CN106636961B - One kind mutually strengthens easily welding steel and preparation method containing Cu nanometers - Google Patents

Abstract

The invention provides a Cu-containing nano-phase strengthened easy-weld steel and a preparation method thereof. The weight percent composition is: C<0.05, Si:0.1~0.3, Mn:0.5~1.5, S<0.002, P<0.004, Cu:1.5~2.5, Ni:4~8, Al:0.3~0.8, Mo:0.2 ～1, Cr<1, Nb: 0.01～0.04, Ti: 0.01～0.05, V: 0.01～0.08, and the rest are Fe and unavoidable impurity elements. Induction melting and casting are carried out under the protective gas of argon; the ingot is heated at 1100-1200°C for 1-3h, and then hot-rolled directly. High-pressure water cooling, hot-rolled deformation of 50%-90%; selective solution and aging heat treatment of the rolled steel plate to obtain high-strength, high-toughness and easy-to-weld steel. The alloy steel of the invention has high strength, good plasticity, good low temperature impact toughness and easy welding. In addition, the processing technology has high controllability, low cost and simple operation.

Description

A kind of Cu nano-phase strengthened easy-weld steel and its preparation method

technical field

The invention relates to an easy-weld steel, and the invention also relates to a preparation method of the easy-weld steel.

Background technique

Copper-containing nano-phase low-alloy steel has high strength, good ductility, low-temperature impact toughness and easy welding performance, so it has a wide range of applications in the fields of shipbuilding, automobile manufacturing, construction, and bridges . The yield strength of general low-alloy steel is usually lower than 700MPa, and it is difficult to ensure good low-temperature toughness and welding performance while usually having high strength.

Traditional high-strength steels are all martensitic or lower bainite structures with high carbon content, and the introduction of a large amount of carbon elements greatly reduces the welding performance of the material. At the same time, in order to ensure the uniform structure of the core, it is necessary to ensure that the thicker steel plate has sufficient hardenability, and a higher content of alloying elements such as Ni, Cr, and Mo needs to be added to the steel. The higher the strength level of the steel is, the content of the added alloy elements will increase accordingly, and the cost of the alloy will naturally increase. With the increase of strength, the carbon equivalent of steel increases greatly, which greatly reduces the welding performance of steel.

At present, high-strength low-alloy steels obtained by adding alloying elements and controlled rolling and controlled cooling have been published at home and abroad. It is difficult to guarantee good elongation for those with a strength level greater than 800 MPa, and their low-temperature properties have not been characterized.

The patent document with publication number CN103361566A discloses a high-strength and high-toughness copper-containing low-alloy steel obtained by controlling casting, rolling and heat treatment processes. But its yield strength is lower than 850MPa.

The patent document with the publication number CN102140606A discloses a hot-rolled high-low alloy multi-phase steel obtained by controlling the interval time of each hot-rolling pass, the amount of deformation, the cooling rate and the isothermal treatment process. Its yield strength is 800MPa, but the elongation is only about 20%, and the low temperature toughness is not explained.

In the patent document with the publication number CN104513927A, a high-strength steel plate obtained by an isothermal heat treatment process is disclosed. Its yield strength is greater than 390MPa, its tensile strength is 800MPa, and its impact energy at -20°C is only 100J.

Contents of the invention

The object of the present invention is to provide a Cu-containing nano-phase strengthened easy-weld steel with high strength, good plasticity and low-temperature toughness. The purpose of the present invention is also to provide a method for preparing Cu-containing nano-phase strengthened easy-weld steel that can effectively control the microstructure and grain size of matrix phase and nano-precipitated phase.

The weight percent composition of the Cu-containing nanophase-strengthened easy-weld steel of the present invention is: C<0.05, Si: 0.1-0.3, Mn: 0.5-1.5, S<0.002, P<0.004, Cu: 1.5-2.5, Ni: 4 ～8, Al: 0.3～0.8, Mo: 0.2～1, Cr<1, Nb: 0.01～0.04, Ti: 0.01～0.05, V: 0.01～0.08, and the rest are Fe and unavoidable impurity elements.

