Heat treatment process for improving superplasticity of duplex stainless steel

Abstract

The invention belongs to the technical field of heat treatment, and discloses a heat treatment process for improving the superplasticity of duplex stainless steel. The heat treatment process comprises the following steps that a duplex stainless steel plate is heated to 1050-1100 DEG C, and heat preservation is conducted for 40 min; then the temperature is reduced to 500 DEG C or below at the cooling speed of 100-110 DEG C / s, and then the temperature is reduced to 20-30 DEG C at the cooling speed of 5-10 DEG C / s; the cooled duplex stainless steel plate is rolled, and the total rolling reduction rate is 50-80%; and the rolled stainless steel plate is subjected to first heating, then superplastic stretching is conducted, and the heat treatment process is completed. After the duplex stainless steel is treated through the technology, precipitation of harmful phases in traditional duplex stainless steel can be effectively reduced, the two-phase structure of ferrite and austenite is guaranteed, and then the ductility of superplastic deformation of the duplex stainless steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment, and in particular to a heat treatment process for improving superplasticity of duplex stainless steel. Background Art

[0002] Duplex stainless steel refers to a type of steel that contains austenite and ferrite in its solid solution structure, with each phase accounting for about half. According to the characteristics of the two structures, the excellent properties of austenite stainless steel and ferrite stainless steel are combined by properly controlling the heat treatment process, so that it has good superplastic properties. By using superplastic forming technology, high-quality, high-precision thin walls, thin webs and other complex-shaped products can be formed, and the fine lines and lines on the mold can be replicated. At the same time, it provides an effective means to reduce costs and reduce the weight of mechanical equipment, which will have a huge impact on the design and manufacturing of ships and coastal city construction and urban beautification and decoration.

[0003] The heat treatment process of duplex stainless steel has an important influence on the microstructure, and the microstructure plays an important role in the superplasticity of duplex stainless steel. Therefore, a reasonable heat treatment process is the key factor to ensure that duplex stainless steel has excellent superplasticity. Summary of the invention

[0004] The object of the present invention is to provide a heat treatment process for improving the superplasticity of duplex stainless steel, so as to improve the elongation of the superplastic deformation of the duplex stainless steel.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a heat treatment process for improving superplasticity of duplex stainless steel, comprising the following steps:

[0007] (1) heating the duplex stainless steel plate to 1050-1100° C. and keeping the temperature for 30-50 min to obtain a heated duplex stainless steel plate;

[0008] (2) cooling the heated duplex stainless steel plate to below 500° C. at a cooling rate of 100 to 110° C. / s, and then cooling the heated duplex stainless steel plate to 20 to 30° C. at a cooling rate of 5 to 10° C. / s, to obtain a cooled duplex stainless steel plate;

[0009] (3) rolling the cooled duplex stainless steel plate, with a total rolling reduction of 50 to 80%, to obtain a rolled duplex stainless steel plate;

[0010] (4) The rolled stainless steel sheet is first heated and then superplastic stretched to complete the heat treatment process.

[0011] Preferably, in the above-mentioned heat treatment process for improving the superplasticity of duplex stainless steel, the duplex stainless steel plate is a 1Cr21Ni5Ti duplex stainless steel plate or a SAF2205 duplex stainless steel plate.

[0012] Preferably, in the above-mentioned heat treatment process for improving superplasticity of duplex stainless steel, the 1Cr21Ni5Ti duplex stainless steel plate comprises the following components in percentage:

[0013] C 0.12%, Cr 21.07%, Ni 5.83%, Mn 0.49%, Si 0.4%, Ti 0.49%, Al 0.035%, N 0.0081%, Cu 2.16% and Fe balance.

[0014] Preferably, in the above-mentioned heat treatment process for improving the superplasticity of duplex stainless steel, the first heating conditions are: a heating rate of 10 to 15°C / s, an initial temperature of 20 to 30°C, a final temperature of 950 to 1100°C, and a holding time at the final temperature of 3 to 5 minutes.

[0015] Preferably, in the above-mentioned heat treatment process for improving the superplasticity of duplex stainless steel, the strain rate of superplastic stretching is ≤2×10 -3 / s.

[0016] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention provides a heat treatment process method for improving the superplasticity of duplex stainless steel by changing the microstructure of duplex stainless steel through controlling the heat treatment process. After the duplex stainless steel is treated by the process of the present invention, the precipitation of harmful phases in traditional duplex stainless steel can be effectively reduced, and the ferrite and austenite two-phase structure can be ensured, thereby improving the elongation of superplastic deformation of duplex stainless steel.

