Softening heat treatment method for high chromium cast iron

Abstract

To provide a softening heat treatment method for high-chromium cast iron, where the machinability of the high-chromium cast iron can be improved by controlling the Rockwell hardness HRC after heat treatment of the high-chromium cast iron to 40 or less.SOLUTION: A method for softening and heat-treating high-chromium cast iron is applied to high-chromium cast iron containing C in a range of 2.1% or more and 4.0% or less and Cr in a range of 30.0% or more and 40.0% or less in weight percentage, the method comprising a heating step in which the high-chromium cast iron is heated and held at a furnace temperature of 700°C or more and 750°C or less and a holding time of 10 hours or more, and a slow cooling step in which the high-chromium cast iron is slowly cooled to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, where the total time required in the heating step and the slow cooling step is 20 hours or more. The Rockwell hardness HRC of the high-chromium cast iron after the heat treatment by the softening heat treatment method is 40 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for softening heat treatment of high chromium cast iron. [Background technology]

[0002] High chromium cast iron is used as a wear-resistant material, and its main constituent elements are iron (Fe), carbon (C), and chromium (Cr). As the C and Cr content of high chromium cast iron increases, its wear resistance improves, but its machinability deteriorates. One of the factors that determines the machinability of high chromium cast iron is its hardness; the lower the hardness, the better the machinability. To improve the machinability of high chromium cast iron, heat treatment to reduce its hardness, i.e., softening heat treatment, is required.

[0003] Regarding high chromium cast iron with low Cr and C contents, for example, the conditions for heat treatment are disclosed in Non-Patent Document 1. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] P.Ortega-Cubillos et.al, Wear resistance of high chromium white cast iron for coal grinding rolls;Revista Facultad de Ingenieria, Universidad de Antioquia, No.76 pp.134-142,2015. Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve the wear resistance and corrosion resistance of high chromium cast iron, it is necessary to increase the C and Cr contents. However, when the Cr content or the C content is increased, softening heat treatment cannot be performed under known heat treatment conditions.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a softening heat treatment method that can improve the machinability of high chromium cast iron in which at least one of the Cr content and the C content is relatively high. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to provide a method for softening high chromium cast iron, which can make the Rockwell hardness HRC of high chromium cast iron 40 or less after heat treatment and improve the machinability of high chromium cast iron. As a result, they have found that by performing heat treatment at a specific furnace temperature for a specific period of time, the Rockwell hardness HRC of high chromium cast iron after heat treatment can be made 40 or less, and the machinability of high chromium cast iron can be improved, thereby arriving at the present invention.

[0008] That is, according to the present invention, The following softening heat treatment method for high chromium cast iron is provided.

