CN107138876B - A low-nickel copper-containing T/P92 steel welding material with high temperature creep resistance - Google Patents

Abstract

The invention provides a low-nickel copper-containing T/P92 steel welding material with high temperature creep resistance, which is characterized in that it includes components C, Mn, Si, Cr, Ni, W, Mo, Nb, V, N, B , Al, Ti, S, P, Fe and Cu, the copper content (wt.%) in the welding material is: 0.8‑1.5. The welding material of the invention adds copper, reduces the nickel element content, does not add the precious element cobalt, reduces the material cost, and the deposited metal of the welding material suppresses the formation of ferrite, while avoiding the significant reduction of the A _C1 point, and its normal temperature mechanical properties The performance reaches or exceeds the existing high nickel or cobalt-added T/P92 steel welding material; the welding material of the invention has excellent high temperature creep resistance, and the long-term permanent fracture life of the deposited metal is closest to the average value of P92 steel .

Description

A low-nickel copper-containing T/P92 steel welding consumable with high temperature creep resistance

technical field

The invention belongs to the technical field of heat-resistant steel, and in particular relates to a high-temperature creep-resistant T/P92 steel welding material for an ultra-supercritical thermal power unit.

Background technique

T/P92 steel is a new type of martensitic heat-resistant steel obtained by adding a certain amount of tungsten element on the basis of T/P91 steel, appropriately reducing the content of molybdenum element, and adding a trace amount of boron element. Thick-walled pipes such as main steam pipes and headers of critical units, as well as heating surface pipes such as superheaters and reheaters, the casting materials (C92) are also used to manufacture cylinders and valves. At present, the main methods of welding T/P92 steel are manual arc welding (SMAW), submerged arc welding (SAW) and tungsten argon arc welding (GATW).

Compared with T/P91 steel, T/P92 steel adds more high-temperature strengthening element tungsten, and its welding material deposited metal or weld is easy to form δ-ferrite during the solidification process, which reduces the impact toughness of the material. and high temperature creep strength. Therefore, preventing the formation of delta-ferrite in the deposited metal or weld is the primary problem to be solved in the design of T/P92 steel welding consumables. At present, there are two composition design methods to suppress the formation of delta-ferrite in the deposited metal of T/P92 steel welding consumables. One method is to increase the content of manganese and nickel in the deposited metal, such as Bole Welding Group (formerly Thyssen Welding) MTS616 series electrodes and wires, Chromet 92 electrodes and 9CrWV electrodes from Manchester Welding Materials, UK, etc.; another method adds cobalt elements that are not found in the base metal in the deposited metal, such as Swiss Olinkon ALCROMOCORD 92 welding rod and ALCROMO WF 92 welding wire, Kobelco's CR-12S welding rod and US-12CRSD welding wire, etc. The disadvantage of the former composition design method is that manganese and nickel are both elements that expand the austenite phase region. Increasing their content will significantly reduce the A _C1 point of the deposited metal, and there is a risk of re-formation of austenite during post-weld heat treatment. For this reason, the upper limit content of Mn+Ni has to be limited, resulting in the residual δ-ferrite in the deposited metal. In addition, increasing the nickel content has a detrimental effect on the high temperature long-term creep properties of the material. Although the latter composition design method has little effect on the point A _C1 of the deposited metal, the price of cobalt is expensive, which increases the cost of the welding material. Therefore, it is necessary to provide a special welding material for T/P92 steel which can not only suppress the formation of delta-ferrite in the deposited metal, but also has a high A _C1 point of the deposited metal, excellent high temperature creep resistance and low cost.

SUMMARY OF THE INVENTION

For the problems existing in the prior art, the technical solutions adopted by the present invention for solving the problems existing in the prior art are as follows:

A low-nickel copper-containing T/P92 steel welding material with high temperature creep resistance, characterized in that: the welding material includes the following components: C, Mn, Si, Cr, Ni, W, Mo, Nb, V, N, B, Al, Ti, S, P, Fe and Cu.

The copper content (wt.%) in the welding material is: 0.8-1.5.

The content (wt.%) of each component in the welding material is: C 0.07-0.12, Mn 0.30-0.60, Si≤0.40, Cr8.50-9.50, Ni≤0.40, W 1.50-2.00, Mo 0.30-0.60 , Cu 0.8-1.5, Nb 0.04-0.07, V 0.15-0.25, N 0.03-0.07, B 0.001-0.005, Al≤0.03, Ti≤0.01, S≤0.01, P≤0.02, and the remainder is Fe.

