JPS605669B2 - Austenitic stainless steel with excellent cold formability and aging cracking resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to austenitic stainless steel that has excellent cold formability and resistance to aging cracking,
It is a low Ni, high Mn austenitic stainless steel that has excellent cold formability in stretch forming, stretch flange forming, bending, etc., as well as season cracking resistance. We propose an inexpensive stainless steel that has good formability and has better deep drawability and resistance to premature cracking than SUS304.

SUS430 is the conventional stainless steel for lining forming.
, SUS301, SUS304, etc. are known as typical steel types.

SUS430 does not contain expensive Ni, so it is inexpensive, but it has a ferrite structure, so it has poor moldability.
Not suitable for stretch forming or deep drawing. Therefore, conventional stainless steels for cold forming include SUS301 and S
US304 is used. However, since the austenite of these stainless steels is relatively unstable, when performing cold forming processing, that is, deep drawing, stretch forming, stretch flanging, and bending, the chemical composition of these stainless steels makes them ``good for deep drawing, but not suitable for deep drawing.'' However, there have been problems with stretch forming, such as thinness, and on the other hand, materials suitable for deep drawing may crack over time.The purpose of the present invention is to improve stretch formability, Flange formability is SUS3
In addition to exhibiting properties equivalent to or better than SUS304 in terms of deep drawing properties and aging cracking resistance, it is also more economical and cheaper than conventional SUS301 and SUS304, with low Ni and high Mn. The purpose is to obtain austenitic stainless steel.

The present invention provides C: 0.001 to 0.15 wt. %, Si;
1. Super inkstone ~ 2.5wt. %, Mn: 5-14wt. %,
Ni: 1 to 4 wt. %, Cr: 14.5-18. ○Wt
．． %, Cu: 0.1-3-5M-%, N: o. 01~0
．． fence t. %, the balance is an austenitic stainless steel consisting of Fe and unavoidable impurities, or the above austenitic stainless steel, and further Mo: 0.1 to 0.5
M. % of austenitic stainless steel, or alternatively, the above austenitic stainless steel is added with Mo.
:0.1~0.5wt. %, as well as Ti, Nb
At least one element selected from Zr and Zr is added instead of Mo or together with Mo, and the total amount is 0.01 to 0.1 wt. % austenitic stainless steel, and the relationship of the composition of each element is as follows;
)147. State-0.3 (Cr-20) 2234.7...
...{1) Equation 2 is 11.8 Mn 3.6 (Ni 1 Cu) + 47. is -0.3(Cr11.9yu-20)2
234.7... It is an austenitic stainless steel for cold forming that has been adjusted to satisfy the {2} formula.

Next, the reason for limiting the chemical composition of the steel of the present invention will be explained.

C has the effect of stabilizing the austenite structure and suppressing deformation-induced martensite, 8-ferrite, etc.

Although it is possible to reduce the C content to less than 0.001 M% in the steelmaking process, from the point of view of industrial production,
Since it cannot be said that decarbonization is economical, the lower limit content is set to 0.00.
It was set to 1 wt%. Furthermore, if the C content exceeds 0.15M%, the corrosion resistance of stainless steel will deteriorate, the strength will increase, and the cold formability will deteriorate;
The range was 1 to 0.15 wt%. Si is an element that is effective in meeting the demands of both suppressing deformation-induced martensite, which is highly susceptible to period cracking, and improving corrosion resistance and ductility. In order to improve the performance, it is necessary to have a content of at least more than 1.0%, and this amount is also a preferable value for economical refining in the steelmaking process, and it is necessary to include more in order to obtain good deep drawability. It is preferable.

However, if the amount exceeds 2.5 wt%, 6 ferrite is generated, so Si is added to 1.5 wt%. Misaki doctor ~ 2.5wt
%. Ni is an element that stabilizes the austenite structure, suppresses the formation of deformation-induced martensite and 6-ferrite, and also contributes to improving corrosion resistance.

Therefore, it is desirable to keep the content as low as possible, but if it is less than IM%, it will be difficult to form an austenitic structure due to the balance with other elements such as Mn and 〇.
%. On the other hand, if the Ni content exceeds 4M%, the price of the alloy of the present invention will only increase, and the properties of the alloy of the present invention will not necessarily improve so much.
%. Like Ni, Mn is an element that stabilizes the austenite structure, suppresses the formation of deformed martensite, and is a low-cost element that does not impair corrosion resistance or weldability.