[0018] (2) Keeping the temperature at 1050-1100℃ for 40 min can make the precipitated phase, especially the hard and brittle σ phase, dissolve back into the matrix structure. Keeping the temperature at 1050-1100℃ for 40 min can prevent the ferrite and austenite from growing. In addition, the content of ferrite and austenite is the same in this temperature range.

[0019] (3) Rapidly cool to below 500°C at a cooling rate of 100-110°C, quickly pass through the precipitation temperature range of harmful precipitates, which can effectively avoid the precipitation of precipitates, and then cool to room temperature at a cooling rate of 5-10°C to ensure that the duplex stainless steel has lower thermal stress during the cooling process.

[0020] (4) Multiple rolling passes of duplex stainless steel can effectively refine the grains. The finer the grains of duplex stainless steel, the better the superplasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0022] Figure 1 This is the microstructure diagram of SAF2205 duplex stainless steel after heat treatment in Example 1;

[0023] Figure 2 This is the microstructure diagram of SAF2205 duplex stainless steel after heat treatment in Example 1 when the superplastic tensile elongation reaches 200%;

[0024] Figure 3 This is the microstructure diagram of 1Cr21Ni5Ti duplex stainless steel after heat treatment in Example 3. DETAILED DESCRIPTION

[0025] The present invention provides a heat treatment process for improving superplasticity of duplex stainless steel, comprising the following steps:

[0026] (1) heating the duplex stainless steel plate to 1050-1100° C. and keeping the temperature for 30-50 min to obtain a heated duplex stainless steel plate;

[0027] (2) cooling the heated duplex stainless steel plate to below 500° C. at a cooling rate of 100 to 110° C. / s, and then cooling the heated duplex stainless steel plate to 20 to 30° C. at a cooling rate of 5 to 10° C. / s, to obtain a cooled duplex stainless steel plate;

[0028] (3) rolling the cooled duplex stainless steel plate, with a total rolling reduction of 50 to 80%, to obtain a rolled duplex stainless steel plate;

[0029] (4) The rolled stainless steel sheet is first heated and then subjected to superplastic stretching, thereby completing the heat treatment process.

[0030] In the present invention, the duplex stainless steel plate is preferably a 1Cr21Ni5Ti duplex stainless steel plate or a SAF2205 duplex stainless steel plate.

[0031] In the present invention, the 1Cr21Ni5Ti duplex stainless steel plate comprises the following components in percentage:

[0032] C 0.12%, Cr 21.07%, Ni 5.83%, Mn 0.49%, Si 0.4%, Ti 0.49%, Al 0.035%, N 0.0081%, Cu 2.16% and Fe balance.

[0033] In the present invention, the cooling in step (2) is performed under atmospheric conditions.

[0034] In the present invention, the rolling is carried out on a twin-roll mill with a fixed roll gap of 1 mm.

[0035] In the present invention, the total reduction ratio of the rolling process may be 50 to 80%, and there is no particular limitation on the number of passes in the rolling process and the reduction ratio of each pass.

[0036] In the present invention, the conditions for the first heating are: the heating rate is preferably 10-15°C / s, more preferably 11-14°C / s, and more preferably 12-13°C / s; the initial temperature is preferably 20-30°C, more preferably 21-28°C, and more preferably 25-26°C; the final temperature is preferably 950-1100°C, more preferably 980-1050°C, and more preferably 1000-1030°C; the insulation time at the final temperature is preferably 3-5 min, more preferably 3.5-4.5 min, and more preferably 4 min.

[0037] In the present invention, the superplastic stretching further comprises:

[0038] An anti-oxidation coating is applied to the surface of the sample obtained after the first heating to prevent oxidation of the surface of the sample during superplastic stretching.

[0039] In the present invention, the strain rate of superplastic stretching is ≤2×10 -3 / s.

[0040] In the present invention, the superplastic stretching is performed on a SK10-70×300 tensile testing machine.

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In the following embodiments, the composition of the 1Cr21Ni5Ti duplex stainless steel plate and the SAF2205 duplex stainless steel plate are shown in Table 1, with a Fe balance and a thickness of 16 mm.

