Heat treatment method for controlling size and morphology of delta ferrite in low-activation steel

Abstract

The invention discloses a heat treatment method for controlling the size and morphology of delta ferrite in low-activation steel, which comprises the following steps: 1) heating the low-activation steel to 1050 DEG C at the heating speed of 20 DEG C / s, and preserving heat for 10 minutes; (2) respectively heating to 1100 DEG C and 1000 DEG C at the heating or cooling speed of 20 DEG C / s, or directly carrying out thermal deformation treatment with the strain rate of 10s <-1 > and the deformation amount of 60% at 1050 DEG C, and then cooling to room temperature; after being treated by the method, the delta ferrite in the low-activation steel structure is changed into a small worm shape from a large block shape, and the grain sizes of the delta ferrite and the original austenite in the steel are obviously reduced.

Description

Technical Field

[0010] The invention relates to the technical field of metal heat treatment, in particular to a heat treatment method for controlling the size and morphology of delta ferrite in low-activation steel. Background Art

[0011] Controlled nuclear fusion is considered to be the only way to solve humanity's ultimate energy problem. While providing clean energy, it can also solve the problem of my country's large energy demand.

[0012] Low activation steel is generally considered to be the preferred structural material for the first wall / cladding in future demonstration fusion reactors due to its excellent geometric stability, small thermal expansion coefficient, low irradiation swelling rate, and good resistance to liquid metal corrosion.

[0013] However, more alloying elements are added to low-activation steel, which makes its austenitization temperature range wider and the austenite phase region smaller, resulting in the easy generation of delta ferrite in actual production; delta ferrite will reduce the mechanical properties of steel; in order to meet the use requirements of fusion reactors, delta ferrite in low-activation steel must be controlled to improve the mechanical properties. Summary of the invention

[0014] In view of the above-mentioned defects or shortcomings in the prior art, it is desired to provide a heat treatment method for controlling the size and morphology of δ ferrite in low activation steel. The method starts from the microstructure of the low activation steel, and through design and introduction of a hot deformation treatment process, the grain size of δ ferrite and original austenite in the low activation steel is significantly reduced, and the morphology of δ ferrite is improved, thereby improving the mechanical properties of the steel.

[0015] The present invention provides a heat treatment method for controlling the size and morphology of delta ferrite in low activation steel, comprising the following steps:

[0016] 1) Heat the low activation steel to 1050°C and then keep it warm;

[0017] 2) The low-activation steel heated in step 1) is heated or cooled to 1100° C. or 1000° C. for thermal deformation treatment, or directly subjected to thermal deformation treatment at 1050° C., and then cooled to room temperature.

[0018] Furthermore, it is characterized in that the heating rate in step 1) is 20°C / s and the insulation time is 10 min.

[0019] Furthermore, the rate of raising or lowering the temperature in step 2) is 20°C / s.

[0020] Furthermore, the thermal deformation treatment method in step 2) is a strain rate of 10s -1 , heat deformation treatment with a deformation amount of 60%.

[0021] Furthermore, it is characterized in that the chemical composition of the low activation steel is C: 0.04wt.%, Cr: 8.93wt.%, W: 1.72wt.%, Mn: 0.44wt.%, Si: 0.04wt.%, V: 0.22wt.%, Ta: 0.07wt.%, and the rest is iron.

[0022] Further, it is characterized in that the size of the low activation steel before heating in step 1) is It is cut by a molybdenum wire cutting machine.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The heat treatment method for controlling the size and morphology of delta ferrite in low-activation steel of the present invention significantly reduces the grain size of delta ferrite and original austenite in low-activation steel and improves the morphology of delta ferrite by introducing a thermal deformation treatment process, thereby improving the mechanical properties of the steel, so that the low-activation steel can be used more safely in actual engineering.

