An optimization method for 304 stainless steel based on cluster-based identification of synergistic change relationships.

Abstract

This invention discloses an optimization method for 304 stainless steel based on establishing synergistic variation relationships in cluster composition. The method includes the following steps: dividing the composition of 304 stainless steel into two main categories: those entering clusters and those not entering clusters; based on a cluster-connected atom model, converting the 304 stainless steel in the national standard into a cluster composition formula, and selecting multiple actually produced 304 stainless steels to convert into cluster compositions, plotting the standard composition range of the 304 stainless steel alloy's cluster composition formula, and determining the synergistic variation relationships between various elements; analyzing the standard composition range of the 304 stainless steel alloy, optimizing the synergistic variation relationships between elements, and obtaining the synergistic variation relationships between the four elements in 304 stainless steel, providing a more accurate element range, and solving the technical problem of unstable alloy performance caused by inaccurate element ranges.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology, and in particular to an optimization method for 304 stainless steel based on establishing synergistic change relationships in a cluster-based manner. Background Technology

[0002] Stainless steel, as defined in GB / T 20878-2007, is steel whose main characteristics are rust resistance and corrosion resistance, with a chromium content of at least 10.5% and a carbon content of no more than 1.2%. Stainless steel is often classified according to its matrix structure into austenitic stainless steel, austenitic-ferritic (duplex) stainless steel, ferritic stainless steel, martensitic stainless steel, precipitation hardening stainless steel, and heat-resistant steel. Stainless steel possesses excellent corrosion resistance, formability, compatibility, and toughness over a wide temperature range, making it widely used in heavy industry, light industry, consumer goods, and construction and decoration industries. Austenitic stainless steel is non-magnetic compared to other types of stainless steel and has excellent toughness and plasticity. 304 austenitic stainless steel, as a representative alloy of austenitic stainless steel, is the most widely used austenitic stainless steel. Like other alloys, the national standard for this steel specifies specific ranges for each alloying element.

[0003] However, based on actual production applications, it has been found that the scope of the existing national standard is too broad, and there is still no specific composition design guidance for stainless steel. 304 stainless steel produced within the scope of the national standard still shows significant differences in performance, resulting in unstable performance of 304 stainless steel alloys. Summary of the Invention

[0004] This invention provides an optimization method for 304 stainless steel based on establishing synergistic variation relationships in a cluster-based manner. This method overcomes the technical problem that the performance of 304 alloy stainless steel varies significantly even when the individual element composition is within the range specified by national standards, and that the inaccurate range of elements leads to unstable alloy performance.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] An optimization method for 304 stainless steel based on clustering to establish synergistic change relationships includes the following steps:

[0007] S1: The composition of 304 stainless steel is divided into two main categories: those that enter clusters and those that do not.

[0008] S2: Based on the cluster plus connected atom model, the 304 stainless steel in the national standard is converted into a cluster composition formula, and several actual 304 stainless steels are selected and converted into cluster formulas. The standard composition range of the cluster composition formula of 304 stainless steel alloy is plotted, and the synergistic change relationship between each element is determined.

[0009] S3: Analyze the standard composition range of 304 stainless steel alloy and further optimize the synergistic variation relationship between (Cr, Si) and (Ni, Mn);

[0010] S4: Convert the optimized synergistic change relationship in step S3 into a mass percentage;

[0011] S5: Considering the alloy sensitization phenomenon, the synergistic change relationship after step S3 optimization is further optimized by introducing equivalents.

[0012] Furthermore, in step S1, the elements that enter the clusters in 304 stainless steel are: Fe, Cr, Si, Ni and Mn, while the elements that do not enter the clusters are C, P and S.

[0013] Furthermore, the elements entering the cluster of 304 stainless steel are classified according to their interaction mode with Fe into ferrite stabilizing elements (Cr, Si), austenite stabilizing elements (Ni, Mn) and matrix element Fe.

[0014] Furthermore, the synergistic relationship of the elements in step S2 is as follows: 18.0≤Cr+1.7Si≤20.6, 8.5≤Ni+1.06Mn≤11.6.

