CN111139409A

CN111139409A - Heat-resistant cast steel and preparation method and application thereof

Info

Publication number: CN111139409A
Application number: CN202010070597.2A
Authority: CN
Inventors: 师帅; 梅林波; 孙林根; 安春香; 许存官; 王煜; 刘霞; 沈红卫
Original assignee: Shanghai Electric Power Generation Equipment Co Ltd
Current assignee: Shanghai Electric Power Generation Equipment Co Ltd
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2020-05-12
Also published as: US20230074936A1; WO2021147810A1; DE112021000275T5

Abstract

The invention provides a heat-resistant cast steel and a preparation method and application thereof, wherein the heat-resistant cast steel comprises the following elements in percentage by mass based on the total mass of the heat-resistant cast steel: 0.08 to 0.18 weight percent of C, 0.10 to 0.40 weight percent of Si, 0.30 to 0.70 weight percent of Mn, 9.80 to 10.70 weight percent of Cr, 3.00 to 3.50 weight percent of Co, 1.60 to 2.00 weight percent of W, 0.45 to 0.85 weight percent of Mo, 0.10 to 0.30 weight percent of V, 0.02 to 0.08 weight percent of Nb, 0.010 to 0.035 weight percent of N, 0.001 to 0.010 weight percent of B, less than or equal to 0.20 weight percent of Ni, and 79 to 85.5 weight percent of Fe. It can meet the use requirements of the turbine parts at 635 ℃ and below 635 ℃.

Description

Heat-resistant cast steel and preparation method and application thereof

Technical Field

The invention relates to the field of metal materials, in particular to heat-resistant cast steel and a preparation method and application thereof.

Background

A steam turbine in turbo machinery is also called a steam turbine engine and is a rotary steam power device, high-temperature and high-pressure steam passes through a fixed nozzle to become accelerated airflow and then is sprayed onto blades, so that a rotor provided with blade rows rotates, and simultaneously, the rotor does work outwards. Steam turbines are the main equipment of modern thermal power plants.

The steam temperature parameter of the thermal power coal-fired unit is improved, the unit efficiency can be improved, the consumption of fossil fuel is reduced, and energy conservation and emission reduction are realized. Whereas the turbine operating temperature is limited by the maximum service temperature of the materials of the critical components (cylinders, valves, rotors and blades, etc.).

High-temperature casting materials for parts such as cylinders and valve casings of steam turbines are developed from Cr-Mo steel into various 9-12% Cr ferrite steels; among the existing high-temperature casting materials, ZG12Cr10Mo1W1VNbN, ZG13Cr9Mo2Co1NiVNbNB and the like are available at present. Wherein the highest working temperature of ZG12Cr10Mo1W1VNbN steel grade cannot exceed 610 ℃, the highest working temperature of ZG13Cr9Mo2Co1NiVNbNB steel grade cannot exceed 625 ℃, and at present, no heat-resistant cast steel material for steam turbine castings, which can meet the working temperature of 635 ℃, exists.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a heat-resistant cast steel, a method of manufacturing the same, and use thereof, for solving the problems of the prior art.

To achieve the above objects and other related objects, the present invention includes the following technical solutions.

The invention provides heat-resistant cast steel, which comprises the following elements in percentage by mass based on the total mass of the heat-resistant cast steel:

C 0.08wt％～0.18wt％，Si 0.10wt％～0.40wt％，Mn 0.30wt％～0.70wt％，Cr9.80wt％～10.70wt％，Co 3.00wt％～3.50wt％，W 1.60wt％～2.00wt％，Mo 0.45wt％～0.85wt％，V 0.10wt％～0.30wt％，Nb 0.02wt％～0.08wt％，N 0.010wt％～0.035wt％，B0.001wt％～0.010wt％，Ni≤0.20wt％，Fe 79wt％～85.5wt％。

according to the technical scheme, the Fe accounts for 80.5-84.7 wt%.

According to the technical scheme, the Fe accounts for 81-83.8 wt%.

According to the technical solution of the heat-resistant cast steel described above in the present application, the heat-resistant cast steel further contains impurities including one or more of Al, P, S, Cu, Ti, and Sn.

