Method for improving performance of welding heat affected zone of reduced-ni type stainless steel

Abstract

This invention discloses a method for improving the weld heat-affected zone properties of Ni-saving stainless steel, belonging to the field of stainless steel hot working technology. This invention controls the Mn / N ratio of the Ni-saving stainless steel to 3.28 or 17.8, sequentially processes the Ni-saving stainless steel raw material through melting, forging, rolling, and solution treatment, and then controls the large heat input range of 3.12 kJ / mm to 5.89 kJ / mm to conduct welding thermal simulation experiments to improve the weldability of the stainless steel. For the welded parts, under a heat input range of 4.56 kJ / mm to 5.82 kJ / mm, samples with a Mn / N ratio of 3.28 underwent welding heat cycling treatment. The resulting weld heat-affected zone exhibited a pitting potential Eb ≥ 1.13 V, an intergranular sensitivity value Ra ≤ 0.022%, an impact energy ≥ 170 J, a tensile strength Rm ≥ 750 MPa, a yield strength Rp0.2 ≥ 1000 MPa, and an elongation A ≥ 40%. For samples with a Mn / N ratio of 17.8 and a heat input range of 3.789 kJ / mm to 5.355 kJ / mm, the resulting weld heat-affected zone exhibited a pitting potential Eb ≥ 1.11 V and an intergranular sensitivity value Ra ≤ 0.1%.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel hot working technology, specifically relating to a method for improving the performance of the heat-affected zone in Ni-type stainless steel welding. Background Technology

[0002] Ni-containing stainless steel not only possesses excellent ductility, toughness, and weldability, but also exhibits good corrosion resistance. Replacing Ni with Mn effectively stabilizes austenite, increases N solubility, and enhances the strength and corrosion resistance of stainless steel. Therefore, Mn-substituted Ni stainless steel has gradually become a hot topic in advanced steel research. Different Mn / N ratios in Mn-substituted Ni stainless steel result in varying weldability, leading to different mechanical and corrosion properties in the weld heat-affected zone. However, under low heat input conditions, the austenite in the weld heat-affected zone may not have enough time to precipitate from the ferrite phase, resulting in a high ferrite volume fraction. This can easily lead to brittle fracture and reduced corrosion resistance in the weld heat-affected zone, severely restricting the application and development of welded components.

[0003] Chinese patent CN114959447A discloses a high-N, low-Ni energy-saving duplex stainless steel and its high-performance weld heat-affected zone hot working method. The method involves welding heat cycling treatment within a heat input range of 2.85 kJ / mm to 2.95 kJ / mm. The resulting weld heat-affected zone exhibits a pitting potential Eb ≥ 0.93, an intergranular sensitivity value Ra ≤ 0.31%, and a tensile strength rm ≥ 796 MPa, an elongation A ≥ 32%, and an impact energy greater than or equal to 57 J when the heat input is between 0.45 kJ / mm and 0.95 kJ / mm. However, the mechanical properties and corrosion resistance of the weld heat-affected zone obtained by this invention are relatively low and do not meet the welding performance requirements. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention proposes a method for improving the performance of the heat-affected zone (HAZ) in Ni-type stainless steel welding. This invention optimizes the Mn / N ratio and controls the heat input, thereby enabling the welded HAZ to exhibit excellent overall performance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for improving the performance of the heat-affected zone in Ni-type stainless steel welding, comprising the following steps: (1) Stainless steel billets are obtained by melting in a vacuum melting furnace with the following mass percentages: C: 0.01-0.02%, Si: 0.04-0.21%, Mn: 2.20% or 8.01%, Cr: 21.99-23.62%, Ni: 0.03-5.36%, Mo: 0.82-2.82%, Cu: 0.13-0.52%, N: 0.45% or 0.67%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe and unavoidable impurities, and the Mn / N ratio being 3.28 or 17.8. (2) The stainless steel billet was forged, rolled and solution treated in sequence, and then cooled to room temperature with water to obtain the sample; (3) Process the sample to 60mm 10 mm A 10 mm pre-compression specimen was subjected to a welding thermal simulation experiment. The maximum heat input range was controlled to be 3.12 kJ / mm to 5.89 kJ / mm, and the peak temperature was set at 1325℃.

