US20070000582A1 - Steel product for induction hardening, induction-hardened member using the same, and methods for production them - Google Patents

Steel product for induction hardening, induction-hardened member using the same, and methods for production them Download PDF

Info

Publication number
US20070000582A1
US20070000582A1 US10/555,511 US55551105A US2007000582A1 US 20070000582 A1 US20070000582 A1 US 20070000582A1 US 55551105 A US55551105 A US 55551105A US 2007000582 A1 US2007000582 A1 US 2007000582A1
Authority
US
United States
Prior art keywords
less
induction
induction quenching
steel
steel material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US10/555,511
Inventor
Akihiro Matsuzaki
Yasuhiro Omori
Nobutaka Kurosawa
Tohru Hayashi
Takaaki Toyooka
Katsumi Yamada
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
JFE Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Assigned to JFE STEEL CORPORATION reassignment JFE STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MATSUZAKI, AKIHIRO, YAMADA, KATSUMI, HAYASHI, TOHRU, KUROSAWA, NOBUTAKA, OMORI, YASUHIRO, TOYOOKA, TAKAAKI
Publication of US20070000582A1 publication Critical patent/US20070000582A1/en
Abandoned legal-status Critical Current

Links

Images

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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
    • C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/28—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for plain shafts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to a steel material for induction quenching, which is suitable for an automobile drive shaft, constant velocity joint, and the like having a hard layer on a surface thereof formed by induction quenching, a induction quenched member using the same, and manufacturing methods thereof.
  • a fatigue strength is imparted to the steel thus treated by induction quenching and tempering, the fatigue strength, such as torsional fatigue strength, bending fatigue strength, rolling contact fatigue strength, and sliding and rolling contact fatigue strength, being important properties for machine structural members.
  • the increase in quenching depth by induction quenching may be considered.
  • the fatigue strength becomes saturated at a certain quenching depth and cannot be further improved.
  • the improvement in grain boundary strength is also effective, and for example, in Japanese Unexamined Patent Application Publication No. 2000-154819, a technique has been proposed in which austenite grains are particularized by precipitating a large amount of fine TiC in heating of induction quenching.
  • this technique although the grain boundary strength can be improved to a certain extent, the recent requirement for the fatigue strength cannot be fully satisfied.
  • a machine structural member having an improved fatigue strength has been proposed in which the fatigue strength is improved by controlling the following properties within respective predetermined ranges in accordance with the amount of C while a ratio CD/R is limited in the range of 0.3 to 0.7, CD being the thickness (depth of quenching) of a hard layer formed by induction quenching of a machine structural member having a circular transverse section, R being the radius thereof.
  • the properties mentioned above are the above CD/R, grain diameter of prior austenite in a region from the surface to 1 mm depth after induction quenching, average Vickers hardness Hf up to a ratio CD/R of 0.1 as obtained by induction quenching, and value A obtained from average Vickers hardness Hc of an axial central portion after induction quenching.
  • the member described above as is the case described above, the recent requirement for the fatigue strength cannot be fully satisfied.
  • the machine structural members such as an automobile drive shaft and constant velocity joint are machined by cutting into a predetermined shape before induction quenching in many cases.
  • a steel material used for the members as described above is required to have superior machinability.
  • the machinability has not been taken into consideration at all. In practice, when the steel disclosed in the publications described above is machined, the life of cutting tool is shortened, and hence the machinability has been a problem.
  • An object of the present invention is to provide a steel material for induction quenching, which has superior machinability and which can obtain a high fatigue strength by induction quenching as compared to that obtained in the past, a induction quenched member using the same, and manufacturing methods thereof.
  • the above object can be achieved by the following steel material for induction quenching and the following induction quenched member.
  • the steel material for induction quenching comprises 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, in which the steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the thickness of the ferrite structure is 30 ⁇ m or less, and the average prior austenite grain diameter of a hard layer obtained after induction quenching is 12 ⁇ m or less.
  • the induction quenched member is formed using the above steel material for induction quenching, and the average prior austenite grain diameter of the hard layer obtained after induction quenching is 12
  • This steel material for induction quenching can be manufactured by a method for manufacturing a steel material for induction quenching, the method comprising a step of hot working a steel material having the above-described composition at a total reduction rate of 80% or more in a temperature region of more than 850° C. to 950° C., and a step of cooling the steel thus hot-worked to 600° C. or less at a cooling rate of less than of 0.6° C./sec.
  • this induction quenched member can be manufactured by a method for manufacturing an induction quenched member, the method comprising a step of performing induction quenching of a steel material for induction quenching, which is already formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
  • FIG. 1 is a schematic view illustrating the thickness of a ferrite structure.
  • FIG. 2 is a graph showing the relationship between the heating temperature in induction quenching and the average prior austenite grain diameter of a hard layer.
  • the total volume fraction of a ferrite structure and a pearlite structure thereof is controlled to be 90% or more, and the thickness of the ferrite structure is controlled to be 30 ⁇ m or less, the machinability can be improved.
  • the average prior austenite grain diameter of a hard layer formed at a surface portion can be decreased to 12 ⁇ m or less, and as a result, a high fatigue strength can be obtained.
  • C has the most significant influence on quenching properties, can make harder the hard layer after quenching, and can make the thickness thereof larger, thereby improving the fatigue strength.
  • the content is less than 0.3 percent by mass, the thickness of the hard layer must be considerably increased in order to ensure a required fatigue strength, and as a result, the generation of quench cracking markedly occurs.
  • the content is more than 0.7 percent by mass, the fatigue strength is decreased due to the decrease in grain boundary strength, and in addition, the machinability, cold forging properties, and quench cracking resistance are also degraded.
  • the content of C is set in the range of 0.3 to 0.7 percent by mass and preferably 0.4 to 0.6 percent by mass.
  • Si increases the number of nucleation sites of austenite in heating of quenching and also particularizes the hard layer by suppressing the growth of the austenite grains. In addition, Si suppresses the decrease in grain boundary strength by suppressing the formation of carbides. Hence, Si is an element effective in improving the fatigue strength.
  • the content of Si is set to 1.1 percent by mass or less.
