CN117561345A - Hot work tool steel excellent in high temperature strength and toughness - Google Patents
Hot work tool steel excellent in high temperature strength and toughness Download PDFInfo
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- 229910001315 Tool steel Inorganic materials 0.000 title claims abstract description 53
- 238000010791 quenching Methods 0.000 claims abstract description 25
- 230000000171 quenching effect Effects 0.000 claims abstract description 25
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 238000004458 analytical method Methods 0.000 claims description 31
- 150000001247 metal acetylides Chemical class 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 24
- 239000000523 sample Substances 0.000 claims description 17
- 238000000034 method Methods 0.000 claims description 15
- 238000010521 absorption reaction Methods 0.000 claims description 12
- 238000000386 microscopy Methods 0.000 claims description 12
- 238000004876 x-ray fluorescence Methods 0.000 claims description 12
- 229910052804 chromium Inorganic materials 0.000 claims description 11
- 238000013507 mapping Methods 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 abstract description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 5
- 150000001875 compounds Chemical class 0.000 abstract description 2
- 229910000831 Steel Inorganic materials 0.000 description 23
- 239000010959 steel Substances 0.000 description 23
- 230000000052 comparative effect Effects 0.000 description 20
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 238000011156 evaluation Methods 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 238000012360 testing method Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 238000005496 tempering Methods 0.000 description 5
- 238000004453 electron probe microanalysis Methods 0.000 description 4
- 238000005242 forging Methods 0.000 description 4
- 238000009863 impact test Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- 238000002791 soaking Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000009497 press forging Methods 0.000 description 3
- 238000005275 alloying Methods 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000001192 hot extrusion Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 238000004452 microanalysis Methods 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 238000011002 quantification Methods 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- -1 MC-based carbides Chemical class 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000004512 die casting Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical compound OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Classifications
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- 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
- 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
- C21D9/22—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for drills; for milling cutters; for machine cutting tools
-
- 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
-
- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Abstract
The present invention aims to provide a hot work tool steel excellent in high-temperature strength and toughness, comprising, in mass%, C:0.20% or more and 0.60% or less, si:0.10% or more and less than 0.30%, mn:0.50% or more and 2.00% or less, ni:0.50% or more and 2.50% or less, cr:1.6% or more and 2.6% or less, mo:0.3% or more and 2.0% or less, V:0.05% or more and 0.80% or less, and the balance: fe and unavoidable impurities, the hot work tool steel is such that according to the following formula a: value a= ([ T)]+273)(log 10 [t]+24)/1000 … (A) [ in the formula, [ T ]]Represents the quenching temperature (. Degree. C.) [ t ]]The quenching temperature holding time (h) is shown.]The calculated value A is in a state of being quenched and tempered in a manner of 27.4 to 29.3, and every 10000 mu m in the hot work tool steel before use 2 Carbon with equivalent circle diameter of 1 μm or moreThe number of the compounds is less than 150.
Description
Technical Field
The present invention relates to hot work tool steel excellent in high-temperature strength and toughness, which is used as a hot work tool such as a hot forging die.
Background
Generally, a hot working tool (for example, a die) for hot press forging, hot extrusion or die casting is generally used, and a Japanese Industrial Standard (JIS) SKD61 steel is generally used, and a die for hot hammer forging is generally used, and a JIS SKT4 steel is generally used. The JIS SKD61 steel is a mold steel having both strength and toughness at a relatively high level, but is often damaged early due to cracks during use, and is not necessarily sufficient in toughness. In addition, JIS SKD61 steel is insufficient in toughness to suppress the development of thermal fatigue cracks. JIS SKT4 steel is considered to have toughness so as to be able to withstand a large impact by hammer forging, and on the other hand, has insufficient wear resistance because of low softening resistance. In addition, if the die-engraved surface is repeatedly cut for the purpose of the renewing process, the hardenability is low, and therefore, the hardness is lowered in the center portion, and cracks, breakage, and the like occur due to the insufficient strength. Further, since the applicable hardness is low, the abrasion resistance and strength are insufficient, and thus, they are not suitable for the use of hot press forging and hot extrusion.
Patent document 1 proposes a hot work tool steel comprising, in mass%, C:0.37 to 0.45 percent of Si:0.3 to 1.2 percent of Mn:0.6 to 1.5 percent of Ni:0.3 to 1.0 percent of Cr:1.0 to 2.0 percent of Mo:1.1 to 1.4 percent of V:0.1 to 0.3%, and the balance Fe and unavoidable impurities, and the values of the formulas L and Y of the alloy components are defined within a specific range. The formula L is-0.4 xSi-9.7 xMn+3.7 xNi+54.4 xMo, and the value of the formula L is 54 to 65. The formula Y is-17.1XC+0.1XSi+0.2XMn+0.2XNi+0.5XCr+Mo+5.0, and the value of the formula Y is 0.0 or more.
However, patent document 1 does not consider a carbide precipitation state before a hot work tool steel is used in a hot state (high temperature) (hereinafter, sometimes referred to as "before high temperature use"), and the high temperature strength is insufficient.
