CN103361566A - High-strength high-toughness Cu-containing steel and production method thereof - Google Patents

Abstract

The invention provides a high-strength and high-toughness Cu-containing steel and a production method thereof. The weight percent of the chemical composition of the steel is: C 0.04%-0.07%, Si 0.25%-0.45%, Mn 0.60%-1.00%, Als0.01 %～0.03%, Ni2.40%～3.20%, Cu 1.20%～1.60%, Cr 0.65%～0.90%, Mo 0.30%～0.60%, Nb 0.02%～0.04%, Ti 0.01%～0.03%, P≤ 0.015%, S≤0.010%, and the balance is iron and unavoidable impurities. The whole molten iron is smelted by the dual method, through the top blowing of the converter or the combined top and bottom blowing, refining treatment outside the furnace, the continuous casting adopts the whole process of protective pouring, and the continuous casting slab is slowly cooled after it goes off the production line; the heating temperature of the billet is controlled at 1150 ~ 1250 ℃, The heating time is 3.5 to 5 hours, the starting temperature of rough rolling is controlled at 1050-1100°C, the starting temperature of finish rolling is controlled at 890-920°C, the temperature of finishing rolling is controlled at 800-860°C; the heat treatment is quenching temperature 860-920 ℃, holding time 0.5-3.5 hours, water cooling; tempering temperature 620-690 ℃, holding time 1-7 hours, air cooling. The yield strength of the steel plate is ≥690MPa, the Charpy V-notch impact energy at -80°C is greater than 120J, and the ductile-brittle transition temperature is lower than -80°C.

Description

A kind of high-strength and high-toughness Cu-containing steel and production method thereof

technical field

The invention relates to Cu-containing steel with yield strength ≥ 690 MPa, good low-temperature toughness (-80°C) and low ductile-brittle transition temperature and a production method thereof, belonging to the field of low-alloy steel manufacturing.

Background technique

Low-carbon (high-strength) low-alloy steel is one of the important engineering structural materials, and is widely used in offshore platforms, shipbuilding, boiler pressure vessels and bridges. It is difficult for general steel to have good low temperature toughness while ensuring high strength. With the development of science and technology, people have put forward higher requirements for the strength and toughness of steel. , in order to reduce the weight of the hull, increase the load capacity of the ship, and increase the speed of the ship, the ship plate steel is required to have higher strength, higher toughness, and certain corrosion resistance.

The study found that after solid solution and aging treatment, Cu-containing steel can produce good precipitation strengthening effect, which can compensate for the strength loss caused by reducing the C content; for the toughness of steel, the effect of copper is slightly lower than that of nickel, which can improve the impact of steel. At the same time, it can reduce the brittle transition temperature of steel; copper can also improve the atmospheric corrosion resistance of steel, high temperature oxidation resistance, and improve the fluidity of molten steel. Therefore, Cu-containing steel has been widely used in the fields of ordinary low alloy steel, structural steel, stainless steel and cast steel.

The patent application publication number CN 101956138A introduces a production method of Cu-containing low-alloy steel. The production process adopted is "steel billet→heating furnace→rough rolling→finish rolling→crimping". This patent focuses on controlling the heating process and rolling process to solve the problem of The surface quality of the Cu-containing steel produced by the traditional hot rolling process does not involve the performance of the Cu-containing steel product.

The patent application publication number CN 102011061A introduces a high-performance Cu-containing steel and its heat treatment process. This patent focuses on controlling the Ni/Cu content, reducing the C content, and improving the weldability of the steel, but does not involve Cu-containing steel. Low temperature (-80°C) performance and manufacturing methods.

Patent 200810035367 introduces a method for manufacturing Cu-containing high-strength and tough steel, but it is mainly used for thin slab production, and the thickness of the finished product is relatively thin.

Contents of the invention

The object of the present invention is to provide a Cu-containing steel plate and its manufacturing technology. Develop Cu-containing steel plates with high strength, high toughness, and low ductile-brittle transition temperature.

The purpose of the present invention is achieved in that the present invention adopts low carbon content design, and its chemical composition scope (Wt%) is: C 0.04%～0.07%, Si 0.25%～0.45%, Mn 0.60%～1.00%, Als0. 01%～0.03%, Ni2.40%～3.20%, Cu 1.20%～1.60%, Cr 0.65%～0.90%, Mo 0.30%～0.60%, Nb 0.02%～0.04%, Ti 0.01%～0.03%, P ≤0.015%, S≤0.010%. The balance is iron and unavoidable impurities.

