WO2022199075A1

WO2022199075A1 - Thin specification nm450 steel plate and manufacturing method therefor

Info

Publication number: WO2022199075A1
Application number: PCT/CN2021/131740
Authority: WO
Inventors: 黄军; 罗元东; 白云; 李经涛; 许晓红; 林涛; 吴建鹏; 李晨潇; 侯美伶; 訾先鹏; 周佩蓉; 许海龙
Original assignee: 江阴兴澄特种钢铁有限公司
Priority date: 2021-03-24
Filing date: 2021-11-19
Publication date: 2022-09-29
Also published as: CN113249644B; CN113249644A; CA3194610A1

Abstract

The present invention relates to a thin specification NM450 steel plate, chemical components of said steel plate, in percentage by weight, being: C: 0.15-0.30, Si: 0.25-0.45, Mn: 0.80-1.20, Cr: 0.20-0.60, Mo: 0.10-0.50, Ni: 0.10-0.50, Al: 0.02-0.08, B: 0.0010-0.0030, P ≤ 0.020, S ≤ 0.010, and the remainder being Fe and unavoidable impurities. The main route of a process is: steel-making → continuous casting → slab compositing or pre-fabricated intermediate slab compositing → rolling → quenching (determining whether to quench after separation according to steel plate thickness) → tempering → finishing → inspecting → warehousing. The thickness of a steel plate made by the present invention is 4-8 mm, the maximum width of a steel plate reaches 3200 mm, and the present invention effectively solves the problems of a hot continuously rolled thin plate having a small width and a portion of wide and thick plate companies lacking coiling and rolling equipment being unable to produce this type of thin steel plate.

Description

A kind of thin gauge NM450 steel plate and its manufacturing method

technical field

The invention relates to a thin gauge NM450 steel plate and a manufacturing method thereof. It belongs to the field of special steel smelting technology.

Background technique

As a steel material with high wear resistance, low alloy wear-resistant steel plate has been widely used in mining, railway and metallurgy and other harsh environments. In addition to wear resistance, it also has high strength and good toughness. , strong weldability and so on. At present, the low-alloy wear-resistant steel plates produced in China are mainly concentrated in NM500 and below grades, of which the use of NM450 steel plates occupies a considerable market share.

The main thickness of NM450 steel plate is concentrated below 50mm, especially the thickness of 8-30mm, and the thickness of some mechanical equipment is as thin as 4mm.

At present, in addition to the steel companies with continuous rolling equipment, the thinnest limit thickness produced by the steel plate manufacturers at home and abroad is generally 6mm. However, even 6mm steel plates are only rolled by rolling mills with furnace coil equipment. , because the coiling furnaces at both ends of the rolling mill can keep the steel plate warm and even heat it to ensure the rolling temperature, and the thinnest thickness of the rolling mill without such equipment is only about 8mm. When the thickness is further reduced, the slab cools down rapidly and the rolling torque force is too large. It affects the life of the equipment, and the rolled steel plate has a poor shape, and the thickness precision control is difficult, especially for high-strength steel plates.

Chinese Patent Publication No. CN1121444A discloses a new process for the production of multi-stand tandem-rolled thin slabs. The multi-stand single-roll rolling mills are arranged in tandem, and the thin slabs are heated and then enter the first stand rolling mill for single-piece rolling. , the second rolling mill performs two-in-one rolling, and the third rolling mill performs four-in-one rolling. The temperature of each stand is controlled during the rolling process, and the temperature of the third and fourth stands is controlled at 400-500 ° C. This method is to stack the semi-finished products during the rolling process and roll them together, which is only suitable for materials with a small single weight. Production.

The Chinese Patent Publication Nos. CN101439348A "a production process for producing extra-thick slabs" and CN101590596A "a method for producing extra-thick slabs by cumulative stacking and welding" all refer to the method of plate grouping, that is, the use of two or more pieces The continuous casting slabs are jointly rolled. However, they are all made by welding two or more original materials together during the rolling process to realize the production of thick-gauge steel plates.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a 4-8mm thick NM450 wide plate and its manufacturing method for the above-mentioned prior art, the maximum width reaches 3200mm, not only the product width exceeds the conventional width of the hot continuous rolling sheet, but also solves some problems. There is a problem that the wide and thick plate enterprises without rolling equipment cannot produce such steel plates, so as to improve the product supply specifications and improve the market competitiveness.

