JP2007154295A - Wear resistant cast steel and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wear resistant high Mn cast steel having excellent wear resistance and toughness, and to provide its production method. <P>SOLUTION: A low-carbon wear resistant cast steel having a specified martensite index, having a chemical componential composition for obtaining a composition in which δferrite is crystallized out as primary crystals and austenite is crystallized out at a peritectic temperature or below, and having a cast steel structure in which the volume fraction of low carbon martensite is 40 to 95%, and the balance retained austenite is obtained by reheating the cast steel under specified conditions, so as to be homogenized, and thereafter subjected the cast steel to quenching treatment under specified conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wear-resistant cast steel that is excellent in wear resistance and toughness, and that is suitable for use as a wear-resistant member of a crusher such as a cone crusher or a jaw crusher for crushing rocks, and a method for producing the same.

  Conventionally, high-Mn cast steel (corresponding to JIS G5131) having both wear resistance and toughness has been frequently used for wear-resistant members used in crushers and the like. High Mn cast steel has a characteristic that its matrix is austenite and has good toughness, and when subjected to plastic deformation, work hardening occurs due to twin deformation or stacking fault, and the hardness of the surface portion subjected to plastic deformation increases. have. For this reason, in a wear resistant member that receives an impact, such as a liner member of a crusher, the hardness of the impacted portion is increased and the wear resistance of the impact surface is improved.

  By the way, in recent years, improvement of the processing capacity of the crusher has been demanded, and the crusher has been increased in size and crushing pressure has been increased. For this reason, there is a strong demand for wear-resistant cast steel with excellent wear resistance that can cope with such severe use conditions.

Conventionally, various techniques have been proposed to improve the wear resistance of high-Mn cast steel (see Patent Documents 1, 2, 3, 4, 5, and 6).
Japanese Patent Laid-Open No. 8-26099 Japanese Patent Laid-Open No. 9-202941 Japanese Patent Laid-Open No. 10-8210 JP 11-61339 A JP-A-11-343543 JP 2001-140039 A

However, these high Mn cast steels have high toughness of about 50 J / cm ^{2 in} terms of Charpy impact value, but their hardness is as low as less than about 600 Hv. For this reason, wear is large especially in the crushing of hard rocks, etc., and the above-mentioned crushing machine cannot sufficiently improve the processing capacity.

It is also conceivable to use high Cr cast steel instead of this high Mn cast steel. However, although these high Cr cast steels have a high hardness of 700 Hv or more, on the contrary, their toughness is as low as about 5 J / cm ^{2 in} Charpy impact value. For this reason, it cannot be used for a wear-resistant member that receives a large impact of a crusher such as a cone crusher or a jaw crusher. In addition, since the initial hardness is high, there is a problem that machining from the cast steel to the wear-resistant member of the crusher becomes particularly difficult.

Furthermore, although it is conceivable to use high alloy steels such as stainless steel such as SUS304, the hardness of these high alloy steels is as high as about 600 Hv due to the martensite structure. It is as low as less than about cm ² . For this reason, for the same reason as high Cr cast steel, it cannot be used for wear-resistant members that are produced by machining due to the great impact of crushers such as cone crushers and jaw crushers.

  The present invention has been made in view of such problems, and an object thereof is to provide a wear-resistant high Mn cast steel excellent in wear resistance and toughness and a method for producing the same.

  In order to achieve this object, the gist of the wear-resistant cast steel of the present invention is mass%, C: 0.1 to 0.3%, Si: 0.3 to 1.0%, Mn: 5 to 15 %, Cr: 5 to 15%, N: 0.05 to 0.2%, and the content of each of these elements is 95 ≧ 460− [480 × (% C) −21 × (% Si ) −8 × (% Mn) −14 (% Cr) −480 × (% N)]> 50, the balance is made of Fe and inevitable impurities, and the volume fraction of martensite in the cast steel structure is 40 % To 95%, and the balance is retained austenite.

  In order to achieve the above object, the gist of the method for producing a wear-resistant cast steel of the present invention is a method for producing a wear-resistant cast steel of the above gist or a preferred embodiment described later, and the chemical components described above or below. After casting the cast steel having the composition, the cast steel is reheated and held in the temperature range of 900 to 1200 ° C. for 1 to 50 hours, and then cooled to a temperature of 500 ° C. or lower at an average cooling rate of 1 ° C./s or higher. It is a quenching treatment, and the volume fraction of martensite in the cast steel structure is 40% or more and 95% or less, and the balance is retained austenite.