According to the technical scheme of the heat-resistant cast steel, based on the total mass of the heat-resistant cast steel, the Al content is less than or equal to 0.030 wt%, the P content is less than or equal to 0.030 wt%, the S content is less than or equal to 0.020 wt%, the Cu content is less than or equal to 0.25 wt%, the Ti content is less than or equal to 0.030 wt%, and the Sn content is less than or equal to 0.030 wt%. More preferably, Al is less than or equal to 0.020 wt%, P is less than or equal to 0.020 wt%, S is less than or equal to 0.015 wt%, Cu is less than or equal to 0.15 wt%, Ti is less than or equal to 0.020 wt%, and Sn is less than or equal to 0.020 wt%.

According to the technical scheme of the heat-resistant cast steel, the heat-resistant cast steel comprises the following elements in percentage by mass based on the total mass of the heat-resistant cast steel: 0.10 to 0.16 weight percent of C, 0.20 to 0.30 weight percent of Si, 0.40 to 0.60 weight percent of Mn, 10.00 to 10.50 weight percent of Cr, 3.10 to 3.40 weight percent of Co, 1.65 to 1.90 weight percent of W, 0.55 to 0.75 weight percent of Mo, 0.15 to 0.25 weight percent of V, 0.03 to 0.07 weight percent of Nb, 0.015 to 0.030 weight percent of N, 0.002 to 0.008 weight percent of B, less than or equal to 0.10 weight percent of Ni, and the balance of Fe and impurity elements.

The invention also discloses the application of the heat-resistant cast steel in turbine machinery, in particular in the field of steam turbines as a casting material.

The reasons for limiting the mass percentage of each element of the heat-resistant cast steel provided by the invention are as follows:

carbon (C): the element C ensures hardenability. During tempering, after being combined with Mo, W and other elements, M is formed in grain boundary and martensite boundary₂₃C₆The carbide, C, in combination with Nb, V, etc., forms MX-type carbonitrides in the martensite. In the above M₂₃C₆After the carbide and MX-type carbonitride are separated and strengthened, the high-temperature strength can be improved. In addition to securing strength and toughness, C is also an indispensable element for suppressing the formation of harmful phases δ -ferrite and BN. In order to provide the heat-resistant cast steel of the present invention with desired strength and toughness, the C content should be 0.08% or more. However, if the amount is excessively added, the toughness is rather lowered, and M₂₃C₆When the carbide is excessively precipitated, the alloy strength is lowered, and the high-temperature strength in long-term use is impaired. Therefore, the C content is limited to 0.08% to 0.18%. Furthermore, the optimal content of the C element is limited to 0.10-0.16%;

silicon (Si): si element is an effective element for deoxidizing molten steel, and can improve the oxidation resistance of steel under the combined action of Si element and Cr element. However, Si promotes the precipitation of Laves phase, which is not favorable for the toughness of steel and adversely affects the creep strength. Therefore, the Si content is limited to 0.10% to 0.40%. Furthermore, the optimal content of Si element should be limited to 0.20-0.30%;

manganese (Mn): mn can remove oxygen and sulfur elements in molten steel and improve the hardenability of the steel. However, as the Mn content increases, the creep rupture strength decreases. Therefore, the Mn content is limited to 0.30 to 0.70%. Furthermore, the optimal content of Mn element should be limited to 0.40% -0.60%;

chromium (Cr): cr is mainly used in steel to improve oxidation resistance and corrosion resistance, and is used as M for improving high-temperature strength by precipitation strengthening₂₃C₆The carbide is an indispensable element. In order to achieve the above effects, the Cr content of the heat-resistant cast steel of the present invention is 9.80% at the lowest. However, if it exceeds 10.70%, δ -ferrite is easily generated, and the high-strength temperature and toughness are lowered. Therefore, the Cr content is limited to 9.80 to 10.70%. Furthermore, the optimal content of the Cr element is limited to 10.00-10.50%;

molybdenum (Mo): the addition of Mo mainly increases the tempering stability of the steel and strengthens the secondary hardening effect. And Mo is subjected to segregation at the grain boundary to improve the grain boundary binding force, so that the strength of the steel is improved, and the loss of toughness is reduced. However, excessive Mo causes the formation of a delta-ferrite phase and an intermetallic compound Laves phase, resulting in a significant decrease in toughness. Therefore, the Mo content is limited to 0.45-0.85%. Furthermore, the optimal content of the Mo element is limited to 0.55-0.75%;

