CN111088456A

CN111088456A - Steel plate for AS/NZS 3678-350L15Z35 structure and manufacturing method thereof

Info

Publication number: CN111088456A
Application number: CN201911065859.XA
Authority: CN
Inventors: 周福功; 李国忠; 许晓红; 苗丕峰; 王新刚
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2019-11-04
Filing date: 2019-11-04
Publication date: 2020-05-01

Abstract

The invention relates to a steel plate for AS/NZS 3678-350L15Z35 structure, wherein for the steel plate with the thickness of 10mm < 50mm, the chemical composition takes Fe AS a basic element and comprises the following element components: c: 0.11-0.16%, Si: 0.10-0.40%, Mn: 1.40-1.70%, P: less than or equal to 0.018%, S: less than or equal to 0.005 percent, Cr: less than or equal to 0.20 percent, Mo: less than or equal to 0.08 percent, Ni: less than or equal to 0.03%, Cu: less than or equal to 0.30 percent, Al: 0.02-0.04%, V: less than or equal to 0.02 percent, Nb: 0.010-0.050%, Ti: 0.01-0.025%, N: less than or equal to 0.008 percent, and the delivery state of the steel plate is controlled rolling state (CR). The yield strength of the product is more than or equal to 390MPa, the tensile strength is more than or equal to 510MPa, and the elongation is more than or equal to 23 percent; the Charpy V-type impact energy at the temperature of minus 15 ℃ is more than or equal to 100J; the Z-direction performance is more than or equal to 40 percent; the comprehensive performance can completely meet the customer requirements of AS/NZS 3678:2016 and steel products for buildings, bridges and engineering machinery.

Description

Steel plate for AS/NZS 3678-350L15Z35 structure and manufacturing method thereof

Technical Field

The invention relates to Z35 structural steel, in particular to AS/NZS3678 and 350 series structural steel.

Background

The Z-direction steel is a common name for a steel sheet having a performance in the thickness direction, and a thicker steel sheet has a specific specification for its mechanical properties in the thickness direction. In the structural steel adopting welded connection, when the thickness of the steel plate is not less than 15mm and the steel plate bears the tensile force along the thickness direction of the steel plate, in order to avoid the lamellar tearing generated in the welding process, the structural steel adopting the welding connection needs to adopt the lamellar tearing resistanceSteel material(often referred to simply as "Z-direction steel"). The thick plate has the problem of layer tearing, so a Z-direction performance test is required. This steel sheet is a steel material obtained by special smelting and treatment of a certain primary structural steel (referred to as a "mother-grade steel"), and has a sulfur content of 1/5 or less, which is the content of sulfur in general steel materials, and a cross-sectional shrinkage of 15% or more. The force-receiving property (mainly ductility property) of the steel sheet in the thickness direction is referred to as Z-direction property. The Z-direction performance of a steel sheet can be obtained by performing a sample tensile test, and is generally measured by reduction of area. The mark of the Z-direction steel plate produced in China is that Z-direction steel plate grade marks Z15, Z25 and Z35 are added behind the steel grade of the mother grade steel, and the number behind the Z is an index (%) of the section shrinkage.

AS/NZS3678, AS produced by the Australia/New Zealand Union Standard Committee BD-023 structural Steel technical Committee: the 2016 standard medium-grade AS/NZS 3678-350L15 structural steel plate product is most widely applied to steel for buildings, bridges and engineering machinery; the thickness specification is mainly dominated by products with the thickness of more than 10-50 mm. The product is required to have good comprehensive properties such as bearing capacity, weldability, low-temperature impact toughness and the like. With the development of the demand in China and the construction of the infrastructure projects of the adjacent countries, AS/NZS 3678-.

Publication No. CN110042315A discloses a low-cost Q355B structural steel plate and a production method thereof, and adopts a production process of 'continuous casting blank, rolling and Acc cooling'. The maximum finished product thickness specification is 50 mm. The delivery state is hot rolled or TMCP product.

The publication No. CN108914008A discloses an economical high-plastic 360 MPa-level structural steel plate and a production method thereof, wherein a continuous casting blank and controlled rolling and controlled cooling process is adopted, the 10-60mm performance yield strength of a produced product is more than or equal to 360MPa, the tensile strength is more than or equal to 500MPa, and the elongation is more than or equal to 30%. The process has difficulty in batch production; and the production cost is high.

