A 520B precipitation hardened stainless steel ingot for ship power equipment and a preparation method thereof

Abstract

The present invention provides a 520B precipitation hardened stainless steel ingot for ship power equipment and a preparation method thereof, and belongs to the technical field of stainless steel. The 520B precipitation hardened stainless steel ingot for ship power equipment provided by the present invention has the following chemical compositions by mass percentage: C≤0.055%, Mn≤0.5%, Si≤1.0%, S≤0.025%, P≤0.030%, Cr 15.00~16.00%, Ni 3.50~5.50%, Cu 2.50~4.50%, Al≤0.050%, Nb 0.15~0.45%, Ti 0.5~1.0% and the remainder Fe. The present invention adds the strengthening alloy element Ti to form the intermetallic compound Ni 3 Ti plays a strengthening role; adding Cu and Al at the same time forms two nano-precipitation phases inside the martensite matrix, and the mechanical properties are improved through composite precipitation strengthening.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel, and in particular to a 520B precipitation hardened stainless steel ingot for ship power equipment and a preparation method thereof. Background Art

[0002] 520B is a martensitic precipitation hardening stainless steel with corrosion resistance, high strength, high hardness and good welding performance. It is widely used in major engineering structures such as aerospace, medical equipment and machinery manufacturing, and ship propulsion. However, with the continuous development of ship propulsion, higher design requirements are put forward for key parts of ship propulsion, especially high strength.

[0003] The current 520B precipitation hardening stainless steel, for example, patent CN201810862324.4 records the chemical composition by weight percentage (wt%): C: 0.042-0.060; Mn: ≤1.00; Si: ≤0.65; S: ≤0.005; P: ≤0.015; Cr: 13.0-14.5; Ni: 5.0-6.0; Mo: 1.30-1.80; Cu: 1.32-2.00; Nb: 0.27-0.45, and the rest is Fe. However, the mechanical properties of this stainless steel are difficult to meet the performance requirements. Therefore, how to improve the mechanical properties of 520B precipitation hardening stainless steel has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] The object of the present invention is to provide a 520B precipitation hardened stainless steel ingot for ship power equipment and a preparation method thereof. The stainless steel provided by the present invention has excellent mechanical properties.

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

[0006] The invention provides a 520B precipitation hardening stainless steel ingot for ship power equipment, wherein the chemical composition comprises, by mass percentage, C≤0.055%, Mn≤0.5%, Si≤1.0%, S≤0.025%, P≤0.030%, Cr 15.00-16.00%, Ni 3.50-5.50%, Cu 2.50-4.50%, Al≤0.050%, Nb 0.15-0.45%, Ti 0.5-1.0% and the balance Fe.

[0007] Preferably, the chemical composition includes, by mass percentage: C 0.045-0.055%, Mn 0.3-0.4%, Si0.1-0.8%, S≤0.015%, P≤0.015%, Cr 15.50-16.00%, Ni 4.0-5.30%, Cu3.0-4.20%, Al 0.025-0.05%, Nb 0.20-0.40%, Ti 0.6-0.9% and the balance Fe.

[0008] Preferably, the chemical composition includes, by mass percentage, C 0.048-0.052%, Mn 0.34-0.38%, Si 0.1-0.8%, S≤0.015%, P≤0.015%, Cr 15.60-15.80%, Ni 4.5-5.0%, Cu 3.5-4.0%, Al 0.030-0.045%, Nb 0.25-0.35%, Ti 0.7-0.8% and the balance Fe.

[0009] Preferably, in terms of mass percentage, 4.2%≤Cu+Ti≤4.5%.

[0010] Preferably, in terms of mass percentage, 3.5%≤Cu+Al≤3.8%.

[0011] The present invention also provides a method for preparing the 520B precipitation hardened stainless steel ingot for ship power equipment described in the above technical solution, comprising the following steps:

[0012] (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel;

[0013] (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a 520B precipitation hardened stainless steel ingot for ship power equipment.

[0014] Preferably, the vacuum refining furnace refining in step (1) comprises a VOD stage, a VCD stage, a VOH stage and a VD stage which are performed in sequence.