  In the present invention, the hardness after work hardening (wear resistance) by work hardening of martensite and hardening by work-induced transformation of retained austenite when machining the high Mn cast steel of the present invention into a wear resistant member. Secure. Therefore, the component composition is very low carbon content, and by quenching treatment (water toughening treatment) of this low carbon cast steel, the high Mn cast steel structure is composed of residual austenite and low carbon martensite mainly composed of low carbon martensite. A complex organization of sites.

  Such a retained austenite and low carbon martensite composite structure is excellent in balance between hardness, ductility, and toughness, and is excellent in work hardening characteristics (work hardening amount, work hardening ability). Low carbon martensite has a very ductile property, although the hardness after work hardening is inferior to austenite. In the present invention, a composite structure of such low carbon martensite and residual austenite that is transformed into martensite by work-induced transformation and becomes extremely hard by work hardening is obtained.

  Thereby, the hardness (initial hardness) of the cast steel before machining into the wear-resistant member is relatively low and the toughness is increased. This facilitates machining. In addition, the hardness of the wear-resistant member becomes very high due to the work hardening of low carbon martensite due to the impact force applied during machining and wear-resistant materials and the hardening due to work-induced transformation of residual austenite. Moreover, since ductility is also maintained, it does not crack during use as a wear-resistant member, and exhibits excellent wear resistance.

  In the present invention, the composite structure of such retained austenite and low carbon martensite structure and its work hardening characteristics are determined in the present invention by reducing the carbon content, increasing the Cr content and the N content, and increasing the Mn content. Achieved by increasing the solubility limit and quenching. At the same time, by reducing carbon and increasing the solid solubility limit of carbon by increasing Mn, the formation of Cr carbide due to the increase in Cr content is suppressed, and the deterioration of toughness is prevented.

  As a result, the wear resistance member made of high Mn cast steel or the rock crushing performance and long life of crushers such as cone crusher and jaw crusher are ensured.

  Conventionally, as machining with work hardening, machining with plastic deformation such as free forging and die forging is performed on cast steel to obtain a wear resistant member. In this machining, the cast steel is naturally work-hardened and the hardness is increased. However, in the conventional high Mn cast steel, any structure such as an austenite single phase, a martensite single phase, or a composite of austenite and martensite has a C or Cr content as compared with the cast steel of the present invention. There are differences in chemical composition, and the amount of work hardening due to the impact force applied during use as the above-mentioned machining and wear-resistant material is extremely small.

  Further, for example, in Patent Document 6 and the like, the work hardening characteristics of high-Mn cast steel are improved, the hardness of the wear-resistant member is increased, and the wear resistance is improved. However, the work hardening intended in Patent Document 6 is not the work hardening when machining high-Mn cast steel into a wear-resistant member as in the present invention, but by the impact of rock crushing when using the wear-resistant member. This is work hardening in the sense of causing work-induced martensitic transformation during plastic deformation. That is, in Patent Document 6, the structure of high-Mn cast steel is made into a composite structure of austenite and martensite, and then processing-induced martensite transformation occurs in austenite due to plastic deformation due to the impact of rock fracture when using wear-resistant members. Thus, the hardness of the member wear surface is increased by the martensite of the structure and the work-induced martensite at the time of plastic deformation, thereby obtaining wear resistance.

  However, high Mn cast steel composed of a composite structure of austenite and martensite, including the difference in chemical composition, such as Cr content, compared to the cast steel of the present invention composed of low carbon martensite structure. The amount of work hardening in is extremely small. In other words, Patent Document 6 relies on work hardening plastic deformation due to the impact of rock crushing when using the wear-resistant member because the work hardening amount in machining is small as in the above-described conventional technology. It can't be helped.

  On the other hand, the cast steel of the present invention can obtain a large work hardening characteristic (work hardening amount) under conditions such as a conventional machining method and a processing amount for the wear resistant member. That is, special conditions such as a special processing method and a large processing amount for obtaining a large work-hardening property are completely unnecessary.

(Cast steel composition)
The chemical composition of the high Mn cast steel of the present invention (all units are mass%) will be described below, including the reasons for limiting each element.

