Classifications

• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium

Definitions

• the present invention relates to a steel material excellent in machinability and a part processed by cutting. More specifically, steel materials that have good machinability and are suitable as materials for structural parts of various machines such as automobiles and other transport machinery, industrial machinery, construction machinery, etc. Shafts, connecting rods, gears, etc., related to various machine structural parts machined by cutting. Background art
• various mechanical structural parts such as transport machines, industrial machines, and construction machines are: (a) rough-worked to a predetermined shape by hot working, and then finished to a desired shape by cutting. In general, quenching and tempering were performed, or (b) hot working and quenching and tempering were performed, followed by cutting to obtain a desired shape.
• machinability improving elements such as Pb, Te, Bi, Ca and S, singly or in combination
• free-cutting elements such as Pb, Te, Bi, Ca and S
• desired mechanical properties for example, toughness / fatigue strength
• a technique of performing the hot working and the quenching / tempering treatment (b) and then performing a cutting work is disclosed in, for example, JP-A-6-212347.
• This is "a hot forged product having high fatigue strength and a method for producing the same", in which steel having a specific chemical composition is quenched immediately after hot forging and then tempered to precipitate TiC.
• the hot forgings described in this publication merely specify the amount of N as the chemical composition of steel as less than 0.1 in N / Ti, which is the ratio to the amount of Ti, so that it is not necessarily a good coating. In some cases, it may not be possible to secure machinability. In other words, if the N content of steel containing 0.01 to 0.20% Ti in weight% is specified as less than 0.1 in NZTi, a large amount of hard TiN is formed and the machinability increases. In some cases, and also in toughness.
• An object of the present invention is to provide a steel material which has good machinability and is suitable as a material for structural parts of various machines such as automobiles, transportation machines, industrial machines, construction machines, and the like.
• the gist of the present invention is as follows.
• the composition is more than 90%
• Ti carbosulfide in the present invention includes simple Ti sulfide.
• maximum diameter (of Ti carbosulfide) refers to "the longest diameter of an individual Ti carbosulfide.”
• the cleanliness of Ti carbosulfide is a value obtained by measuring 60 fields of view using the “microscopic test method for nonmetallic inclusions in steel” specified in JIS G 0555, with the magnification of an optical microscope set to 400 times.
• non-heat treated steel refers to a steel material in which "quenching and tempering” as a so-called “temper treatment” is omitted.
• available steel material it includes “a steel material that has been subjected to aging treatment equivalent to tempering after cooling after hot working”.
• Tempoered steel refers to steel that has been “quenched and tempered”.
• the tissue ratio means the tissue ratio when observed under a microscope, that is, the area ratio.
• 90% or more of ferrite and perlite means that the sum of the proportions of frite and perlite is 90% or more in an organization where ferrite and perlite are mixed. It means something.
• bainite refers to a state in which bainite occupies 90% or more of the organization when no ferrite is included in the organization.
• Boinite is 90% or more means that the sum of the proportions of ferrite and bayite is 90% or more in an organization where vanite and ferrite are mixed.
• “50% or more of martensite” means that 50% or more of the organization is martensite.
• the above (IV) relates to “tempered steel material” which has been quenched and tempered. Therefore, the above martensite refers to a tempered martensite, that is, “tempered martensite”. , Simply referred to as “martensite”.
• the present inventors have found that the chemical composition and microstructure of steel affect machinability and mechanical properties. The experiment was repeated to examine the effects.
• Ti carbosulfide has a greater machinability improvement effect than MnS. This is based on the fact that the melting point of Ti carbosulfide is lower than that of MnS, so that the lubrication of the rake face of the tool during cutting is increased.
• Ti carbosulfide generated during steelmaking does not form a solid solution in the matrix at the normal heating temperature for hot working and the normal heating temperature for tempering. Therefore, Ti carbosulfide exhibits a so-called “pinning effect” in the austenite region, and is effective in preventing austenite grains from becoming coarse.
• Ti carbosulfide is used for normal tempering in tempering. Does not dissolve in the matrix even at the heating temperature or the heating temperature for aging treatment equivalent to tempering.
• the balance between strength and toughness is good for steel materials in which 9% or more of the structure is bainite, or steel with bainite and bainite.
• Non-heat treated steel with a specific chemical composition and 90% or more of the structure is made of graphite and pearlite.
• the proportion of the fluoride is 20 to 70% in area ratio and the particle size of ferrite. If the JIS particle size number is 5 or more, the average value of the pearlite lamellar spacing is 0.2 or less, and at least one of the conditions is satisfied, a good balance between strength and toughness can be obtained.
• fn 3 0.5 S i (%) + n () +1.13 C r (%) +1.98 Ni (%) (3)
• the present invention has been completed based on the above findings.