[0015] Preferably, the process parameters of the VOD stage include: vacuum degree 90-110 mbar, oxygen flow rate 500-550 m 3 / h, argon flow rate 1~5m 3 / h.

[0016] Preferably, the process parameters of the VCD stage include: vacuum degree ≤ 5 mbar, vacuum pumping time 10 to 15 min, argon flow rate 1 to 5 m 3 / h.

[0017] Preferably, the process parameters of the VOH stage include: temperature 1650-1670°C, oxygen flow rate 520-580m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h; the process parameters of the VD stage include: vacuum degree ≤1.0mbar, vacuum time>20min, argon flow rate 1~5m 3 / h.

[0018] The present invention provides a 520B precipitation hardening stainless steel ingot for ship power equipment, the chemical composition of which includes by mass percentage: C≤0.055%, Mn≤0.5%, Si≤1.0%, S≤0.025%, P≤0.030%, Cr 15.00-16.00%, Ni 3.50-5.50%, Cu 2.50-4.50%, Al≤0.050%, Nb 0.15-0.45%, Ti 0.5-1.0% and the balance Fe. The present invention can improve the mechanical properties of steel on the basis of omitting the Mo element through reasonable alloy component matching; wherein, the strengthening alloy element Ti is added to form an intermetallic compound Ni3Ti, thereby playing a strengthening role; excessive Cu is added and a small amount of Al is combined to form two nano-precipitation phases inside the martensite matrix, namely, a Cu-rich precipitation phase and a NiAl precipitation phase, and the mechanical properties of the steel are improved through composite precipitation strengthening. The experimental results show that the R p0.2 It is 836~887MPa, Rm is 933~1020MPa, A is 19~25%, Z is 58~71%, and HBW is 295~315. DETAILED DESCRIPTION

[0019] The invention provides a 520B precipitation hardening stainless steel ingot for ship power equipment, wherein the chemical composition comprises, by mass percentage, C≤0.055%, Mn≤0.5%, Si≤1.0%, S≤0.025%, P≤0.030%, Cr 15.00-16.00%, Ni 3.50-5.50%, Cu 2.50-4.50%, Al≤0.050%, Nb 0.15-0.45%, Ti 0.5-1.0% and the balance Fe.

[0020] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention comprises C≤0.055%, preferably 0.045-0.055%, more preferably C 0.048-0.052%, and most preferably 0.05%. In the present invention, the purity of the steel can be improved and the crack sensitivity can be improved by controlling the carbon element.

[0021] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention further comprises Mn≤0.5%, preferably 0.3-0.4%, more preferably 0.34-0.38%, and most preferably 0.35%. In the present invention, the manganese element can refine carbides and prevent grain growth, thereby improving the strength of the steel.

[0022] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention further comprises Si≤1.0%, preferably 0.1-0.8%, more preferably 0.3-0.6%, and most preferably 0.4-0.5%. In the present invention, the silicon element can remove oxygen in the steel, thereby further improving the strength of the steel.

[0023] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention also includes S≤0.025%, preferably ≤0.015%. In the present invention, the sulfur element is a harmful element, and by reducing its content, the performance of the steel can be further improved.

[0024] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention also includes P≤0.030%, preferably ≤0.015%. In the present invention, the phosphorus element is a harmful element, and by reducing its content, the performance of the steel can be further improved.

[0025] In terms of mass percentage, the 520B precipitation hardening stainless steel ingot for marine power equipment provided by the present invention further comprises Cr15.00-16.00%, preferably 15.50-16.00%, more preferably 15.60-15.80%, and most preferably 15.65%. In the present invention, the chromium is an important element for improving hardenability, and the precipitation of chromium carbide can improve tempering resistance and increase the strength of steel.

[0026] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention further comprises 3.50-5.50% Ni, preferably 4.0-5.30%, more preferably 4.5-5.0%, and most preferably 4.6-4.8%. In the present invention, the nickel can form an intermetallic compound Ni3Ti with Ti, precipitate in the grain boundary, play a pinning role, and greatly improve the strength of the steel.

