CN107287527A - 160mm super-thick steel plate with excellent low-temperature toughness and production method thereof - Google Patents

Abstract

The invention provides a 160mm super-thick steel plate with excellent low-temperature toughness and a production method thereof, wherein the steel plate comprises the following components in percentage by weight: 0.06-0.08% of C, 0.35-0.65% of Si, 1.2-1.4% of Mn, less than or equal to 0.020% of P, less than or equal to 0.004% of S, 0.06-0.08% of Nb0.15-0.35% of Ni0.015-0.035% of Als0.015-0.035% of Fe and inevitable impurities in balance. The method comprises smelting, blank preparation, rolling and heat treatment, wherein the blank is formed by compositely welding two continuous casting blanks with the thickness of 300 mm; the composite blank is rolled at a low speed under a large rolling reduction, and then is subjected to normalizing heat treatment. The steel plate produced by the method has excellent low-temperature toughness, impact energy of-20 ℃ is not lower than 100J, the thickness of the steel plate is 160mm, and the flaw detection meets the GB/T2970I-level standard.

Description

A kind of 160mm extra-thick steel plate with excellent low temperature toughness and production method thereof

technical field

The invention belongs to the field of metal material processing, and in particular relates to an extra-thick steel plate with excellent low-temperature toughness and a production method thereof.

Background technique

Today, with the rapid development of science and technology and modern industry, the market demand for extra-thick steel plates for machinery, hydropower and marine engineering is increasing, and the performance requirements for steel plates are getting higher and higher, and the thickness specification requirements have also expanded to more than 100mm or even more than 150mm. . Extra-thick plates can be widely used in construction machinery, bridges, hydropower, nuclear power, ocean engineering and other structural parts. However, it is difficult to produce steel plates with a thickness of more than 150mm to ensure that the flaw detection and performance are qualified and uniform. At present, large die-cast steel ingots or electroslag remelting technology are generally used to produce extra-thick plates over 150mm, but the metallurgical quality of large steel ingots is poor, the yield is low, and there are a large number of internal defects that lead to a decline in the pass rate and performance of steel plates; electroslag Although remelting can basically eliminate internal defects such as segregation, porosity and shrinkage cavity in steel ingots, its low production efficiency and high production cost make it only suitable for the production of a few special steel types.

"An extra-thick steel plate for a boiler drum above 150 mm and its production method" (public number CN104561818A), the process flow used for the extra-thick plate involved is: high-quality molten iron, KR molten iron pretreatment, 100/120 tons of top and bottom double blowing Converter, LF furnace refining, vacuum degassing treatment, stack cooling of steel ingots for 24-60 hours, heating of steel ingots, billet heating-rolling-stack cooling, intermediate billet heating-rolling-stack cooling, quenching+tempering, the process flow is complex , Slow production pace and low growth rate will inevitably lead to rising costs.

"A 150mmQ245R Extra-Thick Steel Plate and Its Production Method" (Publication No.: CN102345047A) involves a 150mmQ245R container steel with a thickness of only 150mm and a strength of only 250Mpa. Neither the thickness nor the strength meet the requirements of thicker and higher Extra-thick plates of the strength level are required.

"A 160mm Thick Q235C Low Compression Bit Thick Steel Plate and Its Preparation Method" (publication number is CN104451375A), the disclosed content is to adopt a continuous casting slab with a thickness of 320mm, and after heating and rolling, finally produce a 160mm extra-thick steel plate. The compression ratio is only 2, which will inevitably lead to insufficient deformation of the core of the steel plate, and defects such as loose core are prone to occur.

"A 100 mm low-alloy high-strength extra-thick steel plate and its manufacturing method" (publication number CN 101348879A), discloses a low-alloy extra-thick steel plate with a thickness of 100 mm, which contains C0.14-0.17%, Si0.35 ～0.65%, Mn1.2～1.4%, due to its high carbon content, it will not be conducive to the welding and manufacturing of steel plates, and the thickness is only 100mm.

"A 100mm, 400MPa high-strength extra-thick steel plate and its manufacturing method" (public number CN 101476081A), provides a 100mm, 400MPa high-strength extra-thick steel plate, which has a high yield strength and does not require heat treatment. And its production thickness is only 100mm, which cannot meet the increasing demand of the market for steel plate thickness.

From the above public documents, it can be seen that the current production of extra-thick plates has the following deficiencies:

1. The thickness of the product is small and the scope of application is narrow;

2. The strength and toughness of the product are poor, which cannot meet the requirements of high service conditions;

3. The production process is complicated, the production efficiency is low, the cost is high, and defects such as heart segregation and looseness are prone to occur;

Contents of the invention

The object of the present invention is to overcome the above problems and disadvantages and provide an extra-thick steel plate with a production thickness specification of 160mm, which can meet the flaw detection standard and has excellent low-temperature toughness, and its production method.