• C combines with S with Ti to form Ti carbosulfide and has an effect of enhancing machinability. Further, C is an effective element for securing strength. However, if the content is less than 0.05%, these effects cannot be obtained. On the other hand, if C is contained in excess of 0.6%, the toughness will decrease. Therefore, the content of C is set to 0.05 to 0.6%.
• condition X steels in which 90% or more of the structure is fly and pearlite shall be 0.2 to 0.6%. It is more preferably 0.25 to 0.5%.
• the C content of non-heat treated steel materials (90% or more of the structure is bainite or fly and bainite (hereinafter referred to as “condition Y steel” for simplicity)) is 0.05 to 0.3. %, Preferably 0.:! More preferably, it is set to 0.24%.
• condition Z steel a tempered steel material in which 50% or more of the structure is martensite
• the machinability improving effect of S in the present invention can be obtained for the first time by forming Ti carbosulfide by complex addition of an appropriate amount of C and Ti.
• an S content of 0.002% or more is required as described above.
• the effect on machinability does not change even if S is contained in excess of 0.2%, but coarse MnS is regenerated in the steel, causing problems such as ground flaws. I will.
• the hot workability is significantly deteriorated, making hot plastic working difficult and toughness may be reduced. Therefore, the content of S is set to 0.002 to 0.2%.
• the S content of the “steel material under the condition X” is preferably 0.01 to 0.2%, more preferably 0.02 to 0.17%.
• the S content of the “steel material of condition Y” is preferably set to 0.005 to 0.17%.
• Ti is an important alloying element for controlling inclusions in the present invention. If the content is less than 0.04%, S cannot be sufficiently converted to Ti carbosulfide, so that machinability cannot be enhanced. On the other hand, if the content exceeds 1.0%, not only the machinability improvement effect is saturated but the cost is increased, but also the toughness and hot workability are significantly deteriorated. Therefore, the Ti content is set to 0.04 to: L. 0%.
• the Ti content of the “steel under condition X” is preferably in the range of 08 to 0.8%.
• the Ti content of the “steel material with condition ⁇ ” be 0.06 to 0.8%.
• the Ti content of the “steel material of condition Z” is also 0.06 to 0.8%.
• N 0.008% or less
• N has a large affinity for Ti, it easily bonds to Ti to form Ti N and fixes Ti, so that when N is contained in a large amount, the above-mentioned Ti carbosulfide is used.
• the effect of improving machinability cannot be fully exhibited.
• coarse TiN reduces toughness and machinability. Therefore, the N content was set to 0.008% or less.
• the upper limit of the N content is preferably set to ⁇ 0.006%.
• Nd need not be added.
• Nd 2 S 3 has the effect of tip shake and has the effect of improving machinability.
• the content of Nd is preferably 0.005% or more.
• the content of Nd was set to 0 to 0.1%.
• the preferred upper limit of the Nd content is 0.08%.
• Se need not be added. If added, it has the effect of further improving the machinability of the steel. In order to surely obtain this effect, it is preferable that the content of ⁇ 6 is 0.1% or more. However, if the content exceeds 0.5%, the above-mentioned effect is only saturated, and instead, coarse inclusions are formed and the fatigue strength and / or toughness are reduced. Therefore, the content of Se was set to 0 to 0.5%.
• Te need not be added. If added, it has the effect of further increasing the machinability of steel. To ensure this effect, the content of Te is preferably 0.005% or more. However, if the content exceeds 0.05%, not only the above-mentioned effect is saturated, but rather coarse inclusions are formed, resulting in a decrease in fatigue strength and Z or toughness. Furthermore, the addition of a large amount of Te causes deterioration of hot workability, and particularly when the content exceeds 0.05%, flaws are generated on the surface of the hot-worked steel material. Therefore, the content of Te was set to 0 to 0.5%.
• Ca need not be added. If added, it has the effect of greatly enhancing the machinability of steel. To ensure this effect, it is preferable that Ca has a content of 0.001% or more. However, if the content exceeds 0.01%, not only the above-mentioned effect is saturated, but rather coarse inclusions are formed and the fatigue strength and Z or toughness are reduced. Therefore, the content of Ca was set to 0 to 0.01%.
• the content of Pb is preferably set to 0.05% or more.
• the content exceeds 0.5% not only the above-mentioned effect is saturated, but rather, coarse inclusions are formed and the fatigue strength and the Z or toughness are reduced.
• the addition of a large amount of Pb causes deterioration of hot workability, and particularly when the content exceeds 0.5%, flaws are generated on the surface of the hot-worked steel material. Therefore, the content of Pb was set to 0 to 0.5%.
• B i may not be added. When added, it has the effect of greatly improving the machinability of steel.
• the content of Bi is preferably 0.05% or more. However, its content exceeds 0.4% As a result, the above effects are saturated, and instead the force is generated, and coarse inclusions are generated, resulting in a decrease in fatigue strength and Z or toughness. Further, the hot workability is deteriorated, so that the surface of the hot worked steel material is flawed. Therefore, the Bi content was set to 0 to 0.4%.
• Non-heat treated steel material (“Condition X steel”) in which 90% or more of the structure is made of fly and powder
• Si has the effect of deoxidizing steel and strengthening the frit phase.
• the increase in the Si content enhances the lubricating effect on the chip surface during cutting and extends the tool life, thereby improving the machinability.
• the content of S i is preferably set to 0.05 to 1.5%.
• the content of S i is preferably 0.3 to 1.3%, and more preferably 0.5 to 1.3%.