The reasons for the limited amount of alloying elements are described in detail as follows in the present invention:

C: An element necessary to ensure strength, but if the amount added is too large, the weldability of the steel plate will be reduced. In the present invention, its content is controlled at 0.04% to 0.07%.

Si: An effective element to increase the strength of steel through solid solution strengthening. When the content is too high, the toughness and plasticity of steel will be reduced to a certain extent. The present invention limits Si to 0.25% to 0.45%.

Mn: It is an important solid solution strengthening element and deoxidizing element in steel. Mn can form high melting point MnS with S in steel, thereby avoiding the formation of low melting point FeS in steel, but too high Mn content will affect the toughness and welding of steel. performance. In the present invention, Mn is limited to 0.60% to 1.00%.

P, S: All are impurity elements in this steel type. Limit at P≤0.015%; S≤0.010%.

Cu: Improve the strength of steel through solid solution strengthening and precipitation strengthening, and appropriately improve the corrosion resistance of steel. In the present invention, Cu is used as a strengthening element, and its content is controlled at 1.20%-1.60%.

Ni: Improve the strength of steel while improving the low-temperature toughness of steel, reduce the ductile-brittle transition temperature of steel, and improve the corrosion resistance of steel. Adding Ni to Cu-containing steel can reduce the tendency of surface thermal cracking. In the present invention, its content is controlled at 2.40% to 3.20%.

Cr: Increase the strength and corrosion resistance of steel, and improve the tempering stability of steel. In the present invention, its content is 0.65% to 0.90%.

Mo: Improve the hardenability of steel, improve the impact toughness of steel by eliminating or reducing the temper brittleness caused by other alloying elements, and improve the strength and ductility of steel. In the present invention, its content is controlled at 0.30% to 0.60%.

Nb: The addition of a small amount of Nb increases the recrystallization termination temperature and promotes grain refinement, but when its content is too high, it affects the weldability of the steel. In the present invention, its content is controlled at 0.02% to 0.04%.

Ti: A strong carbonitride-forming element in steel, which can prevent the growth of austenite grains in the welding heat-affected zone, thereby improving the welding performance of steel. In the present invention, its content is controlled at 0.01% to 0.03%.

Als: deoxidizing element in steel, its content is controlled at 0.01%-0.03% in the present invention.

The concrete production technology feature of steel of the present invention is as follows:

Production process route: hot metal pretreatment→steelmaking→continuous casting→slab heating→rolling→heat treatment→finished product.

Steel-making process: use double-link method for full iron smelting, through converter top blowing or top-bottom composite blowing, carry out refining treatment outside the furnace, feed silicon-calcium wire as required to control the impurity content in the steel, and carry out micro-alloying to control the molten steel Medium gas content, the continuous casting adopts the whole process of protective pouring, and the continuous casting slabs are stacked and cooled slowly after they come off the production line, and the time is 48 to 96 hours.

Steel rolling process: billet heating temperature is controlled at 1150-1250°C, heating time is 3.5-5 hours, rough rolling start temperature is controlled at 1050-1100°C, finish rolling start temperature is controlled at 890-920°C, finish rolling temperature is controlled At 800-860°C.

Heat treatment process: In order to ensure the stability of the service performance of the steel plate, it is necessary to carry out quenching and tempering treatment on the rolled steel plate. The quenching and tempering treatment method is quenching + high temperature tempering. The fire temperature is 620-690°C, the holding time is 1-7 hours, and air-cooled.

The present invention can produce following beneficial effect after adopting above-mentioned technical scheme:

1. The Cu-containing steel of the present invention has high strength and good low-temperature toughness coordination, yield strength ≥ 690 MPa, and Charpy V-notch impact energy at -80°C greater than 120J.

2. The Cu-containing steel of the present invention has a low ductile-brittle transition temperature, and the ductile-brittle transition temperature is lower than -80°C, which meets the requirements for use in low temperature and severe cold conditions.

3 Produce steel plates with thickness specifications covering 10-80mm, which can meet the needs of extra-thick plates for marine engineering, steel for high-performance engineering machinery, and low-temperature steel for ships.

Description of drawings

Figure 1 is the metallographic structure of a 10mm steel plate;

Figure 2 is the metallographic structure of 16mm steel plate;

Figure 3 is the metallographic structure of 30mm steel plate;

Figure 4 shows the metallographic structure of a quarter of the 80mm steel plate in the thickness direction.

