Ultra-clean stainless steel and preparation method thereof

Abstract

The present invention belongs to the technical field of metal materials, and provides an ultra-clean stainless steel and a preparation method thereof. The present invention controls the formation of high-temperature ferrite phase δ by adding Ni, Cr and Mo and limiting their contents, so that the volume content of high-temperature ferrite phase δ in the ultra-clean stainless steel is ≤0.1%; and controls the contents of Mn, P, S, Al, Ti, Ca, Mg, Ce, La, O, N and H, so that the density of all-size non-metallic inclusions of five categories A, B, C, D and Ds in the ultra-clean stainless steel is ≤0.2 pieces / mm 2 The results of the embodiment show that the ultra-clean stainless steel provided by the present invention is A+B+C+D+Ds≤0.5, and the density of all-size non-metallic inclusions of five categories A, B, C, D and Ds is ≤0.2 / mm 2 , the non-metallic inclusions are only aluminum oxide, and the volume content of high-temperature ferrite phase δ is ≤0.1%.

Description

Technical Field

[0001] The invention relates to the technical field of metal materials, and in particular to ultra-clean stainless steel and a preparation method thereof. Background Art

[0002] Ultra-clean stainless steel is a material that has stricter control over the content of impurity elements in steel. It is often used to prepare equipment such as pipes for transporting high-purity or ultra-pure clean gases. During the preparation and transportation of high-purity or ultra-pure clean gases, the corrosion and shedding of impurity elements and non-metallic inclusions in the ultra-clean stainless steel pipes will contaminate the high-purity gas or ultra-pure clean gas.

[0003] In order to reduce the impurity elements and non-metallic inclusions in ultra-clean stainless steel, the content of impurity elements, especially the content of oxygen and sulfur, which are easy to form non-metallic inclusions, must be strictly controlled during the smelting of ultra-clean stainless steel, and the total of non-metallic inclusions A, B, C, D, and Ds in ultra-clean stainless steel must not exceed 0.5. At present, the smelting method of ultra-clean stainless steel mainly adopts two-way or three-way smelting process in vacuum induction melting, atmosphere protection electroslag remelting and vacuum consumable remelting, and adds Ca, Mg or rare earth in the smelting process for composite deoxidation and desulfurization to obtain ultra-clean stainless steel with low rating of impurity elements such as oxygen and sulfur and non-metallic inclusions. Although the total sum of non-metallic inclusions A, B, C, D, and Ds in the ultra-clean stainless steel prepared by this method does not exceed grade 0.5, the steel contains a large number of composite non-metallic inclusions with a size of less than 2 μm and with Ca, Mg or rare earth elements as the core. Such inclusions do not meet the rating size specified in ASTM E45 and are not included in the non-metallic inclusion rating. However, pipes and valves made of ultra-clean stainless steel with such inclusions will still fall off and cause pollution when transporting high-purity gases. Summary of the invention

[0004] The object of the present invention is to provide an ultra-clean stainless steel and a preparation method thereof. The ultra-clean stainless steel prepared by the present invention has a low impurity content, a low density of full-size non-metallic inclusions of five categories, A, B, C, D and Ds, and all full-size non-metallic inclusions are aluminum oxide.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides an ultra-clean stainless steel, wherein the components are as follows by mass percentage:

[0007] Ni 14.70~15.20%, Cr 17.20~17.70%, Mo 2.30~2.80%, C≤0.008%, Si≤0.02%, Mn≤0.02%, P≤0.003%, S≤0.0008%, Al≤0.005%, Ti≤0.002%, Ca≤0.0002%, Mg≤0.0002%, Ce≤0.0002%, La≤0.0002%, O≤0.0008%, N≤0.003%, H≤0.0001% and the balance is iron.

[0008] Preferably, the components are as follows by mass percentage:

[0009] Ni 14.80%~15.00%, Cr 17.30~17.50%, Mo 2.50~2.70%, C≤0.006%, Si≤0.016%, Mn≤0.01%, P≤0.0025%, S≤0.0007%, Al≤0.004%, Ti≤0.001%, Ca≤0.0001%, Mg≤0.0001%, Ce≤0.0001%, La≤0.0001%, O≤0.0006%, N≤0.002%, H≤0.00005% and the balance is iron.