The technical solution adopted by the present invention to solve the above problems is: a 4-8mm thin NM450 steel plate, the chemical composition of the steel plate is C: 0.15-0.30, Si: 0.25-0.45, Mn: 0.80- 1.20, Cr: 0.20-0.60, Mo: 0.10-0.50, Ni: 0.10-0.50, Al: 0.02-0.08, B: 0.0010-0.0030, P≤0.020, S≤0.010, the rest are Fe and inevitable impurities. The carbon equivalent of the final steel sheet product is not more than 0.52%.

The present invention also provides a method for manufacturing the above-mentioned thin NM450 steel plate. The main steps of the manufacturing method are: formulating a low-carbon equivalent chemical composition for a 4-8mm thin steel plate, and obtaining a 150-400mm steel plate through steelmaking, refining and vacuum continuous casting Thick continuous casting slabs; blanks of the same size or intermediate blanks that are rolled to a certain thickness are composite welded around, and the middle is kept in a non-vacuum state; the composite blanks are heated and rolled to the target thickness, and the rolled steel plate Because the middle non-vacuum state is not rolled and welded, the four sides of the welding can be divided into two steel plates after cutting off the four sides; after the rolled steel plate is cut into four sides, the single steel plate is heat-treated (the steel plate with a thickness of 4-5mm can be heat-treated and then split. ), steel plates with poor flatness need to be straightened before quenching. The final delivery state of the steel plate produced by this manufacturing method is Q+T, the thickness of the finished product is 4-8mm, and the maximum width of the steel plate is 3200mm, and its product performance and appearance quality meet the requirements of GB/T 24186-2009.

The manufacturing method specifically includes the following steps:

1. Blank preparation

(1) Steelmaking, precise control of alloying elements in steel to ensure that the carbon equivalent deviation between different heats is not greater than 0.02%, and precise control of composition helps to stabilize the performance of large-scale steel plates; LF furnace refining is fully deoxidized and desulfurized; RH limit The vacuum time is guaranteed to be more than 20min to reduce the content of H and N in the steel; the calcium treatment operation is carried out to promote the denaturation and floating of inclusions;

(2) Continuous casting of slabs, continuous casting of 150-400mm thick slabs with a direct arc continuous casting machine, using tundish induction heating technology to achieve low superheat and constant pulling speed operation, and using argon gas protection, dynamic light reduction, etc. The technology realizes the production of high-quality continuous casting slabs, and the low-magnification quality of the slabs satisfies: the center segregation is not greater than Class C 1.0; the center porosity is not greater than 1.0; there are no other defects such as triangular cracks.

(3) Prefabricated intermediate slabs, the production of 4-5mm thick steel plates requires composite rolling with thinner prefabricated intermediate slabs. The prefabricated intermediate slabs are heated to about 1220°C by 150-400mm continuous casting slabs for rolling, and the thickness of the prefabricated intermediate slabs is controlled at 60-100mm. For steel plates with a thickness of >5-8mm, 150mm thick slabs can be used for direct composite rolling, and there is no need to roll them into prefabricated intermediate slabs and then composite them. When the width of the finished steel plate exceeds the width of the continuous casting slab, the billet needs to be rolled and widened to a prefabricated intermediate slab larger than the width of the finished product, and the maximum width of the prefabricated intermediate slab is not greater than 3400mm.

2. Billet finishing and compounding

The appearance quality of continuous casting slabs or prefabricated intermediate slabs shall be inspected according to YB/T 2012, and the billets with qualified appearance shall be cut into sections according to the size requirements of the production plan. In the middle of non-vacuum treatment, the welding width from the edge of the billet is controlled at 50-80mm. On the one hand, it ensures that the billet cannot be delaminated around during rolling, and on the other hand, the yield of the steel plate needs to be considered.