[0006] As a preferred embodiment of the present invention, the high heat input range is 4.65kJ / mm to 5.355kJ / mm.

[0007] As a preferred embodiment of the present invention, the initial forging temperature is 1100-1150℃, the final forging temperature is ≥950℃, and the forging ratio is 3.5-5.

[0008] As a preferred embodiment of the present invention, the initial rolling temperature is 1050-1130℃, the final rolling temperature is ≥960℃, and after rolling, the material is cooled by water and then subjected to solution treatment.

[0009] In a preferred embodiment of the present invention, the solution treatment temperature is 950℃~1200℃ and the time is 10min~40min.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, through the combined adjustment of the Mn / N ratio and the high heat input power, subjectes samples with an Mn / N ratio of 3.28 to welding thermal cycling treatment within the range of 4.65 kJ / mm to 5.355 kJ / mm. The resulting samples exhibit excellent mechanical properties and good corrosion resistance.

[0011] Within a heat input range of 3.789 kJ / mm to 5.355 kJ / mm, samples with a Mn / N ratio of 17.8 were subjected to welding thermal cycling treatment. The resulting samples exhibited pitting potential Eb ≥ 1.11 V and intergranular sensitivity Ra ≤ 0.1%, demonstrating excellent corrosion resistance. Attached Figure Description

[0012] Figure 1 The cyclic voltammetric polarization test curves of four different heat inputs and solution-treated samples in the heat-affected zone of welding in Example 1 with a Mn / N ratio of 3.28 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm are shown.

[0013] Figure 2 The cyclic voltammetric polarization test curves of four different heat inputs and solution-treated samples in the heat-affected zone of welding in Example 2 with a Mn / N ratio of 17.8 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm are shown.

[0014] Figure 3 The test curves of the double-ring electrochemical potentiodynamic reactivation method for four different heat inputs and solid solution state samples in the heat-affected zone of welding in Example 1 with a Mn / N ratio of 3.28 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm are shown.

[0015] Figure 4 The figures for Example 2 are test curves of the double-ring electrochemical potentiodynamic reactivation method for four different heat inputs and solid solution state samples in the weld heat-affected zone with a Mn / N ratio of 17.8 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm.

[0016] Figure 5 This is a comparison chart of the intergranular corrosion sensitivity of four different heat inputs and solid solution state samples in the welded heat-affected zone of Example 1 with a Mn / N ratio of 3.28 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm.

[0017] Figure 6 This is a comparison chart of the intergranular corrosion sensitivity of four different heat inputs and solid solution state samples in the welded heat-affected zone of Example 2 with a Mn / N ratio of 17.8 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm.

[0018] Figure 7 Examples and comparative examples compare the impact energy of four different heat inputs and solution-treated samples in the weld heat-affected zone within the range of thermal cycling parameters from 3.12 kJ / mm to 5.89 kJ / mm.

[0019] Figure 8These are examples and comparative examples, comparing the yield strength of welded heat-affected zones with different heat inputs and solution-treated specimens within a thermal cycling parameter range of 3.12 kJ / mm to 5.89 kJ / mm.

[0020] Figure 9 These are examples and comparative examples, comparing the tensile strength of welded heat-affected zones under different heat inputs and in solution-treated states within a thermal cycling parameter range of 3.12 kJ / mm to 5.89 kJ / mm.

[0021] Figure 10 These are examples and comparative examples, comparing the elongation of the weld heat-affected zone under different heat inputs and in solution-treated samples within a thermal cycling parameter range of 3.12 kJ / mm to 5.89 kJ / mm. Detailed Implementation

[0022] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0023] Example 1 In this embodiment, the Ni-saving stainless steel formula is prepared according to Table 1, and the parameters during processing are set according to Table 2.

