CN106148659A - A kind of preparation technology of high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel - Google Patents

Abstract

The invention discloses a preparation process of high-strength plastic ultra-fine grain low-activation ferrite/martensitic steel, belonging to the field of low-activation ferrite/martensitic steel. By introducing the rotary forging deformation process, the present invention not only achieves the purpose of grain size refinement, but also refines the size of carbides and improves the uniform distribution of carbides, and then eliminates dislocation plugging caused by deformation by annealing , to realize the preparation of high-strength plasticity and low activation ferrite/martensitic steel. This process uses the dispersion strengthening effect of ultra-fine grains and fine carbides to improve the strength of the material, and at the same time uses the uniform distribution of carbides to improve the strain hardening ability to improve the plasticity of the material. The strong plasticity of the ultra-fine-grained low-activation ferrite/martensitic steel of the invention is significantly improved, and can be used for preparing a novel high-strength plasticity low-activation ferrite/martensitic steel for the nuclear power industry.

Description

Preparation process of a high-strength plastic ultrafine-grained low-activation ferrite/martensitic steel

Technical field:

The invention relates to the field of low-activation ferrite/martensitic steel, in particular to a preparation process of high-strength plastic ultra-fine grain low-activated ferrite/martensitic steel.

Background technique:

Low-activation ferritic/martensitic steels have excellent thermophysical properties and a mature technical foundation, and are generally considered to be the main candidate materials for future nuclear reactor construction. Since the service environment of low-activation ferritic/martensitic steel is a strong radiation environment, long-term irradiation will cause embrittlement of ferritic/martensitic steel, thus affecting the mechanical properties and fracture behavior of the steel. Recent studies have found that, compared with traditional coarse-grained materials, nano and submicron materials have better radiation resistance, and show good application prospects in the nuclear power industry.

At present, dense bulk nano/submicron structure materials can be prepared by refining the grains to the nanometer or submicron level through severe plastic deformation, which has attracted extensive attention. However, the nano/submicron materials prepared by these methods are difficult to realize industrial application due to the disadvantages of plastic deterioration, complicated preparation process, and limited external dimensions. Therefore, how to obtain nano- or sub-micron structures in larger bulk materials, and how to obtain nano- or sub-micron materials with good strength and toughness matching are problems that need to be solved.

Invention content:

The purpose of the present invention is to provide a method for preparing large-sized block ultrafine-grained low-activation ferrite/martensitic steel, which utilizes the method of combining rotary forging deformation and annealing treatment, through grain size and carbide The refinement and the uniform distribution of carbides are improved, and the strength and plasticity of low-activation ferrite/martensitic steel are improved at the same time, which overcomes the shortcomings of plastic deterioration of ultra-fine grained materials.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A preparation process for high-strength plastic ultra-fine-grained low-activation ferrite/martensitic steel, including smelting, forging, heat treatment, rotary forging deformation and annealing treatment, specifically includes the following steps:

1) After the raw materials are melted and cast into ingots, solution treatment, forging and heat treatment are carried out in sequence. The heat treatment process is as follows: quenching the forged sample at 1000-1150 °C, keeping it warm for 0.5-2 hours, taking out water quenching; and then , tempering treatment at 700-800°C, heat preservation for 1-3 hours, take it out and air-cool to room temperature;

2) Rotary forging deformation: process the heat-treated sample in step 2) into a cylindrical shape, and perform controlled deformation in separate passes on a precision swaging machine. The deformation of each pass is controlled at 5% to 20%, and the total deformation is 80% to 95%;

3) Annealing treatment: Anneal the sample deformed by rotary forging at 650-750°C, keep it warm for 10-30min, take it out and air-cool it to room temperature.

In the above step 1), the smelting process is to batch the raw materials according to the chemical composition of low activation ferrite/martensitic steel, put them into a CaO crucible, and adopt vacuum induction melting to cast ingots; by weight percentage, the low The chemical composition of activated ferrite/martensitic steel is: carbon: 0.08-0.14%, chromium: 8.5-9.5%, tungsten: 1.5-2.0%, vanadium: 0.2-0.3%, tantalum: 0.05-0.15%, manganese : 0.4-0.6%, silicon: 0-0.3%, the balance is iron and unavoidable impurities.

In the above step 1), the solution treatment process is: heating the ingot to 1050-1150 °C and keeping it warm for 1-3 hours; the forging process is: placing the sample obtained after the solution treatment on a hammer forging machine for forging , and then air-cooled to room temperature, the blank forging temperature is 1050-1150°C, and the final forging temperature is above 900°C.

The high-strength plastic ultrafine-grain low-activation ferrite/martensitic steel prepared according to the above-mentioned process has a grain size range of 100-400nm, and carbides are evenly distributed in the matrix, and the carbide size range is 10-80nm.

The elongation of the low-activation ferrite/martensitic steel is ≥28.0%, the yield strength is ≥590MPa, and the tensile strength is ≥760MPa.