Patent document 2 proposes a hot working tool having a composition of, in mass%, C:0.10 to 0.70 percent of Si:0.10 to 2.00 percent, less than or equal to 2.00 percent of Mn, less than or equal to 7.00 percent of Cr, and the W and the Mo are calculated by single or compound (1/2W+Mo): 0.20 to 12.00 percent, V is less than or equal to 3.00 percent, and in addition S: less than 0.005% O less than 30ppm, the balance consisting essentially of Fe.
However, in patent document 2, neither the component fluctuation range nor the carbide precipitation state before use at high temperature is considered, and toughness is insufficient.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open publication No. 2019-19374
Patent document 2: japanese patent laid-open No. 11-106868
Disclosure of Invention
Problems to be solved by the invention
Hot work tool steel produced by precipitating carbide (e.g., MC carbide, M 2 C-based carbide, and M represents a metal element. ) And carbonitride, whereby softening resistance, i.e., high-temperature strength can be obtained. However, at the stage before use at high temperature, M 23 C 6 If the amount of the carbide is large, the carbide in use at high temperature (for example, MC carbide, M 2 C-based carbide, etc.) and the amount of carbonitride precipitated are reduced, and high-temperature strength cannot be obtained. In addition, if a large amount of coarse carbides exist before use at high temperature, there is a problem of low toughness.
Therefore, the present invention has been made to solve the problem of reducing M which may remain after press forging and contributes little to high-temperature strength by limiting the quenching conditions 23 C 6 The carbide is solid-dissolved in the quenching step, and excellent toughness is obtained by controlling the range of component fluctuation. Moreover, M is a factor in the quenching step 23 C 6 Solid solution of carbide causes an increase in the amount of carbon in the matrix, and when used as hot work tool steel at high temperature, the carbide contributes significantly to high temperature strength (e.g., MC carbide, M 2 C-based carbide, etc.) and fine carbonitride precipitation, thereby obtaining excellent high-temperature strength. That is, the present invention aims to provide a hot work tool steel having toughness and high-temperature strength.
Means for solving the problems
In order to solve the above problems, the present inventors have made intensive developments and as a result, have found that a hot work tool steel having both excellent high-temperature strength and toughness can be obtained by specifying an alloy composition, a quenching condition, a carbide state and a composition fluctuation range.
In other words, in order to solve the above problems, the present invention provides the following hot work tool steel.
[1] A hot work tool steel comprising, in mass percent
C:0.20% to 0.60%,
Si:0.10% or more and less than 0.30%,
Mn:0.50% to 2.00%,
Ni:0.50% to 2.50%,
Cr:1.6% to 2.6%,
Mo:0.3% to 2.0%,
V:0.05% to 0.80%, and
the balance: fe and not C the impurities which are avoided are generated by the method,
the hot work tool steel is in a state of being quenched and tempered in such a manner that a value A calculated according to the following formula A is 27.4 or more and 29.3 or less,
value a= ([ T)]+273)(log 10 [t]+24)/1000…(A)
In the formula, [ T ] represents a quenching temperature (. Degree.C.) and [ T ] represents a quenching temperature holding time (h). ]
Every 10000 μm in hot work tool steel before use 2 The number of carbides having an equivalent circle diameter of 1 μm or more is 150 or less.
[2] The hot work tool steel according to [1], which satisfies the following formulas 1 to 4:
([C] max －[C] min )/[C]≤1.0…(1)
([Cr] max －[Cr] min )/[Cr]≤0.5…(2)
([Mo] max －[Mo] min )/[Mo]≤1.5…(3)
([V] max －[V] min )/[V]≤1.5…(4)
[ in the formula, [ C ]] max And [ C ]] min Respectively representing the thermal work by electron probe microscopyHighest concentration and lowest concentration of C, [ Cr ], determined by concentration map of steel] max And [ Cr] min Respectively represent the highest concentration and the lowest concentration of Cr, [ Mo ], determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ Mo] min Represents the highest and lowest concentrations of Mo, respectively, [ V ], determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ V] min Respectively represent the highest concentration and the lowest concentration of V determined by the concentration map of hot work tool steel by electron probe microscopy, [ C ]]The content of C determined by composition analysis of hot work tool steel by infrared absorption method is represented by [ Cr ]]、[Mo]And [ V]The contents of Cr, mo and V determined by the composition analysis of hot work tool steel by the X-ray fluorescence analysis method are shown.]
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, there is provided a hot work tool steel having both high temperature strength and toughness, which has a reduction in initial hardness of 14HRC or less and a pendulum impact test of 70J/cm in impact value 2 And the like.
When the composition fluctuation range is controlled well, the internal segregation is small, and the impact value in the pendulum impact test is 85J/cm 2 Thus, a hot work tool steel having better toughness can be obtained.
Detailed Description
In the present specification, the hot work tool steel before being used in a hot state (high temperature) as a hot work tool such as a hot forging die is referred to as "hot work tool steel before being used". The hot working tool is used, for example, in contact with a workpiece heated to a high temperature for the purpose of improving workability or for the purpose of controlling a structure for obtaining desired characteristics after hot working, and therefore, is exposed to a corresponding temperature (for example, 180 to 1300 ℃) in the vicinity of a heat transfer surface from the workpiece.