This Mn content must be determined in balance with the Ni content, but if it is less than 5M%, an austenitic structure with excellent formability cannot be maintained, so the lower limit content is set to 5M%.
%. Since the Mn content has a lower yield in the steel manufacturing process than Ni, a large amount of Mn must be used. Therefore, if the Mn content exceeds 14 wt%, the price of the alloy of the present invention approaches the price of SUS304, so the Mn content was ultimately set at 5 to 14 M%. Cr is the most effective element for improving corrosion resistance, but since the corrosion resistance of stainless steel cannot be maintained at 14.5 M%, the lower limit content is set to 14.5 wt%.

Ni, which is an austenite-forming element necessary to maintain an austenite structure when C exceeds 1st class t%,
Since the content of Mn etc. increases and the price of the alloy of the present invention increases, the Cr content is set at 14.5 to 18. It was expressed as skin t%. C
U is effective in stabilizing the austenite structure and suppressing deformation induced martensite, and is also necessary to improve ductility.

If the content is less than 0.1 wt%, the above effect will not be exhibited, so the lower limit content was set to 0.1 M%.

On the other hand, if the Cu content exceeds 3.5 M%, hot workability will deteriorate, so the Cu content was set to 0.1 to 3.5 wt%.
N is mixed in during the steelmaking process, but in actual operation it is 0.01
Since it is difficult to reduce the content to less than wt%, the lower limit content is set to 0.
．． 01 wt%.

However, like carbon, N is an element that is effective in stabilizing the austenite structure and suppressing deformation-induced martensite and 6-ferrite, and is also effective in improving corrosion resistance. The more the better, but 0. If N content exceeds fine t%, pro-holes will occur in the steel ingot and hot workability will deteriorate, so the N content will eventually be reduced to 0.0%.
1~0. It was expressed as powder t%. ．． Mo is an effective element for corrosion resistance and aging cracking resistance, but is an expensive metal. 0.1w
If it is less than t%, no significant effect on improving corrosion resistance will be exhibited, so the lower limit content was set to 0.1wt%.

If the content exceeds 0.5 wt%, the stainless steel will be expensive compared to the corrosion resistance of the alloy of the present invention, so the content should be 0.5 wt%.
It was limited to 1 to 0.5 wt%.

The total amount of at least one element selected from Ti, Nb, AI, and Zr is 0.01w.
Addition of t% or more improves the surface properties of the alloy, that is, the appearance of stainless steel, and reduces the risk of surface defects such as surface roughness due to acid bead treatment after intermediate drawing in multi-stage drawing, and improves the alloy manufacturing process. However, you can obtain stainless steel that does not get rough due to pickling.

Since this effect is small if it is less than 0.01 wt%, the lower limit content is set to 0.01 wt%.

On the other hand, when added in excess of 0.1 wt%, Ti, N, Nb
, since Zr is a ferrite-forming element, the microstructural balance will be disrupted and hot workability will be significantly deteriorated, so Ti, N
The total of one or more selected from b, AI, and Zr is 0.
．． It was limited to 0.01-0.1%. Note that since the amounts of Ti, Nb, AI, and Zr added are small, the above {1 or '2
}It does not affect the formula, nor does it affect cold formability. The reasons for limiting each element have been described above, but in order to obtain an austenitic stainless steel that has excellent meltability, excellent inter-sleeve formability, and also excellent resistance to period cracking after deep drawing, Furthermore, within the range of the above-mentioned component composition, the proportions of the main components, basic components, and subcomponents other than Si must satisfy the following formula {1 or {2).

2 points 1.8Mn+3.6(Ni+Cu)+47. but-
0.3(Cr-20)2334.7......[1}Formula 211.8Mn+3.6(Ni+Cu)+47. State-0.
3 (Cr+1.8yu-20)2334.7...
...[Formula 2', in other words, in order to obtain excellent performance in general press forming, the amount of deformation-induced martensite (
Austenite stability calculated from alloy composition)
It is necessary to appropriately control the process to maintain a good level of resistance to aging cracking after deep drawing, while exhibiting excellent deep drawability, stretchability, and stretch flangeability.

Next, embodiments of the present invention will be described.

Table 1 shows the chemical composition and '
1 or '2} indicates the calculated value of the formula.

