CN106906429B - A kind of superhigh intensity martensitic stain less steel and preparation method thereof - Google Patents

Abstract

The invention discloses an ultra-high-strength martensitic stainless steel and a preparation method thereof, which have high yield strength, high tensile strength, low elongation and good impact toughness. The preparation method includes the following steps, step 1, by weight percentage, preparing raw materials according to the stainless steel composition and burning loss, and melting the raw materials in a vacuum environment and pouring them into steel ingots; the composition of the steel ingots is by weight percentage, C 0.10%～0.25%, Cr 11.0%～17.0%, Mn 0.5%～2.0%, Si 1.1%～3.0%, Ni 0.1%～4.0%, Cu 0.1%～0.3%, P≤0.02%, S≤0.02% , the balance is iron and unavoidable impurity elements; step 2, start forging the steel ingot at 1050 ° C ~ 1200 ° C, the final forging temperature is 880 ° C ~ 920 ° C, the forging pressure ratio is greater than or equal to 5, air cooling after forging; step 3, Heat the forging at 950°C-1050°C for 2-4 hours, then water quench, then temper at 200-300°C for 2h-4h, and cool naturally to obtain ultra-high-strength martensitic stainless steel.

Description

A kind of ultra-high strength martensitic stainless steel and preparation method thereof

technical field

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

Background technique

With the rapid development of marine development, petrochemical industry, and aviation and aerospace industries, the demand for high-strength stainless steel with high strength, high toughness, high corrosion resistance, and good comprehensive properties such as welding has increased. Stainless steel is divided into five categories according to metallographic structure, namely austenitic stainless steel, duplex stainless steel, ferritic stainless steel, martensitic stainless steel and precipitation hardening stainless steel. Among them, martensitic precipitation hardening stainless steel has the highest strength level among stainless steels, so it has become a hot spot in research and development. Martensitic precipitation hardening stainless steel is a new type of steel developed in the mid-1960s. It has all the advantages of martensitic precipitation hardening steel, and has the corrosion resistance that martensitic precipitation hardening stainless steel does not have. Due to the excellent comprehensive properties of martensitic precipitation hardening stainless steel, it is commonly used in steam turbine blades, aviation components, reactive components, various containers, pipelines, petrochemical equipment, etc.

Martensitic precipitation hardening stainless steel is a high-strength stainless steel superimposed by two strengthening effects of low-carbon martensitic transformation strengthening and aging strengthening. In order to obtain excellent comprehensive properties, ultra-low carbon (mass fraction <0.05%) is usually required in composition. To ensure sufficient weldability and corrosion resistance, as shown in Table 2, the mechanical properties of typical martensitic precipitation hardening stainless steel at home and abroad. In addition, in order to ensure sufficient precipitation strengthening effect, it is usually necessary to add more alloying elements (such as Cu, Ni, Mo, Ti) to precipitate strengthening phases (such as copper-rich ε phase, NiAl phase, Ni ₃ Al phase, Laves phase). In order to meet the ultra-low carbon composition requirements of martensitic precipitation hardening stainless steel, it is necessary to increase the smelting process and improve the smelting technology, which will greatly increase the smelting cost. In addition, as shown in Table 1, martensitic precipitation hardening stainless steel contains a large amount of precious metals (such as Ni, Mo, Ti, etc.), which makes the alloy cost higher. Therefore, martensitic precipitation hardening stainless steel is often not widely used because of its high price. Therefore, the research and development of stainless steel with low cost, ultra-high strength and good comprehensive performance has very important economic benefits and industrial value.

Table 1 Composition of typical martensitic precipitation hardening stainless steel at home and abroad

Table 2 Mechanical properties of typical martensitic precipitation hardening stainless steel at home and abroad

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides an ultra-high-strength martensitic stainless steel and a preparation method thereof. The martensitic stainless steel has high yield strength, high tensile strength, high elongation, and good impact toughness, and It has excellent plasticity, toughness and corrosion resistance, but the cost is much lower than that of martensitic precipitation hardening stainless steel.