[0015] Furthermore, the synergistic relationship between (Cr, Si) and (Ni, Mn) in step S3 is: 0.5 ≤ {number of (Ni, Mn) atoms / number of (Cr, Si) atoms} ≤ 2.

[0016] Furthermore, the optimized synergistic change relationship in step S3 is converted into a mass percentage (wt.%) as follows:

[0017] (3) In the range of 18.0≤Cr+1.7Si≤19.0, 0.6(Cr+1.7Si)-2.3≤Ni+1.06Mn≤2.5(Cr+1.7Si)-35.9, or 0.4(Ni+1.06Mn)+14.4≤(Cr+1.7Si)≤1.7(Ni+1.06Mn)+3.8;

[0018] (4) In the range of 19.0≤Cr+1.7Si≤20.6, 0.56(Cr+1.7Si)-1.59≤Ni+1.06Mn≤11.6, or Cr+1.7Si≤1.8(Ni+1.06Mn)+2.8.

[0019] Furthermore, step S5 introduces equivalent calculations, and the synergistic variation relationship of alloy composition limited by equivalents can be approximately expressed as: 18.0 ≤ Cr eq ≤20.6, Ni eq ≤11.6+30C, 0.5≤[Nieq -8.3] / [Cr eq -17.6]≤2.

[0020] Furthermore, the alloy composition is defined by the synergistic variation relationship of 304 stainless steel by mass percentage (wt.%):

[0021] (3)8.5≤Ni+30C+0.5Mn≤13.3;

[0022] (4) 0.5(Ni+0.5Mn)+15C+13.5≤Cr+1.5Si≤2(Ni+0.5Mn)+60C+1.04 or 0.5(Cr+1.5Si)-(30C+0.52)≤Ni+0.5Mn≤2(Cr+1.5Si)-(30C+27.0).

[0023] Beneficial effects: This invention provides an optimization method for 304 stainless steel based on cluster-based establishment of synergistic variation relationships. It obtains the synergistic variation relationship of the four elements in 304 stainless steel, gives a more accurate element range, and solves the technical problem of unstable alloy properties caused by inaccurate element range. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This invention discloses a pseudo-ternary composition diagram of (Cr, Si)-(Ni, Mn)-Fe for a 304 stainless steel optimization method based on cluster-based establishment of synergistic variation relationships.

[0026] Figure 2 This is a Schaeffer diagram of a 304 stainless steel optimization method based on clustering to establish synergistic change relationships, as disclosed in this invention.

[0027] Figure 3 This is a schematic diagram illustrating the steps of an optimization method for 304 stainless steel based on clustering to establish synergistic change relationships, as disclosed in this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The concept for optimizing 304 stainless steel in this invention is as follows: The applicant's cluster-based method is used for compositional analysis of 304 stainless steel. Elements form cluster-based structural units according to their interaction modes, which can be represented by a simple cluster composition formula: [cluster](connecting atoms) x, where one cluster is matched with x connecting atoms. For face-centered cubic alloys, the number of connecting atoms x = 1 to 5. Through the cluster model, it can be calculated that, in the case of near-constant diameter, the number of connecting atoms x = 3. This cluster-based compositional analysis method has been successfully applied to the analysis of various engineering alloys, including high-temperature alloys, austenitic stainless steels, low-elasticity β-Ti alloys, and cobalt-based high-temperature alloys, providing new ideas and methods for the compositional analysis of high-performance engineering alloys.

[0030] This embodiment provides an optimization method for 304 stainless steel based on clustering to establish synergistic change relationships, including the following steps: Figure 3 As shown:

[0031] S1: Although the composition of 304 stainless steel varies slightly in different standard grades, it contains Cr, Ni, Si, Mn, C, P, and S. According to the interaction mode between the elements and Fe, they are divided into ferrite stabilizing elements (Cr, Si), austenite stabilizing elements (Ni, Mn), matrix element Fe, and interstitial C that does not enter the clusters, as well as trace amounts of P and S that form inclusions. Therefore, the composition of 304 stainless steel is divided into two main categories: those that enter the clusters and those that do not. The elements that enter the clusters are Fe, Cr, Si, Ni, and Mn, while the elements that do not enter the clusters are C, P, and S.