[0024] A method for improving the performance of the heat-affected zone in Ni-type stainless steel welding specifically includes the following steps: (1) Ni-type stainless steel with different Mn / N ratios was smelted in a 50kg vacuum melting furnace, forged into blocks 130mm wide and 25mm thick, and then hot-rolled into 12mm thick plates. After rolling, the plates were immediately water-cooled.

[0025] (2) The experimental steel was subjected to solution treatment in a high-temperature furnace, and after the solution treatment was completed, the experimental steel was cooled to room temperature by water.

[0026] (3) Process the sample obtained in step (2) into a 60mm diameter. 10 mm A 10 mm pre-compression specimen was subjected to a welding thermal simulation experiment to control the heat input.

[0027] Example 2 In this embodiment, the Ni-saving stainless steel formula is prepared according to Table 1, and the parameters during processing are set according to Table 2.

[0028] A method for improving the performance of the heat-affected zone in Ni-type stainless steel welding specifically includes the following steps: (1) Ni-type stainless steel with different Mn / N ratios was smelted in a 50kg vacuum melting furnace, forged into blocks 130mm wide and 25mm thick, and then hot-rolled into 12mm thick plates. After rolling, the plates were immediately water-cooled.

[0029] (2) The experimental steel was subjected to solution treatment in a high-temperature furnace, and after the solution treatment was completed, the experimental steel was cooled to room temperature by water.

[0030] (3) Process the sample obtained in step (2) into a 60mm diameter. 10 mm A 10 mm pre-compression specimen was subjected to a welding thermal simulation experiment to control the heat input.

[0031] Table 1 Table 2 Example of effect 1. Electrochemical tests were performed on the samples obtained from the welding thermal simulation experiment in step (3) above. The pitting corrosion solution was 3.5 wt.% NaCl, and the intergranular corrosion solution was: H2SO4 (1.2 mol / L) + NaCl (1.1 mol / L) + KSCN (0.01 mol / L). The electrochemical characteristics of the samples were tested using an electrochemical workstation, and the performance is shown in Table 3.

[0032] Table 3 In Table 3, Q represents the maximum thermal input power.

[0033] 2. Impact and tensile tests were conducted on the samples obtained from the welding thermal simulation experiment in step (3) above to measure their mechanical properties. The results are shown in Table 4.

[0034] Table 4 Figure 1 This refers to the cyclic voltammetric polarization test curves of four heat input samples and solution-treated samples in the heat-affected zone of welded metal with a Mn / N ratio of 3.28 and thermal cycling parameters ranging from 3.12 kJ / mm to 5.89 kJ / mm. Table 3 shows the electrochemical parameters fitted to the potentiodynamic polarization curves of Examples 1-2 and Comparative Example 1. As can be seen from Table 3, when the heat input value is between 4.650 kJ / mm and 5.355 kJ / mm, the pitting potential Eb ≥ 1.13 V. Figure 5 It can be seen that the intergranular sensitivity value decreases with the increase of heat input. When the heat input value is between 4.650 kJ / mm and 5.355 kJ / mm, the intergranular corrosion sensitivity value Ra ≤ 0.022%.

[0035] from Figure 2 As can be seen from Table 3, when the heat input value is between 3.789 kJ / mm and 5.355 kJ / mm, the pitting potential Eb ≥ 1.11 V. From... Figure 6It can be seen that the intergranular sensitivity value decreases with the increase of heat input. When the heat input value is 5.35 kJ / mm, the intergranular corrosion sensitivity value Ra≤0.1%.

