HEAT-RESISTANT CAST STEEL, AND PREPARATION METHOD AND USE THEREOF

Abstract

The present invention provides a heat-resistant cast steel, and a preparation method and use thereof. Based on the total mass of the heat-resistant cast steel, the heat-resistant cast steel includes the following elements in mass percentage: 0.08 wt %-0.18 wt % of C, 0.10 wt %-0.40 wt % of Si, 0.30 wt %-0.70 wt % of Mn, 9.80 wt %-10.70 wt % of Cr, 3.00 wt %-3.50 wt % of Co, 1.60 wt %-2.00 wt % of W, 0.45 wt %-0.85 wt % of Mo, 0.10 wt %-0.30 wt % of V, 0.02 wt %-0.08 wt % of Nb, 0.010 wt %-0.035 wt % of N, 0.001 wt %-0.010 wt % of B, <0.20 wt % of Ni and 79 wt %-85.5 wt % of Fe. The heat-resistant cast steel can satisfy the use requirements of turbine parts with a working temperature of 635° C. and below 635° C.

Claims

1. A heat-resistant cast steel, wherein based on the total mass of the heat-resistant cast steel, the heat-resistant cast steel comprises the following elements in mass percentage: 0.08 wt %-0.18 wt % of C, 0.10 wt %-0.40 wt % of Si, 0.30 wt %-0.70 wt % of Mn, 9.80 wt %-10.70 wt % of Cr, 3.00 wt %-3.50 wt % of Co, 1.60 wt %-2.00 wt % of W, 0.45 wt %-0.85 wt % of Mo, 0.10 wt %-0.30 wt % of V, 0.02 wt %-0.08 wt % of Nb, 0.010 wt %-0.035 wt % of N, 0.001 wt %-0.010 wt % of B, ≤0.20 wt % of Ni and 79 wt %-85.5 wt % of Fe.

2. The heat-resistant cast steel according to claim 1, wherein the heat-resistant cast steel further contains impurities, comprising one or more of Al, P, S, Cu, Ti and Sn.

3. The heat-resistant cast steel according to claim 2, wherein based on the total mass of the heat-resistant cast steel, the corresponding mass percentages of Al, P, S, Cu, Ti and Sn are: ≤0.030 wt % of Al, ≤0.030 wt % of P, ≤0.020 wt % of S, ≤0.25 wt % of Cu, ≤0.030 wt % of Ti and ≤0.030 wt % of Sn.

4. The heat-resistant cast steel according to claim 1, wherein based on the total mass of the heat-resistant cast steel, the heat-resistant cast steel comprises the following elements in mass percentage: 0.10 wt %-0.16 wt % of C, 0.20 wt %-0.30 wt % of Si, 0.40 wt %-0.60 wt % of Mn, 10.00 wt %-10.50 wt % of Cr, 3.10 wt %-3.40 wt % of Co, 1.65 wt %-1.90 wt % of W, 0.55 wt %-0.75 wt % of Mo, 0.15 wt %-0.25 wt % of V, 0.03 wt %-0.07 wt % of Nb, 0.015 wt %-0.030 wt % of N, 0.002 wt %-0.008 wt % of B, ≤0.10 wt % of Ni and 81 wt %-83.8 wt % of Fe.

5. The heat-resistant cast steel according to claim 4, wherein the heat-resistant cast steel further contains impurities, comprising one or more of Al, P, S, Cu, Ti and Sn.

6. The heat-resistant cast steel according to claim 5, wherein based on the total mass of the heat-resistant cast steel, the corresponding mass percentages of Al, P, S, Cu, Ti and Sn are: ≤0.020 wt % of Al, ≤0.020 wt % of P, ≤0.015 wt % of S, ≤0.15 wt % of Cu, ≤0.020 wt % of Ti and ≤0.020 wt % of Sn.

7. A preparation method of the heat-resistant cast steel according to claim 1, wherein proportioning of raw materials is determined according to proportioning of components in the formula, and the raw materials are melted, refined and poured into a mold; and then, quenching or normalizing is carried out, and finally tempering is carried out.

8. The preparation method according to claim 7, wherein the quenching or normalizing is carried out at a temperature of 1080-1180° C., and then the tempering is carried out at a temperature of 700-780° C., wherein the tempering is carried out one or more times.

9. Use of the heat-resistant cast steel according claim 1 in preparation of turbomachinery or as a casting material in the field of steam turbines.

10. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a graph showing results of an oxidation weight gain test of materials in embodiments of the present invention at 635° C.

DETAILED DESCRIPTION OF THE INVENTION

[0037] The implementations of the present invention are described below through specific embodiments. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in the specification.

[0038] Before further describing the specific implementations of the present invention, it should be understood that the protection scope of the present invention is not limited to the following specific implementation schemes. It should also be understood that the terms used in the embodiments of the present invention are intended to describe the specific implementation schemes, rather than to limit the protection scope of the present invention. The test methods that do not indicate specific conditions in the following embodiments usually follow the conventional conditions or the conditions recommended by the manufacturer.

[0039] When numerical ranges are given in the embodiments, it should be understood that unless otherwise indicated in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints are all optional. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, equipment and materials used in the embodiments, any method, equipment and material in the prior art similar or equivalent to those in the embodiments of the present invention may be used to implement the present invention according to the mastery of the prior art by those skilled in the art and the description of the present invention.

