WO2018016504A1 - 高周波焼入れ用鋼 - Google Patents
高周波焼入れ用鋼 Download PDFInfo
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- WO2018016504A1 WO2018016504A1 PCT/JP2017/026004 JP2017026004W WO2018016504A1 WO 2018016504 A1 WO2018016504 A1 WO 2018016504A1 JP 2017026004 W JP2017026004 W JP 2017026004W WO 2018016504 A1 WO2018016504 A1 WO 2018016504A1
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Definitions
- the present invention relates to steel, and more particularly, to steel for induction hardening.
- Mechanical parts typified by gears are usually required to have excellent surface fatigue strength. If the surface hardness is high, excellent surface fatigue strength can be obtained. For this reason, mechanical parts that require surface fatigue strength may be manufactured by induction hardening.
- An example of a method for manufacturing such a machine part is as follows. Intermediate products are manufactured by hot forging steel for induction hardening. Induction hardening is applied to intermediate products. Machine parts represented by gears are manufactured by grinding the induction-hardened intermediate product.
- patent 4014042 (patent document 1)
- patent 5742801 (patent document 2).
- the steel bar for induction hardening disclosed in Patent Document 1 is in mass%, C: 0.5 to 0.7%, Si: 0.1 to 1.5%, Mn: 0.2 to 1.5%, Cr: 0 to 1.5%, V: 0 to 0.10%, S: 0.002 to 0.05%, Al: 0.01 to 0.04%, and N: 0.005 to 0.012%
- the balance is Fe and impurities, Ti in the impurities is 0.003% or less, O is 0.0015% or less, P is 0.02% or less, and the X value represented by the formula (1) Is 0.62 to 0.90.
- the number of inclusions other than MnS having an A value of 0.80 or more, an aspect ratio of 3 or less, and a minor axis of 10 ⁇ m or more is 2 / Mm 2 or less.
- C (%), Si (%), Mn (%), and Cr (%) mean the content (% by mass) of each element.
- Mn MIN means the lower limit value (mass%) of the Mn concentration in the surface region
- Mn AVE means the average value (mass%) of the Mn concentration.
- the hot-rolled steel bar or wire disclosed in Patent Document 2 is C: 0.55 to 0.75%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5 by mass%. %, Cr: 0.1-2.0%, S: 0.002-0.05%, Al: 0.01-0.2% and N: 0.002-0.01%, the balance Consists of Fe and impurities, and P and O in the impurities are P: 0.025% or less and O: 0.002% or less, respectively, and Fn1 represented by the following formula (1) is 2.5 to 2.5%. It has a chemical composition that is 4.5.
- the pearlite fraction is 90% or more, the average interval of the pearlite lamella is 150 to 300 nm, and the standard deviation of the pearlite lamella interval is 25 nm or less.
- Patent No. 4014042 Japanese Patent No. 5742801
- An object of the present invention is to provide a steel for induction hardening that has excellent machinability and can obtain excellent surface fatigue strength after induction hardening.
- the steel for induction hardening according to the present invention has a chemical composition of mass%, C: 0.53 to less than 0.58%, Si: 0.70 to 1.40%, Mn: 0.20 to 1.40%. , P: less than 0.020%, S: less than 0.020%, Al: 0.005 to 0.060%, N: 0.0020 to 0.0080%, O: 0.0015% or less, B: 0 .0003 to 0.0040%, Ti: 0.010 to 0.050%, Ca: 0.0005 to 0.005%, Cr: 0 to 0.15%, Cu: 0 to 0.50%, Ni: 0 to 0.30%, Mo: 0 to 0.20%, V: 0 to 0.05%, and Nb: 0 to 0.05%, with the balance being Fe and impurities.
- the steel structure consists of ferrite and pearlite, and the area ratio of pearlite is 85% or more.
- the ratio of the number of composite inclusions to the total number of Al 2 O 3 inclusions and composite inclusions is 20% or more.
- the composite inclusion is an inclusion containing 2.0% or more of SiO 2 and 2.0% or more of CaO by mass%, with the remaining 99% or more being Al 2 O 3 .
- the steel for induction hardening according to the present invention has excellent machinability, and excellent surface fatigue strength can be obtained after induction hardening.
- FIG. 1 is a side view of a small roller test piece used in a roller pitching test in Examples.
- FIG. 2 is a front view of a large roller test piece used in the roller pitching test in the examples.
- the present inventors investigated and examined the machinability of the steel for induction hardening and the surface fatigue strength of the steel (mechanical parts) after induction hardening. As a result, the present inventors obtained the following knowledge.
- the microstructure of the steel for induction hardening is composed of ferrite and pearlite and the area ratio of pearlite in the structure (hereinafter referred to as pearlite fraction) is high.
- Fn1 C + Si / 7 + Mn / 5 + Cr / 9 + Mo / 2.5.
- Fn1 is an index of hardenability. If Fn1 is too high, the hardenability becomes too high. In this case, bainite is generated in the microstructure of the steel for induction hardening, and the pearlite fraction is reduced. As a result, even if induction hardening is performed, a non-uniform structure is likely to be generated on the surface layer. If Fn1 is 0.98 or less, the microstructure of the steel for induction hardening is composed of ferrite (pre-deposited ferrite) and pearlite, and the pearlite fraction is 85% or more. “The microstructure consists of ferrite and pearlite” means that the total area ratio of ferrite (pre-deposited ferrite) and pearlite in the microstructure is 97% or more.
- the microstructure of the steel for induction hardening is a ferrite pearlite structure and the pearlite fraction is 85% or more as described above.
- Fn2 C + Si / 10 + Mn / 20 + Cr / 25.
- Fn2 is an index of the pearlite fraction when the steel microstructure is a ferrite pearlite structure. The higher the Fn2, the higher the pearlite fraction in the microstructure. If Fn2 is less than 0.70, the pearlite fraction in the microstructure is less than 85%, and a non-uniform structure is likely to be generated on the surface layer of the steel material after induction hardening. As a result, the surface fatigue strength of the steel material decreases. If Fn2 is 0.70 or more, the pearlite fraction in the microstructure is 85% or more.
- the cementite in the pearlite easily dissolves during induction hardening. If undissolved cementite remains in the steel material after induction hardening, a heterogeneous structure is formed, and the hardness of the steel material surface after induction hardening decreases. As a result, the surface fatigue strength of the steel material decreases.
- Both Si and Cr narrow the pearlite lamella spacing, making it easier for solid cement to dissolve during induction hardening.
- Si and Cr further increase the temper softening resistance of the steel. Therefore, both Si and Cr suppress the formation of cementite during tempering and increase the surface fatigue strength of the steel material.
- Cr concentrates to cementite and stabilizes cementite. For this reason, if the Cr content is too high, cementite does not easily dissolve during induction heating, and undissolved cementite tends to remain in the steel after induction hardening. If Cr content is reduced with respect to Si content, stabilization of cementite by Cr can be suppressed while narrowing the lamella spacing of pearlite. In this case, the cementite is liable to be dissolved during induction heating, and the cementite does not easily remain after induction hardening.
- Fn3 Cr / Si.
- Fn3 is an index indicating the ease of solid solution of cementite during induction hardening. The lower Fn3, the easier the cementite in the steel dissolves during high-frequency heating. On the other hand, if Fn3 is high, the Cr content is too high relative to the Si content. In this case, cementite hardly dissolves during high-frequency heating. As a result, sufficient hardness cannot be obtained in the steel material after quenching. If Fn3 is 0.20 or less, cementite is sufficiently dissolved during induction hardening. Therefore, in the steel material after induction hardening, sufficient surface hardness is obtained and excellent surface fatigue strength is obtained.
- the form of inclusions in the steel further affects the surface fatigue strength of the steel after induction hardening.
- Steel for machine parts (for example, gears) manufactured by induction hardening is manufactured by Al deoxidation. Therefore, Al 2 O 3 inclusions are present in the steel.
- Al 2 O 3 inclusions tend to aggregate with each other during the solidification process and form a coarse Al 2 O 3 inclusion group (cluster). Such clusters reduce the surface fatigue strength of machine parts after induction hardening.
- the Al 2 O 3 inclusion means an inclusion containing 99% or more of Al 2 O 3 by mass%.
- Al 2 O 3 inclusions have low adhesion to the steel matrix (base material) interface. Therefore, a gap is likely to occur at the interface between the Al 2 O 3 inclusion and the matrix during plastic working such as hot forging. Such a gap reduces the surface fatigue strength of the machine part.
- the present inventors investigated and examined a method for suppressing the aggregation of inclusions and improving the adhesion with the matrix interface. As a result, the present inventors obtained the following new knowledge.
- inclusions containing 2.0% or more of SiO 2 and 2.0% or more of CaO by mass%, and the remaining 99% by mass or more of Al 2 O 3 are referred to as “composite”. It is defined as “inclusion”. Composite inclusions are less likely to aggregate and form clusters. Furthermore, the adhesiveness of the composite inclusion with the matrix interface is higher than that of the Al 2 O 3 inclusion. Therefore, if the ratio of the composite inclusions among the inclusions in the steel is increased, the surface fatigue strength can be increased.