Disclosure of Invention

The invention adopts a continuous casting billet with the thickness of 150-250mm to produce the steel plate for the AS/NZS 3678-350L15Z35 structure with the thickness of more than 10-50mm and the delivery state of CR (controlled rolling state), and the comprehensive performance of the steel plate can completely meet the client requirements of AS/NZS 3678:2016 and steel products for buildings, bridges and engineering machinery, which are prepared by the technical Committee of the Australia/New Zealand Combined Standard Committee BD-023 structural Steel; and the manufacturing method of the steel has the advantages of short production period and low production cost.

The specific technical scheme of the invention is as follows: a steel plate for AS/NZS 3678-350L15Z35 structure has a design thickness range: the steel plate with the thickness of 10mm < 50mm has a chemical composition based on Fe and comprises the following element compositions: c: 0.11-0.16%, Si: 0.10-0.40%, Mn: 1.40-1.70%, P: less than or equal to 0.018%, S: less than or equal to 0.005 percent, Cr: less than or equal to 0.20 percent, Mo: less than or equal to 0.08 percent, Ni: less than or equal to 0.03%, Cu: less than or equal to 0.30 percent, Al: 0.02-0.04%, V: less than or equal to 0.02 percent, Nb: 0.010-0.050%, Ti: 0.01-0.025%, N: less than or equal to 0.008 percent and inevitable impurity elements.

In order to have good weldability, the content relationship of related elements in the chemical composition is further satisfied: the carbon equivalent (C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15) is less than or equal to 0.42 percent.

The steel plate is delivered in a controlled rolling state, namely, controlled cooling, quenching and tempering or other heat treatment for meeting the service performance is not carried out, and the product delivered in a controlled rolling state (CR) has yield strength of more than or equal to 390MPa, tensile strength of more than or equal to 510MPa and elongation of more than or equal to 23 percent; the Charpy V-type impact energy at the temperature of minus 15 ℃ is more than or equal to 100J; the Z-direction performance is more than or equal to 40 percent; the lamellar tearing resistance enables the product of the invention to belong to Z35 product; the performances meet AS/NZS3678 and 350L15Z35 in AS/NZS 3678:2016 standard.

The main functions of the elements in the invention are as follows:

c element can generate great phase change strengthening when existing in the form of cementite or pearlite in the steel structure, and the strength is improved; in order to ensure the strength of the steel plate, the steel plate also needs to have certain welding performance and good low-temperature impact toughness; the invention controls the C content in the steel to be 0.11-0.16%.

Mn element forms solute element of substitutional solid solution in Fe, which has obvious influence on the toughness of steel and effectively improves the strength of steel, so the Mn content in the steel is controlled to be 1.40-1.70%

S: in the micro low alloy steel, the improvement of the content of S can reduce the plasticity and the toughness of the steel; therefore, S.ltoreq.0.005% is preferable.

Nb: nb can prevent the crystal grains from growing when the low alloy steel is heated, so as to refine the crystal grains and have precipitation strengthening effect; can improve the microstructure of steel and improve the performance.

Ti: it is an element for strengthening and fixing N. In the composite low microalloyed steel, N will preferentially form TiN with Ti. The function of TiN for preventing austenite grains from coarsening during heating is larger than that of Nb (CN); the TiN precipitated at high temperature is used for preventing austenite recrystallization grain coarsening.

Si: si does not form carbides in steel. Silicon is mainly formed by solid solution strengthening to improve the strength of the steel, and the toughness of the steel is reduced due to the fact that the content of Si is too high. Therefore, the content thereof is controlled to be appropriate.

Al: al can refine the crystal grains of the steel, improve the strength of the steel and simultaneously improve the impact toughness. Therefore, the Al content is 0.02 to 0.04%.

P: p is a low temperature brittle element. The high-phosphorus alloy is segregated among crystal grains in the steel solidification process to form a high-phosphorus brittle layer, so that the level of a banded structure is improved, the local structure of the steel is abnormal, and the plasticity of the steel is reduced; the steel is easy to generate brittle cracks, and the welding performance is also not good; the content of phosphorus in the steel should be reduced as much as possible. The content of P is controlled below 0.018% in consideration of production cost.