[0027] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention also includes Cu2.50-4.50%, preferably 3.0-4.20%, more preferably 3.5-4.0%, and most preferably 3.6-3.8%. In the present invention, the Cu is combined with a small amount of Al to form two nano-precipitated phases inside the martensite matrix, namely, Cu-rich precipitation phase and NiAl precipitation phase, and the mechanical properties of the steel are improved through composite precipitation strengthening.

[0028] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention also includes Al≤0.050%, preferably 0.025-0.05%, more preferably 0.030-0.045%, and most preferably 0.035-0.040%. In the present invention, the aluminum element can be combined with excess copper to form two nano-precipitated phases inside the martensite matrix, namely, Cu-rich precipitation phase and NiAl precipitation phase, and the mechanical properties of the steel are improved through composite precipitation strengthening.

[0029] The 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention further comprises Nb 0.15-0.45%, preferably 0.20-0.40%, more preferably 0.25-0.35%, and most preferably 0.30%, by mass percentage. In the present invention, the Nb is a strong carbide forming element, and a small amount of addition can refine the grains through the precipitation of nano-carbides, thereby improving the strength and toughness of the steel.

[0030] In terms of mass percentage, the 520B precipitation hardened stainless steel ingot for marine power equipment provided by the present invention further comprises Ti 0.5-1.0%, preferably 0.6-0.9%, more preferably 0.7-0.8%, and most preferably 0.75%. In the present invention, the Ti is a strengthening alloy element that can form an intermetallic compound Ni3Ti to play a strengthening role.

[0031] In terms of mass percentage, the 520B precipitation hardening stainless steel ingot for marine power equipment provided by the present invention further comprises a balance of Fe. In the present invention, the Fe is a matrix element.

[0032] In the present invention, the total mass of Cu+Ti is preferably 4.2-4.5%, more preferably 4.3-4.4%, by mass percentage. The present invention can further improve the mechanical properties of the steel by controlling the contents of copper and titanium.

[0033] In the present invention, the total mass of Cu+Al is preferably 3.5-3.8%, more preferably 3.6-3.7%, by mass percentage. The present invention can further improve the mechanical properties of the steel by controlling the contents of copper and aluminum.

[0034] The present invention can improve the mechanical properties of steel on the basis of omitting the Mo element by reasonably matching alloy components; wherein, the strengthening alloy element Ti is added to form the intermetallic compound Ni3Ti, thereby playing a strengthening role; and an excessive amount of Cu is added together with a small amount of Al to form two nano-precipitated phases inside the martensite matrix, namely, a Cu-rich precipitation phase and a NiAl precipitation phase, and the mechanical properties of the steel are improved through composite precipitation strengthening.

[0035] The present invention also provides a method for preparing the 520B precipitation hardened stainless steel ingot for ship power equipment described in the above technical solution, comprising the following steps:

[0036] (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel;

[0037] (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a 520B precipitation hardened stainless steel ingot for ship power equipment.

[0038] The present invention has no particular limitation on the sources of the raw materials, and the raw materials may be prepared using commercially available products or well-known preparation methods known to those skilled in the art.

[0039] The invention sequentially performs electric arc furnace smelting and vacuum refining furnace refining on alloy raw materials to obtain molten steel.

[0040] In the present invention, the alloy raw materials are preferably scrap steel and alloy; the mass content of P in the scrap steel is preferably ≤0.030%; the mass content of S in the scrap steel is preferably ≤0.030%. The present invention selects pure scrap steel with both S and P ≤0.030% to improve the purity of molten steel.

[0041] The present invention has no particular limitation on the source of the alloy, and any high-purity alloy material well known to those skilled in the art may be used.

[0042] In the present invention, the electric arc furnace smelting preferably includes a melting period, an oxidation period and a reduction period performed in sequence.

[0043] The present invention has no particular limitation on the operation of the melting period, and operations well known to those skilled in the art may be adopted.

[0044] The present invention has no special limitation on the operation of the oxidation period, as long as the decarburization amount is ≥0.40%, C ≥0.70%, P ≤0.008%, and S ≤0.006%.