[0010] Preferably, the density of all-size non-metallic inclusions of all five categories A, B, C, D and Ds in the ultra-clean stainless steel is ≤ 0.2 pieces / mm 2 .

[0011] Preferably, the volume content of high temperature ferrite phase δ in the ultra-clean stainless steel is ≤0.1%.

[0012] The present invention also provides a method for preparing the ultra-clean stainless steel described in the above technical solution, comprising:

[0013] The stainless steel raw material and the deoxidizer are mixed and then vacuum induction melting and refining are performed in sequence to obtain ultra-clean stainless steel; the deoxidizer is carbon; and the refining is electron beam melting.

[0014] Preferably, the raw materials of the stainless steel are calculated by mass percentage as follows: 14.65-15.15% nickel, 18.70-19.20% chromium, 2.25-2.75% molybdenum and the balance pure iron.

[0015] Preferably, the mass of carbon accounts for the mass of the stainless steel raw material as a percentage of: ([%Cr] × [%O] Cr +[%Ni]×[%O] Ni +[%Mo]×[%O] Mo +[%Fe]×[%O] Fe)×0.8; the [%Cr] refers to the mass percentage of Cr in the stainless steel raw material; the [%O] Cr refers to the mass percentage of oxygen in the stainless steel raw material Cr; the [%Ni] refers to the mass percentage of Ni in the stainless steel raw material; the [%O] Ni refers to the mass percentage of oxygen in the stainless steel raw material Ni; the [%Mo] refers to the mass percentage of Mo in the stainless steel raw material; the [%O] Mo refers to the mass percentage of oxygen in the stainless steel raw material Mo; the [%Fe] refers to the mass percentage of Fe in the stainless steel raw material; the [%O] Fe Refers to the mass percentage of oxygen in the stainless steel raw material Fe.

[0016] Preferably, the pressure of the vacuum induction melting is 5-8 Pa, the temperature of the vacuum induction melting is 1550-1570° C., and the time of the vacuum induction melting is 90-120 min.

[0017] Preferably, degassing is performed before the vacuum induction melting.

[0018] Preferably, the refining power is 150-200 kW, the refining pressure is 0.01-0.04 Pa, and the refining melting rate is 1.5-2.0 kg / min.

[0019] The invention provides an ultra-clean stainless steel. The components thereof are calculated by mass percentage as follows: Ni 14.70-15.20%, Cr 17.20-17.70%, Mo 2.30-2.80%, C≤0.008%, Si≤0.02%, Mn≤0.02%, P≤0.003%, S≤0.0008%, Al≤0.005%, Ti≤0.002%, Ca≤0.0002%, Mg≤0.0002%, Ce≤0.0002%, La≤0.0002%, O≤0.0008%, N≤0.003%, H≤0.0001% and the balance of iron. The present invention controls the formation of high-temperature ferrite phase δ by adding Ni, Cr and Mo and limiting their contents, so that the volume content of high-temperature ferrite phase δ in ultra-clean stainless steel is ≤0.1%; and controls the contents of Mn, P, S, Al, Ti, Ca, Mg, Ce, La, O, N and H, so that the density of all-size non-metallic inclusions of five categories A, B, C, D and Ds in ultra-clean stainless steel is ≤0.2 pieces / mm 2 The results of the embodiment show that the ultra-clean stainless steel provided by the present invention is A+B+C+D+Ds≤0.5, and the density of all-size non-metallic inclusions of five categories A, B, C, D and Ds is ≤0.2 / mm 2 , the non-metallic inclusions are only aluminum oxide, and the volume content of high-temperature ferrite phase δ is ≤0.1%. DETAILED DESCRIPTION

[0020] The present invention provides an ultra-clean stainless steel, wherein the components are as follows by mass percentage:

[0021] Ni 14.70~15.20%, Cr 17.20~17.70%, Mo 2.30~2.80%, C≤0.008%, Si≤0.02%, Mn≤0.02%, P≤0.003%, S≤0.0008%, Al≤0.005%, Ti≤0.002%, Ca≤0.0002%, Mg≤0.0002%, Ce≤0.0002%, La≤0.0002%, O≤0.0008%, N≤0.003%, H≤0.0001% and the balance is iron.