• Mn has an effect of improving fatigue strength by solid solution strengthening. However, if the content is less than 0.1%, it is difficult to obtain the effect. On the other hand, if the Mn content exceeds 2.0%, the durability ratio (fatigue strength Z tensile strength) and the yield ratio (yield strength Z tensile strength) may be reduced in the case of the “steel material of condition X”. . Therefore, the content of Mn is preferably set to 0.1 to 2.0%. The Mn content is preferably set to 0.4 to 2.7%, and more preferably set to 0.5 to 1.7%.
• P may be added intentionally. This is because “Steel under condition X” has the effect of increasing the tensile strength and fatigue strength. In order to ensure this effect, it is preferable that the content of P be 0.01% or more. However, if the content exceeds 0.07%, the toughness is remarkably deteriorated, and the hot workability is further reduced. Therefore, the content of P is preferably set to 0.07% or less. In addition, when P is added positively, the content is preferably set to 0.015 to 0.05%.
• A1 is an effective element for deoxidizing steel. However, if the content is less than 0.002%, it is difficult to obtain the desired effect. If the content exceeds 0.05%, the effect is saturated and the machinability may be reduced. Therefore, the content of A1 is preferably set to 0.002 to 0.05%. Preferably, the content of A1 is 0.005 to 0.03%.
• Cu need not be added. If added, it has the effect of improving the strength of the steel, especially the fatigue strength, by precipitation strengthening. To ensure this effect, it is preferable that the content of Cu be 0.2% or more. However, if the content exceeds 1.0%, in addition to the deterioration of hot workability, precipitates may be coarsened and the above-mentioned effects may be saturated or, on the contrary, may be reduced. Furthermore, The costs are only increasing. Therefore, the content of Cu is preferably set to 0 to 1.0%.
• Ni need not be added. If added, it has the effect of increasing the strength. C To ensure this effect, the Ni content is preferably at least 0.02%. However, if the content exceeds 2.0%, this effect is saturated and the cost increases. Therefore, the content of Ni is preferably set to 0 to 2.0%.
• Mo may not be added. If added, it has the effect of refining the microstructure of ferrite and pearlite and improving the strength of the steel, especially the fatigue strength. To ensure this effect, the Mo content is preferably set to 0.05% or more. However, if the content exceeds ⁇ .5%, the structure after hot working is rather abnormally coarsened and the fatigue strength is reduced. Therefore, the content of Mo is preferably set to 0 to 0.5%.
• V need not be added. If added, it precipitates as fine nitrides and carbonitrides, and has the effect of improving the strength of steel, especially fatigue strength. To ensure this effect, V should be contained at a content of 0.05% or more. No. However, if the content exceeds 0.3%, the precipitates become coarse, so that the above-mentioned effects may be saturated or may be rather reduced. In addition, raw material costs are only increasing. Therefore, the content of V is preferably set to 0 to 0.3%.
• N b need not be added. If added, it precipitates as fine nitrides or carbonitrides, preventing the austenite grains from coarsening and has the effect of improving the strength of the steel, particularly the fatigue strength.
• the content of Nb is preferably set to 0.05% or more. However, if the content exceeds 0.1%, the above-mentioned effects are only saturated, and coarse hard carbonitrides are produced, which may damage the tool and cause a decrease in machinability. Therefore, the content of Nb is preferably set to 0 to 0.1%. The upper limit of the Nb content is preferably set to 0.05%.
• ⁇ oxygen
• ⁇ oxygen
• the content of ⁇ as an impurity element is preferably set to 0.015% or less. No.
• the content of ⁇ is more preferably not more than 0.01%.
• Si has the effect of increasing the deoxidizing and hardenability of steel. Further, in the case of “steel material of condition Y”, the machinability is improved because the lubrication of the chip surface during cutting is increased and the tool life is extended with the increase of the Si content. However, if the content is less than 0.05%, the effect of addition is poor. On the other hand, if it exceeds 1.5%, not only the above effect is saturated but also the toughness is deteriorated. Therefore, the content of Si is preferably set to 0.05 to 1.5%. In addition, the Si content is preferably set to 0.5 to 1.3%.
• A1 is a strong deoxidizing element.
• the content is preferably 0.002% or more. However, if the content exceeds 0.05%, the effect is saturated and the cost is increased. Therefore, the content of A1 should be 0.002 to 0.05%. Preferably, the A1 content is 0.005 to 0.04%.
• the content of Cu is preferably set to 0.2% or more. However, if the content exceeds 1.0%, in addition to deterioration of hot workability, precipitates may become coarse and the above-mentioned effects may be saturated, or toughness may be reduced. In addition, costs are only increasing. Therefore, the content of Cu is preferably set to 0 to 1.0%.
• Mo may not be added. If added, it will enhance hardenability and It has the effect of refining the structure and improving the strength of the steel. To ensure this effect, the content of Mo is preferably set to 0.05% or more. However, if its content exceeds 0.5%, the structure after hot working is rather abnormally coarsened and the toughness is reduced. For this reason, the content of Mo is preferably set to 0 to 0.5%.
• V need not be added. If added, it precipitates as fine nitrides and carbonitrides, and has the effect of increasing the strength of steel and enhancing the lubricity of chips during cutting to improve machinability. In order to surely obtain such an effect, it is preferable that the content of V is ⁇ .05% or more. However, if the content exceeds 0.30%, the precipitates become coarse, so that the above effects may be saturated or the toughness may be reduced. In addition, raw material costs are only increasing. Therefore, the content of V is preferably set to 0 to 0.30%.