[0045] In the present invention, a reducing agent is preferably added during the reduction period; the reducing agent is preferably ferrosilicon powder; and the amount of the reducing agent is preferably 3-8 kg / t, more preferably 5 kg / t.

[0046] In the present invention, the temperature of the reduction period is preferably 1600-1700° C. The present invention has no particular limitation on the time of the reduction period, as long as the alloy composition is adjusted to the specified requirements.

[0047] After the arc furnace smelting is completed, the present invention preferably transfers the molten steel obtained by the arc furnace smelting into a tundish, and then removes the slag in the tundish.

[0048] The present invention has no special limitation on the operation of transferring into the tundish, and the operation well known to those skilled in the art may be adopted.

[0049] The present invention has no special limitation on the operation of deslagging in the ladle, and the residue amount can be ≤1.5kg / t.

[0050] In the present invention, the vacuum refining furnace refining preferably includes a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence.

[0051] In the present invention, the process parameters of the VOD stage preferably include: vacuum degree 90-110 mbar, vacuum time 10-15 min, oxygen flow rate 500-550 m 3 / h, argon flow rate 1~5m 3 / h, more preferably: vacuum degree 95-105mbar, vacuum time 13min, oxygen flow rate 510-540m 3 / h, argon flow rate 3~4m 3 / h.

[0052] In the present invention, the process parameters of the VCD stage preferably include: vacuum degree ≤ 5 mbar, vacuum pumping time 10 to 15 min, argon flow rate 1 to 5 m 3 / h, more preferably: vacuum degree 1-3 mbar, vacuum time 12-13 min, argon flow rate 3-4 m 3 / h.

[0053] In the present invention, the process parameters of the VOH stage preferably include: temperature 1650-1670°C, vacuum time 10-15 min, oxygen flow rate 520-580 m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h, more preferably: temperature 1660-1665°C, vacuum time 12min, oxygen flow rate 530-560m 3 / h, vacuum degree 370~400mbar, argon flow rate 3~4m 3 / h.

[0054] In the present invention, when the temperature of the VOH stage cannot meet the above requirements, it is preferred to add Al to increase the temperature. The present invention has no special limitation on the specific operation of using Al to increase the temperature, and the operation well known to those skilled in the art can be used.

[0055] In the present invention, the process parameters of the VD stage preferably include: vacuum degree ≤ 1.0 mbar, vacuum pumping time > 20 min, argon flow rate 1-5 m 3 / h, more preferably: vacuum degree 0.8-1.0 mbar, vacuum time 25-50 min, argon flow rate 3-4 m 3 / h.

[0056] The present invention can further improve the mechanical properties of steel by controlling the refining process parameters of the vacuum refining furnace.

[0057] After the refining in the vacuum refining furnace is completed, the present invention preferably transfers the molten steel obtained by the vacuum refining furnace into a ladle, and then calms it to obtain the molten steel.

[0058] In the present invention, the temperature of the molten steel when transferred into the ladle is preferably 1600-1650°C; the bottom of the ladle is preferably paved with a silicon-calcium deoxidizer; the amount of the silicon-calcium deoxidizer is preferably 1-5 Kg / t. The present invention uses a silicon-calcium deoxidizer to further deoxidize.

[0059] In the present invention, the sedation time is preferably 7 to 8 minutes.

[0060] After obtaining the molten steel, the present invention sequentially casts and anneals the molten steel to obtain a 520B precipitation hardened stainless steel ingot for ship power equipment.

[0061] The present invention has no special limitation on the process parameters of the casting, and operations familiar to those skilled in the art may be adopted.

[0062] In the present invention, the pouring is preferably carried out in an argon protective atmosphere.

[0063] After the pouring is completed, the present invention preferably demoulds the product obtained by pouring.

[0064] The present invention has no particular limitation on the demoulding operation, and any operation well known to those skilled in the art may be used.

[0065] In the present invention, the holding temperature of the annealing treatment is preferably 600-700° C.; the holding time of the annealing treatment is preferably 10-15 hours; and the cooling method of the annealing treatment is preferably air cooling after leaving the furnace.

