Welding performance evaluation method based on stainless steel base metal components and structure characteristics

Abstract

The invention discloses a welding performance evaluation method based on components and structure characteristics of stainless steel base metal, and relates to the technical field of metal processing technologies, and the method comprises the following steps: obtaining chemical components of the stainless steel base metal; according to the chemical components of the stainless steel base metal, the weldability index is calculated through a weldability index empirical formula; predicting the structure and weldability characteristics of a welding joint heat affected zone corresponding to the stainless steel base material according to the weldability index; and according to the prediction results of the weldability index, the structure of the heat affected zone of the welding joint and the weldability characteristics, the welding performance is determined in combination with a preset weldability evaluation standard. According to the welding performance evaluation method based on the stainless steel base metal components and the structure characteristics, the structure type of the welding joint heat affected zone corresponding to the stainless steel base metal and the welding performance of the stainless steel base metal can be rapidly predicted according to the stainless steel base metal chemical components, and data support can be provided for stainless steel welding process formulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal processing, in particular to a welding performance evaluation method based on composition and microstructure characteristics of stainless steel base material. BACKGROUND

[0002] Stainless steel refers to an iron-based alloy with a chromium content of 11-30% and the addition of other alloying elements. There are numerous stainless steel grades, but they can be classified into ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, duplex stainless steel, and precipitation-hardened stainless steel based on their microstructure. Stainless steel is generally subjected to welding during production and application. The heat-affected zone (HAZ) of the welded joint is a weak link in the entire welded joint and is one of the important aspects of welding process and weldability research. In the welding process using filler metal, the composition and properties of the weld metal in the welded joint mainly depend on the fusion ratio of the welding material and the base material, so the composition and properties can be controlled by material selection. In the heat-affected zone of the welded joint of thin plates (walls) and all welding processes using base material self-melting, the composition and microstructure are completely dependent on the base material and welding process. In order to determine the microstructure and properties of the welded joint of stainless steel, the existing technology mainly relies on a large number of experiments, resulting in a long determination period and high determination cost. SUMMARY

[0003] To solve the above-mentioned technical problems in the prior art, the present application provides a welding performance evaluation method based on the composition and microstructure characteristics of stainless steel base material.

[0004] The technical solution of the present application is as follows:

[0005] A welding performance evaluation method based on the composition and microstructure characteristics of stainless steel base material is provided, which comprises:

[0006] Obtaining the chemical composition of the stainless steel base material;

[0007] Calculating the weldability index according to the chemical composition of the stainless steel base material through an empirical formula of the weldability index;

[0008] Predicting the microstructure and weldability characteristics of the heat-affected zone of the welded joint corresponding to the stainless steel base material according to the weldability index;

[0009] Determining the welding performance according to the prediction results of the weldability index, the microstructure, and the weldability characteristics of the heat-affected zone of the welded joint, and combining the preset weldability evaluation standard;

[0010] The empirical formula of the weldability index is expressed as:

[0011] P=a·W C +b·W Cu +c·W Mn +d·WN +e·W Ni -f·W Al -W Cr -g·W Co -h·W Mo -i·W Nb -

[0012] j·W Si -k·W Ti -j·W V ;

[0013] P represents a weldability index, a to k represent preset weight coefficients, the value range of a is 35 to 45, the value range of b is 0.5 to 1.5, the value range of c is 3.5 to 4.5, the value range of d is 28 to 35, the value range of e is 3.5 to 5, the value range of f is 1.5 to 2, the value range of g is 1.5 to 2.5, the value range of h is 3 to 6, the value range of i is 5 to 8, the value range of j is 10 to 14, the value range of k is 6 to 10, and W C , W Cu , W Mn , W N , W Ni , W Al , W Cr , W Co , W Mo , W Nb , W Si , W Ti and W V respectively represent the mass percentage of C element, Cu element, Mn element, N element, Ni element, Al element, Cr element, Co element, Mo element, Nb element, Si element, Ti element and V element in the stainless steel base material;

[0014] If P is greater than or equal to 18, it is predicted that the microstructure of the heat-affected zone of the welded joint is single-phase austenite, which has the characteristics of hot cracking sensitivity;

[0015] If 0 is less than or equal to 5, it is predicted that the microstructure of the heat-affected zone of the welded joint is martensite + austenite, which has the characteristics of hard and brittle sensitivity;

[0016] If -6 is less than 0, it is predicted that the microstructure of the heat-affected zone of the welded joint is ferrite + austenite, which has the characteristics of grain growth sensitivity and second phase precipitation sensitivity;

[0017] If -10 is less than -6, it is predicted that the microstructure of the heat-affected zone of the welded joint is martensite + ferrite, which has the characteristics of hard and brittle sensitivity and grain growth sensitivity;

[0018] If P≤-13, the microstructure of the heat-affected zone of the welded joint is predicted to be single-phase ferrite or ferrite+second phase particles, with grain growth sensitivity characteristics and second phase precipitation sensitivity characteristics.

