CN114277302B - Control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusion - Google Patents
Control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusion Download PDFInfo
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Abstract
The invention discloses a control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusions, and belongs to the field of vacuum melting. The smelting method of the invention is a vacuum induction and vacuum consumable remelting duplex process. The vacuum induction smelting controls A-type sulfide inclusions by a method of selecting low-sulfur raw materials; limiting the content of Al in the deoxidizer to avoid the inclusion of B-type alumina; the vacuum induction smelting adopts the range of 1500-1550 ℃ for refining carbon deoxidation, and the oxygen content control target is less than 0.0020 percent, so as to be beneficial to reducing the content of oxide inclusions; controlling the N, Ti content in the alloy composition to the minimum required by the composition by vacuum induction; and the vacuum self-consumption adopts a molten drop control mode to promote the good removal of nitride inclusions. The process can lead the A, B, C, D-class impurity coarse/fine system of the vacuum induction and vacuum self-consumption austenitic stainless steel containing titanium and nitrogen to be close to 0 grade, and the TiN class to be less than or equal to 1.5 grade, thereby obtaining high-quality purified alloy.
Description
Technical Field
The invention relates to the technical field of vacuum melting, in particular to a control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusions.
Background
The titanium-containing nitrogen-controlling austenitic stainless steel has the comprehensive advantages of high-temperature mechanical property (400-700 ℃), good corrosion resistance, excellent welding performance and the like, particularly has rich application data and mature application experience, and is widely applied to nuclear power, thermal power, aviation, aerospace and other key parts. However, inclusions in titanium-containing nitrogen-controlled austenitic stainless steel are short plates which limit the service performance of the titanium-containing nitrogen-controlled austenitic stainless steel. This is mainly because the non-metallic inclusions destroy the continuity of the alloy matrix, reducing the mechanical properties, fatigue properties and corrosion resistance of the alloy, and deteriorating the quality of the steel.
The inclusions in the titanium-containing nitrogen-controlling austenitic stainless steel are mainly sulfide, oxide and nitride inclusions. Oxide inclusions are mainly formed by adding Al, Si, Ca and the like in the deoxidation process, and the O element can promote solidification segregation, reduce the plasticity of the material, deteriorate the performances of fatigue, corrosion resistance and the like, so the oxide inclusions are removed as much as possible in the smelting process so as to avoid the generation of the oxide inclusions. The nitride inclusions are mainly inevitable nitride inclusions formed with N elements in molten steel when stabilizing elements such as Ti, Nb and the like are alloyed, especially cluster-shaped nitride inclusions are formed, and the high-temperature endurance performance and the fatigue performance of the material are seriously damaged. However, the mechanism of influence of the N content on the alloy performance is complex, and N has a certain beneficial effect on the mechanical property and the corrosion resistance of the alloy, so that the N content cannot be reduced at one step. Therefore, the relationship between the mechanical properties, the corrosion resistance and the formation of nitride inclusions needs to be balanced in the control of the N content. Therefore, a vacuum melting method for removing S, O elements and controlling an N element alloying process so as to control inclusions of sulfide, oxide and nitride is important for preparing high-quality and pure high-performance titanium-containing nitrogen-controlled austenitic stainless steel.
Disclosure of Invention
Aiming at the problems that the inclusions of sulfide, oxide and nitride in the existing preparation engineering titanium-containing nitrogen-controlling austenitic stainless steel exceed the standard and are difficult to control, the invention aims to provide a control method of non-metallic inclusions in the titanium-containing nitrogen-controlling austenitic stainless steel.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a control method of non-metallic inclusion of titanium-containing nitrogen-controlling austenitic stainless steel realizes the control of the non-metallic inclusion in the process of smelting the titanium-containing nitrogen-controlling austenitic stainless steel by using a vacuum induction furnace and vacuum consumable consumption, and specifically comprises the following steps:
(1) selecting raw materials: preparing raw materials according to chemical components of the titanium-containing nitrogen-controlling austenitic stainless steel, and selecting the low-S raw material to ensure that the S content of the raw material is less than 0.0015 wt%, so as to control A-type sulfide inclusions;
(2) vacuum induction melting: melting alloy raw materials, heating to 1500-;
(3) vacuum consumable melting: and a molten drop control mode is adopted to promote good removal of nitride inclusions.