[0066] The present invention has no particular limitation on other operations of the preparation method, and operations familiar to those skilled in the art may be adopted.

[0067] The preparation method provided by the invention has simple process.

[0068] 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.

[0069] Example 1

[0070] The chemical composition of 520B precipitation hardening stainless steel ingot for ship power equipment is calculated by mass percentage: C0.055%, Mn 0.5%, Si 1.0%, S 0.025%, P 0.030%, Cr 15.00%, Ni 5.50%, Cu 2.50%, Al 0.050%, Nb 0.45%, Ti 0.5% and the balance Fe;

[0071] In terms of mass percentage, Cu+Ti is 3.0%, Cu+Al is 2.55%;

[0072] The preparation method of the 520B precipitation hardened stainless steel ingot for ship power equipment comprises the following steps:

[0073] (1) S ≤ 0.030% and P ≤ 0.030% scrap steel and alloy are subjected to electric arc furnace smelting. The electric arc furnace smelting is carried out in sequence: melting period, oxidation period and reduction period; during the oxidation period, the decarburization amount is ≥ 0.40%, C ≥ 0.70%, P ≤ 0.008%, and S ≤ 0.006%; during the reduction period, 5 kg / t of ferrosilicon powder is added to the molten steel to form white slag, which is maintained for 20 minutes. The molten pool temperature is maintained at 1700°C, and then the molten steel is transferred to the tundish and the slag is removed in the tundish. , the residue amount is ≤1.5kg / t, and then it enters the VODC vacuum refining furnace for refining, and then the molten steel is transferred to the ladle at 1600℃, 2.3kg / t silicon calcium deoxidizer is first added to the ladle, and then it is calmed for 8 minutes to obtain molten steel; wherein, the VODC vacuum refining furnace refining is carried out in sequence of VOD stage, VCD stage, VOH stage and VD stage; the process parameters of the VOD stage are: vacuum degree 100mbar, vacuum time 13min, oxygen flow rate 530m 3 / h, argon flow rate 3.5m 3 / h; the process parameters of the VCD stage are: vacuum degree 4.5mbar, vacuum time 13min, argon flow rate 3.5m 3 / h; the process parameters of the VOH stage are: temperature 1650~1670℃, vacuum time 12min, oxygen flow rate 560m 3 / h, vacuum degree 400mbar, argon flow rate 3.5m 3 / h; the process parameters of the VD stage are: vacuum degree 1.0mbar, vacuum time 25min, argon flow rate 3.5m 3 / h;

[0074] (2) The molten steel obtained in step (1) is first poured in an argon atmosphere, then annealed at 680° C. for 13 h, and air-cooled to obtain a 520B precipitation-hardened stainless steel ingot for ship power equipment.

[0075] Example 2

[0076] The chemical composition of 520B precipitation hardening stainless steel ingot for ship power equipment is calculated by mass percentage: C0.055%, Mn 0.5%, Si 1.0%, S 0.025%, P 0.030%, Cr 16.00%, Ni 3.50%, Cu 4.50%, Al 0.050%, Nb 0.15%, Ti 1.0% and the balance Fe;

[0077] In terms of mass percentage, Cu+Ti is 5.50%, and Cu+Al is 4.55%. The preparation method is the same as that in Example 1.

[0078] Example 3

[0079] The chemical composition of 520B precipitation hardening stainless steel ingot for ship power equipment is calculated by mass percentage: C0.048%, Mn 0.38%, Si 0.1%, S 0.015%, P 0.015%, Cr 15.80%, Ni 4.5%, Cu 4.0%, Al 0.030%, Nb 0.35%, Ti 0.7% and the balance Fe;

[0080] In terms of mass percentage, Cu+Ti is 4.70%, and Cu+Al is 4.03%. The preparation method is the same as that in Example 1.

[0081] Example 4

[0082] The chemical composition of 520B precipitation hardening stainless steel ingot for ship power equipment is calculated by mass percentage: C0.052%, Mn 0.34%, Si 0.8%, S 0.015%, P 0.015%, Cr 15.60%, Ni 5.0%, Cu 3.5%, Al 0.045%, Nb 0.25%, Ti 0.8% and the balance Fe;

[0083] In terms of mass percentage, Cu+Ti is 4.3%, and Cu+Al is 3.545%. The preparation method is the same as that in Example 1.