The reason why the chemical components are specified, the reason why the specified value a is specified, and the reason why the number of carbides is specified in the hot work tool steel of the present invention will be described below. The% of the chemical components represents mass%.
C:0.20% or more and 0.60% or less
C is a component for securing sufficient hardenability, and for forming carbide and carbonitride, thereby obtaining high-temperature strength, hardness, and wear resistance. If C is less than 0.20%, sufficient high-temperature strength is not obtained. On the other hand, if C is higher than 0.60%, solidification segregation is promoted, coarse carbides and carbonitrides are generated, and toughness is lowered. Further, the generated carbide remains undissolved during quenching, and the amount of carbide and carbonitride precipitated during use at high temperature as a hot work tool steel is reduced, and improvement of high temperature strength is not expected. Therefore, C is 0.20% or more and 0.60% or less. Preferably, C is 0.40% or more and 0.60% or less.
Si: more than 0.10 percent and less than 0.30 percent
Si is a component required to ensure deoxidizing effect and hardenability in steel making. If Si is less than 0.10%, the effect cannot be sufficiently exhibited. On the other hand, if Si is 0.30% or more, the toughness is reduced. Therefore, si is 0.10% or more and less than 0.30%. Preferably, si is 0.10% or more and 0.20% or less.
Mn:0.50% or more and 2.00% or less
Mn is a component required to ensure deoxidizing effect and hardenability in steel making. If Mn is less than 0.50%, the effect is insufficient. If Mn is more than 2.00%, the workability is lowered. Therefore, mn is 0.50% or more and 2.00% or less. Mn is preferably 0.50% or more and 1.40% or less.
Ni:0.50% or more and 2.50% or less
Ni is a component necessary for ensuring hardenability and improving toughness. If Ni is less than 0.50%, the effect cannot be sufficiently exhibited. If Ni is more than 2.50%, the cost becomes excessive. Therefore, ni is 0.50% or more and 2.50% or less. Preferably, ni is 1.10% or more and 2.30% or less.
Cr:1.6% or more and 2.6% or less
Cr is a component necessary for securing sufficient hardenability. When Cr is less than 1.6%, sufficient hardenability is not obtained. On the other hand, if Cr is added in an amount of more than 2.6%, M mainly composed of Cr and Fe is obtained during quenching and tempering 23 C 6 The carbide is excessively formed, and the high-temperature strength, softening resistance and toughness are reduced. Therefore, cr is 1.6% or more and 2.6% or less. Preferably, cr is 1.6% or more and 2.4% or less.
Mo:0.3% or more and 2.0% or less
Mo is a useful component for obtaining precipitated carbides contributing to hardenability, secondary hardening, and high-temperature strength. If Mo is less than 0.3%, sufficient effects cannot be obtained. If Mo is more than 2.0%, the effect is saturated and the carbide is coarsely agglomerated even if it is excessively added, thereby deteriorating the toughness. In addition, high costs are incurred. Therefore, mo is 0.3% or more and 2.0% or less. Mo is preferably 0.3% or more and 1.7% or less.
V:0.05% to 0.80%
V precipitates fine hard carbides and fine hard carbonitrides during tempering or during use at high temperatures as hot work tool steel, and is a component contributing to strength and wear resistance. If V is less than 0.05%, these effects cannot be sufficiently obtained. If V is more than 0.80%, coarse carbides and carbonitrides crystallize out during solidification, which hinders toughness. Therefore, V is 0.05% or more and 0.80% or less. Preferably, V is 0.05% or more and 0.20% or less.
Value a:27.4 to 29.3
The hot work tool steel before use is quenched and tempered so that the value a becomes 27.4 or more and 29.3 or less.
The value a is calculated according to the following formula a.
Value a= ([ T)]+273)(log 10 [t]+24)/1000…(A)
In the formula A, [ T ] represents a quenching temperature (. Degree. C.) and [ T ] represents a quenching temperature holding time (h).
That is, when evaluating A, the value of the quenching temperature (. Degree.C.) is substituted into [ T ] in the formula A, and the value of the quenching temperature holding time (h) is substituted into [ T ] in the formula A.
The value a is an index for securing solid solubility of carbide by defining the quenching temperature and the holding time. If the value a is less than 27.4, the solid solution of carbide by quenching of steel in the composition of the present invention is insufficient, and toughness and high-temperature strength at the time of use as a hot working tool are insufficient. On the other hand, if the value a exceeds 29.3, coarsening of the prior austenite grains results in a decrease in toughness. Therefore, the value a is set to 27.4 or more and 29.3 or less.
