JP2015507700A - Abrasion-resistant austenitic steel with excellent machinability and ductility and method for producing the same - Google Patents

Abstract

8% to 15% manganese (Mn) by weight%, carbon (C) satisfying the relationship of 23% <33.5C-Mn≰37%, 1.6C-1.4 (%) ≰Cu≰5% Filling copper (Cu), sulfur (S): 0.03-0.1%, calcium (Ca): 0.001-0.01%, balance Fe and other inevitable impurities, machinability and ductility An excellent wear-resistant austenitic steel material and a method for producing the same are provided. According to the present invention, steel material excellent in machinability that can be used for a long time even in a corrosive environment by preventing the deterioration of the steel material by suppressing the formation of carbide inside the steel material and sufficiently ensuring the wear resistance. Can be provided.

Description

  The present invention relates to a wear-resistant austenitic steel material excellent in machinability and ductility and a method for producing the same.

  With the growth of the mining industry, oil and gas industries (Oil and Gas Industries), the wear of steel materials used in mining, transportation and refining processes has become a major problem. In particular, as the development of oil sands (Oil Sands) as a fossil fuel that substitutes for oil has recently become full-fledged, the main cause of the increase in production costs due to the wear of steel due to slurry containing oil, gravel, sand, etc. Therefore, the demand for the development and application of steel materials with excellent wear resistance is greatly increasing.

  In the existing mining industry, Hadfield steel having excellent wear resistance has been mainly used. The above Hadfield steel is a high strength steel with a high manganese content, and in order to increase the wear resistance of such steel materials, a high content of carbon and a large amount of manganese are added to increase the austenite structure and wear resistance. Efforts have been made to do so. However, the high carbon content of hadfield steel produces network-like carbides along the austenite grain boundaries at a high temperature, which sharply lowers the properties of the steel material, particularly the ductility.

  In order to suppress such network-like carbide precipitation, a method has been proposed in which a high manganese steel is produced by solution treatment at a high temperature or by rapid cooling to a normal temperature after hot working. However, if the steel material is thick, the carbide suppression effect due to rapid cooling is not sufficient, and if welding is required, it is difficult to adjust the cooling rate after welding, so this type of networked carbide precipitation is suppressed. This causes a problem that the physical properties of the steel material deteriorate rapidly. In addition, segregation by alloying elements such as manganese and carbon occurs inevitably during the solidification of high manganese steel ingots or slabs, which is further deteriorated during post-processing such as hot rolling, and deepens in the final product. Along with the segregation zone, the partial precipitation of carbides occurs in a network, and as a result, the non-uniformity of the fine structure is promoted and the physical properties are deteriorated.

  In order to improve the wear resistance, it is necessary to increase the carbon content, and in order to prevent deterioration of physical properties due to carbide precipitation, increasing the manganese content can be used as a general method. Increases alloy volume and manufacturing unit price. Moreover, since the above manganese addition causes a decrease in corrosion resistance compared to general carbon steel, there is a limit to application in fields where corrosion resistance is required.

  In addition, austenitic high manganese steel is inferior in machinability due to high work hardening, thereby reducing the life of the cutting tool, increasing the tool cost, increasing the downtime associated with tool replacement, etc. There is a problem of increasing production costs.

  An object of the present invention is to provide an austenitic steel material having improved machinability, ductility and wear resistance by effectively suppressing the formation of carbides and a method for producing the same.

  However, the problem to be solved by the present invention is not limited to the problem described above, and other problems not described can be clearly understood by those skilled in the art from the following description.

  In order to achieve the above object, according to an embodiment of the present invention, 8% to 15% manganese (Mn) and 23% <33.5C-Mn ≦ 37% are satisfied by weight%. Wear-resistant austenitic steel with excellent machinability and ductility, including carbon (C), copper (Cu) satisfying 1.6C-1.4 (%) ≦ Cu ≦ 5%, remaining Fe and other inevitable impurities Steel is provided.