[0022] In the present invention, the composition of the ultra-clean stainless steel includes Ni14.70-15.20% by mass; in the embodiment of the present invention, the Ni may be specifically 14.7%, 14.8%, 14.9%, 15.0%, 15.1% or 15.2%. The present invention limits the content of Ni to fully form austenite, inhibit the formation of high-temperature ferrite phase δ, and improve the strength, plasticity, toughness, corrosion resistance and heat resistance of stainless steel.

[0023] In the present invention, the composition of the ultra-clean stainless steel includes Cr17.20-17.70% by mass percentage; in the embodiment of the present invention, the Cr can be specifically 17.20%, 17.30%, 17.40%, 17.60%, 17.60% or 17.70%. The present invention can fully change the chemical properties of the surface of the ultra-clean stainless steel by limiting the content of Cr, so that it has the ability to resist oxidation and improve the corrosion resistance of the ultra-clean stainless steel; balance the transformation of austenite to ferrite, and improve the strength, plasticity and toughness of the ultra-clean stainless steel.

[0024] In the present invention, the composition of the ultra-clean stainless steel includes Mo2.30-2.80% by mass; in the embodiment of the present invention, the Mo can be specifically 2.30%, 2.40%, 2.50%, 2.60%, 2.70% or 2.80%. The present invention can fully control the formation of high-temperature ferrite phase δ by limiting the content of Mo, thereby improving the strength, plasticity, toughness, corrosion resistance and heat resistance of stainless steel.

[0025] In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes C≤0.008%; in the embodiment of the present invention, the C≤0.006%. In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes Si≤0.02%; in the embodiment of the present invention, the Si≤0.016%. In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes Mn≤0.02%; in the embodiment of the present invention, the Mn≤0.01%. In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes P≤0.003%; in the embodiment of the present invention, the P≤0.0025%. In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes S≤0.0008%; in the embodiment of the present invention, the S≤0.0007%. In the present invention, by mass percentage, the composition of the ultra-clean stainless steel includes Al≤0.005%; in the embodiment of the present invention, the Al≤0.004%. In the present invention, the components of the ultra-clean stainless steel include Ti≤0.002% by mass percentage; in the embodiment of the present invention, the Ti≤0.001%. In the present invention, the components of the ultra-clean stainless steel include Ca≤0.0002% by mass percentage; in the embodiment of the present invention, the Ca≤0.0001%. In the present invention, the components of the ultra-clean stainless steel include Mg≤0.0002% by mass percentage; in the embodiment of the present invention, the Mg≤0.0001%. In the present invention, the components of the ultra-clean stainless steel include Ce≤0.0002% by mass percentage; in the embodiment of the present invention, the Ce≤0.0001%. In the present invention, the components of the ultra-clean stainless steel include La≤0.0002% by mass percentage; in the embodiment of the present invention, the La≤0.0001%. In the present invention, the components of the ultra-clean stainless steel include O≤0.0008% by mass percentage; in the embodiment of the present invention, the O≤0.0006%. In the present invention, the composition of the ultra-clean stainless steel includes N≤0.003% by mass percentage; in the embodiment of the present invention, the N≤0.002%. In the present invention, the composition of the ultra-clean stainless steel includes H≤0.0001% by mass percentage; in the embodiment of the present invention, the H≤0.0001%. The present invention fully reduces the content of impurity elements in ultra-clean stainless steel by limiting the content of Mn, P, S, Al, Ti, Ca, Mg, Ce, La, O, N and H, so that the density of all-series and full-size non-metallic inclusions of five categories A, B, C, D and Ds in ultra-clean stainless steel is ≤0.2 pieces / mm 2 .

[0026] In the present invention, the composition of the ultra-clean stainless steel includes a balance of iron in terms of mass percentage.