  The chemical component composition of the high Mn cast steel of the present invention is determined in order to obtain the retained austenite and martensite composite structure by utilizing solidification segregation during casting. More specifically, the composition is such that δ ferrite crystallizes in the primary crystal and austenite crystallizes below the peritectic temperature. The basic chemical composition for this is as follows: C: 0.1-0.3%, Si: 0.3-1.0%, Mn: 5-15%, Cr: 5-15%, N: 0 0.05 to 0.2%, and the content of each of these elements is 95 ≧ 460− [480 × (% C) −21 × (% Si) −8 × (% Mn) −14 (% Cr) −480 × (% N)]> 50, and the balance is made of Fe and inevitable impurities.

  In the present invention, in order to increase the wear resistance of the high Mn cast steel, it is allowed to contain an element that further increases the wear resistance, if necessary, with respect to the above component composition. Specifically, one or more of Ni: 0.3 to 5.0%, Mo: 0.3 to 2.0%, and / or one or more of Ti, Nb, and Zr May be selectively contained in a total of 0.1 to 1.5%.

C: 0.1 to 0.3%.
C ensures the hardenability for obtaining the martensitic structure containing a retained austenite by quenching treatment (water toughening treatment) of cast steel. Further, it is an element effective for increasing the amount of work hardening of cast steel.

  In the present invention, in spite of the low C amount, in the composition range of the present invention, C is solidified and segregated by casting, resulting in a portion where C is apparently concentrated. For this reason, at the time of quenching, many parts undergo martensite transformation excellent in ductility and toughness, but the portion where the C is concentrated remains as relatively hard austenite, so that low carbon martensite containing residual austenite is contained. Become an organization.

In order to exert these effects, the C content needs to be 0.1% or more. On the other hand, if the C content exceeds 0.3%, Cr carbide such as Cr ₇ C ₃ tends to precipitate along the austenite grain boundaries, and the toughness decreases. Therefore, C is contained in the range of 0.1 to 0.3%.

  In the past, the reason why the Cr content was 5% or less even when Cr was contained in the high-Mn cast steel was exactly because a decrease in toughness due to this Cr carbide precipitation was expected. On the other hand, in the present invention, by reducing the carbon content, the formation of Cr carbide due to the increase in Cr content is suppressed, thereby preventing a decrease in toughness.

Mn: 5 to 15%.
Mn increases the solid solubility limit of C and suppresses the formation of Cr carbides that degrade toughness. Further, the solid solubility limit of N is increased to increase the amount of solid solution N, and the amount of work hardening of the cast steel is increased. In order to exert these effects, a content of 5% or more is necessary. On the other hand, if the Mn content exceeds 15%, the toughness is lowered. Therefore, Mn is contained in the range of 5 to 15%.

Si: 0.3-1.0%.
Si needs to have a content of 0.3% or more for ensuring fluidity of the molten metal during casting and for deoxidation during melting and refining. On the other hand, if the content exceeds 1.0%, precipitation of carbides at grain boundaries is promoted, resulting in a decrease in toughness. Therefore, the Si content is in the range of 0.3 to 1.0%.

Cr: 5 to 15%.
Cr improves the above-mentioned work hardening characteristics of cast steel and enhances wear resistance. Further, the solid solubility limit of N is increased to increase the amount of solid solution N, thereby increasing the work hardening amount. In the present invention, as described above, since precipitation of grain boundary carbides is promoted and there is no fear of lowering toughness, 5% or more of Cr is contained in order to exert these effects. On the other hand, if the Cr content exceeds 15%, nitrides and the like are formed and the toughness is lowered. Therefore, Cr is contained in a range of 5 to 15%.

N: 0.05-0.2%.
N has the effect of improving the above-mentioned work hardening characteristics (work hardening index) of cast steel and improving the wear resistance without generating crystallized substances and precipitates that lower the impact value. In order to exhibit this effect, it is necessary to contain N 0.05% or more. On the other hand, if the N content exceeds 0.2%, nitrides are formed and the toughness is lowered. Therefore, N is contained in the range of 0.05 to 0.2%.

(Martensite index)
In the present invention, the content of each element of C, Si, Mn, Cr, and N is 95 ≧ 460− [480 × (% C) after each element satisfies the content range. −21 × (% Si) −8 × (% Mn) -14 (% Cr) −480 × (% N)]> 50 (hereinafter referred to as the martensite index).

