is less stable against the strain-induced martensitic transformation is more liable to the delayed cracking. This theory well corresponds to sensitivities to delayed cracking of a series of materials including A151 301, 304. 305, etc.

More recently, austenitic stainless steels of this kind in which a portion of Ni is replaced by Cu are known. (US. Pat. No. 3,282,684 0.l5 percent C, 0.40-2.00 percent Mn, 0.15- 1.00 percent Si, 16-19 percent Cr, 5.5-8.0 percent Ni, 0.5-3.5 percent Cu, 0.04-0.10 percent N and balance Fe) and U.S. Pat. No. 3,282,686 0.l5 percent C, 0.5-2.00 percent Mn, 0.15-1.00 percent Si, 16-19 percent Cr, 6.6-7.9 percent Ni, 1.5-2.9 percent Cu, 0.03 percent N and balance Fe)) Cu is effective for inhibiting the strain-induced martensitic transformation as well as Ni.

We extensively and experimentally studied the mechanism of occurrence of delayed cracking and found that the delayed cracking does not occur when the total content of C and N that are present in the state of solid solution in the steel is less than 0.04 percent, even if the austenite phase thereof is very unstable against straininduced martensitic transformation and a large amount of strain-induced martensite is formed in the course of drawing forming, delayed cracking does not occur.

In the above-mentioned A181 301, 304 and 305, the C content is defined as less than 0. 15 percent, 0.08 percent and 0.12 percent respectively. But they usually contain 0.04 percent or more C and 0.015 percent or more N and the total of the two elements is 0.055 percent or more. In the steel of U.S. Pat. No. 3,282,684, 0.04-0.10 percent N is intentionally added.

That is, any attempt to improve resistance to delayed cracking of these steels by restricting the total content of C and N in the solid solution state to less than 0.04 percent had not been made prior to this invention of ours. It was thought that if the content ofC and N in the solid solution state were lowered, the Ni content should be increased to compensate for the decrease in the contents of C and N as the austenite-forming elements, which would result in rise in manufacturing cost and decrease in work hardening coefficient, since the fact that delayed cracking can be prevented by restricting the contents of C and N in the solid solution state was not known.

In this invention of ours, the decrease in work hardening coefficient caused by decrease in the contents of C and N in the solid solution state is compensated for by increase in the contents of Si, Mn and Cu, and thus an austenitic stainless steel which has excellent formability and is highly resistant to delayed cracking after deep drawing is provided at the price of the same level as that of A18] 304.

SUMMARY OF THE INVENTION According to this invention, stainless steel with excellent drawability and stretchability and high resistance to delayed cracking essentially consisting of 10-25 percent Si, l.55.0 percent Mn, 15-19 percent Cr, 10-40 percent Cu, 6.0-9.0 percent Ni, not more than 0.06 percent C, not more than 0.03 percent N and balance Fe with incidental impurities, in which the total content of C and N in the solid solution state is less than 0.04 percent is provided.

The austenitic stainless steel of this invention contains Si in an amount of 1.0-2.5 percent, preferably 10-20 percent and more preferably 1.2-1.8 percent; Mn in an amount of 1.5-5 .0 percent, preferably 15-30 percent, and more preferably 1.8-2.8 percent; Cu in an amount of 10-40 percent, preferably 1 .0-30 percent and more preferably l.5-2.5 percent; Ni in an amount of 6.0-9.0 percent, preferably 6.5-8.5 percent and more preferably 6.7-8 percent; and Cr in an amount of -19 percent, preferably 15.5-17.5 percent and more preferably 16-17 percent; and may contain Al and/or Ti in an amount of up to 0.5 percent, preferably up to 0.4 percent and more preferably up to 0.3 percent in order to fix C and N so that the total amount ofC and N in the solid solution state is less than 0.04 percent. In any case, the total amount ofC and N in the solid solution state must be less than 0.04 percent, and preferably less than 0.03 percent.