[0027] In the present invention, the components are preferably calculated by mass percentage: Ni 14.80% to 15.00%, Cr 17.30 to 17.50%, Mo 2.50 to 2.70%, C≤0.006%, Si≤0.016%, Mn≤0.01%, P≤0.0025%, S≤0.0007%, Al≤0.004%, Ti≤0.001%, Ca≤0.0001%, Mg≤0.0001%, Ce≤0.0001%, La≤0.0001%, O≤0.0006%, N≤0.002%, H≤0.00005% and the balance iron. The present invention further reduces the impurity elements in the ultra-clean stainless steel by limiting the mass percentage of each component of the ultra-clean stainless steel, so that the density of all-series and full-size non-metallic inclusions of five categories A, B, C, D and Ds in the ultra-clean stainless steel is ≤0.13 pieces / mm 2 .

[0028] In the present invention, the density of all-size non-metallic inclusions of the five categories A, B, C, D and Ds in the ultra-clean stainless steel is preferably ≤ 0.2 / mm 2 , more preferably ≤0.15 pieces / mm 2 The present invention limits the density of five types of full-series and full-size non-metallic inclusions A, B, C, D and Ds in ultra-clean stainless steel to obtain cleaner ultra-clean stainless steel.

[0029] In the present invention, the volume content of the high temperature ferrite phase δ in the ultra-clean stainless steel is preferably ≤0.1%. The present invention further reduces the crack propagation caused by the fracture of the δ ferrite when the material is subjected to stress by limiting the volume content of the high temperature ferrite phase δ, thereby improving the overall toughness of the material; and by limiting the volume content of the high temperature ferrite phase δ, the oxidation and metal ionization of the material under the action of high temperature, moisture and corrosive media are fully reduced, thereby improving the corrosion resistance of the material.

[0030] The present invention suppresses the formation of high-temperature ferrite phase δ by adding Ni, Cr and Mo and limiting their contents, so that the volume content of high-temperature ferrite phase δ in ultra-clean stainless steel is ≤0.1%; by controlling the contents of Mn, P, S, Al, Ti, Ca, Mg, Ce, La, O, N and H, the density of all-system and full-size non-metallic inclusions of five categories A, B, C, D and Ds in ultra-clean stainless steel is ≤0.2 pieces / mm 2 .

[0031] The present invention also provides a method for preparing the ultra-clean stainless steel described in the above technical solution, comprising:

[0032] The stainless steel raw material and the deoxidizer are mixed and vacuum induction melting and refining are carried out in sequence to obtain ultra-clean stainless steel.

[0033] In the present invention, the raw materials of the stainless steel are preferably: 14.65-15.15% nickel, 18.70-19.20% chromium, 2.25-2.75% molybdenum and the balance pure iron in terms of mass percentage.

[0034] In the present invention, the mass percentage of nickel in the raw material is preferably the mass content of Ni in ultra-clean stainless steel - 0.05%. In the present invention, the mass percentage of nickel in the stainless steel raw material is preferably 14.65-15.15%; as an embodiment of the present invention, the mass percentage of nickel in the stainless steel raw material is 15.00%. The present invention limits the content of nickel in the stainless steel raw material to ensure that ultra-clean stainless steel with a corresponding Ni content can be prepared.

[0035] In the present invention, the nickel is preferably electrolytic nickel, and the purity of the electrolytic nickel is preferably 99.95-99.98%.

[0036] In the present invention, the mass percentage of chromium in the raw material is preferably the mass content of Cr in the ultra-clean stainless steel + 1.5%. In the present invention, the stainless steel raw material preferably includes 18.70-19.20% chromium by mass percentage; as an embodiment of the present invention, the mass percentage of nickel in the stainless steel raw material is 19.00%. The present invention limits the chromium content in the stainless steel raw material to ensure that ultra-clean stainless steel with a corresponding Cr content can be prepared.