2 Number of carbides of 1 μm or more per 10000 μm equivalent circle diameter: less than 150
In hot work tool steel before use, if too much carbide with an equivalent circle diameter of 1 μm or more is contained, the amount of carbon in the matrix is insufficient, and carbide precipitated as hot work tool steel during use at high temperature (for example, MC-based carbide, M 2 C-series carbide, etc.) and carbonitride. Carbides (e.g., MC-based carbides, M 2 C-based carbide, etc.) and carbonitride are precipitated as hot work tool steel during use at high temperature, contributing to improvement of high temperature strength, and therefore if they are reduced, sufficient high temperature strength is not obtained. If too many carbides having an equivalent circle diameter of 1 μm or more are present, the stresses concentrate and act as a crack initiation point and propagation path, which hinders toughness. Thus, in the hot work tool steel before use, every 10000 μm 2 The number of carbides having an equivalent circle diameter of 1 μm or more is 150 or less.
Every 10,000 μm 2 The number of carbides having an equivalent circle diameter of 1 μm or more was measured using a quenched and tempered steel material as described in the examples. The carbide to be measured is, for example, MC carbide, M 2 Carbide of C series, M 3 Carbide of C series, M 7 C 3 Carbide, M 23 C 6 Carbide, and the like. M represents a metal element.
Every 0000 μm 2 The number of carbides having an equivalent circle diameter of 1 μm or more was measured by the method described in the examples.
The hot work tool steel before use preferably satisfies the following formulas 1 to 4:
([C] max －[C] min )/[C]≤1.0…(1)
([Cr] max －[Cr] min )/[Cr]≤0.5…(2)
([Mo] max －[Mo] min )/[Mo]≤1.5…(3)
([V] max －[V] min )/[V]≤1.5…(4)
in the formulae 1 to 4, [ C] max And [ C ]] min The highest concentration (% by mass) and the lowest concentration (% by mass) of C, [ Cr, [ percent by mass ], respectively, determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ Cr] min Represents the highest concentration (% by mass) and the lowest concentration (% by mass) of Cr, [ Mo ], respectively, determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ Mo] min Represents the highest concentration (% by mass) and the lowest concentration (% by mass) of Mo determined by the concentration map of hot work tool steel by electron probe microscopy, [ V,%] max And [ V] min The highest concentration (% by mass) and the lowest concentration (% by mass) of V determined by the concentration map of hot work tool steel by electron probe microscopy, [ C, ]]The content (mass%) of C determined by composition analysis of hot work tool steel by infrared absorption method, [ Cr]、[Mo]And [ V]The content (mass%) of Cr, mo and V determined by the composition analysis of hot work tool steel by the X-ray fluorescence analysis method is shown.
With respect to alloy element X (x= C, cr, mo, V) ([ X)] max －[X] min )/[X]Is an index of the composition deviation caused by the internal segregation of each alloy element. In the present specification, the term ([ X ] is sometimes used] max －[X] min )/[X]The value of (2) is referred to as "composition fluctuation width of the alloy element X". If the composition deviation caused by the internal segregation of each alloy element is large (i.e., ([ X)] max －[X] min )/[X]Large value of (c), the distribution difference of carbide and carbonitride and the deformation ability difference become large, and thus the toughness is loweredLow. Therefore, the composition fluctuation ranges of C, cr, mo, and V are preferably controlled. That is, the hot work tool steel before use preferably satisfies all of formulas 1 to 4.
([X] max －[X] min )/[X]As described in the examples, the values of (2) were obtained using a quenched and tempered steel material. After mirror polishing the L-plane (plane parallel to the rolling direction and the plate thickness direction of the steel plate, so-called longitudinal cross section), concentration mapping of alloy element X (X= C, cr, mo, V) in the range of 0.5mm by 0.5mm was performed by using electron probe microscopy (Electron Prove Micro Analysis: EPMA), and the highest concentration (mass%) and the lowest concentration (mass%) of metal element X determined by the concentration mapping were respectively designated as [ X ]] max And [ X ]] min . The composition analysis of the steel material by infrared absorption method (analysis of the content of C) and the composition analysis of the steel material by X-ray fluorescence analysis (analysis of the content of Cr, mo and V) were carried out, and the content of C (mass%) determined by infrared absorption method was set to [ C]The content (mass%) of Cr, mo and V determined by X-ray fluorescence analysis was defined as [ Cr]、[Mo]And [ V]. Concentration mapping by electron probe microscopy, composition analysis by infrared absorption and X-ray fluorescence analysis were performed following the methods described in the examples.
The soaking treatment is suitable for soaking the central part of the steel ingot for 10 to 40 hours at the temperature of 1225 to 1300 ℃, and the component variation value can be effectively reduced.
Examples
The present invention will be described in more detail below based on examples and comparative examples.
Inventive examples nos. 1 to 28 and comparative examples nos. 29 to 40 are steels containing the chemical components described in table 1 and the balance Fe and unavoidable impurities, respectively. 100kg of each steel was melted in a vacuum induction melting furnace (VIM) and cast into ingots. For the inventive steels Nos. 1 to 20, soaking treatment was performed under the above conditions (i.e., soaking treatment in which the central portion of the steel ingot was soaked and maintained for 10 to 40 hours at a temperature ranging from 1225℃to 1300 ℃). Thereafter, these ingots were heated to 1220℃and forged into square bars of 15mm (15 mm. Times.15 mm). The composition of each steel in the batch was confirmed by infrared absorption (analysis of the content of C) and X-ray fluorescence (analysis of the content of alloying elements other than C). The infrared absorption method and the X-ray fluorescence analysis method are performed in the following manner.