- the ratio of the number of composite inclusions to the total number of Al 2 O 3 inclusions and composite inclusions in steel is defined as the composite inclusion ratio Ra (%).
- the composite inclusion ratio Ra is high, the ratio of Al 2 O 3 inclusions in the steel decreases. In this case, inclusions are less likely to aggregate and the generation of clusters is suppressed. Furthermore, as described above, the adhesion of the composite inclusion to the matrix interface is high. Therefore, if Al 2 O 3 inclusions are reduced due to the formation of composite inclusions, a reduction in surface fatigue strength due to a decrease in adhesion between the matrix in steel and the inclusions is also suppressed.
- the composite inclusion ratio Ra is 20% or more, generation of clusters of Al 2 O 3 inclusions can be sufficiently suppressed. Furthermore, the adhesion to the matrix inclusions in the steel is also improved. As a result, the surface fatigue strength of the steel material after induction hardening can be increased.
- the steel for induction hardening according to the present embodiment completed based on the above knowledge has a chemical composition of mass%, C: 0.53 to less than 0.58%, Si: 0.70 to 1.40%, Mn : 0.20 to 1.40%, P: less than 0.020%, S: less than 0.020%, Al: 0.005 to 0.060%, N: 0.0020 to 0.0080%, O: 0.0015% or less, B: 0.0003 to 0.0040%, Ti: 0.010 to 0.050%, Ca: 0.0005 to 0.005%, Cr: 0 to 0.15%, Cu: 0 to 0.50%, Ni: 0 to 0.30%, Mo: 0 to 0.20%, V: 0 to 0.05%, and Nb: 0 to 0.05%, the balance being It consists of Fe and impurities and satisfies the formulas (1) to (3).
- the steel structure consists of ferrite and pearlite, and the area ratio of pearlite is 85% or more.
- the ratio of the number of composite inclusions to the total number of Al 2 O 3 inclusions and composite inclusions is 20% or more.
- the composite inclusion is an inclusion containing 2.0% or more of SiO 2 and 2.0% or more of CaO by mass%, with the remaining 99% or more being Al 2 O 3 .
- the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3).
- the chemical composition is as follows: Cr: 0.05 to 0.15%, Cu: 0.03 to 0.50%, Ni: 0.03 to 0.30%, and Mo: 0.01 to 0.20% You may contain 1 type, or 2 or more types selected from the group which consists of.
- the chemical composition may contain one or two selected from the group consisting of V: 0.01 to 0.05% and Nb: 0.01 to 0.05%.
- the chemical composition of the induction hardening steel according to the present embodiment contains the following elements.
- C 0.53 to less than 0.58% Carbon (C) increases the surface fatigue strength of steel after induction hardening. If the C content is too low, this effect cannot be obtained. On the other hand, if the C content is too high, the cold workability and machinability of the steel deteriorate. Accordingly, the C content is 0.53 to less than 0.58%.
- the minimum with preferable C content is 0.54%, More preferably, it is 0.55%.
- the upper limit with preferable C content is 0.57%, More preferably, it is 0.56%.
- Si 0.70 to 1.40% Silicon (Si) deoxidizes steel. Si further increases the resistance to temper softening and suppresses the precipitation of cementite in the tempering process performed after induction quenching. Si further modifies the Al 2 O 3 inclusions to form complex inclusions (Al 2 O 3 —CaO—SiO 2 ) that do not easily aggregate. If a composite inclusion is formed, the surface fatigue strength of the steel material after induction hardening will increase. If the Si content is too low, these effects cannot be obtained. On the other hand, if Si content is too high, the cold workability of steel will fall. Therefore, the Si content is 0.70 to 1.40%. The minimum with preferable Si content is 0.72%, More preferably, it is 0.75%. The upper limit with preferable Si content is 1.38%, More preferably, it is 1.36%.
- Mn 0.20 to 1.40%
- Manganese (Mn) increases the surface fatigue strength of steel after induction hardening. If the Mn content is too low, this effect cannot be obtained. On the other hand, if Mn content is too high, the cold workability of steel will fall. If the Mn content is too high, further segregation occurs. As a result, the grain boundary strength decreases, and the surface fatigue strength of the steel material decreases. If the Mn content is too high, the machinability of the steel may further decrease. Therefore, the Mn content is 0.20 to 1.40%.
- the minimum with preferable Mn content is 0.30%, More preferably, it is 0.35%.
- the upper limit with preferable Mn content is 1.30%, More preferably, it is 1.25%.
- P Phosphorus (P) is an impurity. P segregates at the grain boundary and embrittles the grain boundary. Therefore, P reduces the surface fatigue strength of the steel material after induction hardening. Therefore, the P content is less than 0.020%.
- the upper limit with preferable P content is 0.015%, More preferably, it is 0.012%.
- the P content is preferably as low as possible.
- S Sulfur
- S is an impurity. S forms coarse inclusions (MnS) and reduces the surface fatigue strength of the steel after induction hardening. Therefore, the S content is less than 0.020%.
- the upper limit with preferable S content is 0.018%, More preferably, it is 0.016%.
- the S content is preferably as low as possible.
- Al 0.005 to 0.060%
- Aluminum (Al) deoxidizes steel. Further, Al combines with N in the steel to form AlN, and suppresses the coarsening of crystal grains during induction hardening. If the Al content is too low, these effects cannot be obtained. On the other hand, if the Al content is too high, a large number of coarse Al 2 O 3 inclusions and many Al 2 O 3 clusters in which a plurality of Al 2 O 3 inclusions are aggregated are produced, and the surface fatigue strength of the steel after induction hardening Decreases. Therefore, the Al content is 0.005 to 0.060%. The minimum with preferable Al content is 0.008%, More preferably, it is 0.010%. The upper limit with preferable Al content is 0.058%, More preferably, it is 0.056%.
- the Al content referred to in this specification means the total Al content.
- N 0.0020 to 0.0080% Nitrogen (N) combines with Al to form AlN, and suppresses the coarsening of crystal grains during induction hardening. As a result, the surface fatigue strength of the steel material after induction hardening is increased. If the N content is too low, this effect cannot be obtained. On the other hand, if the N content is too high, N excessively dissolves in the ferrite and causes strain aging, which decreases the cold workability of the steel. If the N content is too high, coarse nitrides are generated, and the surface fatigue strength of the steel material is reduced. Therefore, the N content is 0.0020 to 0.0080%. The minimum with preferable N content is 0.0025%, More preferably, it is 0.0030%. The upper limit with preferable N content is 0.0075%, More preferably, it is 0.0070%.
- Oxygen (O) is an impurity. O combines with Al, Si, and Ca to form oxides (or oxide inclusions), and decreases the surface fatigue strength of the steel material after induction hardening. Therefore, the O content is 0.0015% or less.
- the upper limit with preferable O content is 0.0014%, More preferably, it is 0.0013%.
- the O content is preferably as low as possible.
- B 0.0003 to 0.0040% Boron (B) dissolves in steel and enhances the hardenability of the steel. As a result, the surface fatigue strength of the steel material after induction hardening is increased. B further increases the grain boundary strength and increases the bending fatigue strength of the steel material after induction hardening. If the B content is low, the above effect cannot be obtained effectively. On the other hand, if the B content is too high, the above effect is saturated. Therefore, the B content is 0.0003 to 0.0040%. The minimum with preferable B content is 0.0005%, More preferably, it is 0.0008%. The upper limit with preferable B content is 0.0038%, More preferably, it is 0.0036%.
- Titanium (Ti) forms Ti nitride or Ti carbide and suppresses the coarsening of crystal grains during induction hardening. As a result, the surface fatigue strength of the steel material after induction hardening is increased. Ti further binds to N, thereby suppressing B from binding to N and securing the amount of dissolved B. If the Ti content is too low, the above effect cannot be obtained. On the other hand, if the Ti content is too high, coarse Ti nitrides and Ti carbides are generated, and the cold workability of the steel decreases. Therefore, the Ti content is 0.010 to 0.050%. The lower limit of the Ti content is 0.012%, more preferably 0.013%. The upper limit with preferable Ti content is 0.048%, More preferably, it is 0.046%.
- Ca 0.0005 to 0.005%
- Calcium (Ca) modifies Al 2 O 3 inclusions to form composite inclusions (Al 2 O 3 —CaO—SiO 2 ).
- the surface fatigue strength of the steel material after induction hardening is increased by modifying the Al 2 O 3 inclusions to produce composite inclusions. If the Ca content is too low, this effect cannot be obtained. On the other hand, if the Ca content is too high, coarse inclusions increase, and the surface fatigue strength of the steel material after induction hardening decreases on the contrary. Therefore, the Ca content is 0.0005 to 0.005%.
- the minimum with preferable Ca content is 0.0008%, More preferably, it is 0.0010%.
- the upper limit with preferable Ca content is 0.0048%, More preferably, it is 0.0046%.
- the balance of the chemical composition of the steel for induction hardening according to the present embodiment is composed of Fe and impurities.
- the impurities are mixed from the ore as a raw material, scrap, or the manufacturing environment when the induction hardening steel is industrially manufactured, and adversely affects the induction hardening steel of the present embodiment. It means that it is allowed in the range that does not give.
- the induction hardening steel according to this embodiment may further contain one or more selected from the group consisting of Cr, Cu, Ni, and Mo. All of these elements increase the surface fatigue strength of the steel material after induction hardening.