[0009] [1] A softening heat treatment method for high chromium cast iron containing, by weight%, C in the range of 2.1% to 4.0% and Cr in the range of 30.0% to 40.0%, a heating step of heating and holding the high chromium cast iron at a furnace temperature of 700°C or higher and 750°C or lower for a holding time of 10 hours or longer; a slow cooling step of slowly cooling the high chromium cast iron to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, The total time required for the heating step and the slow cooling step is 20 hours or more, A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron after heat treatment by the softening heat treatment method has a Rockwell hardness HRC of 40 or less. [2] A softening heat treatment method for high chromium cast iron containing, by weight%, C in the range of 4.0% to 7.0% and Cr in the range of 20.0% to 40.0%, a primary heating step of heating and holding the high chromium cast iron at a furnace temperature of 900°C or higher and 1100°C or lower for 10 hours or longer; a secondary heating step in which, after the primary heating step, the high chromium cast iron is further heated and held at a furnace temperature of 700°C or higher and 750°C or lower for a holding time of 10 hours or longer; a slow cooling step of slowly cooling the high chromium cast iron to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron after heat treatment by the softening heat treatment method has a Rockwell hardness HRC of 40 or less. [3] The softening heat treatment method for high chromium cast iron according to the above [1] or [2], A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron further contains, by weight, Si in the range of 0% to 2.0%, Mn in the range of 0% to 5.0%, Fe in the range of 40.0% to 77.9%, and unavoidable impurities in the range of 0% to 0.1%. [4] A softening heat treatment method for high chromium cast iron according to any one of the above [1] to [3], A method for softening heat treatment of high chromium cast iron, wherein the high chromium cast iron further contains one or more elements selected from the group consisting of Mo, W, Nb, V, Co, Ni, Cu, Ti, and rare earth elements. [5] A softening heat treatment method for high chromium cast iron according to any one of the above [1] to [4], After the slow cooling step, a processing step of processing the high chromium cast iron; After the processing step, a quenching step is performed in which the high chromium cast iron is heated and held at a furnace temperature of 850°C to 1200°C for a holding time of 1 hour to 12 hours, and then cooled at a cooling rate of 50°C / min or more to perform quenching. The method for softening heat treatment of high chromium cast iron further comprises: [6] The softening heat treatment method for high chromium cast iron according to the above [5], The method for softening high chromium cast iron, wherein the high chromium cast iron after the quenching step has a Rockwell hardness HRC of 55 or more. [7] The softening heat treatment method for high chromium cast iron according to the above [5] or [6], The method for softening heat treatment of high chromium cast iron, wherein the high chromium cast iron after the quenching step is a part of a pump or a part of a crusher. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a softening heat treatment method for high chromium cast iron, which can make the Rockwell hardness of the high chromium cast iron after heat treatment HRC 40 or less and improve the machinability of the high chromium cast iron. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the relationship between the temperature and time of heat treatment in a heating step and a slow cooling step. [Figure 2] FIG. 1 is a diagram showing the relationship between the temperature and time of heat treatment in a heating step and a slow cooling step. [Figure 3] FIG. 10 is a diagram showing the relationship between the temperature and time of heat treatment in the quenching step. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are schematic diagrams and do not correspond to the actual dimensional ratios. Note that "~" between numbers in the text indicates "above" to "below" unless otherwise specified.

[0013] The softening heat treatment method of this embodiment is a method for softening high chromium cast iron containing, by weight, 2.1% to 4.0% C and 30.0% to 40.0% Cr, and includes a heating step of heating and holding the high chromium cast iron at a furnace temperature of 700°C to 750°C for 10 hours or more, and a slow cooling step of slowly cooling the high chromium cast iron to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, the total time required for the heating step and the slow cooling step being 20 hours or more. The high chromium cast iron after heat treatment by this softening heat treatment method has a Rockwell hardness of 40 or less (HRC). FIG. 1 shows the relationship between the temperature and time in the heating step and the slow cooling step in the softening heat treatment method for high chromium cast iron according to this embodiment.

[0014] As described above, when high chromium cast iron with a Cr content of 30.0 wt% or more or a C content of 2.1 wt% or more is heat treated under conventional conditions, its Rockwell hardness (HRC) usually exceeds 40, making it difficult to machine. The softening heat treatment method for high chromium cast iron in this embodiment includes a heating step in which the high chromium cast iron is heated and held at a furnace temperature of 700°C to 750°C for a holding time of 10 hours or more, and a slow cooling step in which the high chromium cast iron is slowly cooled to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less. By setting the total time required for the heating step and the slow cooling step to 20 hours or more, the Rockwell hardness (HRC) of the high chromium cast iron after heat treatment decreases to 40 or less, thereby improving the machinability of the high chromium cast iron.

[0015] The reason for this is unclear, but it is thought that heating and holding high-chromium cast iron at a furnace temperature of 700°C to 750°C for a holding time of 10 hours or more causes the carbon contained in the ferrite phase of the high-chromium cast iron to precipitate. This allows the iron to achieve both improved wear resistance and corrosion resistance due to the inclusion of chromium, as well as machinability.

[0016] The composition of the high chromium cast iron in this embodiment may be the raw material blending ratio at the time of production, or may be the composition measured by component analysis after production. As the component analysis method, known analytical methods can be used, such as energy dispersive X-ray spectroscopy (SEM-EDS), optical emission spectroscopy (OES), inductively coupled plasma analysis (ICP), etc.

[0017] In the softening heat treatment method for high chromium cast iron according to this embodiment, the temperature inside the furnace in the heating step is 700° C. or higher and 750° C. or lower, preferably 710° C. or higher and 750° C. or lower, and more preferably 720° C. or higher and 750° C. or lower. By setting the furnace temperature within the above range, the machinability of the high chromium cast iron can be improved.