The purpose of the invention is achieved in this way:

A 160mm extra-thick steel plate with excellent low-temperature toughness. The composition of the steel plate is as follows by weight percentage: C0.06-0.08%, Si0.35-0.65%, Mn1.2-1.4%, P≤0.020%, S≤0.004 %, Nb0.06-0.08%, Ni0.15-0.35%, Als0.015-0.035%, and the rest are Fe and unavoidable impurities.

The ingredients are designed for the following reasons:

Carbon: In the chemical composition design of extra-thick plate steel, carbon has a great influence on the strength, toughness, welding performance and smelting cost of the steel. In order to make the steel plate have good weldability and low-temperature impact toughness, the carbon content in the steel must be reduced to the lower limit, because carbon is a strong solid solution strengthening element, which can significantly increase the strength of the steel plate, but If the carbon content is too high, it is not conducive to welding and difficult to control the second phase such as cementite, which will obviously deteriorate the toughness, plasticity and steel plate welding performance. The carbon content in the present invention is set at C0.06-0.08%.

Manganese: Manganese is an effective element to improve strength and toughness. It is a weak carbide forming element. Its role in smelting is to deoxidize and eliminate the influence of sulfur. It can also reduce the austenite transformation temperature and refine ferrite grains. , It is beneficial to improve the strength and toughness of the steel plate. At the same time, it can solid solution strengthen ferrite and increase the hardenability of steel. Generally, when low-carbon high-manganese steel is used as welded structural steel, the greater the manganese/carbon ratio (up to 2.5 or more), the better the low-temperature toughness of the steel. When the manganese content is too high, the steel hardens and the ductility deteriorates. The manganese content in the present invention is set at 1.2-1.4%.

Silicon: Silicon acts as a deoxidizer, and at the same time has a solid solution strengthening effect, which can also greatly delay the formation of carbides, retard the growth of cementite, and increase the stability of austenite. However, the silicon content is high, and inclusions are easy to appear in the steel type, and the steel is easy to rust, and the rust is easily rolled into the surface layer of the steel plate in the hot rolling production. The content is set at 0.35-0.65%.

Phosphorus: Phosphorus is a harmful element in steel. Although it is one of the elements with the best solid solution strengthening effect, phosphorus segregates grain boundaries and deteriorates toughness. The content directly affects the plasticity and toughness of steel plates. Phosphorus is a very harmful element to steel. Its content should be reduced as much as possible, and its content should be controlled to a minimum.

Sulfur: Sulfur is a harmful element in steel. The presence of second-phase particles such as manganese sulfide, oxide inclusions or carbides will reduce the plasticity, strength and toughness of steel, and reduce the elongation of steel. Manganese sulfide has a certain degree of plasticity and elongates with the rolling direction, which increases the anisotropy of the steel, which is very unfavorable to the transverse performance of the steel. The iron sulfide formed by sulfur causes hot brittle cracks in steel during hot rolling and welding. When the sulfur content is high, the ability to resist hydrogen sulfide corrosion is greatly reduced, so try to control its content to a minimum.

Aluminum: Aluminum is a deoxidizing element, which can be used as an aluminum nitride forming element to effectively refine grains. When its content is less than 0.01%, the effect is small; when it exceeds 0.07%, the deoxidation effect reaches saturation; The toughness of the weld heat-affected zone is detrimental. Therefore, the aluminum content is limited in the range of 0.015% to 0.035% in extra thick plates.

Nickel: It contributes little to the strength of steel, but adding appropriate Ni in steel can significantly improve the toughness of steel, especially the low-temperature toughness of steel can be significantly improved, but the effect is no longer obvious after the content exceeds a certain value, so in the present invention , the content of Ni is controlled at 0.15-0.35%;

Niobium: Carbide is formed in the steel, and after high temperature precipitation, it is pinned at the grain boundary to prevent the growth of the grain, and plays the role of refining the grain, so as to improve the strength and toughness of the steel. The Nb content in the present invention is 0.06~ 0.08%.

The present invention is a manufacturing method for producing a 160mm ultra-thick steel plate: after smelting and casting, flaw detection and cleaning are carried out on the slab, two or more mother slabs are subjected to vacuum compound welding, and cross-rolling is adopted on a wide and thick plate rolling mill. The method produces a steel plate that is qualified for flaw detection and has excellent low-temperature toughness.