  • the content of Si is preferably set to 0.3 percent by mass or more.
  • the content of Si is preferably set to less than 0.3 percent by mass.
  • Mn is an indispensable element for improving the quenching properties and for ensuring the thickness of the hard layer.
  • the content is less than 0.2 percent by mass, the effect is not significant.
  • the content is more than 2.0 percent by mass, the amount of retained austenite is increased after quenching, the surface hardness is decreased, and as a result, the fatigue strength is decreased.
  • the content of Mn is set to 0.2 percent by mass or more, preferably 0.3 percent by mass or more, and more preferably in the range of 0.5 to 2.0 percent by mass.
  • the content of Mn is high, the hardness of a mother material is increased, and the machinability tends to be disadvantageously degraded; hence, the content is preferably set to 1.2 percent by mass or less and is more preferably set to 1.0 percent by mass or less.
  • Mo decreases the austenite grain diameter in heating of quenching and particularizes the quenched hard layer, so that the fatigue strength is improved.
  • the heating temperature in quenching is set in the range of 800° C. to 1,000° C. and more preferably set in the range of 800° C. to 950° C.
  • Mo is used for the adjustment thereof.
  • Mo prevents the decrease in grain boundary strength by suppressing the formation of carbides.
  • Mo is a very important element of the present invention; however, when the content thereof is less than 0.05 percent by mass, the prior austenite grain diameter of the hard layer cannot be easily decreased to 12 ⁇ m or less all along the depth of the entire hard layer. On the other hand, when the content is more than 0.6 percent by mass, the machinability is degraded. Hence, the content of Mo is set to 0.05 to 0.6 percent by mass and preferably 0.2 to 0.4 percent by mass.
  • S forms MnS in steel and improves the machinability.
  • the content is more than 0.06 percent by mass, S segregates at the grain boundaries, and as a result, the grain boundary strength is decreased.
  • the content of S is set to 0.06 percent by mass or less and preferably set in the range of 0.01 to 0.06 percent by mass.
  • P segregates at the austenite grain boundaries, decreases the grain boundary strength, and decreases the fatigue strength, and in addition, quench cracking is promoted.
  • the content of P is set to 0.02 percent by mass or less, a smaller P content is more preferable.
  • Al is an element effective in deoxidizing steel.
  • Al suppresses the growth of the austenite grains in heating of quenching, and as a result, the hard layer is particularized.
  • the content of Al is set to 0.25 percent by mass or less and is preferably set in the range of 0.01 to 0.05 percent by mass.
  • Cr Cr is an element effective for the quenching properties and increases the thickness of the hard layer, thereby improving the fatigue strength.
  • the content of Cr is set to 0.3 percent by mass or less.
  • the content is preferably set to 0.1 percent by mass or more.
  • the balance that is, elements other than the elements described above, is Fe and unavoidable impurities.
  • the unavoidable impurities are 0, N, B, and the like; however, even when 0.008 percent by mass or less of O, 0.02 percent by mass or less of N, and 0.0003 percent by mass or less of B are contained, the effects of the present invention will not be degraded.
  • B exceeds 0.0003 percent by mass, (Fe, Mo, Mn) 23 (C, B) 6 tends to be stabilized and precipitated in steel before induction quenching, and thereby small and large prior austenite grains are mixed and are present in the hard layer after quenching, so that a high fatigue strength cannot be achieved.
  • Cu is an element effective for the quenching properties.
  • Cu is dissolved in ferrite and improves the fatigue strength by solid-solution strengthening.
  • Cu suppresses the formation of carbides and prevents the decrease in grain boundary strength, so that the fatigue strength is improved.
  • the content of Cu is set to 1.0 percent by mass or less and is preferably set in the range of 0.03 to 0.2 percent by mass.
  • Ni Since being an element improving the quenching properties, Ni is used for adjustment thereof. In addition, Ni suppresses the formation of carbides, prevents the decrease in grain boundary strength, and improves the fatigue strength. However, since Ni is a very expensive element, when the content thereof is more than 3.5 percent by mass, the manufacturing cost is increased. Hence, the content of Ni is set to 3.5 percent by mass or less. In addition, when the content of Ni is less than 0.05 percent by mass, since the effect of improving the quenching properties and the effect of suppressing the decrease in grain boundary strength are not significant, the content is preferably set to 0.05 percent by mass or more. Furthermore, the content is more preferably set in the range of 0.1 to 1.0 percent by mass.
  • Co is an element which suppresses the formation of carbides, prevents the decrease in grain boundary strength, and improves the strength and the fatigue strength.
  • Co is a very expensive element, when the content thereof is more than 1.0 percent by mass, the manufacturing cost is increased. Hence, the content of Co is set to 1.0 percent by mass or less.
  • the content of Co is preferably set to 0.01 percent by mass or more.
  • the content is more preferably set in the range of 0.02 to 0.5 percent by mass.
  • Nb improves the quenching properties, is bonded with C and N to provide precipitation strengthening of steel, and improves the resistance to temper softening, so that the fatigue strength is improved.
  • the content is more than 0.1 percent by mass, the effect thereof is saturated.
  • the content of Nb is set to 0.1 percent by mass or less.
  • the content of Nb is less than 0.005 percent by mass, since the effects of improving the precipitation strengthening and the resistance to temper softening are not significant, the content is preferably set to 0.005 percent by mass or more.
  • the content is more preferably set in the range of 0.01 to 0.05 percent by mass.
  • Ti is bonded with C and N to provide precipitation strengthening of steel and improves the resistance to temper softening, so that the fatigue strength is improved.
  • the content is set to 0.1 percent by mass or less.
  • the content is preferably set to 0.01 percent by mass or more.
  • V is bonded with C and N to provide precipitation strengthening of steel and improves the resistance to temper softening, so that the fatigue strength is improved.
  • the content is set to 0.5 percent by mass or less.
  • the content of V is preferably set to 0.01 percent by mass or more.
  • the content is more preferably set in the range of 0.03 to 0.3 percent by mass.
  • the machinability is more effectively improved by the following reasons.
