Steel plate for high temperature equipment and manufacturing method therefor

Abstract

A steel plate for high temperature equipment, the steel plate having the following chemical elements, in mass%, are: 0.09%-0.19% C, 0.2%-0.7% Mn, 0.008%-0.02% Ti, 1.80%-3.2% Cr, 0.80%-1.70% Mo, 0.005%-0.015% acid-soluble Al, 0.020%-0.050% Nb, 0.15%-0.50% V, 0.0005%-0.0050% Mg, and the remainder are Fe and unavoidable impurities. A manufacturing method for the steel plate for high temperature equipment is further disclosed. The method includes the steps of: (1) smelting molten steel and continuously casting it to obtain a casting blank: during the smelting process, sequentially adding deoxidizing agents Mn, Al, Ti and Mg / Ni-Mg alloy, and carrying out deoxidation, which includes pre-deoxidation and final deoxidation, in which Mn, Al and Ti are first added sequentially for pre-deoxidation, the oxygen potential of the pre-deoxidized molten steel is 0.0015%-0.0085%, and then Mg / Ni-Mg alloy is added thereto for final deoxidation; (2) rolling the casting blank to obtain a steel plate; and (3) carrying out quenching and tempering heat treatment on the steel plate.

Description

[Technical field]

[0001] The present invention relates to a steel material and a manufacturing method therefor, and more particularly to a steel plate for high-temperature equipment and a manufacturing method therefor. [Background technology]

[0002] background In the energy chemical industry, it is often necessary to use high temperature pressure vessels for the production and processing of energy. In order to improve the energy production efficiency, both the market and users want the reaction vessel to withstand higher temperatures and higher pressures, which imposes higher requirements on the manufacturing materials of the high temperature reaction vessel.

[0003] It is found that one of the main reasons for failure of high temperature reactor is that when the reactor operates at high temperature and pressure for a long time, elements such as As, Sn, Sb and P tend to segregate at grain boundaries, which weakens the bonding strength between grain boundaries of steel, thereby weakening the temper embrittlement resistance of steel, leading to equipment failure and subsequently causing production accidents. Among the above four elements causing temper embrittlement, P is the most harmful to promote temper embrittlement, followed by Sn, As and Sb.

[0004] Since the remaining elements such as Sn, As and Sb cannot be effectively removed by existing steelmaking technology during steelmaking and refining, the contents of these elements in steel can only be limited by reducing the amounts of Sn, As and Sb in the steelmaking raw materials, thereby reducing the temper embrittlement of steel caused by the remaining elements, and the content of P in steel can be reduced by technological means during steelmaking and refining.

[0005] However, in existing technologies, reducing the P content in steel by steelmaking technology currently requires large economic and time costs, especially when the P content in steel is required to be extremely low (P≦70 ppm), and the economic and time costs of the steelmaking process are very high.

[0006] Therefore, it has become an increasingly urgent requirement how to design the composition and production process of steel that can ensure that the steel contains a high content of P but still has a very high temper embrittlement resistance.

[0007] For example, CN103740912A published on April 23, 2014 discloses a processing method for improving the temper embrittlement resistance of steel plate for pressure vessels, in which a weak water-cooling heat treatment process is used after normalizing the steel, so that the microstructure of the steel is a uniform lath bainite structure, and carbides precipitate between the bainite laths and the original austenite grain boundaries, thereby improving the temper embrittlement resistance of the steel plate; however, it is found that the carbides of the steel plate tend to coarsen after pseudo-welding, and this patent does not take into account that the temper embrittlement resistance of the steel plate may deteriorate during subsequent service processes due to the coarsening of the bainite laths and the aggregation and growth of carbides in a long-term high-temperature environment.

[0008] For another example, CN104805380A published on July 29, 2015 is entitled "Low temper brittleness Cr-Mo steel plate for high temperature and pressure resistant equipment and preparation method therefor". According to the patent, the contents of As, Sn and Sb in the steel are strictly controlled, while the contents of Si and Mn in the steel need to be low, and the most important thing is to minimize the content of P in the steel as much as possible to ensure that the steel has lower temper brittleness.

[0009] For further examples, CN108677094A published on October 19, 2018 is entitled "Steel Plate for Process Pipeline for Refining and Reforming Device and Production Method Therefor". According to the patent, the content of P and Sn in the steel is controlled to meet (P+Sn)≦0.014%, and since Sn cannot be removed during the steelmaking process, the control of the lower Sn content in the steel can only be achieved by selecting raw materials for steelmaking, while the content of P in the steel is reduced by steelmaking technology.

[0010] In view of the above, it can be seen that there are mainly two ways to improve the high-temperature temper embrittlement resistance of steel in the prior art. The first way is to control the content of the remaining elements such as As, Sn and Sb in steel, and reduce the content of P in steel as much as possible through steelmaking technology, and appropriately reduce the content of Si and Mn to improve the high-temperature temper embrittlement resistance of steel; the second way is to control the alloy chemical composition of steel (for example, add elements such as W to form W carbide), and further control the phase change structure of steel, form a certain structure type, improve the structural stability of steel, and resist the temper embrittlement process.

[0011] Based on this, unlike the design idea of ​​improving the high-temperature temper embrittlement resistance of steel in the prior art, in the present invention, it is expected to obtain a steel plate for high-temperature equipment and a manufacturing method therefor, which adopt a completely new design idea that a nano-scale precipitate phase functions as a P trap to absorb a large amount of P in the steel, thereby preventing the P element in the steel from dispersing into the austenite grain boundary when the steel plate operates at high temperature, and thereby greatly improving the low-temperature impact toughness of the steel plate. Summary of the Invention

[0012] overview One of the objectives of the present invention is to provide a steel plate for high-temperature equipment, which, through rational chemical composition design and optimized production process, employs nanoscale precipitate phase as P trap to absorb a large amount of P in steel, thereby avoiding P in steel from dispersing into austenite grain boundary when the steel plate works at high temperature, and thereby can greatly improve the low-temperature impact toughness of the steel plate.

