Medium-carbon martensite and austenite duplex stainless steel and preparation method thereof

Abstract

The medium-carbon martensite and austenite duplex stainless steel is prepared from the following components in percentage by mass: 0.4%-0.6% of C, 14%-18% of Cr, 4%-8% of Ni, 1%-2% of Mo and the balance of Fe. The invention also discloses a preparation method of the medium-carbon martensite and austenite duplex stainless steel, which specifically comprises the following steps: mixing the prepared C, Cr, Ni, Mo and Fe, carrying out vacuum melting to obtain a solid solution, then carrying out solid solution and casting to obtain a cast ingot, then carrying out quenching and rolling to obtain a rolled plate, and finally tempering to obtain the martensite and austenite duplex stainless steel. The martensite austenite double-phase structure is obtained by increasing the austenite content, increasing the hydrogen trap concentration and improving the hydrogen embrittlement resistance of the material and changing the heat treatment mode of the martensite stainless steel, and the novel martensite stainless steel material suitable for working conditions such as high-pressure hydrogen transmission and underground hydrogen storage reservoirs is developed.

Description

Technical Field

[0001] This invention belongs to the technical field of stainless steel materials, specifically relating to medium-carbon mortise duplex stainless steel, and also to a method for preparing medium-carbon mortise duplex stainless steel. Background Technology

[0002] Martensitic stainless steel has high strength, toughness, and excellent corrosion resistance, and is widely used in energy, power and other industries.

[0003] Martensitic stainless steel is prone to hydrogen embrittlement under conditions containing H2S or near H2. Therefore, in applications where H2 is present but martensitic stainless steel is still required, a common technique is to introduce a portion of austenitic structure into the martensitic stainless steel, transforming it into a martensitic-austenitic duplex stainless steel. This technique involves controlling the chemical composition to obtain retained austenite during quenching or preparing inverted austenite through appropriate heat treatment during tempering. It is well known that higher-strength steels are more susceptible to hydrogen embrittlement. Therefore, to avoid hydrogen embrittlement, a lower carbon content is used in martensitic-austenitic duplex stainless steels to reduce the likelihood of hydrogen embrittlement.

[0004] However, with the increasing demand for hydrogen storage facilities and high-pressure hydrogen transmission pipelines, there is an urgent need to develop high-strength hydrogen embrittlement resistant materials.

[0005] Therefore, by designing the composition and heat treatment process, the austenite content was increased, improving the resistance to hydrogen embrittlement. However, this resulted in a significant sacrifice in strength. Therefore, a higher carbon content was added to compensate for the strength loss due to the increased austenite. The most significant characteristic is a medium-carbon-martensite-austenite microstructure. Utilizing the strong hydrogen trapping properties of austenite, the increased carbon content compensates for the strength loss, resulting in a high-strength, hydrogen-embrittle-resistant material. This provides a material selection option for the future large-scale construction of underground hydrogen storage facilities and high-pressure hydrogen pipelines, which can greatly promote the widespread adoption of hydrogen energy. Summary of the Invention

[0006] The purpose of this invention is to provide a medium-carbon martensitic duplex stainless steel, which solves the problem of hydrogen embrittlement in existing martensitic stainless steels.

[0007] Another object of the present invention is to provide a method for preparing medium-carbon Maurice duplex stainless steel.

[0008] The technical solution adopted in this invention is a medium-carbon Ma'ao duplex stainless steel, which is composed of the following components by mass percentage: C content of 0.4%-0.6%, Cr content of 14%-18%, Ni content of 4%-8%, Mo content of 1%-2%, and the balance being Fe.

[0009] The second technical solution adopted in this invention is a method for preparing medium-carbon Ma'ao duplex stainless steel, which is implemented according to the following steps:

[0010] Step 1: Prepare the ingredients according to the following mass percentages: C content is 0.4%-0.6%, Cr content is 14%-18%, Ni content is 4%-8%, Mo content is 1%-2%, and the balance is Fe; mix the prepared C, Cr, Ni, Mo and Fe and vacuum melt them to obtain a solid solution;

[0011] Step 2: After smelting, the solid solution obtained in Step 1 is dissolved and then cast to obtain an ingot;

[0012] Step 3: After solution treatment, the ingot obtained in step 2 is first quenched and then rolled to obtain a rolled plate.