The titanium-containing nitrogen-controlling austenitic stainless steel comprises the following chemical components in percentage by weight:
c: 0.03-0.10%; cr: 14.50 to 18.00 percent; ni: 14.50-18.00%; si: 0.30-1.00%; mn is less than 2.00 percent; mo: 1.00-2.00%; ti: 0.30-0.80%; n is less than 0.02 percent; s is less than 0.005 percent; o is less than 0.005 percent; p is less than 0.015 percent; co is less than 0.03 percent; cu is less than 0.05 percent; ca is less than 0.01 percent; b is less than 0.005 percent; the balance of Fe.
When the raw material in the step (1) is selected, controlling the N, Ti content in the raw material to make the N, Ti content slightly larger than the lower limit in the chemical composition range so as to reduce the formation amount of nitride inclusions; specifically, the N content in the raw materials is controlled to be 0.004-0.006wt.%, and the Ti content is controlled to be 0.35-0.40 wt.%.
In the step (2), Si-Ca deoxidizer is added in the later stage of refining, and the addition amount of the Si-Ca deoxidizer accounts for 0.02-0.04 wt% of the total weight of the raw materials. The Si-Ca deoxidizer does not contain Al element, or the content of the Al element in the Si-Ca deoxidizer is less than 0.05 wt% of the total weight of the raw materials.
In the step (3), the vacuum self-consumption adopts a molten drop control mode, and the good removal of impurities in the smelting process is realized through the control of the stability degree of the smelting process.
The control method of the invention can lead the coarse/fine systems of A, B, C and D-type inclusions in the titanium-containing nitrogen-controlled austenitic stainless steel to be close to 0 grade, and TiN types to be less than or equal to 1.5 grade, thereby obtaining high-quality purified alloy.
The design mechanism of the invention is as follows:
the vacuum induction smelting basically has no desulfurization capability, and the method of limiting the total sulfur carrying amount of raw materials can be adopted to solve the problem in order to control the sulfide content. For the reduction of oxide inclusions, firstly the total oxygen content is reduced and secondly the oxide morphology is improved. Carbon deoxidation is the best way to reduce oxides and the deoxidation product does not remain in the steel. During the carbon deoxidation, the problem of oxygenation of molten steel caused by violent decomposition of the oxide crucible needs to be avoided, so that a lower reaction temperature needs to be adopted. The formation of large alumina lumps can also be avoided by limiting the amount of the aluminum-containing deoxidizer used. The content of nitrogen and titanium is reduced, so that a large amount of nitride can be avoided, and the N, Ti content is controlled on the basis of meeting the alloy composition, so that the formation of nitride inclusions is reduced. The selection of a proper control mode in the vacuum consumable process can stabilize the smelting process and is beneficial to the good removal of inclusions during crystallization, and a molten drop control mode is adopted according to the characteristics of the alloy to achieve the removal purpose.
Through the improvement of smelting process parameters, the finally smelted large-specification titanium-containing nitrogen-controlling austenitic stainless steel has lower grades of sulfide, oxide and nitride inclusions, eliminates the nitride inclusions distributed in clusters on the basis of meeting the addition of N, Ti elements, and effectively improves the structure and performance of subsequent deformed products.
The invention has the following advantages and beneficial effects:
(1) the control method can improve the purity of the alloy material, can obviously control the level of the inclusions, and can reach the level that A, B, C, D type inclusions are zero-grade inclusions.
(2) The invention can control the TiN inclusions to be less than or equal to 1.5 grade by reasonably controlling N, Ti elements and combining process selection, thereby improving the high-temperature lasting mechanical property and the corrosion resistance of the material.
(3) The present invention limits the Al content in the Si — Ca deoxidizer used to be less than 0.05wt.% of the total amount of the raw materials so as to avoid the formation of B-type alumina inclusions.