[0025] The process of the present invention is to heat the low activation steel to 1050°C at a heating rate of 20°C / s, keep the temperature for 10 minutes, and then heat to 1100 and 1000°C at a heating or cooling rate of 20°C / s, or directly heat at 1050°C at a strain rate of 10s -1 , heat deformation treatment with a deformation amount of 60%, and then cooling to room temperature;

[0026] After being processed by the process of the present invention, the grain sizes of delta ferrite and original austenite in the microstructure of the low-activated steel are significantly reduced, and the morphology of delta ferrite is improved, changing from a large block to a small worm shape.

[0027] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0029] Figure 1 This is a light microscope image of low-activated steel after being kept at 1050℃ for 10 minutes and then cooled (general heat treatment);

[0030] Figure 2 After the low activation steel was kept at 1050℃ for 10 minutes, it was deformed by 60% at 1050℃ and the strain rate was 10s -1 Light microscope image after cooling after thermal deformation treatment;

[0031] Figure 3 After the low activation steel was kept at 1050℃ for 10 minutes, it was heated to 1100℃ at 20℃ / s and deformed by 60% at a strain rate of 10s -1 Light microscope image after cooling after thermal deformation treatment;

[0032] Figure 4 After the low activation steel was kept at 1050℃ for 10 minutes, it was cooled to 1000℃ at a rate of 20℃ / s and the deformation was 60% at a strain rate of 10s -1 Light microscope image after cooling after thermal deformation treatment;

[0033] Figure 5 Schematic diagram of the heat treatment process for low-activated steel in Examples 1-3. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] refer to Figure 1-5 The embodiment of the present invention provides a heat treatment method for controlling the size and morphology of δ ferrite in low activation steel. The method starts from the microstructure of low activation steel and, through design and introduction of thermal deformation treatment process, significantly reduces the grain size of δ ferrite and original austenite in low activation steel, and improves the morphology of δ ferrite, thereby improving the mechanical properties of steel.

[0037] Example 1

[0038] A heat treatment method for controlling the size and morphology of delta ferrite in low activation steel comprises the following steps:

[0039] Step 1: Use Gleeble 3500 thermal simulator to The small cylindrical specimen of low-activated steel was heated to 1050°C at a heating rate of 20°C / s and kept at this temperature for 10 min.

[0040] Step 2, then directly at 1050 ° C with a strain rate of 10s -1 , heat deformation treatment with a deformation amount of 60%, and then cooled to room temperature.

[0041] The heat-deformed specimens were cut in the middle along the cross section by wire cutting, and then the specimens were inlaid with bakelite powder, and then rough grinding, fine grinding and polishing were performed after inlaying;

[0042] Subsequently, the sample was corroded by saturated picric acid etching agent (mixed by 100 ml of water, 1 g of picric acid, 1.5 g of sodium dodecyl sulfate and 0.3 g of sodium fatty alcohol ether sulfate) at 60-65 ° C for 3-4 min, and then the microstructure of the sample was observed by Leica-DMI 5000m optical microscope, and the morphology and size of the original austenite grain boundary and delta ferrite could be clearly seen.

[0043] Figure 1 This is a light microscope image of low-activated steel after being kept at 1050℃ for 10 minutes and then cooled (general heat treatment);

[0044] Figure 2 This is a light microscope image of the low-activation steel in this embodiment after being improved by the thermal deformation treatment method of the present invention.

[0045] Example 2

[0046] A heat treatment method for controlling the size and morphology of delta ferrite in low activation steel comprises the following steps:

[0047] Step 1: Use Gleeble 3500 thermal simulator to The small cylindrical specimen of low-activated steel was heated to 1050°C at a heating rate of 20°C / s and kept at this temperature for 10 min.

[0048] Step 2: Heat to 1100°C at a rate of 20°C / s and strain at a rate of 10s -1 , heat deformation treatment with a deformation amount of 60%, and then cooled to room temperature.

[0049] The heat-deformed specimens were cut in the middle along the cross section by wire cutting, and then inlaid with bakelite powder, and then rough-grinded, fine-grinded and polished.