  • Ca Since forming a sulfide, which functions as a chip breaker, in combination with MnS and thereby improving the machinability, Ca may be added whenever necessary. However, when the content is more than 0.005 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Ca is set to 0.005 percent by mass or less. When the content of Ca is less than 0.0001 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.0001 percent by mass or more.
  • Mg Since being not only a deoxidizing element but also concentrating stress so as to improve the machinability, Mg may be added whenever necessary. However, when the content is excessive, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Mg is set to 0.005 percent by mass or less. When the content of Mg is less than 0.0001 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.0001 percent by mass or more.
  • Te Since Te is bonded with Mn to form MnTe which functions as a chip breaker, the machinability is improved. However, when the content is more than 0.005 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Te is set to 0.005 percent by mass or less. When the content of Te is less than 0.003 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.003 percent by mass or more.
  • Bi has melting, lubricating, and embrittlement functions in cutting, and thereby the machinability is improved.
  • the content of Bi is set to 0.5 percent by mass or less.
  • the content of Bi is preferably set to 0.01 percent by mass or more.
  • Pb has melting, lubricating, and embrittlement functions in cutting, and thereby the machinability is improved.
  • the content of Pb is set to 0.5 percent by mass or less.
  • the content of Pb is preferably set to 0.01 percent by mass or more.
  • Zr Since Zr forms in combination with MnS a sulfide which functions as a chip breaker, the machinability is improved. However, when the content is more than 0.01 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Zr is set to 0.01 percent by mass or less. When the content of Zr is less than 0.003 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.003 percent by mass or more.
  • the microstructure of steel is composed of a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is set to 90% or more, and the thickness of the ferrite structure is set to 30 ⁇ m or less.
  • the thickness of the ferrite structure is defined as follows.
  • the steel material of the present invention has a microstructure composed of a pearlite structure and a ferrite structure in the form of a rosary disposed therearound.
  • the width of the ferrite structure in the direction perpendicular to the circumferential direction thereof is called the thickness of the ferrite structure. For this measurement, the image of an optical microscope was traced.
  • the machinability is considerably degraded.
  • the width of the ferrite structure exceeds 30 ⁇ m, since hard phases and soft phases are coarsely dispersed, the number of hard phases which function as a chip breaker in machining is decreased, and as a result, the machinability cannot be sufficiently ensured.
  • the width of the ferrite structure is decreased to 30 ⁇ m or less, superior machinability can be obtained, and in addition to that, the average prior austenite grain diameter of the hard layer after induction quenching is advantageously decreased to 12 ⁇ m or less.
  • the reason for this is that since the nucleation of austenite grains in heating of quenching occurs from the ferrite/pearlite interfaces and cementite interfaces, the number of nucleation sites is increased as the thickness of the ferrite structure is decreased, and that as a result, the size of the generated austenite grains is decreased.
  • the average prior austenite grain diameter of the hard layer formed by induction quenching on the surface of the induction quenched member must be controlled to be 12 ⁇ m or less, preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
  • the average prior austenite grain diameter of the hard layer is more than 12 ⁇ m, a sufficient grain boundary strength cannot be obtained, and as a result, the improvement in fatigue strength cannot be expected.
  • the prior austenite grain diameter of the hard layer is measured as described below.
  • the topmost layer of the member thus processed has 100% of a martensite structure on an area fraction basis. From the surface toward the inside, a region composed of 100% of a martensite structure is present to a certain depth, and from this certain depth, the area fraction of the martensite structure is rapidly decreased. In the present invention, a region from the surface of the member processed by induction quenching to a depth at which the area fraction of the martensite structure is decreased to 98% is defined as the hard layer.
  • the average prior austenite grain diameters are measured at depths of one fifth, one half, and four fifths of the thickness of the hard layer from the surface thereof, and when being 12 ⁇ m or less at all the depths described above, the average prior austenite grain diameter is regarded as 12 ⁇ m or less all along the depth of the hard layer.
  • the average prior austenite grain diameter After the cross-section of the hard layer was processed by using an etching solution which was prepared by dissolving 50 g of picric acid into 500 g of water, followed by addition of 11 g of sodium dodecylbenzene sulfonate, 1 g of ferrous chloride, and 1.5 g of oxalic acid, five visual fields of each measurement point were observed at a magnification from 400 (area of one visual field being 0.25 mm ⁇ 0.225 mm) to 1,000 (area of one visual field being 0.10 mm ⁇ 0.09 mm) using an optical microscope, and the average grain diameter was measured by an image analysis device.
  • the thickness of the hard layer is preferably set to 2 mm or more.
  • the thickness described above is more preferably 2.5 mm or more and even more preferably 3 mm or more.
  • a steel material for induction quenching according to the present invention is obtained in which a ferrite structure and a pearlite structure are present, and the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, and the thickness of the ferrite structure is 30 ⁇ m or less.
  • the thickness of the ferrite structure surrounding the pearlite structure cannot be decreased to 30 ⁇ m or less.
  • the cooling rate after the hot working is set to 0.6° C./s or more, a martensite structure and/or a bainite structure may be generated, and as a result, it becomes difficult to control the total volume fraction of the ferrite structure and the pearlite structure to be 90% or more.
  • the prior austenite grain diameter can be decreased to 12 ⁇ m or less all along the depth of the entire hard layer, so that a induction quenched member having a high fatigue strength can be obtained.
  • the heating temperature is less than 800° C., since the generation of the austenite grains is not sufficient, the formation of the hard layer becomes insufficient, and as a result, a high fatigue strength cannot be obtained.
  • the heating temperature is more than 1,000° C., since the growth of the austenite grains is promoted so as to form coarser and larger grains, the hard layer are formed of coarser and larger grains, resulting in decrease in fatigue strength.
  • the heating temperature is more preferably in the range of 800° C. to 950° C.
  • FIG. 2 is a graph showing the relationship between the average prior austenite grain diameter of the hard layer and the heating temperature in induction quenching for steel containing Mo (Mo: 0.05 to 0.6 percent by mass) and steel containing no Mo.
  • the prior austenite grain diameter of the hard layer is decreased.
  • a hard layer formed of significantly fine grains can be obtained at a heating temperature of 1,000° C. or less and preferably 950° C. or less.
  • the heating time in induction quenching must be set to 5 seconds or less and is preferably set to 3 seconds or less.