[0019] In some embodiments, the weldability evaluation criteria include:

[0020] If the microstructure of the heat-affected zone of the welded joint is single-phase austenite, the corresponding stainless steel base material has the best weldability;

[0021] If the microstructure of the heat-affected zone of the welded joint is martensite+austenite, the corresponding stainless steel base material has suboptimal weldability;

[0022] If the microstructure of the heat-affected zone of the welded joint is ferrite+austenite, the corresponding stainless steel base material has good weldability under a welding process with low welding heat input;

[0023] If the microstructure of the heat-affected zone of the welded joint is martensite+ferrite, the corresponding stainless steel base material has good weldability under a welding process with low welding heat input;

[0024] If the microstructure of the heat-affected zone of the welded joint is single-phase ferrite or ferrite+second phase particles, the corresponding stainless steel base material has poor weldability, and the weldability becomes worse as the value of P decreases, and the weldability becomes worse as the welding heat input of the welding process increases.

[0025] In some embodiments, the method further includes:

[0026] According to the prediction results of the weldability index, the microstructure of the heat-affected zone of the welded joint, and the weldability characteristics, and in combination with the pre-set weldability evaluation criteria, the welding heat input corresponding to the stainless steel base material is determined.

[0027] In some embodiments, the value of a is 40, the value of b is 1, the value of c is 4, the value of d is 31.5, the value of e is 4.25, the value of f is 1.75, the value of g is 2, the value of h is 4.5, the value of i is 6.5, the value of j is 12, and the value of k is 8.

[0028] In some embodiments, the method is applied to any weldable stainless steel.

[0029] In some embodiments, the weldable stainless steel includes ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, and duplex stainless steel.

[0030] The main advantages of the technical solution of the present application are as follows:

[0031] The welding performance evaluation method based on the composition and microstructure characteristics of the stainless steel base material of the present application can quickly predict the microstructure type of the heat-affected zone of the welded joint corresponding to the stainless steel base material and the welding performance of the stainless steel base material according to the chemical composition of the stainless steel base material, and can provide data support for the development of the welding process of the stainless steel. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. In the drawings:

[0033] Figure 1 A flowchart of a welding performance evaluation method based on the composition and microstructure characteristics of the stainless steel base material provided for the embodiments of the present application is shown in the figure;

[0034] Figure 2 A stainless steel weldability evaluation diagram provided for the embodiments of the present application is shown in the figure;

[0035] Figure 3 A schematic diagram of the microstructure of the heat-affected zone of the welded joint of 6mm thick 00Cr12Ni stainless steel welded by the MAG method provided for the embodiments of the present application is shown in the figure;

[0036] Figure 4 A schematic diagram of the microstructure of the heat-affected zone of the welded joint of 00Cr12Ni stainless steel welded by the plasma welding method provided for the embodiments of the present application is shown in the figure;

[0037] Figure 5 A schematic diagram of the relationship between the precipitation interval and temperature and time of the second phase in the stainless steel provided for the embodiments of the present application is shown in the figure;

[0038] Figure 6 A schematic diagram of the room temperature microstructure of the 1Cr14Ni2 stainless steel base material in the embodiment 1 of the present application is shown in the figure;

[0039] Figure 7 A schematic diagram of the microstructure of the heat-affected zone of the welded joint of 1Cr14Ni2 stainless steel in the embodiment 1 of the present application is shown in the figure. DETAILED DESCRIPTION

[0040] To make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in detail with reference to the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0041] The technical solutions provided by the embodiments of the present application will be described in detail below with reference to the drawings.