At present, the steel plate products with Q345 or Q355 grade yield strength and thickness of more than 10-50mm produced in China execute the GB/T1591 or GB 712 and other standards. The Q345 or Q355 product produced by adopting the continuous casting blank plus normalizing heat treatment or the delivery state of the continuous casting blank plus tempering, the continuous casting blank plus rolling plus Acc-TMCP (controlled rolling and controlled cooling) is not suitable for AS/NZS3678 produced by the Australia/New Zealand combined Standard Committee BD-023 structural Steel technical Committee: 2016.

Aiming at the export structural steel of the execution region of the latter standard, the applicant researches and develops AS/NZS 3678-350L15Z35 structural steel products with the thickness of more than 10-50 mm; it is widely applied to the field of steel plates for engineering such as buildings, bridges, engineering machinery and the like. The continuous casting blank with the thickness of 150-50 mm is adopted to produce the delivery state CR (controlled rolling) AS/NZS 3678-350L15Z35 steel plate with the thickness of more than 10-50mm, and compared with the steel plate produced by adopting continuous casting blank plus normalizing heat treatment or continuous casting blank plus ACC or continuous casting blank plus tempering, the product performance is stable, the production period is short, and the production cost is low; the yield strength of the product is more than or equal to 390MPa, the tensile strength is more than or equal to 510MPa, and the elongation is more than or equal to 23 percent; the Charpy V-type impact energy at the temperature of minus 15 ℃ is more than or equal to 100J; the Z-direction performance is more than or equal to 40 percent; the comprehensive performance can completely meet the customer requirements of AS/NZS 3678:2016 and steel products for buildings, bridges and engineering machinery.

Drawings

FIG. 1 is a microstructure at section 1/4 of a 50mm thick steel plate product of the present invention.

Detailed Description

The invention is described in further detail below with reference to the embodiments of the drawing, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected or detachably connected, or integrated; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or may be connected through the interconnection of two elements or through the interaction of two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations

The product is formed by hot rolling of blanks, and the delivery state is the controlled rolling state. The embodiment uses the continuous casting billet as the blank, and the continuous casting billet has shorter production cycle and production stability than other shaping billets, supplies goods, guarantees to supply goods cycle all to the batch and is useful. The method for obtaining the continuous casting billet comprises the following steps: the method comprises the following steps of adopting desulfurized molten iron and high-quality scrap steel as raw materials, carrying out bottom (top) blowing smelting in a converter, blowing argon in the whole process, carrying out deoxidation in an LF furnace, desulfurization, removing inclusions, adjusting components and temperature, refining and degassing in an RH furnace, and finally obtaining the molten steel, wherein the molten steel comprises the following component C in percentage by weight and takes Fe as a basic element: 0.11 to 0.16%, Si: 0.10 to 0.40%, Mn: 1.40-1.70%, P: less than or equal to 0.018%, S: less than or equal to 0.005 percent, Cr: less than or equal to 0.20 percent, Mo: less than or equal to 0.08 percent, Ni: less than or equal to 0.03%, Cu: less than or equal to 0.30 percent, Al: 0.02-0.04%, V: less than or equal to 0.02 percent, Nb: 0.010-0.050%, Ti: 0.01-0.025%, N: less than or equal to 0.008 percent and inevitable impurity elements; As/NZS 3678-350L15Z35 continuous casting billet forming molten steel with the carbon equivalent of less than or equal to 0.42 percent, and the description of the AS/NZS 3678-350L15Z35 continuous casting billet means that the chemical components of the continuous casting billet per se meet the limit of the mark.

The molten steel is subjected to constant temperature, constant speed and reasonable secondary cooling process, dynamic soft reduction at the solidification end and electromagnetic stirring to produce 150-sand 250mm blanks by a wide and thick plate continuous casting machine. Sizing the blank; the slow cooling of the blank in the lower line stack is more than or equal to 24 hours. And sending the finished qualified blank to steel rolling production according to a production plan. The blank is examined by a macrostructure to meet the following requirements: center segregation: class B is less than or equal to 1.0 grade, and class C is less than or equal to 1.5 grade; center loosening: less than or equal to 1.0 grade; center cracking: 0-0.5 grade; none of the others.