[0043] Table 11 Composition of Cr21Ni5Ti duplex stainless steel plate and SAF2205 duplex stainless steel plate

[0044] wt% Cr Ni Mo Mn Si C N Cu Ti Al 1Cr21Ni5Ti 21.07 5.83 0.49 0.40 0.120 0.0081 2.16 0.49 0.035 SAF2205 22.15 5.27 3.28 1.11 0.40 0.015 0.1400 0.041

[0045] Example 1

[0046] A heat treatment process for improving the superplasticity of SAF2205 duplex stainless steel comprises the following steps:

[0047] (1) The duplex stainless steel is placed in an energy-saving box-type electric furnace and heated to 1050°C for 40 minutes to ensure that the precipitated phase is dissolved back into the matrix and the ratio of ferrite and austenite is the same;

[0048] (2) the duplex stainless steel after insulation is rapidly cooled to below 500°C at a cooling rate of 100°C / s, and then cooled to room temperature at a cooling rate of 10°C / s;

[0049] (3) The cooled duplex stainless steel is rolled in multiple passes on a twin-roll mill with a fixed roll gap of 1 mm, and the total rolling reduction is 80%;

[0050] (4) The rolled duplex stainless steel was heated from 25°C to 950°C at a heating rate of 15°C / s, kept at this temperature for 5 min, and then subjected to superplastic stretching at a strain rate of 2×10 -3 / s, the heat treatment process is completed.

[0051] The microstructure of SAF2205 duplex stainless steel after heat treatment in Example 1 is as follows Figure 1 As shown. Figure 1 It can be seen that the contents of ferrite and austenite are basically the same, and the interface between ferrite and austenite is clean, without any precipitate.

[0052] After heat treatment in Example 1, the microstructure of SAF2205 duplex stainless steel reaches 200% in superplastic tensile elongation. Figure 2 As shown. After the traditional process (i.e., heating SAF2205 duplex stainless steel to 1050℃ for 30min, cooling to room temperature, and then rolling, with a total rolling reduction of 80%), the superplastic tensile elongation is 590%. After the process of the present invention, the superplastic tensile elongation of SAF2205 duplex stainless steel is 860%, an increase of 46%.

[0053] Example 2

[0054] A heat treatment process for improving the superplasticity of SAF2205 duplex stainless steel comprises the following steps:

[0055] (1) The duplex stainless steel is placed in an energy-saving box-type electric furnace and heated to 1050°C for 40 minutes to ensure that the precipitated phase is dissolved back into the matrix and the ratio of ferrite and austenite is the same;

[0056] (2) the duplex stainless steel after insulation is rapidly cooled to below 500°C at a cooling rate of 100°C / s, and then cooled to room temperature at a cooling rate of 10°C / s;

[0057] (3) The cooled duplex stainless steel is rolled in multiple passes on a twin-roll mill with a fixed roll gap of 1 mm, and the total rolling reduction is 50%;

[0058] (4) The rolled duplex stainless steel was heated from 25°C to 950°C at a heating rate of 15°C / s, kept at this temperature for 5 min, and then subjected to superplastic stretching at a strain rate of 2×10 -3 / s, the heat treatment process is completed.

[0059] After the heat treatment in Example 2, the contents of ferrite and austenite in the SAF2205 duplex stainless steel are substantially the same, and the interface between ferrite and austenite is clean without any precipitation.

[0060] After the SAF2205 duplex stainless steel is treated by the conventional process (i.e., the SAF2205 duplex stainless steel is kept at 1050° C. for 30 minutes, water-cooled to room temperature, and then rolled, with a total rolling reduction of 50%), the superplastic tensile elongation is 360%. After being treated by the process of the present invention, the superplastic tensile elongation of the SAF2205 duplex stainless steel is 470%, an increase of 31%.

[0061] Example 3

[0062] A heat treatment process for improving the superplasticity of SAF2205 duplex stainless steel comprises the following steps:

[0063] (1) The duplex stainless steel is placed in an energy-saving box-type electric furnace and heated to 1100°C for 40 minutes to ensure that the precipitated phase is dissolved back into the matrix and the ratio of ferrite and austenite is the same;

[0064] (2) the duplex stainless steel after insulation is rapidly cooled to below 500°C at a cooling rate of 100°C / s, and then cooled to room temperature at a cooling rate of 10°C / s;

[0065] (3) The cooled duplex stainless steel is rolled in multiple passes on a twin-roll mill with a fixed roll gap of 1 mm, and the total rolling reduction is 50%;

[0066] (4) The rolled duplex stainless steel was heated from 25°C to 950°C at a heating rate of 15°C / s, kept at this temperature for 5 min, and then subjected to superplastic stretching at a strain rate of 2×10 -3 / s, the heat treatment process is completed.