[0032] S2: In clustered structures, when... Centered on the element, it can be calculated that the cluster contains 16 atoms, that is... The elemental composition entering the clusters was converted to 16 atoms. Analysis of the national standard grades in Table 1 revealed that, except for C, P, and S which do not enter clusters and the low-carbon, high-nickel content, the other component ranges for the three 304 stainless steel national standard grades were the same. Taking the upper and lower limits of Si, Mn, Ni, and Cr in 06Cr19Ni10 and 07Cr19Ni10, namely (20Cr, 1Si)-(11Ni, 2Mn)-Fe, (20Cr, 1Si)-(8Ni, 0Mn)-Fe, (18Cr, 0Si)-(11Ni, 2Mn)-Fe, and (18Cr, 0Si)-(8Ni, 0Mn)-Fe, respectively, these were converted into cluster composition formulas with Z=16, namely (Cr, Si). 3.68 -(Ni, Mn) 1.96 -Fe 10.36 (Cr, Si) 3.68 -(Ni, Mn) 1.19 -Fe 11.13 (Cr, Si) 3.07 -(Ni, Mn) 1.98 -Fe 10.95 and (Cr, Si) 3.06 -(Ni, Mn) 1.21 -Fe 11.73 For the low-carbon 022Cr19Ni10, the corresponding cluster composition is (Cr, Si). 3.68 -(Ni, Mn) 2.11 -Fe 10.21 and (Cr, Si) 3.07 -(Ni, Mn) 2.14 -Fe 10.79 This led to the plotting of the composition ranges for the three 304 stainless steel grades specified in the national standard, such as... Figure 1 The area enclosed by the gray dashed line. Several actual produced 304 stainless steel samples were selected, as shown in Table 2, and their cluster composition was converted. These samples were then plotted on [the map / plotting]. Figure 1 In, such as Figure 1 The central cross markings indicate that they are mostly located in the cluster formula (Cr, Si)3-(Ni, Mn). 1.5±0.25 -Fe 11.5±0.25 and (Cr, Si) 3.5 -(Ni, Mn) 1.5±0.25 -Fe 11±0.25 Between these elements, the true composition of 304 stainless steel is revealed, characterized by the total number of the two types of elements satisfying the Cr... 3.0～3.5 and Ni 1.5±0.25That is, the difference in the number of atoms between the composition formulas is 0.5. From this, we can conclude that the alloy composition of 304 stainless steel is determined by the composition formula and the synergistic variation relationship: under the premise of element coordination variation that satisfies 18.0≤Cr+1.7Si≤20.6 and 8.5≤Ni+1.06Mn≤11.6 (the coefficient is introduced from the difference in element mass).

[0033] Table 1. Typical 304 stainless steel national standard grades and their wt.% chemical composition, and national standards.

[0034]

[0035]

[0036] Table 2 lists 24 types of stainless steel with publicly disclosed actual production.

[0037]

[0038]

[0039] The specific conversion relationship is as follows: Taking the upper limit of 06Cr19Ni10 as an example, as shown in the table, the content of each element is different. These are uniformly converted to mass percentages, i.e., (20Cr, 1Si) - (11Ni, 2Mn) - Fe. The coefficient before each element represents the mass percentage. The molar fraction is obtained by dividing the mass percentage by the molar mass. The total molar fraction is obtained by adding the molar fractions of each element. The atomic percentage is obtained by dividing the molar fraction of each element by the total molar fraction. Since the total number of atoms entering the cluster is known to be 16, the number of atoms of each element is obtained by multiplying the atomic percentage by the total number of atoms. Therefore, the cluster composition formula is: (Cr, Si). 3.68 -(Ni, Mn) 1.96 -Fe 10.36 The coefficient indicated by the subscript represents the number of atoms.

