CN102080191B - A niobium-boron composite hot-rolled high-strength container steel plate and its preparation method - Google Patents

Abstract

The invention discloses a niobium-boron composite hot rolled high-strength container steel plate and a preparation method thereof. The container steel plate comprises the following chemical components in percentage by weight: 0.04 to 0.05 percent of C, 0.20 to 0.30 percent of Si, 1.80 to 2.0 percent of Mn, less than 0.0092 percent of P, less than 0.0028 percent of S, less than 0.004 percent of N, 0.04 to 0.05 percent of Nb, less than 0.002 percent of B, 0.2 to 0.4 percent of Ni, 0.3 to 0.5 percent of Cr, 0.3 to 0.5 percent of Cu, 0.01 to 0.03 percent of Ti, and the balance of Fe and inevitable impurities. The preparation method comprises the following steps of: melting low-carbon steel, manufacturing a plate blank, heating the plate blank to the temperature of 1,250 DEG C, preserving the heat for 1 to 2 hours, performing hot rolling at the temperature of between 1,050 and 1,100 DEG C, and performing final rolling at the temperature of between 780 and 830 DEG C, wherein the thickness of the rolled thin plate is less than 2.0 millimeters; and performing laminar cooling at the cooling rate of 20 to 30 DEG C per second to the coiling temperature of between 500 and 510 DEG C, and preserving the heat to obtain the container plate with thin specification (less than 2.0 millimeters) and high strength (more than 700MPa). The method has the advantages that: the cost is low, bainite steel is obtained in a wide cooling rate range, the process is simple and operability is strong, the energy consumption is reduced, transportation expense is reduced, and the method is environmentally-friendly.

Description

A niobium-boron composite hot-rolled high-strength container steel plate and its preparation method

technical field

The invention belongs to the technical field of steel for containers, and in particular relates to a preparation method of a niobium-boron composite strengthened hot-rolled high-strength container plate with a tensile strength greater than 700 MPa.

Background technique

Nowadays, with the rapid increase of international trade, the position of container transportation is becoming more and more important. However, container steel plates must have strong corrosion resistance, high strength, and good formability. Nowadays, the tensile strength of container steel plates produced by many domestic enterprises is mostly greater than 490MPa, while the proportion of thin-gauge high-strength container plates is low and the shape of the plates is difficult to guarantee (especially the flatness), which needs to be imported in large quantities from abroad. If the low-strength steel plate is replaced by thin-gauge high-strength steel plate, it can not only reduce energy consumption, transportation cost, cost, improve factory efficiency, but also bring huge benefits to the environment. Therefore, high-strength (greater than 700MPa) and thin-gauge (<2.0mm) containers will become an inevitable trend of development.

Niobium-boron compound strengthened hot-rolled high-strength container plate is composed of granular bainite + a small amount of lath bainite, and has the characteristics of high strength, good welding and formability. At present, the production of domestic container boards mostly adopts the standards of GB/T4171-2000 and Japanese standard JISG3125-1987. The most common one is SPA-H in Japan. The structure is ferrite and pearlite, and the strength is low. The structure of niobium-boron composite steel plate is granular bainite, because bainite has high strength and toughness, the steel has excellent comprehensive properties. Nb, Ti, B and other trace elements are also added to play the role of phase transformation strengthening, fine grain strengthening, and precipitation strengthening, greatly improving the strength, and at the same time, the low carbon content ensures good welding performance.

Contents of the invention

The object of the present invention is to provide a kind of thin gauge (<2.0mm) high-strength (greater than 700MPa) container plate and its manufacturing method, the container plate adopting this method can obviously increase strength, improve welding performance, formability, reduce cost, reduce Transportation costs and energy consumption are reduced, thus improving environmental benefits.

In order to achieve the above objectives, the technical solution of the present invention is a niobium-boron composite strengthened hot-rolled high-strength container plate, characterized in that the composition of the container plate is: C: 0.03% to 0.06%; Si: 0.10～0.30%; Mn: 1.50～2.0%; P: <0.0092%; S: <0.0028%; N: <0.004%; Nb: 0.03～0.06%; B: <0.002%; Ni: 0.1～0.4%; Cr: 0.3-0.5%; Cu: 0.3-0.5%; Ti: 0.01-0.03%, and the balance is Fe and unavoidable impurities.

