A deoxidation process of electroslag remelting heat-resistant steel containing B type 9Cr in non-protective atmosphere

Abstract

The present invention provides a deoxidation process for B-type 9Cr heat-resistant steel by electroslag remelting in a non-protective atmosphere, and belongs to the technical field of electroslag remelting slag. A deoxidation process for B-type 9Cr heat-resistant steel by electroslag remelting in a non-protective atmosphere, including arcing, slagging, and smelting steps, characterized in that: before the electrode arcs, the deoxidizer is wrapped with a smooth iron sheet and spot welded on the electrode surface; wherein the deoxidizer is composed of the following components in a weight ratio, Si-Fe 60-90 parts, carbon particles 10-40 parts, wherein w(C) in the carbon particles is ≥96%. The present invention adopts a deoxidation process for B-type 9Cr heat-resistant steel by electroslag remelting in a non-protective atmosphere, and the content of easily oxidizable elements in the axial direction of the obtained product is stable, meets the requirements of the composition range, and is easy to realize the domestic substitution production of B-type 9Cr heat-resistant steel.

Description

Technical Field

[0001] The invention relates to a deoxidation process for electroslag remelting of B-type 9Cr heat-resistant steel in a non-protective atmosphere, and belongs to the technical field of electroslag remelting slag. Background Art

[0002] 9Cr martensitic heat-resistant steel has excellent high-temperature durability and good resistance to high-temperature oxidation corrosion. It is widely used as steel for high-temperature pressure-bearing parts of ultra-supercritical steam turbine units and heavy-duty gas turbines. 9Cr steel is based on Cr-Mo steel, with V, Nb, and N added to precipitate MX, adjust C / N, and precipitate M 23 (C, N) 6 In order to improve the service life of 9Cr heat-resistant steel, a trace amount of B is added to 9Cr heat-resistant steel to replace M 23 (C, N) 6 The middle part C forms M 23 (C, N, B) 6 , which stabilizes the carbides at the grain boundaries, inhibits the growth and coarsening of carbides, and improves the high-temperature creep performance and service life of 9Cr steel. In order to improve the high-temperature creep performance of 9Cr steel, the content of deoxidizing elements such as Si, Al and Mn in the material is controlled in a relatively low range, generally requiring w(Si)≤0.1%, w(Al)≤0.01%, and w(Mn)≤0.5%. However, B in steel easily forms BN hard and brittle inclusions with N, which is detrimental to the performance of steel. In order to give full play to the role of B in steel and avoid BN precipitation, w(B) in 9Cr steel is generally ≤0.01%, and the upper and lower limits are controlled in a narrow range, generally with a difference of about 0.003%.

[0003] In order to improve the metallurgical quality of 9Cr heat-resistant steel, electroslag remelting is widely used at home and abroad. In view of the low control of deoxidizing elements in B-type 9Cr heat-resistant steel and the narrow control range of the easily oxidized element B, in order to smelt qualified B-type 9Cr heat-resistant steel, most countries use protective atmosphere electroslag remelting to prepare this material. However, the investment in protective atmosphere electroslag furnaces is huge, and most domestic electroslag furnaces are non-protective or simple protective atmosphere electroslag furnaces. In order to realize the localization and substitution production of B-type 9Cr heat-resistant steel, it is urgently needed to develop a new smelting process under the current equipment conditions to prepare B-type 9Cr heat-resistant steel electroslag ingots with qualified metallurgical quality.

[0004] At present, the main problems in the preparation of B-type 9Cr heat-resistant steel by non-protective atmosphere electroslag remelting are high-temperature oxidation on the electrode surface. As the electrode melts, the oxygen potential of the slag pool increases, resulting in the burning of the easily oxidized element B when the metal droplets pass through the slag pool, and excessive O content in the axial direction of the electroslag ingot. Research on the problems of B burning and O exceeding the standard has important social and economic benefits. Summary of the invention

[0005] The technical problem solved by the invention is to provide a deoxidation process of electroslag remelting heat-resistant steel containing B type 9Cr in a non-protective atmosphere.

[0006] A non-protective atmosphere electroslag remelting deoxidation process for B-type 9Cr heat-resistant steel, comprising arcing, slag melting and smelting steps, characterized in that: before the electrode arcs, a deoxidizer is wrapped with a smooth iron sheet and spot welded to the electrode surface; wherein the deoxidizer is composed of the following components in weight ratio: 60-90 parts of Si-Fe and 10-40 parts of carbon particles, wherein w(C) in the carbon particles is ≥96%.

[0007] Wherein, the Si content in Si-Fe in the deoxidizer is 72wt%.

[0008] After the iron sheet is wrapped, the thickness of the deoxidizer layer is 1 to 2 cm, and the deoxidizer adding rate is adjusted by controlling the thickness of the deoxidizer layer.