  • the heating rate in induction quenching is increased, the grain growth of austenite is likely to be suppressed, and hence the heating rate is preferably set to 200° C./sec or more. Furthermore, the heating rate is more preferably set to 500° C./sec or more.
  • Steel Nos. 1 to 31 having the compositions shown in Table 1 were each molten in a converter and then formed into a steel sheet having a cross-sectional size of 300 ⁇ 400 mm by continuous casting. After the steel sheets were rolled into billets having a size of 150 ⁇ 150 mm through a breakdown step, rolling was performed under the hot working conditions shown in Table 2, so that steel bars having a diameter of 24 to 60 mm were formed.
  • Test pieces having a parallel portion diameter of 8 mm for rotary bending fatigue test were sampled from the above steel bars and were then processed by induction quenching under the conditions shown in Tables 2-1 and 2-2 using a induction quenching device at a frequency of 15 kHz, followed by tempering at 170° C. for 30 minutes, so that test pieces of steel materials No. 1 to 43 were obtained. Subsequently, the rotary bending fatigue test was performed for the test pieces thus obtained at an rpm of 3,000 using an Ono's rotary bending fatigue testing machine by changing stress conditions so as to measure a stress at which a life of 1 ⁇ 10 8 times was obtained, and this stress was defined as the fatigue strength.
  • Test pieces for machinability evaluation were also sampled from the above steel bars and were then repeatedly drilled at an rpm of 1,500 using an SKH-made drill having a diameter of 4.4 mm to form a hole having a length of 12 mm, and the total hole length (mm) was measured at which the drilling could not be further continued, so that the machinability was evaluated. When the total hole length is larger, the machinability is regarded as superior.
  • microstructure of the steel material before induction quenching was observed using an electron microscope and an optical microscope.
  • the thickness of the ferrite structure, the thickness of the hard layer, and the average prior austenite grain diameter were measured by the methods described above.
  • austenite grains having a grain diameter three times or more the average austenite grain diameter of the hard layer was present at an area fraction of 30% or more, the hard layer was defined as a mixed grain layer.
  • All the steel materials according to the present invention have an average prior austenite grain diameter of the hard layer of 12 ⁇ m or less after induction quenching and exhibit a superior bending fatigue strength, the above steel materials having the compositions within the range of the present invention and having microstructures each composed of a ferrite structure and a pearlite structure before induction quenching, the total volume fraction of the ferrite structure and the pearlite structure being 90% or more, the thickness of the ferrite structure being 30 ⁇ m or less.
  • the steel materials described above also have superior machinability.
  • steel materials Nos. 4 and 19 have a small total reduction rate in a temperature region of more than 850° C. to 950° C., the thickness of the ferrite structure is increased, and hence the machinability is degraded.

Abstract

The present invention provides a steel material for induction quenching, containing 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities. The steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the thickness of the ferrite structure is 30 μm or less, and the average prior austenite grain diameter of a hard layer obtained by induction quenching is 12 μm or less. Since having superior machinability and superior fatigue strength after induction quenching, this steel material is suitable, for an automobile drive shaft, constant velocity joint, and the like.

Description

    TECHNICAL FIELD
  • The present invention relates to a steel material for induction quenching, which is suitable for an automobile drive shaft, constant velocity joint, and the like having a hard layer on a surface thereof formed by induction quenching, a induction quenched member using the same, and manufacturing methods thereof.
    • BACKGROUND ART
  • Heretofore, as for machine structural members, such as an automobile drive shaft, constant velocity joint, crank shaft, input shaft, output shaft, gear, and hub, after a hot-rolled steel bar is subjected to hot forging, followed by cutting, cold forging, and the like to have a predetermined shape, in general, a fatigue strength is imparted to the steel thus treated by induction quenching and tempering, the fatigue strength, such as torsional fatigue strength, bending fatigue strength, rolling contact fatigue strength, and sliding and rolling contact fatigue strength, being important properties for machine structural members.
  • In recent years, concomitant with growing demand for reduction in weight of automobile members due to environmental issues, further improvement in fatigue strength of the machine structural members as described above has been increasingly required.
  • In order to improve the fatigue strength, for example, the increase in quenching depth by induction quenching may be considered. However, the fatigue strength becomes saturated at a certain quenching depth and cannot be further improved.
  • In addition, for improvement in fatigue strength, the improvement in grain boundary strength is also effective, and for example, in Japanese Unexamined Patent Application Publication No. 2000-154819, a technique has been proposed in which austenite grains are particularized by precipitating a large amount of fine TiC in heating of induction quenching. However, according to this technique, although the grain boundary strength can be improved to a certain extent, the recent requirement for the fatigue strength cannot be fully satisfied.
  • In Japanese Unexamined Patent Application Publication No. 8-53714, a machine structural member having an improved fatigue strength has been proposed in which the fatigue strength is improved by controlling the following properties within respective predetermined ranges in accordance with the amount of C while a ratio CD/R is limited in the range of 0.3 to 0.7, CD being the thickness (depth of quenching) of a hard layer formed by induction quenching of a machine structural member having a circular transverse section, R being the radius thereof. The properties mentioned above are the above CD/R, grain diameter of prior austenite in a region from the surface to 1 mm depth after induction quenching, average Vickers hardness Hf up to a ratio CD/R of 0.1 as obtained by induction quenching, and value A obtained from average Vickers hardness Hc of an axial central portion after induction quenching. However, by the member described above, as is the case described above, the recent requirement for the fatigue strength cannot be fully satisfied.
  • In addition, as described above, in general, the machine structural members such as an automobile drive shaft and constant velocity joint are machined by cutting into a predetermined shape before induction quenching in many cases. Hence, a steel material used for the members as described above is required to have superior machinability. However, in Japanese Unexamined Patent Application Publication Nos. 2000-154819 and 8-53714, the machinability has not been taken into consideration at all. In practice, when the steel disclosed in the publications described above is machined, the life of cutting tool is shortened, and hence the machinability has been a problem.