tungsten (W): w for inhibition of M₂₃C₆The coarsening of the carbides is very effective and its effect exceeds that of the Mo element. W is added to replace part of Mo, so that the Mo equivalent (Mo +1/2W) is about 1.5%, the creep strength is best, and excessive delta-ferrite is not formed. When the amount of W added exceeds 2%, segregation tends to occur in the cast product. Therefore, the W content is limited to 1.60% to 2.00%. Furthermore, the optimal content of the W element is limited to 1.65-1.90%;

cobalt (Co): co, Mo and W are other important elements for distinguishing in the invention. Co can inhibit the generation of delta-ferrite after high-temperature normalizing or quenching of high-chromium ferrite steel, can fully play the solid solution strengthening role of Mo and W elements, and improves the toughness of the steel, which is very key to the heat-resistant cast steel with higher W content. The content of Co is limited to 3.00-3.50%. Further, the optimum content of Co should be limited to 3.10% to 3.40%.

Vanadium (V), niobium (Nb): v and Nb are easy to combine with C, N to form MX carbonitride in martensite, and fine dispersed precipitation greatly improves the strength and is stable in long-term creep and is a main strengthening phase. However, V, Nb too much will over fix the carbon content and reduce M₂₃C₆The precipitation amount of carbide causes a decrease in high-temperature strength. And Nb is easily segregated in the casting. Therefore, the V content is limited to 0.10-0.30%, and the Nb content is limited to 0.02-0.08%. Furthermore, the optimal content of the V element is limited to 0.15-0.25%, and the optimal content of the Nb element is limited to 0.03-0.07%;

nickel (Ni): the proper amount of Ni can increase the hardenability of the steel, inhibit the generation of delta-ferrite and BN, and improve the strength and the toughness at room temperature. However, the excessive addition is not favorable for the high-temperature creep property of the steel. Therefore, the content of Ni should be as low as possible, desirably not more than 0.20%, and optimally not more than 0.10%;

boron (B): b has a grain boundary strengthening effect and can be in M₂₃C₆Solid solution in carbide with M inhibition₂₃C₆The coarsening effect of the carbide can improve the high-temperature strength. The addition content should be at least 0.001%. However, if the content is 0.010% or more, the castability and weldability are impaired. Therefore, the B content is limited to 0.001% to 0.010%. Furthermore, the optimal content of the B element is limited to 0.002% -0.008%;

nitrogen (N): VN nitride can be separated out from the N and V, and the N and V are combined in a solid solution state, Mo and W, so that the high-temperature strength is improved, and the minimum content is 0.01%. However, when the amount of B added exceeds 0.04%, BN is easily precipitated by bonding with the B element, and the creep properties of the steel are impaired. Therefore, the content of N is limited to 0.010-0.035%. Further, the optimum content of N element should be limited to 0.015% to 0.030%.

In the heat-resistant cast steel for casting provided by the invention, the impurities comprise P and/or S and/or Al and/or Cu and/or Ti and/or Sn. S is a harmful impurity element in steel, and can reduce the thermoplasticity of the steel, influence the hot workability and reduce the corrosion resistance. The S element is segregated to the grain boundary, so that the bonding force of the grain boundary is reduced, and the high-temperature strength is reduced; p is also a harmful impurity element in the steel, and the steel can generate certain brittleness when the content of P is high; al element and N element easily form a precipitated AlN phase, which has adverse effects on the ductility and toughness and long-term creep property of steel; sn element is easy to be segregated in the grain boundary, and the high-temperature strength of the alloy is obviously reduced. P, S, Al, Cu, Ti and Sn as impurity elements have adverse effects on the mechanical properties of the heat-resistant cast steel and the alloy, and the content of the impurity elements is reduced as much as possible.

Table 1 shows the composition range median values of the heat-resistant cast steel for castings according to the invention in comparison with ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB specified in the trade standards JB/T11018-2010.

Table 1 chemical composition comparison (wt.%)

Element(s)	Heat-resistant cast steel CW2 of the present invention	ZG12Cr10Mo1W1VNbN	ZG13Cr9Mo2Co1NiVNbNB
				C	0.08～0.18	0.12	0.13
Si	0.10～0.40	0.30	0.25
				Mn	0.30～0.70	1.00	0.90
P	≤0.030	≤0.020	≤0.020
				S	≤0.020	≤0.010	≤0.010
Cr	9.80～10.70	9.70	9.25
				Co	3.00～3.50	-	1.10
W	1.60～2.00	1.00	-
				Mo	0.45～0.85	1.00	1.60
V	0.10～0.30	0.20	0.20
				Nb	0.02～0.08	0.06	0.06
N	0.010～0.035	0.050	0.0225
				B	0.001～0.010	-	0.0115
Ni	≤0.20	0.70	0.35
				Al	≤0.030	≤0.020	≤0.020

The invention also discloses a preparation method of the heat-resistant steel casting, which comprises the following steps:

determining the mixture ratio of the raw materials according to the mixture ratio of each component in the formula, and smelting the raw materials; refining, casting and forming; then quenching or normalizing treatment and finally tempering heat treatment.