- Chromium (Cr) is an optional element and may not be contained. When contained, Cr dissolves in the steel and increases the surface fatigue strength of the steel material after induction hardening. Further, Cr increases the temper softening resistance of steel and suppresses the formation of cementite during tempering. As a result, the surface fatigue strength of the steel material is increased. If Cr is contained even a little, the above effect can be obtained to some extent. On the other hand, Cr tends to concentrate in cementite and stabilizes cementite. If the cementite is stabilized, the cementite hardly dissolves during induction hardening, and the cementite may remain. Therefore, solid solution C cannot be obtained sufficiently and sufficient hardness of the steel material cannot be obtained.
- Cr Chromium
- the Cr content is 0 to 0.15%.
- a preferable lower limit of the Cr content for further effectively obtaining the above effect is 0.01%, more preferably 0.05%, still more preferably 0.06%, still more preferably 0.07%. It is.
- the upper limit with preferable Cr content is 0.14%, More preferably, it is 0.13%.
- Cu 0 to 0.50% Copper (Cu) is an optional element and may not be contained. When contained, Cu dissolves in steel and increases the surface fatigue strength of the steel material after induction hardening. If Cu is contained even a little, this effect can be obtained to some extent. On the other hand, if the Cu content is too high, the above effect is saturated. Therefore, the Cu content is 0 to 0.50%.
- the minimum with preferable Cu content for acquiring the said effect more effectively is 0.03%, More preferably, it is 0.04%.
- the upper limit with preferable Cu content is 0.45%, More preferably, it is 0.40%.
- Nickel (Ni) is an optional element and may not be contained. When contained, Ni is dissolved in steel and increases the surface fatigue strength of the steel material after induction hardening. If Ni is contained even a little, the above effect can be obtained to some extent. On the other hand, if the Ni content is too high, the above effect is saturated. Therefore, the Ni content is 0 to 0.30%.
- a preferable lower limit of the Ni content for further effectively obtaining the above effect is 0.03%, and more preferably 0.04%.
- the upper limit with preferable Ni content is 0.25%, More preferably, it is 0.20%.
- Mo 0 to 0.20%
- Molybdenum (Mo) is an optional element and may not be contained. When contained, Mo dissolves in the steel and increases the surface fatigue strength of the steel after induction hardening. If Mo is contained even a little, the above effect can be obtained to some extent. On the other hand, if the Mo content is too high, the pearlite ratio in the steel for induction hardening becomes less than 85%, and the cold workability decreases. Therefore, the Mo content is 0 to 0.20%.
- the minimum with preferable Mo content for acquiring the said effect more effectively is 0.01%, More preferably, it is 0.02%.
- the upper limit with preferable Mo content is 0.18%, More preferably, it is 0.16%.
- the induction hardening steel according to the present embodiment may further contain one or more selected from V and Nb in place of part of Fe. All of these elements increase the surface fatigue strength of the steel material.
- V 0 to 0.05%
- Vanadium (V) is an optional element and may not be contained. When contained, V forms V nitride, V carbide, or V carbonitride, and suppresses coarsening of crystal grains during induction hardening. As a result, the surface fatigue strength of the steel material after induction hardening is increased. If V is contained even a little, the above effect can be obtained to some extent. On the other hand, if the V content is too high, coarse V precipitates are generated and the cold workability of the steel is reduced. Therefore, the V content is 0 to 0.05%.
- the minimum with preferable V content is 0.01%, More preferably, it is 0.02%, More preferably, it is 0.025%, More preferably, it is 0.03%.
- the upper limit with preferable V content is 0.045%, More preferably, it is 0.04%.
- Niobium (Nb) is an optional element and may not be contained.
- Nb forms Nb nitride, Nb carbide, or Nb carbonitride, and suppresses coarsening of crystal grains during induction hardening. As a result, the surface fatigue strength of the steel material after induction hardening is increased. If Nb is contained even a little, the above effect can be obtained to some extent. On the other hand, if the Nb content is too high, coarse Nb precipitates are generated, and the cold workability of the steel is reduced. Therefore, the Nb content is 0 to 0.05%.
- the lower limit of the Nb content for obtaining the above effect is 0.01%, more preferably 0.012%.
- the upper limit with preferable Nb content is 0.048%, More preferably, it is 0.046%.
- Fn1 C + Si / 7 + Mn / 5 + Cr / 9 + Mo / 2.5.
- Fn1 is an index of hardenability. If Fn1 exceeds 1.05, the hardenability becomes too high. In this case, hard bainite is generated in a part of the microstructure of the steel for induction hardening after rolling. Therefore, a ferrite pearlite structure cannot be obtained. If Fn1 is 1.05 or less, the microstructure of the steel for induction hardening becomes a ferrite pearlite structure. However, if Fn1 exceeds 0.98, sufficient machinability cannot be obtained. Therefore, Fn1 is set to 0.98 or less.
- the microstructure of the induction hardening steel becomes a ferrite pearlite structure, and further sufficient machinability is obtained.
- the preferable upper limit of Fn1 is 0.97.
- the preferable lower limit of Fn1 for obtaining hardenability is 0.72.
- Fn2 C + Si / 10 + Mn / 20 + Cr / 25.
- Fn2 is an index of the pearlite fraction when the steel microstructure is a ferrite pearlite structure. The higher the Fn2, the higher the pearlite fraction in the microstructure. If Fn2 is less than 0.70, the pearlite fraction in the microstructure is less than 85%. If Fn2 is 0.70 or more, the pearlite fraction in the microstructure is 85% or more. A preferred lower limit of Fn2 is 0.72.
- both Si and Cr narrow the pearlite lamella spacing. If the pearlite lamella spacing is narrow, the cementite is liable to be dissolved during induction hardening.
- Cr concentrates to cementite and stabilizes cementite. If Si content is raised with respect to Cr content, stabilization of cementite by Cr can be suppressed while narrowing the lamella spacing of pearlite. For this reason, the cementite is easily dissolved during induction heating, and the cementite does not easily remain after induction hardening.
- Fn3 Cr / Si.
- Fn3 is an index indicating the degree of cementite solid solution after induction hardening. The lower Fn3, the easier the cementite in the steel dissolves during high-frequency heating. On the other hand, if Fn3 is high, the Cr content is too high relative to the Si content. In this case, cementite hardly dissolves during high-frequency heating. As a result, cementite remains in the steel material after quenching, and the surface fatigue strength of the steel material after induction quenching decreases. If Fn3 is 0.20 or less, cementite is sufficiently dissolved after induction hardening. Therefore, sufficient hardness is obtained in the steel material after induction hardening, and excellent surface fatigue strength is obtained. A preferred lower limit of Fn3 is 0.18.
- the microstructure is composed of ferrite (pre-deposited ferrite) and pearlite. That is, the microstructure of the steel for induction hardening according to the present embodiment is a ferrite pearlite structure.
- the microstructure is composed of ferrite and pearlite means that the total area ratio of ferrite and pearlite in the microstructure is 97% or more.
- the total area ratio of ferrite and pearlite is 100%.
- the balance other than ferrite and pearlite in the microstructure is, for example, bainite.
- the area ratio of pearlite in the microstructure is defined as the pearlite fraction (%).
- the pearlite fraction is 85% or more.
- the total area ratio of ferrite and pearlite in the microstructure and the pearlite fraction are measured by the following method.
- a sample is taken from induction hardening steel.
- the induction hardening steel is a steel bar or a wire
- the center part of the radius R connecting the surface and the central axis (hereinafter referred to as R / 2 part)
- R / 2 part Take a sample from Of the collected sample surfaces, the surface perpendicular to the rolling direction of the steel material is taken as the observation surface.
- the observation surface is polished, it is etched with 3% nitric acid alcohol (nitral etchant).
- the etched observation surface is observed with a 500 ⁇ optical microscope to generate photographic images with arbitrary five fields of view.
- the size of each visual field is 200 ⁇ m ⁇ 200 ⁇ m.
- each phase such as ferrite and pearlite has a different contrast for each phase. Therefore, each phase is specified based on the contrast.
- the total area ([mu] m 2) of the ferrite in each field and determines the total area of perlite ( ⁇ m 2).
- the ratio of the sum of the total area of ferrite and the total area of pearlite in all fields to the total area of all fields is defined as the total area ratio (%) of ferrite and pearlite.
- the ratio of the total pearlite area in all visual fields to the total area in all visual fields is defined as the pearlite fraction (%).
- the steel for induction hardening of the present embodiment contains Al 2 O 3 inclusions and composite inclusions.
- an inclusion containing 2.0% or more of SiO 2 and 2.0% or more of CaO and the remaining 99% or more of Al 2 O 3 is a composite inclusion. It is defined as Note that the upper limit of SiO 2 contained in the composite inclusion is, for example, 15%, and the upper limit of CaO is, for example, 25%.
