Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/002—Heat treatment of ferrous alloys containing Cr
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium

Definitions

• the present invention relates to a method for producing a steel material having a pearlite nose transformation completion point of 30 minutes or more. Specifically, a steel material having a hot work in the previous process, a hot work in the next process, and an intermediate annealing of semi finished steel products performed between the hot process in the previous process and the hot process in the next process. It is related with the manufacturing method.
• the heat history of the conventional method of the above-described hot-working in the previous step ⁇ intermediate annealing ⁇ next-step hot working is shown in FIG. 2, and hot working steps such as hot forging and hot rolling are shown.
• the workpiece steel sini-finished steel
• the heating furnace 25 in Fig. 2
• the annealing process it is heated and held at the desired temperature above the Ac3 point (26 in Fig. 2) and managed to completely transform into austenite.
• it is extremely hardenable!
• the intermediate annealing is completed by controlling so as to achieve slow cooling (27, 28, 29 in Fig. 2) that sufficiently causes pearlite transformation.
• the semi-finished steel material that has been subjected to intermediate annealing is adjusted to a low hardness as well as the metal structure, and becomes a material for hot working in the next process.
• Patent Document 1 JP-A-8-260058
• the object of the present invention is to perform intermediate annealing of steel made of an extremely hardenable alloy with a pearlite nose transformation completion point of 30 minutes or more, equivalent to intermediate annealing using a heating furnace without using a heating furnace. It is providing the manufacturing method of the steel materials from which an effect is acquired. Means for solving the problem
• the present invention has been made in view of the above-described problems.
• the present invention relates to a method of manufacturing a steel material having a pearlite nose transformation completion point of 30 minutes or more, wherein the manufacturing method includes a pre-process hot working, a next process hot working, a pre-process hot working, and a next process.
• Intermediate annealing performed between process hot working, and the intermediate annealing takes the semi-finished steel material after completion of the previous process hot working in a heat retaining tank, reheats the steel material, and the semi-finished product.
• This is a method for producing a steel material comprising the step of subjecting the semi-finished steel material to a pearlite transformation by maintaining the temperature within a temperature range of ⁇ 20 ° C for 30 minutes or more by the latent heat of transformation of the pearlite nose.
• the method is a method for producing a steel material in which the semi-finished steel material that has been manned in the heat retaining tank is kept warm for 2 hours or more within a temperature range of 20 ° C of the pearlite nose transformation completion point.
• it is a method for producing a steel material in which the semi-finished steel material that has been manned in the heat insulation bath is kept warm for 2 hours or more within the temperature range of pearlite nose transformation completion point ⁇ 10 ° C, more preferably, the heat insulation bath.
• it is a method for producing a steel material in which the hardness of the semi-finished steel material after intermediate annealing is 300 HB or less.
• the method for producing a steel material of the present invention is particularly preferable for a semi-finished steel material having a weight of 500 kg or more.
• the production method of the present invention is as follows:% by mass: 0.10 to 2.0%, Si: 2.0% or less, Mn: 2.0% or less, Cr: l. 0 to 15.0%, Contains Mo: 10.0% or less, Ni: 4.0% or less, V: 4.0% or less, W: 20.0% or less, Co: 10.0% or less, one or more It is particularly desirable to apply it to semi-finished steel materials having a chemical composition with the balance being substantially Fe.
• the invention's effect is particularly desirable to apply it to semi-finished steel materials having a chemical composition with the balance being substantially Fe.
• Examples of methods for producing a steel material having a pearlite nose transformation completion point of 30 minutes or more include a melting step in which a steel ingot is produced by forging molten steel, and the steel ingot obtained in this melting step is heated several times. Including annealing, intermediate annealing is performed between hot workings. The material hot-worked after the intermediate annealing can be subjected to heat treatment such as annealing and quenching and tempering.
• the intermediate annealing referred to in the present invention is defined as intermediate annealing, which is performed between the previous process hot working and the next process hot working as described above.
