JP2009215587A - Method for manufacturing steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a steel material, which eliminates an anisotropy of mechanical properties of even a steel material which has been obtained by forging a steel ingot. <P>SOLUTION: The method includes the steps of: forging the steel ingot 11 (forging step S11) to manufacture a steel material 12; subjecting the steel material 12 to a continuous cooling transformation treatment (preliminarily heat-treating step S12) of annealing the steel material 12 by heating the steel material 12 at 850 to 1,000°C and slowly cooling it to 500°C while spending 30 minutes or longer; and then subjecting the steel material 12 to thermal refining treatment (thermal refining treatment step S13) such as quenching and tempering to obtain a steel material 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a steel material by forging a steel ingot.

  For example, steel parts obtained by forging steel ingots are used for parts such as piston crowns of piston engines such as diesel engines.

JP 2000-312907 A

  The steel ingot generates a dendrite structure during solidification and has a specific crystal orientation, that is, a so-called texture, and therefore has anisotropy in mechanical properties. For this reason, the steel material which forged the steel ingot has low ductility and toughness with respect to the perpendicular direction of a forging flow (streamline) from the anisotropy of the mechanical property by the said texture.

  Therefore, for example, as shown in FIG. 6, in the piston crown 1 of a piston engine such as a diesel engine manufactured using the steel material, the streamline f is in the circumferential surface 1a with respect to the piston movement direction m. It exists in the direction parallel to the head portion 1b and crosses the head portion 1b. In particular, the β portion of the head portion 1b is more easily damaged than the α portion of the peripheral surface 1a.

  For these reasons, an object of the present invention is to provide a method for producing a steel material that can eliminate the anisotropy of mechanical properties even if the steel material is obtained by forging a steel ingot.

  The method for manufacturing a steel material according to the first invention for solving the above-described problem is a method for manufacturing a steel material by forging a steel ingot to manufacture a steel material, wherein the steel material is at least one of a ferrite structure and a pearlite structure. Thus, the forged steel material is subjected to preliminary heat treatment.

  According to a second aspect of the present invention, there is provided a method for producing a steel material according to the first aspect, wherein the preliminary heat treatment includes at least one of a ferrite transformation and a pearlite transformation without causing martensitic transformation and bainite transformation from austenite transformation. It is the process which carries out the continuous cooling transformation of the said steel materials so that it may produce.

  A method for producing a steel material according to a third invention is the treatment according to the first invention, wherein the preliminary heat treatment is isothermally transformed so that the austenite structure becomes at least one of a ferrite structure and a pearlite structure. It is characterized by being.

  According to a fourth aspect of the present invention, there is provided a method for producing a steel material according to the second aspect, wherein the steel ingot comprises carbon of 0.38 to 0.43% by weight, silicon of 0.15 to 0.35% by weight, manganese of 0.1%. 60 to 0.90 wt%, molybdenum 0.15 to 0.30 wt%, chromium 0.90 to 1.20 wt%, nickel 0.25 wt% or less, phosphorus 0.03 wt% or less, sulfur 0.03 Annealing which consists of the remaining iron, and the preliminary heat treatment heats the steel material to 850 to 1000 ° C., and then gradually cools to 500 ° C. for 30 minutes or more and performs continuous cooling transformation treatment. It is characterized by being.

  According to a fifth aspect of the present invention, there is provided a method for producing a steel material according to the third aspect, wherein the steel ingot comprises carbon of 0.38 to 0.43% by weight, silicon of 0.15 to 0.35% by weight, manganese of 0.1%. 60 to 0.90 wt%, molybdenum 0.15 to 0.30 wt%, chromium 0.90 to 1.20 wt%, nickel 0.25 wt% or less, phosphorus 0.03 wt% or less, sulfur 0.03 The pre-heat treatment is an annealing in which the steel material is heated to 850 to 1000 ° C. and then held at 600 to 700 ° C. for 1 to 5 hours to perform isothermal transformation treatment. It is characterized by.

  According to a sixth aspect of the present invention, there is provided a method for producing a steel material according to any one of the first to fifth aspects, wherein the preliminary heat treatment is performed a plurality of times.

  A method for manufacturing a steel material according to a seventh aspect is characterized in that, in the sixth aspect, the preliminary heat treatment is performed twice.

  The method for producing a steel material according to an eighth invention is characterized in that, in any of the first to seventh inventions, after the preliminary heat treatment, a tempering heat treatment for tempering the steel material is performed.

  The steel material according to the ninth aspect of the present invention is manufactured by the method for manufacturing a steel material according to any one of the first to eighth aspects of the invention.

