CN104911501A - Super-strength high-carbon potential dislocation martensitic steel, and preparation method thereof - Google Patents

Abstract

The invention discloses an ultra-high-strength high-carbon dislocation martensitic steel and a preparation method thereof. The chemical composition of the ultra-high-strength high-carbon dislocation martensitic steel is: C: 0.6-0.85%; Si: 0.01 ~0.8%; Mn: 0.1~0.5%; Cr: 0.8~2.0%; Cu: 0.05~0.4%; Ni: 0.05~0.3%; Ti: 0.02~0.1%; V: 0.02~0.2%; Nb: 0.02~ 0.15%; P: <0.02%; S: <0.02%, the balance is Fe. The method includes: 1) melting the raw material components into an ingot; 2) heating the ingot to 1100-1200° C. for 2 hours, then forging or rolling to obtain a green body, and then air-cooling to room temperature; 3) heating the green body to 500 Roll at ～700℃ for 1.5h, and the reduction is 50～90%; 4) Heat the rolled material to 750～900℃ and keep it for 5～30min, then quickly quench to room temperature, and then temper at 160～350℃ Processing made of ultra-high strength martensitic steel. The ultra-high-strength martensitic steel has good comprehensive mechanical properties, and both strength and plasticity exceed most maraging steels; the preparation process is simple, and the operation process is highly controllable.

Description

A kind of ultra-high-strength high-carbon dislocation martensitic steel and its preparation method

technical field

The invention belongs to the technical field of high-strength steel preparation, and in particular relates to an ultra-high-strength high-carbon dislocation martensitic steel and a preparation method thereof.

Background technique

With the continuous development of modern industry, the application fields of ultra-high-strength steel continue to expand, and the demand is increasing. High-alloy ultra-high-strength steel, such as secondary hardening ultra-high-strength steel such as AerMet100, AF1410, 9Ni-4Co and 9Ni-4Co, and maraging steel, such as 18Ni(250), 18Ni(300), Custom465, Custom475, etc. , although it has a high combination of strength and toughness, but because it contains more precious alloying elements Co, Ni and Mo, the material cost is expensive, which limits its application field. Nano-bainite steel is a new generation of high-strength steel developed in recent years. Its ultimate tensile strength can reach 2.5GPa, yield strength can reach 1.7GPa, and it has good plasticity. However, the precious alloying element Co is often added to the steel, and it needs to be austempered for several days to several months at a lower temperature for a long time, so that the production cycle is too long, the cost is high, and there are certain restrictions on the size of the material. It is not suitable for large-scale materials. In addition, nanobainite has poor toughness when subjected to impact loads, which limits its application.

Therefore, the research and development of low-cost ultra-high strength steel is the development trend of steel materials in the future. C is one of the most effective elements in steel to improve the strength of materials, but the carbon content in low-temperature tempered martensitic steel is generally controlled within 0.30wt.%. Excessive carbon will lead to a large number of twins in the quenched structure Martensite, and the amount of twinned martensite will increase as the carbon content increases, resulting in an increase in the brittleness of the material. High-carbon martensite in low-temperature tempering is often used in fields that bear less impact load, such as cutting tools, molds, bearings, etc. In the current research reports, it has not been possible to obtain ultra-high strength and ductility martensitic steel materials after quenching high-carbon martensite and tempering at low temperature.

Contents of the invention

The purpose of the present invention is to provide an ultra-high-strength high-carbon dislocation martensitic steel and its preparation method. The comprehensive mechanical properties of the ultra-high-strength martensitic steel are good, and the strength and plasticity are higher than most martensitic steels. Aging steel: the preparation method has simple process and strong controllability in the operation process, and can adjust the size of austenite grains in the martensitic steel according to the temperature and time of heat treatment.

The present invention is realized through the following technical solutions:

An ultra-high-strength high-carbon dislocation martensitic steel. In terms of mass percentage, the chemical composition of the ultra-high-strength martensitic steel is: C: 0.6%-0.85%; Si: 0.01%-0.8%; Mn Cr: 0.8% to 2.0%; Cu: 0.05% to 0.4%; Ni: 0.05% to 0.3%; Ti: 0.02% to 0.1%; V: 0.02% to 0.2%; Nb: 0.02 %～0.15%; P: <0.02%; S: <0.02%, the balance is Fe.