[0042] Reference Figure 1 The embodiment of the present application provides a welding performance evaluation method based on the composition and the organization characteristics of the stainless steel base material, which comprises the following steps:

[0043] Obtaining the chemical composition of the stainless steel base material;

[0044] According to the chemical composition of the stainless steel base material, the weldability index is calculated through the weldability index empirical formula;

[0045] According to the weldability index, the organization and the weldability characteristics of the heat affected zone of the welded joint corresponding to the stainless steel base material are predicted;

[0046] According to the prediction results of the weldability index, the organization and the weldability characteristics of the heat affected zone of the welded joint, and combining with the preset weldability evaluation standard, the welding performance is determined.

[0047] In the embodiment of the present application, the weldability index empirical formula is expressed as:

[0048] P=a·W C +b·W Cu +c·W Mn +d·W N +e·W Ni -f·W Al -W Cr -g·W Co -h·W Mo -i·W Nb -

[0049] j·W Si -k·W Ti -j·W V ;

[0050] P represents the weldability index, a~k represents the preset weight coefficient, the value range of a is 35~45, the value range of b is 0.5~1.5, the value range of c is 3.5~4.5, the value range of d is 28~35, the value range of e is 3.5~5, the value range of f is 1.5~2, the value range of g is 1.5~2.5, the value range of h is 3~6, the value range of i is 5~8, the value range of j is 10~14, the value range of k is 6~10, W C , W Cu , W Mn , W N , W Ni , W Al , W Cr , W Co , W Mo , W Nb , W Si , WTi and W V respectively represent the mass percentage of C element, Cu element, Mn element, N element, Ni element, Al element, Cr element, Co element, Mo element, Nb element, Si element, Ti element and V element in the stainless steel base material;

[0051] In the embodiment of the present application, if P is greater than or equal to 18, the microstructure of the heat-affected zone of the welded joint is predicted to be single-phase austenite, which has the characteristic of hot cracking sensitivity;

[0052] If 0 is less than or equal to 5, the microstructure of the heat-affected zone of the welded joint is predicted to be martensite + austenite, which has the characteristic of hard and brittle sensitivity;

[0053] If -6 is less than 0, the microstructure of the heat-affected zone of the welded joint is predicted to be ferrite + austenite, which has the characteristics of grain growth sensitivity and second phase precipitation sensitivity;

[0054] If -10 is less than -6, the microstructure of the heat-affected zone of the welded joint is predicted to be martensite + ferrite, which has the characteristics of hard and brittle sensitivity and grain growth sensitivity;

[0055] If P is less than or equal to -13, the microstructure of the heat-affected zone of the welded joint is predicted to be single-phase ferrite or ferrite + second phase particles, which has the characteristics of grain growth sensitivity and second phase precipitation sensitivity.

[0056] In the embodiment of the present application, by analyzing the main chemical components of the stainless steel, and then combining the welding index empirical formula to predict the microstructure and performance of the heat-affected zone of the welded joint, the type and distribution of the main phase (phase ratio ≥ 50%), the secondary phase (phase ratio ≥ 5% and ≤ 50%) and the second phase particles (volume fraction ≤ 1%) in the stainless steel are determined, the type of the stainless steel is determined, and the welding performance of the stainless steel is determined. In the stainless steel, the main phase includes ferrite, austenite, martensite; the second phase particles include intermetallic compounds such as σ phase, Laves phase, χ phase, Cr 23 C6, Cr7C3, CrN, Cr2C, Cu-rich ε phase, niobium and titanium carbonitride. From the perspective of weldability, the following weldability characteristics are defined for stainless steel: hot cracking sensitivity, hard and brittle sensitivity, grain growth sensitivity, and second phase precipitation sensitivity. Among them, hot cracking sensitivity, hard and brittle sensitivity, and grain growth sensitivity are performance deterioration characteristics, and whether second phase precipitation sensitivity is a performance deterioration characteristic or a performance optimization characteristic depends on the actual situation.

[0057] Reference Figure 2 , Figure 2 The stainless steel weldability evaluation diagram provided in the embodiment of the present application. In the attached Figure 2In the present application, feature A represents a hot cracking sensitivity feature, feature B represents a hard and brittle sensitivity feature, feature C represents a grain growth sensitivity feature, and feature D represents a second phase precipitation sensitivity feature. In the present application, the weldability evaluation criteria correspond to the weldability evaluation diagram of the stainless steel shown in FIG. 1. Figure 2

[0058] Specifically, in the present application, the weldability evaluation criteria include:

[0059] If the microstructure of the heat-affected zone of the welded joint is single-phase austenite, the corresponding stainless steel base material has the best weldability;

[0060] If the microstructure of the heat-affected zone of the welded joint is martensite + austenite, the corresponding stainless steel base material has suboptimal weldability;

[0061] If the microstructure of the heat-affected zone of the welded joint is ferrite + austenite, the corresponding stainless steel base material has good weldability under a welding process with low welding heat input;

[0062] If the microstructure of the heat-affected zone of the welded joint is martensite + ferrite, the corresponding stainless steel base material has good weldability under a welding process with low welding heat input;

[0063] If the microstructure of the heat-affected zone of the welded joint is single-phase ferrite or ferrite + second phase particles, the corresponding stainless steel base material has poor weldability, and the weldability becomes worse as the P value decreases and as the welding heat input of the welding process increases.