  According to another embodiment of the present invention, by weight percent, 8-15% manganese (Mn), carbon (C) satisfying the relationship 23% <33.5C-Mn ≦ 37%, 1.6C-1 Re-heating the steel slab containing copper (Cu) satisfying 4 (%) ≦ Cu ≦ 5%, the balance Fe and other inevitable impurities to a temperature of 1050 to 1250 ° C., and a temperature of 800 ° C. to 1050 ° C. Machinability and ductility, including a step of producing a steel sheet by finish hot rolling and a step of cooling the hot-rolled steel sheet to 600 ° C. or less at a cooling rate of 10 to 100 ° C./s. A method for producing a wear-resistant austenitic steel material having excellent resistance is provided.

  According to the present invention, it is possible to provide a steel material that can be used for a long time even in a corrosive environment by preventing the deterioration of the steel material by suppressing the formation of carbide inside the steel material and sufficiently ensuring the wear resistance. .

FIG. 1 is a graph showing the relationship between manganese and carbon according to an embodiment of the present invention. FIG. 2 is a photograph of the microstructure inside the steel material according to one embodiment of the present invention. FIG. 3 is a graph showing the relationship between the sulfur content and machinability according to an embodiment of the present invention.

  Hereinafter, the austenitic steel material excellent in machinability and ductility of the present invention and the manufacturing method thereof will be described in detail so that those having ordinary knowledge in the technical field to which the present invention belongs can easily carry out.

  The present inventors have confirmed that it is necessary to appropriately control the components of the steel material in order to improve the machinability without causing the problem of reduced ductility due to the carbide and having high wear properties. The present invention has been achieved.

  That is, the present invention adds manganese and carbon to ensure wear resistance, adjusts the carbon content by manganese content to minimize carbide formation by carbon, and further adds carbides by adding elements. A steel material that not only improves wear resistance by actively suppressing formation, but also sufficiently improves ductility, and significantly improves the machinability of austenitic high manganese steel by adjusting the content of calcium and sulfur. The composition has been found.

  The steel material of the present invention is 8% to 15% manganese (Mn) by weight%, carbon (C) satisfying the relationship of 23% <33.5C-Mn ≦ 37%, 1.6C-1.4 (%). It may have a composition containing copper (Cu) satisfying ≦ Cu ≦ 5%, the balance Fe and other inevitable impurities.

  The reason for limiting the numerical values of the respective components will be described as follows. In addition, the unit of the content of the following each component is weight% unless otherwise indicated.

Manganese (Mn): 8-15%
Manganese is the most important element added to the high manganese steel as in the present invention, and is an element that serves to stabilize austenite. In the present invention, in order to obtain austenite as the main structure, 8% or more of manganese is preferably contained. That is, when the manganese content is less than 8%, ferrite is formed and the austenite structure cannot be sufficiently secured. On the other hand, when the manganese content exceeds 15%, there are problems such as a decrease in corrosion resistance due to the addition of manganese, difficulty in the production process, and an increase in production unit cost, and there is a disadvantage that the work strength is reduced by reducing the tensile strength.

Carbon (C): 23% <33.5C-Mn ≦ 37%
Carbon is an element that stabilizes austenite so that an austenite structure can be obtained at room temperature, and increases the strength of steel materials. It is the most important element for ensuring wear resistance. However, as described above, when carbon is not sufficiently added, martensite is formed because of insufficient austenite stability, or it is difficult to obtain sufficient wear resistance due to small work hardening of austenite. On the other hand, if the carbon content is too high, it is difficult to suppress carbide formation.

  Therefore, in the present invention, the carbon content is preferably determined in consideration of the relationship between carbon and other elements added together. For this purpose, the relationship between carbon and manganese related to carbide formation found by the present inventors is shown in FIG. Although carbide is formed by carbon, carbon does not independently affect carbide formation, but carbon acts in a complex manner with manganese to affect its tendency to form. FIG. 1 shows the proper carbon content in relation to manganese.