The technical scheme of the invention is to obtain the minimum copper content required to inhibit the formation of δ-ferrite by calculating the chromium equivalent of the deposited metal and optical metallographic observation and analysis; quantitatively study the effect of copper content on the deposited metal through material thermodynamic calculation and thermal expansion method The influence of A and _C1 points; the influence of copper content on the creep properties of the deposited metal is studied by high temperature creep rupture test, and the distribution and size of copper particles in the deposited metal creep sample are studied by microscopic analysis experiments such as electron microscopy, so as to master the copper content. The high temperature strengthening mechanism of elements in T/P92 steel determines the copper content range with the best strengthening effect. Based on the research results of the above three aspects, the copper content range of the welding consumables for copper-containing T/P92 steel is determined, and the content of austenitizing elements such as manganese and nickel is adjusted accordingly.

The composition characteristics of the deposited metal of the T/P92 steel welding material for high temperature creep resistance of the present invention consider the following factors:

Carbon: C is an austenite stabilizing element, which can stabilize the tempered martensite microstructure and form carbides to improve creep strength. When the C content is lower than 0.07%, the weld is easy to form delta-ferrite, and the number of carbides is small, which is not good for the creep strength. But the C content is too high, which increases the susceptibility to welding cracks, so the C content of the present invention is controlled in the range of 0.07-0.12%.

Manganese and nickel: Mn is an austenite stabilizing element, which is beneficial to inhibit δ-ferrite, and at the same time, Mn has the effect of deoxidation and desulfurization, which can increase the strength and toughness of the weld. However, too high Mn content significantly reduces the A _C1 point of the weld, resulting in the re-formation of austenite in the weld at the highest post-weld heat treatment temperature, and more than 1.5% Mn content significantly reduces the creep strength. Ni is also an austenite forming element, which has a positive effect on inhibiting the formation of δ-ferrite and stabilizing the martensite structure, so it can improve the impact toughness of the weld. In order to suppress the formation of delta-ferrite in the welds of new 9% Cr hot-strength steels such as T/P91 and T/P92, the European BS EN standard specifies a maximum Ni content of 0.8% or even 1.0%, which is significantly higher than that of T/P91, The upper limit of the Ni content of T/P92 steel (0.4%). However, increasing the Ni content significantly reduces the A _C1 point, resulting in the re-formation of austenite in the weld at the highest post-weld heat treatment temperature. In addition, studies have shown that when the Ni content in high-chromium hot-strength steel exceeds 0.4%, accelerated long-term The coarsening of M ₂₃ C ₆ -type carbides and the formation of Z phase during the creep process reduce the creep performance. Taking all into consideration, the present invention controls the Mn content within 0.30-1.0%, the Ni content within 0.40%, and the total content of Mn+Ni under 1.0%, which is better than the current foreign brands such as MTS616, Chromet 92 and 9CrWV T/P92 The Ni content and the total content of Mn+Ni in the deposited metal of the steel welding material are reduced by about 50%.

Silicon: Si is an important deoxidizer and can improve the oxidation resistance of welds. Appropriately low Si content is beneficial to improve the toughness of the weld metal. According to some technical standards in the United States, the Si content of the weld should be less than 0.30%. The Si content of the present invention is controlled at 0.1%-0.40%, which is higher than that of P92 steel. The upper limit (0.5%) is lower.

Chromium: Cr is the most important element to guarantee resistance to steam oxidation and hot corrosion. As the Cr content increases, the steam corrosion resistance of the weld is better. However, Cr is a ferrite-forming element, and if its content is too high, delta-ferrite will be generated in the weld, reducing the impact toughness and creep strength of the weld. Therefore, the Cr content of the present invention is controlled at 8.5-9.5%.

Tungsten and Molybdenum: Both W and Mo are ferrite forming elements, which are not conducive to preventing the formation of delta-ferrite in welds, but they are the most important solid solution strengthening elements in T/P92 steel and can improve the stability of carbides Sex and play an indirect reinforcement role. In order to ensure the high temperature creep strength of the welded seam, the W and Mo content ranges of the present invention are equivalent to those of T/P92 steel, which are 1.5-2.0% and 0.3-0.6% respectively.