3. Heating and rolling of composite billets

(1) Heating the composite billet, the low temperature section is heated to 850±20°C at a rate of 60-100°C/h, and the temperature is kept for 2-3 hours; 3h; in the high temperature section, the temperature is raised to 1200-1250°C at a rate of not more than 100°C/h, and the temperature is kept for 5-9 hours. Appropriately reducing the heating rate of the high temperature section and prolonging the holding time after reaching the temperature is beneficial to the bonding of metals in the welding area.

(2) Rolling of the composite billet, on the wide and thick plate rolling mill, rolling 10-15 passes, rolling to twice the target thickness of the finished single steel plate, and the thickness tolerance of the composite steel plate is controlled at 0-0.6mm. There is no widening rolling during the rolling process, and all longitudinal rolling is performed. In the first 2 passes of rolling, a small reduction is used, and in the middle passes, the reduction is 30-50 mm in 2-3 passes to realize the welding of the welding area. After the steel plate is cooled by the hot leveling machine, it is cooled on the cooling bed. When the steel plate is cooled to about 300 ℃, if there is a buckling, it can be straightened on the cold leveling machine.

4. Heat treatment of steel plate

(1) Quenching, the 4-5mm thick composite steel plate is quenched by a quenching machine. After quenching, the four sides of the composite steel plate are cut off and the upper and lower plates are separated to obtain two steel plates with the same thickness; Due to the limitation of hardenability, it is necessary to cut off the four sides of the composite steel plate and separate the upper and lower plates for single steel plate quenching treatment. The quenching process of the steel plate is: the heating temperature is 900-940℃, the holding time is (20-25)min+3min/mm×the thickness of the steel plate (the composite steel plate is calculated according to the total thickness of the upper and lower plates), and it is water-cooled after being released.

(2) Tempering, using a continuous furnace to temper the steel plate at low temperature, tempering process: heating temperature 180-220 ℃, holding time 1-2 hours, air cooling after release. The curved steel plate can be subjected to strong straightening treatment with temperature after being released from the furnace, so that the unevenness of the steel plate is not more than 5mm/m.

5. Inspection and inspection

The finished NM450 steel plate is inspected for appearance and quality according to GB/T 24186-2009, and samples are taken for various performance inspections, and the judgment is made according to the requirements of GB/T 24186-2009.

Compared with the prior art, the advantages of the present invention are:

The invention provides a 4-8mm NM450 wide plate manufacturing method, the maximum width reaches 3200mm, not only the product width exceeds the conventional width of hot continuous rolling sheet, but also solves the problem that some wide and thick plate enterprises without rolling equipment cannot produce such steel sheet problems, improve product supply specifications, and improve market competitiveness.

Detailed ways

The present invention will be described in further detail below in conjunction with examples and comparative examples.

Example 1

The thickness of the thin NM450 wide plate involved in this embodiment is 4mm and the width is 3200mm, and its chemical composition in terms of mass percentage is: C: 0.20, Si: 0.35, Mn: 1.10, Cr: 0.30, Mo: 0.20, Ni: 0.20 , Al: 0.03, B: 0.0020, P: 0.005, S: 0.002, the rest are Fe and inevitable impurities, and the carbon equivalent is 0.50%.

The manufacturing process of this steel plate is as follows:

Steel making → continuous casting → prefabricated intermediate slab → compounding → rolling → quenching → upper and lower plate cutting → tempering → finishing → inspection → storage.

The specific operations of the main process are as follows:

Steelmaking: The five harmful elements in the steel are strictly controlled in the steelmaking process, among which N is not more than 25ppm, O is not more than 8ppm, and H is not more than 1.2ppm. The refining and degassing processes need to be treated with calcium to control the size and composition of inclusions.

Continuous casting: The molten steel is continuously cast into a slab with a thickness of 300mm and a width of 2500mm by a straight arc continuous casting machine.

Rolling and compounding of prefabricated intermediate slabs: After heating, the continuous casting slabs are first widened and rolled to 3350mm, and then longitudinally rolled to 65mm. the straightness. Cut out two prefabricated intermediate slabs of the same size from the hot-rolled steel plate for surface milling, and then carry out composite welding around them, without vacuum in the middle. The composite welding position is within 50-80mm from the edge of the blank, and the thickness of the composite blank is 124 mm. ±2mm.