The yield strength Rp _0.2 of the ultra-high-strength high-carbon dislocation martensitic steel is 1950-2250 MPa, the tensile strength Rm is 2150-2400 MPa, and the elongation is 6-10%.

The average grain size of original austenite in the ultra-high-strength high-carbon dislocation martensitic steel is less than 10 μm; the microstructure of the ultra-high-strength high-carbon dislocation martensitic steel is full dislocation martensite or The substructure martensite is mainly accompanied by twin substructure martensite, and the volume fraction of twin substructure martensite is controlled within 20% of the microstructure.

A method for preparing an ultra-high-strength high-carbon dislocation martensitic steel, characterized in that it comprises the following steps:

1) According to the ratio of the chemical composition of the ultra-high-strength high-carbon dislocation type martensitic steel described in claim 1, the raw material steel, ferrochrome, ferrosilicon and pig iron are heated and heated until the raw materials are melted into molten steel, and then poured into molten steel successively Add ferrovanadium, ferroniobium, electrolytic nickel, pure copper, ferromanganese and titanium, keep warm until the added ingredients are homogenized, and then cast into steel ingots, and the casting temperature does not exceed 1550°C;

2) Heating the steel ingot to 1100-1200°C and keeping it warm for 2 hours, then forging or rolling to obtain a green body, and air-cooling to room temperature;

3) Heat the green body to 500-700°C, keep it warm for 1.5h, and then roll it. During the rolling process, the reduction is 50-90%;

4) Heat the material treated in step 3) to 750-900°C, keep it warm for 5-30 minutes, cool to room temperature, and then temper at 160-350°C for 1-2.5 hours to obtain an ultra-high-strength, high-carbon dislocation type horse Tensitic steel.

Step 2) is to forge or roll the ingot several times to make a slab or a round bar.

Step 2) The temperature of the final forging or final rolling for forging or rolling is 800-900°C.

The rolling process in step 3) is completed in 2 to 5 passes.

Step 4) cooling to room temperature is to cool the material in water or quenching oil.

Step 1) is to put raw steel, ferrochrome, ferrosilicon and pig iron into an intermediate frequency induction furnace and heat up until the raw materials are melted into molten steel.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. The present invention adds an appropriate amount of grain-refining elements V, Ti and Nb to the alloy, and controls the growth of austenite grain size through the adjustment of heating temperature and holding time in the heat treatment process, so that the austenite The grain size is controlled within 10 μm, and the microstructure of ultra-high-strength high-carbon dislocation martensitic steel is full dislocation martensite or mainly dislocation substructure martensite with twin substructure Martensite, the volume fraction of the twinned substructure martensite is within 20% of the microstructure; a small amount of undissolved carbide is also allowed to exist in the microstructure.

2. The highest tensile strength of the ultra-high-strength high-carbon dislocation martensitic steel of the present invention can reach 2.4GPa, and has an elongation of 10%, and the toughness of the material reaches that of 18Ni (C350) maraging steel Level, and Rp _0.2 ≥ 1950Mpa, Rm ≥ 2300MPa, elongation A ≥ 6%, but the cost of the material used is less than 1/100 of the cost of maraging steel.

3. The chemical composition of the ultra-high-strength high-carbon dislocation martensitic steel of the present invention does not contain precious alloy elements, the material cost is low, and the preparation method and processing technology are simple, which is comparable to the existing super bainite austempering process. Compared with this process, the quenching and tempering process does not require long-term isothermal treatment, and the production efficiency is high and easy to implement.

4. The application of the ultra-high-strength high-carbon dislocation martensitic steel of the present invention is not limited by the shape of the workpiece, and the material can be processed into workpieces of various shapes before heat treatment, and then heat treated, so the application range is wide.

