RESISTANCE OF STAINLESS STEEL TO LIQUID ALUMINUM ATTACK

BACKGROUND

Certain structural steel components may be aluminized to provide additional benefits, e.g., corrosion resistance. In some cases, the base structural component may be a stainless steel, such as T316L stainless steel, that is directed to an aluminizing pot. Often, protective coatings such as refractory coatings are used with the structural components to prevent or reduce the attack on these structural components by the liquid metal, e.g., liquid aluminum, in the pot at the aluminizing line. In some cases, there may be damage to the protective coating that then exposes the base stainless steel material of the structural component to the liquid metal in the aluminizing pot. In other cases, over time and with exposure to the liquid metal in the aluminizing pot, these protective coatings may wear down or be otherwise destroyed or compromised. In these cases, the liquid metal in the aluminizing pot attacks or dissolves the structural stainless steel component.

SUMMARY

In the circumstance described above, a problem to be solved may involve finding ways to ensure there is no damage to any protective coating on the component or substrate to be aluminized. However, a novel approach to the problem of a compromised protective coating that is disclosed in the following paragraphs and pages involves modifying the underlying substrate to improve its resistance to attack by the liquid metal in the aluminizing pot. Accordingly, this novel solution adds a safety margin to significantly increase the life of the structural components exposed to the attack by the liquid aluminum.

Embodiments described herein, include a stainless steel having by weight percentage about 20% chromium (Cr), about 1.94% to about 6.74% molybdenum (Mo), about 1.14% to about 1.27% silicon (Si), about 7.88% to about 14.41% nickel (Ni), about 1.25% to about 2.3% manganese (Mn), about 0.0276% to about 0.0307% carbon (C), about 0.031% to about 0.160% nitrogen (N), and the balance impurities. Additionally, the average ferrite is 0% to about 28.08% based on Feritscope measurements. In some examples the Mo is equal or greater than about 6.71%. In some examples with or without the higher Mo of about 6.71%, the N is equal or greater than about 0.160%. In some examples with either or both of the higher Mo of about 6.71% and/or the higher N of about 0.160%, the average ferrite is 0%.

Some embodiments described herein, include a stainless steel having by weight percentage about 20% chromium (Cr), about 1.94% to about 6.74% molybdenum (Mo), about 1.14% to about 1.27% silicon (Si), about 7.88% to about 14.41% nickel (Ni), about 1.25% to about 2.3% manganese (Mn), about 0.0276% to about 0.0307% carbon (C), about 0.120% or more nitrogen (N), and the balance impurities. Additionally, the average ferrite is 0% to about 28.08% based on Feritscope measurements. In some examples of this steel the average ferrite is about 17.61%.

Some embodiments described herein, include a stainless steel having by weight percentage about 20% chromium (Cr), about 6.74% molybdenum (Mo), about 1.14% to about 1.27% silicon (Si), about 7.88% to about 14.41% nickel (Ni), about 1.25% to about 2.3% manganese (Mn), about 0.0276% to about 0.0307% carbon (C), about 0.160% or more nitrogen (N), and the balance impurities. Additionally, the average ferrite is about 0% on Feritscope measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

It is believed the present invention will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements.

FIG. 1 depicts a Schaeffler-DeLong diagram showing the phases present in solidified, as-cast stainless steel at room temperature.

FIG. 2 depicts compositions of melted T316L stainless steel showing the Ni-Equi and Cr-Equi of the compositions.

FIG. 3 depicts a photo of stainless steel composition samples in an initial state before being subjected to liquid metal.

FIG. 4 depicts a bubble plot of Feritscope measurements on the Schaeffler-Delong diagram.

FIG. 5 depicts a photo of the stainless steel composition samples of FIG. 3 after a seven day immersion test.

FIG. 6 depicts a photo of the stainless steel composition samples of FIG. 3 after a three day immersion test.

FIG. 7 depicts a photo of the stainless steel composition samples of FIG. 6 with most free aluminum removed.

FIG. 8 depicts a photo of the stainless steel composition samples of FIG. 7, shown in cross section.

The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.