[0018] In the softening heat treatment method for high chromium cast iron according to the present embodiment, the lower limit of the holding time in the heating step is 10 hours or more, preferably 12 hours or more, and more preferably 15 hours or more. By setting the lower limit of the holding time to be equal to or greater than the above lower limit, the machinability of the high chromium cast iron can be improved. Moreover, the upper limit of the holding time is preferably 48 hours or less, more preferably 36 hours or less, and even more preferably 24 hours or less. By setting the upper limit of the holding time to the above upper limit or less, it is possible to more suitably improve the productivity of high chromium cast iron.

[0019] In the softening heat treatment method for high chromium cast iron of this embodiment, the cooling rate of the high chromium cast iron in the slow cooling step is 100°C / hour or less, preferably 50°C / hour or less, and more preferably 30°C / hour or less. By keeping the upper limit of the cooling rate below the upper limit, the machinability of the high chromium cast iron can be made more suitable. The lower limit of the cooling rate is not particularly limited, but may be, for example, 5°C / hour or more, 10°C / hour or more, or 20°C / hour or more. The cooling method at this time is not particularly limited, and any known cooling method can be used, but slow cooling in a furnace is preferred.

[0020] In the softening heat treatment method for high chromium cast iron of this embodiment, the total time required for the heating step and the slow cooling step is 20 hours or more, preferably 25 hours or more, and more preferably 30 hours or more. By making the total time required for the heating step and the slow cooling step equal to or greater than the lower limit, the hardness of the high chromium cast iron is reduced, and machinability can be improved. Furthermore, the upper limit of the total required time is not particularly limited, but may be, for example, 60 hours or less, 50 hours or less, or 40 hours or less.

[0021] The softening heat treatment method for high chromium cast iron according to this embodiment includes a primary heating step in which the high chromium cast iron is heated to a furnace temperature of 900°C to 1100°C for at least 10 hours. The secondary heating step, after the primary heating step, further heats the high chromium cast iron to a furnace temperature of 700°C to 750°C for at least 10 hours. The secondary heating step also includes a slow cooling step in which the high chromium cast iron is slowly cooled to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less. The high chromium cast iron after the softening heat treatment has a Rockwell hardness (HRC) of 40 or less. This improves the machinability of the high chromium cast iron. FIG. 2 shows the relationship between the temperature and time in the heating step and the slow cooling step in the softening heat treatment method for high chromium cast iron according to this embodiment.

[0022] The reason for this is unclear, but it is thought that the carbon contained in the austenite phase precipitates when high-chromium cast iron is heated and held at a furnace temperature of 900°C to 1100°C for 10 hours or more in the primary heating process. The carbon contained in the ferrite phase of the high-chromium cast iron is then precipitated by heating and holding at a furnace temperature of 700°C to 750°C for 10 hours or more in the secondary heating process. This reduces the hardness of the high-chromium cast iron and improves its machinability.

[0023] In the softening heat treatment method for high chromium cast iron of this embodiment, the temperature inside the furnace in the primary heating step is 900° C. or higher and 1100° C. or lower, preferably 950° C. or higher and 1100° C. or lower, and more preferably 950° C. or higher and 1050° C. or lower. By setting the furnace temperature within the above numerical range, the machinability of the high chromium cast iron can be improved.

[0024] In the softening heat treatment method for high chromium cast iron of this embodiment, the upper limit of the cooling rate when transitioning from the primary heating step to the secondary heating step is preferably 100°C / hour or less, more preferably 50°C / hour or less, and even more preferably 30°C / hour or less. By setting the upper limit of the cooling rate to the above upper limit or less, the machinability of the high chromium cast iron can be improved. Furthermore, the lower limit of the cooling rate when transitioning from the primary heating step to the secondary heating step is not particularly limited, but is, for example, 5°C / hour or more, 10°C / hour or more, or 15°C / hour or more.

[0025] In the softening heat treatment method for high chromium cast iron of this embodiment, the temperature inside the furnace in the secondary heating step is 700° C. or higher and 750° C. or lower, preferably 710° C. or higher and 750° C. or lower, and more preferably 720° C. or higher and 750° C. or lower. By setting the temperature inside the furnace within the above numerical range, the machinability of the high chromium cast iron can be improved.