• Nb need not be added. If added, it precipitates as fine nitrides or carbonitrides, has the effect of preventing austenite grains from coarsening and improving the strength and toughness of the steel.
• the content of Nb is preferably set to 0.005% or more. However, if the content exceeds 0.1%, not only the above-mentioned effects are saturated, but also coarse hard carbonitrides are formed, which may damage the tool and cause a decrease in machinability. Therefore, the content of Nb is preferably set to 0 to 0.1%.
• the B content is preferably 0.0003% or more. However, if the content exceeds 0.02%, the above effect may be saturated or, on the contrary, the toughness may be reduced. For this reason, the content of B is preferably set to 0 to 0.02%.
• the value of fn3 represented by the above equation (3) has a correlation with the structure and toughness of a non-heat treated steel having a specific chemical composition, and this value is 2.5 to 4.5. %,
• the main structure of the non-heat treated steel is bainite or ferrite and bainite, and a good balance of strength and toughness can be obtained.
• Si, Mn, Cr and Ni related to fn 3 have the effect of increasing the hardenability of steel.However, if the value of fn 3 is less than 2.5%, the desired effect of improving the hardenability is not obtained, and the toughness is reduced. May drop.
• the value of fn 3 represented by the equation (3) is preferably set to 2.5 to 4.5%.
• the content of each element other than Si described above need not be particularly limited, since the above fn3 may satisfy 2.5 to 4.5%.
• the contents of Mn, Cr and Ni are preferably 0.4 to 3.5%, 3.0% or less, and 2.0% or less, respectively.
• ⁇ (oxygen) as an impurity element forms hard oxide-based inclusions, which may damage the cutting tool during cutting and reduce machinability.
• the content of ⁇ as an impurity element is preferably set to 0.015% or less in order to maintain good machinability.
• the content of ⁇ is more preferably not more than 0.01%.
• the content of P as an impurity element is preferably set to 0.05% or less from the viewpoint of securing the toughness of the steel.
• Si has the effect of increasing the deoxidizing and hardenability of steel. Furthermore, in the case of “steel material of condition Z”, the machinability is improved because the lubrication of the chip surface during cutting is increased and the tool life is prolonged as the Si content increases. However, if the content is less than ..05%, the effect of addition is poor, while if it exceeds 1.5%, not only the above effect is saturated, but also the toughness is deteriorated. Therefore, the content of S i is preferably set to 0.05 to 1.5%.
• Mn has the effect of improving the hardenability of steel and improving the fatigue strength by solid solution strengthening. However, if the content is less than 0.4%, the effect cannot be obtained. If the content exceeds 2.0%, not only this effect is saturated, but also the hardness becomes too hard to lower the toughness. Therefore, the content of Mn is preferably set to 0.4 to 2.0%.
• A1 is a strong deoxidizing element.
• the content is preferably 0.002% or more. However, if the content exceeds 0.05%, the effect is saturated and the cost is increased. Therefore, the content of A1 should be 0.002 to 0.05%.
• the A1 content is preferably 0.005 to 0.04%.
• Cu need not be added. If added, it has the effect of increasing the strength of the steel without lowering the toughness and further enhancing the machinability. To ensure this effect, it is preferable that the content of (11 is 0.2% or more. However, if the content exceeds 1.0%, the hot workability is deteriorated. However, the above-mentioned effect may be saturated or may be rather deteriorated due to coarsening of the precipitates, and the cost may be increased only, so that the content of Cu should be 0 to 1.0%. Is good.
• Ni need not be added. If added, it has the effect of improving the hardenability of steel. To ensure this effect, the Ni content is preferably set to 0.02% or more. However, if the content exceeds 2.0%, this effect is saturated and the cost increases. Therefore, the content of Ni is preferably set to 0 to 2.0%.
• the content of Cr is 0.03% or more. However, if the content exceeds 2.0%, not only the above-mentioned effects are saturated, but also the steel becomes too hard and the toughness is reduced. For this reason, the content of Cr is preferably set to 0 to 2.0%.
• Mo may not be added. If added, it has the effect of increasing the hardenability of steel. To ensure this effect, the content of Mo is preferably set to 0.05% or more. However, if the content exceeds 0.5%, not only this effect is saturated, but also the hardness becomes too high, the toughness is reduced, and the cost is increased. For this reason, the content of Mo is 0-0. A good value is 5%.
• V need not be added. If added, it precipitates as fine nitrides and carbonitrides, and has the effect of improving the strength of steel, especially fatigue strength. To ensure this effect, it is preferable that V has a content of 0.05% or more. However, when the content exceeds 0.3%, the precipitates are coarsened, so that the above-mentioned effects may be saturated or may be reduced. In addition, raw material costs are only increasing. Therefore, the content of V is preferably set to 0 to 0.3%.
• Nb need not be added. If added, it precipitates as fine nitrides or carbonitrides, prevents austenite grains from coarsening, and has the effect of improving the strength of steel, particularly fatigue strength and toughness. To ensure this effect, it is preferable that the content of Nb be 0.005% or more. However, if the content exceeds 0.1%, not only the above effect is saturated, but also coarse hard carbonitrides are generated, which may damage the tool and lower the machinability. Therefore, the content of Nb is preferably set to 0 to 0.1%. The upper limit of the Nb content is preferably 0.05%.