[0013] The steel plate for high-temperature equipment according to the present invention has excellent temper embrittlement resistance and can be effectively applied in the energy and chemical industries. As a manufacturing material for high-temperature reaction vessels, it has great practical significance and very wide application prospects.

[0014] In order to achieve the above object, the present invention provides a steel plate for high temperature equipment, which has the following chemical elements, in mass %: The composition is 0.09%~0.19% C, 0.2%~0.7% Mn, 0.008%~0.02% Ti, 1.80%~3.2% Cr, 0.80%~1.70% Mo, 0.005%~0.015% acid-soluble Al, 0.020%~0.050% Nb, 0.15%~0.50% V, 0.0005%~0.0050% Mg, and the remainder is Fe and unavoidable impurities.

[0015] Preferably, the high temperature equipment steel plate has the following chemical elements, in mass %: 0.09%~0.19% C, 0.2%~0.7% Mn, 0.008%~0.02% Ti, 1.80%~3.2% Cr, 0.80%~1.70% Mo, 0.005%~0.015% acid-soluble Al, 0.020%~0.050% Nb, 0.15%~0.50% V, 0.0005%~0.0050% Mg, and the remainder being Fe and unavoidable impurities; the high-temperature equipment steel plate contains nano-scale Mg-containing inclusions in a dispersed distribution.

[0016] In this application, the term "nanoscale" is used to denote lengths equal to or greater than 1 nm, but not exceeding 1000 nm (ie, 1 μm).

[0017] In the present invention, the steel plate for high-temperature equipment according to the present invention can generate a large amount of nano-scale Mg-containing inclusions with a dispersed distribution through a rational chemical composition design and an optimized production process, and these nano-scale inclusions can act as nucleation particles to induce a large amount of precipitation of nano-scale MC precipitate phases (M represents one or more of Nb, V, Mo and Cr) in the steel during the operation process of the high-temperature equipment made from the steel plate, while the nano-scale MC precipitate phases can act as P traps to absorb a large amount of P in the steel, thereby avoiding significant segregation of P in the steel toward the austenite grain boundary when the steel plate operates at high temperature, and greatly increasing the temper embrittlement resistance of the steel plate.

[0018] In the steel plate for high temperature equipment according to the present invention, the design principles of each chemical element are specifically as follows: C: In the steel plate for high-temperature equipment according to the present invention, C is an important element in the steel. In order to ensure the suitability of the steel plate for welding process, the content of C in the steel should not be too high, and the upper limit of the content of C is controlled to be 0.19%. When the content of C in the steel is higher than 0.19%, the low-temperature impact toughness of the steel plate substrate after welding and the heat-affected zone in the weld will be deteriorated. Therefore, in order to ensure the appropriate strength of the steel plate, it is necessary to control the mass% of C in the steel to 0.09% or more. Based on this, in the steel plate for high-temperature equipment according to the present invention, the mass% of C is controlled to be 0.09% to 0.19%.

[0019] Mn: In the steel plate for high-temperature equipment according to the present invention, Mn is a weak deoxidizing element, and the oxygen potential in the steel can be adjusted by adopting Mn as a deoxidizing agent. Moreover, Mn is also a strengthening element, and can effectively improve the strength of the steel, so that the lower limit of Mn is 0.2% in order to ensure the strength of the steel. Moreover, Mn is also an element that tends to segregate in the steel. If the content of Mn in the steel is high, the center segregation of the steel plate will be further deteriorated, thereby reducing the low-temperature impact toughness of the steel plate, and therefore the upper limit of the content of Mn is limited to 0.7%. On this basis, in the steel plate for high-temperature equipment according to the present invention, the mass% of Mn is controlled to be 0.2%-0.7%.

[0020] Ti: In the steel plate for high-temperature equipment according to the present invention, Ti is also a deoxidizing element, and the deoxidizing ability of Ti is better than Mn, but weaker than Al and Mg. In the present invention, Ti is appropriately added to the steel according to the deoxidizing effect of Mn, so that the oxygen potential in the steel can be controlled. Meanwhile, after Ti deoxidization, Ti2O3 particles can be formed to promote the formation of intragranular ferrite and improve the low-temperature impact toughness of the steel. However, it should be noted that the content of Ti in the steel should not be too high, and when the content of Ti in the steel is too high, the size of the Ti2O3 particles formed will become larger, and thus will no longer have the ability to form intragranular ferrite, but will easily become the source of crack initiation and reduce the low-temperature impact toughness of the steel. Therefore, the upper limit of Ti is 0.02%. Based on this, in the steel plate for high-temperature equipment according to the present invention, the mass% of Ti is controlled to be 0.008%-0.02%.

[0021] Cr: In the steel plate for high-temperature equipment according to the present invention, adding an appropriate amount of Cr can improve the hardenability of the steel plate, and improve the oxidation resistance and corrosion resistance of the steel plate when operating at high temperatures. Based on this, in the steel plate for high-temperature equipment according to the present invention, the mass% of Cr is controlled to be 1.80% to 3.2%.

[0022] Mo: In the steel plate for high-temperature equipment according to the present invention, Mo is mixed with interstitial elements such as carbon and nitrogen and can be dissolved to improve the high-temperature creep strength of the steel plate. Adding an appropriate amount of Mo can also form small precipitates and achieve the precipitation strengthening effect. When the content of Mo in the steel is higher, the precipitates tend to become coarse and their size increases, so that the precipitation strengthening effect is weakened. On this basis, in the steel plate for high-temperature equipment according to the present invention, the mass% of Mo is controlled to be 0.80%-1.70%.