[0026] In the softening heat treatment method for high chromium cast iron of this embodiment, the lower limit values ​​of the holding times in the primary heating step and the secondary heating step are both 10 hours or more, preferably 12 hours or more, and more preferably 15 hours or more. By setting the lower limit values ​​of the holding times to be equal to or greater than the above lower limit values, the machinability of the high chromium cast iron can be improved. Moreover, the upper limit of the holding time is preferably 48 hours or less, more preferably 36 hours or less, and even more preferably 24 hours or less. By making the upper limit of the holding time equal to or less than the upper limit, the machinability and productivity of the high chromium cast iron can be made more suitable.

[0027] In the softening heat treatment method for high chromium cast iron of this embodiment, the cooling rate of the high chromium cast iron in the slow cooling step is 100°C / hour or less, preferably 50°C / hour or less, and more preferably 30°C / hour or less. By keeping the upper limit of the cooling rate below the upper limit, the machinability of the high chromium cast iron can be improved. The lower limit of the cooling rate is not particularly limited, but may be, for example, 5°C / hour or more, 10°C / hour or more, or 20°C / hour or more. The cooling method at this time is not particularly limited, and any known cooling method can be used, but slow cooling in a furnace is preferred.

[0028] In the softening heat treatment method for high chromium cast iron of this embodiment, it is preferable that the high chromium cast iron further contains, by weight %, 0% to 2.0% Si, 0% to 5.0% Mn, 40.0% to 77.9% Fe, and 0% to 0.1% unavoidable impurities. The contents of these elements can be appropriately determined depending on the application of the high chromium cast iron according to this embodiment.

[0029] Each component will be described in detail below.

[0030] Si: 0% or more and 2.0% or less (weight%) Silicon is an element that improves the fluidity of molten high-chromium cast iron and acts as a deoxidizer during melting. Therefore, the Si content is preferably 0% to 2.0% by weight, more preferably 0.2% to 1.5%, and even more preferably 0.3% to 1.0%. By setting the Si content within the above numerical range, the strength of the martensite phase that is formed when the high-chromium cast iron is quenched can be increased.

[0031] Mn: 0% or more and 5.0% or less (weight%) The Mn content is preferably 0% to 5.0% by weight, more preferably 0.3% to 3.0%, and even more preferably 0.5% to 2.0%. By setting the Mn content within the above range, the strength of the martensite phase formed when high chromium cast iron is quenched can be increased, and the corrosion resistance of the quenched product can be improved.

[0032] Fe: 40.0% or more and 77.9% or less (weight%) The Fe content is preferably 40.0% or more and 77.9% or less by weight, more preferably 45.0% or more and 77.5% or less, and even more preferably 50.0% or more and 77.0% or less. By keeping the Fe content within the above numerical range, it is possible to improve the machinability of the high chromium cast iron without reducing the wear resistance and corrosion resistance.

[0033] Inevitable impurities: 0% to 0.1% (by weight) Inevitable impurities are elements that cannot be completely removed from the raw materials used to produce high chromium cast iron. Examples of such unavoidable impurities include P, S, B, Al, Pb, and Zn. The content of unavoidable impurities is preferably 0% to 0.1% by weight, more preferably 0% to 0.05%, and even more preferably 0% to 0.01%. By keeping the content of unavoidable impurities within the above range, it is possible to prevent performance degradation, including embrittlement of the high chromium cast iron and a decrease in corrosion resistance.

[0034] In the softening heat treatment method for high chromium cast iron of this embodiment, it is preferable that the high chromium cast iron further contains one or more elements selected from the group consisting of Mo, W, Nb, V, Co, Ni, Cu, Ti, and rare earth elements. By including the above elements in the high chromium cast iron of this embodiment, the corrosion resistance and toughness of a quench-formed product using the high chromium cast iron of this embodiment can be further improved, and cracking during quench-forming can be prevented. The contents of these elements can be determined as appropriate depending on the application of the high chromium cast iron according to this embodiment, but for example, the total of the above elements is 0% or more and 1.0% or less by weight.