[0013] Step 4: Temper the rolled plate to obtain medium carbon Maurice duplex stainless steel.

[0014] The second technical solution of the present invention is further characterized by:

[0015] In step 1, the melting temperature is between 1500℃ and 1800℃, and the vacuum degree before melting is not less than 1×10⁻⁶. -3 Pa.

[0016] In step 2, the solution temperature is 1000℃-1200℃, the solution treatment time is 2-4 hours, and the ingot temperature is not less than 950℃.

[0017] In step 3, the quenching medium is water, and the rolling deformation is 40%-70%.

[0018] In step 4, the tempering temperature is 580℃-650℃, and the tempering time is 1 hour-2 hours.

[0019] The beneficial effects of this invention are:

[0020] In this invention, the hydrogen trap concentration of the carbon-martensitic duplex stainless steel is increased by increasing the austenite content, thereby improving the material's resistance to hydrogen embrittlement. Furthermore, by changing the heat treatment method of the martensitic stainless steel, a martensitic-austenitic duplex structure is obtained, thus developing a new martensitic stainless steel material suitable for high-pressure hydrogen transportation, underground hydrogen storage facilities, and other working conditions. Attached Figure Description

[0021] Figure 1 These are stress-strain curves of the Maau duplex stainless steel prepared in Examples 1 and 2 of this invention;

[0022] Figure 2 This is a microstructure diagram of the Maau duplex stainless steel prepared in Example 1 of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] In this invention, a new high-strength, hydrogen-embrittle-resistant duplex stainless steel is obtained by high-temperature tempering of martensitic stainless steel at austenitic temperatures to form a martensitic-austenitic duplex structure. Austenite acts as a strong hydrogen trap, which can improve the hydrogen embrittlement resistance of stainless steel, but it will reduce the strength of stainless steel. By increasing the austenite content and rolling the martensitic stainless steel, the strength reduction caused by heat treatment is compensated, thus obtaining a new high-strength, hydrogen-embrittle-resistant duplex stainless steel material.

[0025] The carbon-martensite duplex stainless steel of this invention is composed of the following components by mass percentage: C 0.4%-0.6%, Cr 14%-18%, Ni 4%-8%, Mo 1%-2%, and the balance Fe. Adding an appropriate amount of Ni to martensitic stainless steel ensures sufficient stability of the remaining untransformed austenite, directly improving the steel's plasticity and toughness. Considering temper brittleness, Mo is used to suppress it, and it also plays a role in substitutional solid solution strengthening. Cr is an element needed to improve hardenability and corrosion resistance. After tempering, the martensite content of martensitic stainless steel decreases, leading to a reduction in strength. Increasing the C content can improve the strength of the stainless steel and compensate for the strength loss due to the reduced martensite content, resulting in a material with high strength. Tempering is necessary to obtain a martensitic + austenitic stainless steel structure. Mo acts as an austenite stabilizing element, ensuring the production of the austenitic phase after tempering.

[0026] The preparation method of carbon-mao duplex stainless steel in this invention is specifically implemented according to the following steps:

[0027] Step 1, Vacuum melting:

[0028] The ingredients are prepared according to the following mass percentages: C 0.4%-0.6%, Cr 14%-18%, Ni 4%-8%, Mo 1%-2%, and the balance Fe. The prepared C, Cr, Ni, Mo, and Fe mixtures are then vacuum-melted at a temperature of 1500℃-1800℃, with a vacuum degree of not less than 1×10⁻⁶ before melting. -3 Pa yields a solid solution;

[0029] Step 2, solution treatment:

[0030] After smelting, the solid solution obtained in step 1 is dissolved at a temperature of 1000℃-1200℃ for 2-4 hours, and then cast to obtain an ingot. The temperature of the ingot is not less than 950℃.

[0031] Step 3, Quenching and Rolling:

[0032] After solution treatment, the ingot obtained in step 2 is first quenched with water as the quenching medium, and then rolled with a deformation of 40%-70% to obtain a rolled plate.

[0033] Step 4, Tempering:

[0034] The rolled plate is tempered at a temperature of 580℃-650℃ for 1-2 hours to obtain medium carbon martensitic-austenitic duplex stainless steel. The microstructure of this material is martensitic-austenitic duplex structure. The yield strength of this material is not less than 800MPa, the tensile strength is not less than 900MPa, the elongation is not less than 18%, and the austenite content is 20%-40%.