Description of drawings

Fig. 1 is the electron micrograph of structure after rolling and quenching of 1# material;

Among them, (a) is the structure of sample 1# after warm rolling; (b) is the grain boundary display of sample 1# after heat treatment; (c) is the structure of sample 1# under TEM after quenching;

Fig. 2 is the electron micrograph of structure after rolling and quenching of 2# material;

Among them, (a) is the structure of 2# sample after warm rolling; (b) is the structure of 2# sample after quenching under TEM;

Fig. 3 is the electron micrograph of structure after rolling and quenching of 3# material;

Among them, (a) is the structure of 3# sample after warm rolling; (b) is the structure of 3# sample after quenching under TEM;

Fig. 4 is the electron micrograph of structure after rolling and quenching of 4# material;

Among them, (a) is the structure of 4# sample after warm rolling; (b) is the structure of 4# sample after quenching under TEM;

Fig. 5 is the electron micrograph of structure after rolling and quenching of 5# material;

Among them, (a) is the structure of 5# sample after warm rolling; (b) is the structure of 5# sample after quenching under TEM

Fig. 6 is the electron micrograph of structure after rolling and quenching of 6# material;

Among them, (a) is the structure of 6# sample after warm rolling; (b) is the structure of 6# sample after quenching under TEM.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

The chemical composition of the ultra-high-strength high-carbon dislocation martensitic steel of the present invention is (wt.%): C: 0.6-0.85, Si: 0.01-0.8, Mn: 0.1-0.5, Cr: 0.8-2.0, Cu: 0.05-0.4, Ni: 0.05-0.3, Ti: 0.02-0.1, V: 0.02-0.2, Nb: 0.02-0.15, P: <0.02, S: <0.02, and the balance is Fe.

The ultra-high-strength and high-carbon dislocation martensitic steel with the above-mentioned composition is smelted and cast into an ingot by vacuum or conventional methods; Pass rolling or forging into slab or round bar, the final rolling or final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; then the forged or rolled material is heated to 500-700°C and kept for 1.5h Warm rolling is carried out, and the rolling process is completed in 2 to 5 passes according to the size of the material, and the reduction is 50 to 90%.

The ultra-high-strength high-carbon dislocation martensitic steel is obtained by adding an appropriate amount of grain-refining elements V, Ti, and Nb to the alloy, and controlling the austenite grain size by adjusting the heating temperature and holding time during the heat treatment process. The growth of grain size, the grain size of austenite should be controlled within 10μm. The material after warm rolling is heated to 750-900°C and kept for 5-30 minutes, then quickly cooled to room temperature in water or quenching oil, and then tempered at 160-350°C for 1-2.5 hours.

The quenched microstructure of the ultra-high-strength high-carbon dislocation martensitic steel is mainly full dislocation martensite or dislocation substructure martensite with a small amount of twin substructure martensite, twin martensite The volume fraction of the body should be controlled within 20%, and a small amount of undissolved carbide is allowed in the structure; after tempering, the structure is tempered martensite or tempered martensite and a small amount of undissolved carbide.

The steel of the invention prepared according to the above chemical composition, treatment process and structure control technology not only has super high tensile strength, but also has good plasticity, and the comprehensive mechanical properties reach the level of 18Ni (C350). The specific properties are: Rp _0.2 ≥ 1950Mpa, Rm ≥ 2300MPa, A ≥ 6%.

According to the composition design requirements of the present invention, the composition of 6 furnaces of steel is designed below, numbered 1#～6#, which is smelted by electromagnetic induction furnace vacuum melting or conventional methods, and cast into Ф100mm round bars. The chemical composition of 6 furnaces of steel is shown in the table 1.

Table 1 Chemical composition of ultra-high strength steel (wt.%)

Example 1

Heat the 1# sample after vacuum induction melting to 1100-1200°C for 2 hours and then forge it to form a thick slab with a thickness of 25mm. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; The material was heated to 600°C for 1.5h and then warm rolled. The rolling process was completed in 3 passes with a reduction of 80% to obtain a plate with a thickness of 5mm. The material structure after rolling is that nano-carbides are dispersed on the ultra-fine ferrite matrix, as shown in Fig. 1(a). After the rolled material is kept at 850°C for 10 minutes, it is quickly quenched into water. The grain size of the prior austenite is 4-7 μm, as shown in Figure 1(b). body, as shown in Figure 1(c). The mechanical properties of the quenched sample after tempering at 160°C for 1 hour are: R _p0.2 = 2023MPa, R _m = 2400MPa, A = 10%.

Example 2

Heat the 2# sample smelted by the conventional method to 1100-1200°C for 2 hours and then forge it to form a Ф40mm rod. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; After holding at ℃ for 1.5h, warm rolling is carried out. The rolling process is completed in 2 passes with a reduction of 50% to obtain a Ф20mm rod. The material structure after rolling is that nano-carbides are dispersed on the ultra-fine ferrite matrix, as shown in Fig. 2(a). After the rolled material was kept at 800°C for 20 minutes, it was quickly quenched into water. The grain size of the prior austenite was 4-6 μm. Show. The mechanical properties of the quenched sample after tempering at 200°C for 1.5h are: R _p0.2 = 1987MPa, R _m = 2311MPa, A = 7.2%.