[0037] In the present invention, the mass percentage of molybdenum in the raw material is preferably the mass content of Mo in ultra-clean stainless steel -0.05%. In the present invention, the stainless steel raw material preferably includes 2.25-2.75% molybdenum by mass percentage; as an embodiment of the present invention, the mass percentage of nickel in the stainless steel raw material is 2.50%. The present invention limits the content of molybdenum in the stainless steel raw material to ensure that ultra-clean stainless steel with a corresponding Mo content can be prepared.

[0038] In the present invention, the stainless steel raw material preferably includes a balance of pure iron by mass percentage. The present invention limits the content of pure iron to ensure that ultra-clean stainless steel with a corresponding iron content can be prepared.

[0039] In the present invention, the deoxidizer is preferably carbon. The present invention limits the deoxidizer to carbon to ensure that the carbon undergoes an oxidation-reduction reaction with oxygen or oxides in the molten steel to generate carbon monoxide gas, and then the carbon monoxide gas quickly overflows the molten steel under vacuum conditions to achieve the deoxidation task. In the present invention, the mass of the carbon is preferably a percentage of the mass of the stainless steel raw material: ([%Cr]×[%O] Cr +[%Ni]×[%O] Ni +[%Mo]×[%O] Mo+[%Fe]×[%O] Fe )×0.8. In the present invention, [%Cr] refers to the mass percentage of Cr in the stainless steel raw material; [%O] Cr Refers to the mass percentage of oxygen in the stainless steel raw material Cr. In the present invention, the [%Ni], [%O] Ni 、[%Mo]、[%O] Mo 、[%Fe]、[%O] Fe With [%Cr], [%O] Cr The meanings correspond to each other and will not be repeated here. The present invention limits the mass percentage of carbon to ensure that the oxygen content of the ultra-clean stainless steel is lower.

[0040] In the present invention, the oxygen content of the stainless steel raw material is preferably detected by an oxygen-nitrogen combined detector.

[0041] The present invention has no special limitation on the mixing of the stainless steel raw material and the deoxidizer, and any mixing method known in the art can be used.

[0042] In the present invention, degassing is preferably performed before vacuum induction melting. The present invention reduces the gas content of stainless steel by degassing before vacuum induction melting to remove the gas adsorbed on the surface of the stainless steel raw material. In the present invention, the degassing pressure is preferably ≤10Pa; the degassing temperature is preferably 350-380°C; and the degassing time is preferably 1-3h. The present invention more fully removes the gas adsorbed on the surface of the stainless steel raw material by limiting the degassing parameters, reduces the inclusions and grain boundary widening of the stainless steel caused by the gas, and improves the purity and plasticity of the stainless steel.

[0043] In the present invention, the pressure of the vacuum induction melting is preferably 5-8Pa; in an embodiment of the present invention, the pressure of the vacuum induction melting may be specifically 5Pa, 6Pa, 7Pa or 8Pa. In the present invention, the temperature of the vacuum induction melting is preferably 1550-1570°C; in an embodiment of the present invention, the temperature of the vacuum induction melting may be specifically 1550°C, 1560°C or 1570°C. In the present invention, the time of the vacuum induction melting is preferably 90-120min; in an embodiment of the present invention, the time of the vacuum induction melting may be specifically 90min, 100min, 110min or 120min. The present invention limits the pressure, temperature and time of vacuum induction melting to ensure that the melting and solid solution of each stainless steel raw material are more uniform, the carbon-oxygen reaction is more sufficient, and the deoxidation is more sufficient.

[0044] In the present invention, the crucible used for vacuum induction melting is preferably made of alumina. The alumina crucible of the present invention avoids mixing with other types of impurities, ensuring that the oxide inclusions in the product obtained by vacuum induction melting are single alumina, which is beneficial to carbon deoxidation during subsequent refining and purification.

[0045] After vacuum induction melting is completed, the present invention preferably sequentially casts the melt obtained by vacuum induction melting into a billet and performs surface grinding. The present invention removes oxide scale and slag inclusion defects on the surface of the billet by surface grinding.

[0046] The present invention has no special limitation on the method of casting into blanks and surface grinding, and the casting into blanks method well known in the art can be adopted.