The preparation method of the Cu-containing nano-phase strengthened easy-weld steel of the present invention is as follows: induction melting and casting are carried out under the protection of argon according to the designed composition, and the ingot is heated at 1100-1200 ° C for 1-3 hours for uniform optimization annealing, and then controlled Rolling controlled cooling technology is used for rolling, and the rolling specifically includes the following stages:

The first stage is rough rolling, the homogenized annealed ingot is directly rough rolled, the initial temperature of rough rolling is 1050-1150 ℃, the final rolling temperature is 1000-1050 ℃, and the total compression ratio of rough rolling is 50-80%;

The second stage is finishing rolling, the starting temperature of finishing rolling is 950-1000°C, the finishing rolling temperature is 850-900°C, and the total compression ratio of finishing rolling is 10%-30%;

The third stage is rapid water cooling. After finishing rolling, direct high-pressure watering for rapid cooling, and the final cooling temperature is below 50°C.

The steel plate after controlled rolling and cooling is subjected to solid solution and aging treatment, the solution temperature is 800°C-1000°C, the holding time is 5 minutes to 2 hours, and then rapidly cooled to room temperature; the aging temperature is 500°C-700°C, and the holding time 5 minutes to 10 hours, then rapidly cooled to room temperature with water.

The invention provides a Cu-containing nano-phase strengthened high-strength, high-toughness, easy-to-weld steel and a preparation method thereof. The invention controls the proportion relationship of Cu, Mn, Ni, and Al main elements, and adds other alloy elements, and combines reasonable rolling The process and heat treatment process effectively control the microstructure and grain size of the matrix phase and nano-precipitated phase, so as to obtain an easily weldable steel with high strength, good plasticity and low temperature toughness.

The effect of the main components contained in the Cu-containing nano-phase strengthened easy-weld steel of the present invention is:

Cu: Cu is an austenite stabilizing element, which can lower the austenite transformation temperature, inhibit the formation of high-temperature transformation products, and affect the transformation and refinement of the structure. At the same time, Cu can induce the precipitation of fine precipitates under certain heat treatment conditions, and make Ni, Al, Mn and other alloying elements aggregate to the precursors of the precipitates to form copper-rich nanophases, which can effectively replace carbon Strengthening, thereby reducing the carbon content. Therefore, adding a certain amount of copper can improve the strength, corrosion resistance, fatigue resistance, creep strength and impact toughness of the steel, and at the same time improve the welding performance, formability and machinability of the material.

Ni: Ni in solid solution form can increase the strength of ferrite. When the Ni content increases, it can ensure higher plasticity and improve strength at the same time. When the Ni content increases, the strength can be increased while ensuring higher plasticity. Ni can also ensure the uniformity of steel properties and significantly improve low temperature impact toughness.

Al: Al in steel has the ability of deoxidation and denitrification. A small amount of Al can inhibit the aging effect of low carbon steel, refine grains, improve impact toughness, and reduce the cold brittle transition temperature of steel. Al has no carbides, and alumina is a hard and brittle phase. When the aluminum content is high, during the forging and rolling process, the alumina particles form strips along the processing direction, which affects the plasticity and toughness of the steel.

Mn: The role of Mn in steel is to deoxidize and desulfurize. In steel, Mn has a certain effect on solid solution strengthening. In addition, Mn is also beneficial to improve the mechanical properties of steel such as strength and toughness, process performance, hardenability and hot workability. However, if the content of Mn in the steel is too high, it will affect the segregation phenomenon of the steel during casting, and the rolling is easy to crack.

The contents of various elements in the Cu-containing nano-phase strengthened easy-weld steel, especially the relatively noble metal elements of the present invention are all less, so that the cost of the steel is greatly reduced.

The alloy of the present invention is designed with precise composition ratio, while ensuring its strength, its carbon equivalent CE and cold crack sensitivity index Pcm are all low, and the heat-affected zone after welding is not easy to produce cold cracking tendency, so that the alloy of the invention has great Good welding performance, it can be welded without preheating or with low preheating temperature.