Example 3

Heat the 3# sample smelted by the conventional method to 1100-1200°C for 2 hours and then forge it into a Ф45mm rod. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; After holding at ℃ for 1.5h, warm rolling is carried out. The rolling process is completed in 5 passes with a reduction of 90% to obtain a Ф5mm rod. The material structure after rolling is that nano-carbides are dispersed on the ultra-fine ferrite matrix, as shown in Fig. 3(a). After the rolled material is kept at 830°C for 15 minutes, it is quickly quenched into the oil. The grain size of the original austenite is 4-7 μm. The structure after quenching is mainly dislocation substructure martensite and twin martensite. The amount is less than 10%, as shown in Fig. 3(b). The mechanical properties of the quenched sample after tempering at 250°C for 2.5 hours are: R _p0.2 = 2052MPa, R _m = 2407MPa, A = 9.3%.

Example 4

Heat the 4# sample after vacuum induction melting to 1100-1200°C for 2 hours, then roll it into a thick slab with a thickness of 45mm. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; The finished material was heated to 500°C for 1.5h and then warm rolled. The rolling process was completed in 3 passes, with a reduction of 55%, and a plate with a thickness of 20mm was obtained. After rolling, the material structure was nano carbide dispersed in super On the fine ferrite matrix, as shown in Fig. 4(a). After the rolled material is kept at 750°C for 30 minutes, it is quickly quenched into the oil. The grain size of the original austenite is 4-6 μm, and the structure after quenching is dislocation substructure martensite, with a small amount of undissolved carbide , as shown in Figure 4(b). The mechanical properties of the quenched sample after tempering at 200°C for 1.5h are: R _p0.2 =2056MPa, _Rm =2317MPa, A=6.7%.

Example 5

Heat the 5# sample after vacuum induction melting to 1100-1200°C for 2 hours and then forge it to form a thick slab with a thickness of 40mm. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; The material is heated to 650°C for 1.5h and then warm rolled. The rolling process is completed in 5 passes, with a reduction of 75%, and a plate with a thickness of 10mm is obtained. After rolling, the material structure is nanometer carbide dispersed in ultrafine iron On the matrix of the body, as shown in Figure 5(a). After the rolled material is kept at 880°C for 20 minutes, it is quickly quenched into the oil. The grain size of the original austenite is 6-10 μm. The structure after quenching is mainly dislocation substructure martensite and twin martensite. The amount is less than 15%, as shown in Fig. 5(b). The mechanical properties of the quenched sample after tempering at 250°C for 2 hours are: R _p0.2 = 2127MPa, R _m = 2412MPa, A = 6.1%.

Example 6

Heat the 6# sample after vacuum induction melting to 1100-1200°C for 2 hours, then forge it into a thick slab with a thickness of 45mm. The final forging temperature is controlled at 800-900°C, and then air-cooled to room temperature; The material was heated to 620°C for 1.5h and then warm rolled. The rolling process was completed in 5 passes with a reduction of 85% to obtain a plate with a thickness of 5mm. The material structure after rolling is that nano-carbides are dispersed on the ultra-fine ferrite matrix, as shown in Fig. 6(a). After the rolled material is kept at 860°C for 12 minutes, it is quickly quenched into the oil. The grain size of the original austenite is 5-8 μm. The structure after quenching is mainly dislocation substructure martensite and twin martensite. The amount is less than 20%, as shown in Figure 6(b). The mechanical properties of the quenched sample after tempering at 350°C for 1 hour are: R _p0.2 = 2176MPa, R _m = 2426MPa, A = 6%.

In summary, the original austenite grain size in the ultra-high strength martensitic steel of the present invention is less than 10 μm, and the microstructure after quenching is mainly full dislocation martensite or dislocation substructure martensite with some A small amount of twinned substructure martensite, the volume fraction of twinned martensite should be less than 20%; in addition, a small amount of undissolved carbide is allowed in the structure. The ultra-high-strength martensitic steel of the present invention has good comprehensive mechanical properties: Rp0.2≥1950MPa, Rm≥2300MPa, A≥6%.