[0040] S3: In addition to the austenite and ferrite stabilizing elements each satisfying a certain composition range. Figure 1 The measured alloy compositions given are mostly constrained within two linear intervals with slopes of (1.5-1.25) / (3.5-3) = 0.5 and (1.75-1.25) / (3.25-3) = 2 (yellow shaded area, abcFd). The synergistic relationship between (Cr, Si) and (Ni, Mn) satisfies 0.5 ≤ (Ni, Mn) atoms / (Cr, Si) atoms ≤ 2. These two lines also conform to the synergistic relationship between Cr and Ni in stable austenite, meaning that an increase in Cr inevitably leads to a proportional increase in Ni content. Clearly, this synergistic relationship exists within the respective intervals of synergistic changes of elements of the same type (Cr, Si). 3.0-3.5 and(Ni,Mn) 1.25-1.75Based on this, there is also a synergy between (Cr, Si) and (Ni, Mn), that is, 0.5 ≤ (Ni, Mn) atoms / (Cr, Si) atoms ≤ 2. These two straight lines reflect the synergy between Cr and Ni in stabilizing austenite, that is, when a certain amount of Cr is increased, it is necessarily accompanied by a proportional increase in Ni content.

[0041] like Figure 1 As shown, composition points A to F are the composition points of the new standard 16-atom composition formula, where A: (Cr, Si)3-(Ni, Mn) 1.25 -Fe 11.75 B: (Cr, Si) 3.5 -(Ni, Mn) 1.25 -Fe 11.25 C: (Cr, Si)3-(Ni, Mn) 1.5 -Fe 11.5 D: (Cr, Si) 3.5 -(Ni, Mn) 1.5 -Fe 11 E: (Cr, Si)3-(Ni, Mn) 1.75 -Fe 11.25 F: (Cr, Si) 3.5 -(Ni, Mn) 1.75 -Fe 10.75 The dashed line represents the stainless steel composition range under the industrial standard GB / T 20878-2007, and the plus sign represents the 304 stainless steel composition reported in the literature. The lower and upper limits of (Ni, Mn) are defined by line segments aD with a slope of 0.5, bc with a slope of 2, and cF, respectively. The range enclosed by the circular symbol abcFD represents the composition range with a cooperative variation relationship. All reported alloy compositions that do not fall within the enclosed 304 stainless steel composition range with a cooperative variation relationship are considered unqualified alloy compositions.

[0042] Converting the abcFD composition formula surrounding the composition interval into a mass percentage, and introducing coefficients at Si and Mn such that their sums with Cr and Ni remain essentially unchanged as Si replaces Cr and Mn replaces Ni, we obtain:

[0043] a: Cr+1.7Si=18.0, Ni+1.06Mn=8.5

[0044] b: Cr+1.7Si=18.0, Ni+1.06Mn=9.1

[0045] c: Cr+1.7Si=19.0, Ni+1.06Mn=11.6

[0046] F: Cr+1.7Si=20.5, Ni+1.06Mn=11.6

[0047] D: Cr+1.7Si=20.6, Ni+1.06Mn=10.0

[0048] The mass percentage component interval is therefore divided into two intervals by the line connecting the midpoints of c and AD:

[0049] 1) Within the range of 18.0 ≤ Cr + 1.7Si ≤ 19.0 (wt.%), the lower limit of Ni + 1.06Mn is equal to {[(Cr + 1.7Si) - 18.0] / (19.0 - 18.0)}(9.1 - 8.5) + 8.5 = 0.6(Cr + 1.7Si) - 2.3, and the upper limit of Ni + 1.06Mn is equal to {[(Cr + 1.7Si) - 18] / (19.0 - 18.0)}(11.6 - 9.1) + 9.1 = 2.5(Cr + 1.7Si) - 35.9, i.e.

[0050] 0.6(Cr+1.7Si)-2.3≤Ni+1.06Mn≤2.5(Cr+1.7Si)-35.9, or

[0051] 0.4(Ni+1.06Mn)+14.4≤(Cr+1.7Si)≤1.7(Ni+1.06Mn)+3.8 (1).