Thereafter, the mixture is heated to 850 to 960 ℃ and maintained for various periods of time (30 minutes to 3 hours), thereby obtaining an austenite structure. Then oil quenching is carried out, and after the oil quenching is heated to 500-700 ℃, air cooling tempering is carried out for 2 times, and the quenching and tempering are 39-41 HRC. And then obtaining the test material through machining.
In table 1, the balance of each steel is Fe and unavoidable impurities.
(calculation of value A)
The value a of each steel was calculated according to the following formula a. The quenching temperature (. Degree. C.), holding time (h) and value A of each steel are shown in Table 2.
Value a= ([ T)]+273)(log 10 [t]+24)/1000…(A)
In the formula, [ T ] represents a quenching temperature (. Degree.C.) and [ T ] represents a quenching temperature holding time (h). ]
(determination of carbide content)
After mirror polishing the center of each sample, the matrix was etched with a picric acid alcohol solution, and a portion where light gray or white carbide was observed in a large amount was selected from 30 fields of view, and the number of carbides having an equivalent circle diameter of 1 μm or more, which was observed with an electron microscope at 10,000 times, was measured by image analysis. Every 10,000 μm 2 The number of carbides having an equivalent circle diameter of 1 μm or more is 150 or less, which is "A", and the number is more, which is "C". The results of the carbide measurements are shown in Table 2.
(evaluation of component fluctuation Width)
In each sample, the L surface (surface parallel to the rolling direction and the plate thickness direction of the steel plate, so-called longitudinal cross section) was mirror polished, and then, by using an electron probe microanalysis method (Electron Prove Micro Analysis: EPMA), concentration mapping of alloy element X (X= C, cr, mo, V) was performed in the range of 0.5mm by 0.5 mm.
EPMA was carried out under the following conditions.
Analysis device: EPMA1600 manufactured by Shimadzu corporation
Acceleration voltage: 15kV
Beam diameter: 2 μm
Irradiation current: 0.1 mu A
Scanning mode: stage scanning
Step size (1 measurement area): 2.5 μm by 2.5. Mu.m
Step length (number of measurement positions): 200×200
Measurement time (1 step): 50ms
A spectroscopic crystal: c LS12L
Mo PET
Cr、V LIF
For each sample, a composition analysis (analysis of the content of C) was performed by infrared absorption method, and a composition analysis (analysis of the content of Cr, mo, and V) was performed by X-ray fluorescence analysis method.
Composition analysis by infrared absorption was performed using a carbon-sulfur analyzer EMIA-Expert manufactured by horiba, ltd., in accordance with JIS Z2615: 2015, "carbon quantification of metallic Material" is performed by "infrared absorption method" of conventional "carbon quantification.
The composition analysis by X-ray fluorescence analysis (XRF) was carried out using MXF-2400 manufactured by Shimadzu corporation, according to JIS G1256: 2013, "iron and steel-X-ray fluorescence analysis method".
The highest concentration (mass%) and the lowest concentration (mass%) of the alloy element X determined by the concentration map are respectively set as [ X ]] max And [ X ]] min The content (mass%) of C determined by infrared absorption method was set to [ C]The content (mass%) of Cr, mo and V determined by X-ray fluorescence analysis was defined as [ Cr]、[Mo]And [ V]Calculation ([ X)] max －[X] min )/[X]As the component fluctuation width. The evaluation results of the component fluctuation ranges are shown in tables 3A to 3D.
Among all alloying elements of C, cr, mo and V, ([ X)] max －[X] min )/[X]When the value of (2) satisfies the predetermined requirement, the value of (A) is evaluated as "A" in order to satisfy the excellent level of the predetermined requirement of the component fluctuation range, even if the component fluctuation range is largeThe difference was also evaluated as "C" because the predetermined condition was not satisfied. The evaluation results of the component fluctuation ranges are shown in table 2.
C. The predetermined requirements for Cr, mo and V are as follows.
([C] max －[C] min )/[C]≤1.0
([Cr] max －[Cr] min )/[Cr]≤0.5
([Mo] max －[Mo] min )/[Mo]≤1.5
([V] max －[V] min )/[V]≤1.5
(evaluation of high temperature Strength)
After measuring the HRC hardness of each test piece, the test piece was further kept at 600 ℃ for 100 hours, and then air-cooled, the HRC hardness at room temperature was measured, and the high-temperature strength was evaluated from the reduction value of the initial hardness. The reduction value is below 14HRC as "a", and the reduction value is greater than this as "C". The evaluation results of the high temperature strength are shown in table 2.