Further, the composition of the container board is as follows: C: 0.04% to 0.05%; Si: 0.20 to 0.30%; Mn: 1.80 to 2.0%; P: <0.0092%; S: <0.0028%; N: < 0.004%; Nb: 0.04～0.05%; B: <0.002%; Ni: 0.2～0.4%; Cr: 0.35～0.45%; Cu: 0.35～0.45%; Avoid impurities.

Another object of the present invention is to provide a method for preparing the above-mentioned niobium-boron composite strengthened hot-rolled high-strength container plate, which specifically includes the following steps:

1. Smelting low-carbon steel: C: 0.03% to 0.06% by weight; Si: 0.10 to 0.30%; Mn: 1.50 to 2.0%; P: <0.0092%; S: <0.0028%; N: <0.004% ; Nb: 0.03～0.06%; B: <0.002%; Ni: 0.1～0.4%; Cr: 0.35～0.45%; Cu: 0.35～0.45%; impurities;

2. Heat the steel billet made in the above steps to 1250-1300°C and keep it warm for 1-2 hours;

3. After the surface oxide scale of the billet is removed by the descaler, it enters the hot rolling mill. The starting rolling temperature is 1050-1100°C, the final rolling temperature is 780-880°C, and the average rolling speed is 4m/s. The thickness of the thin plate is less than 2.0mm, and then laminar cooling is performed at a cooling rate of 10-30°C/s, and the temperature is cooled to 500-550°C for coiling to obtain a niobium-boron composite strengthened hot-rolled high-strength container plate.

Further, the starting temperature of the hot rolling in step 3 is 1080-1100°C, the finish rolling temperature is 780-830°C, the thickness of the rolled sheet is less than 2.0mm, and laminar cooling is carried out at a cooling rate of 20-30°C/s , coiling temperature 500 ~ 510 ℃.

Further, the tensile strength of the prepared niobium-boron composite strengthened hot-rolled high-strength container plate is greater than 700MPa, the yield strength is greater than 500MPa, the elongation is more than 15.0%, and the yield ratio is 0.65-0.76. Innovation point and advantage of the present invention:

1 Add a small amount of Nb (0.04-0.05%) and a very small amount of B to the steel. Niobium has a drag effect and can delay the recrystallization process of austenite, which is very meaningful for non-recrystallization rolling; boron is rich in solid solution Concentrating on the grain boundary reduces the grain boundary energy, which can significantly delay the transformation of ferrite, which can play the role of phase transformation strengthening, fine grain strengthening, and precipitation strengthening, which can increase the strength and improve the plasticity and toughness. At the same time, low carbon content can ensure good welding performance.

2. This type of steel obtains a bainite structure instead of the traditional ferrite and pearlite structure, which can greatly improve the strength and plastic toughness, and obtain excellent comprehensive mechanical properties. And the structure can be obtained when the cooling rate is between 5°C/s and 30°C/s, and bainite steel can be obtained in a wide range of cooling rates. In addition, this steel grade adds a very small amount of B instead of Mo, which can reduce the cost of the steel grade.

Description of drawings

Accompanying drawing 1 is the schematic flow chart of the hot-rolling process for preparing the hot-rolled slab of high-strength thin-gauge container plate according to the present invention.

Accompanying drawing 2 is the metallographic structure schematic diagram of the sample after hot rolling of the present invention.

Accompanying drawing 3 is the tensile curve schematic diagram of the sample of the present invention.

Accompanying drawing 4 is the bright field schematic diagram of TEM of lath bainitic ferrite structure of the slab after hot rolling in the present invention.

Accompanying drawing 5 is the bright-field schematic diagram of TEM of the M-A island structure of the hot-rolled slab of the present invention.

Accompanying drawing 6 is the TEM bright field schematic diagram of the fine structure of twin martensite inside the island M-A of the slab after hot rolling according to the present invention.

Detailed ways:

Example 1

Smelting low-carbon steel, its chemical composition by weight percentage is C: 0.045%; Si: 0.26%; Mn: 1.94%; P: <0.0092%; S: <0.0028%; N: <0.004%; Nb: 0.045%; B: 0.012%; Ni: 0.26%; Cr: 0.40%; Cu: 0.40%; Ti: 0.022%, the balance being Fe; place the slab in a high temperature resistance furnace and heat it to 1250°C at 10°C/s After 1 hour, go through the descaling machine to remove the surface oxide scale and then enter the hot rolling mill, start rolling at 1100°C, and continue rolling for several passes; when the temperature drops to 950°C, roll for several passes, and control the final rolling temperature to 780 ℃, the average rolling speed is 4m/s, the cumulative reduction is 92-95%, the thickness of the rolled sheet is less than 2.0mm, and the temperature of 10℃/s, 20℃/s, 30℃/ s cooling, cooling to about 500 ° C, and then put the sample into the holding furnace (500 ° C) for 1 hour and then cool to room temperature with air.