Si improves work hardening property of austenite phase itself, and the effect is proportional to the content. The austenitic stainless steel, in which the content of C and N in the solid solution state is restricted. is inferior in work hardening coefficient. Therefore, in this invention Si is an indispensable element that conpensates for the drop of the work hardening coefficient. Also Si improves resistance to pitting corrosion. At least 1.0 percent Si is required to accomplish this object. But Si in excess of 2.5 percent will cause formation of S-ferrite, which impairs hot workability or causes hot cracking. The Si content is preferably 1.0-2.0 percent, and more preferably 1.2-1.8 percent.

Mn has the effect of inhibiting strain-induced martensitic transformation of the austenite phase as well as Ni, but is different from Ni in that it strengthens the strain-induced rnartensite and enhances work hardening coefficient and improves stretchability and drawability of the material. However, the S-ferrite-inhibiting effect of Mn is not so strong as Ni. And a rather high percentage thereof is lost during steel making. So this element does not contribute so much to cost cutting as expected from the difference in prices of these elements. The reasonable content of Mn is within a range of 1.0-5.0 percent, preferably 1.5-3.0 percent and more preferably 1.8-2.8 percent.

Cu, as well as Ni, has the effect of inhibiting straininduced martensitic transformation of austenite phase and strengthens the strain-induced rnartensite, and improves work hardening coefficient of the material as the result. However, too much Cu impairs hot workability. The reasonable content of Cu is 1.0-4.0 percent, preferably 1.0-3.0 percent and more preferably 1.5-2.5 percent.

Ni, which is an expensive element, does not contribute so much to work hardening property of the austenite phase or strain-induced rnartensite per se and therefore it is desirable to use this element at a content as low as possible. The reasonable content, thereof, is 6.0-9.0 percent, preferably 6.5-8.5 percent and more preferably 6.7-8 percent.

Cr contributes to corrosion resistance in proportion to the content thereof. But at too high content, it causes formation of S-ferrite and impairs hot workability. Thus the Cr content is limited to 15-19 percent, the preferable content range being 15.5-17.5 percent and more preferably range is 16-17 percent.

The total content of C and N in the solid solution state must be less than 0.04 percent. This can be achieved by reducing the amounts of C and N by the so-called Vacuum Oxygen Decarbonization Process or Argon Oxygen Decarbonization Process. In the ordinary electric steel making process the total amount of C and N cannot be reduced to less than 0.04 percent, so up to 0.5 percent of Al and/or Ti is added to the melt so as to reduce C and N in the solid solution state to less than 0.04 percent.

A1 fixes N as MN and is effective to reduce N in the solid solution state when the N content is high. But high 4 content thereof contributes to formation of S-ferrite. Ti fixes C and N as Ti(C, N) and is effective to reduce C and N in the solid solution state. Therefore the content of Al and/or Ti is limited to less than 0.5 percent and preferably 0.3 percent.

The total amount of C (both of the fixed and that in the solid solution state) should be 0.06 percent or less. And the total amount of N (both of the fixed and that in the solid solution state) should be 0.03 percent or less. In order to reduce the total amount of C and N in the solid solution state to less than 0.04 percent, the amounts of the total C and the total N should preferably be not more than 0.06 percent and 0.03 percent respectively. As to the other impurities, the S content should be 0.03 percent or less, and the P content should be 0.04 percent or less.

The austenitic stainless steel of this invention can be made by the Vacuum Oxygen Decarbonization Process or Argon Oxygen Decarbonization Process or by the ordinary electric steel making with the aid of Al and/or Ti as mentioned above. And there is no necessity of explaining the manufacturing process for the steel in detail here.

The austenitic stainless steel of this invention is characterized in that it is provided with excellent drawability and stretchability and is highly resistant to delayed cracking.

BRIEF DESCRIPTION OF THE DRAWING The attached drawing shows drawing test specimen of the steels of this invention and of the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The invention is illustrated by way of examples and comparative examples.