(evaluation of toughness)
A U-shaped notched test piece of the JIS rule (JIS Z2242) of 10mm square and 55mm length was formed from each test piece, and the test piece was subjected to quenching and tempering to a hardness of 39 to 41HRC, and subjected to a pendulum impact test at normal temperature to evaluate toughness. Impact value 70J/cm 2 Above "A", in particular 85J/cm 2 The above is "A + ", less than 70J/cm 2 Is "C". The evaluation results of toughness are shown in table 2.
[ Table 1]
Table 1: inventive examples (Nos. 1 to 28) and comparative examples (Nos. 29 to 40)
[ Table 2]
Table 2: inventive examples (No. 1 to 28) and comparative examples (No. 29 to 40)
[ Table 3A ]
Table 3A: inventive examples (Nos. 1 to 28) and comparative examples (Nos. 29 to 40)
| No. | [C]max | [C]min | ([C]max-[C]min)/[C] |
| 1 | 0.26 | 0.16 | 0.5 |
| 2 | 0.78 | 0.49 | 0.5 |
| 3 | 0.41 | 0.25 | 0.5 |
| 4 | 0.80 | 0.40 | 0.7 |
| 5 | 0.71 | 0.43 | 0.6 |
| 6 | 0.41 | 0.22 | 0.7 |
| 7 | 0.51 | 0.27 | 0.7 |
| 8 | 0.54 | 0.31 | 0.6 |
| 9 | 0.44 | 0.23 | 0.7 |
| 10 | 0.49 | 0.29 | 0.6 |
| 11 | 0.72 | 0.39 | 0.6 |
| 12 | 0.74 | 0.43 | 0.6 |
| 13 | 0.63 | 0.42 | 0.4 |
| 14 | 0.35 | 0.19 | 0.6 |
| 15 | 0.44 | 0.26 | 0.5 |
| 16 | 0.69 | 0.45 | 0.5 |
| 17 | 0.51 | 0.26 | 0.7 |
| 18 | 0.55 | 0.27 | 0.7 |
| 19 | 0.56 | 0.32 | 0.6 |
| 20 | 0.62 | 0.34 | 0.6 |
| 21 | 0.70 | 0.32 | 1.1 |
| 22 | 0.78 | 0.42 | 0.7 |
| 23 | 0.57 | 0.34 | 0.6 |
| 24 | 0.74 | 0.45 | 0.6 |
| 25 | 0.98 | 0.39 | 1.3 |
| 26 | 0.51 | 0.32 | 0.5 |
| 27 | 1.00 | 0.44 | 1.2 |
| 28 | 0.87 | 0.37 | 1.2 |
| 29 | 0.15 | 0.08 | 0.7 |
| 30 | 1.60 | 0.58 | 1.3 |
| 31 | 0.29 | 0.18 | 0.5 |
| 32 | 0.63 | 0.34 | 0.6 |
| 33 | 0.30 | 0.17 | 0.7 |
| 34 | 0.42 | 0.27 | 0.5 |
| 35 | 0.87 | 0.49 | 0.6 |
| 36 | 0.32 | 0.19 | 0.6 |
| 37 | 0.40 | 0.23 | 0.6 |
| 38 | 0.46 | 0.25 | 0.6 |
| 39 | 0.47 | 0.23 | 0.7 |
| 40 | 0.65 | 0.35 | 0.6 |
[ Table 3B ]
Table 3B: inventive examples (Nos. 1 to 28) and comparative examples (Nos. 29 to 40)
| No. | [Cr]max | [Cr]min | ([Cr]max-[Cr]min)/[Cr] |
| 1 | 2.98 | 2.04 | 0.4 |
| 2 | 2.66 | 1.87 | 0.4 |
| 3 | 2.71 | 2.03 | 0.3 |
| 4 | 2.74 | 1.91 | 0.3 |
| 5 | 3.12 | 2.19 | 0.4 |
| 6 | 2.15 | 1.59 | 0.3 |
| 7 | 1.99 | 1.39 | 0.4 |
| 8 | 2.02 | 1.44 | 0.3 |
| 9 | 2.20 | 1.55 | 0.4 |
| 10 | 3.09 | 2.11 | 0.4 |
| 11 | 2.12 | 1.50 | 0.3 |
| 12 | 2.26 | 1.63 | 0.3 |
| 13 | 2.66 | 1.88 | 0.4 |
| 14 | 3.00 | 2.13 | 0.3 |
| 15 | 2.54 | 1.81 | 0.3 |
| 16 | 2.16 | 1.47 | 0.4 |
| 17 | 2.24 | 1.64 | 0.3 |
| 18 | 2.22 | 1.58 | 0.3 |
| 19 | 2.14 | 1.44 | 0.4 |
| 20 | 3.09 | 2.17 | 0.4 |
| 21 | 3.17 | 2.16 | 0.4 |
| 22 | 3.38 | 2.12 | 0.6 |
| 23 | 2.09 | 1.42 | 0.4 |
| 24 | 2.83 | 2.05 | 0.3 |
| 25 | 3.23 | 2.00 | 0.6 |
| 26 | 3.50 | 2.00 | 0.7 |
| 27 | 3.36 | 1.96 | 0.6 |
| 28 | 3.90 | 2.20 | 0.7 |
| 29 | 2.66 | 1.83 | 0.4 |
| 30 | 2.60 | 1.82 | 0.3 |
| 31 | 2.02 | 1.46 | 0.3 |
| 32 | 2.56 | 1.67 | 0.4 |
| 33 | 4.41 | 2.70 | 0.6 |
| 34 | 1.95 | 1.32 | 0.4 |
| 35 | 2.42 | 1.59 | 0.4 |
| 36 | 2.89 | 2.07 | 0.3 |
| 37 | 2.15 | 1.53 | 0.3 |
| 38 | 1.86 | 1.27 | 0.4 |