[0023] Acid-soluble Al: In the steel plate for high-temperature equipment according to the present invention, the mass% of acid-soluble Al in the steel needs to be strictly controlled. When the content of acid-soluble aluminum in the steel is lower than 0.005%, the steel tends to generate mixed crystal phenomenon during rolling and phase change, which reduces the structural uniformity of the steel plate and thus reduces the impact toughness of the steel; therefore, the content of acid-soluble aluminum in the steel should not be too high, and when the content of acid-soluble aluminum in the steel is higher than 0.015%, magnesia-alumina spinel inclusions are easily formed in the steel, which not only impairs the mechanical properties of the steel plate, but is also disadvantageous to the formation of Mg-containing inclusions in the steel. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass% of acid-soluble Al is controlled to be 0.005%-0.015%.

[0024] Nb: In the steel plate for high temperature equipment according to the present invention, Nb can play a role in refining the structure of the steel and improving the strength and toughness of the steel. However, it should be noted that the content of Nb in the steel should not be too high. When the content of Nb in the steel is too high, the toughness of the heat affected zone in the weld will be reduced. Therefore, in the steel plate for high temperature equipment according to the present invention, the mass% of Nb is controlled to be 0.020%-0.050%.

[0025] V: In the steel plate for high-temperature equipment according to the present invention, an appropriate amount of V is added to bond with C in the steel to generate nano-scale VC precipitate phase, thereby obtaining the effect of precipitation strengthening; when an excessive amount of V is added, the excess V will dissolve in the ferrite matrix, thereby weakening the bonding force between atoms. Based on this, in the steel plate for high-temperature equipment according to the present invention, the mass% of V is controlled to be 0.15%-0.50%.

[0026] Mg: In the steel plate for high temperature equipment according to the present invention, Mg has a very strong deoxidizing ability. After adding Mg to the molten steel, a large amount of Mg-containing inclusions can be formed, and these Mg-containing inclusions greatly reduce the activity of [O] in the steel, so that the larger size Al2O3 and / or Ti2O3 inclusions in the steel are greatly reduced. These larger size inclusions can easily act as a source of crack initiation and reduce the low temperature impact toughness of the steel plate. Therefore, by adding a small amount of Mg to the steel, the formation of the larger size inclusions can be reduced, and the low temperature impact toughness of the steel can be improved. Furthermore, the nano-Mg-containing inclusions formed can absorb P during the subsequent high temperature heat treatment and service of the steel, thereby reducing the proportion and concentration of P dispersed in the austenite grain boundaries, thereby inducing a large amount of nano-scale MC precipitate phases, which increase the temper embrittlement resistance of the steel. Based on this, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of Mg is controlled to be 0.0005% to 0.0050%.

[0027] Furthermore, the reason for controlling the mass% of Mg in the molten steel to 0.0005%-0.0050% is that when the mass% of Mg added into the molten steel is less than 0.005%, the density of Mg-containing inclusions formed in the molten steel is too low to induce a large amount of MC precipitate phases, and on the other hand, when the mass% of Mg added into the molten steel is more than 0.050%, a large amount of Mg / Ni-Mg alloy needs to be added, which increases the production cost of steel, and the addition efficiency of Mg decreases because the total content of Mg in the molten steel is already close to its saturation concentration.

[0028] Preferably, the steel plate for high-temperature equipment according to the present invention further has at least one of the following chemical elements, and the chemical element is: 0 < Ca ≤ 0.0050%, 0 < Ni ≤ 0.6%, 0 < B ≤ 0.0015%, and 0 < Cu ≤ 0.5%.

[0029] In the above technical solution of the present invention, Ca, Ni, B, and Cu can all further improve the properties of the steel plate for high-temperature equipment according to the present invention.

[0030] Ca: In the steel plate for high-temperature equipment according to the present invention, Ca easily combines with O and S in the steel to form calcium oxide and calcium sulfide inclusions. When the content of Ca in the steel is high and exceeds 0.005%, large-sized calcium oxide and calcium sulfide inclusions are easily formed in the steel, which is not good for the properties of the steel. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of Ca is preferably controlled such that 0 < Ca ≤ 0.0050%.

[0031] Ni: In the steel plate for high-temperature equipment according to the present invention, Ni can effectively improve the low-temperature toughness and strength of the steel plate. However, it should be noted that the price of Ni is high, and considering the production cost of the steel, it is not appropriate to add excessive Ni to the steel. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of Ni is controlled such that 0 < Ni ≤ 0.6%.

[0032] B: In the steel plate for high-temperature equipment according to the present invention, B combines with N to form BN, thereby reducing the content of N dissolved in the steel and improving the low-temperature toughness of the steel. However, it should be noted that excessive B tends to segregate significantly at the grain boundaries, which is harmful to the properties of the steel. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of B is preferably controlled such that 0 < B ≤ 0.0015%.

[0033] Cu: In the steel plate for high-temperature equipment according to the present invention, Cu can increase the strength of the steel and improve the corrosion resistance of the steel. However, when the content of Cu in the steel is too high, hot brittleness is easily generated at high temperatures. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of Cu is preferably controlled such that 0 < Cu ≦ 0.5%.

[0034] It should be noted that the addition of the above elements Ca, Ni, B, and Cu will increase the cost of raw materials. Considering comprehensively the performance and cost control, in the technical solution of the present invention, at least one of the above elements is preferably added.

[0035] In the steel plate for high-temperature equipment according to the present invention, among the inevitable impurities, it is preferable that P ≦ 0.016%, S ≦ 0.010%, N ≦ 0.004%, and O ≦ 0.005%.

[0036] In the above technical solution, P, S, N, and O are all impurity elements in the steel. And in order to obtain steel with better properties and better quality, the content of impurity elements in the steel should be reduced as much as possible technically.

[0037] P: When the content of P in the steel is too high, the toughness of the steel will deteriorate further. P can segregate at the grain boundaries, resulting in weakening the bonding force between the grain boundaries, which is the main reason for temper embrittlement generated in the steel plate. Furthermore, like Mn, P is also an element that tends to segregate, and the segregation of P will reduce the structural homogeneity of the steel plate and ultimately lead to unevenness in the properties of the steel. Therefore, in the steel plate for high-temperature equipment according to the present invention, the mass percentage of P is controlled such that P ≦ 0.016%.