- the ratio of the number of composite inclusions to the total number of Al 2 O 3 inclusions and composite inclusions is defined as a composite inclusion ratio Ra (%). If the composite inclusion ratio Ra is high, the Al 2 O 3 inclusions in the steel decrease. In this case, Al 2 O 3 inclusions are less likely to aggregate, and the generation of clusters is suppressed. Further, as described above, the adhesiveness of the Al 2 O 3 inclusions to the matrix interface is low, whereas the adhesiveness of the composite inclusions to the matrix interface is high. Therefore, if the number of Al 2 O 3 inclusions is reduced due to the formation of composite inclusions, a reduction in surface fatigue strength due to a decrease in adhesion between the matrix in the steel and the inclusions is also suppressed.
- Ra composite inclusion ratio
- the composite inclusion ratio Ra is 20% or more, generation of clusters of Al 2 O 3 inclusions can be sufficiently suppressed. Furthermore, the adhesion to the matrix inclusions in the steel is also improved. As a result, the surface fatigue strength of the steel material after induction hardening can be increased.
- Identification of Al 2 O 3 inclusions and composite inclusions in steel and measurement of the composite inclusion ratio Ra can be performed by the following method.
- a sample is taken from any position of induction hardening steel.
- the induction hardening steel is a steel bar or wire
- a sample is taken from the R / 2 part of the steel bar or wire.
- 20 visual fields evaluation area per visual field: 100 ⁇ m ⁇ 100 ⁇ m
- SEM scanning electron microscope
- Al 2 O 3 inclusions and composite inclusions are specified using energy dispersive X-ray spectroscopy (EDX). Specifically, when the Al content and the O content are 99% or more by mass% in the elemental analysis result of the specified inclusion, the inclusion is specified as the Al 2 O 3 inclusion. As a result of elemental analysis, it contains 2.0% or more of SiO 2 and 2.0% or more of CaO, and the balance substantially consists of Al 2 O 3 and impurities (specifically, 99% of the balance) When the above is Al 2 O 3 ), the inclusion is defined as a composite inclusion.
- EDX energy dispersive X-ray spectroscopy
- inclusions to be specified are inclusions having a circle equivalent diameter of 10 ⁇ m or more.
- the equivalent circle diameter means the diameter of a circle when the area of each inclusion is converted into a circle having the same area.
- inclusions having an equivalent circle diameter of at least twice the beam diameter of EDX are included, the accuracy of elemental analysis is enhanced.
- the beam diameter of EDX used for specifying inclusions is 5 ⁇ m.
- inclusions having an equivalent circle diameter of less than 10 ⁇ m cannot improve the accuracy of elemental analysis by EDX.
- Inclusions having a circle-equivalent diameter of less than 10 ⁇ m have a very small effect on fatigue strength. Therefore, in the present embodiment, Al 2 O 3 inclusions and composite inclusions having an equivalent circle diameter of 10 ⁇ m or more are measured.
- the upper limit of the equivalent circle diameter of Al 2 O 3 inclusions and composite inclusions is not particularly limited, but is, for example, 200 ⁇ m.
- the total number TN1 of Al 2 O 3 inclusions having a specified equivalent circle diameter of 10 ⁇ m or more is obtained in all 20 fields of view.
- the total number TN2 of the composite inclusions having a specified circle equivalent diameter of 10 ⁇ m or more is obtained.
- inclusions of the same composition are adjacent to each other and the shortest distance between the adjacent inclusions is less than 1 ⁇ m, these inclusions are regarded as one individual.
- An example of a manufacturing method includes a steel making process in which molten steel is refined and cast to manufacture a material (slab or ingot), and a hot working process in which the material is hot worked to produce induction hardening steel.
- a steel making process in which molten steel is refined and cast to manufacture a material (slab or ingot)
- a hot working process in which the material is hot worked to produce induction hardening steel.
- the steel making process includes a refining process and a casting process.
- refining process In the refining process, first, refining in the converter (primary refining) is performed on the hot metal produced by a known method. Secondary refining is performed on the molten steel produced from the converter. In secondary refining, addition of alloy elements for component adjustment is performed to produce molten steel that satisfies the above chemical composition.
- deoxidation treatment is performed by adding Al to the molten steel discharged from the converter.
- the removal treatment is performed.
- secondary refining is performed.
- composite refining is performed.
- LF Laddle Furnace
- VAD Vauum Arc Degassing
- RH Rasterstahl-Hausen vacuum degassing
- final adjustment of other alloy components excluding Si and Ca is performed.
- the next treatment (heating and holding step and final component adjusting step) is performed on the molten steel.
- Vg gas flow rate (Nm 3 / min)
- M l molten steel mass (ton) in the ladle
- T l molten steel temperature (K)
- h 0 gas blowing depth (m)
- P 0 molten steel Surface pressure (Pa)
- ⁇ stirring power value (W / ton)
- ⁇ uniform mixing time (s).
- the holding time ts is less than twice the uniform mixing time ⁇ , the Al 2 O 3 inclusion is not sufficiently modified into a composite inclusion. That is, the composite inclusion ratio Ra is as low as less than 20%. If the holding time ts is twice or more the uniform mixing time ⁇ , the composite inclusion ratio Ra becomes 20% or more on condition that other conditions are satisfied.
- Si and Ca are added to the molten steel after the heating and holding step to produce a molten steel that satisfies the above chemical composition and formulas (1) to (3).
- Si and Ca may be added to the molten steel as independent raw materials.
- a Si—Ca alloy may be used as a raw material and added to the molten steel.
- the composite inclusion ratio Ra in the steel for induction hardening can be made 20% or more.
- Si is added before adding Al to the molten steel, composite inclusions are unlikely to be formed.
- Si and Ca are added to molten steel in which Al 2 O 3 inclusions are present, the Al 2 O 3 inclusions are modified into composite inclusions, and composite inclusions are generated. Therefore, in this embodiment, Al is added to molten steel, and then Si and Ca are added.
- the order of addition of Si and Ca is not particularly limited. Si and Ca may be added simultaneously. Either Si or Ca may be added first.
- a raw material (slab or ingot) is manufactured using the molten steel manufactured by the refining process. Specifically, a slab is manufactured by continuous casting using molten steel. Or you may ingot by the ingot-making method using molten steel.
- the manufactured material is hot-worked to manufacture a steel material for induction hardening (bar or wire).
- the hot working step one or more hot workings are usually performed.
- the first hot working is, for example, block rolling or hot forging, and the next hot working is finish rolling using a continuous rolling mill.
- the continuous rolling mill horizontal stands having a pair of horizontal rolls and vertical stands having a pair of vertical rolls are alternately arranged in a line.
- the induction-quenched steel after finish rolling is cooled to room temperature. At this time, the average cooling rate until the surface temperature of the steel for induction hardening reaches 800 to 500 ° C. is set to 1 ° C./second or less.
- bainite is generated in an area ratio of 3% or more in the microstructure of the steel for induction hardening after cooling.
- the average cooling rate is 1 ° C./second or less, the microstructure of the steel for induction hardening after cooling is composed of ferrite and pearlite.
- a preferred lower limit of the average cooling rate is 0.1 ° C./second.
- a preferable upper limit of the average cooling rate is 0.7 ° C./second.
- the steel for induction hardening according to the present embodiment can be manufactured.
- hot forging is performed on the prepared steel for induction hardening to produce an intermediate product.
- the intermediate product is subjected to stress relief annealing.
- the intermediate product after hot forging or after stress-relieving annealing is cut to produce a crude product.
- the machine part is a gear
- the crude product has a coarse gear shape.
- grinding is performed to manufacture mechanical parts represented by gears.
- the above formulas (1) to (3) are satisfied, and the composite inclusion ratio Ra is 20% or more. Therefore, the machinability of induction hardening steel can be improved, and the surface fatigue strength of machine parts after induction hardening can be increased.
- “-” In Table 1 means that the content of the corresponding element is at the impurity level. Specifically, “-” in the B content means that the B content is less than 0.0001%. “ ⁇ ” In the Ti content means that the Ti content is less than 0.001%. “ ⁇ ” In the Ca content means that the Ca content is less than 0.0001%. “ ⁇ ” In the Cr, Cu, Ni, and Mo contents means that the content of each element is less than 0.01%. “ ⁇ ” In the V content means that the V content is less than 0.001%. “ ⁇ ” In Nb content means that the Nb content is less than 0.001%.
- the molten steel of each test number was manufactured by the following method. Primary refining in the converter was carried out under the same conditions for the hot metal produced by a known method.
- a heating and holding step was performed.
- the ratio (ts / ⁇ ) of the holding time ts to the uniform mixing time ⁇ in each test number was as shown in Table 1.
- Si—Ca alloy was added to the molten steel other than test number 40 to adjust the Si content and the Ca content, and molten steel having the chemical composition shown in Table 1 was manufactured.
- Slabs having a cross section of 400 mm ⁇ 300 mm were manufactured by the continuous casting method using molten steel of test numbers 1 to 41.
- the manufactured slab was heated to 1250 ° C. Using the heated slab, a steel slab having a cross section of 162 mm ⁇ 162 mm was produced by split rolling. The manufactured steel slab was air-cooled to room temperature (25 ° C.). The billet was again heated to 1200 ° C. The heated steel slab was hot-rolled (finish rolling) using a continuous rolling mill and then allowed to cool to produce a steel bar for induction hardening having a diameter of 70 mm.
- Table 1 shows the average cooling rate until the surface temperature of the steel bar after finish rolling reaches 800 to 500 ° C. in each test number.