  In the present invention, in order to ensure the hardness after work hardening (abrasion resistance), low carbon martensite is contained at 40% or more and 95% or less by the quenching treatment (water toughening treatment) of cast steel, and the balance is retained austenite. And a composite structure with retained austenite mainly composed of martensite. The martensite index (formula) is a rule for this, and when the martensite index exceeds 50, the low-carbon martensite structure is obtained, and preferably the low-carbon martensite structure is 70 or more. Can be obtained stably. When the martensite index is 50 or less, the low-carbon martensite structure of 40% or more cannot be obtained even by quenching the cast steel.

  On the other hand, when the martensite index exceeds 95, the retained austenite is insufficient, and it cannot be expected that the retained austenite will be hardened by processing-induced transformation. Therefore, the upper limit of the martensite index is 95, and the range of the martensite index is more than 50 and 95 or less.

Ni: 0.3-5.0%.
Ni, like Mn and Cr, has the effect of increasing the work hardening amount and enhancing the wear resistance. In order to make this effect exhibited selectively, the content is made 0.3% or more. On the other hand, if the Ni content exceeds 5.0%, the austenite is overstabilized and the processing-induced transformation of residual austenite does not occur. For this reason, abrasion resistance falls. Therefore, Ni in the case of containing selectively is made into 0.3 to 5.0% of range.

Mo: 0.3-2.0%.
Mo has the effect of suppressing the formation of carbides at the grain boundaries in the quenching process (water toughening process) of cast steel, improving the ductility, and increasing the wear resistance. In order to obtain this effect of Mo, 0.3% or more is selectively contained. On the other hand, if it exceeds 2.0%, the effect is lost. Therefore, the Mo amount in the case of selective inclusion is set in the range of 0.3 to 2.0%.

Ti, Nb, Zr is 0.1 to 1.5% or less in total.
Ti, Nb, and Zr have the effect of improving the above-mentioned work hardening characteristics of cast steel and increasing the wear resistance by forming carbides and precipitating. In addition, there is an effect of improving the work hardening characteristics and toughness by refining crystal grains. However, as described above, carbides also have an effect of reducing toughness and ductility by forming at grain boundaries or forming nitrides during the quenching process of cast steel. Accordingly, when one or more of these elements are selectively contained, the lower limit is 0.1% or more in terms of the total content, and the upper limit is 1.5% or less in terms of the total content. .

(Cast steel structure)
The cast steel structure of the present invention is made into a wear-resistant member by machining hardened high-Mn cast steel to a wear-resistant member and by work hardening of martensite due to impact force received during trial use as a wear-resistant member and by processing-induced transformation of residual austenite. In order to ensure hardness (wear resistance) during use, a composite structure of retained austenite and low carbon martensite is formed by quenching treatment (water toughening treatment) of cast steel.

  The composite structure of retained austenite and low carbon martensite in the present invention is a structure in which retained austenite is dispersed in low carbon martensite, as shown in FIG. FIG. 1 is a structure observation photograph (photograph substituted for drawing) with an optical microscope of about 100 times that of an invention example (a martensite volume fraction of 40% or more and 95% or less) in Examples described later (measurement method is paragraph 0051). Described in). In FIG. 1, the black part is the low-carbon martensite of the main phase, and the white part is the retained austenite.

  The austenite in this composite structure has a face-centered cubic crystal structure, and due to its thermodynamic properties, C, Si, Mn, Cr, and N are more distributed than martensite, which is a body-centered cubic crystal. The concentration is high. For this reason, the austenite in this composite structure has a higher work hardening amount under wear conditions (during use as a wear member) and higher hardness than martensite in combination with work-induced transformation.

  On the other hand, when an austenite single phase without martensite is used, the work hardening amount under wear conditions is large together with the work-induced transformation, resulting in a very high hardness. However, since the toughness is lowered at the same time, cracking occurs during use as a wear-resistant member. On the other hand, if the low carbon martensite composite structure containing retained austenite of the present invention is used, the low carbon martensite portion exhibits ductility and toughness is ensured, so that it cracks during use as a wear resistant member. There is no.