Nine (9) sample heats within the scope of this invention, one sample heat each of the steels of AISI 301, AISI 304, A151 305, U.S. Pat. No. 3,282,684 and U.S. Pat. No. 3,282,686 were prepared by melting in a high frequency electric furnace of 30 kg capacity. The ingot of each heat was made into 0.6 mm X mm X 100 mm plates by successively subjecting to hot forging, solution treatment 1,100C, 1 hr, W.Q. machining, cold rolling, annealing I050C, 10 min, A.C.) and cold rolling. The plates were finally annealed at l ,O50C for 5 minutes and air-cooled. All the specimen were prepared under the same conditions.

The chemical analysis of these samples are summarized in Table I. In this table the steel of U.S. Pat. No. 3,282,684 is designated as Cr-Ni-Cu-N and the steel of U.S. Pat. No. 3,282,686 is designated as Cr-Ni-Cu steel.

In the Cr-Ni-Cu-N steel and the Cr-Ni-Cu steel, the Si present is the residual of the Si that was used for deoxidation and does not function at all to improve the steel properties. In contrast, in the steels of this invention, Si is intentionally added for the enhancement of work hardening coefficient and it is contained in an amount of 1.0 percent or more.

In the Cr-Ni-Cu-N steel, N is intentionally added in an amount of 0.04-0.10 percent in order to stabilize its austenite phase against the strain-induced martensitic transformation. In the Cr-Ni-Cu steel, the N content is defined as not more than 0.03 percent and the C content is defmed as not more than 0.15 percent. But in the specification proper, it is explained that the C content should be at least 0.04 percent and the preferred range is 0.05-0.08 percent. And none of the examples is the total content of C and N less than 0.08 percent.

Among the steels of this invention, the total content ofC and N of 48A02, 48AO3 and 48A09 is in excess of 6 delayed cracking, there is significant difference between them. That is to say, the austenite phase of AlSl 305 is markedly stable against the strain-induced martensitic transformation as duly anticipated from the ex- 0.04 percent. But these numerical values include the 5 perimental results of Schaller et al. On the other hand, amounts of the fixed C and N. That is. these samples the austenite phase of the steels of this invention is very were dissolved in an iodine-alcohol solution and the sounstable and martensitic transformation takes place lution was filtered with a filter paper having the pore more easily than in AlSl 30l when suffering plastic dediameter of 0.2 micron. The collected residue. which is formation. But, none the less, its delayed cracking sus- Ti(C, N) and/or AlN, was analyzed. and in 48AO2 and ceptibility is remarkably low.

Table 2 Properties Hard- 0.2 7( Tensile Elon- Martensite Erichsen Conical Limiting ness Yield strength gation percentage (mm) cup drawing Hv( 10) (kg/mm) (kg/mm 1%) value ratio Sample 1mm) Steels of 411M01 125 23 60 61 35 12.6 27.2 23.10 this 48M07 121 23 60 60 13 12.5 27.4 invention 48M) 130 24 61 58 30 13.0 27.0 411M114 118 60 55 33 12.5 27.4 48M05 122 20 58 59 24 12.9 27.3 48M06 113 19 56 59 [8 12.4 27.0 48A02 I08 17 55 60 42 13.1 261.8 48A03 115 20 59 58 12.11 27.2 48A09 113 19 60 61 211 13.4 26.9 Comparative AIS] 301 169 2s 30 61 32 14.5 27.0 2.03 samples A151 304 165 28 68 53 s 12.0 27.6 2.61 AISI 305 140 26 62 57 0 11.6 27.3 23.10 Cr-NiCu-N 165 31 67 5s 18 13.0 20.8 2.41 Cr-Ni-Cu l53 3t) 68 56 2| l2.8 27.2 2.32

48A03 respectively 0.022 percent and 0.021 percent N Although AlSl 305 is parallel with the steels of this were found as AlN and there was no carbon. Therefore invention in delayed cracking susceptibility, the former N in the solid solution state was 0.0[0 percent and i is inferior to the latter in stretchability and drawability. 0.009 percent respectively, and all the carbon existed AlSl 301, Cr-Ni-Cu-N steels and Cr-Ni-Cu steels are in the solid solution state in both 48A02. and 48A03. ln equal to the steels of this invention in stretchability and 48A09 the content of N in the solid solution state was drawability, but are highly susceptible to delayed trace and the content of C in the solid solution state is cracking. was 0.017 percent.