[0009] During the electroslag remelting process, the electrode melting rate is 0.85 to 0.95 times the electrode diameter, wherein the electrode melting rate is expressed in kg.h-1 and the electrode diameter is expressed in mm.

[0010] The deoxidizer addition rate is 0.35 to 0.45 times of the electrode melting rate, wherein the deoxidizer addition rate is expressed in g / min and the electrode melting rate is expressed in kg / min.

[0011] The deoxidizer in the lower part of 10-15% of the electrode length is added at a speed of 0.45 times the stable melting rate, and the deoxidizer in the remaining part is added at a speed of 0.43 times the stable melting rate of the electrode.

[0012] The composition of the B-type 9Cr heat-resistant steel is as follows: w(B): 0.008% to 0.011%, w(Al): ≤0.007%, w(Si): ≤0.1%, w(Mn): 0.2% to 0.5%, w(O): ≤0.003%, and the remainder is iron and unavoidable impurities.

[0013] Among them, in order to ensure uniform distribution of elements in the axial direction of the electroslag ingot, the deoxidizer should be added continuously.

[0014] Among them, the diameter of the iron sheet wrapping should be adapted to the melting speed of the electrode. At the same time, the diameter of the iron sheet wrapping can also be adjusted by adjusting the proportion of effective deoxidation components to achieve easy operation and welding during the iron sheet wrapping, with less impact on the smooth operation and safety during the smelting process.

[0015] The deoxidizer is added in the whole process of electroslag remelting; in the arc starting stage, in order to ensure the subsequent deoxidation, the amount of effective deoxidizing components added in the early stage is added according to the upper limit, accounting for about 10% to 15% of the electrode length.

[0016] Furthermore, in the deoxidation process of the non-protective atmosphere electroslag remelting heat-resistant steel containing B-type 9Cr of the present invention, on the one hand, the deoxidizer needs to react with the FeO brought in by the electrode melting to reduce the oxygen potential of the slag and avoid the oxidation and burning of easily oxidized elements during the process of the electrode molten droplets passing through the slag pool; on the other hand, it is also necessary to avoid the deoxidizer from entering the metal molten pool, causing the types and contents of alloy elements in the electroslag ingot to change significantly and exceed the target range.

[0017] The requirements for Al, Si and O content in B-type 9Cr steel are relatively strict, among which w(Si)≤0.1% and the range is relatively wide, so Si deoxidation can be used to reduce the oxygen potential of the slag. In order to ensure the quality of spot welding, the diameter of the iron sheet wrapping cannot be too thin, so Si-Fe deoxidation is used. At the same time, in order to further adjust the diameter of the iron sheet wrapping, carbon powder can be used as a skeleton. After entering the slag pool, the carbon powder is on the surface of the slag pool and in the atmosphere. 2 reaction, forming an oxygen-deficient layer, which can reduce the O 2 The molten pool is infiltrated through the slag pool, so it is necessary to add 10% to 40% carbon particles to the deoxidizer.

[0018] During the electroslag remelting process, the shape of the molten pool is directly related to the electrode melting rate. Generally, the higher the electrode melting rate, the deeper the molten pool is, and the lower the melting rate, the shallower the metal molten pool is. During the electroslag remelting process, the depth and shape of the molten pool are directly related to the solidification quality of the electroslag ingot. In order to improve the solidification quality of the electroslag ingot, a shallow and flat metal molten pool is necessary. Electrode melting rate (unit: kg.h -1 ) is 0.85 to 0.95 times of the electrode diameter (unit: mm), the metal molten pool can be shallow and flat, and the electrode melts faster, taking into account the metallurgical quality and production efficiency of the electroslag ingot.

[0019] During the electroslag remelting process, the increase in oxygen potential in the slag is mainly due to the high-temperature oxidation of the electrode surface under non-protective atmosphere. Therefore, the rate of adding effective deoxidizer is related to the electrode melting rate. According to the oxidation law of 9Cr steel, it is known that it is completely neutralized with FeO brought in by electrode melting. When the effective deoxidizing component addition amount (g / min) is 0.35 to 0.45 times the electrode melting rate (kg / min), it can completely neutralize FeO brought in by electrode melting, reduce the oxygen potential of the slag pool, and avoid high-temperature oxidation and burning of easily oxidized elements.

[0020] The deoxidation process of the non-protective atmosphere electroslag remelting heat-resistant steel containing type B 9Cr provided by the present invention can achieve the stability of the content of easily oxidized elements in the axial direction of the electroslag ingot containing type B 9Cr heat-resistant steel in the non-protective atmosphere electroslag remelting, meet the requirements of the composition range, obtain the type B 9Cr heat-resistant steel containing type B with qualified metallurgical quality, and realize the domestic substitution production of the type B 9Cr heat-resistant steel under the existing equipment conditions. DETAILED DESCRIPTION

[0021] The embodiments of the present invention are described in detail below in conjunction with specific examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out under normal conditions.