According to the technical scheme of the preparation method, the quenching temperature is 1080-1180 ℃; the tempering temperature is 700-780 ℃, and the tempering is carried out once or for many times.

The invention also discloses the application of the heat-resistant cast steel for preparing the turbo machine.

The invention also discloses the application of the heat-resistant cast steel as a casting material in the field of steam turbines.

Compared with the existing casting material ZG12Cr10Mo1W1VNbN, the alloy provided by the invention has the advantages that Co and B are added to the components, the proportion of solid solution strengthening elements Mo and W is adjusted, the contents of Mn, N and Ni elements are reduced, and the high-temperature creep strength is improved. Compared with the existing casting material ZG13Cr9Mo2Co1NiVNbNB, the W element is added, the proportion of B and N is adjusted, the content of Cr and Co elements is improved, the content of Mn, Mo and Ni elements is reduced, the high-temperature creep strength and the oxidation resistance are improved, the service temperature of the casting material is increased, the heat efficiency of a generator set is improved, and the coal consumption and the carbon dioxide emission are reduced. The material grade of the novel heat-resistant cast steel is determined as ZG12Cr10Co3W2MoVNbNB, which is called CW2 for short.

The heat-resistant cast steel provided by the invention can be used for preparing turbine machinery, particularly turbine castings, and the prepared turbine castings have good high-temperature strength and oxidation resistance in high-temperature environments of 635 ℃ and below 635 ℃, and can meet the use requirements of turbines with the working temperatures of 635 ℃ and below 635 ℃.

Drawings

FIG. 1 is a graph showing the results of an oxidative weight gain test at 635 ℃ for materials of the examples of the present invention.

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.

Before the present embodiments are further described, it is to be understood that the scope of the invention is not limited to the particular embodiments described below; it is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Test methods in which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under conditions recommended by the respective manufacturers.

When numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition to the specific methods, devices, and materials used in the examples, any methods, devices, and materials similar or equivalent to those described in the examples may be used in the practice of the invention in addition to the specific methods, devices, and materials used in the examples, in keeping with the knowledge of one skilled in the art and with the description of the invention.

In the embodiment of the application, the raw material proportion is determined according to the proportion of each component in the formula, and the raw materials are smelted; refining, casting and forming; then quenching or normalizing treatment and finally tempering heat treatment.

The method comprises the following steps of taking industrial pure iron as a raw material as a source of Fe, taking elemental carbon as a raw material as a source of C, taking industrial silicon as a source of Si, electrolytic manganese as a source of Mn, metallic chromium and chromium nitride as sources of Cr, electrolytic cobalt as a source of Co, tungsten strips as a source of W, metallic vanadium as a source of V, niobium strips as a source of Nb, chromium nitride as a source of N, elemental boron as a source of B, and electrolytic nickel as a source of Ni.

Example 1

Smelting a certain amount of raw materials according to the theoretical calculation; refining again; casting and forming to form the steam turbine cylinder, quenching at 1150 ℃ and tempering at 730 ℃.

Example 2

Smelting a certain amount of raw materials according to the theoretical calculation; refining again; casting and forming to form the turbine valve casing, quenching at 1120 ℃, and tempering at 755 ℃.

The heat-resistant cast steels of examples 1 and 2 were subjected to chemical composition analysis, and the results are shown in Table 2, and both satisfy the chemical composition index requirements in terms of wt%.