The rolling process of the present invention adopts advanced controlled rolling and controlled cooling technology, and has the advantages of fast processing speed, precise temperature control and drop, high cooling rate, uniform plate deformation and the like. By controlling the rough rolling temperature in the austenite recrystallization zone, rough rolling deformation, and the finish rolling temperature in the austenite or austenite-ferrite two-phase zone, controlling the cooling method and cooling rate, the apparent appearance of the matrix phase is controlled. Therefore, the alloy has better comprehensive mechanical properties in the as-rolled state. It also expands the operating range for the subsequent heat treatment process.

On the basis of the rolling process, the invention further optimizes the mechanical properties of the high-strength, high-toughness and easy-to-weld steel containing Cu nano phases by using reasonable solid solution and aging treatment processes. Through reasonable solution treatment, the austenite structure undergoes phase transformation to form polygonal ferrite or acicular ferrite. Then, the nano-precipitation is controlled by reasonable aging temperature and aging time, and the optimized size and number density matching of the precipitated phase are obtained. The nano-precipitated phase is evenly distributed in the matrix, and the hindrance to dislocations significantly improves the strength. At the same time, because the core of the precipitated phase is relatively small For the soft Cu element, the dislocations pass through the precipitated phase through the cutting mechanism, so the plasticity does not decrease significantly while the strength increases. Ni element is added to the steel to refine the grains, strengthen the grain boundaries, and significantly improve the low temperature toughness.

To sum up, the low-alloy steel of the present invention has low carbon content and carbon equivalent, and has super high strength while maintaining good plasticity and toughness. The low carbon equivalent makes it difficult to obtain horsepower during welding and cooling. It has excellent welding performance, which is extremely important for the shipbuilding industry to reduce material costs and welding costs. Copper-containing nano-phase strengthened high-strength, high-toughness and easy-to-weld steel is based on the design technology of ultra-low carbon alloy steel. A certain amount of alloying elements such as Cu, Mn, Ni, Al are added to the steel, and nano-scale The size of the precipitated phase, the precipitated phase can significantly improve the strength of the material, make up for the strength loss caused by the reduction of C, and add other microalloying elements to make the steel have high strength, high ductility, good low temperature toughness and welding performance .

Description of drawings

Fig. 1 is that embodiment 1 uses the metallographic photograph of the present invention.

Fig. 2 is that embodiment 2 uses the metallographic photograph of the present invention.

Fig. 3 is that embodiment 3 uses the metallographic photograph of the present invention.

Fig. 4 is the metallographic photograph of embodiment 4 using the present invention.

Fig. 5 is the metallographic photograph of embodiment 5 using the present invention.

Detailed ways

The technical solution of the present invention is described in detail below through specific examples. It should be understood that these examples are used to illustrate the present invention, rather than to limit the present invention. The present invention is simply improved under the concept of the present invention. All belong to the protection scope of the present invention.

Example 1:

This embodiment is a high-strength, high-toughness low-alloy steel containing Cu nanophase and its preparation method. The chemical composition (mass percentage) of the alloy is: C<0.05, Si:0.2, Mn:1, S:<0.003, P:< 0.004, Cu: 2, Ni: 4, Al: 0.5, Nb: 0.03, Ti: 0.05, the balance is Fe and unavoidable impurities. After homogenizing annealing at 1150°C for 2 hours, roll on the continuous rolling and continuous casting machine; the rough rolling start temperature is 1000°C, rolling 4 passes, the average reduction per time is 12%, and the total reduction rate is 50%. , the rolling temperature is controlled between 950°C and 1050°C; the starting temperature of finish rolling is 800°C, rolling 6 passes, the reduction of each pass is 15%, the total reduction rate is 80%, and the final rolling temperature is not more than 850°C, the final rolling thickness is 14mm; ultra-fast cooling water is used after rolling, and the final cooling temperature is below 50°C. Not undergone solution and aging treatment. The photo of metallographic structure is shown in Figure 1, and its mechanical properties are shown in Table 1