The present invention is realized through the following technical solutions:

An ultra-high-strength martensitic stainless steel. The composition of the ultra-high-strength martensitic stainless steel includes, by weight percentage, 0.10% to 0.25% of C, 11.0% to 17.0% of Cr, 0.5% to 2.0% of Mn, and 1.1% of Si %～3.0%, Ni0.1%～4.0%, Cu 0.1%～0.3%, P≤0.02%, S≤0.02%, and the balance is iron and unavoidable impurity elements.

Preferably, the main metallographic structure of the ultra-high-strength martensitic stainless steel is a lath martensite structure, 10-100nm scale carbides and a small amount of retained austenite distributed on the matrix.

Preferably, the weight percentage of the C is 0.10%-0.24%.

Preferably, the weight percentage of Si is 1.2%-2.5%.

Preferably, the weight percentage of Cr is 12.0%-16.0%.

Preferably, the weight percentage of Ni is 0.1%-3.8%.

A method for preparing an ultra-high-strength martensitic stainless steel, comprising the steps of,

Step 1, by weight percentage, prepare raw materials according to the stainless steel composition and burning loss, and melt the raw materials in a vacuum environment and pour them into steel ingots; the composition of the steel ingots is, by weight percentage, C 0.10% to 0.25%, Cr11. 0%～17.0%, Mn 0.5%～2.0%, Si 1.1%～3.0%, Ni 0.1%～4.0%, Cu 0.1%～0.3%, P≤0.02%, S≤0.02%, the balance is iron and non Avoided impurity elements;

Step 2, start forging the steel ingot at 1050°C-1200°C, the final forging temperature is 880°C-920°C, the forging-pressure ratio is greater than or equal to 5, and air-cool after forging;

Step 3, heat the forging at 950°C-1050°C for 2-4h, then water quench, then temper at 200°C-300°C for 2h-4h, and cool naturally to obtain ultra-high-strength martensitic stainless steel.

Preferably, the ultra-high-strength martensitic stainless steel prepared in step 3 has a yield strength of not less than 1300MPa, a tensile strength of not less than 1600MPa, an elongation of not less than 16%, and an impact toughness of not less than 60J/cm ² .

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

The invention provides a stainless steel with excellent comprehensive mechanical properties. Through the proportion of high content of carbon and silicon, and the synergy with other elements, the tensile strength can reach 1600Mpa, the elongation can reach 16%, and the impact toughness can reach 60J /cm ² . Such mechanical properties have exceeded the level of many martensitic precipitation hardening stainless steels, such as 17-4PH, 15-5PH. Although the martensitic stainless steel has such excellent comprehensive properties, it does not require an ultra-low carbon smelting process and a large amount of precious alloying elements. It only needs a simple heat treatment process, that is, conventional quenching and low temperature tempering, which makes it have the advantages of high performance and low cost. The ultra-high-strength martensitic stainless steel of the present invention not only has excellent corrosion resistance, can reduce material damage caused by corrosion, but also has excellent welding performance, and can meet the application on some workpieces that need to be welded. Therefore, it can be widely used in steam turbine blades, hydraulic machine valves, aviation structural parts, reactor components, petrochemical equipment, etc.

Further, by limiting the carbon content in ultra-high-strength martensitic stainless steel, it can better play the following three parts: (1) Make the material obtain martensite structure after quenching, so as to obtain martensite phase (2) Solid solution in martensite to form solid solution strengthening; (3) A certain amount of carbides are formed in the tempering process to obtain a certain precipitation strengthening.

Furthermore, by limiting the Cr content in the ultra-high-strength martensitic stainless steel, it can better meet the corrosion resistance requirements of stainless steel.

Further, by limiting the Si content in ultra-high-strength martensitic stainless steel, it can better suppress the precipitation and growth of carbides in the martensitic matrix during tempering, thereby preventing the appearance of Cr-deficient regions and Reduce the corrosion resistance, and also avoid the damage of the plasticity and toughness of the material by coarse carbides.