Table 1 Sample Element C Si Mn P 5 Cr Ni N Cu Ti Al 516615 or 41-1M01 0.007 1.60 3.00 0.012 0.009 16.73 6.99 0.030 1.99 "13136 0.016 this 48M07 0.012 1.71 1.53 0.008 0.01 1 l8.l2 8.90 0.025 1.921 ULICE 0.010 invention 48Ml0 0.014 1.20 2.59 0.01 1 0.01 1 17.25 7.53 0.027 2.14 trace 0.007 48MU4 0.010 1.53 3.15 0.011 0.010 16.23 15.07 0.0211 1.26 0.27 0.021 48M05 0.010 1.62 3.17 0.008 0.008 16.19 11.07 0.026 2.97 0.24 0.010 48M06 0.010 2.40 1.55 0.009 0.008 16.01 8.6] 0.0211 2.00 0.29 0.010 48A02 0.016 1.53 1.89 0.010 0.010 16.74 11.23 0.032 1.31 mm 0.43 48A03 0.020 1.14 2.32 0.009 0.010 16.47 7.73 0.030 2.11 U'IJCB 0.37 4sA09 0.029 1.62 2.1 1 0.01 1 0.008 16.96 11.25 0.0211 1.78 0.25 0.30 Comparative AlSl 301 0.1 1 0.57 0.99 0.026 0.015 17.20 7.58 0.012 0.04 tracc 0.01 1 samples AISI 304 0.07 0.55 1.08 0.021 0.018 19.06 9.25 0015 0.03 trace 0.01s AISI 305 0.08 0.58 0.98 0.024 0.0l6 18.91 11.46 0.025 0.05 (face 0.020 Cr-Ni-Cu-N 0.06 0.46 1.43 0.020 0.015 17.43 6.59 0.000 2.05 [face 0.007 Cr-Ni-Cu 0.06 0.23 1.20 0.022 0.016 17.30 7.04 0.024 1.94 mm. 0.01 1

'"us. Pill. No. 3211 6114 us. Pat. N0. 3.211 636 In Table 2, mechanical properties, martensite per- Table 3 to drawin and stretch- .Cemdge and properties relating g step of drawing 1.91 2nd 3rd 41h mg of the Samples of Table I are Shawl-L drawing drawing drawing drawing Martensite Percentage means the amount of mar Zi ra 411mm 315 mm 27.5 mm mm tensite that is determined by a samplevibrating magne- 0 an tometer with samples to which 40 percent elongation 4 mm 1. 2.03 2.33 2.61 b t f 70 mm 1.75 2.25 2.55 286 has een given at a strain ra e 0 m n 73 mm L83 232 2% Limiting Drawing Ration means a drawing ratio over 60 76 mm 1.90 2.41 2.76 3.10 which the delayed cracking occurs when sample sheets are drawn stepwise by means of the tools the dimension of which are shown in Table 3. Table 2 shows that the The differences in delayed cracking susceptibility besteels of this invention and AlSl 305 do not suffer detween these steels are apparently demonstrated in the 65 layed cracking even if they undergo the most severe drawing test.

Although the steel of this invention and the steel of AlSl 305 are similar in that they are very resistant to attached drawing. The specimens shown in the drawing (photograph) are of the steel of this invention (48M0l AlSl 301, Cr-Ni-Cu-N steel and Cr'Ni-Cu steel from the left to the right respectively. The sample sheet of 48M01 did not suffer delayed cracking even after having undergone drawing of drawing ratio 3.10. The sample sheet of A181 30] suffered remarkable delayed cracking after having undergone drawing of drawing ration 2.03. The sample sheet of Cr-Ni-Cu-N steel suffered slight delayed cracking after having undergone drawing of drawing ratio 2.41. The steel sheet of Cr-Ni-Cu steel suffered delayed cracking after having undergone drawing of drawing ratio 2.32.