[0035] Although various elements have been exemplified above, other elements may be added in addition to the elements exemplified above as long as the effect of this embodiment is not impaired. The composition of the various elements may be the raw material blending ratio during production, or may be a composition measured by component analysis after production. Component analysis can be performed using known analytical methods, such as energy dispersive X-ray spectroscopy (SEM-EDS), optical emission spectroscopy (OES), and inductively coupled plasma analysis (ICP).

[0036] The softening heat treatment method for high chromium cast iron of this embodiment preferably further includes, after the slow cooling step, a processing step of processing the high chromium cast iron, and, after the processing step, a quenching step of heating and holding the high chromium cast iron at a furnace temperature of 850°C to 1200°C for a holding time of 1 hour to 12 hours, and then cooling at a cooling rate of 50°C / min or more to perform quenching.

[0037] (Processing process) In the softening heat treatment method for high chromium cast iron according to the present embodiment, the high chromium cast iron is finally processed into a desired shape in the processing step. Processing can be performed by a conventionally known method, such as lathe processing, milling, cutting such as drilling, grinding, polishing, and electric discharge machining.

[0038] (Quenching process) In the softening heat treatment method for high chromium cast iron according to this embodiment, the quenching step is a step in which the high chromium cast iron processed in the processing step is further heated and cooled to harden the high chromium cast iron. As shown in Fig. 3, the temperature conditions in the quenching step are preferably such that the high chromium cast iron is heated and held at a furnace temperature of 850°C to 1200°C for a holding time of 1 hour to 12 hours, and then cooled at a cooling rate of 50°C / min or more.

[0039] In the softening heat treatment method for high chromium cast iron of this embodiment, the temperature inside the furnace in the quenching step is preferably 850° C. or higher and 1200° C. or lower, more preferably 900° C. or higher and 1150° C. or lower, and even more preferably 950° C. or higher and 1100° C. By keeping the furnace temperature within the above numerical range, it is possible to improve the hardness of the quenched high chromium cast iron product without reducing its wear resistance and corrosion resistance.

[0040] In the softening heat treatment method for high chromium cast iron according to this embodiment, the lower limit of the holding time in the quenching step is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 4 hours or more. By setting the lower limit of the holding time to be equal to or greater than the above lower limit, it is possible to improve the hardness of the quenched high chromium cast iron product without reducing its wear resistance and corrosion resistance. The upper limit of the holding time is preferably 12 hours or less, more preferably 10 hours or less, and even more preferably 8 hours or less. By keeping the upper limit of the holding time at or below the upper limit, the wear resistance and corrosion resistance of the quench-formed product of high chromium cast iron can be made more favorable.

[0041] In the softening heat treatment method for high chromium cast iron according to the present embodiment, the lower limit of the cooling rate of the high chromium cast iron in the quenching step is preferably 50°C / min or more, more preferably 60°C / min or more. The cooling rate is preferably at least 70°C / min, and more preferably at least 70°C / min. By ensuring that the lower limit of the cooling rate is at least the above lower limit, it is possible to improve the hardness of the quench-formed high chromium cast iron product without reducing the wear resistance and corrosion resistance. The upper limit of the cooling rate is preferably 150°C / min or less, more preferably 140°C / min or less, and even more preferably 130°C / min or less. By keeping the upper limit of the cooling rate below the upper limit, the wear resistance and corrosion resistance of the quench-formed product of high chromium cast iron can be made more favorable. The cooling method at this time is not particularly limited, and any known cooling method can be used, but forced air cooling is preferred.

[0042] In the softening heat treatment method for high chromium cast iron of this embodiment, the lower limit of the Rockwell hardness HRC of the high chromium cast iron after the quenching step is preferably not less than 55, more preferably not less than 57, and even more preferably not less than 60. By having a Rockwell hardness HRC not less than the above lower limit, the wear resistance and corrosion resistance of the quenched product of high chromium cast iron can be made more favorable. The upper limit of the Rockwell hardness HRC is not particularly limited, but is, for example, 100 or less.

[0043] In the softening heat treatment method for high chromium cast iron according to the present embodiment, the high chromium cast iron after the quenching step is preferably one that operates while in contact with other parts or substances such as liquids, solids, or liquid-solid mixtures, particularly pump parts or crusher parts.