Further, by limiting the Ni content in ultra-high-strength martensitic stainless steel, it can better play the following two roles: (1) to improve the hardenability of steel; (2) to a certain extent toughness of steel.

Description of drawings

Fig. 1 is a metallographic structure diagram of the ultra-high strength martensitic stainless steel of the present invention after quenching and tempering.

Fig. 2 is the test comparison between the ultra-high strength martensitic stainless steel of the present invention and AISI420 and 17-4PH plan curve.

Fig. 3 is a scanning diagram of the impact fracture morphology of the ultra-high-strength martensitic stainless steel of the present invention.

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.

Example 1

The chemical composition by weight percentage is, C: 0.11%, Cr: 11%, Mn: 0.6%, Si: 1.2%, Ni: 0.1%, Cu: 0.1%, P≤0.02%, S:≤0.02%, Yu Feedstock in the form of iron is smelted in a vacuum induction furnace. After the smelted casting is kept at 1100°C for 2 hours, forging begins, and the final forging temperature is 880°C. Then the obtained forging is heated to 980°C for 4 hours and then quickly taken out of the furnace for water quenching, followed by tempering at 220°C for 4 hours.

The main metallographic structure of the obtained material is lath martensite structure and nano-carbide precipitation, has excellent strength, plasticity and toughness, and has good corrosion resistance and weldability. The yield strength is 1310MPa, the tensile strength is 1610MPa, the elongation is 16%, and the impact toughness at room temperature is 61J/cm ² .

Example 2

The chemical composition by weight percentage is, C: 0.24%, Cr: 12%, Mn: 2.0%, Si: 2.5%, Ni: 3.8%, Cu: 0.3%, P≤0.02%, S:≤0.02%, The raw material with the balance being iron is smelted in a vacuum induction furnace. After the smelted casting is kept at 1150°C for 2 hours, forging begins, and the final forging temperature is 890°C. Then the obtained forgings are heated to 1000°C for 4 hours and then quickly taken out of the furnace for water quenching, followed by tempering at 250°C for 4 hours.

The main metallographic structure of the obtained material is lath martensite structure and nano-carbide precipitation, has excellent strength, plasticity and toughness, and has good corrosion resistance and weldability. The yield strength is 1320MPa, the tensile strength is 1620MPa, the elongation is 16%, and the impact toughness at room temperature is 65J/cm ² .

Example 3

For the chemical composition by weight percentage, C: 0.25%, Cr: 16%, Mn: 1.1%, Si: 1.1%, Ni: 1%, Cu: 0.2%, P≤0.02%, S:≤0.02%, The raw material with the balance being iron is smelted in a vacuum induction furnace. After the smelted casting is held at 1180°C for 2 hours, forging begins, and the final forging temperature is 900°C. Then the obtained forging is heated to 1050°C for 4 hours and then quickly taken out of the furnace for water quenching, followed by tempering at 240°C for 4 hours.

The main metallographic structure of the obtained material is lath martensite structure and nano-carbide precipitation, has excellent strength, plasticity and toughness, and has good corrosion resistance and weldability. The yield strength is 1330MPa, the tensile strength is 1650MPa, the elongation is 16%, and the impact toughness at room temperature is 64J/cm ² .

Example 4

The chemical composition by weight percentage is, C: 0.15%, Cr: 15%, Mn: 1.5%, Si: 1.8%, Ni: 2%, Cu: 0.2%, P≤0.02%, S:≤0.02%, The raw material with the balance being iron is smelted in a vacuum induction furnace. After smelting, the castings are kept at 1200°C for 2 hours and then forged. The final forging temperature is 910°C. Then the obtained forgings are heated to 1050°C for 4 hours and then quickly taken out of the furnace for water quenching, followed by tempering at 300°C for 2 hours.