Detailed ways

The example of the present invention uses the chemical composition of steel in Table 1

Table 1 Chemical Composition (wt%)

Example C Si Mn P S Ni Cu Cr Mo Nb Ti Als 1 0.04 0.40 0.89 0.004 0.001 3.01 1.52 0.75 0.55 0.031 0.014 0.02 2 0.06 0.42 0.92 0.005 0.002 2.74 1.40 0.69 0.46 0.028 0.019 0.025 3 0.06 0.44 0.92 0.004 0.001 2.46 1.28 0.66 0.43 0.026 0.020 0.021 4 0.07 0.36 0.77 0.004 0.002 2.88 1.43 0.68 0.41 0.033 0.021 0.018

The production process of this embodiment is: pretreatment of molten iron, refining treatment after steelmaking in the converter, continuous casting after adjusting the temperature of the molten steel to the required temperature for tapping, the thickness of the continuous casting slab is 230mm, and the continuous casting slab is stacked slowly. Cool for 72 hours and heat after cleaning for rolling. The billet heating temperature is controlled at 1150-1250°C, the heating time is 3.5-5 hours, the rough rolling start temperature is controlled at 1050-1100°C, and the finish rolling start temperature is controlled at 890-920 ℃, and the finishing rolling temperature is controlled at 800-860 ℃.

The rolling process of table 2 example of the present invention

The surface of the rolled steel plate is subjected to quenching and tempering treatment after shot peening. Quenching temperature 860-920°C, holding time 0.5-3.5 hours, water cooling, tempering temperature 620-690°C, holding time 1-7 hours, air cooling. The heat treatment process is shown in Table 3.

Table 3 Steel plate heat treatment process

After heat treatment, the head and tail of each steel plate shall be sampled and inspected respectively, and the transverse properties of the steel plate shall be tested. Among them, the inspection item of the steel plate with a thickness specification of 10mm is the plate tensile force, and the rest is the circular tensile force. The drop weight sample is P-3 type, and the performance of the 50mm and 80mm steel plates is a quarter of the thickness of the steel plate. The performance of the steel plate after heat treatment is shown in Table 4 .

Table 4 Properties of steel plates after heat treatment

The finished steel plate meets the design requirements of yield strength ≥ 690MPa, -80°C Charpy V-notch impact energy greater than 120J, ductile-brittle transition temperature lower than -80°C, and the thickness specification covers 10-80mm, and the metallographic structure of the finished steel plate is tempered Sorbitite (Figure 1-4).

Claims (4)

1. a high-strength and high ductility contains the Cu steel, the weight percent that it is characterized in that the chemical composition of steel is: C0.04%～0.07%, Si 0.25%～0.45%, Mn 0.60%～1.00%, Als0.01%～0.03%, Ni2.40%～3.20%, Cu 1.20%～1.60%, Cr 0.65%～0.90%, Mo 0.30%～0.60%, Nb 0.02%～0.04%, Ti 0.01%～0.03%, P≤0.015%, S≤0.010%, surplus are iron and inevitable impurity.

2. one kind is used for the production method that high-strength and high ductility claimed in claim 1 contains the Cu steel, mainly comprise hot metal pretreatment → steel-making → continuous casting → heating steel billet → rolling → thermal treatment, it is characterized in that: the full molten iron smelting of duplex practice is adopted in steel-making, by converter top-blow or top bottom blowing, carrying out external refining processes, feed silicon-calcium wire and reduce S content, and carry out microalloying; Continuous casting adopts the whole process protection cast, the continuously cast bloom rear slow cooling of rolling off the production line; Billet heating temperature is controlled at 1150～1250 ℃, and 3.5～5 hours heat-up times, the roughing start rolling temperature is controlled at 1050～1100 ℃, and the finish rolling start rolling temperature is controlled at 890～920 ℃, and the finish rolling finishing temperature is controlled at 800～860 ℃; Thermal treatment is quenching+high tempering, 860～920 ℃ of quenching temperatures, and soaking time 0.5～3.5 hour, water-cooled, tempering temperature are 620～690 ℃, soaking time 1～7 hour, air cooling.

3. high-strength and high ductility according to claim 2 contains the production method of Cu steel, it is characterized in that: stacking slow cooling, 48～96 hours time are adopted in slow cooling.

4. high-strength and high ductility according to claim 2 contains the production method of Cu steel, it is characterized in that: steel rolling compression ratio 〉=2.8.

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