DETAILED DESCRIPTION

The following description of certain examples of the invention should not be used to limit the scope of the present invention. Other examples, features, aspects, embodiments, and advantages of the invention will become apparent to those skilled in the art from the following description. As will be realized, the invention is capable of other different and obvious aspects, all without departing from the invention. Accordingly, the examples, drawings and descriptions should be regarded as illustrative in nature and not restrictive. Furthermore, unless indicated to the contrary, any numerical parameters set forth in the following description and the attached claims are approximations that may vary depending upon the desired properties one seeks to obtain in the product and methods according to the present disclosure. Percentages represent weight percentages unless otherwise specified. Words of approximation such as “substantially,” “about,” and similar terms should be interpreted in accordance with the understanding of those of ordinary skill in the art of those terms in the given context. In some instances, these or other similar words of approximation when used to describe numerical values may be understood to represent a range about the stated values of plus or minus ten percent.

In the following examples, various alloying element modifications of a T316L stainless steel composition (cast name CF3M) were fabricated and tested for resistance to liquid metal attack. These various modified compositions of the T316L stainless steel were subjected to liquid aluminum metal using a pot of Type 2 nearly pure aluminum as this is known to be more aggressive or reactive with respect to its attack of steel components than a more common Type 1 bath of aluminum and silicon. With this approach, those compositions that show improved resistance to attack by the liquid aluminum ought to show even further improved resistance to liquid metal attack when subjected to the less aggressive Type 1 bath of aluminum and silicon.

Referring to FIG. 1, the Schaeffler-DeLong diagram was used as the basis for the modifications of the T316L stainless steel compositions. As shown, the diagram represents the phases that are present when a weld metal solidifies to room temperature as a function of its composition. In some circumstances, the castings are annealed to remove or decrease the delta ferrite that is present in the as-cast structure. In the examples described and evaluated herein, as-cast samples were evaluated, but it should be understood that in other examples the same evaluations can be conducted with samples that were annealed after casting.

Certain stainless steels described herein, include a stainless steel having by weight percentage about 20% chromium (Cr), about 1.94% to about 6.74% molybdenum (Mo), about 1.14% to about 1.27% silicon (Si), about 7.88% to about 14.41% nickel (Ni), about 1.25% to about 2.3% manganese (Mn), about 0.0276% to about 0.0307% carbon (C), about 0.031% to about 0.160% nitrogen (N), and the balance impurities. Additionally, the average ferrite is 0% to about 28.08% based on Feritscope measurements. As described further in the following examples, within these above percentages and percentage ranges higher Mo amounts, higher N amounts, varying ferrite amounts, and combinations of these were evaluated.

Carbon: Less than about 0.03%

C is an austenite phase stabilizer and inhibits the deformation-induced martensitic transformation. The stainless steels described herein have up to 0.0307% C.

Chromium: About 20%

Cr provides corrosion resistance to stainless steels. Cr also stabilizes the austenitic phase with respect to martensitic transformation. Cr is a ferrite stabilizer and so other alloying elements, such as nickel or cobalt, may be required to keep the ferrite content acceptably low. The stainless steels described herein have about 20% Cr.

Molybdenum: About 2% to about 7%

Mo stabilizes the passive oxide film that forms on the surface of stainless steels and protects against pitting corrosion by the action of chlorides. Mo is also a ferrite stabilizer. In the present steels, higher Mo levels provide for improved resistance to liquid metal attack. The stainless steels described herein have about 2% to about 7% Mo.

Silicon: About 1.25%

Si is a ferrite stabilizer and thus minimizing Si helps achieve lower ferrite phase. Greater than 2% Si promotes the formation of embrittling phases and reduces the solubility of nitrogen in the alloy. The stainless steels described herein have about 1.25% Si with some steels being in the range of about 1.1% to about 1.2%.

Manganese: At Least about 1.25%

Mn is an austenitic stabilizer and increases the solubility of N. The stainless steels described herein have at least about 1.25% with some steels having at least about 2.3% Mn. In other examples, the Mn can be higher, at least about 6%.

Nitrogen: About 0.03% to about 0.16%

N stabilizes the austenite phase at room temperature. N also increases strength and corrosion resistance. In the present steels, higher N levels provide for improved resistance to liquid metal attack. The stainless steels described herein have about 0.031% to about 0.16%.