The main metallographic structure of the obtained material is lath martensite structure and nano-carbide precipitation, has excellent strength, plasticity and toughness, and has good corrosion resistance and weldability. The yield strength is 1300MPa, the tensile strength is 1670MPa, the elongation is 16%, and the impact toughness at room temperature is 68J/cm ² .

Example 5

The chemical composition by weight percentage is, C: 0.10%, Cr: 17%, Mn: 0.5%, Si: 3.0%, Ni: 4.0%, Cu: 0.2%, P≤0.02%, S:≤0.02%, The raw material with the balance being iron is smelted in a vacuum induction furnace. After the smelted casting is kept at 1060°C for 2 hours, forging begins, and the final forging temperature is 920°C. Then the obtained forging is heated to 950°C for 3 hours and then quickly taken out of the furnace for water quenching, followed by tempering at 200°C for 4 hours.

The main metallographic structure of the obtained material is lath martensite structure and nano-carbide precipitation, has excellent strength, plasticity and toughness, and has good corrosion resistance and weldability. The yield strength is 1310MPa, the tensile strength is 1630MPa, the elongation is 16%, and the impact toughness at room temperature is 65J/cm ² .

The above description is only a preferred example of the present invention, and it is only illustrative and non-restrictive for the present invention; those of ordinary skill in the art understand that it can be carried out within the spirit and scope defined by the claims of the present invention. Many modifications and adjustments will fall within the protection scope of the present invention.

Claims (7)

1. An ultra-high-strength martensitic stainless steel, characterized in that, the composition of the ultra-high-strength martensitic stainless steel is composed of the following components by weight percentage, C 0.10%～0.25%, Cr 11.0%～17.0% , Mn 0.5%~2.0%, Si 1.1%~3.0%, Ni 0.1%~4.0%, Cu 0.1%~0.3%, P≤0.02%, S≤0.02%, the balance is iron and unavoidable impurity elements; The main metallographic structure of the ultra-high-strength martensitic stainless steel is a lath martensite structure, 10-100nm scale carbides and a small amount of retained austenite distributed on the matrix. 2. An ultra-high-strength martensitic stainless steel according to claim 1, characterized in that the weight percentage of said C is 0.10%-0.24%. 3. An ultra-high-strength martensitic stainless steel according to claim 1, characterized in that the weight percentage of Si is 1.2%-2.5%. 4. An ultra-high-strength martensitic stainless steel according to claim 1, characterized in that the weight percentage of Cr is 12.0%-16.0%. 5. An ultra-high-strength martensitic stainless steel according to claim 1, characterized in that the weight percentage of Ni is 0.1%-3.8%. 6. A method for preparing an ultra-high-strength martensitic stainless steel, comprising the steps of, Step 1, by weight percentage, prepare raw materials according to the stainless steel composition and burning loss, and melt the raw materials in a vacuum environment and pour them into steel ingots; the composition of the steel ingots is, by weight percentage, C 0.10% to 0.25%, Cr11. 0%～17.0%, Mn 0.5%～2.0%, Si 1.1%～3.0%, Ni 0.1%～4.0%, Cu 0.1%～0.3%, P≤0.02%, S≤0.02%, the balance is iron and non Avoided impurity elements; Step 2, start forging the steel ingot at 1050°C-1200°C, the final forging temperature is 880°C-920°C, the forging-pressure ratio is greater than or equal to 5, and air-cool after forging; Step 3, heat the forging at 950°C-1050°C for 2-4h, then water quench, then temper at 200°C-300°C for 2h-4h, and cool naturally to obtain ultra-high-strength martensitic stainless steel. 7. The preparation method of a kind of ultra-high-strength martensitic stainless steel according to claim 6, characterized in that, the ultra-high-strength martensitic stainless steel prepared in step 3 has a yield strength of not less than 1300MPa, and a tensile strength of not less than Less than 1600MPa, elongation not less than 16%, impact toughness not less than 60J/cm ² .