[0064] In combination with the accompanying drawings, Figure 2 In the present application, low welding heat input means welding heat input less than 1.5 KJ / mm, and high welding heat input means welding heat input greater than or equal to 1.5 KJ / mm.

[0065] Further, in the present application, the method further includes: according to the weldability index, the microstructure of the heat-affected zone of the welded joint, and the prediction result of the weldability feature, in combination with the preset weldability evaluation criteria, determining the corresponding welding heat input of the stainless steel base material.

[0066] Specifically, if the microstructure of the heat-affected zone of the welded joint is ferrite + austenite, the welding heat input is selected to be 0-1.5 KJ / mm; if the microstructure of the heat-affected zone of the welded joint is martensite + ferrite, the welding heat input is selected to be 0-1.5 KJ / mm; and if the microstructure of the heat-affected zone of the welded joint is single-phase ferrite or ferrite + second phase particles, the welding heat input is selected to be 0-1.5 KJ / mm.

[0067] ​Further, in the embodiments of the present application, in order to facilitate the calculation of the weldability index and ensure the accuracy and reliability of the predicted microstructure type and weldability characteristics of the heat-affected zone of the welded joint of the stainless steel base material according to the weldability index, the value of a is 40, the value of b is 1, the value of c is 4, the value of d is 31.5, the value of e is 4.25, the value of f is 1.75, the value of g is 2, the value of h is 4.5, the value of i is 6.5, the value of j is 12, and the value of k is 8.

[0068] In the embodiments of the present application, the microstructure types of the stainless steel are determined according to the weldability index, and the weldability of the stainless steel of different microstructure types is summarized as follows: Figure 2 The weldability of the stainless steel of different microstructure types determined by the weldability index is summarized as follows:

[0069] Weldability of austenitic stainless steel (P≥18)

[0070] In the welding process, the phase of the austenitic stainless steel does not change, the heat-affected zone does not change, and the grain does not obviously coarsen, so that post-weld heat treatment is not required. The austenitic grain coarsening tendency of the heat-affected zone is small, and the austenitic stainless steel has excellent mechanical properties and corrosion resistance. When the austenitic stainless steel contains other harmful elements, thermal cracks are easily generated in the heat-affected zone, which leads to joint failure, which is a problem that needs to be paid attention to in the welding of austenitic stainless steel. In addition, the solubility of gap elements such as C and N in austenite is large, so the second phase particle precipitation problem is not significant. The chromium carbide formed by carbon and chromium reduces the corrosion resistance of the stainless steel, and short-term heating in the temperature range of 425-900°C will cause the generation of sensitization phenomenon, which can be eliminated by heating at 980-1180°C and then rapidly cooling.

[0071] Weldability of low-carbon martensitic stainless steel (0≤P≤5)

[0072] The martensite in stainless steel has high strength and hardness. The low carbon lath martensite stainless steel has good weldability and the performance can be further improved by post-weld heat treatment. It is widely used in the water and electricity industry and the mechanical manufacturing industry for components with low corrosion resistance requirements. The as-welded microstructure of the heat affected zone of the weldable martensitic stainless steel weld joint is mainly martensite, with a small amount of austenite and high temperature ferrite, and has good mechanical properties. In order to further improve the weldability, appropriate post-weld heat treatment process (PWHT) must be adopted. For example, the 13Cr4NiMo super martensitic stainless steel weld joint is quenched after 950°C x 1h holding to eliminate δ ferrite, and then is double tempered at 750°C x 2h and 650°C x 2h, so that the δ ferrite in the microstructure is completely eliminated, the martensite is fully tempered and inverse austenite is formed, and the proportion of austenite phase is increased by more than 2 times (from about 8% to 22%), and the low temperature impact toughness is also increased by more than 2 times (the impact toughness at -77°C is increased from 18J to 64J), and the hardness is reduced from HRC37 to HRC25, and the yield strength is reduced from 1136MPa to 722MPa, and the performance reaches the optimum. At this time, the room temperature microstructure obtained is (inverse) austenite and tempered martensite. In general, the low carbon martensitic stainless steel has good weldability.