Copper: Adding Cu is the main innovation point of the present invention, because neither the T/P92 steel nor the existing T/P92 steel welding material deposited metal does not contain Cu. The main functions of Cu are: Cu is an austenite-forming element, which can inhibit the formation of delta-ferrite in the weld. In addition, the inventor's experimental study shows that the copper-containing T/P92 steel weld undergoes post-weld heat treatment. , the solid solution Cu in the welding state is precipitated as ε-Cu particles, which are dispersed in the lath and at the lath boundary, and the number density at the lath boundary is higher, as shown in Figure 1. Therefore, like M ₂₃ C ₆ type carbides, it can prevent the migration of subgrain boundaries and improve the creep strength during long-term creep, as shown in Fig. 2. The determination of the Cu content range needs to consider three factors: inhibiting the formation of ferrite, giving full play to its high-temperature strengthening effect, and avoiding the obvious reduction of the A _C1 point. The present invention determines its content range in this way: according to the calculation method of ferrite content determined according to the chromium equivalent concept (refer to Chinese patent ZL201210192206.X), in terms of the ability to inhibit the formation of ferrite, Cu is equivalent to Co, which is about 1.5 of that of Mn. times, about 60% of Ni, that is, to maintain the same effect of inhibiting ferrite, every 1% of Cu added to the weld can reduce 1.5% of Mn, or 0.6% of Ni. For the effect of high temperature strengthening, when the Cu content is less than 0.5%, the Cu element is basically solid-dissolved in the matrix, the amount of ε-Cu precipitated is very small, and the precipitation strengthening effect is not large; experimental studies show that when the Cu content exceeds 1.5% , ε-Cu aggregates and coarsens during long-term creep (Fig. 3 and Fig. 4), which not only weakens the strengthening effect, but also reduces the permanent plasticity. Regarding the influence of Cu content on the A _C1 point, although Cu is an element that expands the austenite phase region and reduces the A _C1 point, the patent No. ZL201210131877.5 shows that the reduction of the A _C1 point by Cu is smaller than that of Mn and Ni. , the thermodynamic calculation and actual measurement results show that when the Cu content exceeds 0.7%, continuing to increase the Cu content has little effect on the A _C1 point, as shown in Figures 5-7. Comprehensively considering the copper addition amount of the above three factors, the copper content range of the present invention is finally determined as: 0.8-1.5%.

Niobium: Nb is a strong carbide forming element. It forms finely dispersed MX-type second phase precipitates with C and N, which are very stable at high temperature, thereby improving the high temperature creep strength of the weld. When its content is less than 0.04%, the amount of precipitates is small, and sufficient strengthening effect cannot be obtained, but it is found that high Nb content reduces the impact toughness of the weld. Therefore, in the present invention, the Nb content is controlled at 0.04%-0.07%, and the upper limit is slightly lower than 0.09% of T/P92 steel.

Vanadium: V is a strong carbide forming element. It forms fine, dispersed and stable MX-type second phase precipitates with C and N to improve the high temperature creep strength of the weld. It has little effect on the toughness of the weld. In order to ensure the high temperature creep resistance of the weld, the V content of the present invention is equivalent to that of T/P92 steel, and is controlled at 0.15%-0.25%.

Nitrogen: N forms finely dispersed MX-type second phase precipitates with Nb and V, which significantly improves the high temperature creep strength of the weld. It has little effect on the toughness of the weld. In order to ensure the high temperature creep resistance of the weld, the N content of the present invention is equivalent to that of T/P92 steel, and is controlled at 0.04%-0.07%.

Boron: B is a grain boundary strengthening element, which can improve the high temperature creep strength of the weld, but boron is easy to burn during the welding process. In order to ensure the high temperature creep resistance of the weld, the B content of the present invention is controlled at 0.001%-0.005%, which is slightly lower than the upper limit (0.006%) of T/P92 steel.

Aluminum: Al is added as a deoxidizer in the welding material, and the residual Al content in the weld is too high, which reduces the permanent plasticity of the weld. In addition, Al is easy to preferentially combine with N, so that the solid solution of N in the weld is approximately zero, and the precipitation strengthening effect cannot be formed, which reduces the high temperature creep strength of the weld. For this reason, the Al content of the present invention is controlled to be less than 0.03%.

Titanium: Ti is a very strong carbide forming element, which affects the combination of Nb and V with C and N, and forms TiN once, which is not conducive to precipitation strengthening. Therefore, the Ti content of the present invention is controlled to be less than 0.01%.

Sulfur and Phosphorus: S and P are unavoidable impurity elements in welds, which increase the crack tendency of welds and reduce the creep fracture plasticity of welds. Therefore, the present invention controls the S and P contents within 0.01% and 0.02%, respectively.