[0038] S: When the content of S in steel is too high, it will cause center segregation of slab, and S can combine with Mn to form large Mns inclusions, which will reduce the strength and toughness of steel plate. Therefore, in the steel plate for high temperature equipment according to the present invention, the mass% of S is controlled to be S≦0.010%.

[0039] N: When the content of N in the steel is too high, the toughness of the steel will be adversely affected, and especially when the content of solute N exceeds 0.004%, the solute N will reduce the low temperature toughness of the steel plate. Therefore, in the steel plate for high temperature equipment according to the present invention, the mass% of N is controlled so that N≦0.004%.

[0040] O: When the content of O in the steel is too high, it will also have a detrimental effect on the steel. Therefore, in the steel plate for high temperature equipment according to the present invention, the mass% of O is controlled to be O≦0.005%.

[0041] Preferably, in the steel plate for high temperature equipment according to the present invention, the bulk density of Mg-containing inclusions having a size smaller than 800 nm is less than 6×10 6 / mm 3 Greater than.

[0042] Preferably, in the steel plate for high temperature equipment according to the present invention, the steel plate further contains nano-scale MC precipitate phases, M represents one or more of Nb, V, Mo and Cr, the MC precipitate phases are spherical or nearly spherical, and the MC precipitate phases have an average grain size smaller than 200 nm. In the present application, the average grain size refers to the average grain size of all MC precipitates in the precipitate phase.

[0043] Preferably, in the steel plate for high temperature equipment according to the present invention, the bulk density of the MC precipitate phase having a size smaller than 500 nm is 3.0 × 10 6 / mm 3 Greater than.

[0044] Preferably, in the steel plate for high-temperature equipment according to the present invention, the ratio of the MC precipitate phases having a size smaller than 100 nm in all the MC precipitate phases is greater than 50%. In the present application, the ratio refers to the ratio of the number of the MC precipitate phases (i.e., the ratio of the number of the MC precipitate phases having a size smaller than 100 nm in the total number of all the MC precipitate phases).

[0045] In this application, the "bulk density" for Mg inclusions and MC precipitates is measured according to the method described in YB / T 5320-2006.

[0046] In this application, "size" with respect to Mg inclusions and MC precipitates refers to the size of a single Mg inclusion or MC precipitate, and specifically refers to the length of the longest line passing through the center of the inclusion or precipitate, such as the diameter (for spherical or approximately spherical material) or major axis (for elliptical or approximately elliptical material).

[0047] Preferably, in the steel plate for high temperature equipment according to the invention, the thickness of the steel plate is ≧5 mm.

[0048] Preferably, in the steel plate for high-temperature equipment according to the present invention, the steel plate has a temper embrittlement resistance T tr has.

[0049] Therefore, a further object of the present invention is to provide a manufacturing method for a steel plate for high-temperature equipment, which is simple, and the manufactured steel plate for high-temperature equipment has excellent temper embrittlement resistance, can be effectively applied in the energy and chemical industries as a manufacturing material for high-temperature reaction vessels, and has very important practical significance and very wide application prospects.

[0050] In order to achieve the above object, the present invention provides a manufacturing method for the above steel plate for high temperature equipment, the manufacturing method comprising the steps of: (1) smelting molten steel and continuously casting it to obtain a casting blank: during the smelting process, sequentially adding deoxidizing agents Mn, Al, Ti and Mg / Ni-Mg alloy into the molten steel, and carrying out deoxidation, which includes pre-deoxidation and final deoxidation, in which Mn, Al and Ti are first added sequentially for pre-deoxidation, the oxygen potential of the pre-deoxidized molten steel is 0.0015%-0.0085%, and then Mg / Ni-Mg alloy is added for final deoxidation; (2) rolling the cast blank to obtain a steel plate; and (3) A step of subjecting the steel plate to quenching and tempering heat treatment.

[0051] In the above technical solution of the present invention, a large amount of uniformly dispersed nano-scale Mg-containing inclusions need to be generated in the steel plate for high-temperature equipment according to the present invention, and these nano-scale Mg-containing inclusions can act as nucleation cores in the subsequent heat treatment process to induce a large amount of MC precipitate phases to precipitate in the steel, and these MC precipitate phases can absorb P in the steel, thereby reducing the phenomenon of significant segregation of P toward grain boundaries in the steel plate, and thereby improving the temper embrittlement resistance of the steel plate.

[0052] In order to form a large amount of Mg-containing inclusions with a dispersed distribution in the steel sheet of the present invention, it is necessary to control the oxygen potential of the molten steel during the deoxidation process, and to select suitable deoxidizing elements and deoxidize it in a specific addition order. Therefore, in the present invention, the process of smelting molten steel is optimized by first sequentially adding Mn, Al and Ti as deoxidizers during the smelting process for pre-deoxidation, so that the oxygen potential of the pre-deoxidized molten steel is 0.0015%-0.0085%, and then adding Mg / Ni-Mg alloy as deoxidizer for final deoxidation.

[0053] Preferably, the Ni-Mg alloy is a Ni-Mg alloy wrapped in an iron sheet.

[0054] In this application, the term "oxygen potential" refers to the oxygen content in mass %, measured according to the method for determining the oxygen content in liquid steel described in ISO 14284:1996.