Composite billet heating and rolling: The composite billet is heated in stages, the low temperature section is heated to 850±20°C at a rate of 70°C/h, and kept for 2 hours; the medium temperature section is heated to 1000±20°C at a rate of 100°C/h, and kept for 2 hours; In the high temperature section, the temperature was raised to 1220±20°C at a rate of 80°C/h, and the temperature was maintained for 5.5 hours. During the rolling process of the composite billet, there is no widening rolling, all longitudinal rolling, a total of 12 passes, of which the reductions of the first two passes are 5mm and 8mm, and the reductions of the 5th and 6th passes are respectively 35mm and 32mm, the rolled steel plate is cooled by the cooling bed after passing through the hot leveling machine, and there is no obvious buckling. The thickness of the clad steel plate after rolling is 8.2mm

Heat treatment: heat the composite steel plate to 920°C in a continuous furnace, and keep it for 48 minutes, and then enter the quenching machine for water cooling. After the steel plate is cooled, the four-sided welding area is cut off and the upper and lower plates are separated to obtain a quenched steel plate with a width of 3200mm; the continuous furnace is used to quench the steel plate Tempering heat treatment is carried out in time, the steel plate is heated to 200°C and kept for 1 hour before being released from the furnace, and the steel plate is subjected to strong straightening treatment to obtain an NM450 sheet with an unevenness not greater than 5mm/m.

The 4mm thick, 3200mm wide NM450 steel plate obtained through the above manufacturing process has good shape and uniform hardness, and its main properties are shown in Table 1.

Example 2

The thickness of the thin NM450 wide plate involved in this embodiment is 6mm and the width is 2500mm. , Al: 0.03, B: 0.0018, P: 0.006, S: 0.002, the rest are Fe and inevitable impurities, and the carbon equivalent is 0.49%.

The manufacturing process of this steel plate is as follows:

Steel making → continuous casting → compounding → rolling → upper and lower plate cutting → quenching → tempering → finishing → inspection → storage.

The specific operations of the main process are as follows:

Continuous casting: The molten steel is continuously cast into a slab with a thickness of 150mm and a width of 2600mm by a straight arc continuous casting machine.

Billet compounding: The surface of two continuous casting slabs with the same size is milled, and then compound welding is performed around them, without vacuum in the middle. The compound welding position is within 50-80mm from the edge of the billet, and the thickness of the compounded billet is 294±2mm. .

Composite billet heating and rolling: The composite billet is heated in stages, the low temperature section is heated to 850 ± 20 °C at a rate of 70 °C/h, and kept for 3 hours; the medium temperature section is heated to 1000 ± 20 °C at a speed of 100 °C/h, and kept for 3 hours; In the high temperature section, the temperature was raised to 1220±20°C at a rate of 80°C/h, and the temperature was kept for 9 hours. During the rolling of the composite billet, there is no widening rolling, all longitudinal rolling, and a total of 14 passes, of which the reductions of the first two passes are 5mm and 8mm, and the reductions of the 5th, 6th, and 7th passes are 50mm respectively. , 50mm and 45mm, the rolled steel plate is cooled by the cooling bed after the hot leveling machine, and there is no obvious buckling. The thickness of the clad steel plate after rolling is 12.3mm

Heat treatment: Before the heat treatment of the clad steel plate, the welding area on the four sides is cut off, and the upper and lower plates are separated to obtain a hot-rolled steel plate with a width of 2500mm. The split steel plate is heated to 920°C in a continuous furnace, and kept for 40 minutes before entering the quenching machine for water cooling; the quenched steel plate is tempered and heat treated in a continuous furnace in time, and the steel plate is heated to 190°C and kept for 1.2 hours before being released from the furnace, and the steel plate is heated with temperature. After strong straightening treatment, NM450 sheet with unevenness not more than 5mm/m is obtained.

The 6mm thick, 2500mm wide NM450 steel plate obtained through the above manufacturing process has a good shape and uniform hardness, and its main properties are shown in Table 1.