[0073] Ferrite + austenite duplex stainless steel weldability (-6≤P<0)

[0074] The ferrite + austenite type stainless steel is called duplex stainless steel, which has high corrosion resistance, high strength and hardness, etc. The most ideal phase proportion of this type of stainless steel is 50% each, and typical grades are 2304, 2205 and 2507, etc. The duplex structure has the advantages of ferrite phase and austenite phase respectively, and makes up for their respective shortcomings. The ferrite can disrupt the crystal direction of the austenite, and the hot crack sensitivity is lower than that of the austenitic steel; the austenite has more soluble hydrogen, and the hydrogen-induced cold cracking tendency is low, but due to the existence of brittle σ phase (700-950°C) and 475°C brittleness (α' phase), appropriate welding heat input and cooling rate should be adopted during welding. When the post-weld rapid cooling is adopted, more high-temperature formed ferrite phase will remain at room temperature, which is easy to cause the corrosion resistance and embrittlement of the welded joint to decrease. If the σ phase and α' phase (475°C brittleness) are found after the post-weld inspection, they can be eliminated by solid solution treatment. Therefore, under the premise of adopting appropriate welding process, the duplex stainless steel has good weldability.

[0075] Ferrite + low carbon martensite two-phase structure stainless steel weldability (-10≤P<-6)

[0076] This type of stainless steel chromium content is generally 11-14%, into the α+γ two-phase region at 850~1150 ℃ temperature range, at 1020 ℃ austenite phase maximum volume fraction can reach 92%. In order to obtain good weldability, control C content is less than 0.01%, increase the manganese content, and add a small amount of nickel element, obtain room temperature structure for ferrite + martensite two phase structure of stainless steel, typical brand such as 1.4003, 3CR12 etc. The type of stainless steel has ferrite grain coarsening sensitivity and martensite brittle hard, under the premise of taking appropriate welding process, can obtain good welding joint structure and performance.

[0077] Reference Figure 3 , Figure 3 The welding joint heat affected zone microstructure diagram of 6mm thickness 00Cr12Ni stainless steel welded by MAG method provided by the embodiment of the present application, the welding heat input is 0.8KJ / mm, and the welding wire used is austenitic E308LSi welding wire. It can be seen that the martensite phase in the two phase structure plays a role in preventing the ferrite grain from excessive coarsening, and the austenite phase formed in the α+γ two phase region during the welding thermal cycle is transformed into low carbon martensite structure during the post welding rapid cooling process, so the proportion of martensite phase in the heat affected zone increases significantly. Impact test shows that the average value of the heat affected zone impact energy of the half specimen at-20 ℃ is 20J. Reference Figure 4 , Figure 4 The welding joint heat affected zone microstructure diagram of 00Cr12Ni stainless steel welded by plasma welding method provided by the embodiment of the present application, the welding heat input is 1.5KJ / mm, because the welding process is different, the heat affected zone experiences different welding thermal cycles, the plasma welding heat input and energy density are larger, and the cooling speed is smaller than that of the MAG method, so the welding joint obtained not only has small martensite proportion, but also has coarse ferrite grain, which has an adverse effect on plasticity and toughness, and the heat affected zone is also brittle at room temperature. Therefore, the ferrite + low carbon martensite two phase structure stainless steel is not suitable for using welding process with large heat input.

[0078] Ferritic stainless steel weldability (P≤-13)

[0079] The single phase structure ferritic stainless steel has a relatively simple structure, no phase change occurs in the heat affected zone during the welding thermal cycle, and because it is sensitive to heat input, the grain coarsening tendency of the heat affected zone is large during the welding thermal cycle, the smaller the P value is, the larger the grain coarsening tendency is, and the worse the performance of the welding joint is, and the worse the weldability is. Therefore, the thickness of the stainless steel that can be welded is generally less than 3mm. In order to improve the performance of the welding joint, by adding alloy elements such as niobium and titanium, second phase particles can be precipitated in the ferrite matrix, which can inhibit the grain growth to a certain extent.