A continuous casting billet heating process: before rolling of a continuous casting billet, austenitizing needs to be heated, and the temperature of a preheating section of a heating furnace is as follows: 600 ℃ and 950 ℃, and heating for a period of time: 900 ℃ and 1100 ℃, and the heating second-stage temperature: 1100 ℃ and 1240 ℃, and the temperature of the soaking section: 1160-1250 ℃; the total heating time is more than or equal to 1.05 multiplied by H minutes, wherein H is the thickness of the blank and is mm. After the blank is discharged from the furnace and in the rolling process, high-pressure water is adopted to remove the iron scale, and the water pressure for rough descaling and fine descaling is more than or equal to 18 MPa.

The controlled rolling process comprises the following steps: the rolling is divided into two stages: 1) first stage (i.e., roughing rolling stage): rolling in the austenite recrystallization zone, which is a stage where coarse columnar structures during casting can be broken by rolling at a large reduction at a high temperature. Austenite grains are refined by repeated and staggered deformation and recrystallization. Therefore, the initial rolling temperature of rough rolling is more than or equal to 1000 ℃, the rough rolling is rolled into an intermediate billet after 5-9 times, the thickness of the intermediate billet is 1.9-3.5 Hmm, and H is the thickness of a finished product of the steel plate. In order to prevent the crystal grains from growing after the rolled piece is rolled, the rolled piece is technically designed to be transferred into an austenite non-recrystallization region for rolling or a two-phase region for rolling, namely a second stage. In the second stage of rolling, austenite grains are elongated along the rolling direction, the boundary area is increased, the nucleation density of ferrite is increased, and the grain refinement, the uniform structure, the excellent comprehensive performances of the strength, the toughness and the like of the final steel plate are facilitated. After the intermediate billet is warmed, the initial rolling temperature for finish rolling is 830-920 ℃, and the final rolling temperature is 780-860 ℃ after 5-7 passes of rolling; the three accumulated reduction rates after finish rolling are more than or equal to 28 percent.

After rolling, directly sending the rolled piece to a thermal straightening machine for straightening, wherein the thermal straightening temperature of the rolled piece is more than or equal to 450 ℃; then the mixture is sent to a cooling bed for natural cooling; wherein, for the product with the thickness of more than or equal to 30mm, the product is cooled to more than or equal to 320 ℃, and the reactor is cooled slowly, and the reactor cooling time is more than or equal to 24 hours. Flaw detection, apparent quality detection, physical and chemical property detection, shearing (cutting) and warehousing.

Example 1

This example relates to the rolling of a steel sheet of 12mm thickness, using a continuous casting slab of 150mm x 2400mm x 3200mm gauge and a final product of 12 x 3000 x L (length) mm gauge. Cold loading the blank into a heating furnace, wherein the preheating section temperature of the heating furnace is as follows: 680 ℃ and 700 ℃, and heating for a period of time: 950 ℃ and 1000 ℃, and the heating temperature of the second stage: 1180-: 1240 ℃ and 1250 ℃; the total heating time was 166 minutes. Removing scale with high-pressure water after discharging, and then rolling, wherein rough rolling is carried out for 5 times, the thickness of the intermediate blank is 40mm when the temperature is high, the rolling temperature of a finishing mill is 910 ℃ after the temperature is high, and the rolling temperature is 816 ℃ after 7 times of rolling; and after the rolling is finished, straightening for 3-5 times or flattening by a straightening machine, sending the steel plate to a cooling bed for cooling to room temperature, and finally, carrying out fine finishing, quality inspection and sampling inspection to obtain the mechanical properties of the product, wherein the mechanical properties are shown in table 1.