| 39 | 2.13 | 1.55 | 0.3 |
| 40 | 2.64 | 1.80 | 0.4 |
[ Table 3C ]
Table 3C: inventive examples (Nos. 1 to 28) and comparative examples (Nos. 29 to 40)
| No. | [Mo]max | [Mo]min | ([Mo]max-[Mo]min)/[Mo] |
| 1 | 1.24 | 0.50 | 0.9 |
| 2 | 2.77 | 1.07 | 1.0 |
| 3 | 0.87 | 0.31 | 1.1 |
| 4 | 2.02 | 0.79 | 0.9 |
| 5 | 2.31 | 0.85 | 1.1 |
| 6 | 1.97 | 0.67 | 1.1 |
| 7 | 1.78 | 0.64 | 1.0 |
| 8 | 1.45 | 0.51 | 1.0 |
| 9 | 0.72 | 0.25 | 1.2 |
| 10 | 1.91 | 0.68 | 1.1 |
| 11 | 0.47 | 0.18 | 0.9 |
| 12 | 3.20 | 1.32 | 0.9 |
| 13 | 3.26 | 1.09 | 1.2 |
| 14 | 2.69 | 0.86 | 1.2 |
| 15 | 2.92 | 1.19 | 1.0 |
| 16 | 0.94 | 0.40 | 0.9 |
| 17 | 1.49 | 0.56 | 1.0 |
| 18 | 2.45 | 0.99 | 0.9 |
| 19 | 2.69 | 1.00 | 1.1 |
| 20 | 0.81 | 0.29 | 1.0 |
| 21 | 2.21 | 0.83 | 1.0 |
| 22 | 2.70 | 0.93 | 1.1 |
| 23 | 2.93 | 0.76 | 2.0 |
| 24 | 0.91 | 0.34 | 1.1 |
| 25 | 1.38 | 0.46 | 1.2 |
| 26 | 5.28 | 1.48 | 1.9 |
| 27 | 1.81 | 0.57 | 1.2 |
| 28 | 4.90 | 1.40 | 1.8 |
| 29 | 2.51 | 1.00 | 1.0 |
| 30 | 2.81 | 0.95 | 1.1 |
| 31 | 2.63 | 0.99 | 1.1 |
| 32 | 2.07 | 0.82 | 1.0 |
| 33 | 0.81 | 0.28 | 1.1 |
| 34 | 0.15 | 0.07 | 0.9 |
| 35 | 4.90 | 0.95 | 1.6 |
| 36 | 2.62 | 1.01 | 1.0 |
| 37 | 2.25 | 0.86 | 1.1 |
| 38 | 1.78 | 0.64 | 1.1 |
| 39 | 1.99 | 0.70 | 1.2 |
| 40 | 1.58 | 0.54 | 1.2 |
[ Table 3D ]
Table 3D: inventive examples (Nos. 1 to 28) and comparative examples (Nos. 29 to 40)
| No. | [V]max | [V]min | ([V]max-[V]min)/[V] |
| 1 | 0.96 | 0.37 | 1.0 |
| 2 | 1.30 | 0.42 | 1.2 |
| 3 | 0.34 | 0.13 | 1.0 |
| 4 | 1.21 | 0.42 | 1.1 |
| 5 | 1.34 | 0.44 | 1.1 |
| 6 | 0.86 | 0.32 | 1.1 |
| 7 | 0.12 | 0.04 | 1.2 |
| 8 | 1.32 | 0.45 | 1.1 |
| 9 | 1.30 | 0.38 | 1.2 |
| 10 | 0.52 | 0.17 | 1.1 |
| 11 | 0.72 | 0.24 | 1.1 |
| 12 | 0.19 | 0.07 | 1.1 |
| 13 | 0.09 | 0.03 | 1.1 |
| 14 | 1.39 | 0.46 | 1.2 |
| 15 | 0.47 | 0.16 | 1.1 |
| 16 | 0.17 | 0.06 | 1.2 |
| 17 | 0.89 | 0.32 | 1.1 |
| 18 | 1.02 | 0.31 | 1.2 |
| 19 | 1.14 | 0.35 | 1.2 |
| 20 | 0.95 | 0.34 | 1.1 |
| 21 | 1.33 | 0.40 | 1.2 |
| 22 | 0.19 | 0.07 | 1.1 |
| 23 | 1.09 | 0.41 | 1.0 |
| 24 | 0.17 | 0.05 | 1.7 |
| 25 | 0.55 | 0.20 | 1.1 |
| 26 | 0.14 | 0.05 | 1.1 |
| 27 | 0.20 | 0.05 | 1.9 |
| 28 | 0.80 | 0.18 | 1.8 |
| 29 | 0.79 | 0.29 | 1.1 |
| 30 | 0.53 | 0.16 | 1.2 |
| 31 | 0.18 | 0.05 | 1.2 |
| 32 | 0.81 | 0.28 | 1.1 |
| 33 | 1.05 | 0.41 | 1.0 |
| 34 | 0.90 | 0.30 | 1.2 |
| 35 | 0.88 | 0.30 | 1.1 |
| 36 | 0.04 | 0.01 | 1.1 |
| 37 | 2.61 | 0.72 | 1.6 |
| 38 | 1.23 | 0.37 | 1.2 |
| 39 | 1.04 | 0.32 | 1.2 |
| 40 | 0.22 | 0.07 | 1.2 |
As shown in tables 1 and 2, each of the chemical components of invention examples No.1 to 28 satisfies the value of formula A, and the number of carbides having an equivalent circle diameter of 1 μm or more is small. Thus, the impact value in the pendulum impact test showed 70J/cm 2 As described above, the toughness was evaluated as a, and the reduction in the initial hardness was also within 14HRC, and the high-temperature strength (softening resistance) was also evaluated as a, whereby a hot work tool steel having both excellent high-temperature strength and toughness was obtained.