  According to the method for producing a steel material according to the present invention, since the pre-heat treatment is performed on the forged steel material so that the steel material has at least one of a ferrite structure and a pearlite structure, the steel material is forged. Even if it is a steel material, the anisotropy of mechanical properties can be eliminated.

  Although the embodiment of the manufacturing method of the steel materials concerning the present invention is described below based on a drawing, the present invention is not limited only to the embodiment described below based on a drawing.

[First embodiment]
1st embodiment of the manufacturing method of the steel materials concerning this invention is described based on FIGS. 1-3. FIG. 1 is a flow diagram of a method for manufacturing a steel material, FIG. 2 is a continuous cooling transformation (CCT) curve diagram, and FIG. 3 is a schematic structural diagram of a piston crown.

  As shown in FIG. 1, the method for manufacturing a steel material according to this embodiment includes, for example, carbon 0.38 to 0.43 wt%, silicon 0.15 to 0.35 wt%, and manganese 0.60 to 0.90. % By weight, molybdenum 0.15 to 0.30% by weight, chromium 0.90 to 1.20% by weight, nickel 0.25% by weight or less, phosphorus 0.03% by weight or less, sulfur 0.03% by weight or less, balance When the steel ingot 11 made of iron is forged (stepping step S11) to produce the steel material 12 (for example, “SCM440”), the steel material 12 is heated to 850 to 1000 ° C., and then to 500 ° C. for 30 minutes. By slowly cooling the steel material 12 as described above, the steel material 12 is annealed and subjected to continuous cooling transformation treatment (preliminary heat treatment step S12), and then subjected to tempering heat treatment such as quenching and tempering ( Conditioning heat treatment step S13), steel 1 Obtained.

  In the steel material 13 which performed such preliminary heat treatment process S12, as shown in FIG. 2, it transforms to an austenite (A) structure | tissue by heating to 850-1000 degreeC, and it is 30 minutes or more to 500 degreeC. In short, by slow cooling, ferrite (F) transformation and pearlite (P) transformation are produced without causing martensite (M) transformation and bainite (Zw) transformation. It becomes at least one of a tissue and a perlite (P) tissue.

  In the steel material 13 that has been subjected to the preliminary heat treatment step S12 so as to become at least one of a ferrite (F) structure and a pearlite (P) structure in this way, That is, since it is a nucleated structure independently of the texture of the steel ingot 11 which has a specific crystal orientation by generating a dendrite structure during solidification, the orientation with respect to the texture Since there is no dependence at all and the forging texture is divided, anisotropy is removed.

  For this reason, in the piston crown 100 of the piston engine such as a diesel engine as shown in FIG. 3 manufactured using the steel material 13, anisotropy occurs between the peripheral surface 100a and the head portion 100b. Thus, the mechanical properties of the α portion of the peripheral surface 100a and the β portion of the head portion 100b can be made substantially equal.

  Therefore, according to the manufacturing method of the steel material 13 which concerns on this embodiment, even if it is the steel material 12 obtained by forging the steel ingot 11, the anisotropy of a mechanical property can be eliminated.

  Further, since the crystal has no anisotropy due to the preliminary heat treatment step S12, the coarsening of the crystal grains is suppressed and the crystal grains can be refined even if the tempering heat treatment step S13 is performed. Therefore, the mechanical strength of the steel material 13 can be increased, ductility and toughness can be increased, and the mechanical properties can be further improved.

[Second Embodiment]
A second embodiment of the method for manufacturing a steel material according to the present invention will be described with reference to FIGS. FIG. 4 is a flow diagram of a method for manufacturing a steel material, and FIG. 5 is an isothermal transformation (TTT) curve diagram. However, for the same parts as the first embodiment described above, the same reference numerals as those used in the description of the first embodiment described above are used, so that the first embodiment described above is used. The description overlapping with the description of is omitted.

  As shown in FIG. 4, in the method of manufacturing a steel material according to the present embodiment, when the steel ingot 11 is forged (stepping process S11) and the steel material 12 is manufactured, the steel material 12 is increased to 850 to 1000 ° C. After heating and holding at 600 to 700 ° C. for 1 to 5 hours, the steel material 12 is annealed and subjected to isothermal transformation by cooling to room temperature (preliminary heat treatment step S22), and then quenched. By performing tempering heat treatment such as tempering (tempering heat treatment step S13), the steel material 23 is obtained.

  In the steel material 23 which performed such preliminary heat treatment process S22, as shown in FIG. 5, by heating to 850-1000 degreeC, it transforms to an austenite (A) structure | tissue, and 1-600 at 600-700 degreeC. By being held for 5 hours, the ferrite (F) transformation and the pearlite (P) transformation are caused from the austenite (A) composition to become at least one of a ferrite (F) structure and a pearlite (P) structure.