  In order to prevent the formation of carbides, 33.5C-Mn (C and Mn are the contents of each component in units of% by weight under the premise that the other components satisfy the range specified in the present invention. It is better to control the value of 37) or less. This means an inclined right boundary in the parallelogram region of the drawing. When 33.5C-Mn exceeds 37, a carbide | carbonized_material may be produced | generated so that it may have a bad influence on the ductility of steel materials. However, when the carbon content is too low, that is, when 33.5C-Mn is less than 23, the effect of improving the wear resistance by work hardening of the steel material cannot be obtained. Therefore, the 33.5C-Mn is preferably 23 or more. From the above, in the present invention, carbon is preferably added so as to satisfy 23 <33.5C-Mn ≦ 37.

Copper (Cu): 1.6C-1.4 (%) ≦ Cu ≦ 5%
Copper has a very low solid solubility in carbides and is slow to diffuse in austenite, and therefore tends to be concentrated at the interface between austenite and carbide. As a result, when fine carbide nuclei are generated, surrounding the periphery of the nuclei slows the growth of the carbides due to further diffusion of carbon, and as a result, the formation and growth of carbides is suppressed. Therefore, in the present invention, copper is added to obtain such an effect. Such a copper addition amount is not determined independently, but is preferably determined by a tendency to form carbides. That is, determining the copper content to be 1.6C-1.4% by weight or more is advantageous for suppressing the formation of carbides. When the copper content is less than 1.6C-1.4, it is difficult to suppress the formation of carbides by carbon, and when the copper content exceeds 5% by weight, the hot workability of the steel is reduced. Therefore, it is preferable to limit the upper limit to 5% by weight. In particular, in the present invention, considering the carbon content added for improving the wear resistance, 0.3% by weight or more is preferably added in order to sufficiently obtain the above carbide formation suppressing effect. It is more preferable to add at least wt%.

  The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintended impurities may be inevitably mixed from the raw material or the surrounding environment, and thus cannot be excluded. Since those skilled in the art can understand these impurities, detailed description thereof is omitted in this specification.

  In addition to the said component, the steel materials of this invention can further contain sulfur (S) and calcium (Ca) in order to improve machinability.

Sulfur (S): 0.03-0.1%
Sulfur is generally known as an element that is added together with manganese to form manganese sulfide, which is a compound, and is easily cut and separated during cutting to improve machinability. Since it is melted by the cutting heat, the frictional force between the tip and the cutting tool is reduced, and this brings about effects such as reduction of wear of the cutting tool due to surface lubrication of the tool and prevention of accumulation of cutting tips on the cutting tool. Therefore, the life of the cutting tool is increased. However, if the sulfur content is too high, the mechanical properties of the steel material may be reduced by the large amount of coarse manganese sulfide drawn during hot working, and hot workability may be impaired by the formation of iron sulfide. The upper limit is preferably 0.1%. On the other hand, when less than 0.03% of sulfur is added, since there is no effect of improving machinability, it is preferable to limit the lower limit to 0.03%.

Calcium (Ca): 0.001 to 0.01%
Calcium is an element mainly used to control the shape of manganese sulfide. Since calcium has a large affinity for sulfur, it forms calcium sulfide and is dissolved in manganese sulfide. Since manganese sulfide crystallizes with the calcium sulfide as a nucleus, it is sulfided during hot working. Machinability is improved by suppressing the extension of manganese and maintaining a spherical shape. However, when the calcium content exceeds 0.01%, the effect is saturated, and since the actual yield of calcium is low, it is necessary to add a large amount to increase the content, which is preferable in terms of production cost. However, when the content is less than 0.001%, the effect is small.

  The steel material of the present invention can further improve the corrosion resistance by further containing chromium (Cr) in addition to the above components.