Design idea of the present invention is:

By introducing the rotary forging deformation process, the present invention not only achieves the purpose of grain size refinement, but also refines the size of carbides and improves the uniform distribution of carbides, and then eliminates dislocation plugging caused by deformation by annealing , to realize the preparation of high-strength plasticity and low activation ferrite/martensitic steel. The strength of the material is improved by using the dispersion strengthening effect of ultra-fine grains and fine carbides, and the plasticity of the material is improved by improving the strain hardening ability caused by uniformly distributed carbides.

The present invention has the following advantages:

1. The present invention significantly improves the mechanical properties of low-activation ferrite/martensitic steel. The method of combining rotary forging deformation and annealing treatment is used to prepare an ultra-fine grain structure with uniform distribution of fine carbides, which significantly improves the strength and plasticity of the material. While the plasticity is good (the elongation rate is greater than 28.0%), it has a relatively high quality. High strength (yield strength is above 590MPa, tensile strength can reach above 760MPa).

2. The present invention adopts the combination process of rotary forging deformation and annealing treatment, and the preparation method is simple. By controlling the deformation process parameters and heat treatment system, the ultra-fine-grained low-activation ferrite/martensitic steel with high strength and plasticity can be prepared.

Description of drawings:

Fig. 1 is the microstructure photo of low activation ferrite/martensitic steel before the process of the present invention is handled; Wherein, (a) grain size and carbide distribution (scanning electron microscope observation 8000 *); (b) lath Carbide (transmission electron microscope observation 38000×).

Fig. 2 is the microstructure photo of low-activation ferrite/martensitic steel after the process of the present invention; wherein, (a) carbide distribution (scanning electron microscope observation 8000 ×); (b) grain size and carbonization Object distribution (transmission electron microscope observation 80000×).

Fig. 3 is the engineering stress-strain curve of the low activation ferrite/martensitic steel before and after the process of the present invention.

detailed description:

Example 1

Using industrial pure iron, metal chromium, tungsten, vanadium, titanium and manganese as raw materials, the chemical composition of the alloy prepared according to the mass fraction (wt.%) is: C: 0.11%, Cr: 8.86%, W: 1.62%, V: 0.24%, Ta: 0.11%, Mn: 0.45%, Si: 0.05%, and the balance is an alloy of Fe.

The specific production process steps are as follows:

1) Melting: Put the prepared raw materials into a CaO crucible, melt them in a vacuum induction furnace, and cast them into ingots. After the ingots are completely solidified, open the mold and take them out;

2) Solution treatment: heat the ingot to 1100°C for solution treatment, and keep it warm for 2 hours;

3) Forging: quickly place the sample in step 2) on a hammer forging machine for forging, then air-cool to room temperature, the blank forging temperature is about 1050°C, and the final forging temperature is above 900°C; Finally forged into a 30mm thick plate;

4) Heat treatment: quench the forged alloy at 1050°C, hold it for 1 hour, take it out and quench it quickly; then, carry out tempering treatment at 750°C, hold it for 2 hours, take it out and cool it to room temperature;

5) Rotary forging deformation: the alloy in step 4) is processed into a cylindrical sample with a diameter of 20 mm, and the controlled deformation is carried out in separate passes on the precision swaging machine. The deformation amount of each pass is controlled at 10%, and the total deformation amount is 90%, wherein, deformation amount=(cross-sectional area before deformation-cross-sectional area after deformation)/cross-sectional area before deformation;

6) Annealing treatment: Annealing the alloy deformed by rotary forging at 700° C., keeping it warm for 30 minutes, taking it out and air cooling to room temperature.

Fig. 2 is the microstructural figure of low-activation ferrite/martensitic steel after process treatment of the present invention, as can be seen from Fig. 2 (a), fine carbide is evenly distributed in matrix; By Fig. 2 (b) It can be seen that the grain size of the alloy is relatively uniform, the grain size is 200-300nm, the carbide size is 50-70nm, and they are evenly distributed in the matrix. And without the microstructure of the process alloy of the present invention (except the rotary forging deformation and the annealing process, all the other processes and parameters are the same as the embodiment case 1) see Fig. 1, as can be seen from Fig. 1 (a), its The grain size is about 30 μm, which is 100 times that of ultra-fine-grained ferrite/martensitic steel, and the carbides are mainly distributed in the grain boundaries and between martensitic laths; it can be seen from Figure 1(b) that the rod-shaped carbides are The size is: the long axis direction is about 200nm, and the short axis direction is about 100nm, which is much larger than the carbide size of ultrafine grain ferrite/martensitic steel. This remarkable grain refinement and the dispersed distribution of fine carbides have significantly improved the mechanical properties of ultrafine-grained ferritic/martensitic steels. The engineering stress-strain curve of ferrite/martensitic steel before and after the process of the present invention is processed as shown in Figure 3, as can be seen, the mechanical properties of the ultrafine-grained ferrite/martensitic steel after the present invention is processed It is: the yield strength of 606MPa, the tensile strength of 783MPa and the elongation of 28.0%, which are greatly improved compared with the mechanical properties of the ferrite/martensitic steel before the process of the present invention.