  Thus, in the steel material 23 subjected to the preliminary heat treatment step S22 so as to be at least one of a ferrite (F) structure and a pearlite (P) structure, as in the case of the first embodiment described above, Since there is no orientation dependency on the texture and the forging texture is divided, anisotropy is removed.

  For this reason, for example, in the piston crown 100 manufactured using the steel material 23, as in the case of the first embodiment described above, the α portion of the peripheral surface 100a and the β portion of the head portion 100b. The mechanical properties can be made almost equal.

  Therefore, according to the manufacturing method of the steel material 23 according to the present embodiment, even in the case of the steel material 12 obtained by forging the steel ingot 11 as in the case of the first embodiment described above, mechanical properties are obtained. The anisotropy can be eliminated.

  Further, as in the case of the first embodiment described above, the preliminary heat treatment step S22 eliminates anisotropy in the crystal and refines the crystal grain, thereby increasing the mechanical strength of the steel material 23. In addition, the ductility and toughness can be increased, and the mechanical properties can be further improved.

[Other Embodiments]
In the above-described embodiment, the tempering heat treatment step S13 is performed after the preliminary heat treatment steps S12 and S22 are performed once. However, as another embodiment, for example, the preliminary heat treatment steps S12 and S22 are performed. Is preferably performed a plurality of times because the transformation rate (the ratio of the ferrite structure and the pearlite structure) of the steel materials 13 and 23 can be increased.

  The confirmation test performed in order to confirm the effect of the manufacturing method of the steel material which concerns on this invention is demonstrated below.

[Confirmation test 1: Number of preliminary heat treatments]
The preliminary heat treatment based on the first and second embodiments described above is repeated for each of the three specimens (SCM440) 1A to 1C and 2A to 2C, and each specimen (SCM440) 1A to 1C, The transformation rate (the ratio of the ferrite structure and pearlite structure) of 2A to 2C was determined. The results are shown in Table 1 below. The transformation rate was evaluated as 100% when a Vickers hardness test was performed and the obtained value was HV230 or less.

  As can be seen from Table 1 above, when the pre-heat treatment is performed once, the transformation rate becomes uneven. However, when the pre-heat treatment is performed twice, all the transformation rates are 90% or more, and the pre-heat treatment is performed three times. When done, the transformation rate was approximately 100%. From this, it was confirmed that the transformation rate can be increased by performing the preliminary heat treatment a plurality of times. Moreover, when performing preliminary heat processing in multiple times, if it was not 3 times or less, it has been confirmed that a waste of time and cost will occur. Furthermore, when the transformation rate, labor and cost balance are taken into consideration, it was confirmed that 2 times was most preferable.

[Confirmation test 2: Tensile test and impact test]
A piston crown 100 of a piston engine such as a diesel engine shown in FIG. 3 is produced using steel materials (SCM440) manufactured based on the respective embodiments described above, and the α portion of the peripheral surface 100a and the head portion 100b are formed. Two test pieces were cut out from each β part and subjected to a tensile test and an impact test at room temperature. The results are shown in Table 2 below.

  In addition, based on 1st embodiment mentioned above, (alpha) part and (beta) part of the piston crown 100 produced using the steel material 13 which performed the said preliminary heat treatment process S12 (continuous cooling transformation process process) once, and was manufactured. The test pieces cut out from the specimens were used as specimens 11αA, 11αB, 11βA, and 11βB, respectively, and the α of the piston crown 100 produced by using the steel material 13 produced by performing the preliminary heat treatment step S12 (continuous cooling transformation treatment step) twice. Test pieces cut out from the portion and the β portion were designated as test bodies 12αA, 12αB, 12βA, and 12βB, respectively.

  Based on the second embodiment described above, from the α portion and the β portion of the piston crown 100 manufactured using the steel material 23 manufactured by performing the preliminary heat treatment step S22 (isothermal transformation step) once. The cut test pieces are used as specimens 21αA, 21αB, 21βA, and 21βB, respectively, and the α portion of the piston crown 100 manufactured by using the steel material 23 manufactured by performing the preliminary heat treatment step S22 (isothermal transformation treatment step) twice, and Test pieces cut out from the β portion were designated as test specimens 22αA, 22αB, 22βA, and 22βB, respectively.

  For comparison, the steel plate (SCM440) manufactured by omitting the preliminary heat treatment steps S12 and S22 is cut out from the α portion of the peripheral surface 1a of the conventional piston crown 1 and the β portion of the head portion 1b. The test pieces (test bodies 00αA, 00αB, 00βA, 00βB) were also subjected to a tensile test and an impact test at room temperature. The results are also shown in Table 2 below.