  When the proportion of low carbon martensite in the cast steel structure of the present invention is less than 40%, in other words, when other residual austenite exceeds 60%, ductility and toughness are lowered. For this reason, machining becomes difficult, and the toughness and wear resistance of the wear-resistant member also deteriorate. Accordingly, the proportion of low carbon martensite in the cast steel structure of the present invention is 40% or more. Preferably, the ratio is 50% or more, more preferably 60% or more. On the other hand, if the proportion of low carbon martensite in the cast steel structure of the present invention exceeds 95%, the amount of retained austenite becomes too small, and the effect of retained austenite cannot be exhibited effectively. Is 95% or less. Preferably, the ratio is 90% or less, more preferably 85% or less.

(Production method)
Preferred production conditions for the cast steel of the present invention will be described below. The cast steel of the present invention is once cooled to room temperature after casting the cast steel having the chemical composition described above. Thereafter, this cast steel is reheated from room temperature and subjected to a homogenization treatment in which the cast steel is maintained in a temperature range of 900 to 1200 ° C. for 1 to 50 hours, and then cooled to a temperature of 500 ° C. or less at an average cooling rate of 1 ° C./s or more. The quenching treatment (water toughening treatment) is performed by water cooling or the like, so that the martensite volume fraction in the cast steel structure is 40% or more and 95% or less, and the balance is retained austenite.

  The low carbon martensite composite structure containing the retained austenite of the present invention is obtained by utilizing solidification segregation during casting. For this reason, in the as-cast steel ingot, the concentration gradient of contained elements at the interface between the low carbon martensite and austenite becomes relatively large (steep). For this reason, it becomes easy to crack when it is work-hardened during use as a wear-resistant material. In order to prevent this, it is necessary to perform a homogenization treatment under the above-mentioned conditions for relaxing the above-mentioned concentration gradient.

  Regarding the homogenization temperature, it is highly possible that the concentration gradient cannot be relaxed at 900 ° C. or lower. On the other hand, when it exceeds 1200 ° C., homogenization proceeds too much, so that solidification segregation during casting cannot be used, and the low carbon martensite composite structure containing retained austenite of the present invention cannot be obtained.

  As for the soaking time, at least one hour or more is necessary to alleviate the above-mentioned concentration gradient. On the other hand, if it exceeds 50 hours, homogenization proceeds too much and solidification segregation during casting cannot be used. The low carbon martensite composite structure containing the retained austenite of the present invention cannot be obtained.

  Quenching treatment such as water cooling after soaking treatment is important for obtaining a structure mainly composed of low carbon martensite in which retained austenite is dispersed. In order to obtain such a structure and to prevent or suppress the precipitation of carbides at the grain boundaries, it is desirable that the cooling rate during the quenching treatment of the cast steel be as large as possible.

  The cast steel after the quenching treatment is subjected to machining with work hardening to be a wear resistant member. The machining with work hardening at this time is a process with plastic deformation by a conventional method such as free forging or die forging. That is, as described above, the cast steel of the present invention can obtain a large work hardening characteristic (work hardening amount) under conditions such as a conventional machining method and a processing amount for wear-resistant members. There is no need for special conditions such as large machining amount. This is also a great advantage of the present invention. At this time, since the hardness (initial hardness) of the high Mn cast steel before machining on the wear resistant member is relatively low, the machining is facilitated as described above.

  Examples of the present invention will be described below. High Mn cast steels with various composition and structure were obtained, and their hardness, work hardening ability, toughness, wear resistance, etc. were evaluated.

  That is, 20 kg of cast steel was melted in a high frequency induction melting furnace with high-Mn cast steel having the compositions 1 to 4039 shown in Table 1 (Invention Example) and Table 2 (Comparative Example) below. These cast steels cooled to room temperature are commonly heated to a temperature of 1100 ° C. and held for 6 hours, and then quenched by water cooling to 500 ° C. at an average cooling rate of 2 ° C./s. (Water toughening treatment) and cooled to room temperature.

  Test pieces were sampled from the central portions of the obtained cast steels, and the structure, hardness, work hardening ability, toughness, wear resistance, etc. were evaluated. These results are shown in Table 3 (Invention Example) and Table 4 (Comparative Example).