- S (Slow) indicates that the average cooling rate until the surface temperature of the steel bar after finish rolling reaches 800 to 500 ° C. is 1 ° C./second or less for the corresponding test number. It shows that it was.
- cooling rate column of Table 1
- F (Fast) indicates that the average cooling rate until the surface temperature of the steel bar after finish rolling reaches 800 to 500 ° C. is 1 ° C./second for the corresponding test number. Indicates that it has been exceeded.
- the chemical composition of the steel bar of each manufactured test number was measured. As a result, the chemical composition of the steel bars of each test number was as shown in Table 1.
- a surface fatigue strength test piece simulating a machine part was produced by the following method.
- the steel bars of each test number were heated at 1200 ° C. for 30 minutes.
- hot forging was performed at a finishing temperature of 950 ° C. or higher to produce a round bar having a diameter of 35 mm.
- a round bar having a diameter of 35 mm was machined to produce a small roller test piece as a surface fatigue strength test piece.
- a plurality of small roller test pieces for roller pitching test shown in FIG. 1 were prepared for each test number (the unit of dimensions in FIG. 1 is mm).
- Induction hardening was performed on each manufactured test piece. Specifically, heating is performed on the peripheral surface FP (portion having a diameter of 26 mm) of the small roller test piece using a high-frequency heating device with an output of 20 kW and a frequency of 50 kHz so that the hardened layer depth is 1.5 mm. Induction hardening was performed by adjusting the time within a range of 5 to 10 seconds. At that time, the heating temperature of the surface of the small roller test piece was 900 to 1100 ° C. Then, tempering was performed at 160 ° C. for 1 hour using a normal heat treatment furnace.
- FIG. 2 is a front view of the large roller test piece (the unit of dimensions in FIG. 2 is mm).
- the large roller test piece is made of steel that meets the standard of JIS SCM420H, and is manufactured by the general manufacturing process, that is, normalization, test piece processing, eutectoid carburization by gas carburizing furnace, low temperature tempering and polishing. It was done.
- the conditions of the roller pitching test are as follows.
- Tester Roller pitching tester Test piece: Small roller test piece (diameter 26 mm), Large roller test piece (diameter 130mm), contact part 150mmR Maximum surface thickness: 3600 MPa Number of tests: 6 Slip rate: -40% Small roller rotation speed: 2000rpm Peripheral speed: Small roller: 2.72 m / s, Large roller: 3.81 m / s Lubricating oil temperature: 90 ° C Oil used: Automatic oil
- the number of tests in the roller pitching test was six.
- an SN diagram was prepared with the surface pressure on the vertical axis and the number of repetitions until the occurrence of pitching on the horizontal axis. Of those in which no pitching occurred until the number of repetitions was 2.0 ⁇ 10 7 times, the highest surface pressure was defined as the surface fatigue strength.
- the area of the largest thing became 1 mm ⁇ 2 > or more among the places where the surface of a small roller test piece was damaged, it defined as generating pitting.
- Table 2 shows the surface fatigue strength obtained by the test. With respect to the surface fatigue strength in Table 2, the surface fatigue strength of test number 21 was used as a reference value (100%). And the surface fatigue strength of each test number was shown by ratio (%) with respect to a reference value. If the surface fatigue strength was 105% or more, it was judged that excellent surface fatigue strength was obtained.
- a machinability evaluation test piece was prepared by the following method. Similar to the surface fatigue strength test pieces, the steel bars of each test number were heated at 1200 ° C. for 30 minutes. Next, hot forging was performed on the heated steel bar to produce a round bar having a diameter of 35 mm. The finishing temperature during hot forging was 950 ° C. or higher. A round bar produced by hot forging was machined to finish a disk-shaped test piece (hereinafter referred to as a machinability test piece) having a diameter of 30 mm and a height of 15 mm.
- a machinability test piece disk-shaped test piece having a diameter of 30 mm and a height of 15 mm.
- Machineability evaluation test A machinability evaluation test by drilling was performed on the fabricated machinability test piece. Specifically, drilling was performed at a constant cutting speed until the total depth of the processed holes reached 1000 mm. When the drilled hole depth was 1000 mm, the drilling was once terminated. Then, the cutting speed was further increased and set, and drilling was performed again at the set cutting speed until the total depth of the processed holes reached 1000 mm. Similarly, drilling was performed sequentially while increasing the cutting speed, and the maximum cutting speed (m / min) at which the total depth of the processed holes was 1000 mm or more was obtained. The maximum cutting speed is normally used as an evaluation index of the tool life, and it can be determined that the tool life is better as the maximum cutting speed is higher. The maximum cutting speed was determined for each test number.
- the drilling conditions of the machinability evaluation test are as follows, and water-soluble cutting oil was used at the time of drilling.
- Cutting drill ⁇ 3mm high-speed drill
- Cutting speed 10-90m / min
- Feed 0.25mm / rev
- Table 2 shows the machinability evaluation obtained by the test.
- the machinability evaluation of test number 21 was set as a reference value (100%). And the machinability evaluation of each test number was shown by ratio (%) with respect to a reference value. If the maximum cutting speed was 115% or more, it was judged that excellent machinability was obtained.
- the Si content was too low. Therefore, Al 2 O 3 inclusions could not be sufficiently modified into composite inclusions, and the composite inclusion ratio Ra was less than 20%. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- the Mn content was too high. Therefore, bainite was generated in the structure after rolling, and the pearlite fraction was less than 85%.
- the Vickers hardness of the steel material after induction hardening was less than 730HV.
- the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- the machinability was less than 115%, and excellent machinability was not obtained.
- test number 24 the Mn content was too low. Therefore, the strength of the steel material after induction hardening was low, and the Vickers hardness of the steel material after induction hardening was less than 730 HV. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- test number 25 the Cr content was too high. Therefore, the strength of the steel material after induction hardening was low, and the Vickers hardness of the steel material after induction hardening was less than 730 HV. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained. This is probably because cementite was not sufficiently dissolved during induction hardening, and martensite was not uniformly formed by quenching.
- test number 26 the Al content was too high. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained. This is probably because a large amount of coarse Al 2 O 3 inclusions were generated.
- test number 27 the Al content was too low. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained. This is probably because the crystal grains became coarse during induction hardening.
- test number 28 the B content was too low. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- test number 29 the Ti content was too low. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- test number 30 the Ca content was too high. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained. This is thought to be due to the formation of coarse oxide inclusions.
- the Ca content was too low. Therefore, the composite inclusion ratio Ra was less than 20%. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- test number 40 the chemical composition was appropriate, and the expressions (1) to (3) were satisfied.
- the order of addition of Al, Si, and Ca was not appropriate. Therefore, the composite inclusion ratio Ra was less than 20%. As a result, the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- test number 41 the chemical composition was appropriate, and the expressions (1) to (3) were satisfied.
- the average cooling rate after finish rolling was too fast. Therefore, bainite was generated in the microstructure.
- the pearlite fraction was less than 85%.
- the Vickers hardness was less than 730 HV.
- the surface fatigue strength was less than 105%, and an excellent surface fatigue strength could not be obtained.
- the machinability was less than 115%, and excellent machinability was not obtained.