• the B need not be added. If added, it has the effect of improving the hardenability and increasing the strength and toughness of the steel. To ensure this effect, the B content is preferably 0.0003% or more. However, if the content exceeds 0.02%, the above effect may be saturated or, on the contrary, the toughness may be reduced. For this reason, the content of B is preferably set to 0 to 0.02%.
• ⁇ (oxygen) as an impurity element forms hard oxide-based inclusions, which may damage the cutting tool during cutting and reduce machinability.
• ⁇ content exceeds 0.015%, the machinability may be significantly reduced. Therefore, even in the case of "steel material of condition Z", the content as an impurity element should be reduced in order to maintain good machinability.
• the content of 0 is more preferably set to 0.01% or less.
• the content of P is determined from the viewpoint of securing the toughness of steel.
• Ti carbosulfide in the present invention also includes a single Ti sulfide.
• the amount of Ti carbosulfide having a maximum diameter of 10 m or less is less than 0.05% in cleanliness, the effect of improving the machinability by Ti carbosulfide cannot be exhibited.
• the above-mentioned cleanliness is preferably set to 0.08% or more. If the cleanliness value of the above-mentioned Ti carbosulfide is too large, the fatigue strength may be reduced. Therefore, the upper limit of the cleanliness of the above-mentioned Ti carbosulfide is preferably about 2.0%. No. The reason for limiting the size of Ti carbosulfide to a maximum diameter of 10 m or less is that if it exceeds 10 m, the fatigue strength and Z or toughness are reduced.
• the maximum diameter of Ti carbosulfide be 7 ⁇ m or less. If the maximum diameter of Ti carbosulfide is too small, the effect of improving machinability will be reduced. Therefore, the lower limit of the maximum diameter of Ti carbosulfide is preferably about 0.5 ⁇ m.
• Ti carbosulfide is basically determined by the contents of Ti, S and N in the steel. However, to keep the size and cleanliness of Ti carbosulfide at specified values, it is important to prevent excessive formation of Ti oxides. For this purpose, it may not be sufficient if the steel has the chemical composition described in the above item (A). For example, a steelmaking method in which deoxidation is sufficiently performed with Si and A1 and finally Ti is added. It is desirable to adopt
• Ti carbosulfide can be easily distinguished from other inclusions by color and shape when the specimen taken from steel material is mirror-polished and the polished surface is used as a test surface and observed with an optical microscope at a magnification of 400 or more. it can. That is, when observed under an optical microscope under the above conditions, the “color” of Ti carbosulfide is extremely light gray, and its “shape” is recognized as a granular shape (spherical shape) corresponding to the B-based inclusion of JIS.
• the detailed determination of Ti carbosulfide can also be performed by observing the test surface with an electron microscope equipped with an analysis function such as an EDX (energy dispersive X-ray analyzer).
• the cleanliness of Ti carbosulfides was measured in 60 visual fields using the ⁇ microscopic test method for steel nonmetallic inclusions '' specified in JIS G 0555, with the magnification of the optical microscope set to 400 times. It refers to the measured value.
• the steel slab having the chemical composition described in ( ⁇ ) described above is used, for example, from 150 After heating to 130 ° C, hot working such as hot forging is performed, and after finishing at a temperature of 900 ° C or more, at a cooling rate of 60 ° C / min or less, at least 5 ° C ⁇ Air cooling or cooling to 0 ° C is sufficient.
• the term “cooling rate” as used herein refers to a cooling rate of a steel material surface.
• the percentage of ferrite is 20 to 70% in area ratio
• the grain size of ferrite is 5 or more in JIS grain size number
• the average value of pearlite lamellar intervals is 0.
• the balance between strength and toughness is improved. Therefore, if a good balance between strength and toughness is required, 90% or more of the structure should be bainite or X-lite and bainite. Further, when the above-mentioned steel material is a non-heat treated steel material, it is possible to reduce the cost and energy required for the heat treatment.
• the steel slab having the chemical composition described in ( ⁇ ) described above must be used.
• hot forging After finishing at a temperature of 900 ° C or more, air cooling or cooling to at least 300 ° C at a cooling rate of 60 ° C / min or less is recommended.
• the “forming ratio” is A. ( ⁇ . ⁇ ) when is the cross-sectional area before processing and A is the cross-sectional area after processing.
• the grain size of old austenite grains in the organization is 4 or more in JIS grain size number
• 90% or more of the structure is bainite or a non-heat treated steel material composed of ferrite and bainite (that is, A good balance between strength and toughness can be ensured in “condition Y steel”.
• “old austenite grains” in non-heat treated steel materials refer to austenite grains immediately before transformation of bainite diplite or the like occurs due to heating and hot working.
• the former austenite grains can be easily corroded with nickel and observed with an optical microscope. Judgment is completed.