[0044] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations can also be adopted. [Example]

[0045] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0046] The methods for melting, casting, heat treating, quenching and measuring the hardness of high chromium cast iron to confirm the effects of this embodiment will be described in detail below.

[0047] [Melting and casting of high chromium cast iron] High-chromium cast iron was melted using a high-frequency vacuum furnace. Fe, C, Cr, Si, Mn, and other elements with a purity of 99.9% (by weight) were mixed in the composition shown in Table 1 to obtain a total weight of 2.8 kg. The mixture was then poured into a magnesia crucible and heated and melted under an argon atmosphere. After melting, the molten liquid was cast into a sand mold to produce a high-chromium cast iron sample measuring 140 mm long, 49 mm wide, and 12 mm high.

[0048] [Annealing heat treatment of high chromium cast iron] The high chromium cast iron samples prepared in the above "Melting and casting of high chromium cast iron" were annealed and heat treated using an electric furnace in an air atmosphere under the furnace temperature program shown in Figure 1 or Figure 2 and the temperature conditions shown in Table 1, thereby obtaining high chromium cast iron samples after annealing and heat treatment.

[0049] [Quenching heat treatment of high chromium cast iron] The annealed high-chromium cast iron samples prepared in the above [Annealing heat treatment of high-chromium cast iron] were machined by electrical discharge machining to a size of 20 mm length x 20 mm width x 6 mm height.The annealed high-chromium cast iron samples prepared in the above [Annealing heat treatment of high-chromium cast iron] were then quenched in an electric furnace under the temperature program shown in Figure 3 and the temperature conditions shown in Table 2 in an air atmosphere, thereby obtaining quenched high-chromium cast iron samples.

[0050] [Hardness measurement of high chromium cast iron] The high-chromium cast iron samples prepared in the above [Annealing Heat Treatment of High-Chromium Cast Iron] and [Quenching Heat Treatment of High-Chromium Cast Iron] after annealing and quenching heat treatment were polished to test pieces measuring 20 mm in length, 20 mm in width, and 5.5 mm in height. The hardness of the test pieces was measured at nine points using a Rockwell (HRC) hardness tester under conditions of a load of 150 kgf and a load holding time of 15 seconds. Of the nine measurement data points, the maximum and minimum hardness data were excluded, and the average value of seven points was used as the hardness data for each test piece.

[0051] Example 1 As shown in Table 1, high-chromium cast iron Fe61.1C2.75Cr35.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 10 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 39.9. In Example 1, the total time required at a furnace temperature of 600°C to 750°C was 20 hours.

[0052] (Comparative Example 1) As shown in Table 1, high-chromium cast iron Fe61.1C2.75Cr35.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 2 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 42.7. In Comparative Example 1, the total time required at a furnace temperature of 600°C to 750°C was 12 hours.

[0053] Example 2 As shown in Table 1, high-chromium cast iron Fe61.1C2.75Cr35.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 24 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 36.5. In Example 2, the total time required at a furnace temperature of 600°C to 750°C was 34 hours. Then, using the electric furnace again, quenching was performed under the conditions of a heating rate of 350°C / hour, a furnace temperature of 1050°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 64.6 (HRC).

[0054] (Comparative Example 2) As shown in Table 1, high-chromium cast iron Fe61.1C2.75Cr35.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 850°C for a holding time of 2 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. The resulting Rockwell hardness HRC was 44.1. In Comparative Example 2, the total time required at a furnace temperature of 600°C to 750°C was 10 hours.

[0055] Example 3 As shown in Table 1, high-chromium cast iron Fe59.6C2.75Cr35.0Si0.4Mn0.75Ni0.5Mo1.0 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 24 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. The resulting Rockwell hardness (HRC) was 38.6. In Example 3, the total time required at furnace temperatures of 600°C to 750°C was 34 hours. Thereafter, the specimen was again quenched in an electric furnace under the conditions of a heating rate of 350°C / hour, a furnace temperature of 1050°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 64.1 (HRC).