[0084] Example 5

[0085] The contents of Cu, Al, Ti and Fe were changed on the basis of Example 4, while other conditions remained unchanged, wherein Cu was 2.5%, Al was 0.050%, and Ti was 0.9%;

[0086] In terms of mass percentage, Cu+Ti is 3.4% and Cu+Al is 2.55%.

[0087] Example 6

[0088] The contents of Cu, Al, Ti and Fe were changed on the basis of Example 4, while other conditions remained unchanged, wherein Cu was 4.1%, Al was 0.035%, and Ti was 0.6%;

[0089] In terms of mass percentage, Cu+Ti is 4.7% and Cu+Al is 4.135%.

[0090] Comparative Example 1

[0091] The chemical composition of the 520B precipitation hardening stainless steel ingot is, by mass percentage, C 0.042%, Mn 0.77%, Si 0.32%, S 0.003%, P 0.013%, Cr 13.58%, Ni 5.45%, Mo 1.43%, Cu 1.50, Nb 0.28% and the balance Fe, and other conditions are the same as in Example 1.

[0092] The 520B precipitation hardened stainless steel ingots prepared in Examples 1 to 6 and Comparative Example 1 were prepared into forgings in the following steps:

[0093] (1) performing a first heat treatment on the steel ingot after cutting to obtain a pretreated workpiece; the heating procedure of the first heat treatment is: heating to 650°C at a heating rate of 55°C / h for a first heat treatment of 7h; continuing to heat to 970°C at a heating rate of 55°C / h for a second heat treatment of 8h; continuing to heat to 1190°C at a heating rate of 35°C / h for a third heat treatment of 9h, followed by air cooling;

[0094] (2) subjecting the pretreated workpiece to forging deformation treatment, wherein the initial forging temperature is controlled at 1150° C. to obtain a forging blank, and then cooling to 930° C. at a furnace cooling rate of 50° C. / h, and performing final forging and air cooling to obtain a casting;

[0095] (3) The casting is subjected to rough machining and a second heat treatment in sequence to obtain a forging; wherein the program package of the second heat treatment is: high temperature tempering: 670°C, 13h; solution treatment: 1030°C, 8h, air cooling to below 30°C; aging treatment: 810°C, 2h, air cooling; 600°C, 8h, air cooling.

[0096] The mechanical properties of the forgings were tested, and the results are shown in Table 1 (the room temperature tensile test used a Φ5mm standard specimen, using a WE-300 tensile testing machine, the test temperature was 25°C, and the tensile strength Rm and yield strength R P0.2 , elongation after fracture A and cross-sectional shrinkage Z; room temperature tensile test method: GB / T228.1, hardness test method: GB / T231.1, delta ferrite test method: YB / T4402 method A, non-metallic inclusion test method: GB / T10561.1, A method, grain size test method: GB / T6394, metallographic test on forgings; Brinell hardness test method: test equipment: Brinell hardness tester, test principle: use a carbide ball of a certain diameter to press into the surface of the sample under the action of a specified load, keep it for a certain time and then remove the load. The Brinell hardness value is expressed as the load per unit indentation area, represented by the symbol HBW. The specific calculation formula is HBW = \frac{SF}{0.102\times\pi D(D^2-d^2)}HBW = 0.102×πD(D^2-d^2)SF, where F is the load (N), S is the indentation area of ​​the sample surface (mm2), D is the diameter of the indenter (mm), and d is the diameter of the indentation (mm). The size of the indentation diameter d is measured by a reading microscope, and then the hardness value is obtained by calculation or by looking up a special hardness table. It is customary not to mark the unit of Brinell hardness, and the results are shown in Table 2.

