CN114277302B - A method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel - Google Patents

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

A method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel

technical field

The invention relates to the technical field of vacuum smelting, in particular to a method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel.

Background technique

Titanium-containing nitrogen-controlled austenitic stainless steel has comprehensive advantages such as high high-temperature mechanical properties (400-700 ° C), good corrosion resistance, and excellent welding performance, especially with rich application data and relatively mature application experience. It has been widely used in nuclear power, thermal power, aviation, aerospace and other key components. However, the inclusions in the titanium-containing nitrogen-controlled austenitic stainless steel are the shortcomings that restrict its service performance. This is mainly because non-metallic inclusions destroy the continuity of the alloy matrix, reduce the mechanical properties, fatigue properties and corrosion resistance of the alloy, and deteriorate the quality of the steel.

The inclusions in the titanium-containing nitrogen-controlled austenitic stainless steel are mainly sulfide, oxide and nitride inclusions. Oxide inclusions are mainly formed due to the addition of Al, Si, Ca, etc. during the deoxidation process, and O element can promote solidification segregation, reduce material plasticity, deteriorate fatigue and corrosion resistance and other properties, so it should be removed in the smelting process to avoid oxidation. generation of inclusions. Nitride inclusions are mainly formed when Ti, Nb and other stabilizing elements are alloyed, and it is inevitable to form nitride inclusions with N elements in molten steel, especially the formation of clustered nitride inclusions, which seriously damages the high temperature durability of the material. Fatigue performance. However, the influence mechanism of N content on the properties of the alloy is complex, and N has a certain beneficial effect on the mechanical properties and corrosion resistance of the alloy, and the N content cannot be reduced blindly. Therefore, it is necessary to balance the relationship between mechanical properties, corrosion resistance and formation of nitride inclusions in the control of N content. Therefore, a vacuum smelting method for removing S and O elements, controlling the alloying process of N elements, and thus controlling the inclusion of sulfides, oxides and nitrides is required for the preparation of high-quality, pure high-performance titanium-containing nitrogen-controlled austenitic stainless steels to important.

SUMMARY OF THE INVENTION

Aiming at the problems that the inclusions of sulfides, oxides and nitrides in the existing preparation of engineered titanium-containing nitrogen-controlled austenitic stainless steel exceed the standard and are difficult to control, the purpose of the present invention is to provide a non-metallic titanium-containing nitrogen-controlled austenitic stainless steel Inclusion control methods.

In order to achieve the above object, technical scheme of the present invention is as follows:

A method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel, the method is to realize the control of non-metallic inclusions in the process of smelting titanium-containing nitrogen-controlled austenitic stainless steel by using a vacuum induction furnace and vacuum self-consumption , including the following steps:

(1) Raw material selection: prepare raw materials according to the chemical composition of titanium-containing nitrogen-controlled austenitic stainless steel, and control A-type sulfide inclusions by selecting low-S raw materials so that the S content of the raw materials is less than 0.0015wt.%;

(2) Vacuum induction melting: melt the alloy raw material, then heat up to 1500-1550 ℃ for refining, refining time is 0.5-1h, through refining to achieve carbon deoxidation, so that the control target of oxygen content is less than 0.0020wt.%, thereby reducing oxide inclusions content;

(3) Vacuum consumable smelting: the droplet control method is adopted to promote the good removal of nitride inclusions.

The chemical composition by weight percentage of the titanium-containing nitrogen-controlled austenitic stainless steel is:

C: 0.03-0.10%; Cr: 14.50-18.00%; Ni: 14.50-18.00%; Si: 0.30-1.00%; Mn<2.00%; Mo: 1.00-2.00%; Ti: 0.30-0.80%; %; S<0.005%; O<0.005%; P<0.015%; Co<0.03%; Cu<0.05%; Ca<0.01%; B<0.005%; Fe balance.

Step (1) During the selection of raw materials, the content of N and Ti in the raw materials is controlled, so that the contents of N and Ti are slightly larger than the lower limit of the chemical composition range, so as to reduce the formation amount of nitride inclusions; specifically, the content of N in the raw materials is controlled to be 0.004-0.006wt .%, the Ti content is 0.35-0.40wt.%.

In step (2), a Si-Ca deoxidizer is added in the later stage of refining, and the added amount of the Si-Ca deoxidizer accounts for 0.02-0.04wt.% of the total weight of the raw materials. The Si-Ca deoxidizer does not contain Al element, or the content of Al element in the Si-Ca deoxidizer is less than 0.05wt.% of the total weight of the raw material.

In step (3), the vacuum self-consumption adopts a droplet control method, and the inclusions in the smelting process are well removed by controlling the stability of the smelting process.

By adopting the control method of the invention, the coarse/fine series of A, B, C and D inclusions in titanium-containing nitrogen-controlled austenitic stainless steel can be close to grade 0, and the TiN type is less than or equal to grade 1.5, and a high-quality purified alloy can be obtained.

The design mechanism of the present invention is as follows:

Vacuum induction smelting basically does not have the ability to desulfurize. In order to control the sulfide content, it can only be solved by limiting the total amount of sulfur introduced in the raw materials. For the reduction of oxide inclusions, the first is to reduce the total oxygen content, and the second is to improve the oxide morphology. Deoxidation with carbon is the best way to reduce oxides, and the deoxidized products will not remain in the steel. During carbon deoxidation, it is necessary to avoid the problem of oxygenation of molten steel caused by the violent decomposition of the oxide crucible, so a lower reaction temperature is required. Limiting the amount of aluminum-containing deoxidizer used can also avoid the formation of large alumina blocks. Reducing the content of nitrogen and titanium can avoid the formation of a large number of nitrides, and control the content of N and Ti on the basis of satisfying the alloy composition to reduce the formation of nitride inclusions. The selection of the appropriate control method in the vacuum self-consumption process can stabilize the smelting process and facilitate the good exclusion of inclusions during crystallization. According to the characteristics of the alloy, the droplet control method is adopted to achieve the purpose of exclusion.