Among the comparative materials, AI to A5 have Si contents outside the range of the present invention alloy, and also do not satisfy the relationship of formula [1 or ■], and SUS301, SUS304-1 to
SUS304-3 is a commercially available stainless steel. Table 2 shows the mechanical properties, line-to-wall formability, and period cracking resistance of the alloy steel of the present invention and comparative materials. The Erichsen value of the alloy of the present invention is inferior to SUS301, but is equivalent to SUS304 and comparative materials AI to A4, and the pore expansion rate is superior to SUS301, and is equal to that of comparative materials AI to A4 or SUS304.
is equivalent to This Elichsen value is used to evaluate stretch formability, and the hole expansion rate is used to evaluate stretch flangeability. From the above, it can be seen that the stretch formability and stretch flangeability of the alloy of the present invention are almost the same as SUS304. The Eriksen test was performed according to the Eriksen test B method of JIS Z2247. A punched hole with a hole expansion rate of 100 was expanded using a 30o conical punch, and the hole depth D was measured when a crack occurred at the edge of the hole. (D-10)/
10}×loo. The critical drawing ratio of the alloy of the present invention is 2.18 or more, which is equivalent to SUS301 but superior to SUS304. None of the alloys of the present invention cause period cracking, but SUS301 and SUS3
All of the 04 comparative materials exhibited period cracking. As mentioned above, the present alloy has a critical drawing ratio of SUS3, which is an evaluation of deep drawability.
It is equivalent to 01, and has excellent characteristics that do not cause time lag. In addition, the limit drawing ratio was calculated from the results of deep drawing at a drawing speed of 32 ratios/min, with the punch raised 5 degrees, the punch shoulder radius 7 ribs, the blank spaced between 100 and 11 degrees, and 2 skins apart. be. The time cracking test is 100
A container made by deep drawing a Gaga blank at a drawing speed of 32 pieces/min was left in the atmosphere for one month, and the presence or absence of cracking was examined. Table 1 Chemical composition of the alloy of the present invention and comparative material Table 2 Mechanical properties, cold formability and resistance to cracking of the alloy of the present invention and comparative material From the above explanation, it is clear that
The alloy of the present invention has stretch formability equivalent to SUS304,
It has stretch flange formability, and on the other hand, it has much superior deep drawability and resistance to aging cracking compared to SUS304, and as a low-cost alloy, it has features not found in existing alloys.

Claims (1)

[Claims] 1C: 0.001 to 0.15wt. %, Si: 1.0
Super~2.5wt. %, Mn: 5-14wt. %, Cr: 14.5-18.0wt. %, Ni: 1 to 4 wt. %, Cu: 0.1-3.5wt. %, N: 0.01-0.3wt. %, the remainder consists of unavoidable impurities and Fe, and the relationship between these component compositions is as follows: 26C + 1.8Mn + 3.6 (
Ni+Cu)+47.2N-0.3(Cr-20)^2
An austenitic stainless steel having excellent cold formability and aging cracking resistance, which is adjusted to satisfy ≧34.7. 2C: 0.001-0.15wt. %, Si: 1.0
Super~2.5wt. %, Mn: 5-14wt. %, Cr: 14.5-18.0wt. %, Ni: 1 to 4 wt. %, Mo: 0.10-0.5wt. %, Cu: 0.1-3.5wt. %, N: 0.01-0.3wt. %, the remainder consists of unavoidable impurities and Fe, and the relationship between these component compositions is as follows: 26C + 1.8Mn + 3.6 (
Ni+Cu)+47.2N-0.3(Cr+1.5Mo
-20) An austenitic stainless steel having excellent cold formability and resistance to aging cracking, which is adjusted to satisfy ^2≧34.7. 3C: 0.001-0.15wt. %, Si: 1.0
Super~2.5wt. %, Mn: 5-14wt. %, Cr: 14.5-18.0wt. %, Ni: 1 to 4 wt. %, Cu: 0.1-3.5wt. %, N: 0.01-0.3wt. %, and at least one element selected from Ti, Nb, Zr, and Al.
t. %, with the remainder consisting of unavoidable impurities and Fe, and the relationship between these component compositions is expressed by the following formula: 26C
+1.8Mn+3.6(Ni+Cu)+47.2N-0
．． 3(Cr-20)^2 An austenitic stainless steel having excellent cold formability and period cracking resistance, which is adjusted to satisfy 34.7. 4C: 0.001-0.15wt. %, Si: 1.0
Super~2.5wt. %, Mn: 5-14wt. %, Cr: 14.5-18.0wt. %, Ni: 1 to 4 wt. %, Mo: 0.10-0.5wt. %, Cu: 0.1-3.5wt. %, N: 0.01-0.3wt. %, and at least one element selected from Ti, Nb, Zr, and Al as unavoidable impurities and Fe.
, and the relationship between the compositions of each component is expressed by the following formula; 2
6C+1.8Mn+3.6(Ni+Cu)+47.2N
-0.3(Cr+1.5Mo-20)^2≧34.7 An austenitic stainless steel having excellent cold formability and resistance to aging cracking.