[0056] (Comparative Example 3) As shown in Table 1, high-chromium cast iron Fe59.6C2.75Cr35.0Si0.4Mn0.75Ni0.5Mo1.0 (wt%) was heat-treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. The resulting Rockwell hardness HRC was 43.7. In Comparative Example 3, the total time required at a furnace temperature of 600°C to 750°C was 10 hours.

[0057] Example 4 As shown in Table 1, high-chromium cast iron Fe59.06C2.79Cr35.0Si0.4Mn0.75Ni0.5Mo1.0Nb0.5 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 24 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. The resulting Rockwell hardness (HRC) was 37.9. In Example 4, the total time required at furnace temperatures of 600°C to 750°C was 34 hours. Then, using the electric furnace again, quenching was performed under the conditions of a heating rate of 350°C / hour, a furnace temperature of 1050°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 64.6 (HRC).

[0058] Comparative Example 4 As shown in Table 1, high-chromium cast iron Fe59.06C2.79Cr35.0Si0.4Mn0.75Ni0.5Mo1.0Nb0.5 (wt%) was heat-treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 40.6. In Comparative Example 4, the total time required at a furnace temperature of 600°C to 750°C was 10 hours.

[0059] Example 5 As shown in Table 1, high-chromium cast iron Fe66.1C2.75Cr30.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 750°C for a holding time of 24 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 39.7. In Example 5, the total time required at a furnace temperature of 600°C to 750°C was 34 hours. Then, using the electric furnace again, quenching was performed under the conditions of a heating rate of 350°C / hour, a furnace temperature of 1050°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 65.4 (HRC).

[0060] (Comparative Example 5) As shown in Table 1, high-chromium cast iron Fe66.1C2.75Cr30.0Si0.4Mn0.75 (wt%) was heat-treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 40.9. In Comparative Example 5, the total time required at a furnace temperature of 600°C to 750°C was 10 hours.

[0061] Example 6 As shown in Table 1, high-chromium cast iron Fe65.2C4.5Cr28.0Si0.8Mn1.5 (wt%) was first heat-treated in an electric furnace at a furnace temperature of 950°C for 24 hours, and then slowly cooled to 750°C at a cooling rate of 30°C / hour. It was then heat-treated at a furnace temperature of 750°C for 24 hours, and then slowly cooled to room temperature at a cooling rate of 30°C / hour. The resulting Rockwell hardness (HRC) was 38.0. Then, using the electric furnace again, quenching was performed under the conditions of a heating rate of 350°C / hour, a furnace temperature of 950°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 69.1 (HRC).

[0062] (Comparative Example 6) As shown in Table 1, high-chromium cast iron Fe65.2C4.5Cr28.0Si0.8Mn1.5 (wt%) was heat treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness (HRC) was 47.5.

[0063] Example 7 As shown in Table 1, high-chromium cast iron Fe65.0C4.55Cr28.15Si0.8Mn1.5 (wt%) was first heat-treated in an electric furnace at a furnace temperature of 950°C for 24 hours, and then slowly cooled to 750°C at a cooling rate of 30°C / hour. This was followed by a secondary heat-treatment at a furnace temperature of 750°C for 24 hours, and then slowly cooled to room temperature at a cooling rate of 30°C / hour. The resulting Rockwell hardness (HRC) was 37.1. Thereafter, the specimen was again quenched in an electric furnace under the conditions of a heating rate of 350°C / hour, a furnace temperature of 950°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 67.0 (HRC).

[0064] (Comparative Example 7) As shown in Table 1, high-chromium cast iron Fe65.0C4.55Cr28.15Si0.8Mn1.5 (wt%) was heat treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness (HRC) was 41.5.

[0065] Example 8 As shown in Table 1, high-chromium cast iron Fe63.7C4.5Cr28Si0.8Mn1.5Ni0.5Mo1.0 (wt%) was first heat-treated in an electric furnace at a furnace temperature of 950°C for 24 hours, and then slowly cooled to 750°C at a cooling rate of 30°C / hour. This was followed by a secondary heat treatment at a furnace temperature of 750°C for 24 hours, and then slowly cooled to room temperature at a cooling rate of 30°C / hour. The resulting Rockwell hardness (HRC) was 39.8. Then, using the electric furnace again, quenching was performed under the conditions of a heating rate of 350°C / hour, a furnace temperature of 950°C, and a holding time of 4.5 hours, as shown in Table 2, and then rapidly cooled to room temperature at a cooling rate of 3000-6000°C / hour. As a result, the Rockwell hardness after quenching was 67.1 (HRC).