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Abstract
Description
C+Si/7+Mn/5+Cr/9+Mo/2.5≦0.98 (1)
C+Si/10+Mn/20+Cr/25≧0.70 (2)
Cr/Si≦0.20 (3)
ここで、式(1)~式(3)の各元素記号には、対応する元素の含有量(質量%)が代入される。
C+Si/7+Mn/5+Cr/9+Mo/2.5≦0.98 (1)
C+Si/10+Mn/20+Cr/25≧0.70 (2)
Cr/Si≦0.20 (3)
ここで、式(1)~式(3)の各元素記号には、対応する元素の含有量(質量%)が代入される。
本実施形態による高周波焼入れ用鋼の化学組成は、次の元素を含有する。
炭素(C)は、高周波焼入れ後の鋼材の面疲労強度を高める。C含有量が低すぎれば、この効果が得られない。一方、C含有量が高すぎれば、鋼の冷間加工性及び切削性が低下する。したがって、C含有量は0.53~0.58%未満である。C含有量の好ましい下限は0.54%であり、さらに好ましくは0.55%である。C含有量の好ましい上限は0.57%であり、さらに好ましくは0.56%である。
シリコン(Si)は鋼を脱酸する。Siはさらに、焼戻し軟化抵抗を高め、高周波焼入れ後に行われる焼戻し処理において、セメンタイトの析出を抑制する。Siはさらに、Al2O3介在物を改質して、凝集しにくい複合介在物(Al2O3-CaO-SiO2)を形成する。複合介在物が形成されれば、高周波焼入れ後の鋼材の面疲労強度が高まる。Si含有量が低すぎれば、これらの効果が得られない。一方、Si含有量が高すぎれば、鋼の冷間加工性が低下する。したがって、Si含有量は0.70~1.40%である。Si含有量の好ましい下限は0.72%であり、さらに好ましくは0.75%である。Si含有量の好ましい上限は1.38%であり、さらに好ましくは1.36%である。
マンガン(Mn)は高周波焼入れ後の鋼材の面疲労強度を高める。Mn含有量が低すぎれば、この効果が得られない。一方、Mn含有量が高すぎれば、鋼の冷間加工性が低下する。Mn含有量が高すぎればさらに、偏析が生じる。その結果、粒界強度が低下し、鋼材の面疲労強度が低下する。Mn含有量が高すぎればさらに、鋼の切削性が低下する場合がある。したがって、Mn含有量は0.20~1.40%である。Mn含有量の好ましい下限は0.30%であり、さらに好ましくは0.35%である。Mn含有量の好ましい上限は1.30%であり、さらに好ましくは1.25%である。
リン(P)は不純物である。Pは粒界に偏析して粒界を脆化する。そのため、Pは高周波焼入れ後の鋼材の面疲労強度を低下する。したがって、P含有量は0.020%未満である。P含有量の好ましい上限は0.015%であり、さらに好ましくは0.012%である。P含有量はなるべく低い方が好ましい。
硫黄(S)は不純物である。Sは粗大な介在物(MnS)を形成し、高周波焼入れ後の鋼材の面疲労強度を低下させる。したがって、S含有量は0.020%未満である。S含有量の好ましい上限は0.018%であり、さらに好ましくは0.016%である。S含有量はなるべく低い方が好ましい。
アルミニウム(Al)は鋼を脱酸する。Alはさらに、鋼中のNと結合してAlNを形成し、高周波焼入れ時の結晶粒の粗大化を抑制する。Al含有量が低すぎれば、これらの効果が得られない。一方、Al含有量が高すぎれば、粗大なAl2O3介在物や、複数のAl2O3介在物が凝集したAl2O3クラスタが多数生成し、高周波焼入れ後の鋼材の面疲労強度が低下する。したがって、Al含有量は0.005~0.060%である。Al含有量の好ましい下限は0.008%であり、さらに好ましくは0.010%である。Al含有量の好ましい上限は0.058%であり、さらに好ましくは0.056%である。本明細書にいうAl含有量は、全Alの含有量を意味する。
窒素(N)はAlと結合してAlNを形成し、高周波焼入れ時の結晶粒の粗大化を抑制する。その結果、高周波焼入れ後の鋼材の面疲労強度を高める。N含有量が低すぎれば、この効果が得られない。一方、N含有量が高すぎれば、Nが過剰にフェライトに固溶してひずみ時効を生じ、鋼の冷間加工性が低下する。N含有量が高すぎればさらに、粗大な窒化物が生成して、鋼材の面疲労強度が低下する。したがって、N含有量は0.0020~0.0080%である。N含有量の好ましい下限は0.0025%であり、さらに好ましくは0.0030%である。N含有量の好ましい上限は0.0075%であり、さらに好ましくは0.0070%である。
酸素(O)は不純物である。OはAl、Si及びCaと結合して酸化物(又は酸化物系介在物)を形成し、高周波焼入れ後の鋼材の面疲労強度を低下する。したがって、O含有量は0.0015%以下である。O含有量の好ましい上限は0.0014%であり、さらに好ましくは0.0013%である。O含有量はなるべく低い方が好ましい。
ボロン(B)は鋼に固溶して鋼の焼入れ性を高める。その結果、高周波焼入れ後の鋼材の面疲労強度を高める。Bはさらに、粒界強度を高め、高周波焼入れ後の鋼材の曲げ疲労強度を高める。B含有量が低ければ、上記効果が有効に得られない。一方、B含有量が高すぎれば、上記効果が飽和する。したがって、B含有量は0.0003~0.0040%である。B含有量の好ましい下限は0.0005%であり、さらに好ましくは0.0008%である。B含有量の好ましい上限は0.0038%であり、さらに好ましくは0.0036%である。
チタン(Ti)は、Ti窒化物又はTi炭化物を形成して、高周波焼入れ時の結晶粒の粗大化を抑制する。その結果、高周波焼入れ後の鋼材の面疲労強度が高まる。Tiはさらに、Nと結合することにより、BがNと結合するのを抑制し、固溶B量を確保する。Ti含有量が低すぎれば、上記効果が得られない。一方、Ti含有量が高すぎれば、粗大なTi窒化物、Ti炭化物が生成して、鋼の冷間加工性が低下する。したがって、Ti含有量は0.010~0.050%である。Ti含有量の下限は0.012%であり、さらに好ましくは0.013%である。Ti含有量の好ましい上限は0.048%であり、さらに好ましくは0.046%である。
カルシウム(Ca)は、Al2O3介在物を改質して、複合介在物(Al2O3-CaO-SiO2)を形成する。Al2O3介在物を改質して複合介在物を生成することにより、高周波焼入れ後の鋼材の面疲労強度を高める。Ca含有量が低すぎれば、この効果が得られない。一方、Ca含有量が高すぎれば、粗大な介在物が増加して、高周波焼入れ後の鋼材の面疲労強度がかえって低下する。したがって、Ca含有量は0.0005~0.005%である。Ca含有量の好ましい下限は0.0008%であり、さらに好ましくは0.0010%である。Ca含有量の好ましい上限は0.0048%であり、さらに好ましくは0.0046%である。
クロム(Cr)は任意元素であり、含有されなくてもよい。含有される場合、Crは鋼に固溶して、高周波焼入れ後の鋼材の面疲労強度を高める。Crはさらに、鋼の焼戻し軟化抵抗を高め、焼戻し時のセメンタイトの生成を抑制する。その結果、鋼材の面疲労強度が高まる。Crが少しでも含有されれば、上記効果がある程度得られる。一方、Crはセメンタイトに濃化しやすく、セメンタイトを安定化する。セメンタイトが安定化すれば、高周波焼入れ時にセメンタイトが固溶しにくく、セメンタイトが残存する場合がある。そのため、固溶Cが十分に得られず、十分な鋼材の硬さが得られない。その結果、面疲労強度が低下する。したがって、Cr含有量は0~0.15%である。上記効果をさらに有効に得るためのCr含有量の好ましい下限は0.01%であり、より好ましくは0.05%であり、さらに好ましくは0.06%であり、さらに好ましくは0.07%である。Cr含有量の好ましい上限は0.14%であり、さらに好ましくは0.13%である。
銅(Cu)は任意元素であり、含有されなくてもよい。含有される場合、Cuは鋼に固溶して、高周波焼入れ後の鋼材の面疲労強度を高める。Cuが少しでも含有されれば、この効果がある程度得られる。一方、Cu含有量が高すぎれば、上記効果が飽和する。したがって、Cu含有量は0~0.50%である。上記効果をさらに有効に得るためのCu含有量の好ましい下限は0.03%であり、さらに好ましくは0.04%である。Cu含有量の好ましい上限は0.45%であり、さらに好ましくは0.40%である。
ニッケル(Ni)は任意元素であり、含有されなくてもよい。含有される場合、Niは鋼に固溶して、高周波焼入れ後の鋼材の面疲労強度を高める。Niが少しでも含有されれば、上記効果がある程度得られる。一方、Ni含有量が高すぎれば、上記効果が飽和する。したがって、Ni含有量は0~0.30%である。上記効果をさらに有効に得るためのNi含有量の好ましい下限は0.03%であり、さらに好ましくは0.04%である。Ni含有量の好ましい上限は0.25%であり、さらに好ましくは0.20%である。
モリブデン(Mo)は任意元素であり、含有されなくてもよい。含有される場合、Moは鋼に固溶して、高周波焼入れ後の鋼材の面疲労強度を高める。Moが少しでも含有されれば、上記効果がある程度得られる。一方、Mo含有量が高すぎれば、高周波焼入れ用鋼材中のパーライト比率が85%未満となり、冷間加工性が低下する。したがって、Mo含有量は0~0.20%である。上記効果をさらに有効に得るためのMo含有量の好ましい下限は0.01%であり、さらに好ましくは0.02%である。Mo含有量の好ましい上限は0.18%であり、さらに好ましくは0.16%である。
バナジウム(V)は任意元素であり、含有されなくてもよい。含有される場合、VはV窒化物、V炭化物、又は、V炭窒化物を形成して、高周波焼入れ時の結晶粒の粗大化を抑制する。その結果、高周波焼入れ後の鋼材の面疲労強度が高まる。Vが少しでも含有されれば、上記効果がある程度得られる。一方、V含有量が高すぎれば、粗大なV析出物が生成して、鋼の冷間加工性が低下する。したがって、V含有量は0~0.05%である。V含有量の好ましい下限は0.01%であり、さらに好ましくは0.02%であり、さらに好ましくは0.025%であり、さらに好ましくは0.03%である。V含有量の好ましい上限は0.045%であり、さらに好ましくは0.04%である。
ニオブ(Nb)は任意元素であり、含有されなくてもよい。含有される場合、NbはNb窒化物、Nb炭化物、又は、Nb炭窒化物を形成して、高周波焼入れ時の結晶粒の粗大化を抑制する。その結果、高周波焼入れ後の鋼材の面疲労強度が高まる。Nbが少しでも含有されれば、上記効果がある程度得られる。一方、Nb含有量が高すぎれば、粗大なNb析出物が生成して、鋼の冷間加工性が低下する。したがって、Nb含有量は0~0.05%である。上記効果を得るためのNb含有量の下限は0.01%であり、さらに好ましくは0.012%である。Nb含有量の好ましい上限は0.048%であり、さらに好ましくは0.046%である。