Figure 2 shows the metallographic structure of the niobium-boron composite high-strength container plate after hot rolling, where (a) the finishing temperature is 780°C and the cooling rate is 10°C/s; (b) the cooling rate is 30°C/s.

Figure 3 is the stress-strain curve of the sample stretched after hot rolling of the niobium-boron composite high-strength container plate. Example 1 The mechanical properties of niobium-boron composite high-strength container plate

Example 2

Smelting low-carbon steel, its chemical composition by weight percentage is C: 0.045%; Si: 0.26%; Mn: 1.94%; P: <0.0092%; S: <0.0028%; N: <0.004%; Nb: 0.045%; B: 0.012%; Ni: 0.26%; Cr: 0.40%; Cu: 0.40%; Ti: 0.022%, the balance being Fe; place the slab in a high temperature resistance furnace and heat it to 1250°C at 10°C/s After 1.5 hours, go through the descaling machine to remove the surface oxide scale and then enter the hot rolling mill, start rolling at 1100°C, and continue rolling for several passes; when the temperature drops to 950°C, roll for several passes, and control the final rolling temperature to 830 ℃, the average rolling speed is 4m/s, the cumulative reduction is 92-95%, the thickness of the rolled sheet is less than 2.0mm, and the temperature of 10℃/s, 20℃/s, 30℃/ s cooling, cooling to about 500 ° C, and then put the sample into the holding furnace (500 ° C) for 1 hour and then cool to room temperature with air.

Figure 2 shows the metallographic structure of the niobium-boron composite high-strength container plate after hot rolling, where (c) the final rolling temperature is 830°C and the cooling rate is 10°C/s; (d) the cooling rate is 30°C/s.

Example 2 Mechanical properties of niobium-boron composite high-strength container board

Example 3

Smelting low-carbon steel, its chemical composition by weight percentage is C: 0.045%; Si: 0.26%; Mn: 1.94%; P: <0.0092%; S: <0.0028%; N: <0.004%; Nb: 0.045%; B: 0.012%; Ni: 0.26%; Cr: 0.40%; Cu: 0.40%; Ti: 0.022%, the balance being Fe; place the slab in a high temperature resistance furnace and heat it to 1250°C at 10°C/s After 2 hours, after removing the surface oxide scale by the descaler, enter the hot rolling mill, start rolling at 1100°C, and continue rolling for several passes; when the temperature drops to 950°C, roll for several passes, and control the final rolling temperature to 880 ℃, the average rolling speed is 4m/s, the cumulative reduction is 92-95%, the thickness of the rolled sheet is less than 2.0mm, and the temperature of 10℃/s, 20℃/s, 30℃/ s cooling, cooling to about 500 ° C, and then put the sample into the holding furnace (500 ° C) for 1 hour and then cool to room temperature with air.

Example 3 Mechanical properties of niobium-boron composite high-strength container plate

Claims (1)

1. the preparation method of the compound hot-rolled high-strength container steel plate of niobium boron is characterized in that:

(1) smelting low carbon steel is C:0.04%～0.045% according to weight percent; Si:0.20～0.30%; Mn:1.80～2.0%; P:＜0.0092%; S:＜0.0028%; N:＜0.004%; Nb:0.04～0.05%; B:＜0.002%; Ni:0.2～0.4%; Cr:0.35～0.45%; Cu:0.35～0.45%; Ti:0.01～0.022%, surplus are Fe and unavoidable impurities;

(2) steel billet with above-mentioned steps system is heated to 1250～1300 ℃, is incubated 1～2 hour;

(3) get into hot rolls after the process scale breaker is removed said billet surface iron scale; The hot rolled start rolling temperature is 1080～1100 ℃, 780～830 ℃ of finishing temperatures, and rolling V-bar is 4m/s; Sheet gauge after rolling is less than 2.0mm; Carry out laminar flow cooling with the cooling rate of 20～30 ℃/s then, be cooled to temperature to 500～510 and ℃ batch, obtain niobium-boron complex intensifying hot-rolled high-strength container steel plate.

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