Comparative example No.29 has low high temperature strength because of the small amount of C.
In comparative example No.30, since the amount of C is large, the number of carbides having an equivalent circle diameter of 1 μm or more is large, and the component fluctuation range is large, the toughness and the high-temperature strength are low.
In comparative example No.31, the Si content was large and the toughness was low.
In comparative example No.32, the Ni content was small and the toughness was low.
In comparative example No.33, the toughness and high-temperature strength were low because the amount of Cr was large, the number of carbides having an equivalent circle diameter of 1 μm or more was large, and the component fluctuation range was large.
In comparative example No.34, the amount of Mo was small and the high temperature strength was low.
In comparative example No.35, since the amount of Mo is large, the number of carbides having an equivalent circle diameter of 1 μm or more is large, and the component fluctuation range is large, the toughness and the high-temperature strength are low.
In comparative example No.36, the amount of V was small and the high temperature strength was low.
In comparative example No.37, the toughness was low because the V content was large, the number of carbides having an equivalent circle diameter of 1 μm or more was large, and the component fluctuation range was large.
In comparative example No.38, the value of formula A is small, and the number of carbides having an equivalent circle diameter of 1 μm or more is large, so that toughness and high-temperature strength are low.
In comparative example No.39, the value of formula A was large and the toughness was low.
In comparative example No.40, the number of carbides having an equivalent circle diameter of 1 μm or more is large, and toughness and high-temperature strength are low.
Claims (2)
1. A hot work tool steel comprising, in mass percent
C:0.20% to 0.60%,
Si:0.10% or more and less than 0.30%,
Mn:0.50% to 2.00%,
Ni:0.50% to 2.50%,
Cr:1.6% to 2.6%,
Mo:0.3% to 2.0%,
V:0.05% to 0.80%, and
the balance: fe and not C the impurities which are avoided are generated by the method,
the hot work tool steel is in a state of being quenched and tempered in such a manner that a value A calculated according to the following formula A is 27.4 or more and 29.3 or less,
value a= ([ T)]+273)(log 10 [t]+24)/1000…(A)
Wherein [ T ] represents a quenching temperature in terms of a unit of a temperature and [ T ] represents a quenching temperature holding time in terms of a unit of h,
every 10000 μm in hot work tool steel before use 2 The number of carbides having an equivalent circle diameter of 1 μm or more is 150 or less.
2. The hot work tool steel according to claim 1, wherein the following formulas 1 to 4 are satisfied:
([C] max －[C] min )/[C]≤1.0…(1)
([Cr] max －[Cr] min )/[Cr]≤0.5…(2)
([Mo] max －[Mo] min )/[Mo]≤1.5…(3)
([V] max －[V] min )/[V]≤1.5…(4)
in the formula, [ C ]] max And [ C ]] min Respectively represent the highest concentration and the lowest concentration of C, [ Cr ], determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ Cr] min Respectively represent the highest concentration and the highest concentration of Cr determined by the concentration mapping of hot work tool steel by electron probe microscopyLow concentration of [ Mo ]] max And [ Mo] min Represents the highest and lowest concentrations of Mo, respectively, [ V ], determined by the concentration map of hot work tool steel by electron probe microscopy] max And [ V] min Respectively represent the highest concentration and the lowest concentration of V determined by the concentration map of hot work tool steel by electron probe microscopy, [ C ]]The content of C determined by composition analysis of hot work tool steel by infrared absorption method is represented by [ Cr ]]、[Mo]And [ V]The contents of Cr, mo and V determined by the composition analysis of hot work tool steel by the X-ray fluorescence analysis method are shown.
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