Example 2

An example of rolled 50mm thick steel sheet was produced. A continuous casting slab of 250X 2400X 3500mm is used, and a rolled finished slab of 50X 2700X L (length) mm is used. The blank was cold-charged into a heating furnace and heated as in example 1 for a total heating time of 276 minutes. Carrying out rough rolling for 7 times, when the temperature is 107mm, and the starting temperature of a finishing mill is 830 ℃ after the temperature is increased, and carrying out finish rolling for 7 times, wherein the final rolling temperature is 801 ℃; after rolling, straightening by a straightener, cooling by a cooling bed, and cooling to 360 ℃ for slow cooling of a wire stack; sampling after 26 hours, and performing physical and chemical inspection and quality inspection. The results of physical and chemical property tests are shown in Table 1, and the metallographic structure is shown in FIG. 1

TABLE 1

Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that modifications and variations of the present invention are possible to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A kind of AS/NZS 3678-: for this steel sheet of 10mm < thickness < 50mm, the chemical composition is based on Fe and comprises the following elements: c: 0.11-0.16%, Si: 0.10-0.40%, Mn: 1.40-1.70%, P: less than or equal to 0.018%, S: less than or equal to 0.005 percent, Cr: less than or equal to 0.20 percent, Mo: less than or equal to 0.08 percent, Ni: less than or equal to 0.03%, Cu: less than or equal to 0.30 percent, Al: 0.02-0.04%, V: less than or equal to 0.02 percent, Nb: 0.010-0.050%, Ti: 0.01-0.025%, N: less than or equal to 0.008 percent and inevitable impurity elements.

2. The steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 1, wherein: the carbon equivalent (C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15) is less than or equal to 0.42 percent.

3. The steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 1, wherein: the product in a controlled state (CR) has yield strength of more than or equal to 390MPa, tensile strength of more than or equal to 510MPa and elongation of more than or equal to 23 percent; the charpy V-type impact energy at the temperature of minus 15 ℃ is more than or equal to 100J.

4. A method for preparing the steel plate for the AS/NZS 3678-350L15Z35 structure AS defined in any one of claims 1-3, wherein the method comprises the following steps: comprises the following steps

(1) Blank material: preparing a continuous casting blank or a casting blank which accords with the chemical components as a blank, wherein the blank meets the following requirements through macroscopic structure inspection: center segregation: class B is less than or equal to 1.0 grade, and class C is less than or equal to 1.5 grade; center loosening: less than or equal to 1.0 grade; center cracking: 0-0.5 grade; none of the others;

(2) heating;

(3) descaling: removing oxide scales by a descaler after the blank is discharged from the furnace and in the controlled rolling process;

(4) controlling rolling: the method comprises rough rolling control rolling and finish rolling control rolling, wherein the rough rolling control rolling comprises the following steps: rolling in an austenite recrystallization zone at the rolling temperature of more than or equal to 1000 ℃ to form an intermediate blank by 5-9 times, wherein the thickness of the intermediate blank is (1.9-3.5) × Hmm, and H is the thickness of a finished steel plate; and (3) finish rolling control rolling: rolling in an austenite non-recrystallization region or a two-phase region, rolling at the beginning temperature of 830-920 ℃ after the temperature is reached, and rolling to the thickness of the finished product by 5-7 passes, wherein the final rolling temperature is 780-860 ℃;

(4) after rolling, directly sending the rolled piece to a thermal straightening machine for straightening, wherein the thermal straightening temperature of the rolled piece is more than or equal to 450 ℃;

(5) cooling by a cooling bed: and (3) naturally cooling the hot-rectified steel plate in a cooling bed, wherein the product with the thickness of more than or equal to 30mm is subjected to slow cooling in a downward mode when the product is cooled to the temperature of more than or equal to 320 ℃, and the slow cooling time in the pile is more than or equal to 24 hours.

5. The method for preparing the steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 4, wherein the method comprises the following steps: the thickness of the blank is 150mm-250 mm.

6. The method for preparing the steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 4, wherein the method comprises the following steps: the descaling water pressure in the step (3) is more than or equal to 18 MPa.

7. The method for preparing the steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 4, wherein the method comprises the following steps: and (4) after finish rolling, the cumulative reduction rate of the three passes is more than or equal to 28 percent.

8. The method for preparing the steel plate for AS/NZS 3678-350L15Z35 structure AS recited in claim 4, wherein the method comprises the following steps: the temperature of the preheating section of the heating furnace in the step (2) is as follows: 600 ℃ and 950 ℃, and heating for a period of time: 900 ℃ and 1100 ℃, and the heating second-stage temperature: 1100 ℃ and 1240 ℃, and the temperature of the soaking section: 1160-1250 ℃, the total heating time is more than or equal to 1.05H, and H is the thickness of the blank in mm.