[0066] (Comparative Example 8) As shown in Table 1, high-chromium cast iron Fe63.7C4.5Cr28Si0.8Mn1.5Ni0.5Mo1.0 (wt%) was heat treated in an electric furnace at a furnace temperature of 850°C for a holding time of 4 hours, and then slowly cooled to room temperature at a cooling rate of 15°C / hour. As a result, the Rockwell hardness HRC was 47.2.

[0067] [Table 1]

[0068] [Table 2]

[0069] As a result of heat treating the high chromium cast irons of Examples 1 to 8 using the softening heat treatment method of the present invention, the high chromium cast irons after softening heat treatment had a Rockwell hardness of HRC 40 or less, making them suitable for machining processes such as lathe processing, milling, drilling, grinding, and polishing. After machining, the high chromium cast irons were quenched to have a Rockwell hardness of HRC 60 or more, giving them excellent wear resistance. On the other hand, when the heat treatment conditions deviated from those of this embodiment, as in Comparative Examples 1 to 8, the high chromium cast iron could not be softened.

Claims

1. A softening heat treatment method for high chromium cast iron containing, by weight%, C in the range of 2.1% to 4.0% and Cr in the range of 30.0% to 40.0%, a heating step of heating and holding the high chromium cast iron at a furnace temperature of 700°C or higher and 750°C or lower for a holding time of 10 hours or longer; a slow cooling step of slowly cooling the high chromium cast iron to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, The total time required for the heating step and the slow cooling step is 20 hours or more, A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron after heat treatment by the softening heat treatment method has a Rockwell hardness HRC of 40 or less.

2. A softening heat treatment method for high chromium cast iron containing, by weight%, C in the range of 4.0% to 7.0% and Cr in the range of 20.0% to 40.0%, a primary heating step of heating and holding the high chromium cast iron at a furnace temperature of 900°C or higher and 1100°C or lower for a holding time of 10 hours or longer; a secondary heating step of further heating and holding the high chromium cast iron at a furnace temperature of 700°C or higher and 750°C or lower for a holding time of 10 hours or longer after the primary heating step; a slow cooling step of slowly cooling the high chromium cast iron to a furnace temperature of 600°C at a cooling rate of 100°C / hour or less, A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron after heat treatment by the softening heat treatment method has a Rockwell hardness HRC of 40 or less.

3. 3. The softening heat treatment method for high chromium cast iron according to claim 1 or 2, The method for softening heat treatment of high chromium cast iron, wherein the high chromium cast iron further contains, by weight, Si in the range of 0% to 2.0%, Mn in the range of 0% to 5.0%, Fe in the range of 40.0% to 77.9%, and unavoidable impurities in the range of 0% to 0.1%.

4. 3. The softening heat treatment method for high chromium cast iron according to claim 1 or 2, A softening heat treatment method for high chromium cast iron, wherein the high chromium cast iron further contains one or more elements selected from the group consisting of Mo, W, Nb, V, Co, Ni, Cu, Ti, and rare earth elements.

5. 3. The softening heat treatment method for high chromium cast iron according to claim 1 or 2, After the slow cooling step, a processing step of processing the high chromium cast iron; After the processing step, the high chromium cast iron is heated and held at a furnace temperature of 850°C to 1200°C for a holding time of 1 hour to 12 hours, and then cooled at a cooling rate of 50°C / min or more to perform a quenching step. The method for softening heat treatment of high chromium cast iron further comprises:

6. 6. The softening heat treatment method for high chromium cast iron according to claim 5, The method for softening high chromium cast iron, wherein the high chromium cast iron after the quenching step has a Rockwell hardness HRC of 55 or more.

7. 6. The softening heat treatment method for high chromium cast iron according to claim 5, The method for softening heat treatment of high chromium cast iron, wherein the high chromium cast iron after the quenching step is a part of a pump or a part of a crusher.

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