• a slab having the chemical composition described in (IV) described above is used, for example, by adding 105 After heating to 0 to 130 ° C, hot working such as hot forging is performed at a forming ratio of 1.5 or more, and after finishing at a temperature of 900 ° C or more, 60 ° CZ Air cooling or cooling to at least 300 ° C at a cooling rate of less than 1 minute, then heating to 800 ° C (: up to 950 ° C and holding for 20-150 minutes And then quenched using a cooling medium such as water or oil, and further heated to a temperature range of 400 to 700 ° C, held for 20 to 150 minutes, and then cooled for 2 ° CZ or more. It may be air-cooled, allowed to cool, or in some cases, water-cooled, oil-cooled, and tempered. , So-called "direct quenching" may be used
• the structure be martensite.
• the remaining part of the structure other than martensite is composed of two phases: austenite and frit, a structure transformed from austenite by quenching, a perlite and bainite tempered. This is the structure in which the ferrite when quenched from the region has been tempered, or the structure in which the austenite that remains without transformation after quenching (so-called “retained austenite”) has been tempered. Substantially 100% of the organization may be martensite.
• the grain size of the former austenite grains is 5 or more in the JIS grain size number, extremely good strength and toughness can be obtained for tempered steel materials (50% or more of the tissue is made of martensite) A stable balance can be ensured.
• "old austenite grains" in the tempered steel material means austenite grains immediately before quenching. In the case of a tempered steel material in which 50% or more of the structure is martensite, for example, after quenching the steel material, or after quenching and tempering the steel material, cut out a sample and add a surfactant Corrosion with an acid-based aqueous solution and observation with an optical microscope Thus, the old austenite grains can be easily determined.
• Steels 1 to 36 in Tables 1 to 3 are steels of the examples of the present invention whose chemical composition is within the range specified in the present invention.
• steels 37 to 46 in Table 4 are steels of comparative examples in which any of the elements is out of the range of the content specified in the present invention (
• these steels were heated to 1250 ° C and then hot forged to finish at 1 000 ° C to produce round bars with a diameter of 60 mm.
• the cooling conditions after hot forging were air-cooled or allowed to cool to 300 ° C so that the cooling rate was 5 to 35 ° CZ, and the structure of the round bar was adjusted to achieve a tensile strength of approximately 845 to 35 ° C. 8
• the range was set to 70 MPa.
• Steel 6, Steel 7, Steel 9, Steel 11 Steel 29 to 36, Steel 40, Steel 45 and Steel 46 were cooled to 770 to 900 ° C for 1 hour after cooling after hot forging. Heating, water quenching, and tempering at 550 to 560 (air cooling after tempering) were performed to adjust the structure and strength level.
• a test specimen was sampled in accordance with JIS G 0555, Fig. 3 centering on the R / 2 part, and a mirror-polished surface with a width of 15 mm and a height of 20 mm was taken.
• the maximum diameter of Ti carbosulfide was also investigated by observing 60 visual fields with a 400-fold optical microscope. After this, the mirror-polished test surface was further corroded with nails and observed with an optical microscope with a magnification of 100 times to observe the structure at the R / 2 part, and the ratio (area ratio) of each structure was determined. investigated.
• Machinability was also evaluated by drill drilling tests. That is, a hole with a depth of 5 O mm was drilled in the length direction using a round bar with a length of 55 mm and a round bar with a diameter of 60 mm, and the hole immediately before it became impossible to drill due to abrasion of the cutting edge
• the machinability was investigated using the number of as the machinability evaluation index.
• the drilling conditions were 6 mm straight shank drills of JIS high speed tool steel S KH59. Using water-soluble lubricant, feed 0.20 mm / rev, speed 980 r
• Tables 5 to 8 show the results of the above various tests. Tables 5 to 8 also show the conditions of quenching and tempering for steel 6, steel 9, steel 9, steel 11, steel 29 to 36, steel 40, steel 45, and steel 46.
• F indicates flight
• P indicates perlite
• B indicates bainite
• M indicates martensite
• F indicates flight
• P indicates perlite
• B indicates bainite
• M indicates martensite
• F indicates the flight
• P indicates the perlite
• B indicates the bainite
• M indicates the martensite.
• F indicates a light
• P indicates a perlite
• B indicates a bainite
• M indicates a martensite.
• the asterisk indicates that the condition is outside the conditions specified in the present invention.
• the * mark in steel indicates that the chemical composition is out of condition.
• the steel contains C, S, Ti and N within the range specified in the present invention, and the maximum diameter of Ti carbosulfide in steel is 10 m or less and its cleanliness is 0.05%.
• the machinability evaluation index exceeds 200.
• the cleanliness of the Ti carbosulfide is low. Since it is less than 0.05%, the machinability index is as low as 51. In the case of Test Nos.
• any one of the C, Ti and N contents of the test steels Steel 37, Steel 39 and Steel 40 was out of the range specified in the present invention.
• the gender index is low at 58, 40 and 45 respectively.
• the S content of the test steel, Steel 38 was outside the range specified in the present invention, and the cleanliness of Ti carbosulfide was below 0.05%. Is as low as 3 1.
• steels 41 to 46 whose Nd, Se, Te, Ca, Pb, and Bi contents were out of the ranges specified in the present invention were used as test steels.
• the machinability is good, compared to the case of Test Nos. 2 to 7 where steels 2 to 7 in which the contents of each of the above elements are within the range specified in the present invention are used as test steels, It is clear that the strength and / or toughness is poor.