[0035] Example 1

[0036] The stainless steel prepared in this embodiment is 0.4C15Cr8Ni1MoFe, wherein the content of C is 0.4%, the content of Cr is 15%, the content of Ni is 8%, the content of Mo is 1%, and the balance is Fe.

[0037] Step 1, Vacuum Melting: The prepared C, Cr, Ni, Mo and Fe are mixed and vacuum melted at a temperature of 1600℃. The vacuum degree before melting is 1×10⁻⁶. -3 Pa yields a solid solution;

[0038] Step 2, Solution treatment: After smelting, the solid solution obtained in Step 1 is solution treated at a temperature of 1200℃ for 4 hours, and then cast to obtain an ingot at a temperature of 1200℃.

[0039] Step 3, Quenching and Rolling: After solution treatment, the ingot obtained in Step 2 is first quenched with water as the quenching medium, and then rolled with a deformation of 50% to obtain a rolled plate.

[0040] Step 4, Tempering: Temper the rolled plate at 650℃ for 1 hour.

[0041] The tensile curve of 0.4C15Cr8Ni1MoFe obtained in this embodiment is as follows: Figure 1 As shown, the stainless steel has a yield strength of 840 MPa, a tensile strength of 980 MPa, an elongation of 30%, and an austenite content of 20%. The microstructure of the Ma'ao duplex stainless steel prepared in this embodiment is shown in the image. Figure 2 As shown.

[0042] Example 2

[0043] The only difference between this embodiment and Example 1 is that the tempering time in Example 2 is 2 hours, except that the components are the same.

[0044] The tensile curve of 0.4C15Cr8Ni1MoFe obtained in this embodiment is as follows: Figure 1 As shown, the stainless steel has a yield strength of 860 MPa, a tensile strength of 950 MPa, an elongation of 33%, and an austenite content of 22%.

[0045] Example 3

[0046] The stainless steel prepared in this embodiment is 0.5C14Cr5Ni1.5MoFe, wherein the C content is 0.5%, the Cr content is 14%, the Ni content is 5%, the Mo content is 1.5%, and the balance is Fe.

[0047] Step 1, Vacuum Melting: The prepared C, Cr, Ni, Mo and Fe are mixed and vacuum melted at a temperature of 1700℃. The vacuum degree before melting is 1.5×10⁻⁶. -4 Pa yields a solid solution;

[0048] Step 2, Solution treatment: After smelting, the solid solution obtained in Step 1 is solution treated at a temperature of 1100℃ for 3 hours, and then cast to obtain an ingot at a temperature of 1100℃.

[0049] Step 3, Quenching and Rolling: After solution treatment, the ingot obtained in Step 2 is first quenched with water as the quenching medium, and then rolled with a deformation of 60% to obtain a rolled plate.

[0050] Step 4, Tempering: Temper the rolled plate at 600℃ for 2 hours.

[0051] The 0.5C14Cr5Ni1.5MoFe stainless steel obtained in this embodiment has a yield strength of 800MPa, a tensile strength of 1000MPa, an elongation of 20%, and an austenite content of 25%.

[0052] Example 4

[0053] The stainless steel prepared in this embodiment is 0.6C14Cr5Ni1.5MoFe, wherein the C content is 0.6%, the Cr content is 14%, the Ni content is 5%, the Mo content is 1.5%, and the balance is Fe.

[0054] Step 1, Vacuum Melting: The prepared C, Cr, Ni, Mo and Fe are mixed and vacuum melted at a temperature of 1650℃. The vacuum degree before melting is 8×10⁻⁶. -4 Pa yields a solid solution;

[0055] Step 2, Solution treatment: After smelting, the solid solution obtained in Step 1 is solution treated at a temperature of 1000℃ for 2 hours, and then cast to obtain an ingot at a temperature of 1000℃.

[0056] Step 3, Quenching and Rolling: After solution treatment, the ingot obtained in Step 2 is first quenched with water as the quenching medium, and then rolled with a deformation of 40% to obtain a rolled plate.

[0057] Step 4, Tempering: Temper the rolled plate at 630℃ for 2 hours.

[0058] The 0.5C14Cr5Ni1.5MoFe stainless steel obtained in this embodiment has a yield strength of 850MPa, a tensile strength of 1050MPa, an elongation of 18%, and an austenite content of 31%.