[0055] It should be noted that in the above step (1) of the present invention, there are two main purposes of using the deoxidizer Mn first for pre-deoxidation: the first purpose is to reduce the concentration of free oxygen in the molten steel to create a good oxygen potential condition for the subsequent addition of deoxidizer; and the second purpose is that after deoxidation by Mn, low melting point inclusions are formed, which tend to aggregate, grow and float to the steel slag in the molten steel, and thus be removed. Generally, Al also easily combines with free oxygen in the molten steel to produce alumina inclusions. When the concentration of free oxygen in the molten steel is high, the size of the alumina inclusions formed is large, and due to the larger interfacial energy of the alumina inclusions, the adsorption ability between the alumina inclusions is strong, and these alumina inclusions easily aggregate into clusters, blocking the outlet of the casting water, or remain in the steel to form large inclusions, which leads to improper defect inspection of the steel plate. However, if the oxygen potential in the molten steel is low, when Al is added, the size of the alumina inclusions formed will be small, and the alumina inclusions will not easily aggregate, and part of Al will exist in the molten steel in the form of acid-soluble aluminum, which is favorable for controlling the phase change process of austenite. Secondly, the addition of Ti will further reduce the concentration of free oxygen in the steel, and the Ti2O3 inclusions formed after deoxidation will be favorable for the formation of part of the acicular ferrite structure during solidification and the subsequent phase change, thereby improving the toughness of the steel plate; furthermore, Ti can also combine with N in the steel to form part of TiN. On the one hand, the deleterious effect of solute nitrogen on the toughness of the steel is reduced, and on the other hand, TiN precipitates at high temperature during solidification, plays a role in pinning the growth of austenite, and refines the original austenite grains.

[0056] Therefore, in the above step (1) of the present invention, Mg needs to be used for final deoxidation, and in some embodiments, the final deoxidation can be performed by using Ni-Mg alloy instead of Mg. This is because: Mg is a very active element, the boiling point of Mg is lower than the melting point of Fe, and adding Mg alone to the molten steel will cause Mg to evaporate and oxidize immediately at the surface of the molten steel, i.e., it is difficult to add Mg into the molten steel. Using Ni-Mg alloy instead of adding Mg alone can reduce the activity of Mg, so that Mg has a longer time in the molten steel to react with the molten steel, and can reduce the loss caused by Mg evaporating into Mg vapor. Preferably, the addition mode of Ni-Mg alloy is controlled. In order to ensure that the Mg is finally distributed uniformly in the molten steel, the Ni-Mg alloy can be wrapped in an iron sheet (e.g., an iron sheet with a diameter of 5 mm) and added rapidly to the bottom of the ladle through a feeding device, so that the Ni-Mg alloy can be dissolved as much as possible at the bottom of the ladle, and the homogenization of Mg can be accelerated by stirring slightly with argon blowing, thereby improving the deoxidation effect of Mg.

[0057] Furthermore, it should be noted that in the present invention, the reason for controlling the oxygen potential of molten steel to be 0.0015%-0.0085% before final deoxidation with Mg is that when the oxygen potential in molten steel is lower than 0.0015%, the amount of Mg-containing inclusions formed after Mg is added to steel for deoxidation is small, so it is difficult to induce the precipitation of a large amount of MC carbides during the subsequent heat treatment, and the effect of MC to absorb P in steel is not significant; on the other hand, when the oxygen potential in molten steel is high and exceeds 0.0085%, the size of Mg-containing inclusions formed by the reaction between added Mg and free oxygen in steel is too large, and the ability of the inclusions to induce MC precipitation is reduced or disappeared, so it is difficult to use a large amount of MC precipitate phase to absorb P in steel.

[0058] Preferably, in the manufacturing method of the present invention, in step (2), the cast blank is heated to 1120-1230°C for rolling, the final rolling temperature is 930°C or higher, and the cumulative reduction is greater than 70%.

[0059] In step (2) of the manufacturing method according to the present invention, the reason for heating the cast blank to 1120-1230°C for rolling is that when the heating temperature of the cast blank is lower than 1120°C, the carbides and nitrides of Nb in the cast blank cannot be completely dissolved, thereby reducing the pinning effect of Nb on the austenite grains during rolling; on the other hand, when the heating temperature of the cast blank is higher than 1230°C, it is easy to cause the rapid growth of austenite grains and deteriorate the properties of the steel.

[0060] Therefore, when rolling the cast blank, in order to ensure the steel fully recrystallizes during rolling and ensure the continuous refinement of austenite, the final rolling temperature is preferably not less than 930°C, and the cumulative reduction of rolling is greater than 70%. By controlling the above process conditions, the formation of larger-sized austenite grains in the steel can be suppressed, and the low-temperature toughness of the steel is improved.

[0061] Preferably, in the manufacturing method according to the present invention, in step (3), the quenching temperature is 890-950°C, and the quenching hot storage time is T-2.5T minutes. After the hot storage is completed, the steel plate is discharged from the furnace and cooled to room temperature by water cooling, where T represents the thickness of the steel plate in mm.

[0062] It should be noted that during quenching, when the quenching temperature is lower than 890°C, it takes a long time to homogenize the austenite of the steel, which will reduce the efficiency of the heat treatment; if the quenching temperature of the steel is higher than 950°C, some of the austenite in the steel will tend to grow and form a mixed crystal structure, which is not conducive to the structural homogeneity of the steel. Correspondingly, when the heat storage time of the steel at the quenching temperature is less than T minutes, the steel tends not to be able to austenitize completely. On the other hand, when the heat storage time of the steel is more than 2.5T minutes, it will exceed the required austenitization time of the steel, which will reduce the efficiency of the quenching process.

[0063] Preferably, in the manufacturing method described in the present invention, in step (3), the tempering temperature is 695 to 745° C., and the tempering heat storage time is 2.0T to 3.5T minutes, where T represents the thickness of the steel plate in mm.

[0064] In the above technical solution, by further optimizing the range of tempering temperature and heat storage time in step (3) of the manufacturing method according to the present invention, a better implementation effect can be obtained. In the tempering process, when the tempering temperature of the steel is lower than 695°C, a long tempering time is required to remove the remaining quenching stress in the steel, which will reduce the tempering efficiency; on the other hand, when the tempering temperature of the steel is higher than 745°C, the precipitation phase in the steel will experience Ostwald coarsening and tend to aggregate and grow, which is not conducive to the formation of the MC precipitation phase finely distributed in the steel. Correspondingly, when the tempering heat storage time is less than 2.0T minutes, the quenching stress of the steel tends not to be completely removed, and when the tempering heat storage time is more than 3.5T minutes, the MC precipitation phase in the steel will easily coarsen and the production efficiency of the tempering process will be reduced.