Through the improvement of smelting process parameters, the final smelted engineering large-scale titanium-containing nitrogen-controlled austenitic stainless steel has a lower grade of sulfide, oxide and nitride inclusions, and on the basis of satisfying the addition of N and Ti elements, eliminating the need for The cluster-like distribution of nitride inclusions effectively improves the structure and properties of subsequent deformed products.

The advantages and beneficial effects of the present invention are as follows:

(1) The control method of the present invention can improve the purity of the alloy material, can obviously control the level of inclusions, and can reach the zero level of A, B, C and D inclusions.

(2) The general purpose of the present invention is to control the TiN inclusions to be less than or equal to grade 1.5 by reasonably controlling the elements of N and Ti, combined with process selection, thereby improving the high-temperature durable mechanical properties and corrosion resistance of the material.

(3) The present invention limits the Al content in the Si-Ca deoxidizer used, so that the Al content is less than 0.05wt.% of the total raw material, so as to avoid the formation of B-type alumina inclusions.

Description of drawings

Figure 1 shows the morphology of inclusions at different positions of the austenitic stainless steel ingot in Example 1.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that these small implementation examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Example 1:

This embodiment is a method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel, using equipment and parameters: vacuum induction melting furnace + 3T vacuum consumable furnace.

(1) Raw materials:

Configure the raw materials in the following element ratios:

C: 0.03-0.10%; Cr: 14.50-18.00%; Ni: 14.50-18.00%; Si: 0.30-1.00%; Mn<2.00%; Mo: 1.00-2.00%; -0.006%; S<0.005%; O<0.005%; P<0.015%; Co<0.03%; Cu<0.05%; Ca<0.01%; B<0.005%; Fe balance.

Select low-S pure iron and other low-sulfur raw materials to ensure that the S content of the raw materials is less than 0.0015wt.%, control N: 0.004-0.006wt.%, Ti: 0.35-0.40wt.%;

(2) During vacuum induction melting, the refining temperature is selected to be 1520 °C, and the refining time is 0.8 hours;

(3) Add Si-Ca deoxidizer without Al in the later stage of refining, and the amount of deoxidizer added is 0.035% of the total weight of the raw materials.

(4) Droplet control is adopted for self-time consumption.

Chemical analysis (Table 1) and microstructure observation (Table 2) of the prepared consumable ingots after thermal deformation showed that the content of O and S was less than 0.0015%, and the content of N and Ti was controlled. The coarse/fine series of C and D inclusions are close to grade 0, and the TiN type is less than or equal to grade 1.5, obtaining high-quality and purified alloys.

Table 1 Example alloy key control components (wt.%)

Table 2 The results of rating of inclusions in austenitic stainless steel ingots of the embodiment

Claims (3)

1. a control method of titanium-containing nitrogen-controlled austenitic stainless steel non-metallic inclusions, is characterized in that: the method is to realize in the process of using vacuum induction furnace and vacuum self-consumption to carry out smelting titanium-containing nitrogen-controlled austenitic stainless steel The control of non-metallic inclusions specifically includes the following steps: (1) Selection of raw materials: Prepare raw materials according to the chemical composition of titanium-containing nitrogen-controlled austenitic stainless steel, and control the A-type sulfide inclusions by selecting low-S raw materials so that the S content of the raw materials is less than 0.0015wt.%; the N content in the raw materials is controlled to 0.004 -0.006wt.%, Ti content is 0.35-0.40wt.%; (2) Vacuum induction melting: melting alloy raw materials, then heating up to 1500-1550 ℃ for refining, refining time 0.5-1h, through refining to achieve carbon deoxidation, so that the control target of oxygen content is less than 0.0020wt.%, thereby reducing oxide inclusions content; wherein, a Si-Ca deoxidizer is added in the later stage of refining, and the addition amount of the Si-Ca deoxidizer accounts for 0.02-0.04wt.% of the total weight of the raw materials; the Si-Ca deoxidizer does not contain Al element, or The content of Al element in the Si-Ca deoxidizer is less than 0.05wt.%; (3) Vacuum consumable smelting: the droplet control method is adopted to promote the good removal of nitride inclusions. 2. The control method of titanium-containing nitrogen-controlling austenitic stainless steel non-metallic inclusions according to claim 1, wherein: by weight percentage, the chemical composition of the titanium-containing nitrogen-controlling austenitic stainless steel is: C: 0.03-0.10%; Cr: 14.50-18.00%; Ni: 14.50-18.00%; Si: 0.30-1.00%; Mn<2.00%; Mo: 1.00-2.00%; Ti: 0.30-0.80%; %; S<0.005%; O<0.005%; P<0.015%; Co<0.03%; Cu<0.05%; Ca<0.01%; B<0.005%; Fe balance. 3. The method for controlling non-metallic inclusions of titanium-containing nitrogen-controlled austenitic stainless steel according to claim 1, characterized in that: in step (3), the vacuum self-consumption adopts a droplet control method, and the stability of the smelting process is determined by the control method. Control achieves good removal of inclusions during smelting.

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