Example 2:

This embodiment is a high-strength, high-toughness low-alloy steel containing Cu nanophase and its preparation method. The chemical composition (mass percentage) of the alloy is: C<0.05, Si:0.2, Mn:1, S:<0.003, P:< 0.004, Cu: 2, Ni: 4, Al: 0.5, Nb: 0.03, Ti: 0.05, the balance is Fe and unavoidable impurities. After homogenizing annealing at 1150°C for 2 hours, roll on the continuous rolling and continuous casting machine; the rough rolling start temperature is 1000°C, rolling 4 passes, the average reduction per time is 12%, and the total reduction rate is 50%. , the rolling temperature is controlled between 950°C and 1050°C; the starting temperature of finish rolling is 800°C, rolling 6 passes, the reduction of each pass is 15%, the total reduction rate is 80%, and the final rolling temperature is not more than 850°C, the final rolling thickness is 14mm; ultra-fast cooling water is used after rolling, and the final cooling temperature is below 50°C. Solution treatment was carried out at 800°C, and the holding time was 2h. Aging treatment is carried out at 550°C, and the holding time is 1h. The photo of the metallographic structure is shown in Figure 2, and its mechanical properties are shown in Table 1

Example 3:

This embodiment is a high-strength, high-toughness low-alloy steel containing Cu nanophase and its preparation method. The chemical composition (mass percentage) of the alloy is: C<0.05, Si:0.2, Mn:1, S:<0.003, P:< 0.004, Cu: 2, Ni: 6, Al: 0.5, Mo: 0.5, Cr: 0.5, Nb: 0.03, Ti: 0.05, the balance is Fe and unavoidable impurities. After homogenizing annealing at 1150°C for 2 hours, roll on the continuous rolling and continuous casting machine; the rough rolling start temperature is 1000°C, rolling 4 passes, the average reduction per time is 12%, and the total reduction rate is 50%. , the rolling temperature is controlled between 950°C and 1050°C; the starting temperature of finish rolling is 900°C, rolling 6 passes, the reduction of each pass is 15%, the total reduction rate is 80%, and the final rolling temperature is not more than 920°C, the final rolling thickness is 14mm; ultra-fast cooling water is used after rolling, and the final cooling temperature is below 50°C. Aging treatment is carried out at 550°C, and the holding time is 2h. The photo of the metallographic structure is shown in Figure 3, and its mechanical properties are shown in Table 1

Example 4:

This embodiment is a high-strength, high-toughness low-alloy steel containing Cu nanophase and its preparation method. The chemical composition (mass percentage) of the alloy is: C<0.05, Si:0.2, Mn:1, S:<0.003, P:< 0.004, Cu: 2, Ni: 6, Al: 0.5, Nb: 0.03, Ti: 0.05, the balance is Fe and unavoidable impurities. After homogenizing annealing at 1150°C for 2 hours, roll on the continuous rolling and continuous casting machine; the rough rolling start temperature is 1000°C, rolling 4 passes, the average reduction per time is 12%, and the total reduction rate is 50%. , the rolling temperature is controlled between 950°C and 1050°C; the starting temperature of finish rolling is 800°C, rolling 6 passes, the reduction of each pass is 15%, the total reduction rate is 80%, and the final rolling temperature is not more than 850°C, the final rolling thickness is 14mm; ultra-fast cooling water is used after rolling, and the final cooling temperature is below 50°C. Solution treatment was carried out at 880°C for 5 minutes, and aging treatment was carried out at 565°C for 1 hour. The photo of metallographic structure is shown in Figure 4, and its mechanical properties are shown in Table 1

Example 5:

This embodiment is a high-strength, high-toughness low-alloy steel containing Cu nanophase and its preparation method. The chemical composition (mass percentage) of the alloy is: C<0.05, Si:0.2, Mn:1, S:<0.003, P:< 0.004, Cu: 2, Ni: 6, Al: 0.5, Nb: 0.03, Ti: 0.05, the balance is Fe and unavoidable impurities. After homogenizing annealing at 1150°C for 2 hours, roll on the continuous rolling and continuous casting machine; the rough rolling start temperature is 1000°C, rolling 4 passes, the average reduction per time is 12%, and the total reduction rate is 50%. , the rolling temperature is controlled between 950°C and 1050°C; the starting temperature of finish rolling is 800°C, rolling 6 passes, the reduction of each pass is 15%, the total reduction rate is 80%, and the final rolling temperature is not more than 850°C, the final rolling thickness is 14mm; ultra-fast cooling water is used after rolling, and the final cooling temperature is below 50°C. Solution treatment was carried out at 880°C with a holding time of 44 minutes, and aging treatment was carried out at 540°C with a holding time of 73 minutes. The photo of the metallographic structure is shown in Figure 5, and its mechanical properties are shown in Table 1.

Table 1 Mechanical properties of the invented steel

Claims (3)

1. A Cu-containing nanophase-strengthened easy-to-weld steel, characterized in that it is composed of: C<0.05, Si: 0.1-0.3, Mn: 0.5-1.5, S<0.002, P<0.004, Cu: 1.5-2.5 , Ni: 4-8, Al: 0.3-0.8, Mo: 0.2-1, Cr<1, Nb: 0.01-0.04, Ti: 0.01-0.05, V: 0.01-0.08, and the rest are Fe and unavoidable impurity elements , prepare the resulting Cu-containing nanophase-strengthened easy-weld steel according to the following method: According to the design composition, induction melting and casting are carried out under the protection of argon. The ingot is heated at 1100-1200°C for 1-3 hours for homogenization annealing, and then rolling is carried out by controlled rolling and controlled cooling technology. The rolling specifically includes the following stages : The first stage is rough rolling, the homogenized annealed ingot is directly rough rolled, the initial temperature of rough rolling is 1050-1150 ℃, the final rolling temperature is 1000-1050 ℃, and the total compression ratio of rough rolling is 50-80%; The second stage is finishing rolling, the starting temperature of finishing rolling is 950-1000°C, the finishing rolling temperature is 850-900°C, and the total compression ratio of finishing rolling is 10%-30%; The third stage is rapid water cooling. After finishing rolling, direct high-pressure watering for rapid cooling, and the final cooling temperature is below 50°C. 2. A preparation method for Cu-containing nanophase-strengthened easy-to-weld steel, characterized in that it consists of: C<0.05, Si: 0.1～0.3, Mn: 0.5～1.5, S<0.002, P<0.004, Cu:1.5～2.5, Ni:4～8, Al:0.3～0.8, Mo:0.2～1, Cr<1, Nb:0.01～0.04, Ti:0.01～0.05, V:0.01～0.08, the rest are Fe and The design composition of unavoidable impurity elements is induction smelted and casted under the protection of argon, and the ingot is heated at 1100-1200°C for 1-3 hours for homogenization annealing, and then rolled by controlled rolling and controlled cooling technology. Specifically, the system includes the following stages: The first stage is rough rolling, the homogenized annealed ingot is directly rough rolled, the initial temperature of rough rolling is 1050-1150 ℃, the final rolling temperature is 1000-1050 ℃, and the total compression ratio of rough rolling is 50-80%; The second stage is finishing rolling, the starting temperature of finishing rolling is 950-1000°C, the finishing rolling temperature is 850-900°C, and the total compression ratio of finishing rolling is 10%-30%; The third stage is rapid water cooling. After finishing rolling, direct high-pressure watering for rapid cooling, and the final cooling temperature is below 50°C. 3. The preparation method of Cu-containing nano-phase strengthened easy-weldable steel according to claim 2, characterized in that: the steel plate after controlled rolling and controlled cooling is subjected to solution and aging treatment, the solution temperature is 800 ° C to 1000 ° C, and the heat preservation The time is 5 minutes to 2 hours, followed by rapid water cooling; the aging temperature is 500°C to 700°C, and the holding time is 5 minutes to 10 hours, followed by rapid water cooling.