[0065] Compared with the prior art, the steel plate for high temperature equipment and the manufacturing method therefor according to the present invention have the following advantages and beneficial effects: In the present invention, the steel plate for high-temperature equipment according to the present invention has greatly improved temper embrittlement resistance. In the present invention, the chemical composition of the steel is rationally designed, the production process of the steel plate is optimized, and the type of deoxidizer, the order of deoxidization and the amount of deoxidizer added in the steel smelting process are controlled, so that after the final deoxidization by using Mg, a large amount of nano-scale Mg-containing inclusions with dispersed distribution are generated in the steel, and these nano-scale inclusions can act as nucleation sites to induce significant precipitation of nano-scale MC precipitate phases in the steel during the operation process of the high-temperature equipment manufactured by the steel plate, while the nano-scale MC precipitate phases can act as P traps to absorb a large amount of P in the steel, thereby avoiding the significant segregation of P in the steel toward the austenite grain boundary when the steel plate operates at high temperature, and thus greatly increasing the temper embrittlement resistance of the steel plate.

[0066] Compared with the prior art, the present invention adopts a unique composition design technology and production process technology of high temperature equipment steel plate, and can produce a steel grade with excellent temper embrittlement resistance. The present invention is significantly different from the prior art in the structure, composition and process design of high temperature equipment steel plate.

[0067] The high-temperature equipment steel plate produced according to the present invention has excellent temper embrittlement resistance and can be effectively applied in the energy and chemical industries as a manufacturing material for high-temperature reaction vessels, and has very important practical significance and very wide application prospects.

[0068] Therefore, the manufacturing method of the steel plate for high-temperature equipment according to the present invention can be used to manufacture medium-temperature to high-temperature heating resistant steel plate to improve the high-temperature temper embrittlement resistance of the steel, and even when the content of P in the steel is high, it can ensure that the steel plate has very strong temper embrittlement resistance, and can ensure long-term stable operation of the equipment manufactured by using such steel plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Detailed Description In the following, the steel plate for high temperature equipment and its manufacturing method according to the present invention will be further described and illustrated by using specific examples. However, these descriptions and illustrations are not intended to unduly limit the technical solutions of the present invention.

[0070] Examples 1 to 7 and Comparative Examples 1 to 3 All of the high temperature equipment steel plates of Examples 1 to 7 were prepared by the following steps: (1) Smelting and continuous casting the chemical composition shown in Table 1 to prepare a casting blank: 400 kg of industrial pure iron is first added into the induction furnace to smelt molten steel in a 500 kg vacuum induction furnace, and appropriate amounts of Cr, Mo, V and Nb alloy and appropriate amounts of CaO are further added into the induction furnace according to the alloy composition ratio of the steel for the steel plate, CaO is added for slag formation during smelting; vacuum smelting is carried out at a minimum vacuum of about 20 Pa, and argon gas is filled for protection; during smelting, when the pure iron is completely melted, deoxidizer Mn, Al and Ti were added sequentially for pre-deoxidation, and the alloy adding amount was properly adjusted according to the online monitoring result of the molten steel composition, and the oxygen potential of free oxygen in the molten steel was controlled; the oxygen potential of the molten steel was controlled to be 0.0015%~0.0085%, and then the final deoxidation was carried out by adding Ni-Mg alloy wrapped with iron sheet through the feed port, and the molten steel was cast into ingots, and then cast into casting blanks continuously. (2) rolling the cast blank to obtain a steel plate, the cast blank is heated to 1120-1230°C for rolling, the final rolling temperature is above 930°C, and the cumulative reduction is greater than 70%. (3) performing quenching and tempering heat treatment on the steel plate: the steel plate is subjected to quenching treatment at a quenching temperature of 890-950°C and with a quenching heat storage time of T-2.5T minutes; after the heat storage is completed, the steel plate is discharged from the furnace and cooled to room temperature by water cooling; thereafter, the steel plate is subjected to tempering treatment at a tempering temperature of 695-745°C and with a tempering heat storage time of 2.0T-3.5T, and further subjected to air cooling after being discharged from the furnace, where T represents the thickness of the steel plate in mm.

[0071] In the present invention, the chemical composition designs and related processes of the steel plates for high-temperature equipment in Examples 1 to 7 all satisfy the design specification requirements of the present invention.

[0072] Therefore, the comparative steel plates of Comparative Examples 1-3 were produced using the same process steps as in Example 1, except that the Mg content in the comparative steel plates of Comparative Examples 1-3 was lower than the design range, and in the smelting and continuous speed casting operation of step (1) above, only the deoxidizing agents Mn, Al and Ti were added for deoxidation in Comparative Examples 1-3, but no Ni-Mg alloy was added for final deoxidation.

[0073] Table 1 lists the mass % of each chemical element in the steel plates for high-temperature equipment of Examples 1-7 and the comparative steel plates of Comparative Examples 1-3.

[0074] [Table 1]

[0075] Table 2 lists the specific process parameters for the steel plates for high temperature equipment of Examples 1-7 and the comparative steel plates of Comparative Examples 1-3 in the above process steps.

[0076] [Table 2]

[0077] The steel plates for high-temperature equipment obtained in Examples 1-7 and the comparative steel plates of Comparative Examples 1-3 are sampled separately, and the precipitated phases in the steel are extracted from the steel by electrolytic extraction, and the precipitated phases of different size ranges are separated by filter membranes of different particle sizes; the type and content of the precipitated phases in the steel are analyzed by XRD (X-ray diffraction) technology, and the chemical composition of the inclusions and precipitated phases is confirmed by combining transmission electron microscope and EDS (energy dispersive spectrometry) technology; the particle size distribution of the precipitated phases is detected by using a laser particle size analyzer, and the number, bulk density, type, size distribution range and average size of the MC precipitated phases (M represents one or more of Nb, V, Mo and Cr) in the steel plates of each Example and each Comparative Example can be finally confirmed by using image analysis software. The data obtained through the final observation and analysis are listed in Tables 3-1 and 3-2.