Nickel: About 7.88% to about 14.41%

Ni is an austenite stabilizer and also decreases the N solubility. The stainless steels described herein have about 7.88% to about 14.41% Ni.

EXAMPLES
Example 1

The T316L stainless steel composition of Example 1 represents a reference T316L stainless steel having a target composition, by weight percent, shown in Table 1 below. This Example 1 steel is identified with an ID of C and Heat No. of 2073-1 as shown both in Table 1 and FIG. 2. With the target composition for this steel C, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel C, showing the alloying elements by weight percentage.

Example 2

The T316L stainless steel composition of Example 2 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target molybdenum (Mo) content was increased to 3% from the 2% of steel C. This Example 2 steel is identified with an ID of D and Heat No. of 2073-2 as shown both in Table 1 and FIG. 2. With the target composition for this steel D, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel D, showing the alloying elements by weight percentage.

Example 3

The T316L stainless steel composition of Example 3 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was decreased to 0.1% from the 2% of steel C. This Example 3 steel is identified with an ID of A and Heat No. of 2072-1 as shown both in Table 1 and FIG. 2. With the target composition for this steel A, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel A, showing the alloying elements by weight percentage.

Example 4

The T316L stainless steel composition of Example 4 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was decreased to 1% from the 2% of steel C. This Example 4 steel is identified with an ID of B and Heat No. of 2072-2 as shown both in Table 1 and FIG. 2. With the target composition for this steel B, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel B, showing the alloying elements by weight percentage.

Example 5

The T316L stainless steel composition of Example 5 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was the same as in steel C, but the target nickel (Ni) content increased from about 10.23% to 14.23%. This Example 5 steel is identified with an ID of F and Heat No. of 2074-1 as shown both in Table 1 and FIG. 2. With the target composition for this steel F, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel F, showing the alloying elements by weight percentage.

Example 6

The T316L stainless steel composition of Example 6 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was increased to 7% from the 2% in steel F, while the target Ni remained at 14.23% like with steel F. This Example 6 steel is identified with an ID of E and Heat No. of 2074-2 as shown both in Table 1 and FIG. 2. With the target composition for this steel E, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel E, showing the alloying elements by weight percentage.

Example 7

The T316L stainless steel composition of Example 7 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target composition matches that of steel E. This Example 7 steel is identified with an ID of I and Heat No. of 2075-1 as shown both in Table 1 and FIG. 2. With the target composition for this steel I, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel I, showing the alloying elements by weight percentage.

Example 8

The T316L stainless steel composition of Example 8 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo and Ni contents were unchanged from that of steels E and I, but the target nitrogen (N) content increased from about 0.03% to 0.1%. This Example 8 steel is identified with an ID of J and Heat No. of 2075-2 as shown both in Table 1 and FIG. 2. With the target composition for this steel J, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel J, showing the alloying elements by weight percentage.

Example 9

The T316L stainless steel composition of Example 9 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was the same as in Example 1, but the target Ni content decreased from about 10.23% to 8.23%. This Example 9 steel is identified with an ID of G and Heat No. of 2076-1 as shown both in Table 1 and FIG. 2. With the target composition for steel G, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the chemical analysis of steel G, showing the alloying elements by weight percentage.

Example 10

The T316L stainless steel composition of Example 10 represents a modified T316L stainless steel having a target composition, by weight percent, shown in Table 1 below, and as seen the target Mo content was the same as in steel C, but the target Ni content decreased from about 10.23% to 8.23% while the target N content increased from about 0.03% to 0.1%. This Example 10 steel is identified with an ID of H and Heat No. of 2076-2 as shown both in Table 1 and FIG. 2. With the target composition for steel H, the Ni-Eq and Cr-Eq are also shown in Table 1 based on the equations shown in the Schaeffler-DeLong diagram of FIG. 1. Table 2 below shows the analyzed chemical analysis of steel H, showing the alloying elements by weight percentage.