Example 2

Using industrial pure iron, metal chromium, tungsten, vanadium, titanium and manganese as raw materials, the chemical composition of the alloy prepared according to the mass fraction (wt.%) is: C: 0.12%, Cr: 8.79%, W: 1.78%, V: 0.24%, Ta: 0.09%, Mn: 0.52%, Si: 0.22%, and the balance is an alloy of Fe.

The specific production process steps are as follows:

1) Melting: Put the prepared raw materials into a CaO crucible, melt them in a vacuum induction furnace, and cast them into ingots. After the ingots are completely solidified, open the mold and take them out;

2) Solution treatment: heat the ingot to 1100°C for solution treatment, and keep it warm for 2 hours;

3) Forging: quickly place the sample in step 2) on a hammer forging machine for forging, then air-cool to room temperature, the blank forging temperature is about 1050°C, and the final forging temperature is above 900°C; Finally forged into a 32mm thick plate;

4) Heat treatment: quench the forged alloy at 1030°C, hold it for 1 hour, take it out and quench it quickly; then, carry out tempering treatment at 740°C, hold it for 2 hours, take it out and cool it to room temperature;

5) Rotary forging deformation: Process the plate in step 4) into a cylindrical sample with a diameter of 22 mm, and carry out controlled deformation in separate passes on a precision swaging machine. The deformation of each pass is controlled at 6%, and the total deformation is 93%; Wherein, deformation amount=(cross-sectional area before deformation-cross-sectional area after deformation)/cross-sectional area before deformation;

6) Annealing treatment: the alloy deformed by rotary forging is annealed at 720° C., kept for 20 minutes, taken out and air-cooled to room temperature.

The microstructure of the ultrafine-grained ferrite/martensitic steel obtained under this process condition is the same as that in Example 1, the grain size has no obvious change, about 200-300nm, and the carbide size is about 50-300nm. 70nm, and evenly distributed in the matrix. The mechanical properties of ultra-fine-grained ferrite/martensitic steel at room temperature: the yield strength of 598MPa, the tensile strength of 760MPa and the elongation of 28.5%, compared with the mechanical properties of ferrite/martensitic steel before the process of the present invention is processed Performance has been greatly improved.

The invention adopts the combination process of rotary forging deformation and annealing treatment, not only prepares large-sized block ultra-fine grain low-activation ferrite/martensitic steel, but also meets the requirements of high-strength plasticity of the material, and the prepared ultra-fine Crystal low activation ferrite/martensitic steel has excellent mechanical properties.

Claims (7)

1. the preparation technology of a high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel, it is characterised in that: should Preparation technology comprises the steps:

1) by after raw material melting ingot casting, solution treatment, forging and heat treatment are carried out successively, described heat treated Cheng Wei: the sample after forging is carried out Quenching Treatment at 1000～1150 DEG C, is incubated 0.5～2h, take out shrend； Then, carry out temper at 700～800 DEG C, be incubated 1～3h, take out air cooling to room temperature；

2) swaging deformation is rotated: by step 2) sample after heat treatment is processed into cylindric, at accurate swager On carry out shunting time controllable deforming, every time deformation amount controlling is 5%～20%, and total deformation is 80%～95%；

3) annealing: the sample after rotating swaging deformation makes annealing treatment at 650～750 DEG C, insulation 10～30min, take out air cooling to room temperature.

2. according to the preparation work of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 Skill, it is characterised in that: step 1) in, described fusion process is that raw material loads CaO crucible in proportion, Use vacuum induction melting ingot casting.

3. according to the preparation of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 or 2 Technique, it is characterised in that: step 1) in, raw material is according to the chemical composition of low activation ferrite/martensite steel Carry out dispensing；By weight percentage, the chemical composition of described low activation ferrite/martensite steel is: carbon: 0.08～0.14%, chromium: 8.5～9.5%, tungsten: 1.5～2.0%, vanadium: 0.2～0.3%, tantalum: 0.05～0.15%, manganese: 0.4～0.6 %, silicon: 0～0.3%, surplus is ferrum and inevitable impurity.

4. according to the preparation work of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 Skill, it is characterised in that: step 1) in, described solution treatment is ingot casting to be heated to 1050～1150 DEG C and protects Temperature 1～3h.

5. according to the preparation work of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 Skill, it is characterised in that: step 1) in, described forging process is: be placed on by gained sample after solution treatment Forging on swager, then air cooling is to room temperature, and cogging forging temperature is 1050～1150 DEG C, final forging temperature More than 900 DEG C.

6. according to the preparation work of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 Skill, it is characterised in that: through step 3) crystallite dimension of gained low activation ferrite/martensite steel after annealing Scope is 100～400nm, and carbide is uniformly distributed in matrix, and carbide size scope is 10～80nm.

7. according to the preparation work of the high-strength plasticity Ultra-fine Grained low activation ferrite/martensite steel described in claim 1 Skill, it is characterised in that: elongation percentage >=28.0% of described low activation ferrite/martensite steel, yield strength >= 590MPa, tensile strength >=760MPa.