[0067] After the heat treatment of Example 3, the contents of ferrite and austenite in the SAF2205 duplex stainless steel are substantially the same, and the interface between ferrite and austenite is clean without any precipitated phase.

[0068] The superplastic tensile elongation of SAF2205 duplex stainless steel is 400% after being treated by conventional process (i.e., SAF2205 duplex stainless steel is kept at 1100°C for 30 minutes, cooled to room temperature, and then rolled, with a total reduction rate of 50%). After being treated by the process of the present invention, the superplastic tensile elongation of SAF2205 duplex stainless steel is 490%, an increase of 22.5%.

[0069] Example 4

[0070] A heat treatment process for improving the superplasticity of 1Cr21Ni5Ti duplex stainless steel comprises the following steps:

[0071] (1) The duplex stainless steel is placed in an energy-saving box-type electric furnace and heated to 1050°C for 40 minutes to ensure that the precipitated phase is dissolved back into the matrix and the ratio of ferrite and austenite is the same;

[0072] (2) the duplex stainless steel after insulation is rapidly cooled to below 500°C at a cooling rate of 100°C / s, and then cooled to room temperature at a cooling rate of 10°C / s;

[0073] (3) The cooled duplex stainless steel is rolled in multiple passes on a twin-roll mill with a fixed roll gap of 1 mm, and the total rolling reduction is 80%;

[0074] (4) The rolled duplex stainless steel was heated from 25°C to 950°C at a heating rate of 15°C / s, kept at this temperature for 5 min, and then subjected to superplastic stretching at a strain rate of 2×10 -3 / s, the heat treatment process is completed.

[0075] The microstructure of 1Cr21Ni5Ti duplex stainless steel after heat treatment in Example 3 is as follows: Figure 3 As shown. Figure 3 It can be seen that the contents of ferrite and austenite are basically the same, and the interface between ferrite and austenite is clean, without any precipitate.

[0076] The superplastic tensile elongation of 1Cr21Ni5Ti duplex stainless steel after being treated by conventional process (i.e., keeping 1Cr21Ni5Ti duplex stainless steel at 1050°C for 30 minutes, cooling to room temperature, and then rolling, with a total rolling reduction of 80%) is 480%. After being treated by the process of the present invention, the superplastic tensile elongation of SAF2205 duplex stainless steel is 730%, an increase of 52%.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A heat treatment process for improving the superplasticity of duplex stainless steel, characterized in that: The following steps are involved: (1) heating the duplex stainless steel plate to 1050-1100° C. and keeping the temperature for 30-50 min to obtain a heated duplex stainless steel plate; (2) cooling the heated duplex stainless steel plate to below 500° C. at a cooling rate of 100 to 110° C. / s, and then cooling the heated duplex stainless steel plate to 20 to 30° C. at a cooling rate of 5 to 10° C. / s, to obtain a cooled duplex stainless steel plate; (3) rolling the cooled duplex stainless steel plate, with a total rolling reduction of 50 to 80%, to obtain a rolled duplex stainless steel plate; (4) The rolled stainless steel sheet is first heated and then superplastic stretched to complete the heat treatment process.

2. The heat treatment process for improving superplasticity of duplex stainless steel according to claim 1, characterized in that: The duplex stainless steel plate is a 1Cr21Ni5Ti duplex stainless steel plate or a SAF2205 duplex stainless steel plate.

3. The heat treatment process for improving superplasticity of duplex stainless steel according to claim 2, characterized in that: The 1Cr21Ni5Ti duplex stainless steel plate comprises the following components in percentage: C 0.12%, Cr 21.07%, Ni 5.83%, Mn 0.49%, Si 0.4%, Ti 0.49%, Al 0.035%, N 0.0081%, Cu 2.16% and Fe balance.

4. The heat treatment process for improving superplasticity of duplex stainless steel according to claim 3, characterized in that: The first heating conditions are as follows: a heating rate of 10 to 15°C / s, an initial temperature of 20 to 30°C, a final temperature of 950 to 1100°C, and a holding time of 3 to 5 minutes at the final temperature.

5. The heat treatment process for improving superplasticity of duplex stainless steel according to claim 3 or 4, characterized in that: The strain rate of superplastic stretching is ≤2×10 -3 / s.

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