TABLE 1

Requested Chemical Analyses of the Ten Lab Melted Heats

Melt
HeatNo
ID
Cr
Mo
Si
Ni
Mn
C
N
Ni-Eq
Cr-Eq

2072-1
A
20
0.1
1.25
8.71
1.25
0.025
0.03
11.0
22.0

2072-2
B
20

1

1.25
9.43
1.25
0.025
0.03
11.7
22.9

REF
2073-1
C
20

2

1.25
10.23
1.25
0.025
0.03

12.5

23.9

2073-2
D
20

3

1.25
11.03
1.25
0.025
0.03
13.3
24.9

2074-1
F
20
2
1.25
14.23
1.25
0.025
0.03

16.5

23.9

2074-2
E
20

7

1.25
14.23
1.25
0.025
0.03
16.5
28.9

2075-1
I
20
7
1.25
14.23
1.25
0.025
0.03
16.5
28.9

2075-2
J
20
7
1.25
14.23
1.25
0.025

0.1

18.6
28.9

2076-1
G
20
2
1.25
8.23
1.25
0.025
0.03

10.5

23.9

2076-2
H
20
2
1.25
8.23
1.25
0.025

0.1

12.6
23.9

(bold italics = vary Mo; bold underline = vary N; bold italic underline = vary ferrite)

TABLE 2

Analyzed Chemical Analyses of the Ten Lab Melted Heats

Melt
HeatNo
ID
Al
B
C
Co
Cr
Cu
Mn
Mo
N

2072-1
A
0.000
0.0000
0.0291
0.008
20.32
0.015
1.29

0.09

0.041

2072-2
B
0.000
0.0000
0.0288
0.007
19.81
0.016
1.28

0.39

0.041

REF
2073-1
C
0.005
0.0006
0.0276
0.008
19.95
0.017
1.26
2.22
0.038

2073-2
D
0.005
0.0006
0.0284
0.008
20.12
0.018
1.25

2.64

0.038

2074-1
F
0.005
0.0006
0.0284
0.006
20.00
0.019
1.27
1.95
0.031

2074-2
E
0.011
0.0013
0.0296
0.006
19.90
0.021
1.26

5.68

0.033

2075-1
I
0.014
0.0015
0.0303
0.007
20.03
0.022
1.25
6.71
0.054

2075-2
J
0.012
0.0017
0.0307
0.006
19.83
0.023
2.64
6.74

0.160

2076-1
G
0.005
0.0005
0.0280
0.006
19.91
0.016
1.32
1.95
0.049

2076-2
H
0.004
0.0006
0.0278
0.006
19.98
0.017
2.30
1.94

0.120

Melt
HeatNo
ID
Ni
P
S
Si
Ti
V
W
Ni-Eq
Cr-Eq

2072-1
A
8.49
0.0030
0.0013
1.24
0.0030
0.0060
0.0000
11.2
22.3

2072-2
B
9.36
0.0040
0.0012
1.27
0.0030
0.0060
0.0000
12.1
22.1

REF
2073-1
C
10.08
0.0050
0.0012
1.23
0.0030
0.0060
0.0000
12.7
24.0

2073-2
D
10.94
0.0050
0.0012
1.21
0.0030
0.0060
0.0000
13.6
24.6

2074-1
F
14.09
0.0040
0.0012
1.22
0.0030
0.0060
0.0000

16.5

23.8

2074-2
E
14.41
0.0060
0.0012
1.20
0.0030
0.0060
0.0030
16.9
27.4

2075-1
I
14.23
0.0060
0.0014
1.16
0.0040
0.0070
0.0030
17.4
28.5

2075-2
J
14.20
0.0070
0.0016
1.14
0.0040
0.0070
0.0030
21.2
28.3

2076-1
G
8.08
0.0040
0.0013
1.26
0.0030
0.0060
0.0030

11.1

23.8

2076-2
H
7.88
0.0040
0.0014
1.21
0.0030
0.0070
0.0000
13.5
23.7

Based on the above example steels, variable Mo contents from 0.3% to 7% at the same delta ferrite level (about 15% as-cast) were evaluated. Compositions with three levels of delta ferrite at the same Mo content (2%) were evaluated. And example steels were evaluated with two levels of N. In the present examples, increasing N was done by using nitrided manganese. This resulted in slightly higher manganese (Mn) levels for example steels with the higher N content.