[0080] Second phase precipitation characteristics in stainless steel welding

[0081] Reference Figure 5 , Figure 5 The schematic diagram of the relationship between the precipitation range of the second phase in the stainless steel and the temperature and time provided by the embodiment of the present application, the second phase particles in the stainless steel include intermetallic compounds such as sigma phase, Laves phase, chi phase, Cr 23 C6, Cr7C3, CrN, Cr2C, Cu-rich epsilon phase, carbonitride of niobium and titanium, etc. The type of the second phase particle precipitation depends on the chemical composition of the stainless steel, and the temperature and time.

[0082] The effect of the second phase precipitation on the welded joint depends on the type, distribution and size, etc., which can be summarized as follows:

[0083] The inhibition ability of the precipitated phase particles to the grain growth can be expressed as:

[0084] P z =(3 / 2)(f v γ i / d);

[0085] Wherein, P z represents the inhibition ability value of the precipitated phase particles to the grain growth, f v represents the volume fraction of the second phase particles, γ i represents the grain boundary energy, and d represents the average diameter of the particles.

[0086] The resistance of the second phase particles to the grain growth can be expressed as:

[0087] A=3f v / d;

[0088] Wherein, A represents the resistance value of the second phase particles to the grain growth, f v represents the volume fraction of the second phase particles, and d represents the average diameter of the particles.

[0089] According to the above formula, the greater the volume fraction of the second phase particles and the smaller the average diameter of the particles, the stronger the ability to inhibit the grain coarsening, and the greater the grain boundary energy. At high temperature, the driving force of the grain growth is offset or weakened under the interaction between the grain boundary and the particles, so that the grain will not be excessively coarsened, thereby ensuring the plasticity and toughness of the stainless steel welded joint. If there is a higher tendency of sigma phase or Laves phase precipitation in the stainless steel, or large particles of titanium nitride, etc., the performance of the heat-affected zone will be deteriorated by the second phase precipitation.

[0090] Further, in the embodiment of the present application, the method can be applied to any weldable stainless steel.

[0091] The weldable stainless steel includes ferrite stainless steel, austenitic stainless steel, martensitic stainless steel, and duplex stainless steel.

[0092] The welding performance evaluation method based on the composition and structure characteristics of the stainless steel base material can quickly predict the structure type of the heat-affected zone of the welded joint corresponding to the stainless steel base material and the welding performance of the stainless steel base material according to the chemical composition of the stainless steel base material, and can provide data support for the welding process of the stainless steel.

[0093] To make the above technical solutions of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments.

[0094] Example 1

[0095] In this embodiment 1, the welding performance evaluation method provided by the present application is used to predict the welding performance of 1Cr14Ni2 stainless steel, and welding test is performed on the 1Cr14Ni2 stainless steel.

[0096] Reference Figures 6-7 1Cr14Ni2 stainless steel is a low-carbon martensitic stainless steel with good weldability, and the chemical composition of the test material is 0.14C-0.4Si-0.64Mn-13.64Cr-1.84Ni (wt%), the room temperature structure is lath martensite + a small amount of second phase particles, and the heat treatment state is 950℃×1h (oil cooling) + 650℃×2h (air cooling). The 1Cr14Ni2 stainless steel base material has excellent mechanical properties, with a yield strength of 775MPa, a fracture strength of 875MPa, an elongation of 19% after fracture, and a hardness of HB269. According to the empirical formula for calculating the welding index, the corresponding P value is 3.2, so the weldability is good, and there is a tendency of brittleness and hardness. Based on the calculated P value, it is predicted that the structure of the welding heat-affected zone is mainly martensite and contains a small amount of austenite, and the austenitic welding material E308L is used for welding test, and the heat input is 1.2KJ / mm. The results show that the grains in the heat-affected zone of the as-welded welded joint do not coarsen obviously, and the impact test results show that the average impact energy of the heat-affected zone at room temperature, -20℃ and -40℃ (the sample size is 7.5×10×55mm 3 ) is 82J, 65J and 45J respectively. The heat-affected zone of the welded joint has good low-temperature impact toughness, and the tensile test results show that the fracture position is in the weld, and the fracture strength is 699MPa, indicating that the strength of the heat-affected zone of the joint is not reduced. In addition, if post-weld heat treatment (PWHT) is performed, the performance of the joint can be further improved.

[0097] According to the test results, it can be seen that the welding performance predicted by the welding performance evaluation method provided in the embodiments of the present application is basically consistent with the test results.