• intermediate annealing which is performed between the previous process hot working and the next process hot working as described above.
• first and second annealing are the present invention. It is an intermediate annealing.
• steel materials with good hardenability with a pearlite nose transformation completion point of 30 minutes or more, which was considered essential for independent intermediate annealing for strict temperature control, are used.
• Typical steel materials having a transformation completion point of the pearlite nose of the present invention of 30 minutes or more are alloy tool steels such as SKD11, SKD61, and SKT4.
• the steel material annealing method of the present invention is more effective when applied to steel materials having a pearlite nose transformation completion point of 60 minutes or more. More preferably, the pearlite nose transformation completion point is more than 90 minutes, and the pearlite nose transformation completion point is more than 2 hours.
• the transformation completion point of the pearlite nose may be measured as follows.
• the pearlite transformation starts after a certain period of time, and the transformation ends with the passage of time. . If it is cooled during the transformation, the remaining austenite is martensiteed, so the time until the transformation is completed can be determined by hardness measurement.
• a diagram (TTT curve) as shown in Fig. 4 can be obtained.
• the part of the curve that approaches the shortest time at which the hardness sharply decreases at a certain temperature is pearlite. This is the transformation completion point.
• austenite cannot be confirmed.
• the steel material heated to the hot forging temperature is placed in a furnace maintained at 25 ° C intervals in the temperature range of 700 ° C to 775 ° C for 2, 5, 15, 24 hours.
• the steel material held at the above temperature and time is taken out of the furnace and air-cooled, the hardness of the steel material is measured, and the pearlite nose is around the shortest 5 hours at 750 ° C where the hardness sharply decreases. This is the transformation completion point.
• the transformation completion point of the pearlite nose is 30 minutes or more with reference to Fig. 3.
• the pearlite nose is plotted on the TTT curve with the vertical axis indicating the holding temperature (° C) and the horizontal axis indicating the holding time (min).
• the transformation completion point is located at a holding time of 30 minutes, it is called the pearlite nose transformation completion point 30 minutes (the curve shown by the dotted line in Fig. 3).
• Those located at are called the perlite nose transformation completion point of 30 minutes or more (curved line in Fig. 3).
• the semi-finished steel After finishing the hot working process such as hot forging and hot rolling (1 in Fig. 1), the semi-finished steel is cooled (2 in Fig. 1: cooling process after hot working). Then, in the middle of the cooling process after hot working, the semi-finished steel material is transferred to the heat insulation tank and the process goes to annealing process 3. Using semi-finished steel in a heat insulation tank, recover the surface temperature of the semi-finished steel (21 in Fig. 1).
• Recuperation means that a semi-finished steel material is inserted into a heat insulation tank, and the surface temperature of the semi-finished steel material is increased by heat conduction from the inside of the semi-finished steel material and radiation heat from the heat insulation tank wall. It is to reduce the temperature difference from the steel surface temperature. In this way, preparations are made to insulate the semi-finished steel material by the latent heat of transformation.
• the heat insulation tank (22 in Fig. 1) by the latent heat of transformation of the semi-finished steel material.
• the heat insulation uses the heat generated when the semi-finished steel material is transformed. That is, in the present invention, the semi-finished steel material is kept at a predetermined temperature and time by using the latent heat of transformation of the semi-finished steel material, and the semi-finished steel material is pearlite transformed. Therefore, the temperature range for keeping warm and the time required for keeping warm are extremely important. In the present invention, the heat insulation condition is 30 minutes or more within the temperature range of 20 ° C of the pearlite nose transformation completion point.
• the reason for setting the pearlite nose transformation completion point 20 ° C. at the heat retaining temperature is that this temperature range is a temperature range in which the pearlite transformation is completed in a shorter time, and the latent heat of transformation is used. It is also a force that can reduce the hardness. If the pearlite nose transformation completion point is higher than + 20 ° C when the temperature is kept, it takes time to complete the pearlite transformation, which is uneconomical and the metal structure tends to become rough. The In addition, the pearlite nose transformation completion point—in the temperature range below 20 ° C, it takes time to complete the pearlite transformation, which is uneconomical, and the hardness of the pearlite nose is less likely to occur. Decrease may be insufficient.