[0022] Example 1

[0023] The electroslag of this embodiment has the following composition: w(B): 0.0092%, w(Al): ≤0.004%, w(Si): 0.05%, w(Mn): 0.35%, w(O): 0.0022%.

[0024] The deoxidizer for electroslag remelting B-type 9Cr heat-resistant steel in a non-protective atmosphere is composed of the following components in weight ratio: Si-Fe is 80% and the rest is carbon particles.

[0025] During the electroslag remelting of B-type 9Cr heat-resistant steel in a non-protective atmosphere, the electrode diameter is 75 mm and the electrode melting rate is 1.1 kg.min -1 , the deoxidizer addition rate is 0.60g / min.

[0026] The specific process of electroslag remelting of B-type 9Cr heat-resistant steel in non-protective atmosphere is as follows:

[0027] (1) According to the stable smelting stage, the deoxidizer is added at a rate, the deoxidizer is wrapped with iron sheet and spot welded on the electrode surface. The thickness of the deoxidizer layer is 1.2 cm, of which the Si-Fe effective deoxidizing component accounts for 0.8.

[0028] (2) To ensure that the alloying element content at the bottom of the electroslag ingot is qualified, the amount of deoxidizer added to the lower part of the electrode is 0.45 times the stable melting rate (about 15% of the electrode length), and the amount of deoxidizer added to the remaining part is 0.43 times the stable melting rate of the electrode.

[0029] (3) The electrode arc is started by iron cutting. After arc starting, the slag melting time is about 5 minutes;

[0030] (4) After slag melting, the stable smelting stage begins, and the electrical parameters are adjusted to ensure that the electrode melting rate is 0.88 times the electrode diameter, so as to achieve a balance between the quality of the electroslag ingot and the smelting efficiency.

[0031] (5) According to the above operation flow, the operation without adding deoxidizer and with adding deoxidizer were carried out respectively. After the smelting was completed, the element analysis was carried out in the axial direction of the electroslag ingot. The results are shown in Table 1.

[0032] Table 1

[0033]

[0034]

[0035] It can be seen that in the process of electroslag remelting of B-type 9Cr heat-resistant steel in non-protective atmosphere, the above deoxidation process can be used to control the content of easily oxidizable alloy elements and O in the axial direction of the ingot, and obtain qualified ingots with metallurgical quality that meets the requirements.

[0036] This specific embodiment is only an explanation of the present invention, not a limitation of the present invention. After reading the specification of the present invention, those skilled in the art may make some modifications or improvements on the basis of the present invention. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A non-protective atmosphere electroslag remelting deoxidation process containing B-type 9Cr heat-resistant steel, including arc starting, slag melting, and smelting steps, characterized in that: Before the electrode starts arcing, the deoxidizer is wrapped with a smooth iron sheet and spot welded on the electrode surface; wherein the deoxidizer is composed of the following components in weight ratio: 60-90 parts of Si-Fe and 10-40 parts of carbon particles, wherein w(C) in the carbon particles is ≥96%; The deoxidizer addition rate is 0.35 to 0.45 times the electrode melting rate, wherein the deoxidizer addition rate unit is g / min, and the electrode melting rate unit is kg / min.

2. The deoxidation process of non-protective atmosphere electroslag remelting heat-resistant steel containing B type 9Cr according to claim 1, characterized in that: The Si content in the Si-Fe in the deoxidizer is 72 wt %.

3. The deoxidation process of non-protective atmosphere electroslag remelting heat-resistant steel containing B type 9Cr according to claim 1, characterized in that: After the iron sheet is wrapped, the thickness of the deoxidizer layer is 1 to 2 cm, and the deoxidizer adding rate is adjusted by controlling the thickness of the deoxidizer layer.

4. The deoxidation process of non-protective atmosphere electroslag remelting heat-resistant steel containing B type 9Cr according to claim 3, characterized in that: During electroslag remelting, the electrode melting rate is 0.85 to 0.95 times the electrode diameter, where the electrode melting rate is expressed in kg.h -1 , the unit of electrode diameter is mm.

5. The deoxidation process of non-protective atmosphere electroslag remelting heat-resistant steel containing B type 9Cr according to claim 1, characterized in that: The deoxidizer addition rate of the lower part of 10-15% of the electrode length is 0.45 times of the stable melting rate, and the deoxidizer addition rate of the remaining part is 0.43 times of the stable melting rate of the electrode.

6. The deoxidation process of non-protective atmosphere electroslag remelting heat-resistant steel containing B type 9Cr according to claim 1, characterized in that The components of the B-type 9Cr heat-resistant steel are as follows: w(B): 0.008% to 0.011%, w(Al): ≤0.007%, w(Si): ≤0.1%, w(Mn): 0.2% to 0.5%, and w(O): ≤0.003%.

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