[0098] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms“front”,“rear”,“left”,“right”,“upper”, and“lower” as used herein refer to the positions of the elements as shown in the figures.

[0099] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for evaluating the weldability of stainless steel base material based on its composition and microstructure, characterized in that, include: Obtain the chemical composition of stainless steel base material; The weldability index is calculated based on the chemical composition of the stainless steel base material using an empirical formula. Predict the microstructure and weldability characteristics of the heat-affected zone of the welded joint corresponding to the stainless steel base material based on the weldability index; Based on the predicted results of weldability index, microstructure of heat-affected zone of weld joint and weldability characteristics, and in conjunction with the preset weldability evaluation criteria, the welding performance is determined. The empirical formula for the weldability index is expressed as follows: P=a·W C +b·W Cu +c·W Mn +d·W N +e·W Ni -f·W Al -W Cr -g·W Co -h·W Mo -i·W Nb -j·W Si - k·W Ti -j·W V ; P represents the weldability index, a to k represent preset weighting coefficients, with a ranging from 35 to 45, b from 0.5 to 1.5, c from 3.5 to 4.5, d from 28 to 35, e from 3.5 to 5, f from 1.5 to 2, g from 1.5 to 2.5, h from 3 to 6, i from 5 to 8, j from 10 to 14, and k from 6 to 10. W C W Cu W Mn W N W Ni W Al W Cr W Co W Mo W Nb W Si W Ti and W V These represent the mass percentages of C, Cu, Mn, N, Ni, Al, Cr, Co, Mo, Nb, Si, Ti, and V in the stainless steel base material, respectively. If P≥18, the microstructure of the heat-affected zone of the welded joint is predicted to be single-phase austenite, which has the characteristics of hot cracking sensitivity. If 0≤P≤5, the predicted microstructure of the heat-affected zone of the welded joint is martensite + austenite, which has the characteristics of hardness and brittleness sensitivity. If -6≤P<0, the predicted microstructure of the heat-affected zone of the welded joint is ferrite + austenite, with grain growth sensitivity and second phase precipitation sensitivity characteristics. If -10≤P<-6, the predicted microstructure of the heat-affected zone of the welded joint is martensite + ferrite, which has the characteristics of hard brittleness sensitivity and grain growth sensitivity. If P≤-13, the microstructure of the heat-affected zone of the welded joint is predicted to be single-phase ferrite or ferrite + second-phase particles, exhibiting characteristics of grain growth sensitivity and second-phase precipitation sensitivity.

2. The welding performance evaluation method based on the composition and microstructure characteristics of stainless steel base material according to claim 1, characterized in that, The weldability evaluation criteria include: If the microstructure of the heat-affected zone of the welded joint is single-phase austenite, then the corresponding stainless steel base material has the best weldability. If the microstructure of the heat-affected zone of the welded joint is martensite + austenite, then the weldability of the corresponding stainless steel base material is second best. If the microstructure of the heat-affected zone of the welded joint is ferrite + austenite, then the corresponding stainless steel base material has good weldability under welding processes with low welding heat input. If the microstructure of the heat-affected zone of the welded joint is martensite + ferrite, then the corresponding stainless steel base material has good weldability under welding processes with low welding heat input. If the microstructure of the heat-affected zone of the welded joint is single-phase ferrite or ferrite + second-phase particles, the weldability of the corresponding stainless steel base material is poor. The weldability worsens as the P value decreases and the weldability also worsens as the welding heat input of the welding process increases.

3. The welding performance evaluation method based on the composition and microstructure characteristics of stainless steel base material according to claim 1, characterized in that, The method further includes: Based on the predicted results of weldability index, microstructure of heat-affected zone of weld joint and weldability characteristics, and in conjunction with the preset weldability evaluation criteria, the corresponding welding heat input for stainless steel base material is determined.

4. The welding performance evaluation method based on the composition and microstructure characteristics of stainless steel base material according to claim 1, characterized in that, The values ​​of a are 40, b is 1, c is 4, d is 31.5, e is 4.25, f is 1.75, g is 2, h is 4.5, i is 6.5, j is 12, and k is 8.

5. The method for evaluating weldability based on the composition and microstructure of stainless steel base material according to claim 1, characterized in that, The method is applicable to any type of weldable stainless steel.

6. The method for evaluating weldability based on the composition and microstructure of stainless steel base material according to claim 5, characterized in that, The weldable stainless steels include: ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, and duplex stainless steel.

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