The present invention has the following advantages:

(1) The welding material of the present invention adds copper, reduces the content of nickel element, does not add the precious element cobalt, reduces the material cost, and the deposited metal avoids the significant reduction of the A _C1 point while suppressing the formation of ferrite, and Its normal temperature mechanical properties reach or exceed the existing high nickel or cobalt T/P92 steel welding consumables;

(2) The welding material of the present invention has excellent high temperature creep resistance, and the long-term permanent fracture life of the deposited metal is closest to the average value of P92 steel.

Description of drawings

Fig. 1 Precipitation phase of the welding material deposited metal of the present invention after tempering at 760°C × 4h;

Fig. 2 Precipitation phase after the 650°C/100MPa/4897.1h endurance test of the welding material embodiment of the present invention;

Fig. 3 Precipitation phase of the deposited metal of T/P92 welding material containing 1.69% Cu after tempering at 760℃×4h;

Fig. 4 Precipitates of the deposited metal of T/P92 welding consumables containing 1.69% Cu after the endurance test at 650℃/100MPa/3896.5h;

Figure 5 shows the thermodynamic calculation results of the effect of copper content on the A _C1 point of the P92 weld;

Fig. 6 The actual measurement result of thermal expansion method of the deposited metal A _C1 point of the welding material embodiment of the present invention;

Fig. 7 is the thermal expansion method actual measurement result of the deposited metal A _C1 point of the comparative example of the welding material of the present invention;

Fig. 8 is the microstructure (electrode arc welding) of the deposited metal of the welding material of the present invention after tempering at 760°C × 4h;

FIG. 9 is a comparison of the permanent fracture time at 650°C/100MPa between the embodiment of the welding material of the present invention and the comparative example;

Detailed ways

The technical solutions of the present invention are further described in detail below through the examples and in conjunction with the accompanying drawings, as shown in Figures 1-9:

It can be seen from Fig. 1 that after the welding material deposited metal of the present invention is tempered at 760°C × 4h, in addition to the precipitation of M ₂₃ C ₆ type carbides on the martensitic lath boundary, finer ε-Cu particles are also precipitated .

It can be seen from Fig. 2 that the ε-Cu particles on the martensitic lath boundary are very stable after creeping at 650°C/100MPa/4897.1h of the welding material deposited metal of the present invention, and there is no obvious aggregation and growth.

It can be seen from Fig. 3 and Fig. 4 that when the Cu content in the T/P92 weld exceeds 1.5%, the ε-Cu precipitated on the martensitic lath boundary of the weld metal after tempering at 760°C × 4h Although the particles are relatively small, they have obvious aggregation and growth after the endurance test at 650℃/100MPa/3896.5h.

It can be seen from Fig. 5 that when the Cu content exceeds 0.7%, the Cu content continues to increase, which has little effect on the A _C1 point.

It can be seen from FIG. 6 that the A _C1 point of the welding material of the present invention is 809° C., which is 49° C higher than the post-weld heat treatment temperature (760° C.), which satisfies that the post-weld heat treatment temperature is 20-30° C lower than the A _C1 point. The above requirements have a large margin.

It can be seen from Figure 7 that the A _C1 point of the weld metal of the welding material containing 1.69% Cu is 805 ° C, which is not much different from the A _C1 point of the weld metal containing 0.86 Cu%. The experiment has confirmed that when the Cu content exceeds 0.7% When the Cu content continues to increase, it has almost no effect on the A _C1 point of the T/P92 weld metal.

It can be seen from FIG. 8 that the weld metal of the welding material of the present invention is a tempered lath martensite structure without ferrite.

It can be seen from Figure 9 that the T/P92 steel welding material weld metal (1#) of the present invention has the longest lasting life at 650°C/100MPa, which exceeds the average value of the lasting life of T/P92 steel, and is significantly higher than the existing high Nickel or cobalt-added T/P92 steel welding consumables weld metal (5#-7#).

The lasting life of the T/P92 welding material deposited metal (4#) containing 1.69% Cu is lower than that of 1#, indicating that when the Cu content exceeds the upper limit of the present invention (1.5%), the adverse effect on the lasting performance is greater.