Referring again to FIGS. 1 and 2, the Schaeffler-DeLong diagram served as a guide to predict ferrite levels based on the composition and modifications thereto. More specifically, the nickel (Ni) and chromium (Cr) equivalents are calculated based on the given formulas in FIG. 1 for a given composition to arrive at the predicted constitution. Referring to FIG. 2, example steels A-J are shown plotted on a Schaeffler-DeLong diagram along with an original line that represents an about 20% ferrite constitution. As shown in FIG. 2, several of the evaluated compositions reasonably closely followed this 20% ferrite constitution original line, namely steels A, B, C, D E, H, and I. As shown, steel G was predicted to have a higher ferrite constitution based on its composition while steels F and J were predicted to have a low ferrite constitution.

In addition to Tables 1 and 2 showing the target and actual compositions of steels A-J, and FIGS. 1 and 2 showing the predicted ferrite constitutions for steels A-J, Table 3 below shows the average Feritscope measurements for these steels. In addition to measuring the ferrite content before the samples were immersed in the liquid metal, they were also weighed, and dimensions were recorded as shown in Table 4 below. Also, FIG. 4 shows a bubble plot of the Feritscope measurements overlaid on the Schaeffler-DeLong diagram.

TABLE 3

Average of the Feritscope Measurements (Sample

8/J with Excellent Properties Noted)

ID
Feritscope-AVE % Fe

1 = C = 73-1M
17.46

2 = D = 73-2M
15.29

3 = A = 72-1M
12.60

4 = B = 72-2M
13.25

5 = F = 74-1M
2.60

6 = E = 74-2M
0.06

7 = I = 75-1M
0.00

8 = J = 75-2M
0.00

9 = G = 76-1M
28.08

10 = H = 76-2M
17.61

TABLE 4

Weights and Widths of the Samples from Test 3

(Sample 8/J with Excellent Properties Noted)

Test 3
Melt
Orig Wt
Wt Stripped
RoughWidth
Weight ⅝″

ID
ID
(gm)
(gm)
(mm)
Section (gm)

1
73-1
1606.40
520.39
5.5
5.03

2
73-2
1536.64
241.86
4.0
1.66

3
72-1
1492.02

0
0

4
72-2
1468.53

0
0

5
74-1
1522.70
549.23
9
14.32

6
74-2
1449.26
544.34
8.7
12.61

7
75-1
1356.29
755.32
15.7
57.29

8
75-2
1515.96
1382.64
24.5
152.44

9
76-1
1401.90
540.54
8.3
15.03

10
76-2
1432.43
623.83
11.3
41.08

When examining FIG. 4, the data from Table 3 is plotted in the bubble plot format where the magnitude of the measured ferrite percentage is proportional to the size of the circle or bubble on the bubble plot. Based on a comparison of FIG. 4 to FIG. 2, first, the bubbles representing steels A, B, C, D, and H reasonably follow the original line for 20% ferrite and are generally of similar magnitude. Second, steel G is represented by the large bubble below the original line for 20% ferrite, which again is consistent with the Feritscope measurements of Table 3. Third, steels E, F, I, and J are represented by smaller bubbles that are above the original line for 20% ferrite indicating that these steels had a lower ferrite constitution. According to Table 3 the measured ferrite percentages for steels E, F, I, and J range from 0-2.6%. As shown, the steels with the higher Ni Equivalent composition were measured as essentially ferrite free.

When fabricating the example steels, ingots were cast from the melted and modified compositions. These cast ingots were then formed into samples with an eye bolt attached to the top of each sample piece so it could be hung in the Type 2 liquid aluminum bath. FIG. 3 depicts steel samples of steels A-J, with the eye bolt attached and prior to immersion in the Type 2 bath.

A first group of ten samples of steels A-J were evaluated after immersion in the Type 2 liquid aluminum bath for a period of ten days. A second group of ten samples of steels A-J were evaluated after immersion in the Type 2 liquid aluminum bath for a period of seven days. A third group of ten samples of steels A-J were evaluated after immersion in the Type 2 liquid aluminum bath for a period of three days.