上記化学組成はさらに、式(1)を満たす。
C+Si/7+Mn/5+Cr/9+Mo/2.5≦0.98 (1)
ここで、式(1)中の各元素記号には、対応する元素の含有量(質量%)が代入される。
上記化学組成はさらに、式(2)を満たす。
C+Si/10+Mn/20+Cr/25≧0.70 (2)
ここで、式(2)中の各元素記号には、対応する元素の含有量(質量%)が代入される。
上記化学組成はさらに、式(3)を満たす。
Cr/Si≦0.20 (3)
ここで、式(3)の各元素記号には、対応する元素の含有量(質量%)が代入される。
高周波焼入れ用鋼が上記化学組成を有し、式(1)~式(3)を満たす場合、ミクロ組織は、フェライト(初析フェライト)及びパーライトからなる。つまり、本実施形態による高周波焼入れ用鋼のミクロ組織は、フェライト・パーライト組織である。本明細書において、「ミクロ組織がフェライト及びパーライトからなる」とは、ミクロ組織におけるフェライト及びパーライトの総面積率が97%以上であることを意味する。好ましくは、高周波焼入れ用鋼のミクロ組織において、フェライト及びパーライトの総面積率が100%である。フェライト及びパーライトの総面積率が100%でない場合、ミクロ組織中のフェライト及びパーライト以外の残部はたとえばベイナイトである。ミクロ組織中のパーライトの面積率をパーライト分率(%)と定義する。本実施形態による高周波焼入れ用鋼のミクロ組織において、パーライト分率は85%以上である。
本実施形態の高周波焼入れ用鋼は、Al2O3介在物と、複合介在物とを含有する。本明細書において、上述のとおり、2.0%以上のSiO2と、2.0%以上のCaOとを含有し、残部の99%以上がAl2O3である介在物を、複合介在物と定義する。なお、複合介在物中に含有されるSiO2の上限はたとえば15%であり、CaOの上限はたとえば25%である。
Ra=TN2/(TN1+TN2)×100
本実施形態による高周波焼入れ用鋼の製造方法の一例を説明する。本実施形態では、高周波焼入れ用鋼の一例として、棒鋼又は線材の製造方法を説明する。しかしながら、本実施形態の高周波焼入れ用鋼は、棒鋼又は線材に限定されない。
製鋼工程は、精錬工程と鋳造工程とを含む。
精錬工程では初めに、周知の方法で製造された溶銑に対して転炉での精錬(一次精錬)を実施する。転炉から出鋼した溶鋼に対して、二次精錬を実施する。二次精錬において、成分調整の合金元素の添加を実施して、上記化学組成を満たす溶鋼を製造する。
二次精錬(最終成分調整)後の取鍋内の溶鋼に対して、1500~1600℃の温度で下記式によって算定される均一混合時間τ(s)の2倍以上の保持時間tsで加熱する。
τ=800×ε-0.4
ε=((6.18×Vg×Tl)/Ml)ln(1+(h0/(1.46×10-5×P0)))
ここで、Vg:ガス流量(Nm3/min)、Ml:取鍋内溶鋼質量(ton)、Tl:溶鋼温度(K)、h0:ガス吹き込み深さ(m)、P0:溶鋼表面圧力(Pa)、ε:攪拌動力値(W/ton)、τ:均一混合時間(s)である。
加熱保持工程後の溶鋼にSi及びCaを添加して、上述の化学組成及び式(1)~式(3)を満たす溶鋼を製造する。Si及びCaはそれぞれ単独の原料として溶鋼に添加してもよい。Si-Ca合金を原料として、溶鋼に添加してもよい。
上記精錬工程により製造された溶鋼を用いて、素材(鋳片又はインゴット)を製造する。具体的には、溶鋼を用いて連続鋳造法により鋳片を製造する。又は、溶鋼を用いて造塊法によりインゴットしてもよい。
製造された素材を熱間加工して、高周波焼入れ用鋼材(棒鋼又は線材)を製造する。熱間加工工程では通常、1又は複数回の熱間加工を実施する。複数回熱間加工を実施する場合、最初の熱間加工はたとえば、分塊圧延又は熱間鍛造であり、次の熱間加工は、連続圧延機を用いた仕上げ圧延である。連続圧延機では、一対の水平ロールを有する水平スタンドと、一対の垂直ロールを有する垂直スタンドとが交互に一列に配列される。仕上げ圧延後の高周波焼入れ用鋼材を、室温になるまで冷却する。このとき、高周波焼入れ用鋼材の表面温度が800~500℃になるまでの平均冷却速度を1℃/秒以下にする。平均冷却速度が1℃/秒を超えれば、冷却後の高周波焼入れ用鋼材のミクロ組織において、ベイナイトが面積率で3%以上生成する。平均冷却速度が1℃/秒以下であれば、冷却後の高周波焼入れ用鋼材のミクロ組織は、フェライト及びパーライトからなる。平均冷却速度の好ましい下限は0.1℃/秒である。平均冷却速度の好ましい上限は0.7℃/秒である。
上述の高周波焼入れ用鋼は、歯車に代表される機械部品に製造される。機械部品の製造方法の一例は次のとおりである。
各試験番号の棒鋼のR/2部から、組織観察用の試験片を採取した。試験片の表面のうち、棒鋼の長手方向(つまり、圧延方向又は延伸方向)と平行な断面を観察面と定義した。上述の方法に基づいて、フェライト及びパーライトの総面積率(%)を求めた。総面積率が97%以上のミクロ組織について、「F+P」として表2に示す。一方、総面積率が97%未満であり、残部にベイナイトが観察されたミクロ組織について、「F+P+B」として表2に示す。
高周波焼入れ用棒鋼に対して、上述の方法で、複合介在物比率Ra(%)を測定した。円相当径で10μm以上のAl2O3介在物及び複合介在物を特定し、上述の方法で複合介在物比率Ra(%)を求めた。その結果を表2に示す。
[面疲労強度試験片の作製]
機械部品を模擬した面疲労強度試験片を次の方法で作製した。各試験番号の棒鋼を、1200℃で30分加熱した。次に、仕上げ温度を950℃以上として熱間鍛造し、直径35mmの丸棒を製造した。直径35mmの丸棒を機械加工して、面疲労強度試験片として、小ローラ試験片を作製した。具体的に、図1に示すローラピッチング試験用小ローラ試験片を試験番号ごとに複数作製した(図1中の寸法の単位はmm)。
高周波焼入れ後の各試験番号の小ローラ試験片の周面FP(直径26mmの部分)のビッカース硬さを測定した。具体的には、小ローラ試験片の周面の任意の3点に対して、JIS Z 2244(2009)に準拠したビッカース硬さ試験を実施した。このときの試験力は9.8Nとした。得られたビッカース硬さの平均値を、その試験番号のビッカース硬さ(HV)と定義した。測定結果を表2に示す。
ローラピッチング試験により、面疲労強度を求めた。ローラピッチング試験は、上記の小ローラ試験片と大ローラ試験片とを組合せて実施した。図2は大ローラ試験片の正面図である(図2中の寸法の単位はmm)。大ローラ試験片は、JIS規格SCM420Hの規格を満たす鋼からなり、一般的な製造工程、つまり、焼きならし、試験片加工、ガス浸炭炉による共析浸炭、低温焼戻し及び研磨、の工程によって作製された。ローラピッチング試験の条件は次のとおりである。
試験片:小ローラ試験片(直径26mm)、
大ローラ試験片(直径130mm)、接触部150mmR
最大面厚:3600MPa
試験数 :6個
すべり率:-40%
小ローラ回転数:2000rpm
周速:小ローラ:2.72m/s、大ローラ:3.81m/s
潤滑油温度:90℃
使用オイル:オートマチック用オイル
切削性評価試験片を次の方法で作製した。面疲労強度試験片と同様に、各試験番号の棒鋼を、1200℃で30分加熱した。次に、加熱後の棒鋼に対して熱間鍛造を実施し、直径35mmの丸棒を製造した。熱間鍛造時の仕上げ温度は950℃以上であった。熱間鍛造により製造された丸棒を機械加工して、直径30mm、高さ15mmの円盤状試験片(以下、切削性試験片という)に仕上げた。
作製された切削性試験片に対して、ドリル加工による切削性評価試験を実施した。具体的に、加工穴の総深さが1000mmとなるまで、一定の切削速度でドリル加工を実施した。加工穴深さが1000mmとなった場合、ドリル加工をいったん終了した。そして、切削速度をさらに高めて設定し、設定された切削速度で、加工穴の総深さが1000mmとなるまで、ドリル加工を再度実施した。同様に、切削速度を高めながら順次ドリル加工を実施し、加工穴の総深さが1000mm以上可能な最大切削速度(m/min)を求めた。最大切削速度は通常、工具寿命の評価指標として用いられており、最大切削速度が大きいほど工具寿命が良好であると判断できる。各試験番号について最大切削速度を求めた。
切削ドリル:φ3mmハイスドリル
切削速度:10~90m/min
送り:0.25mm/rev
表1及び表2を参照して、試験番号1~20の鋼では、化学組成が適切であり、式(1)~式(3)を満たした。さらに、精錬工程における製造条件は適切であった。そのため、ミクロ組織はフェライト・パーライト組織であり、パーライト分率は85%以上であった。さらに、複合介在物比率Raは20%以上であった。その結果、ビッカース硬さは730HV以上であった。さらに、面疲労強度は105%以上であり、優れた面疲労強度が得られた。さらに、切削性も115%以上であり、優れた切削性が得られた。
Claims (3)
- 化学組成が、質量%で、
C:0.53~0.58%未満、
Si:0.70~1.40%、
Mn:0.20~1.40%、
P:0.020%未満、
S:0.020%未満、
Al:0.005~0.060%、
N:0.0020~0.0080%、
O:0.0015%以下、
B:0.0003~0.0040%、
Ti:0.010~0.050%、
Ca:0.0005~0.005%、
Cr:0~0.15%、
Cu:0~0.50%、
Ni:0~0.30%、
Mo:0~0.20%、
V:0~0.05%、及び、
Nb:0~0.05%を含有し、残部はFe及び不純物からなり、式(1)~式(3)を満たし、
鋼組織が、フェライト及びパーライトからなり、前記パーライトの面積率が85%以上であり、
鋼中において、Al2O3介在物及び複合介在物の総個数に対する、前記複合介在物の個数の比率は、20%以上であり、前記複合介在物は、質量%で、2.0%以上のSiO2及び2.0%以上のCaOを含有し、残部の99%以上がAl2O3である、高周波焼入れ用鋼。
C+Si/7+Mn/5+Cr/9+Mo/2.5≦0.98 (1)
C+Si/10+Mn/20+Cr/25≧0.70 (2)
Cr/Si≦0.20 (3)
ここで、式(1)~式(3)の各元素記号には、対応する元素の含有量(質量%)が代入される。 - 請求項1に記載の高周波焼入れ用鋼であって、
前記化学組成は、
Cr:0.05~0.15%、
Cu:0.03~0.50%、
Ni:0.03~0.30%、及び、
Mo:0.01~0.20%からなる群から選択される1種又は2種以上を含有する、高周波焼入れ用鋼。 - 請求項1又は請求項2に記載の高周波焼入れ用鋼であって、
前記化学組成は、
V:0.01~0.05%、及び、
Nb:0.01~0.05%からなる群から選択される1種又は2種を含有する、高周波焼入れ用鋼。
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KR1020197004117A KR20190028757A (ko) | 2016-07-19 | 2017-07-19 | 고주파 담금질용 강 |