• Steels 47 to 54 having the chemical compositions shown in Table 9 were melted using a 150 kg vacuum melting furnace or a 3-ton vacuum melting furnace. Steels 47-49 were melted in a 3-ton vacuum melting furnace, and all others were melted in a 150 kg vacuum melting furnace. In order to prevent the formation of Ti oxides, the size and cleanliness of Ti carbosulfide were adjusted by adding Ti at the end of the deoxidation with Si and A1 and adding various elements. Steels 47 to 54 in Table 9 are all steels according to the present invention whose chemical composition is within the range specified in the present invention.
• these steels were heated to 1250 ° C and then hot forged to finish at 1 000 ° C to produce round bars with a diameter of 60 mm.
• the cooling conditions after hot forging were air-cooled or allowed to cool to 400 ° C so that the cooling rate was 5 to 35 ° CZ, and the structure was mainly composed of ferrite and perlite. The tensile strength was adjusted.
• test pieces were collected from the round bar obtained in the same manner as in Example 1 and investigated.
• a JIS 14A tensile test specimen from the R / 2 part position from the surface of the round bar, a JIS 14A tensile test specimen, an Ono-type rotating bending test specimen (parallel part having a diameter of 8 mm and a length of 18.4 mm) and JIS No. 3 impact test specimens (2 mm U notch test specimens) were sampled, and their tensile strength, fatigue strength (fatigue limit) and toughness (impact value) at room temperature were investigated.
• a test piece was taken from the surface of the round bar, centering on the RZ2 position, in accordance with Figure 3 of JIS G 0555, and a mirror-polished test surface with a width of 15 mm and a height of 20 mm was magnified. Observed 60 visual fields with a 400 ⁇ optical microscope, and measured the cleanliness of Ti carbosulfide while separating it from other inclusions. The maximum diameter of Ti carbosulfide was also investigated by observing 60 visual fields with a 400-fold optical microscope. Thereafter, the mirror-polished test surface was further corroded with sodium and observed with an optical microscope having a magnification of 100 times to observe the structure of the RZ2 portion, and the ratio (area ratio) of each structure was examined. For steels 51 to 53 of test numbers 51 to 53, the average particle diameter lamella spacing was measured by taking JIS fine grain size numbers and taking scanning electron micrographs. I asked.
• Machinability was also evaluated by drill drilling tests.
• the test conditions and evaluation method are as described in Example 1.
• Table 10 shows the results of the various tests described above.
• F stands for frilite
• P stands for pearlite
• B stands for bainite
• M stands for mancite
• Steels 55 to 59 having the chemical compositions shown in Table 11 were melted using a 150 kg vacuum melting furnace or a 3-ton vacuum melting furnace. Steel 55 and steel 56 were melted in a 3-ton vacuum melting furnace, and all others were melted in a 150 kg vacuum melting furnace. In this example, too, in order to prevent the formation of Ti oxides, sufficient deoxidation was performed with Si and A1 and various elements were added. The degree was adjusted. Steels 55 to 59 in Table 11 are all steels of the present invention whose chemical composition is within the range specified in the present invention.
• these steels were heated to 1250 ° C and then hot forged to finish at 1 000 ° C to produce round bars with a diameter of 60 mm.
• the cooling conditions after hot forging were air-cooled or allowed to cool to 300 ° C so that the cooling rate was 5 to 35 ° CZ, and the structure was mainly composed of bainite or ferrite.
• the tensile strength was adjusted so as to be composed of paynight.
• Steel 57 and steel 58 were also subjected to aging treatment (Test Nos. 60 and 61) which were cooled after hot forging, then heated at 560 ° C for 1 hour and air-cooled.
• test pieces were collected from the round bar obtained in the same manner as in Example 1 and investigated.
• JIS 14A tensile test specimen, Ono-type rotary bending test specimen (parallel part having a diameter of 8 mm and length of 18.4 mm) and JIS 3A No. 2 impact test specimens (2 mmU notch rupee test specimens) were sampled and their tensile strength, fatigue strength (fatigue limit) and toughness (impact value) at room temperature were investigated.
• a test piece was taken from the surface of the round bar, centering on the RZ2 position, in accordance with Figure 3 of JIS G 0555, and a mirror-polished test surface with a width of 15 mm and a height of 20 mm was magnified. Observed 60 visual fields with a 400 ⁇ optical microscope, and measured the cleanliness of Ti carbosulfide while separating it from other inclusions. The maximum diameter of Ti carbosulfide was also investigated by observing 60 visual fields with a 400-fold optical microscope. Thereafter, the mirror-polished test surface was further corroded with nickel and observed with an optical microscope at a magnification of 1 ⁇ 0 to observe the structure at the RZ2 portion, and the ratio (area ratio) of each structure was investigated.
• Machinability was also evaluated by drill drilling tests.
• the test conditions and evaluation method are as described in Example 1.
• Table 12 shows the results of the various tests described above. Table 12 also shows the conditions of aging treatment performed on steel 57 and steel 58 in test numbers 60 and 61 ( 1 2
• Steels 60 to 64 with the chemical compositions shown in Table 13 were melted using a 150 kg vacuum melting furnace or a 3-ton vacuum melting furnace. Steel 60 and steel 61 were melted in a 3-ton vacuum melting furnace, and the others were melted in a 150 kg vacuum melting furnace. In this example, too, in order to prevent the formation of Ti oxide, Ti and A1 were sufficiently deoxidized and various elements were added. The cleanliness was adjusted. Steels 60 to 64 in Table 13 are all steels according to the present invention whose chemical compositions are within the range specified by the present invention.