For the ten-day immersion evaluation, the liquid aluminum fully dissolved the steel of steels A-J. For the seven-day immersion evaluation, FIG. 5 depicts samples of steels A-J at the conclusion of the seven-day period. As shown, steels D and J had the most steel remaining. For the three-day immersion evaluation, FIG. 6 depicts samples of steels A-J at the conclusion of the three-day period. FIG. 7 depicts the samples steels A-J from FIG. 6 with the free Al removed to observe the remaining steel. As shown, steels A and B had totally dissolved after removal of the Al in a NaOH solution, and steel J had the most steel remaining. This is also shown in FIG. 8, which shows cross sections of steels C-J from FIG. 7 after a ⅝ inch thick piece had been saw-cut from each sample for metallographic examination.

The steel samples had different original weights and they were not all immersed to the same depth in the liquid aluminum. However, by measuring the widths of the samples, or the weights of the ⅝ inch thick pieces saw-cut for metallographic examination a semi-quantitative measure of the resistance of these alloys to attack by the liquid aluminum is determined. For instance, Table 4 shows the relative widths of the remaining samples after the free aluminum has been removed as measured on a photograph. Also shown in Table 4 is the original pretest weights, the weights of the free aluminum stripped tested samples, and the weights of the ⅝ inch thick sections that were saw-cut for metallographic examination.

From the qualitative and quantitative analysis shown and mentioned, steel J showed the best resistance to attack by immersion in the liquid aluminum. Steel J again had the higher N, the higher Mo content, and no delta ferrite. Steel I was the second best in terms of resistance to attack by immersion in the liquid aluminum. Steel I again had the higher Mo content, only slightly higher N, and no ferrite. Steel H was the third best in terms of resistance to attack by immersion in liquid aluminum. Steel H again had the higher N content, the nominal 2% Mo, and much more delta ferrite phase. It is noted that Steels J, I, and H all provided significantly better Al attack resistance than the reference steel, steel C.

In considering the impact of adding N to the composition at higher levels, there is a benefit observed as seen by comparing steel I and steel J. Both steel I and J have nominally the same composition with the high Mo content and the same single phase austenite—the difference being the increase in the soluble N with steel J. Based on the post immersion qualitative and quantitative metrics in the FIGS. 6-8 and Table 4, the higher N significantly improved the resistance to attack by the liquid Al.

In certain compositions, modifications are made to increase the solubility of N to avoid porosity in the casting. For instance, additions of Cr and Mn improve N solubility, while Si and Ni, which decrease N solubility, would be minimized. Also, to minimize the ferrite content, the amount of austenite stabilizer is increased, e.g., by increasing Ni, Mn, and N. In a similar manner, the ferrite stabilizer would be minimized, e.g., by decreasing Cr, Si, and Mo. In balancing these factors an essentially ferrite free stainless steel with a high soluble N content, or with a high soluble N and Mo contents, can be achieved.

When referring to the tables and figures, it should be noted that Table 3 includes a column that associates each steel A-J with a number 1-10. Furthermore, an association is shown to a heat No. or melt ID. Based on this, those of ordinary skill in the art will understand the precise steel sample being shown and described in the tables and figures based on any one or more of these identifying associations. In many instances the figures have been annotated to include reference to one or more of these identifying characters.

It should be understood that any one or more of the teachings, expressions, embodiments, examples, etc. described herein may be combined with any one or more of the other teachings, expressions, embodiments, examples, etc. that are described herein. The following-described teachings, expressions, embodiments, examples, etc. should therefore not be viewed in isolation relative to each other. Various suitable ways in which the teachings herein may be combined will be readily apparent to those of ordinary skill in the art in view of the teachings herein. Such modifications and variations are intended to be included within the scope of the claims.

Having shown and described various embodiments of the present invention, further adaptations of the methods and systems described herein may be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. Several of such potential modifications have been mentioned, and others will be apparent to those skilled in the art. For instance, the examples, embodiments, geometrics, materials, dimensions, ratios, steps, and the like discussed above are illustrative and are not required. Accordingly, the scope of the present invention should be considered in terms of the following claims and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.

RESISTANCE OF STAINLESS STEEL TO LIQUID ALUMINUM ATTACK

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