Chromium (Cr): 8% or less (excluding 0%)
In general, manganese is an element that lowers the corrosion resistance of steel, and there is a disadvantage that the corrosion resistance is lower than that of ordinary carbon steel in the above-mentioned range of manganese content, but in the present invention, corrosion resistance is improved by adding chromium. I am letting. Further, the strength can be improved by adding chromium in the above range. However, if the content exceeds 8% by weight, the production cost is increased, and carbides are formed along the grain boundaries together with carbon dissolved in the material, and ductility, in particular, sulfide stress-induced cracks. It is preferable to limit the upper limit to 8% by weight because resistance is reduced and ferrite is generated and austenite cannot be obtained as the main structure. In particular, in order to maximize the effect of improving the corrosion resistance, it is better to add 2% by weight or more of chromium. Thus, by adding corrosion resistance by adding chromium, it can be widely applied to steel materials for slurry pipes or sour steel materials.

  The steel material of the composition mentioned above is an austenitic steel material, and means a steel material in which austenite is contained in the internal structure by 90% or more by area fraction. The austenite imparts high hardness to the steel material by high work hardening in the subsequent working process. In addition to the austenite, an inevitably formed impurity structure such as martensite, bainite, pearlite, and ferrite may be included. In addition, the content of each structure | tissue is a content when the thing which does not contain precipitates, such as a carbide | carbonized_material, and adds up the quantity of the phase (steel) of steel materials is set to 100%.

  Moreover, it is preferable that the steel material of the present invention contains 10% or less (based on the total area) of carbide in an area fraction. Since the above-mentioned carbide deteriorates the ductility of the steel material, the amount is preferably as small as possible. Since the steel material of the present invention has an area ratio of the carbide of 10% or less, it does not cause problems such as early breakage due to insufficient ductility and reduction in impact toughness when used in wear-resistant steel.

  Hereinafter, a method for producing the above-described wear-resistant austenitic steel material of the present invention will be described. The steel material can be manufactured by a normal steel material manufacturing method, and the normal steel material manufacturing method can include a normal hot rolling method in which rough rolling and finish rolling are performed after reheating the slab. After hot rolling, a process of cooling in a normal range can be performed. A preferred example found by the present inventors is as follows.

  First, 8% to 15% manganese (Mn) by weight%, carbon (C) satisfying the relationship of 23% <33.5C-Mn ≦ 37%, 1.6C-1.4 (%) ≦ Cu ≦ 5 %, A steel slab containing copper (Cu), the balance Fe, and other inevitable impurities is prepared.

  As described above, the steel slab can further include sulfur (S) and calcium (Ca).

  Moreover, the steel slab can further include chromium (Cr) as described above.

  Next, the steel slab is reheated to a temperature of 1050 to 1250 ° C.

  A step of reheating the slab or ingot in a heating furnace is necessary for hot rolling. At this time, if the reheating temperature is too low as less than 1050 ° C., there is a problem that a large load is applied during rolling, and the alloy components are not sufficiently dissolved. On the other hand, when the reheating temperature is too high, there is a problem that the crystal grains grow excessively and the strength becomes low. In particular, in the composition range of the inventive steel, the grain boundary of the carbide is melted or the steel material Since the steel sheet may be reheated beyond the solidus temperature, the hot rolling property of the steel material may be impaired, so the upper limit is limited to 1250 ° C.

  Next, finish hot rolling is performed at a temperature of 800 ° C. to 1050 ° C. to manufacture a steel plate.

  The rolling temperature is 800 ° C to 1050 ° C. When rolling is performed at a temperature lower than 800 ° C., a large rolling load is applied, and the target ductility cannot be obtained by precipitation of carbides or coarse growth. Therefore, the upper limit is set to 1050 ° C.

  Next, the hot-rolled steel plate is cooled to 600 ° C. or lower at a cooling rate of 10 to 100 ° C./s.

  The steel material after finish rolling must be cooled at a cooling rate sufficient to suppress the formation of grain boundary carbides. When the cooling rate is less than 10 ° C./s, it is not sufficient to avoid carbide formation, and carbide precipitates at the grain boundaries during cooling, resulting in a decrease in ductility and early wear resistance degradation due to early fracture of steel. Therefore, the higher the cooling rate, the more advantageous. There is no need to particularly limit the upper limit of the cooling rate within the range of accelerated cooling. However, it is difficult for the cooling rate to exceed 100 ° C./s even during normal accelerated cooling.