    • DISCLOSURE OF INVENTION
  • An object of the present invention is to provide a steel material for induction quenching, which has superior machinability and which can obtain a high fatigue strength by induction quenching as compared to that obtained in the past, a induction quenched member using the same, and manufacturing methods thereof.
  • The above object can be achieved by the following steel material for induction quenching and the following induction quenched member. The steel material for induction quenching comprises 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, in which the steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the thickness of the ferrite structure is 30 μm or less, and the average prior austenite grain diameter of a hard layer obtained after induction quenching is 12 μm or less. The induction quenched member is formed using the above steel material for induction quenching, and the average prior austenite grain diameter of the hard layer obtained after induction quenching is 12 μm or less.
  • This steel material for induction quenching can be manufactured by a method for manufacturing a steel material for induction quenching, the method comprising a step of hot working a steel material having the above-described composition at a total reduction rate of 80% or more in a temperature region of more than 850° C. to 950° C., and a step of cooling the steel thus hot-worked to 600° C. or less at a cooling rate of less than of 0.6° C./sec.
  • In addition, this induction quenched member can be manufactured by a method for manufacturing an induction quenched member, the method comprising a step of performing induction quenching of a steel material for induction quenching, which is already formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a schematic view illustrating the thickness of a ferrite structure.
  • FIG. 2 is a graph showing the relationship between the heating temperature in induction quenching and the average prior austenite grain diameter of a hard layer.
    • BEST MODE FOR CARRYING OUT THE INVENTION
  • Through intensive research carried out by the inventors of the present invention on a steel material for induction quenching which has superior machinability and which can obtain high fatigue strength by induction quenching as compared to that obtained in the past, the following knowledge was obtained.
  • (1) When the chemical composition of a steel material is optimized, the total volume fraction of a ferrite structure and a pearlite structure thereof is controlled to be 90% or more, and the thickness of the ferrite structure is controlled to be 30 μm or less, the machinability can be improved.
  • (2) When induction quenching is performed for a steel material having the chemical composition and the structure described in the above (1), the average prior austenite grain diameter of a hard layer formed at a surface portion can be decreased to 12 μm or less, and as a result, a high fatigue strength can be obtained.
  • (3) When induction quenching is performed for a steel material having the chemical composition and the structure described in the above (1) in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less, the average prior austenite grain diameter over the entire hard layer can be decreased to 12 μm or less, and as a result, a high fatigue strength can be stably obtained.
  • The present invention was made based on the above knowledge, and the details thereof will be described below.
  • 1. Steel Material for Induction Quenching
  • 1-1. Components
  • C: C has the most significant influence on quenching properties, can make harder the hard layer after quenching, and can make the thickness thereof larger, thereby improving the fatigue strength. However, when the content is less than 0.3 percent by mass, the thickness of the hard layer must be considerably increased in order to ensure a required fatigue strength, and as a result, the generation of quench cracking markedly occurs. On the other hand, when the content is more than 0.7 percent by mass, the fatigue strength is decreased due to the decrease in grain boundary strength, and in addition, the machinability, cold forging properties, and quench cracking resistance are also degraded. Hence, the content of C is set in the range of 0.3 to 0.7 percent by mass and preferably 0.4 to 0.6 percent by mass.
  • Si: Si increases the number of nucleation sites of austenite in heating of quenching and also particularizes the hard layer by suppressing the growth of the austenite grains. In addition, Si suppresses the decrease in grain boundary strength by suppressing the formation of carbides. Hence, Si is an element effective in improving the fatigue strength. However, when the content is more than 1.1 percent by mass, ferrite is solution-hardened, and as a result, the machinability and cold forging properties are degraded. Hence, the content of Si is set to 1.1 percent by mass or less. In addition, in order to improve the fatigue strength, the content of Si is preferably set to 0.3 percent by mass or more. However, since the increase in Si is disadvantageous to the machinability, in order to improve the machinability, the content of Si is preferably set to less than 0.3 percent by mass.
  • Mn: Mn is an indispensable element for improving the quenching properties and for ensuring the thickness of the hard layer. However, when the content is less than 0.2 percent by mass, the effect is not significant. On the other hand, when the content is more than 2.0 percent by mass, the amount of retained austenite is increased after quenching, the surface hardness is decreased, and as a result, the fatigue strength is decreased. Hence, the content of Mn is set to 0.2 percent by mass or more, preferably 0.3 percent by mass or more, and more preferably in the range of 0.5 to 2.0 percent by mass. In addition, when the content of Mn is high, the hardness of a mother material is increased, and the machinability tends to be disadvantageously degraded; hence, the content is preferably set to 1.2 percent by mass or less and is more preferably set to 1.0 percent by mass or less.
  • Mo: Mo decreases the austenite grain diameter in heating of quenching and particularizes the quenched hard layer, so that the fatigue strength is improved. In particular, when the heating temperature in quenching is set in the range of 800° C. to 1,000° C. and more preferably set in the range of 800° C. to 950° C., the effect described above becomes more significant. Furthermore, since being effective in improving the quenching properties, Mo is used for the adjustment thereof. In addition, Mo prevents the decrease in grain boundary strength by suppressing the formation of carbides. As described above, Mo is a very important element of the present invention; however, when the content thereof is less than 0.05 percent by mass, the prior austenite grain diameter of the hard layer cannot be easily decreased to 12 μm or less all along the depth of the entire hard layer. On the other hand, when the content is more than 0.6 percent by mass, the machinability is degraded. Hence, the content of Mo is set to 0.05 to 0.6 percent by mass and preferably 0.2 to 0.4 percent by mass.
  • S: S forms MnS in steel and improves the machinability. However, when the content is more than 0.06 percent by mass, S segregates at the grain boundaries, and as a result, the grain boundary strength is decreased. Hence, the content of S is set to 0.06 percent by mass or less and preferably set in the range of 0.01 to 0.06 percent by mass.
  • P: P segregates at the austenite grain boundaries, decreases the grain boundary strength, and decreases the fatigue strength, and in addition, quench cracking is promoted. Hence, although the content of P is set to 0.02 percent by mass or less, a smaller P content is more preferable.