Example 3

The thickness of the thin NM450 wide plate involved in this embodiment is 8mm and the width is 3000mm, and its chemical composition in terms of mass percentage is: C: 0.21, Si: 0.25, Mn: 1.11, Cr: 0.25, Mo: 0.23, Ni: 0.17 , Al: 0.03, B: 0.0016, P: 0.005, S: 0.003, the rest are Fe and inevitable impurities, and the carbon equivalent is 0.50%.

The manufacturing process of this steel plate is as follows:

Steel making → continuous casting → prefabricated intermediate slab → compounding → rolling → upper and lower plate cutting → quenching → tempering → finishing → inspection → storage.

The specific operations of the main process are as follows:

Continuous casting: The molten steel is continuously cast into a slab with a thickness of 370mm and a width of 2200mm by a straight arc continuous casting machine.

Rolling and compounding of prefabricated intermediate slabs: After heating, the continuous casting slabs are first widened and rolled to 3150mm, and then longitudinally rolled to 80mm. the straightness. Cut out two prefabricated intermediate slabs of the same size from the hot-rolled steel plate for surface milling, and then carry out compound welding around them without vacuum in the middle. The compound welding position is within 50-80mm from the edge of the blank, and the thickness of the compounded blank is 154 mm. ±2mm.

Composite billet heating and rolling: The composite billet is heated in stages, the low temperature section is heated to 850±20°C at a rate of 70°C/h, and the temperature is kept for 2.5 hours; ; In the high temperature section, the temperature is raised to 1220±20°C at a rate of 85°C/h, and the temperature is kept for 6.5 hours. There is no widening rolling during the rolling process of the composite billet, all longitudinal rolling, and a total of 12 passes, of which the reductions of the first two passes are 5mm and 8mm, and the reductions of the 5th and 6th passes are 50mm and 45mm respectively. , The rolled steel plate is cooled by the cooling bed after the hot leveling machine, and there is no obvious buckling. The thickness of the clad steel sheet after rolling was 16.3 mm.

Heat treatment: Before the heat treatment of the clad steel plate, the welding area on the four sides is cut off, and the upper and lower plates are separated to obtain a hot-rolled steel plate with a width of 3000mm. The split steel plate was heated to 910°C in a continuous furnace, and kept for 46 minutes before entering the quenching machine for water cooling; the quenched steel plate was promptly tempered and heat-treated in a continuous furnace, and the steel plate was heated to 200°C and kept for 1.5 hours before being released from the furnace. After strong straightening treatment, NM450 sheet with unevenness not more than 5mm/m is obtained.

Table 1 Mechanical properties and unevenness of NM450 steel plates produced in each example

In addition to the above-mentioned embodiments, the present invention also includes other embodiments, and all technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the claims of the present invention.

Claims

A thin gauge NM450 steel plate, characterized in that the chemical composition of the steel plate is C: 0.15-0.30, Si: 0.25-0.45, Mn: 0.80-1.20, Cr: 0.20-0.60, Mo: 0.10- 0.50, Ni: 0.10-0.50, Al: 0.02-0.08, B: 0.0010-0.0030, P≤0.020, S≤0.010, the rest are Fe and inevitable impurities.
A thin-size NM450 steel plate according to claim 1, characterized in that: the carbon equivalent of the final steel plate product is not more than 0.52%.
A thin NM450 steel plate according to claim 1, characterized in that the thickness of the final steel plate product is 4-8mm, the maximum width reaches 3200mm, and the unevenness is not more than 5mm/m.
A method for manufacturing a thin NM450 steel plate as claimed in claim 1, wherein the method is: formulating a low-carbon equivalent chemical composition for a 4-8mm thin steel plate, and obtaining through steelmaking, refining and vacuum continuous casting Continuous casting slabs with a thickness of 150-400mm; the blanks of the same size or the intermediate blanks after rolling to a certain thickness are composite welded around, and the middle is kept in a non-vacuum state; the composite blanks are heated and rolled to the target thickness, rolling The final steel plate is not rolled and welded due to the non-vacuum state in the middle, and the four sides of the welds are cut off and divided into two steel plates; the rolled steel plate is cut and divided into four sides, and then the single steel plate is heat treated, and the steel plate with poor flatness is before quenching. Straighten.
The method for manufacturing a thin-gauge NM450 steel plate according to claim 4, wherein the method comprises the following steps:

1. Blank preparation

(1) Steelmaking, precise control of alloying elements in steel to ensure that the carbon equivalent deviation between different heats is not greater than 0.02%, LF furnace refining is fully deoxidized and desulfurized, and RH ultimate vacuum time is guaranteed to be more than 20min;

(2) Continuous casting of slab, continuous casting of 150-400mm thick slab with direct arc continuous casting machine, using tundish induction heating technology, and adopting argon gas protection and dynamic light reduction technology to achieve high-quality continuous casting slab production, The low magnification quality of the slab meets: the center segregation is not greater than Class C 1.0; the center porosity is not greater than 1.0;

(3) Prefabricated intermediate slabs. For the production of 4-5mm thick steel plates, prefabricated intermediate slabs with thinner thickness are used for composite rolling, and prefabricated intermediate slabs are heated to about 1220 ° C by using 150-400mm continuous casting slabs for rolling. The thickness of the prefabricated intermediate slab is controlled at 60-100mm; for the steel plate with a thickness of >5-8mm, the slab with a thickness of 150mm is used for direct composite rolling, and there is no need to roll it into a prefabricated intermediate slab and then composite it. When the width of the finished steel plate exceeds the continuous casting When the slab width is used, for the prefabricated intermediate slab that is rolled and widened to be larger than the width of the finished product, the maximum width of the prefabricated intermediate slab is not more than 3400mm;

2. Billet finishing and compounding

The appearance quality of continuous casting slabs or prefabricated intermediate slabs shall be inspected according to YB/T 2012, and the billets with qualified appearance shall be cut into sections according to the size requirements of the production plan. Non-vacuum treatment in the middle, the welding width from the edge of the blank is controlled at 50-80mm;

3. Heating and rolling of composite billets

(1) Heating the composite billet, the low temperature section is heated to 850±20°C at a rate of 60-100°C/h, and the temperature is kept for 2-3 hours; 3h; in the high temperature section, the temperature is raised to 1200-1250°C at a rate of not more than 100°C/h, and the temperature is kept for 5-9 hours;

(2) Rolling of composite billets, on the wide and thick plate rolling mill, rolling 10-15 passes, rolling to twice the target thickness of the finished single steel plate, the thickness tolerance of the composite steel plate is controlled at 0-0.6mm, and the steel plate is hot straightened After the machine, the cooling bed is cooled, and the steel plate is cooled to about 300 ℃;

4. Heat treatment of steel plate

(1) Quenching, the quenching process of the steel plate is as follows: the heating temperature is 900-940°C, the holding time is 20-25min+3min/mm×the thickness of the steel plate, the composite steel plate is calculated according to the total thickness of the upper and lower plates, and it is water-cooled after being released;

(2) Tempering, using a continuous furnace for low-temperature tempering of the steel plate, tempering process: heating temperature 180-220 ° C, holding time 1-2 hours, air cooling after release;

5. Inspection and inspection

The finished NM450 steel plate is inspected for appearance and quality according to GB/T 24186-2009, and samples are taken for various performance inspections, and the judgment is made according to the requirements of GB/T 24186-2009.
The method for manufacturing a thin-gauge NM450 steel plate according to claim 4, characterized in that: during the rolling process of the composite billet, there is no widening rolling, all longitudinal rolling is performed, and a small reduction is used in the first two passes of rolling, There are 2-3 passes in the middle pass with a reduction of 30-50mm to realize the welding of the welding area.
The method for manufacturing a thin NM450 steel plate according to claim 4, characterized in that: the steel plate quenching stage: the 4-5mm thick composite steel plate is quenched by a quenching machine, and after quenching, the four sides of the composite steel plate are cut off and the upper and lower sides of the composite steel plate are cut off. The plates are separated to obtain two kinds of steel plates with the same thickness; the four sides of the composite steel plate with a thickness of >5-8mm are cut off and the upper and lower plates are separated, and then the single steel plate is quenched.