[0097] Table 1 Room temperature mechanical properties of forgings made from the steel ingots of Examples 1 to 6 and Comparative Example 1

[0098] project <![CDATA[R p0.2 / MPa]]> Rm / MPa A％ Z / ％ HBW standard 760～900 900 18 55 277～321 Example 1 852 961 22 60 310 Example 2 836 977 19 58 295 Example 3 875 992 23 63 305 Example 4 887 1020 25 71 315 Example 5 856 952 21 65 312 Example 6 836 933 20 64 309 Comparative Example 1 810 921 18 56 283

[0099] Table 2 Metallographic test results of forgings made from steel ingots of Examples 1 to 6 and Comparative Example 1

[0100] Metallographic test δ Ferrite (average value ≤) / (worst field ≤) Non-metallic inclusions (grain size) standard 5％ / 10％ ≤3 Example 1 3％ / 5％ 2.5 Example 2 3％ / 6％ 2.2 Example 3 3％ / 5％ 2.1 Example 4 2％4％ 2 Example 5 3％ / 5％ 2.2 Example 6 3％ / 5％ 2.3 Comparative Example 1 4％ / 6％ 2.7

[0101] As can be seen from Table 1, through Examples 1 to 6 and Comparative Example 1, it can be seen that the present invention can improve the mechanical properties of steel on the basis of omitting the Mo element through a reasonable combination of alloy components; it can be seen from Examples 1 and Examples 4 to 6 that the present invention can further improve the mechanical properties of steel by controlling the contents of copper and titanium and the contents of copper and aluminum.

[0102] It can be seen from the above embodiments and comparative examples that the stainless steel provided by the present invention has excellent mechanical properties.

[0103] 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. A 520B precipitation hardened stainless steel ingot for ship power equipment, the chemical composition by mass percentage includes: C≤0.055%, Mn≤0.5%, Si≤1.0%, S≤0.025%, P≤0.030%, Cr15.00~16.00%, Ni 3.50~5.50%, Cu 2.50~4.50%, Al≤0.050%, Nb 0.15~0.45%, Ti 0.5~1.0% and the balance of Fe; By mass percentage, 4.2%≤Cu+Ti≤4.5%; In terms of mass percentage, 3.5%≤Cu+Al≤3.8%.

2. The 520B precipitation hardened stainless steel ingot for ship power equipment according to claim 1, characterized in that: The chemical composition, by mass percentage, includes: C 0.045-0.055%, Mn 0.3-0.4%, Si0.1-0.8%, S≤0.015%, P≤0.015%, Cr 15.50-16.00%, Ni 4.0-5.30%, Cu3.0-4.20%, Al 0.025-0.05%, Nb0.20-0.40%, Ti 0.6-0.9% and the balance Fe.

3. The 520B precipitation hardened stainless steel ingot for ship power equipment according to claim 2, characterized in that: The chemical composition, by mass percentage, includes: C 0.048-0.052%, Mn 0.34-0.38%, Si 0.1-0.8%, S≤0.015%, P≤0.015%, Cr 15.60-15.80%, Ni 4.5-5.0%, Cu3.5-4.0%, Al 0.030-0.045%, Nb 0.25-0.35%, Ti 0.7-0.8% and the balance Fe.

4. The method for preparing the 520B precipitation hardened stainless steel ingot for marine power equipment according to any one of claims 1 to 3, comprising the following steps: (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel; (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a 520B precipitation hardened stainless steel ingot for ship power equipment.

5. The preparation method according to claim 4, characterized in that: The vacuum refining furnace refining in step (1) includes a VOD stage, a VCD stage, a VOH stage and a VD stage which are performed in sequence.

6. The preparation method according to claim 5, characterized in that: The process parameters of the VOD stage include: vacuum degree 90-110 mbar, oxygen flow rate 500-550 m 3 / h, argon flow rate 1~5m 3 / h.

7. The preparation method according to claim 5, characterized in that: The process parameters of the VCD stage include: vacuum degree ≤ 5 mbar, vacuum pumping time 10 to 15 min, argon flow rate 1 to 5 m 3 / h.

8. The preparation method according to claim 5, characterized in that: The process parameters of the VOH stage include: temperature 1650-1670°C, oxygen flow rate 520-580m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h; the process parameters of the VD stage include: vacuum degree ≤1.0mbar, vacuum time>20min, argon flow rate 1~5m 3 / h.