  • Al: Al is an element effective in deoxidizing steel. In addition, Al suppresses the growth of the austenite grains in heating of quenching, and as a result, the hard layer is particularized. However, when the content is more than 0.25 percent by mass, the effect is saturated, and the manufacturing cost is adversely increased. Hence, the content of Al is set to 0.25 percent by mass or less and is preferably set in the range of 0.01 to 0.05 percent by mass.
  • Cr: Cr is an element effective for the quenching properties and increases the thickness of the hard layer, thereby improving the fatigue strength. However, when the content is excessive, carbides are stabilized, the growth of residual carbides is promoted, and the grain boundary strength is decreased; hence, as a result, the fatigue strength is decreased. Accordingly, the content of Cr is set to 0.3 percent by mass or less. In addition, in view of the improvement in quenching properties, the content is preferably set to 0.1 percent by mass or more.
  • The balance, that is, elements other than the elements described above, is Fe and unavoidable impurities. The unavoidable impurities are 0, N, B, and the like; however, even when 0.008 percent by mass or less of O, 0.02 percent by mass or less of N, and 0.0003 percent by mass or less of B are contained, the effects of the present invention will not be degraded. In particular, when the content of B exceeds 0.0003 percent by mass, (Fe, Mo, Mn)23(C, B)6 tends to be stabilized and precipitated in steel before induction quenching, and thereby small and large prior austenite grains are mixed and are present in the hard layer after quenching, so that a high fatigue strength cannot be achieved.
  • Besides the elements described above, when at least one element selected from the group consisting of 1.0% or less of Cu, 3.5% or less of Ni, 1.0% or less of Co, 0.1% or less of Nb, 0.1% or less of Ti, and 0.5% or less of V on a mass basis is contained, it is effective since the fatigue strength is improved by the following reasons.
  • Cu: Cu is an element effective for the quenching properties. In addition, Cu is dissolved in ferrite and improves the fatigue strength by solid-solution strengthening. Furthermore, Cu suppresses the formation of carbides and prevents the decrease in grain boundary strength, so that the fatigue strength is improved. However, when the content is more than 1.0 percent by mass, cracking is liable to occur in hot working. Hence, the content of Cu is set to 1.0 percent by mass or less and is preferably set in the range of 0.03 to 0.2 percent by mass.
  • Ni: Since being an element improving the quenching properties, Ni is used for adjustment thereof. In addition, Ni suppresses the formation of carbides, prevents the decrease in grain boundary strength, and improves the fatigue strength. However, since Ni is a very expensive element, when the content thereof is more than 3.5 percent by mass, the manufacturing cost is increased. Hence, the content of Ni is set to 3.5 percent by mass or less. In addition, when the content of Ni is less than 0.05 percent by mass, since the effect of improving the quenching properties and the effect of suppressing the decrease in grain boundary strength are not significant, the content is preferably set to 0.05 percent by mass or more. Furthermore, the content is more preferably set in the range of 0.1 to 1.0 percent by mass.
  • Co: Co is an element which suppresses the formation of carbides, prevents the decrease in grain boundary strength, and improves the strength and the fatigue strength. However, since Co is a very expensive element, when the content thereof is more than 1.0 percent by mass, the manufacturing cost is increased. Hence, the content of Co is set to 1.0 percent by mass or less. In addition, when the content of Co is less than 0.01 percent by mass, since the effect of suppressing the decrease in grain boundary strength is not significant, the content is preferably set to 0.01 percent by mass or more. Furthermore, the content is more preferably set in the range of 0.02 to 0.5 percent by mass.
  • Nb: Nb improves the quenching properties, is bonded with C and N to provide precipitation strengthening of steel, and improves the resistance to temper softening, so that the fatigue strength is improved. However, when the content is more than 0.1 percent by mass, the effect thereof is saturated. Hence, the content of Nb is set to 0.1 percent by mass or less. In addition, when the content of Nb is less than 0.005 percent by mass, since the effects of improving the precipitation strengthening and the resistance to temper softening are not significant, the content is preferably set to 0.005 percent by mass or more. Furthermore, the content is more preferably set in the range of 0.01 to 0.05 percent by mass.
  • Ti: Ti is bonded with C and N to provide precipitation strengthening of steel and improves the resistance to temper softening, so that the fatigue strength is improved. However, when the content is more than 0.1 percent by mass, a large amount of TiN is formed which functions as a point of initiating fatigue failure, and as a result, the fatigue strength is considerably decreased. Hence, the content of Ti is set to 0.1 percent by mass or less. In addition, when the content of Ti is less than 0.01 percent by mass, since the effect of improving the fatigue strength is not significant, the content is preferably set to 0.01 percent by mass or more.
  • V: V is bonded with C and N to provide precipitation strengthening of steel and improves the resistance to temper softening, so that the fatigue strength is improved. However, when the content is more than 0.5 percent by mass, the effect is saturated. Hence, the content of V is set to 0.5 percent by mass or less. In addition, when the content of V is less than 0.01 percent by mass, since the effect of improving the fatigue strength is not significant, the content is preferably set to 0.01 percent by mass or more. Furthermore, the content is more preferably set in the range of 0.03 to 0.3 percent by mass.
  • In addition to the basic components described above, or in addition to the above basic components and the component more effective in improving the fatigue strength, when at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis is contained, the machinability is more effectively improved by the following reasons.
  • Ca: Since forming a sulfide, which functions as a chip breaker, in combination with MnS and thereby improving the machinability, Ca may be added whenever necessary. However, when the content is more than 0.005 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Ca is set to 0.005 percent by mass or less. When the content of Ca is less than 0.0001 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.0001 percent by mass or more.
  • Mg: Since being not only a deoxidizing element but also concentrating stress so as to improve the machinability, Mg may be added whenever necessary. However, when the content is excessive, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Mg is set to 0.005 percent by mass or less. When the content of Mg is less than 0.0001 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.0001 percent by mass or more.
  • Te: Since Te is bonded with Mn to form MnTe which functions as a chip breaker, the machinability is improved. However, when the content is more than 0.005 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Te is set to 0.005 percent by mass or less. When the content of Te is less than 0.003 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.003 percent by mass or more.
  • Bi: Bi has melting, lubricating, and embrittlement functions in cutting, and thereby the machinability is improved. However, when the content is more than 0.5 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Bi is set to 0.5 percent by mass or less. When the content of Bi is less than 0.01 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.01 percent by mass or more.