The microstructure characteristics and properties of the deposited metal of the welding material after tempering at 760℃×4h are designed according to the material composition ratio in the technical solution of the present invention:

(1) The weld is a fully tempered martensitic structure without ferrite;

(2) Welding seam A _C1 point ≥ 805 ℃;

(3) Room temperature mechanical properties of welds: R _p0.2 (σ _0.2 )≥550MPa, R _m (σ _b )≥680MPa, A(δ _0.5 )≥18, KV ₂ ≥47J, meeting the GB/T5118-2012 standard And the requirements of ASME SFA-5.5-2015 standard for the mechanical properties of T/P92 steel welding consumables deposited metal at room temperature: R _p0.2 (σ _0.2 )≥530MPa, R _m (σ _b )≥620MPa, A(δ _0.5 )≥ 15 or 17% (15% in GB/T5118 and 17% in ASME);

(4) Durable performance: Durable life at 650℃/100MPa ≥4500h.

According to the composition range of the present invention, taking the electrode as an example, several groups of examples have been made for the low-nickel copper-containing T/P92 steel welding material of the present invention, and the copper element is added through the coating or the welding core. The copper content range of Comparative Example 1 exceeds the upper limit of the present invention (1.5%), in order to illustrate the influence of excessive copper content on the weld performance. For comparison, under the same welding process (preheating 200-250°C, current 130-180A, voltage 24-30V, interlayer temperature ≤350°C) and post-weld heat treatment process (760°C×4h), it is different from the current three Typical T/P92 steel electrodes - German Thyssen MTS616 electrode (increased manganese and nickel content), Japan Kobelco CR-12S electrode (cobalt added), ALCROMOCORD 92 electrode from Olyncon (cobalt added), Comparison of deposited metal properties. Table 1 lists the chemical composition of the deposited metal of seven T/P92 steel electrodes.

The chemical composition (wt%) of the deposited metal in the embodiment and comparative example of table 1

The performance test results of the embodiments of the present invention are shown in Tables 2-3. It can be seen from Table 2 that the room temperature mechanical properties of the electrode deposited metal of the present invention are comparable to those of the MTS616 electrode deposited metal, and the room temperature impact toughness is lower than that of the CR-12S electrode deposited metal, but the room temperature tensile strength and impact toughness are overall better than those of ALCROMOCORD 92. Electrode deposits metal. It can be seen from Table 3 that the impact energy of the electrode deposited metal of the present invention after long-term aging is comparable to that of the electrode deposited metal of MTS616, CR-12S and ALCROMOCORD 92. It can be seen from Table 4 that in terms of the most important performance index of the welding material for high temperature creep resistance, the long-term durability performance of the electrode deposited metal of the present invention is obviously better than that of the CR-12S electrode deposited metal, and also better than that of MTS616 and ALCROMOCORD 92. For the electrode deposited metal, its creep rupture life at 650℃/100MPa exceeds the average creep rupture life (4735h) of P92 steel published by ECCC in 2005. The copper content of Comparative Example 1 exceeds the upper limit of the present invention, and its lasting life is lower than that of the Examples.

The room temperature mechanical properties of table 2 embodiment and comparative example

Table 3 Room temperature impact energy (J) after 650°C of the examples and comparative examples

Table 4 Durable rupture time (h) of examples and comparative examples at 650°C under different stresses

To sum up, the alloy composition design of the high-temperature creep-resistant P92 welding material of the present invention replaces the nickel element or the expensive cobalt element with the low-cost copper element, which can ensure the room temperature mechanical properties and long-term aging of the deposited metal. Under the premise of impact energy, the most important performance index of the long-term durability of the deposited metal is improved, and it has the advantage of high cost performance.

The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications belong to the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims (1)

1. A low-nickel copper-containing type T/P92 steel welding material with high temperature creep resistance is characterized in that: the welding material comprises the following components of C, Mn, Si, Cr, Ni, W, Mo, Nb, V, N, B, Al, Ti, S, P, Fe and Cu;

the welding material comprises the following components in percentage by weight: 0.08 to 0.12 percent of C, 0.30 to 0.60 percent of Mn, less than or equal to 0.40 percent of Si, 8.50 to 9.50 percent of Cr, less than or equal to 0.40 percent of Ni, 1.50 to 2.00 percent of W, 0.30 to 0.60 percent of Mo, 0.8 to 1.5 percent of Cu, 0.04 to 0.07 percent of Nb, 0.15 to 0.25 percent of V, 0.03 to 0.07 percent of N, 0.001 to 0.005 percent of B, less than or equal to 0.03 percent of Al, less than or equal to 0.01 percent of Ti, less than or equal to 0.01 percent of S, less than or equal to 0.02 percent of P, the balance of Fe, and the total content of Mn and Ni is less than 1.0.

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