  On the other hand, if the cooling stops at a high temperature even if the cooling is performed at a high speed, carbides may be generated or grow. Therefore, in one embodiment of the present invention, it is necessary to perform the cooling to 600 ° C. or less.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are merely examples for explaining the present invention in more detail, and do not limit the scope of rights of the present invention.

[Example 1]
After producing a slab satisfying the component system and composition range described in Table 1 by the series of reheating, hot rolling and cooling processes described in Table 2, the microstructure, stretch ratio, strength, carbide ratio, etc. are measured. The results are shown in Table 3 below. In addition, the unit of the content of each component in Table 1 is% by weight.

  Moreover, the corrosion rate test by the abrasion experiment based on ASTM G65 and the immersion experiment based on ASTM G31 was performed with respect to the steel material corresponding to each said comparative example and invention example, The result was shown in Table 4.

  Comparative Example A1 has a value of 33.5C-Mn of 6.8 and does not fall within the range controlled by the present invention. As a result, the target is formed by the formation of a large amount of martensite due to insufficient carbon content of the austenite stabilizing element. No austenite structure was obtained.

  In Comparative Example A2, the manganese and carbon contents fall within the range controlled by the present invention. However, since copper was not added, the formation of carbides could not be suppressed, and a large amount of carbides were crystal grains. Since it was formed along the boundary, the target microstructure and stretch ratio could not be obtained. It can be seen that the amount of wear is relatively high because sufficient work hardening has not been obtained due to the reduction of solute carbon due to carbide formation and the early fracture of the steel material.

  In addition, Comparative Examples A3 and A4 also fall within the range where the contents of manganese and carbon are limited by the present invention, but since the amount of copper addition does not reach the range defined by the present invention, the same as Comparative Example A2 above. Since a large amount of carbide was formed, the target microstructure and stretch ratio could not be obtained. If the amount of copper added does not fall within the range controlled by the present invention, carbide formation cannot be effectively suppressed, and sufficient work hardening cannot be obtained by early rupture due to a decrease in solid solution carbon and a reduction in stretch rate. This shows that the wear resistance is reduced.

  In Comparative Example A5, the composition satisfies the conditions of the present invention, but since the cooling rate after rolling is slow outside the range specified in the present invention, it is difficult to suppress the formation of carbides. Decreased.

  In contrast, Invention Examples A1 to A6 are steel types that satisfy all the component systems and composition ranges controlled by the present invention, and there is no deterioration in physical properties because the formation of grain boundary carbides is effectively suppressed by the addition of copper. Specifically, even when the carbon content was high, the carbides were effectively suppressed by the addition of copper, and the target microstructure and physical properties were obtained. Since carbon was sufficiently dissolved in austenite and grain boundary carbide formation was effectively suppressed, a stable stretch ratio and high tensile strength were obtained, so sufficient work hardening was ensured and the amount of wear decreased. .

  In particular, Invention Examples A5 to A6 were further added with chromium, so that the corrosion rate was slow and the corrosion resistance was improved in the corrosion evaluation experiment. That is, by adding chromium, the effect of improving corrosion resistance is superior to that of Invention Examples A1 to A4. Moreover, the strength improvement by solid solution strengthening was also obtained by chromium addition.

  FIG. 2 shows a microstructure photograph of the steel material produced by the invention example A2. From this, it can be confirmed that there is no carbide even at a high carbon content by adding copper within the range controlled by the present invention.

[Example 2]
Steel slabs were manufactured using continuous casting as invention examples and comparative examples satisfying the component systems described in Table 5 below. The unit of the content of each component in Table 5 is% by weight.

  The steel slab thus produced was reheated under the conditions shown in Table 6, then hot finish rolled and cooled to produce a steel plate.