Table 2 examples 1 and 2 chemical composition analysis results (wt.%) of heat-resistant cast steel for steam turbine castings

According to the trade standard JB/T11018-. Meanwhile, room temperature tensile tests were performed on the heat-resistant cast steel materials obtained in examples 1 and 2 in accordance with the GB/T228.1 standard, creep rupture strength tests were performed in accordance with the GB/T2039 standard, and then the creep rupture strength limit R at 635 ℃/10 ten thousand hours was derived in accordance with the extrapolation method specified in the GB/T2039 standard_u _{100000h/635℃}And the creep rupture strength at 635 ℃ for 10 ten thousand hours was compared with those of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB, and the results are shown in Table 3, wherein R in Table 3_p0.2For yield strength, R_mIs the tensile strength. It can be found that: strength (including R) obtained in examples 1 and 2 of the present invention_p0.2Yield strength and R_mTensile strength) meets the index requirements of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1 NiVNbNB. Meanwhile, the material provided by the invention has the creep rupture strength extrapolated value higher than 80MPa, the creep rupture strength extrapolated value of the comparative casting material ZG12Cr10Mo1W1VNbN is improved by more than 30%, the creep rupture strength extrapolated value of the comparative casting material ZG13Cr9Mo2Co1NiVNbNB is improved by more than 20%, the strengthening effect is obvious, and the use requirements of a steam turbine cylinder and a valve casing at 635 ℃ can be met.

TABLE 3 mechanical Properties of Heat-resistant cast steels for steam turbine castings in examples 1 and 2

The oxidation weight gain test at 635 ℃ is carried out on the samples 1 and 2, ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB, the samples of the four materials are placed in a flowing water vapor environment at 635 ℃ and 27MPa for a period of time as long as 2000h, and the weight gain change of each sample in the test period is tested, wherein the smaller the oxidation weight gain is, the better the oxidation resistance of the material is. The test results are shown in FIG. 1. As can be seen from FIG. 1, the oxidation resistance of examples 1 and 2 is significantly better than that of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1 NiVNbNB.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. The heat-resistant cast steel is characterized by comprising the following elements in percentage by mass based on the total mass of the heat-resistant cast steel:

2. the heat-resistant cast steel according to claim 1, characterized in that it further contains impurities including one or more of Al, P, S, Cu, Ti and Sn.

3. The heat-resistant cast steel according to claims 1 to 2, wherein the Al, P, S, Cu, Ti and Sn are, in mass percent based on the total mass of the heat-resistant cast steel: less than or equal to 0.030 wt% of Al, less than or equal to 0.030 wt% of P, less than or equal to 0.020 wt% of S, less than or equal to 0.25 wt% of Cu, less than or equal to 0.030 wt% of Ti and less than or equal to 0.030 wt% of Sn.

4. The heat-resistant cast steel according to claims 1 to 3, characterized by comprising the following elements in mass percent based on the total mass of the heat-resistant cast steel: 0.10 to 0.16 weight percent of C, 0.20 to 0.30 weight percent of Si, 0.40 to 0.60 weight percent of Mn, 10.00 to 10.50 weight percent of Cr, 3.10 to 3.40 weight percent of Co, 1.65 to 1.90 weight percent of W, 0.55 to 0.75 weight percent of Mo, 0.15 to 0.25 weight percent of V, 0.03 to 0.07 weight percent of Nb, 0.015 to 0.030 weight percent of N, 0.002 to 0.008 weight percent of B, less than or equal to 0.10 weight percent of Ni, and 81wt to 83.8 weight percent of Fe.

5. The heat-resistant cast steel according to claims 1 to 4, characterized in that it further contains impurities including one or more of Al, P, S, Cu, Ti and Sn.

6. The heat-resistant cast steel according to claims 1 to 5, wherein the Al, P, S, Cu, Ti and Sn are, in mass percent based on the total mass of the heat-resistant cast steel: less than or equal to 0.020 wt% of Al, less than or equal to 0.020 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.15 wt% of Cu, less than or equal to 0.020 wt% of Ti, and less than or equal to 0.020 wt% of Sn.

7. A method for preparing the heat-resistant cast steel as claimed in any one of claims 1 to 6, characterized in that the raw material ratio is determined according to the ratio of each component in the formula, and the raw materials are smelted, refined and cast to form; then quenching or normalizing treatment and finally tempering treatment.

8. The method according to claim 7, wherein the temperature of quenching or normalizing treatment is 1080 to 1180 ℃, and then the temperature of tempering treatment is 700 to 780 ℃, and the tempering treatment is carried out once or more times.

9. Use of the heat-resistant cast steel according to any one of claims 1 to 6 for the production of turbomachinery.

10. Use of the heat-resistant cast steel according to any one of claims 1 to 6 as a casting material in the field of steam turbines.