  • Pb: Pb has melting, lubricating, and embrittlement functions in cutting, and thereby the machinability is improved. However, when the content is more than 0.5 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Pb is set to 0.5 percent by mass or less. When the content of Pb is less than 0.01 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.01 percent by mass or more.
  • Zr: Since Zr forms in combination with MnS a sulfide which functions as a chip breaker, the machinability is improved. However, when the content is more than 0.01 percent by mass, the effect is not only saturated but the manufacturing cost is also increased. Hence, the content of Zr is set to 0.01 percent by mass or less. When the content of Zr is less than 0.003 percent by mass, since the effect of improving the machinability is not significant, the content is preferably set to 0.003 percent by mass or more.
  • 1-2. Microstructure
  • For improvement in machinability and fatigue strength after induction quenching, in addition to the necessary components described above, it is also required that the microstructure of steel is composed of a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is set to 90% or more, and the thickness of the ferrite structure is set to 30 μm or less.
  • In the case described above, the thickness of the ferrite structure is defined as follows.
  • As shown in FIG. 1, the steel material of the present invention has a microstructure composed of a pearlite structure and a ferrite structure in the form of a rosary disposed therearound. The width of the ferrite structure in the direction perpendicular to the circumferential direction thereof is called the thickness of the ferrite structure. For this measurement, the image of an optical microscope was traced.
  • When the total volume fraction of the ferrite structure and the pearlite structure is less than 90%, and the volume fraction of the bainite structure and that of the martensite structure are increased, the machinability is considerably degraded. In addition, when the width of the ferrite structure exceeds 30 μm, since hard phases and soft phases are coarsely dispersed, the number of hard phases which function as a chip breaker in machining is decreased, and as a result, the machinability cannot be sufficiently ensured.
  • When the width of the ferrite structure is decreased to 30 μm or less, superior machinability can be obtained, and in addition to that, the average prior austenite grain diameter of the hard layer after induction quenching is advantageously decreased to 12 μm or less. The reason for this is that since the nucleation of austenite grains in heating of quenching occurs from the ferrite/pearlite interfaces and cementite interfaces, the number of nucleation sites is increased as the thickness of the ferrite structure is decreased, and that as a result, the size of the generated austenite grains is decreased.
  • 2. Induction Quenched Member
  • In order to manufacture a induction quenched member having a high fatigue strength by induction quenching using a steel material for induction quenching which has the composition and the microstructure described above, the average prior austenite grain diameter of the hard layer formed by induction quenching on the surface of the induction quenched member must be controlled to be 12 μm or less, preferably 10 μm or less, and more preferably 5 μm or less. When the average prior austenite grain diameter of the hard layer is more than 12 μm, a sufficient grain boundary strength cannot be obtained, and as a result, the improvement in fatigue strength cannot be expected.
  • In this embodiment, the prior austenite grain diameter of the hard layer is measured as described below.
  • After induction quenching, the topmost layer of the member thus processed has 100% of a martensite structure on an area fraction basis. From the surface toward the inside, a region composed of 100% of a martensite structure is present to a certain depth, and from this certain depth, the area fraction of the martensite structure is rapidly decreased. In the present invention, a region from the surface of the member processed by induction quenching to a depth at which the area fraction of the martensite structure is decreased to 98% is defined as the hard layer.
  • In addition, as for this hard layer, the average prior austenite grain diameters are measured at depths of one fifth, one half, and four fifths of the thickness of the hard layer from the surface thereof, and when being 12 μm or less at all the depths described above, the average prior austenite grain diameter is regarded as 12 μm or less all along the depth of the hard layer.
  • For the measurement of the average prior austenite grain diameter, after the cross-section of the hard layer was processed by using an etching solution which was prepared by dissolving 50 g of picric acid into 500 g of water, followed by addition of 11 g of sodium dodecylbenzene sulfonate, 1 g of ferrous chloride, and 1.5 g of oxalic acid, five visual fields of each measurement point were observed at a magnification from 400 (area of one visual field being 0.25 mm×0.225 mm) to 1,000 (area of one visual field being 0.10 mm×0.09 mm) using an optical microscope, and the average grain diameter was measured by an image analysis device.
  • In addition, in the case of the rolling contact fatigue which is present only in a microstructure located very close to the topmost surface, even when the thickness of the hard layer is approximately 1 mm, the effect may be obtained to some extent. However, in the case of the bending fatigue and the torsional fatigue, since it is more preferable as the thickness of the hard layer is increased, the thickness thereof is preferably set to 2 mm or more. In addition, the thickness described above is more preferably 2.5 mm or more and even more preferably 3 mm or more.
  • 3. Method for Manufacturing Steel Material for Induction Quenching
  • When hot working such as rolling or forging at a total reduction rate of 80% or more is performed for steel having the composition in the range defined by the present invention in a temperature region of more than 850° C. to 950° C., and the steel processed by the hot working is then cooled to 600° C. or less at a cooling rate of less than 0.6° C./s, a steel material for induction quenching according to the present invention is obtained in which a ferrite structure and a pearlite structure are present, and the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, and the thickness of the ferrite structure is 30 μm or less.
  • When the total reduction rate of the hot working is less than 80%, since recrystallization of austenite will not sufficiently proceed, and the austenite grains are not particularized, ferrite generated therefrom grows, and as a result, the thickness of the ferrite structure surrounding the pearlite structure cannot be decreased to 30 μm or less.
  • In addition, when the cooling rate after the hot working is set to 0.6° C./s or more, a martensite structure and/or a bainite structure may be generated, and as a result, it becomes difficult to control the total volume fraction of the ferrite structure and the pearlite structure to be 90% or more.
  • 4. Method for Manufacturing Induction Quenched Member
  • After formed into a predetermined shape by cutting or the like, when the above steel material for induction quenching of the present invention is processed by induction quenching in a temperature region of 800° C. to 1,000° C. for 5 seconds or less, the prior austenite grain diameter can be decreased to 12 μm or less all along the depth of the entire hard layer, so that a induction quenched member having a high fatigue strength can be obtained.