  About the manufactured said steel plate, the austenite fraction, the carbide | carbonized_material fraction, the extending | stretching rate, the yield strength, and the tensile strength were measured, and it showed in following Table 7. For machinability evaluation, a high-speed tool steel drill with a diameter of 10 mm was used to repeatedly drill holes in the steel material at a rotational speed of 130 rpm and a drill advance speed of 0.08 mm / rev until the drill was worn out and the life was exhausted. The number of holes was measured and shown in Table 7.

  Moreover, the corrosion rate by the abrasion experiment based on ASTM G65 and the immersion experiment based on ASTM G31 was measured about the steel plate of the said comparative example and invention example, The result was shown in Table 8.

  This example is a steel type in which the carbon and manganese contents satisfy all the component systems and composition ranges controlled by the present invention, and there is no deterioration in physical properties because the formation of grain boundary carbides is effectively suppressed by the addition of copper. Specifically, even when the carbon content was high, the carbides were effectively suppressed by the addition of copper, and the target microstructure and physical properties were obtained. Since carbon was sufficiently dissolved in austenite and grain boundary carbide formation was effectively suppressed, a stable stretch ratio and high tensile strength were obtained, so sufficient work hardening was ensured and the amount of wear decreased. .

  Comparative Examples B1 to B5 are inferior in machinability because sulfur and calcium are not added or are out of the range controlled by the present invention.

  In contrast, Invention Examples B1 to B5 are steel types in which the addition amounts of sulfur and calcium satisfy all the component systems and composition ranges controlled by the present invention, and are excellent in machinability as compared with Comparative Examples. In particular, Invention Examples B2 to B4 were obtained by changing the sulfur content, and the machinability was further improved by increasing the sulfur content.

  FIG. 3 shows the machinability depending on the sulfur content. Referring to FIG. 3, it can be confirmed that the machinability is increased by increasing the sulfur content.

Claims (8)

  8% to 15% manganese (Mn) by weight%, carbon (C) satisfying the relationship of 23% <33.5C-Mn ≦ 37%, 1.6C-1.4 (%) ≦ Cu ≦ 5% A wear-resistant austenitic steel material excellent in machinability and ductility, including copper (Cu) filling, balance Fe and other inevitable impurities.   The machinability and ductility according to claim 1, wherein the steel material further includes, by weight%, sulfur (S): 0.03-0.1% and calcium (Ca): 0.001-0.01%. Excellent wear-resistant austenitic steel.   The wear-resistant austenitic steel material having excellent machinability and ductility according to claim 1 or 2, wherein the steel material further contains 8% by weight or less (excluding 0%) of chromium (Cr).   The wear-resistant austenitic steel material excellent in machinability and ductility according to claim 1 or 2, wherein the microstructure of the steel material is 90% or more in area fraction of austenite.   The wear-resistant austenitic steel material excellent in machinability and ductility according to claim 1 or 2, wherein the steel material contains carbide in an area fraction of 10% or less. 8% to 15% manganese (Mn) by weight%, carbon (C) satisfying the relationship of 23% <33.5C-Mn ≦ 37%, 1.6C-1.4 (%) ≦ Cu ≦ 5% Reheating the steel slab containing copper (Cu), balance Fe and other inevitable impurities to a temperature of 1050-1250 ° C .;
A step of producing a steel sheet by hot rolling at a temperature of 800 ° C. to 1050 ° C .;
A method for producing a wear-resistant austenitic steel material excellent in machinability and ductility, comprising the step of cooling the hot-rolled steel sheet at a cooling rate of 10 to 100 ° C./s to 600 ° C. or less.   The steel slab, by weight%, further includes sulfur (S): 0.03-0.1% and calcium (Ca): 0.001-0.01%. A method for producing wear-resistant austenitic steel with excellent ductility.   The method for producing a wear-resistant austenitic steel material excellent in machinability and ductility according to claim 6 or 7, wherein the steel slab further contains 8% by weight or less (excluding 0%) of chromium (Cr).

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