[0047] In the present invention, the refining is electron beam melting. In the present invention, the power of the refining is preferably 150-200kW; in an embodiment of the present invention, the power of the refining may be specifically 150kW, 160kW, 170kW, 180kW, 190kW or 200kW. In the present invention, the pressure of the refining is preferably 0.01-0.04Pa; in an embodiment of the present invention, the pressure of the refining may be specifically 0.01Pa, 0.02Pa, 0.03Pa or 0.04Pa. In the present invention, the melting rate of the refining is preferably 1.5-2.0kg / min. In an embodiment of the present invention, the melting rate of the refining may be specifically 1.5kg / min, 1.6kg / min, 1.7kg / min, 1.8kg / min, 1.9kg / min or 2.0kg / min. The present invention adopts electron beam melting and limits the refining power, pressure and melting rate, so that carbon and impurity aluminum oxide in the melt fully react under higher vacuum conditions, and the generated carbon monoxide gas quickly overflows the molten steel under high vacuum, further deoxidizing and reducing the carbon content to C≤0.008%; and the impurity elements Mn, P, S, Al, Ti, Ca, Mg, Ce, La, O, N and H are more fully volatilized and removed under high vacuum and high temperature melting conditions, so as to further reduce the content of each impurity element.

[0048] After refining, the present invention preferably melts and casts the refined melt into an ingot. The present invention has no particular limitation on the method of melting and casting the ingot, and any melting and casting ingot method known in the art can be used.

[0049] The present invention obtains ultra-clean stainless steel by mixing stainless steel raw materials and deoxidizer carbon and then performing vacuum induction melting and refining in sequence. Among them, vacuum induction melting is used to make the melting and solid solution of each stainless steel raw material more uniform, the carbon oxygen reaction is more complete, and the deoxidation is more complete; refining is used to further make carbon and aluminum oxide fully react under higher vacuum conditions, and the generated carbon monoxide gas quickly overflows the molten steel under high vacuum, further deoxidizing and reducing the carbon content to C≤0.008%; and impurity elements are more fully volatilized and removed under high vacuum and high temperature melting conditions, further reducing the content of each impurity element.

[0050] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] An ultra-clean stainless steel, the components are calculated by mass percentage as follows:

[0053] Ni 14.90%, Cr 17.4%, Mo 2.60%, C 0.005%, Si 0.014%, Mn 0.009%, P0.0023%, S 0.0006%, Al 0.0036%, Ti 0.0007%, Ca<0.0001%, Mg<0.0001%, Ce<0.0001%, La<0.0001%, O≤0.0008%, N≤0.003%, H≤0.0001% and the balance is iron.

[0054] The method for preparing the ultra-clean stainless steel comprises the following steps:

[0055] 14.85% of electrolytic nickel, 18.9% of chromium, 2.55% of molybdenum after shot blasting or grinding, the remaining pure iron after shot blasting or grinding, and 0.02% of deoxidizer are loaded into an alumina crucible of a vacuum induction melting furnace, degassed at a pressure of less than 10Pa and a temperature of 350°C for 2h, and then melted at a vacuum induction melting pressure of 7Pa and a vacuum induction melting temperature of 1560°C for 90min, cast into a billet and surface polished; then the polished billet is put into an electron beam furnace, refined under the conditions of a refining pressure of 0.03Pa, a refining power of 150kW, and a refining melting rate of 1.5kg / min, and then melted into an ingot to obtain ultra-clean stainless steel;

[0056] The stainless steel raw material contains 14.85% electrolytic nickel, 18.9% chromium, 2.55% molybdenum, and the remainder of pure iron. The oxygen content is measured by an oxygen-nitrogen joint tester: [%O] Cr 0.1143%, [%O] Ni 0.0057%, [%O] Mo 0.0046%, [%O] Fe 0.0039%; the mass percentage of carbon is: ([%Cr]×[%O] Cr +[%Ni]×[%O] Ni +[%Mo]×[%O] Mo +[%Fe]×[%O] Fe )×0.8=0.02%;

[0057] The chromium and molybdenum are loaded into the middle and lower part of the alumina crucible; the carbon is isolated by electrolytic nickel and does not contact the metal chromium and the crucible wall.