[0078] Table 3-1 lists the number of MC precipitates in the steel plates for high-temperature equipment of Examples 1 to 7 and the comparative steel plates of Comparative Examples 1 to 3 (according to the context, when the number of nano-scale MC precipitates is too small, the P absorption effect is not good). Table 3-2 lists the bulk density of Mg-containing inclusions having a size smaller than 800 nm, the proportion of MC precipitates having a size smaller than 100 nm in all MC precipitates, and the bulk density of MC precipitates having a size smaller than 500 nm in the steel plates for high-temperature equipment of Examples 1 to 7 and the comparative steel plates of Comparative Examples 1 to 3.

[0079] [Table 3-1]

[0080] [Table 3-2]

[0081] Therefore, after analyzing the microstructures of the steel plates for high-temperature equipment of Examples 1 to 7 and the comparative steel plates of Comparative Examples 1 to 3, the temper embrittlement resistance of the steel plates of Examples 1 to 7 and Comparative Examples 1 to 3 was further tested, and the temper embrittlement resistance of the steel plates of the Examples and Comparative Examples was evaluated.

[0082] In the present invention, the obtained steel plates for high-temperature equipment of Examples 1 to 7 and the comparative steel plates of Comparative Examples 1 to 3 were sampled separately, and specific temper embrittlement resistance evaluation was carried out according to a stepwise embrittlement cooling test.

[0083] When evaluating the temper embrittlement resistance of the steel plates of Examples 1 to 7 and Comparative Examples 1 to 3, the steel plates were first subjected to a simulated minimum postweld heat treatment and then to a stepwise embrittlement cooling test.

[0084] The specific steps of the simulated minimum post-weld heat treatment are as follows: Simulated minimum postweld heat treatment (Min. PWHT) process: When it was below 400°C, the sample blank was plunging into a furnace, heated to 705±14°C using a furnace (heating rate 125°C / h), cooled to 400°C using a furnace after 8 hours of heat storage (cooling rate 160°C / h), and then air-cooled outside the furnace.

[0085] The specific process steps of the embrittlement cooling test adopted in the present invention are as follows: At room temperature, the steel plate was fed into a heat treatment furnace; the furnace temperature was increased to 593°C at a heating rate of 200°C / h and kept at 693°C for 1 hour; the furnace temperature was then reduced to 538°C at a cooling rate of 5.6°C / h and kept at 693°C for 1 hour; the furnace temperature was then further reduced to 524°C at a cooling rate of 5.6°C / h and kept at 524°C for 24 hours; the furnace temperature was then reduced to 500°C at a cooling rate of 5.6°C / h and kept at 500°C for 60 hours; the furnace temperature was then reduced to 468°C at a cooling rate of 2.8°C / h and kept at 468°C for 100 hours; finally, the furnace temperature was reduced to 316°C at a cooling rate of 28°C / h; after being discharged from the furnace, the steel plate was air-cooled to room temperature in still air.

[0086] Transverse standard impact samples were taken from the steel plates that had undergone the simulated minimum postweld heat treatment and the steel plates that had undergone the simulated minimum postweld heat treatment and stepwise embrittlement cooling, respectively, and impact experiments were carried out at a series of temperatures, namely, 20° C., 0° C., -20° C., -40° C., -60° C., -80° C., -100° C. and -120° C. Three impact samples were made at each experimental temperature, and the average value was taken as the impact absorbed energy value at this temperature.

[0087] According to the above experimental results, the ductile-brittle transition temperature curves of the steel plate undergoing the simulated minimum postweld heat treatment and the steel plate undergoing the simulated minimum postweld heat treatment and the stepwise embrittlement cooling can be plotted respectively, and the high temperature temper embrittlement resistance of the steel plate can be calculated by the formula T tr =vTr 60 +3.0×△vTr 60 The T of the steel plate can be judged according to tr The smaller the value, the stronger the temper embrittlement resistance of the steel plate.

[0088] The above formula T tr =vTr 60 +3.0×△vTr 60 So, vTr 60 represents the corresponding transition temperature when the impact absorption energy of the steel plate that has undergone the simulated minimum post-weld heat treatment is 60 J, and △vTr 60 It should be noted that represents the value obtained by subtracting the corresponding transition temperature at an impact energy of 60 J for a steel plate that has undergone a simulated minimum postweld heat treatment from the corresponding transition temperature at an impact energy of 60 J for a steel plate that has undergone a simulated minimum postweld heat treatment and gradual embrittlement cooling.

[0089] Table 4 lists the test results of the steel plates for high-temperature equipment of Examples 1-7 and the comparative steel plates of Comparative Examples 1-3.

[0090] [Table 4]

[0091] With reference to Tables 3 and 4, both the steel plates for high-temperature equipment of Examples 1 to 7 and the comparative steel plates of Comparative Examples 1 to 3 contain MC precipitate phases, but in the steel plates for high-temperature equipment of Examples 1 to 7, the bulk density of Mg-containing inclusions having a size smaller than 800 nm is 7.6 × 10 6 / mm 3 ~15.5×10 6 / mm 3 The bulk density of the MC precipitates with a size smaller than 500 nm is 3.5 × 10 6 / mm 3 ~9.1×10 6 / mm 3 It can be seen that the average grain size of the MC precipitates is 102 nm to 178.4 nm, and the percentage of the MC precipitates with a size smaller than 100 nm in all the MC precipitates is 59.31% to 83.77%.

[0092] On the other hand, in the comparative steel sheets of Comparative Examples 1 to 3, the average diameter of the MC precipitates in the steel sheets was greater than 200 nm, and the bulk density of the MC precipitates having a size smaller than 500 nm was all 3.0 × 10 6 / mm 3 The proportion of MC precipitates with a size smaller than 100 nm in all MC precipitates was smaller than 50%, and the bulk density of Mg-containing inclusions with a size smaller than 800 nm was 6×10 6 / mm 3 This is because in Comparative Examples 1-3, only the deoxidizing agents Mn, Al and Ti are added for deoxidation, but no Ni-Mg alloy is added for final deoxidation, resulting in the lack of sufficient Mg-containing oxides in the steels that can induce the nucleation of the MC precipitate phases.