[0050] Subsequently, a saturated picric acid corrosive agent (a mixture of 100 ml of water, 1 g of picric acid, 1.5 g of sodium dodecyl sulfate and 0.3 g of sodium fatty alcohol ether sulfate) was used to corrode the sample at 60-65°C for 3-4 min, and then a Leica-DMI 5000m optical microscope was used to observe the microstructure of the sample, and the morphology and size of the original austenite grain boundaries and delta ferrite could be clearly seen.

[0051] Figure 3 This is a light microscope image of the low-activation steel in this embodiment after being improved by the thermal deformation treatment method of the present invention.

[0052] Example 3

[0053] A heat treatment method for controlling the size and morphology of delta ferrite in low activation steel comprises the following steps:

[0054] Step 1: Use Gleeble 3500 thermal simulator to The small cylindrical specimen of low-activated steel was heated to 1050°C at a heating rate of 20°C / s and kept at this temperature for 10 min.

[0055] Step 2: Cool down to 1000°C at a cooling rate of 20°C / s and perform the strain rate test for 10s. -1 , heat deformation treatment with a deformation amount of 60%, and then cooled to room temperature.

[0056] The heat-deformed specimens were cut in the middle along the cross section by wire cutting, and then inlaid with bakelite powder. After inlaying, they were subjected to rough grinding, fine grinding and polishing.

[0057] Subsequently, a saturated picric acid corrosive agent (a mixture of 100 ml of water, 1 g of picric acid, 1.5 g of sodium dodecyl sulfate and 0.3 g of sodium fatty alcohol ether sulfate) was used to corrode the sample at 60-65°C for 3-4 min, and then a Leica-DMI 5000m optical microscope was used to observe the microstructure of the sample, and the morphology and size of the original austenite grain boundaries and delta ferrite could be clearly seen.

[0058] Figure 4 This is a light microscope image of the low-activation steel in this embodiment after being improved by the thermal deformation treatment method of the present invention.

[0059] In summary, Figure 2 , Figure 3 and Figure 4 Respectively Figure 1 By comparison, after being treated by the process method of the present invention, the grain sizes of delta ferrite and original austenite in the microstructure of low-activated steel are significantly reduced, and the morphology of delta ferrite is improved, changing from large blocks to small worms, thereby improving the mechanical properties of the steel.

[0060] In the description of this specification, the terms "connection", "installation", "fixation" and the like should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0061] In the description of this specification, the description of the terms "one embodiment", "some embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0062] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A heat treatment method for controlling the size and morphology of delta ferrite in low activation steel, characterized in that: The following steps are involved: 1) Heat the low activation steel to 1050°C and then keep it warm; 2) The low-activation steel heated in step 1) is heated or cooled to 1100° C. or 1000° C. for thermal deformation treatment, or directly subjected to thermal deformation treatment at 1050° C., and then cooled to room temperature.

2. The heat treatment method for controlling the size and morphology of delta ferrite in low activation steel according to claim 1, characterized in that: The heating rate in step 1) is 20°C / s and the holding time is 10 min.

3. The heat treatment method for controlling the size and morphology of delta ferrite in low activation steel according to claim 1, wherein the rate of raising or lowering the temperature in step 2) is 20°C / s.

4. The heat treatment method for controlling the size and morphology of delta ferrite in low activation steel according to claim 1, wherein the thermal deformation treatment method in step 2) is a strain rate of 10s -1 , heat deformation treatment with a deformation amount of 60%.

5. The heat treatment method for controlling the size and morphology of delta ferrite in low activation steel according to claim 1, characterized in that: The chemical composition of the low activation steel is C: 0.04wt.%, Cr: 8.93wt.%, W: 1.72wt.%, Mn: 0.44wt.%, Si: 0.04wt.%, V: 0.22wt.%, Ta: 0.07wt.%, and the rest is iron.

6. The heat treatment method for controlling the size and morphology of delta ferrite in low activation steel according to claim 1, characterized in that: The size of the low-activated steel before heating in step 1) is φ8×12 mm, which is cut by a molybdenum wire cutting machine.

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