  Tissue: The martensite fraction of each test piece was measured by three fields of view using a 100 × optical microscope after each test piece was mirror-polished and then corroded with a nital solution. This was image-analyzed with image analysis software (Image-Pro Prus made by MEDIA CYBERNETICSTM). In this image analysis, it is assumed that a smooth portion (white portion in FIG. 1) in which no fine structure is seen is a retained austenite structure, and the other portion (black portion in FIG. 1) is a martensite structure, The total measurement area of the martensite structure in the visual field was calculated. Then, the martensite fraction (%) is calculated from the ratio of the total area of martensite to the measured visual field area, the results of the three visual fields are averaged to obtain the volume fraction of martensite, and the remainder is the volume fraction of residual austenite. Rate.

Hardness: Using a Vickers hardness meter, the load was 30 kg, the surface hardness (Hv) of each test piece was measured at five points, and the averaged hardness was defined as the hardness before processing. Then, after simulating the actual machining with work hardening and the impact force received during use as a wear resistant material, each test piece (Φ60 mm × 120 mml) was subjected to 50% compression processing at a strain rate of 10 ⁻³ m / s. The surface hardness (Hv) of each test piece was measured at five points, and the averaged hardness was taken as the hardness after processing. And the hardness difference ((DELTA) Hv) before and after these processes was calculated | required.

Impact value: A Charpy impact test was performed using a 2 mm U-notch JIS No. 3 test piece at a hammer load of 294.2 N (30 kgf) and a test temperature of room temperature. The Charpy impact value (J) was determined as J / cm ² by dividing the absorbed energy by the cross-sectional area of the test piece. A Charpy impact value of 70 J / cm ² or higher was evaluated as acceptable.

Abrasion resistance test: Abrasion resistance was evaluated by simulating an actual machine crusher such as a cone crusher. That is, a plate material of 6 × 25 × 75 mm was cut out from each cast steel and used as an abrasion resistance test material. The abrasion resistance of these test materials was evaluated by a testing machine shown in FIG. Specifically, the test material was rotatably mounted and fixed together with the rotation shaft on the rotation shaft portion in the central portion of the cylindrical outer container to which the test machine shown in FIG. 2 was fixed. Then, after accommodating a large number of quartz rough rock blocks containing 75% SiO ₂ in a cylindrical outer container, the test material was rotated counterclockwise with a rotating shaft at a rotational speed of 60 rpm for 420 minutes to obtain a coarse quartz The collision with the surface rock mass was repeated.

  Then, the specific wear amount was calculated from the weight reduction amount of the test material before and after the test. Specific wear amount (%) = [(weight loss: g) / (weight before test: kg)] × 100. Each example was performed on three test materials, and the specific wear amount was the average value. And the specific abrasion loss made 0.4 g / kg or less into the pass ((circle)), and the thing exceeding it was evaluated as the disqualification (x).

  At this time, the presence or absence of occurrence of cracks in the test material after the test was observed, and the case where even one crack occurred was evaluated as cracked, and the case where no crack occurred in all three was evaluated as not cracked.

  As is apparent from Tables 1 and 3, the cast steels of Invention Examples 1 to 24 are within the chemical component composition range of the present invention, and the martensite volume fraction in the cast steel structure is 40% or more and 95% or less.

As a result, the cast steels of Invention Examples 1 to 24 have high hardness and work hardening ability after the processing, and have a Charpy impact value of 70 J / cm ² or more. Moreover, the wear resistance as a wear-resistant member as an actual machine crusher such as a cone crusher is also good.

  On the other hand, as is clear from Tables 2 and 4, the cast steels of Comparative Examples 25 to 37 are out of the chemical composition range of the present invention. For this reason, any of the hardness, work hardenability, Charpy impact value, and wear resistance after the above processing can be achieved even if the cast steel structure condition is not satisfied or the cast steel structure condition is satisfied, even though it is manufactured under preferable manufacturing conditions. It is remarkably inferior to the inventive examples. As a result, the comparative example is not suitable as a wear-resistant member in an actual machine crusher such as a cone crusher.