Drawings
FIG. 1 shows the appearance of inclusions in different positions of an austenitic stainless steel ingot in example 1.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It should be understood that these small embodiments are merely illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1:
the embodiment is a control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusion, and the used equipment and parameters are as follows: a vacuum induction melting furnace and a 3T vacuum consumable electrode furnace.
(1) Raw materials:
preparing raw materials according to the following element proportions:
c: 0.03-0.10%; cr: 14.50-18.00%; ni: 14.50-18.00%; si: 0.30-1.00%; mn is less than 2.00 percent; mo: 1.00-2.00%; ti:0.35 to 0.40 percent; n: 0.004-0.006%; s is less than 0.005 percent; o is less than 0.005 percent; p is less than 0.015 percent; co is less than 0.03 percent; cu is less than 0.05 percent; ca is less than 0.01 percent; b is less than 0.005 percent; the balance of Fe.
Selecting low-S pure iron and other low-sulfur raw materials to ensure that the content of S in the raw materials is less than 0.0015wt.%, controlling N to be 0.004-0.006wt.% and Ti to be 0.35-0.40 wt.%;
(2) the refining temperature is 1520 ℃ during vacuum induction melting, and the refining time is 0.8 hour;
(3) and Si-Ca deoxidizer without Al is added in the later stage of refining, and the addition amount of the deoxidizer is 0.035% of the total weight of the raw materials.
(4) And molten drop control is adopted during self consumption.
After the thermal deformation of the prepared consumable ingot, the head and the tail of the consumable ingot are sampled for chemical analysis (table 1) and structure observation (table 2), and the fact that the O, S content is less than 0.0015 percent and the N, Ti content is controlled can be seen, the coarse/fine system of A, B, C, D type inclusions is close to 0 grade, the TiN type inclusions is less than or equal to 1.5 grade, and high-quality purified alloy is obtained.
Table 1 example alloy key control ingredients (wt.%) of the examples
TABLE 2 evaluation results of inclusions in austenitic stainless steel ingots of examples
Claims (3)
1. A control method of non-metallic inclusion of titanium-containing nitrogen-controlling austenitic stainless steel is characterized in that: the method realizes the control of non-metallic inclusions in the process of smelting the titanium-containing nitrogen-controlled austenitic stainless steel by using a vacuum induction furnace and vacuum consumable, and specifically comprises the following steps:
(1) selecting raw materials: preparing raw materials according to chemical components of the titanium-containing nitrogen-controlling austenitic stainless steel, and selecting the low-S raw material to ensure that the S content of the raw material is less than 0.0015 wt%, so as to control A-type sulfide inclusions; controlling the N content in the raw material to be 0.004-0.006wt.% and the Ti content to be 0.35-0.40 wt.%;
(2) vacuum induction melting: melting alloy raw materials, heating to 1500-; wherein, Si-Ca deoxidizer is added in the later period of refining, and the addition amount of the Si-Ca deoxidizer accounts for 0.02 to 0.04wt.% of the total weight of the raw materials; the Si-Ca deoxidizer does not contain Al element, or the content of the Al element in the Si-Ca deoxidizer is less than 0.05 wt.%;
(3) vacuum consumable melting: and a molten drop control mode is adopted to promote good removal of nitride inclusions.
2. The method for controlling the non-metallic inclusions in the austenitic stainless steel containing titanium and controlling nitrogen according to claim 1, wherein: the titanium-containing nitrogen-controlling austenitic stainless steel comprises the following chemical components in percentage by weight:
c: 0.03-0.10%; cr: 14.50-18.00%; ni: 14.50-18.00%; si: 0.30-1.00%; mn is less than 2.00 percent; mo: 1.00-2.00%; ti: 0.30-0.80%; n is less than 0.02 percent; s is less than 0.005 percent; o is less than 0.005 percent; p is less than 0.015 percent; co is less than 0.03 percent; cu is less than 0.05 percent; ca is less than 0.01 percent; b is less than 0.005 percent; the balance of Fe.
3. The method for controlling the non-metallic inclusions in the austenitic stainless steel containing titanium and controlling nitrogen according to claim 1, wherein: in the step (3), the vacuum self-consumption adopts a molten drop control mode, and the good removal of impurities in the smelting process is realized through the control of the stability degree of the smelting process.
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