[0058] The alloy element content of the ultra-clean stainless steel obtained in Example 1 was detected by a spark direct-reading spectrometer, a carbon-sulfur meter, an oxygen-nitrogen-hydrogen joint tester, and an inductively coupled plasma emission spectrometer. The results were as follows: Cr: 17.38%, Ni: 14.92%, Mo: 2.61%, C: 0.005%, Si: 0.014%, Mn: 0.009%, P: 0.0023%, S: 0.0006%, Al: 0.0036%, Ti: 0.0007%, Ca﹤0.0001%, Mg﹤0.0001%, Ce﹤0.0001%, La﹤0.0001%, O: 0.0005%, N: 0.0019%, H﹤0.00005%, and the remainder of iron.

[0059] The non-metallic inclusions in the ultra-clean stainless steel obtained in Example 1 were detected using a metallographic microscope and a scanning electron microscope. The results showed that according to ASTM E45, the non-metallic inclusions were graded A+B+C+D+Ds≤0.5, and the density of the full-size non-metallic inclusions was 0.13 / mm. 2 ; Non-metallic inclusions are aluminum oxide.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that rare earth cerium is used as the deoxidizer, and the rest is the same as Example 1.

[0062] The non-metallic inclusions in the ultra-clean stainless steel obtained in Example 1 were detected by scanning electron microscopy. The results showed that the density of non-metallic inclusions in all sizes was 0.89 / mm 2 The non-metallic inclusions are composite oxides containing cerium, and have a higher density than the non-metallic inclusions in the ultra-clean stainless steel obtained in Example 1 of the present invention.

[0063] The cerium element in the ultra-clean stainless steel prepared in Comparative Example 1 was detected by inductively coupled plasma emission spectrometry. The results showed that the cerium content in the ultra-clean stainless steel prepared in Comparative Example 1 was 0.0013%, further indicating the presence of cerium composite oxide non-metallic inclusions.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that a vacuum consumable remelting furnace is used for refining, the refining pressure is 0.1 Pa, the refining power is 230 kW, and the refining melting rate is 3.3 kg / min; the rest is the same as Example 1.

[0066] The impurity element content in the ultra-clean stainless steel obtained in Comparative Example 2 was detected by using a spark direct-reading spectrometer, a carbon-sulfur meter, an oxygen-nitrogen-hydrogen joint tester, and an inductively coupled plasma emission spectrometer. The results were as follows: C: 0.007%, Si: 0.02%, Mn: 0.039%, P: 0.0036%, S: 0.0017%, Al: 0.0043%, Ti: 0.0008%, Ca﹤0.0001%, Mg﹤0.0001%, Ce﹤0.0001%, La﹤0.0001%, O: 0.0016%, N: 0.0047%, H﹤0.00005%, which is higher than the impurity element content of the ultra-clean stainless steel obtained in Example 1 of the present invention.

[0067] The non-metallic inclusions in the ultra-clean stainless steel obtained in Comparative Example 2 were detected by scanning electron microscopy. The results showed that the density of all-size non-metallic inclusions was 2.79 / mm. 2 The non-metallic inclusions are aluminum oxide and sulfide, which have a higher density and more types of non-metallic inclusions than those in the ultra-clean stainless steel prepared in Example 1 of the present invention.