The production process of the invention is simple, the strength and plasticity exceed most maraging steels, and the material does not need to add a large amount of alloy elements, so the cost can be greatly reduced. The steel prepared by the invention has ultra-high strength, can reach the level of 18Ni (C350), the highest tensile strength of the material can reach 2.4GPa, and has an elongation of 10%. The material does not contain precious alloy elements, the material cost is low, and the treatment process is simple. Compared with the super bainite isothermal quenching process, this quenching and tempering process does not require long-term isothermal treatment, and has high production efficiency and is easy to implement. The application of the steel of the invention is not limited by the shape of the workpiece, and the material can be processed into workpieces of various shapes before heat treatment, and then heat treated, which expands its application range.

Claims (9)

1. An ultra-high-strength high-carbon dislocation martensitic steel, characterized in that, in terms of mass percentage, the chemical composition of the ultra-high-strength high-carbon dislocation martensitic steel is: C: 0.6% to 0.85 %; Si: 0.01% to 0.8%; Mn: 0.1% to 0.5%; Cr: 0.8% to 2.0%; Cu: 0.05% to 0.4%; Ni: 0.05% to 0.3%; V: 0.02%-0.2%; Nb: 0.02%-0.15%; P: <0.02%; S: <0.02%, the balance being Fe. 2. An ultra-high-strength high-carbon dislocation martensitic steel according to claim 1, characterized in that the yield strength Rp _0.2 of the ultra-high-strength high-carbon dislocation martensitic steel is 1950-2250 MPa , the tensile strength Rm is 2150-2400MPa, and the elongation is 6-10%. 3. A kind of ultra-high-strength high-carbon dislocation martensitic steel according to claim 1, characterized in that, the average grain size of primary austenite in the ultra-high-strength high-carbon dislocation martensitic steel is less than 10 μm; the microstructure of ultra-high-strength high-carbon dislocation martensitic steel is full dislocation martensite or dislocation substructure martensite mainly accompanied by twin substructure martensite, in which twin The volume fraction of the grain substructure martensite is controlled within 20% of the microstructure. 4. A method for preparing an ultra-high-strength high-carbon dislocation martensitic steel, comprising the following steps: 1) According to the ratio of the chemical composition of the ultra-high-strength high-carbon dislocation type martensitic steel described in claim 1, the raw material steel, ferrochrome, ferrosilicon and pig iron are heated and heated until the raw materials are melted into molten steel, and then poured into molten steel successively Add ferrovanadium, ferroniobium, electrolytic nickel, pure copper, ferromanganese and titanium, keep warm until the added ingredients are homogenized, and then cast into steel ingots, and the casting temperature does not exceed 1550°C; 2) Heating the steel ingot to 1100-1200°C and keeping it warm for 2 hours, then forging or rolling to obtain a green body, and air-cooling to room temperature; 3) Heat the green body to 500-700°C, keep it warm for 1.5h, and then roll it. During the rolling process, the reduction is 50-90%; 4) Heat the material treated in step 3) to 750-900°C, keep it warm for 5-30 minutes, cool to room temperature, and then temper at 160-350°C for 1-2.5 hours to obtain an ultra-high-strength, high-carbon dislocation type horse Tensitic steel. 5. A method for preparing an ultra-high-strength high-carbon dislocation martensitic steel according to claim 4, wherein step 2) is to forge or roll the ingot several times to make a slab or round stick. 6. the preparation method of a kind of ultra-high-strength high-carbon dislocation martensitic steel according to claim 4, is characterized in that, the temperature of step 2) carrying out the final forging or final rolling of forging or rolling is 800 ~900°C. 7. The method for preparing an ultra-high-strength high-carbon dislocation martensitic steel according to claim 4, characterized in that the rolling process in step 3) is completed in 2-5 passes. 8 . The method for preparing an ultra-high-strength high-carbon dislocation martensitic steel according to claim 4 , wherein the step 4) cooling to room temperature is cooling the material in water or quenching oil. 9. The preparation method of a kind of ultra-high-strength high-carbon dislocation martensitic steel according to claim 4, characterized in that, step 1) is to load raw material steel, ferrochrome, ferrosilicon and pig iron into intermediate frequency induction The furnace is heated to raise the temperature until the raw materials are melted into molten steel.