In Comparative Example 25, since C is too low, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 26, C was too high, so the initial toughness was low, and it broke during the wear resistance test.
In Comparative Example 27, since N is too low, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 28, since N was too high, blowholes were generated during casting and could not be tested.
In Comparative Example 29, since Mn is too low, the amount of martensite is excessive, and the amount of retained austenite is small. For this reason, the initial toughness was low, and cracking occurred during the wear resistance test.
Since the comparative example 30 has too high Mn, the carbide | carbonized_material has produced | generated. For this reason, the initial toughness was low, and cracking occurred during the wear resistance test.
Since Comparative Example 31 has too low Cr, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 32, Cr was too high, so the initial toughness was low, and cracking occurred during the wear resistance test.
In Comparative Example 33, the martensite index was too low below the lower limit and the initial toughness was high, but the ductility was insufficient due to work hardening, and cracking occurred during the wear resistance test.
In Comparative Example 34, the martensite index exceeds the upper limit and is too high, and the residual austenite in the low carbon martensite is insufficient (not observed). For this reason, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 35, since Si was too high, the initial toughness was low, and cracking occurred during the wear resistance test.
In Comparative Example 36, since Ni is too high, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 37, the total amount of Ti, Nb, and Zr was too high, so the initial toughness was low, and cracking occurred during the wear resistance test.

  From the above results, the significance of the chemical composition of the high-Mn cast steel of the present invention and the structure definition is supported.

  Next, the high Mn cast steel of Invention Example 1 in Table 1 was subjected to homogenization treatment and quenching treatment under various conditions shown in Table 5 and cooled to room temperature. The hardness, work hardening ability, toughness, wear resistance, etc. of these high Mn cast steels were evaluated in the same manner as in the above examples. These results are shown in Table 5.

As is apparent from Table 5, the cast steels of Invention Examples 38 to 45 are manufactured within a preferable range of manufacturing conditions, and the martensite volume fraction in the cast steel structure is 40% or more and 95% or less. As a result, the hardness and work hardening ability after the processing are high, and the Charpy impact value is 70 J / cm ² or more. Moreover, the wear resistance as a wear-resistant member as an actual machine crusher such as a cone crusher is also good.

  On the other hand, the cast steels of Comparative Examples 46 to 48 are out of the preferable production condition range. For this reason, in spite of being within the chemical component composition range of the present invention, any one of the hardness, work hardening ability, Charpy impact value, and abrasion resistance after processing is significantly inferior to the inventive examples. As a result, Comparative Examples 46 to 48 are unsuitable as wear-resistant members in actual machine crushers such as cone crushers.

In Comparative Example 46, the heating temperature in the homogenization treatment is too low. For this reason, cracks occurred during the wear resistance test.
In Comparative Example 47, the heating temperature in the homogenization treatment is too high. For this reason, homogenization progresses too much and the residual austenite is insufficient. For this reason, the work hardening amount is low and the specific wear amount is large.
In Comparative Example 48, the average cooling rate in the quenching process is too small. For this reason, the initial toughness was low and it broke during the wear resistance test.

  From the above results, the significance of the production conditions defined by the production method of the high Mn cast steel of the present invention is supported.

  As described above, according to the present invention, it is possible to provide a wear-resistant high-Mn cast steel excellent in wear resistance and toughness and a method for producing the same. For this reason, it is suitable for being used as a wear-resistant member of a crusher such as a cone crusher or a jaw crusher for crushing rocks.

It is a microscope picture (drawing substitute photograph) which shows the structure | tissue of this invention abrasion-resistant cast steel. It is sectional drawing which shows the abrasion resistance tester used for the Example.

Claims (3)

  In mass%, C: 0.1 to 0.3%, Si: 0.3 to 1.0%, Mn: 5 to 15%, Cr: 5 to 15%, N: 0.05 to 0.2% , And the content of each of these elements is 95 ≧ 460− [480 × (% C) −21 × (% Si) −8 × (% Mn) −14 (% Cr) −480 × (% N)]> 50, the balance is made of Fe and inevitable impurities, the martensite volume fraction in the cast steel structure is 40% to 95%, and the balance is made of residual austenite. Wear resistant cast steel.   The cast steel further includes one or two of Ni: 0.3 to 5.0% and Mo: 0.3 to 2.0%, and / or one or two of Ti, Nb, and Zr. The wear-resistant cast steel according to claim 1, comprising 0.1 to 1.5% in total.   A method for producing the wear-resistant cast steel according to claim 1 or 2, wherein after casting the cast steel having the chemical composition of claim 1 or 2, the cast steel is reheated in a temperature range of 900 to 1200 ° C. Hold for 1 to 50 hours, and then quench by cooling at an average cooling rate of 1 ° C./s or higher to a temperature of 500 ° C. or less, the martensite volume fraction in the cast steel structure is 40% or more and 95% or less, and the remainder remains A method for producing a wear-resistant cast steel, characterized in that it is austenite.

Images