[0052] 2) In the range of 19.0 ≤ Cr + 1.7Si ≤ 20.6 (wt.%), the lower limit of Ni + 1.06Mn is equal to {[(Cr + 1.7Si) - 19.0] / (20.6 - 19.0)}(10.0 - 9.1) + 9.1 = 0.56(Cr + 1.7Si) - 1.59, and the upper limit of Ni + 1.06Mn is always equal to 11.6, that is...

[0053] 0.56(Cr+1.7Si)-1.59≤Ni+1.06Mn≤11.6, or

[0054] Cr+1.7Si≤1.8(Ni+1.06Mn)+2.8 (2).

[0055] Considering that sensitization occurs in stainless steel, it can cause Cr... 23 C6 carbides precipitate, and since C does not enter the clusters, an equivalent calculation is introduced. 304 stainless steel is austenitic, and according to the equivalent formula proposed by Schaeffler et al., Cr... eq =Cr + Mo + 1.5Si + 0.5Nb, wt.% and Ni eq =Ni+30C+0.5Mn, wt.%, calculate the equivalent range of the three national standard grades, the equivalent range of the composition formula, and the equivalent value corresponding to the measured alloy composition.

[0056] The actual alloys are shown in Table 2 for Cr. eq and Ni eq Draw Figure 2 It can be observed that they basically fall within a narrower range than the national standard equivalent range and the component equivalent range, namely the abdFD region. Figure 2 The (abdFD) region corresponds to Figure 1 The (abdFD) region differs in that it uses equivalents to reflect the component range, thus reflecting the influence of C. In fact, Figure 2 The measured alloy is densely distributed near the CF line in the (abdFD) region, which is equivalent to Figure 1 The line AD corresponding to the lower limit of (Ni, Mn) is shifted upwards by 0.25 Ni atoms. According to Ni... eq =Ni + 30C, therefore 0.25 / 16 × M Ni / M Fe / 30≈0.055wt.%C, so 0.25 Ni atoms are equivalent to 0.055wt.%, which is basically in the middle of the usual 0.04-0.08C. This explains why the actual alloy composition is mostly in the (abdFD) region.

[0057] Shifting the weight upwards by 0.25 Ni atoms, or reaching a C content of 0.11 wt.%, yields the equivalent upper limit for all actual 304 alloys, which is very close to the 0.1 wt.% specified for the grade.

[0058] Actual alloy compositions are classified into low-carbon (0–0.055C), medium-carbon (0.055–0.11C), and high-carbon (>0.11C) categories based on the 0.055C standard. Actual alloy compositions containing elements other than those specified in the standard designation are listed separately. For example… Figure 2 As shown, low-carbon stainless steel is mostly concentrated below the straight line CF in the (abdFD) region, while medium-carbon stainless steel is densely distributed above the straight line CF in the (abdFD) region.

[0059] Ni eq The carbon content is highly sensitive; in reality, the equivalent coefficient of carbon is between 20 and 40. Therefore, the above classification of carbon content can only be used as a reference. If we assume that the equivalent coefficient of carbon in 304 stainless steel is 21.9, then 0.25 Ni atoms are approximately equivalent to 0.08 C. In this case, the actual alloy is almost entirely located in the shaded area.

[0060] This proves that, in addition to meeting the limitations on the number of atoms and mass percentage, the alloy composition must also meet the equivalent range limitation, approximately expressed as 18.0 ≤ Cr eq ≤20.6, Ni eq ≤11.6+30C, 0.5≤[Ni eq -8.3] / [Creq -17.6]≤2 (The data in the latter formula are the equivalent coordinates of point A).

[0061] Substituting the equivalent formula, the first 18.0≤Cr+1.7Si≤20.6 almost overlaps with the previous equations (1) and (2), requiring no further processing. Taking the upper limit of 0.055C, the latter two equations are further simplified to...