EP17831020.7A EP3489379A4 (en) | 2016-07-19 | 2017-07-19 | STEEL FOR INDUCTION HARDNESS |
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Publication number | Priority date | Publication date | Assignee | Title |
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US10295819B1 (en) | 2018-03-22 | 2019-05-21 | Corning Incorporated | Naphtyl based high index hydrophobic liquids and transmission recovery agents for liquid lens formulations |
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US20190300994A1 (en) * | 2016-07-19 | 2019-10-03 | Nippon Steel & Sumitomo Metal Corporation | Steel for Induction Hardening |
US10808304B2 (en) * | 2016-07-19 | 2020-10-20 | Nippon Steel Corporation | Steel for induction hardening |
CN109477179B (zh) * | 2016-07-19 | 2021-07-09 | 日本制铁株式会社 | 高频淬火用钢 |
CN109563579A (zh) * | 2016-07-19 | 2019-04-02 | 新日铁住金株式会社 | 高频淬火用钢 |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH0379741A (ja) * | 1989-08-22 | 1991-04-04 | Daido Steel Co Ltd | 転動疲労特性に優れた鋼 |
US5902423A (en) * | 1998-03-16 | 1999-05-11 | Stelco Inc. | Heat treatment of grinding rod |
JPH11131135A (ja) * | 1997-10-28 | 1999-05-18 | Kawasaki Steel Corp | 高周波焼入部品およびその製造方法 |
JP2004183016A (ja) * | 2002-11-29 | 2004-07-02 | Sumitomo Metal Ind Ltd | 高周波焼入れ用棒鋼 |
JP2009041046A (ja) * | 2007-08-07 | 2009-02-26 | Sumitomo Metal Ind Ltd | 高周波焼入れ用鋼材及びその製造方法 |
JP2014037592A (ja) * | 2012-08-20 | 2014-02-27 | Nippon Steel & Sumitomo Metal | 熱間圧延棒鋼または線材 |
Family Cites Families (17)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5742801A (en) | 1980-08-27 | 1982-03-10 | Tohoku Electric Power Co Inc | Measuring rule for diagonal size |
US4912399A (en) | 1987-06-09 | 1990-03-27 | Tektronix, Inc. | Multiple lead probe for integrated circuits in wafer form |
JPH11181542A (ja) * | 1997-12-16 | 1999-07-06 | Nippon Steel Corp | 冷間加工性と高周波焼入れ性に優れた高周波焼入れ用鋼材とその製造方法 |
EP1541377A4 (en) * | 2002-07-15 | 2008-01-02 | Nsk Ltd | ROLLER BEARING UNIT FOR SUPPORT WHEEL |
JP3931797B2 (ja) * | 2002-12-03 | 2007-06-20 | 住友金属工業株式会社 | 高周波焼入れ用鋼材 |
JP4507494B2 (ja) * | 2003-01-17 | 2010-07-21 | Jfeスチール株式会社 | 疲労強度に優れた高強度鋼材の製造方法 |
EP1584700A4 (en) * | 2003-01-17 | 2007-03-28 | Jfe Steel Corp | HIGH STRENGTH STEEL PRODUCT HAVING EXCELLENT WEAR RESISTANCE, AND PROCESS FOR PRODUCING THE SAME |
EP2003221B1 (en) * | 2006-04-04 | 2016-05-25 | Nippon Steel & Sumitomo Metal Corporation | Hard extra-thin steel sheet and method for manufacturing the same |
BRPI1006852A2 (pt) * | 2009-01-16 | 2017-07-11 | Nippon Steel Corp | Aço para endurecimento de superfície para uso estrutural em máquinas e peça para uso estrutural em máquinas |
JP5912778B2 (ja) * | 2012-03-30 | 2016-04-27 | 株式会社神戸製鋼所 | 耐剥離性および耐衝撃疲労特性に優れた歯車 |
KR101681435B1 (ko) * | 2012-08-16 | 2016-11-30 | 신닛테츠스미킨 카부시키카이샤 | 고주파 담금질용 강재 |
JP5994924B2 (ja) * | 2013-03-08 | 2016-09-21 | 新日鐵住金株式会社 | 高周波焼入れ部品の素形材及びその製造方法 |
JP6354455B2 (ja) * | 2014-08-27 | 2018-07-11 | 愛知製鋼株式会社 | クランクシャフト及びクランクシャフト用鋼材 |
CN109563579A (zh) * | 2016-07-19 | 2019-04-02 | 新日铁住金株式会社 | 高频淬火用钢 |
US10808304B2 (en) * | 2016-07-19 | 2020-10-20 | Nippon Steel Corporation | Steel for induction hardening |
US20190300994A1 (en) * | 2016-07-19 | 2019-10-03 | Nippon Steel & Sumitomo Metal Corporation | Steel for Induction Hardening |
CN109477179B (zh) * | 2016-07-19 | 2021-07-09 | 日本制铁株式会社 | 高频淬火用钢 |
-
2017
- 2017-07-19 EP EP17831020.7A patent/EP3489379A4/en not_active Withdrawn
- 2017-07-19 CN CN201780044357.1A patent/CN109477176A/zh active Pending
- 2017-07-19 JP JP2017567498A patent/JP6384628B2/ja active Active
- 2017-07-19 KR KR1020197004117A patent/KR20190028757A/ko not_active Application Discontinuation
- 2017-07-19 WO PCT/JP2017/026004 patent/WO2018016504A1/ja unknown
- 2017-07-19 US US16/316,751 patent/US20190241997A1/en not_active Abandoned
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH0379741A (ja) * | 1989-08-22 | 1991-04-04 | Daido Steel Co Ltd | 転動疲労特性に優れた鋼 |
JPH11131135A (ja) * | 1997-10-28 | 1999-05-18 | Kawasaki Steel Corp | 高周波焼入部品およびその製造方法 |
US5902423A (en) * | 1998-03-16 | 1999-05-11 | Stelco Inc. | Heat treatment of grinding rod |
JP2004183016A (ja) * | 2002-11-29 | 2004-07-02 | Sumitomo Metal Ind Ltd | 高周波焼入れ用棒鋼 |
JP2009041046A (ja) * | 2007-08-07 | 2009-02-26 | Sumitomo Metal Ind Ltd | 高周波焼入れ用鋼材及びその製造方法 |
JP2014037592A (ja) * | 2012-08-20 | 2014-02-27 | Nippon Steel & Sumitomo Metal | 熱間圧延棒鋼または線材 |
Non-Patent Citations (1)
Title |
---|
See also references of EP3489379A4 * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US10295819B1 (en) | 2018-03-22 | 2019-05-21 | Corning Incorporated | Naphtyl based high index hydrophobic liquids and transmission recovery agents for liquid lens formulations |
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