[0093] As shown in Table 4, in the steel plates for high-temperature equipment of Examples 1 to 7 of the present invention, the high-temperature temper embrittlement index T tr are all below -65°C, significantly lower than those in the comparative examples. Therefore, it can be seen that the temper embrittlement resistance of the high-temperature equipment steel plates of Examples 1 to 7 is significantly superior to that of the comparative steel plates of Comparative Examples 1 to 3.

[0094] In short, it can be seen that the steel plate for high-temperature equipment according to the present invention has greatly improved temper embrittlement resistance. In the present invention, the chemical composition of the steel is rationally designed, the production process of the steel plate is optimized, and the type of deoxidizer, the order of deoxidization and the amount of deoxidizer added in the steel smelting process are controlled, so that after the final deoxidization by using Mg / Ni-Mg alloy, a large amount of nano-scale Mg-containing inclusions with dispersed distribution are generated in the steel, and these nano-scale inclusions can act as nucleation sites to induce significant precipitation of nano-scale MC precipitate phases in the steel during the operation process of the high-temperature equipment manufactured by the steel plate, while the nano-scale MC precipitate phases can act as P traps to absorb a large amount of P in the steel, thereby avoiding significant segregation of P in the steel toward the austenite grain boundary when the steel plate operates at high temperature, and thus greatly increasing the temper embrittlement resistance of the steel plate.

[0095] Furthermore, it should be noted that the combination of the technical solutions in the present invention is not limited to those described in the claims attached hereto or to the specific examples. All the technical features in the present invention can be freely combined or grouped together in any manner as long as there is no contradiction between them.

[0096] It should also be noted that the above-mentioned examples are merely specific examples of the present invention. It is obvious that the present invention is not limited to the above examples, and all similar variations or modifications that are obvious or easily conceivable to those skilled in the art from the disclosure of the present invention belong to the scope of the present invention.

Claims

1. A steel plate for high temperature equipment, the steel plate for high temperature equipment having the following chemical elements, the chemical elements being in mass %: 0.09% to 0.19% C, 0.2% to 0.7% Mn, 0.008% to 0.02% Ti, 1.80% to 3.2% Cr, 0.80% to 1.70% Mo, 0.005% to 0.015% acid-soluble Al, 0.020% to 0.050% Nb, 0.15% to 0.50% V, 0.0005% to 0.0050% Mg, and the balance being Fe and unavoidable impurities; Among the unavoidable impurities, P≦0.016%, S≦0.010%, N≦0.004%, and O≦0.005%; The steel plate for high-temperature equipment has nano-scale Mg-containing inclusions dispersed in the steel plate, the density of Mg-containing inclusions, the length of the longest line segment passing through the center of which is less than 800 nm in the steel plate, is greater than 6×10 6 pieces per mm 3 ; The steel plate for high-temperature equipment.

2. 2. The steel plate for high temperature equipment according to claim 1, wherein the steel plate further comprises at least one of the following chemical elements: 0<Ca≦0.0050%, 0<Ni≦0.6%, 0<B≦0.0015%, and 0<Cu≦0.5%.

3. 2. The steel plate for high temperature equipment according to claim 1, further comprising nano-scale MC precipitate phases, M representing one or more of Nb, V, Mo and Cr, and the MC precipitate phases having an average grain size smaller than 200 nm.

4. The density of MC precipitates in which the length of the longest line segment passing through the center of the steel sheet is less than 500 nm is 3.0×10 per mm ６ The steel plate for high-temperature equipment according to claim 3, wherein the steel plate has a diameter of more than 1 / 100 mm.

5. The steel plate for high-temperature equipment according to claim 3, wherein the ratio of MC precipitates having a length of the longest line segment passing through the center of less than 100 nm to all MC precipitates in the steel plate is greater than 50%.

6. 2. The steel plate for high temperature equipment according to claim 1, wherein the steel plate has a thickness that is ≧5 mm.

7. The temper embrittlement resistance T of the steel sheet is ≦-60°C. ｔｒ The steel plate for high-temperature equipment according to claim 1 , having

8. 2. A manufacturing method for a steel plate for high temperature equipment according to claim 1, the manufacturing method comprising the steps of: (1) smelting molten steel and continuously casting it to obtain a casting blank: during smelting, sequentially adding deoxidizing agents Mn, Al, Ti and Mg / Ni-Mg alloy into the molten steel, and carrying out deoxidation on the molten steel, the deoxidation including pre-deoxidation and final deoxidation, where Mn, Al and Ti are added sequentially for pre-deoxidation first, and then the Mg / Ni-Mg alloy is added for final deoxidation, and the oxygen potential of the pre-deoxidized molten steel is 0.0015%-0.0085%; (2) rolling the cast blank to obtain a steel plate; and (3) performing quenching and tempering heat treatment on the steel plate; The manufacturing method.

9. The manufacturing method according to claim 8, wherein in step (2), the cast blank is heated to 1120-1230°C for rolling, the final rolling temperature is 930°C or higher, and the cumulative reduction is greater than 70%.

10. The manufacturing method according to claim 8, wherein in step (3), the quenching temperature is 890-950°C, the quenching hot storage time is T-2.5T minutes, and after the hot storage is completed, the steel plate is discharged from the furnace and cooled to room temperature by water cooling, where T represents the thickness of the steel plate in mm.

11. The manufacturing method according to claim 8 or 10, wherein in step (3), the quenched steel plate is tempered at a tempering temperature of 695 to 745 ° C. for a tempering heat storage time of 2.0T to 3.5T minutes, where T represents a thickness of the steel plate in mm.

12. The method according to any one of claims 8 to 10, wherein the Ni-Mg alloy is a Ni-Mg alloy wrapped in an iron sheet.

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