[0040] In the embodiments of the present application, proportioning of raw materials is determined according to proportioning of components in the formula; the raw materials are melted, refined and poured into a mold; and then, quenching or normalizing is carried out, and finally tempering is carried out.

[0041] Industrial pure iron is used as the raw material to serve as the source of Fe. Elemental carbon is used as the raw material to serve as the source of C. Industrial silicon is used as the raw material to serve as the source of Si. Electrolytic manganese is used as the raw material to serve as the source of Mn. Metallic chromium and chromium nitride are used as the raw materials to serve as the source of Cr. Electrolytic cobalt is used as the raw material to serve as the source of Co. Tungsten bars are used as the raw material to serve as the source of W. Metallic vanadium is used as the raw material to serve as the source of V. Niobium bars are used as the raw material to serve as the source of Nb. Chromium nitride is used as the raw material to serve as the source of N. Elemental boron is used as the raw material to serve as the source of B. Electrolytic nickel is used as the raw material to serve as the source of Ni.

Embodiment 1

[0042] According to the above theoretical calculation, certain amounts of raw materials were melted, refined, and poured into a mold to form a steam turbine cylinder, which was quenched at 1150° C. and tempered at 730° C.

Embodiment 2

[0043] According to the above theoretical calculation, certain amounts of raw materials were melted, refined, and poured into a mold to form a steam turbine valve casing, which was quenched at 1120° C. and tempered at 755° C.

[0044] Chemical composition analysis was carried out on the heat-resistant cast steel in Embodiment 1 and Embodiment 2. The analysis results are shown in Table 2 in wt %. Both satisfy the requirements of chemical composition indicators.

TABLE-US-00002 TABLE 2 Results of chemical composition analysis of heat-resistant cast steel for steam turbine castings in Embodiments 1 and 2 (wt %) Heat-resistant cast steel CW2 of the present invention Embodiment 1 Embodiment 2 C 0.08-0.18 0.15 0.11 Si 0.10-0.40 0.32 0.21 Mn 0.30-0.70 0.40 0.55 P ≤0.030 0.006 0.005 S ≤0.020 0.005 0.003 Cr 9.80-10.70 10.10 10.35 Co 3.00-3.50 3.15 3.35 Mo 0.45-0.85 0.58 0.69 W 1.60-2.00 1.85 1.70 V 0.10-0.30 0.15 0.21 Nb 0.02-0.08 0.04 0.06 N 0.010-0.035 0.015 0.025 B 0.001-0.010 0.0026 0.0060 Ni ≤0.20 0.10 0.05 Al ≤0.030 0.015 0.010

[0045] According to the industry standard JB/T 11018-2010, the mechanical property indicators of the existing casting materials ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB are listed in Table 3. The heat-resistant cast steel materials obtained in Embodiments 1 and 2 were subjected to the room temperature tensile test according to the standard GB/T 228.1, and subjected to the creep rupture strength test according to the standard GB/T 2039. Then, according to the extrapolation method specified in the standard GB/T 2039, the creep rupture strength limit R.sub.u 100,000 h/635° C. at 635° C./100,000 h was deduced, and compared with the creep rupture strength of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB at 635° C./100,000 h. The results are shown in Table 3. In Table 3, R.sub.p0.2 is the yield strength, and Rm is the tensile strength. As can be seen, the strengths (including R.sub.p0.2 yield strength and Rm tensile strength) obtained in Embodiment 1 and Embodiment 2 of the present invention satisfy the requirements of the indicators of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB. In addition, the extrapolated value of the creep rupture strength of the material of the present invention is higher than 80 MPa, which is increased by 30% or above as compared with the extrapolated value of the creep rupture strength of the casting material ZG12Cr10Mo1W1VNbN, and by 20% or above as compared with the extrapolated value of the creep rupture strength of ZG13Cr9Mo2Co1NiVNbNB. As a result, the material of the present invention has an obvious strengthening effect, and can satisfy the use requirements of the steam turbine cylinder and valve casing with a working temperature of 635° C.

TABLE-US-00003 TABLE 3 Mechanical properties of heat-resistant cast steel for steam turbine castings in Embodiments 1 and 2 635.sup.o C./ 100,000 h creep rupture strength R.sub.p0.2/MPa R.sub.m/MPa A/% Z/% KV.sub.2/J MPa Embodiment 1 595 746 17 47 35 85 Embodiment 2 560 724 17.5 51 37 88 ZG12Cr10Mo1W1VNbN ≥520 680~850 ≥15 ≥40 ≥35 65 ZG13Cr9Mo2Co1NiVNbNB ≥500 630~750 ≥15 ≥40 ≥30 71

[0046] Embodiments 1 and 2, ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB were subjected to the oxidation weight gain test at 635° C. Samples of the four materials were placed in a flowing steam environment of 635° C. and 27 MPa for a maximum time of 2000 h. The weight gain of each sample was measured in this time period. The smaller the oxidation weight gain, the better the oxidation resistance of the material. The test results are shown in FIG. 1. As can be seen from FIG. 1, the oxidation resistance of Embodiments 1 and 2 is significantly better than that of ZG12Cr10Mo1W1VNbN and ZG13Cr9Mo2Co1NiVNbNB.

[0047] The above embodiments merely exemplarily illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present invention should still be covered by the claims of the present invention.