• these steels were heated to 1250 ° C and then hot forged to finish at 1 000 ° C to produce round bars with a diameter of 60 mm.
• the cooling conditions after hot forging were air-cooled or allowed to cool to 300 ° C so that the cooling rate was 5 to 35 ° C / min. After that, it was heated to 850 to 900 ° C for 1 hour, water-quenched, and tempered at 550 ° C (cooling after tempering was air-cooled) to adjust the tissue and strength level.
• test pieces were sampled from the thus obtained round bar in the same manner as in Example 1 and investigated.
• a JIS 14A tensile test specimen from the R / 2 part position from the surface of the round bar, a JIS 14A tensile test specimen, an Ono-type rotating bending test specimen (parallel part having a diameter of 8 mm and a length of 18.4 mm) and JIS No. 3 impact test specimens (2 mm U notch test specimens) were sampled, and the tensile strength, fatigue strength (fatigue limit) and toughness (impact value) at room temperature were investigated.
• a test piece was sampled in accordance with Fig. 3 of J1S G0555, centering on the RZ2 position, and a mirror-polished test surface with a width of 15 mm and a height of 20 mm was magnified.
• the maximum diameter of Ti carbosulfide was also investigated by observing 60 visual fields with a 400-fold optical microscope. After this, the mirror-polished test surface was further corroded with sodium and observed with an optical microscope at a magnification of 100 to observe the structure at the R / 2 position, and the ratio (area ratio) of each structure was investigated. .
• Machinability was also evaluated by drill drilling tests.
• the test conditions and evaluation method are as described in Example 1.
• Table 14 shows the results of the various tests described above. Table 14 also shows the quenching and tempering conditions for steels 60 to 64. 14
• F indicates X-lite
• P indicates perlite
• B indicates bainite
• M indicates martensite
• hot die forging is performed so that the finishing temperature becomes 1 000 ° C or more, and the cooling rate after hot die forging is set at a cooling rate of 5 to 35 ° C. / Min and air cooled or allowed to cool to 300 ° C to produce a crankshaft base material, which was cut and finished into the final crankshaft.
• the cooling rate after hot die forging is set at a cooling rate of 5 to 35 ° C. / Min and air cooled or allowed to cool to 300 ° C to produce a crankshaft base material, which was cut and finished into the final crankshaft.
• Specimens were sampled according to JIS G 0555, Fig. 3, centered at a position 15mm from the surface of the pin (diameter 70mm) of the cast material of the crankshaft, and the mirror-polished width was used.
• the surface to be inspected having a height of 15 mm and a height of 20 mm, was observed in 60 visual fields with an optical microscope having a magnification of 400 times, and its cleanliness was measured while distinguishing Ti carbosulfide from other inclusions.
• the maximum diameter of Ti carbosulfide was also investigated by observing 60 fields of view with an optical microscope with a magnification of 400x.
• the mirror-polished test surface was further corroded with Na and observed under an optical microscope at a magnification of 100 to observe the structure, and the ratio (area ratio) of each structure was examined.
• the test specimen was collected in a direction parallel to the axial direction of the crankshaft, and the JIS 14A tensile test specimen and the Ono-type rotary bending test specimen (the diameter of the parallel part was 8 mm and its length was 18.4 mm) and JIS No. 3 impact test specimens (2 mm U notched Charby test specimens) were sampled and the tensile strength, fatigue strength (fatigue limit) and toughness (impact value) at room temperature were investigated.
• Table 15 shows the results of the above various tests. Table 15 also shows the hardening and tempering conditions for test numbers 68, 69, 73, 79, and 80.
• F indicates ferrite
• P indicates private
• B indicates bainite
• M indicates martensite.
• the asterisk indicates that the condition is out of the conditions specified in the present invention.
• the * mark in steel indicates that the chemical composition is out of condition.
• crankshaft base material manufactured from the steel material according to the present invention has excellent machinability. Further, it is apparent that the crankshaft using the steel material according to the present invention as a raw material has a better balance between strength and toughness than the crankshaft using a steel material of a comparative example as a material.
• the steel material of the present invention has excellent machinability and a good balance of strength and toughness, it is used as a material for structural parts of various machines such as automobiles, transportation machines, industrial machines, and construction machines. can do. By using this steel material as a material and performing cutting, various mechanical structural parts can be manufactured relatively easily.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Shafts, Cranks, Connecting Bars, And Related Bearings (AREA)

Priority Applications (5)

Applications Claiming Priority (14)

Related Child Applications (1)

Publications (1)

Family

ID=27563166

Family Applications (1)

Country Status (6)

Cited By (1)

Families Citing this family (36)

Citations (2)

Family Cites Families (5)

• 1997
  • 1997-11-25 EP EP97913441A patent/EP0903418B1/en not_active Expired - Lifetime
  • 1997-11-25 WO PCT/JP1997/004297 patent/WO1998023784A1/ja active IP Right Grant
  • 1997-11-25 KR KR1019980704909A patent/KR100268536B1/ko not_active IP Right Cessation
  • 1997-11-25 CN CN97191416A patent/CN1095503C/zh not_active Expired - Lifetime
  • 1997-11-25 CA CA002243123A patent/CA2243123C/en not_active Expired - Fee Related
  • 1997-11-25 DE DE69718784T patent/DE69718784T2/de not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events