• a preferred temperature range is a pearlite nose transformation completion point ⁇ 10 ° C.
• the reason why the heat retention time is set to 30 minutes or more is that if it is less than 30 minutes, the pearlite transformation may not proceed sufficiently, and problems such as insufficient soft cracking and cracking due to insufficient precipitation of carbides occur.
• a preferred heat retention time is 1 hour or longer, more preferably 2 hours or longer.
• a more preferable range of the incubation time is 2 to 24 hours.
• the hardness after intermediate annealing can be reduced to 300HB or less, which is suitable as an intermediate annealing material.
• the hardness after the intermediate annealing is preferably 270 HB or less, more preferably 250 HB or less.
• the preferred temperature of the semi-finished steel surface is that the maximum temperature on the surface of the semi-finished steel is the pearlite nose transformation completion point + 100 ° C to the pearlite nose transformation completion point-200 ° C. Is within.
• the preferable upper limit temperature for entering the semi-finished steel material is set to 100 ° C of the completion point of the pearlite nose transformation in consideration of reheating of the semi-finished steel material.
• the temperature of the surface of the semi-finished steel material exceeds the pearlite nose transformation completion point + 200 ° C after the semi-finished steel material is added, a part of the heat insulation tank described later is released to make the semi-finished steel material. It is desirable to suppress the temperature rise of steel products.
• the preferable lower limit temperature at which the semi-finished steel material is introduced into the heat insulation tank is set such that the maximum temperature on the steel surface is the pearlite nose transformation completion point-200 ° C.
• the maximum temperature of the steel surface falls below the pearlite nose transformation completion point of 200 ° C, it is difficult for the semi-finished steel material to reheat up to ⁇ 20 ° C transformation completion point of the pearlite nose in the thermal insulation bath. Because.
• the range of the temperature at which the semi-finished steel material is fed into the preferred thermal insulation tank is that the maximum temperature of the surface of the semi-finished steel material is the transformation completion point of the pearlite nose + 50 ° C to the transformation completion point of the pearlite nose 150 ° C.
• the transformation completion point of the pearlite nose is + 50 ° C. to the transformation completion point of the pearlite nose—100 ° C.
• the maximum temperature of the steel material surface is the highest temperature of the entire surface of the steel material and the temperature of the region.
• the reason for the surface of the semi-finished steel material is that the heat of the hot processing still remains inside the semi-finished steel material, and the surface intersecting with the outside air is the position where the temperature is the lowest. It is defined as the temperature of the product steel surface. Note that the temperature of the surface of the semi-finished steel material can be measured, for example, with a radiation thermometer.
• the heat insulation tank referred to in the present invention is, for example, a box-shaped or lid-shaped one that covers the semi-finished steel material.
• This heat-insulating tank does not have a heating source, for example, a heat insulating material is provided inside the box-shaped or lid-shaped.
• the structure should be such that a semi-finished steel material can be pearlite transformed by forming a sealed space and keeping the semi-finished steel material in a certain range of temperature and time by the latent heat of transformation of the semi-finished steel material.
• a hole for inserting a thermocouple thermometer into a part of the heat insulation tank a hole for visually checking the color of the steel material inside the heat insulation tank, and for adjusting the surface temperature of the semi-finished steel material It is not always necessary to form a sealed space that completely shuts off the outside air.
• FIGS. 5A to 5D The structure of the heat insulation tank is shown in FIGS. 5A to 5D, for example, as shown in a schematic diagram of a front view and a side view.
• the semi-finished steel material 4 is placed on the tank base 5 and the heat insulation tank base 5 is covered with the heat insulation tank upper cover 6 so as to form a sealed space that covers the semi-finished steel material 4.