As has been explained in detail in the above, this invention provides a novel austenitic stainless steel which is provided with excellent drawability and stretchability and remarkably resistant to delayed cracking, by restricting the total content of C and N in solid solution state to less than 0.04 percent and adding rather high amounts of Si and Mn. The steel of this invention can be supplied at the price of the same level as that of A181 304.

What we claim is:

l. Austenitic stainless steel that is provided with excellent drawability and stretchability and is highly resistant to delayed cracking essentially consisting of 1.0-2.5 percent Si, 1.5-5.0 percent Mn, 1.0-4.0 percent Cu, 6.0-9.0 percent Ni, 15.0-19.0 percent Cr, -0.5 percent of at least one of Al and Ti, not more than 0.06 percent C, not more than 0.03 percent N and balance Fe and incidental impurities, in which the total 8 amount ol'(" 11ml l\ in the solid solution state is less than 0.04 percent.

2. The austenitic stainless steel as set forth in claim 1, which essentially consists of 1.0-2.0 percent Si. 1.5-3.0 percent Mn, 1.0-3.0 percent Cu, 6.5-8.5 percent Ni, 15.5-17.5 percent Cr, 0-0.4 percent of at least one of Al and Ti, not more than 0.06 percent C, not more than 0.03 percent N and balance Fe and incidental impuri ties, in which the total amount of C and N in the solid solution state is less than 0.03 percent.

3. The austenitic stainless steel as set forth in claim 1, which essentially consists of 1.2-1.8 percent Si, 1.8-2.8 percent Mn, 1.5-2.5 percent Cu, 6.7-8 percent Ni, 16-17 percent Cr, 0-0.3 percent of at least one of Al and Ti, not more than 0.06 percent C, not more than 0.03 percent N in the solid solution state is less than 0.03 percent.

4. The austenitic stainless steel as set forth in claim 1, wherein at least one of Al and Ti is contained in an amount of 0O.4 percent.

5. The austenitic stainless steel as set forth in claim 4, wherein at least one of Al and Ti is contained in an amount 00.3 percent.

6. The austenitic stainless steel as set forth in claim 2, wherein at least one of Al and Ti is contained in an amount 00.3 percent.

Claims

1. AUSTENITIC STAINLESS STEEL THAT IS PROVIDED WITH EXCELLENT DRAWABILITY AND STRETCHABILITY AND IS HIGHLY RESISTANT TO DELAYE CRACKING ESSENTIALLY CONSISTING OF 1.0-2.5 PERCENT SI, 1.5-5.0 PERCENT MN, 1.0-4.0 PERCENT CU, 6.0-9.0 PERCENT NI, 15.0-19.0 PERCENT CR, 0-0.5 PERCENT OF AT LAST ONE OF AL AND TI, NOT MORE THAN 0.06 PERCENT C, NOT MORE THAN 0.03 PERCENT N AND BALANCE FE INCIDENTAL IMPURITIES, IN WHICH THE TOTAL AMOUNT OF C AND N IN THE SOLID SOLUTION STATE IS LESS THAN 0.04 PERCENT.

2. The austenitic stainless steel as set forth in claim 1, which essentially consists of 1.0-2.0 percent Si, 1.5-3.0 percent Mn, 1.0-3.0 percent Cu, 6.5-8.5 percent Ni, 15.5-17.5 percent Cr, 0-0.4 percent of at least one of Al and Ti, not more than 0.06 percent C, not more than 0.03 percent N and balance Fe and incidental impurities, in which the total amount of C and N in the solid solution state is less than 0.03 percent.

4. The austenitic stainless steel as set forth in claim 1, wherein at least one of Al and Ti is contained in an amount of 0-0.4 percent.

5. The austenitic stainless steel as set forth in claim 4, wherein at least one of Al and Ti is contained in an amount 0-0.3 percent.

6. The austenitic stainless steel as set forth in claim 2, wherein at least one of Al and Ti is contained in an amount 0-0.3 percent.