  As can be seen from Table 2 above, the specimen 00β (conventional head) has lower mechanical properties than the specimen 00α (peripheral surface of the conventional article), and in particular, has a large elongation, squeezing and impact properties. It is falling. In contrast, the specimens 11β, 12β, 21β, and 22β (the head portion of the present invention) are inferior in mechanical properties to the specimens 11α, 12α, 21α, and 22α (the peripheral surface of the present invention). There was no.

  Further, the rate of decrease in the mechanical properties (particularly, elongation, squeezing, impact properties) of the test specimens 11β, 12β (isothermal transformation treatment head portion) relative to the test specimens 11α, 12α (the isothermal transformation treatment peripheral surface) 21α, 22α (peripheral surface of continuous cooling transformation treatment) is smaller than the decrease rate of the mechanical properties of the specimens 21β, 22β (head portion of the continuous cooling transformation treatment), and the specimens 12α, 22α (of the two treatments) The decrease rate of the mechanical properties (especially elongation, squeezing, impact properties) of the test bodies 12β and 22β (two-time processing head portion) with respect to the peripheral surface) is relative to the test samples 11α and 21α (single-processing peripheral surface). It became much smaller than the decreasing rate of the mechanical properties of the test bodies 11β and 21β (head portion after one treatment).

  From these results, it was recognized that according to the method for producing a steel material according to the present invention, mechanical strength can be increased, ductility and toughness can be increased, and mechanical properties can be improved.

  Even if the steel material manufacturing method according to the present invention is a steel material obtained by forging a steel ingot, the anisotropy of mechanical properties can be eliminated. It can be used beneficially.

It is a flowchart of 1st embodiment of the manufacturing method of the steel materials concerning this invention. It is a continuous cooling transformation (CCT) curve figure in 1st embodiment of the manufacturing method of the steel materials concerning this invention. It is a schematic structural drawing of the piston crown produced using the steel materials manufactured by 1st embodiment. It is a flowchart of 2nd embodiment of the manufacturing method of the steel materials which concern on this invention. It is an isothermal transformation (TTT) curve figure in 2nd embodiment of the manufacturing method of the steel materials concerning this invention. It is a schematic structural drawing of the piston crown produced using the steel materials manufactured by the conventional method.

Explanation of symbols

100 piston crown 100a peripheral surface 100b head

Claims (9)

In the method of manufacturing a steel material forging a steel ingot to manufacture a steel material,
A pre-heat treatment is performed on the forged steel material so that the steel material has at least one of a ferrite structure and a pearlite structure. In the manufacturing method of the steel materials according to claim 1,
The preliminary heat treatment is a process of continuously cooling and transforming the steel material so as to cause at least one of ferrite transformation and pearlite transformation without causing martensitic transformation and bainite transformation from austenite transformation. Steel manufacturing method. In the manufacturing method of the steel materials according to claim 1,
The method for producing a steel material, wherein the preliminary heat treatment is a process of isothermally transforming the steel material so as to change from an austenite structure to at least one of a ferrite structure and a pearlite structure. In the manufacturing method of the steel materials according to claim 2,
The steel ingot is carbon 0.38 to 0.43% by weight, silicon 0.15 to 0.35% by weight, manganese 0.60 to 0.90% by weight, molybdenum 0.15 to 0.30% by weight, chromium 0.90 to 1.20% by weight, nickel 0.25% or less, phosphorus 0.03% or less, sulfur 0.03% or less, the balance iron,
The preliminary heat treatment is an annealing in which the steel material is heated to 850 to 1000 ° C., and then slowly cooled to 500 ° C. for 30 minutes or more and subjected to continuous cooling transformation treatment. Production method. In the manufacturing method of the steel materials according to claim 3,
The steel ingot is carbon 0.38 to 0.43 wt%, silicon 0.15 to 0.35 wt%, manganese 0.60 to 0.90 wt%, molybdenum 0.15 to 0.30 wt%, chromium 0.90 to 1.20% by weight, nickel 0.25% or less, phosphorus 0.03% or less, sulfur 0.03% or less, the balance iron,
The method for producing a forged steel material, wherein the preliminary heat treatment is an annealing in which the steel material is heated to 850 to 1000 ° C. and then held at 600 to 700 ° C. for 1 to 5 hours to perform an isothermal transformation treatment. . In the manufacturing method of the steel materials as described in any one of Claims 1-5,
The method for producing a steel material, wherein the preliminary heat treatment is performed a plurality of times. In the manufacturing method of the steel materials according to claim 6,
The method for producing a steel material, wherein the preliminary heat treatment is performed twice. In the manufacturing method of the steel materials as described in any one of Claims 1-7,
A tempering heat treatment for tempering the steel material is performed after the preliminary heat treatment.   A steel material manufactured by the method for manufacturing a steel material according to any one of claims 1 to 8.

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