[0068] In summary, the ultra-clean stainless steel prepared by the present invention has low impurity content, low density of full-size non-metallic inclusions of five categories A, B, C, D and Ds, and all full-size non-metallic inclusions are aluminum oxide.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An ultra-clean stainless steel, the components of which are calculated by mass percentage as follows: Ni 14.70~15.20%, Cr 17.20~17.70%, Mo 2.60%, C≤0.008%, Si≤0.02%, Mn≤0.02%, P≤0.003%, S≤0.0008%, Al≤0.005%, Ti≤0.002%, Ca≤0.0002%, Mg≤0.0002%, Ce≤0.0002%, La≤0.0002%, O≤0.0008%, N≤0.003%, H≤0.0001% and the balance of iron; The method for preparing the ultra-clean stainless steel comprises: The stainless steel raw material and the deoxidizer are mixed and then vacuum induction melting and refining are performed in sequence; The crucible used in the vacuum induction melting is made of alumina; The deoxidizer is carbon; The mass of carbon accounts for the mass of the stainless steel raw material as a percentage: ([%Cr] × [%O] Cr +[%Ni]×[%O] Ni +[%Mo]×[%O] Mo +[%Fe]×[%O] Fe )×0.8; the [%Cr] refers to the mass percentage of Cr in the stainless steel raw material; the [%O] Cr refers to the mass percentage of oxygen in the stainless steel raw material Cr; the [%Ni] refers to the mass percentage of Ni in the stainless steel raw material; the [%O] Ni refers to the mass percentage of oxygen in the stainless steel raw material Ni; the [%Mo] refers to the mass percentage of Mo in the stainless steel raw material; the [%O] Mo refers to the mass percentage of oxygen in the stainless steel raw material Mo; the [%Fe] refers to the mass percentage of Fe in the stainless steel raw material; the [%O] Fe Refers to the mass percentage of oxygen in the stainless steel raw material Fe; The refining is electron beam melting; The vacuum induction melting pressure is 5-8 Pa, the vacuum induction melting temperature is 1550-1570° C., and the vacuum induction melting time is 90-120 min; The refining power is 150-200 kW, the refining pressure is 0.01-0.04 Pa, and the refining melting rate is 1.5-2.0 kg / min.

2. The ultra-clean stainless steel according to claim 1, characterized in that: The weight percentage of each component is: Ni 14.80%~15.00%, Cr 17.30~17.50%, Mo 2.60%, C≤0.006%, Si≤0.016%, Mn≤0.01%, P≤0.0025%, S≤0.0007%, Al≤0.004%, Ti≤0.001%, Ca≤0.0001%, Mg≤0.0001%, Ce≤0.0001%, La≤0.0001%, O≤0.0006%, N≤0.002%, H≤0.00005% and the balance of iron.

3. The ultra-clean stainless steel according to claim 1 or 2, characterized in that: The density of all-size non-metallic inclusions of all five categories A, B, C, D and Ds in the ultra-clean stainless steel is ≤0.2 pieces / mm 2 .

4. The method for preparing the ultra-clean stainless steel according to any one of claims 1 to 3, comprising: The stainless steel raw material and the deoxidizer are mixed and then vacuum induction melting and refining are performed in sequence to obtain ultra-clean stainless steel; The crucible used in the vacuum induction melting is made of alumina; The deoxidizer is carbon; The mass of carbon accounts for the mass of the stainless steel raw material as a percentage: ([%Cr] × [%O] Cr +[%Ni]×[%O] Ni +[%Mo]×[%O] Mo +[%Fe]×[%O] Fe )×0.8; the [%Cr] refers to the mass percentage of Cr in the stainless steel raw material; the [%O] Cr refers to the mass percentage of oxygen in the stainless steel raw material Cr; the [%Ni] refers to the mass percentage of Ni in the stainless steel raw material; the [%O] Ni refers to the mass percentage of oxygen in the stainless steel raw material Ni; the [%Mo] refers to the mass percentage of Mo in the stainless steel raw material; the [%O] Mo refers to the mass percentage of oxygen in the stainless steel raw material Mo; the [%Fe] refers to the mass percentage of Fe in the stainless steel raw material; the [%O] Fe Refers to the mass percentage of oxygen in the stainless steel raw material Fe; The refining is electron beam melting; The vacuum induction melting pressure is 5-8 Pa, the vacuum induction melting temperature is 1550-1570° C., and the vacuum induction melting time is 90-120 min; The refining power is 150-200 kW, the refining pressure is 0.01-0.04 Pa, and the refining melting rate is 1.5-2.0 kg / min.

5. The preparation method according to claim 4, characterized in that: The stainless steel raw materials are calculated by mass percentage as follows: Nickel 14.65~15.15%, chromium 18.70~19.20%, molybdenum 2.25~2.75% and the balance iron.

6. The preparation method according to claim 4, characterized in that: Degassing is performed before the vacuum induction melting.