[0036] according to Figure 7-10 As shown in Table 4, under the same heat input conditions, the sample with a Mn / N ratio of 3.28 exhibits the highest impact energy, yield strength, tensile strength, and elongation. Furthermore, for the sample with a Mn / N ratio of 3.28, the impact energy, yield strength, and tensile strength gradually increase with increasing heat input, while the elongation remains relatively stable. At a heat input of 4.65 kJ / mm, the impact energy is greater than 170 J, the tensile strength Rm ≥ 750 MPa, the yield strength Rp0.2 ≥ 1000 MPa, and the elongation A ≥ 40%.

[0037] Based on the above, the optimal parameters were obtained. In Example 1, Ni-type stainless steel with a Mn / N ratio of 3.28 underwent welding thermal cycling treatment with a heat input of 4.56 kJ / mm to 5.82 kJ / mm. The pitting potential Eb in the weld heat-affected zone was ≥1.13 V, and the intergranular corrosion sensitivity Ra was ≤0.022%, exhibiting excellent corrosion resistance. Ni-type stainless steel with a Mn / N ratio of 17.80 underwent welding thermal cycling treatment with a heat input of 3.789 kJ / mm to 5.355 kJ / mm. The pitting potential Eb in the weld heat-affected zone was ≥1.11 V, and the intergranular corrosion sensitivity Ra was ≤0.1%. Observing the fracture morphology of the welded part of Comparative Example 1, inclusions were found in some dimples, which is detrimental to the improvement of mechanical properties. Example 1: Ni-type stainless steel with a Mn / N ratio of 3.28 was subjected to welding heat cycle treatment with a heat input of 4.650 kJ / mm to 5.355 kJ / mm. The impact energy of the weld heat-affected zone was ≥170 J, the tensile strength Rm was ≥750 MPa, the yield strength Rp0.2 was ≥1000 MPa, and the elongation A was ≥40%. It has excellent corrosion resistance and mechanical properties.

[0038] Under low heat input conditions, austenite in the weld heat-affected zone (HAZ) does not have enough time to precipitate from the ferrite phase, resulting in a high ferrite volume fraction. This can easily lead to brittle fracture and reduced corrosion resistance in the HAZ. In this invention, with increasing heat input, the impact energy and tensile strength of the HAZ of Ni-type stainless steel with a Mn / N ratio of 3.28 increase, while corrosion resistance also improves. Welding thermal simulation refines the microstructure of the HAZ, enhancing impact toughness and tensile properties.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for improving the performance of the heat-affected zone in Ni-type stainless steel welding, characterized in that, Includes the following steps: (1) Stainless steel billets were obtained by melting in a vacuum melting furnace with the following mass percentages: C: 0.01~0.02%, Si: 0.04~0.21%, Mn: 2.20%, Cr: 21.99~23.62%, Ni: 0.03~5.36%, Mo: 0.82~2.82%, Cu: 0.13~0.52%, N: 0.67%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe and unavoidable impurities, and the Mn / N ratio being 3.

28. (2) The stainless steel billet was forged, rolled and solution treated in sequence, and then cooled to room temperature with water to obtain the sample; (3) The sample was processed into a 60mm×10mm×10mm pre-pressed sample and subjected to a welding thermal simulation experiment, with the peak temperature set at 1325℃. The maximum heat input range is controlled to be 4.65 kJ / mm to 5.355 kJ / mm.

2. The method for improving the performance of the heat-affected zone in Ni-type stainless steel welding as described in claim 1, characterized in that, The initial forging temperature is 1100~1150℃, the final forging temperature is ≥950℃, and the forging ratio is 3.5-5.

3. The method for improving the performance of the heat-affected zone in Ni-type stainless steel welding as described in claim 1, characterized in that, The initial rolling temperature is 1050~1130℃, the final rolling temperature is ≥960℃, and after rolling, the product is water-cooled and then subjected to solution treatment.

4. The method for improving the performance of the heat-affected zone in Ni-type stainless steel welding as described in claim 1, characterized in that, The solution treatment temperature is 950℃~1200℃, and the time is 10min~40min.

Images