[0062] 8.5≤Ni+30C+0.5Mn≤13.3, (3),

[0063] 0.5(Ni+0.5Mn)+15C+13.5≤Cr+1.5Si≤2(Ni+0.5Mn)+60C+1.04, or 0.5(Cr+1.5Si)-(30C+0.52)≤Ni+0.5Mn≤2(Cr+1.5Si)-(30C+27.0)(4).

[0064] The final relationship (4) represents the coupling relationship between Cr and Ni defined by equivalence.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] A novel cluster-based approach was adopted to clarify the synergistic variation relationships of alloy composition defined by composition formula and by equivalence, fundamentally overcoming the compositional uncertainty caused by traditional compositional regions. This type of synergistic variation relationship can directly guide compositional control in industrial production and provides a model for sorting out the composition of stainless steel grades.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optimization method for 304 stainless steel based on cluster-based establishment of synergistic change relationships, characterized in that, Includes the following steps: S1: The composition of 304 stainless steel is divided into two main categories: clustered and non-clustered. The elements that enter the clusters in 304 stainless steel are Fe, Cr, Si, Ni and Mn, while the elements that do not enter the clusters are C, P and S. The elements that enter the cluster of 304 stainless steel are classified according to their interaction mode with Fe into ferrite stabilizing elements (Cr, Si), austenite stabilizing elements (Ni, Mn) and matrix element Fe. S2: Based on the cluster-connected atom model, the 304 stainless steel in the national standard is converted into a cluster composition formula, and several actual 304 stainless steels are selected and converted into cluster formulas. The standard composition range of the cluster composition formula of 304 stainless steel alloy is plotted, and the synergistic variation relationship between each element is determined. The synergistic variation relationship between each element is: 18.0≤Cr+1.7Si≤20.6, 8.5≤Ni+1.06Mn≤11.

6. S3: Analyze the standard composition range of 304 stainless steel alloy and further optimize the synergistic variation relationship between (Cr, Si) and (Ni, Mn); S4: Convert the optimized synergistic change relationship in step S3 into a mass percentage; S5: Considering the alloy sensitization phenomenon, the synergistic change relationship after step S3 optimization is further optimized by introducing the equivalent. The synergistic variation relationship of alloy composition, limited by equivalence, can be approximately expressed as: 18.0 ≤ Cr eq ≤20.6, Ni eq ≤11.6+30C, 0.5≤[Ni eq -8.3] / [Cr eq -17.6]≤2; The mass percentage (wt.%) of 304 stainless steel under the equivalent-limited synergistic variation relationship of alloy composition: (3)8.5≤Ni+30C+0.5Mn≤13.3; (4) 0.5(Ni+0.5Mn)+15C+13.5≤Cr+1.5Si≤2(Ni+0.5Mn)+60C+1.04 or 0.5(Cr+1.5Si)-(30C+0.52)≤Ni+0.5Mn≤2(Cr+1.5Si)-(30C+27.0).

2. The optimization method for 304 stainless steel based on cluster-based establishment of synergistic change relationships as described in claim 1, characterized in that, The synergistic relationship between (Cr, Si) and (Ni, Mn) in step S3 is: 0.5 ≤ {number of (Ni, Mn) atoms / number of (Cr, Si) atoms} ≤ 2.

3. The optimization method for 304 stainless steel based on cluster-based establishment of synergistic change relationships according to claim 1, characterized in that, The optimized synergistic change relationship in step S3 is converted into a mass percentage (wt.%) as follows: (1) In the range of 18.0≤Cr+1.7Si≤19.0, 0.6(Cr+1.7Si)-2.3≤Ni+1.06Mn≤2.5(Cr+1.7Si)-35.9, or 0.4(Ni+1.06Mn)+14.4≤(Cr+1.7Si)≤1.7(Ni+1.06Mn)+3.8; (2) In the range of 19.0≤Cr+1.7Si≤20.6, 0.56(Cr+1.7Si)-1.59≤Ni+1.06Mn≤11.6, or Cr+1.7Si≤1.8(Ni+1.06Mn)+2.8.

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