• the heat insulation tank 7 has a structure in which the semi-finished steel material 4 is placed inside the heat insulation tank lower cover 8 and the heat insulation tank upper cover 6 is covered to form a sealed space covering the steel material 4.
• the semi-finished steel material 4 is placed on the heat insulating tank base 5, and the heat insulating tank 7 with moving wheels 10 capable of traveling on the rail 11 is moved in the direction of the arrow to make the semi-finished steel material 4
• It may be a cart type structure that forms a sealed space that covers.
• the heat insulating tank 7 may be fixed, and a moving wheel may be provided on the heat insulating tank base to move the heat insulating tank base.
• the structure of the heat insulation tank is determined in consideration of the shape and weight of the semi-finished steel material.
• the cross-sectional shape of the heat insulation tank lower lid 7 triangular, accommodate the round bar steel 4 and cover the heat insulation tank upper cover 6.
• a heat insulation tank lower lid fall prevention member 9 for preventing the heat insulation tank lower lid 8 from falling.
• the heat insulation tank lower lid falling prevention member 9 may have a cross-sectional shape such as a force M-shape or a V block as an example of a pillar shape.
• FIG. 5A, 5B, 6A, 6B and 7A, 7B is not a sealed space
• FIGS. 5C, 5D, 6C, 6D, and 7C, 7D are sealed spaces. It is in a formed state.
• the annealing process 3 is performed in which the semi-finished steel material is kept warm using the above-described heat-retaining tank, and the semi-finished steel material is also taken out from the heat-sink tank 23 (23 in Fig. 1). (24 in Fig. 1) is applied, and annealing process 3 is completed.
• the weight of the semi-finished steel material it is particularly preferable to apply the weight of the semi-finished steel material to a large semi-finished steel material having a weight of 500 kg or more.
• a large semi-finished steel with a weight of 500 kg or more can retain the heat from the double heat described above by the latent heat of transformation, and can secure the amount of heat necessary for sufficient heat retention time for pearlite transformation.
• the above-mentioned effects can be further exerted, and a semi-finished steel material of 4 tons or more
• the product steel material can sufficiently exhibit the above-mentioned effects.
• the present invention by using the pearlite transformation latent heat of the semi-finished steel material, it is possible to obtain the same effect as the intermediate annealing using the conventional heating furnace without converting the metal structure to martensite. Can do.
• steel products refers to steel processed into a desired shape by rolling, forging, drawing, or the like.
• the semi-finished steel material referred to in the present invention corresponds to a steel slab in JIS terms and refers to a material that becomes the steel material by hot working. For example, «Slab, bloom, billet, sheet bar or slab of circular shape with a diameter exceeding 130mm.
• the filling rate of the semi-finished steel material is 15% or more, the amount of heat of the semi-finished steel material is large, so the time until recuperation is short, and the pearlite nose transformation completion point is within the temperature range of ⁇ 20 ° C. This is because a warming effect with a margin can be obtained.
• the amount of charge is small! /, Which is uneconomical, and the amount of heat of the semi-finished steel material is small.
• the preferred upper limit is 95%, and when it reaches 100%, a heat insulation tank with the same dimensions as the semi-finished steel material is required, and the degree of freedom of the semi-finished steel material size is lost, making it unusable. Become. Therefore, the preferred upper limit should be 95%.
• the method for producing a semi-finished steel material of the present invention is effective for alloys belonging to the category of tool steel defined by JIS. Among these, it is particularly effective for an alloy having the following composition. In addition, content of each following element is the mass%.
• the C content is set to 0.10% to 2.0% because when C is less than 0.10%, C does not diffuse into the crystal grains, and the pearlite transformation does not occur in the crystal grains. May not progress. A content of at least 0.1% is preferable. 2. If it exceeds 0%, the carbides become excessive and the toughness is lowered. Preferably, C: 0.20-0.60%. Si: 2.0% or less
• Si is added as a deoxidizer during dissolution.
• the toughness decreases. Therefore, in the present invention, it was made 2.0% or less.