A production method of 160mm extra-thick steel plate with excellent low-temperature toughness, including smelting, continuous casting, billet preparation, rolling, heat treatment,

Smelting: use RH for vacuum treatment, RH cycle time ≥ 10min, [H] in the steel is controlled below 2ppm, [O] is controlled below 25ppm; the target superheat of the tundish is less than 25°C; the whole process of protection pouring, guaranteed before starting the machine Ladle static argon blowing time ≥ 5min; after casting slabs off the assembly line, they are stacked with hot slabs and slowly cooled, and the slow cooling time is greater than or equal to 24 hours;

Billet preparation: The billet is made of two 300mm thick continuous casting slabs by composite welding; before composite welding, the surface and side of the continuous casting slab must be processed by a milling machine. The roughness of the welding surface is greater than 8um. The vacuum degree is higher than 0.1pa, the welding voltage is controlled at 65KV-85KV, the welding current is controlled at 305mA-315mA, and the welding speed is controlled at 200mm/min-250mm/min. The arc starting and arc ending areas are consistent continuous welds, and there is no weld discontinuity area.

Rolling: The composite billet should be covered and packaged with cold-rolled steel plates before loading to prevent excessive oxidation during heating; the furnace temperature is controlled at 500-650°C during furnace loading, and the heating temperature is controlled at 1150-1180°C; Descale the upper and lower surfaces; use low speed and large reduction during rolling, control the pass reduction rate at 15%-30%, and control the rolling speed at 1.0m/s-1.1m/s. During the rolling process, the steel plate The lower surface is sprayed with water to prevent warping of the steel plate; after the steel plate is rolled, it is rolled off the assembly line and stacked with hot steel plates for slow cooling, and the slow cooling time is not less than 24 hours.

Heat treatment: Carry out normalizing heat treatment, the temperature of the heating furnace is controlled at 885°C-895°C, the holding time is controlled at 300min-330min, and air-cooled after being released from the furnace.

The beneficial effect of the present invention is that: the steel plate produced by the method of the present invention has excellent low-temperature toughness, the impact energy at -20°C is not less than 100J, and the steel plate is 160mm thick, and the flaw detection meets the GB/T 2970 Class I standard.

detailed description

Below by embodiment the present invention will be further described.

The embodiment of the present invention includes smelting, continuous casting, billet preparation, rolling, and heat treatment according to the component ratio of the technical solution. The composition of the steel of the embodiment of the present invention is shown in Table 1. Table 2 of the composite welding process parameters of steel in the embodiment of the present invention. The main process parameters of the steel of the embodiment of the present invention are shown in Table 3. The performance of the steel of the embodiment of the present invention is shown in Table 4.

Table 1 Composition of the steel of the embodiment of the present invention

Example C Si mn P S Nb Ni ALs 1 0.06 0.65 1.40 0.015 0.0013 0.07 0.035 0.025 2 0.08 0.56 1.26 0.012 0.002 0.06 0.015 0.035 3 0.07 0.35 1.30 0.011 0.0015 0.08 0.03 0.015 4 0.065 0.60 1.20 0.018 0.004 0.072 0.02 0.020

Table 2 Composite welding process parameters of the steel of the embodiment of the present invention

Table 3 Main process parameters of rolling and heat treatment of the steel of the embodiment of the present invention

Table 4 The performance of the steel of the embodiment of the present invention

Claims (2)

1. A 160mm extra-thick steel plate with excellent low-temperature toughness, characterized in that the composition of the steel plate is as follows by weight percentage: C0.06-0.08%, Si0.35-0.65%, Mn1.2-1.4%, P≤ 0.020%, S≤0.004%, Nb0.06～0.08%, Ni0.15～0.35%, Als0.015～0.035%, and the rest are Fe and unavoidable impurities. 2. A method for producing a 160mm extra-thick steel plate with excellent low-temperature toughness as claimed in claim 1, comprising smelting, blank preparation, rolling, and heat treatment, characterized in that: (1) Billet preparation: The billet is made of two 300mm thick continuous casting slabs by compound welding; before composite welding, the surface and side of the continuous casting slab must be processed by a milling machine. The vacuum degree of the vacuum chamber is higher than 0.1pa, the welding voltage is controlled at 65KV-85KV, the welding current is controlled at 305mA-315mA, the welding speed is controlled at 200mm/min-250mm/min, the weld is full, and there is no pit at the place where the welding fluid flows , the arc start and arc end areas of the weld seam are consistent continuous weld seams, and there is no weld seam discontinuity area. (2) Rolling: The composite billet should be covered and packaged with cold-rolled steel plates before loading into the furnace. Carry out descaling; low speed and large reduction are used during rolling, the pass reduction rate is controlled at 15%-30%, the rolling speed is controlled at 1.0m/s-1.1m/s, and the lower surface of the steel plate is affected during the rolling process Spray water for cooling; after the steel plate is rolled, it is rolled off the assembly line and stacked with hot steel plates for slow cooling, and the slow cooling time is not less than 24 hours. (3) Heat treatment: Carry out normalizing heat treatment, the temperature of the heating furnace is controlled at 885°C-895°C, the holding time is controlled at 300min-330min, and air-cooled after being released from the furnace.