[0059] Example 5

[0060] The stainless steel prepared in this embodiment is 0.6C15Cr8Ni2MoFe, wherein the C content is 0.6%, the Cr content is 15%, the Ni content is 8%, the Mo content is 2%, and the balance is Fe.

[0061] Step 1, Vacuum Melting: The prepared C, Cr, Ni, Mo and Fe are mixed and vacuum melted at a temperature of 1620℃. The vacuum degree before melting is 6×10⁻⁶. -4 Pa yields a solid solution;

[0062] Step 2, Solution treatment: After smelting, the solid solution obtained in Step 1 is solution treated at a temperature of 1200℃ for 2 hours, and then cast to obtain an ingot at a temperature of 1200℃.

[0063] Step 3, Quenching and Rolling: After solution treatment, the ingot obtained in Step 2 is first quenched with water as the quenching medium, and then rolled with a deformation of 40% to obtain a rolled plate.

[0064] Step 4, Tempering: Temper the rolled plate at 580℃ for 2 hours.

[0065] The 0.5C14Cr5Ni1.5MoFe stainless steel obtained in this embodiment has a yield strength of 800MPa, a tensile strength of 980MPa, an elongation of 25%, and an austenite content of 24%.

[0066] Comparative Example 1

[0067] The stainless steel prepared in this comparative example is 14Cr5Ni1.5MoFe, wherein the Cr content is 14%, the Ni content is 5%, the Mo content is 1.5%, and the balance is Fe.

[0068] The comparative example is identical to the one in Example 4 in terms of preparation process, except for the different components.

[0069] This method can produce a Maurice duplex stainless steel microstructure, but the yield strength is 350 MPa and the tensile strength is 650 MPa, which is significantly lower than that of the Maurice duplex stainless steel microstructure containing carbon.

[0070] Comparative Example 2

[0071] The stainless steel prepared in this comparative example is 0.2C14Cr5Ni1.5MoFe, wherein the C content is 0.2%, the Cr content is 14%, the Ni content is 5%, the Mo content is 1.5%, and the balance is Fe.

[0072] The comparative example is identical to the one in Example 4 in terms of preparation process, except for the different components.

[0073] This method can produce a Maurice duplex stainless steel microstructure, but the yield strength is 550 MPa and the tensile strength is 850 MPa, which is significantly lower than that of medium carbon Maurice duplex stainless steel.

Claims

1. Medium-carbon Maurice duplex stainless steel, characterized in that, It consists of the following components by mass percentage: 0.4%-0.6% C, 14%-18% Cr, 4%-8% Ni, 1%-2% Mo, and the balance being Fe.

2. The method for preparing medium-carbon Maurice duplex stainless steel according to claim 1, characterized in that, The specific steps are as follows: Step 1: Prepare the ingredients according to the following mass percentages: C content is 0.4%-0.6%, Cr content is 14%-18%, Ni content is 4%-8%, Mo content is 1%-2%, and the balance is Fe; mix the prepared C, Cr, Ni, Mo and Fe and vacuum melt them to obtain a solid solution; Step 2: After smelting, the solid solution obtained in Step 1 is dissolved and then cast to obtain an ingot; Step 3: After solution treatment, the ingot obtained in step 2 is first quenched and then rolled to obtain a rolled plate. Step 4: Temper the rolled plate to obtain medium carbon Maurice duplex stainless steel.

3. The method for preparing medium-carbon Maurice duplex stainless steel according to claim 2, characterized in that, In step 1, the melting temperature is between 1500℃ and 1800℃, and the vacuum degree before melting is not less than 1×10⁻⁶. -3 Pa.

4. The method for preparing medium-carbon Maurice duplex stainless steel according to claim 2, characterized in that, In step 2, the solution temperature is 1000℃-1200℃, the solution treatment time is 2-4 hours, and the ingot temperature is not less than 950℃.

5. The method for preparing medium-carbon Maurice duplex stainless steel according to claim 2, characterized in that, In step 3, the quenching medium is water, and the rolling deformation is 40%-70%.

6. The method for preparing medium-carbon Maurice duplex stainless steel according to claim 2, characterized in that, In step 4, the tempering temperature is 580℃-650℃, and the tempering time is 1 hour-2 hours.

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