• Mn is added as a deoxidizing and desulfurizing agent during dissolution.
• the toughness decreases. Therefore, in the present invention, it was made 2.0% or less. Preferably it is 0.30 ⁇ : L 00%.
• Cr improves hardenability and improves tensile strength and toughness. However, if it is contained in a large amount, the toughness is reduced. Therefore, in the present invention, it was set to 1.0 to 15.0%. Preferably it is 1.0 to 13.0%.
• Mo improves hardenability.
• fine carbides are formed by tempering to increase the high-temperature tensile strength.
• the toughness is lowered. Therefore, it was made 10.0% or less.
• it is 0.20-5.0%.
• Ni, V, W, and Co are selective elements and contain one or more.
• Ni improves hardenability and improves toughness. However, if contained in a large amount, the transformation point is lowered and the high temperature strength is lowered. Therefore, if Ni is contained, the content should be 4.0% or less. Preferably it is 2.0% or less.
• V improves the toughness by vigorously crystallizing the grains.
• tempering forms high hardness carbonitrides and increases tensile strength.
• the toughness is lowered. Therefore, if it contains V, it should be 4.0% or less. Preferably it is 0.10 to 1.10%.
• w improves hardenability.
• fine carbides are formed by tempering to increase the high-temperature tensile strength. However, if contained in a large amount, the toughness is lowered. Therefore, if it contains W, it should be 4.0% or less. Preferably from 0.10 to L: 10%. Co: 10.0% or less
• Co increases red hot hardness and increases high temperature tensile strength. However, if contained in a large amount, the toughness is lowered. Therefore, when it contains Co, it was made 10.0% or less.
• the balance is substantially Fe
• the elements other than those specified are substantially Fe, but impurities inevitably contained are naturally included.
• Nb and Ti are effective elements for refining crystal grains, so they may be contained within a range of 0.20% or less to the extent that toughness does not deteriorate.
• A1 is an element that accelerates the diffusion of carbon, and has the effect of promoting the precipitation of carbides by pearlite transformation. Therefore, it may be contained in the range of 0.20% or less.
• the measurement of the pearlite nose transformation completion point of semi-finished steel (JIS grade SKD61) with the chemical composition No. 1 was performed at the hot forging temperature (1150 ° C). Heated and then manned in a furnace maintained at 25 ° C intervals in a temperature range of 700 ° C to 775 ° C and held for 2, 5, 15, 24 hours. After the isothermal holding was completed, the test piece was taken out of the furnace and air-cooled, and the hardness of the test piece was measured. The point at which the hardness decreased by holding for the shortest time was estimated as the transformation completion point of the pearlite nose. The completion point was about 750 ° C for about 5 hours.
• Transformation of pearlite nose of semi-finished steel CFIS steel grade SKT4) with chemical composition No. 2 The completion point is measured by heating the test piece of the pearlite nose transformation completion point to the hot forging temperature (11 50 ° C). After that, personnel were placed in a furnace maintained at 25 ° C intervals in the temperature range of 600 ° C to 750 ° C and held for 2, 5, 10, 24, 48 hours. After completion of the isothermal holding, the test piece was also cooled with air and the hardness of the test piece was measured. The point at which the hardness decreased with the shortest holding time was estimated as the pearlite nose transformation completion point.
• the pearlite nose transformation completion point of No. 2 semi-finished steel was around 10 hours at 650 ° C.
• the measurement of the pearlite nose transformation completion point of semi-finished steel (JIS grade SKD11) with the chemical composition of No. 3 was performed at the hot forging temperature (1150 ° C). Heated and then manned in a furnace held at 25 ° C intervals in the temperature range of 675 ° C to 775 ° C and held for 2, 5, 10, 24 hours. After completion of isothermal holding, the test piece was also cooled with air by applying a furnace force, and the hardness of the test piece was measured. The point at which the hardness decreased by holding for the shortest time was estimated as the completion point of the pearlite nose, and the pearlite nose transformation completion point of No. 3 semi-finished steel was around 725 ° C for about 2 hours.
• the size of the semi-finished steel after hot forging is 430mm (t) x 430mm (w) x 3000mm x 2 (1) for the semi-finished steel of No. 1 composition, and the weight is about 8600kg, No 2 half-finished B semi-finished steel, 520mm (t) x 830mm (w) x 2400mm x 2 and weighs about 8000kg, No. 3 composition C semi-finished steel 370mm (t) x 370mm (w ) X 3 500mm x 2 and the weight was about 7500kg.
• These semi-finished steel materials are equivalent to billets or blooms in JIS terms, and are materials that become steel after hot annealing after intermediate annealing.
• Semi-finished steel No. A was hot forged at 1250 ° C (1 in Fig. 1) and then moved to the cooling process after hot working by cooling (2 in Fig. 1).
• the steel material 4 was placed on the heat insulation tank base 5 to prepare for the intermediate annealing 3. Then, measure the maximum surface temperature of the semi-finished steel with a radiation thermometer and keep it at 620 ° C.
• the steel material 4 was covered with the upper lid 6, and the steel material 4 was put into the heat insulating tank 7.
• the steel material filling rate of the thermal insulation tank was 35.6%.
• the surface temperature of the semi-finished steel material was measured with a sheath thermocouple attached to the heat insulation bath.
• the semi-finished steel is reheated to 800 ° C in the heat insulation tank (21 in Fig. 1), and then kept warm for 5 hours within the pearlite nose transformation completion point ⁇ 20 ° C (730 to 770 ° C) ( 22) in Fig. 1 and semi-finished steel was transformed into pearlite.
• the semi-finished steel material was extracted from the heat insulation tank at 500 ° C (23 in Fig. 1) and allowed to cool (24 in Fig. 1).
• Semi-finished steel No. B was hot forged at 1250 ° C (1 in Fig. 1) and then moved to the cooling process after hot working by allowing it to cool (2 in Fig. 1).
• the semi-finished steel material 4 was placed on the heat insulation tank base 5 to prepare for the intermediate annealing. Then, measure the maximum surface temperature of the semi-finished steel material with a radiation thermometer, cover the semi-finished steel material 4 with the heat insulation tank upper cover 6 at 600 ° C, and insert the semi-finished steel material 4 into the heat insulation tank 7. Completed.
• the steel material filling rate of the thermal insulation bath was 33.2%.
• the temperature of the semi-finished steel was measured with a sheath thermocouple attached to the heat insulation tank.
• Semi-finished steel is reheated to 700 ° C in the heat insulation tank (2 in Fig. 1) and then kept warm for 15 hours within the range of pearlite nose transformation completion point ⁇ 20 ° C (630 to 670 ° C) (22 in Fig. 1), the semi-finished steel was transformed into pearlite.
• the semi-finished steel material was extracted from the heat insulation tank at 500 ° C (23 in Fig. 1) and allowed to cool (24 in Fig. 1).
• Semi-finished steel No. C was hot forged at 1150 ° C (1 in Fig. 1) and then moved to the cooling process after hot working by cooling (2 in Fig. 1). During the cooling process after hot working, as shown in FIGS. 5A and 5B, the semi-finished steel material 4 was placed on the heat insulation tank base 5 to prepare for the intermediate annealing. Then, measure the maximum surface temperature of the semi-finished steel material with a radiation thermometer, cover the semi-finished steel material 4 with the upper cover 6 of the heat insulation tank at 680 ° C, and insert the semi-finished steel material 4 into the heat insulation tank 7 Completed. The steel material filling rate of the heat insulation tank was 30.7%.
• the temperature of the steel material was measured with a sheath thermocouple attached to the heat insulation bath.
• Semi-finished steel is reheated to 850 ° C (21 in Fig. 1) in the heat insulation bath, and then the transformation time of the light nose is within ⁇ 20 ° C (705 to 745 ° C) for 4 hours. Insulating (22 in Fig. 1), the semi-finished steel was transformed into pearlite. Semi-finished steel from 500 ° C The material was collected (23 in Fig. 1) and allowed to cool (24 in Fig. 1).
• the semi-finished steel material used in the comparative example having the same material and the semi-finished steel material used in the example of the present invention had the same hot forging conditions and dimensions of the steel material after hot forging.
• the semi-finished steel used in the comparative example with the same material and the semi-finished product used in the example of the present invention have the same hot forging conditions and dimensions of the steel after hot forging, and an annealing temperature of Ac3 or higher
• the holding time was 870 ° CX 5h for semi-finished steel No. D, 750 ° CX 5h for semi-finished steel No. E, and 870 ° CX 5h for semi-finished steel No. F.
• Table 2 shows the results of the microstructure and hardness of the semi-finished steel materials after the intermediate annealing of the inventive examples, comparative examples, and conventional examples.
• the heat retention time within the temperature range of ⁇ 10 ° C for the pearlite nose transformation of the steel material that was manned in the thermal insulation tank is 2.5 hours for semi-finished steel No. A and 7. for semi-finished steel No. B. 5 hours, semi-finished steel No. C was 2 hours.
• the semi-finished steel No. D, the semi-finished steel No. E, and the semi-finished steel No. F are compared with the same material.
• the semi-finished steel No. A, the semi-finished steel No. B and the semi-finished steel No. C to which the intermediate annealing of the present invention was applied differed in the metal structure and resulted in higher hardness.
• intermediate annealing could be performed without using a heating furnace.
• semi-finished steel No. A semi-finished steel No. B, semi-finished steel No. C to which the intermediate annealing of the present invention is applied
• semi-finished steel No. G semi-finished to which the intermediate annealing of the conventional method is applied.
• Steel No. H and semi-finished steel No. I were subjected to the next process hot working (hot forging) after intermediate annealing and processed into steel, but the next process hot working could be performed without any problems. .
• the same effect as in the intermediate annealing using a heating furnace in which the metal yarn and the weave is not made into martensite is maintained by utilizing the pearlite transformation latent heat of the steel material. Therefore, for example, it is possible to carry out annealing using the time for transporting steel materials on land or at sea, thereby promoting the distribution of steel materials and further contributing to energy saving.
• FIG. 1 is a schematic diagram of a heat pattern showing an example of intermediate annealing of the present invention.
• FIG. 2 is a schematic diagram of a heat pattern showing an example of conventional intermediate annealing.
• FIG. 3 is a schematic diagram of the transformation completion point of the pearlite nose.
• FIG. 4 is a schematic diagram of a TTT curve showing the transformation completion point of the pearlite nose of SKD61.
• FIG. 5A is a schematic front view showing an unsealed state of an example of the heat insulating tank of the present invention.
• FIG. 5B is a schematic side view of the heat insulation tank of FIG. 5A.
• FIG. 5C is a schematic front view showing a sealed state of the heat insulating tank in FIG. 5A.
• FIG. 5D is a schematic side view of the heat insulation tank of FIG. 5C.
• FIG. 6A is a schematic front view showing a sealed state of another example of the heat insulation tank of the present invention.
• FIG. 6B is a schematic side view of the heat insulation tank of FIG. 6A.
• [6C] A schematic front view showing the heat insulation tank of FIG. 6A in a sealed state.
• FIG. 6D is a schematic side view of the heat insulation tank of FIG. 6C.
• [7A] A schematic front view showing an unsealed state of still another example of the heat insulation tank of the present invention.
• [7B] A schematic side view of the heat insulation tank of FIG. 7A.
• FIG. 7C A schematic front view of the heat insulation tank of FIG. 7A in a sealed state.
• FIG. 7D A schematic side view of the heat insulation tank of FIG. 7C.
• FIG. 8 is a schematic view showing still another example of the heat insulating tank of the present invention.

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• 2007
  • 2007-04-10 EP EP07741346.6A patent/EP2006398B1/en not_active Not-in-force
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