  • In this case, when the heating temperature is less than 800° C., since the generation of the austenite grains is not sufficient, the formation of the hard layer becomes insufficient, and as a result, a high fatigue strength cannot be obtained. In addition, when the heating temperature is more than 1,000° C., since the growth of the austenite grains is promoted so as to form coarser and larger grains, the hard layer are formed of coarser and larger grains, resulting in decrease in fatigue strength. The heating temperature is more preferably in the range of 800° C. to 950° C.
  • The influence of the heating temperature in induction quenching is more clearly observed when steel containing Mo is used as is the case of the present invention.
  • FIG. 2 is a graph showing the relationship between the average prior austenite grain diameter of the hard layer and the heating temperature in induction quenching for steel containing Mo (Mo: 0.05 to 0.6 percent by mass) and steel containing no Mo.
  • In both cases of the steel containing Mo and the steel containing no Mo, when the heating temperature in induction quenching is decreased, the prior austenite grain diameter of the hard layer is decreased. In particular, in the steel containing Mo, a hard layer formed of significantly fine grains can be obtained at a heating temperature of 1,000° C. or less and preferably 950° C. or less.
  • In order to suppress the grain growth of austenite and to obtain a very fine prior austenite grain diameter of 12 μm or less after quenching, the heating time in induction quenching must be set to 5 seconds or less and is preferably set to 3 seconds or less.
  • In addition, when the heating rate in induction quenching is increased, the grain growth of austenite is likely to be suppressed, and hence the heating rate is preferably set to 200° C./sec or more. Furthermore, the heating rate is more preferably set to 500° C./sec or more.
    • EXAMPLE 1
  • Steel Nos. 1 to 31 having the compositions shown in Table 1 were each molten in a converter and then formed into a steel sheet having a cross-sectional size of 300×400 mm by continuous casting. After the steel sheets were rolled into billets having a size of 150×150 mm through a breakdown step, rolling was performed under the hot working conditions shown in Table 2, so that steel bars having a diameter of 24 to 60 mm were formed.
  • Test pieces having a parallel portion diameter of 8 mm for rotary bending fatigue test were sampled from the above steel bars and were then processed by induction quenching under the conditions shown in Tables 2-1 and 2-2 using a induction quenching device at a frequency of 15 kHz, followed by tempering at 170° C. for 30 minutes, so that test pieces of steel materials No. 1 to 43 were obtained. Subsequently, the rotary bending fatigue test was performed for the test pieces thus obtained at an rpm of 3,000 using an Ono's rotary bending fatigue testing machine by changing stress conditions so as to measure a stress at which a life of 1×108 times was obtained, and this stress was defined as the fatigue strength.
  • Test pieces for machinability evaluation were also sampled from the above steel bars and were then repeatedly drilled at an rpm of 1,500 using an SKH-made drill having a diameter of 4.4 mm to form a hole having a length of 12 mm, and the total hole length (mm) was measured at which the drilling could not be further continued, so that the machinability was evaluated. When the total hole length is larger, the machinability is regarded as superior.
  • In addition, the microstructure of the steel material before induction quenching, the presence of carbide (Fe, Mo, Mn)23(C, B)6, and the microstructure after induction quenching were observed using an electron microscope and an optical microscope.
  • The thickness of the ferrite structure, the thickness of the hard layer, and the average prior austenite grain diameter were measured by the methods described above. In addition, when austenite grains having a grain diameter three times or more the average austenite grain diameter of the hard layer was present at an area fraction of 30% or more, the hard layer was defined as a mixed grain layer.
  • The results are shown in FIGS. 2-1 and 2-2.
  • All the steel materials according to the present invention have an average prior austenite grain diameter of the hard layer of 12 μm or less after induction quenching and exhibit a superior bending fatigue strength, the above steel materials having the compositions within the range of the present invention and having microstructures each composed of a ferrite structure and a pearlite structure before induction quenching, the total volume fraction of the ferrite structure and the pearlite structure being 90% or more, the thickness of the ferrite structure being 30 μm or less. In addition, the steel materials described above also have superior machinability.
  • In particular, as it is apparent when steel Nos. 1 and 16, steel Nos. 5 and 20, steel Nos. 6 and 21, steel Nos. 7 and 22, steel Nos. 9 and 24, steel Nos. 10 and 25, and steel Nos. 11 and 26 are compared therebetween, when the content of Si is increased, the average prior austenite grain diameter of the hard layer can be further decreased, and as a result, a higher bending fatigue strength can be obtained. However, when the content of Si is increased, the total hole length is decreased, and hence the machinability is disadvantageously degraded.
  • For steel materials Nos. 38 to 40, the influence of the heating rate in induction quenching was measured. It is understood that when the heating rate is higher, the bending fatigue strength is increased.
  • On the other hand, in steel materials No. 2 and 17, which are comparative examples, since the heating temperature in induction quenching is high, the average prior austenite grain diameter of the hard layer becomes coarser and larger, and hence the bending fatigue strength is low.
  • In addition, in steel materials Nos. 3 and 18, since the holding time in heating of induction quenching is long, the average prior austenite grain diameter becomes coarser and larger, and hence the bending fatigue strength is low.
  • Since steel materials Nos. 4 and 19 have a small total reduction rate in a temperature region of more than 850° C. to 950° C., the thickness of the ferrite structure is increased, and hence the machinability is degraded.
  • In steel materials Nos. 8, 12, and 27, since the content of Mo is small, the average prior austenite grain diameter becomes coarser and larger, and hence the bending fatigue strength is low.
  • In steel materials Nos. 13 and 28, since the content of Mo is excessively large, the machinability thereof is inferior.
  • In steel materials Nos. 14 and 29, since the content of C is small, the bending fatigue strength is low, and on the other hand, in steel materials Nos. 15 and 30, since the content of C is excessively large, the machinability thereof is inferior.
  • In steel materials Nos. 34 and 35 containing B, which are comparative examples, the total volume fraction of the ferrite structure and the pearlite structure before induction quenching is decreased due to the addition of B, and hence the machinability is inferior. In addition, although the prior austenite grain diameter of the hard layer of the above steel materials is equivalent to that of steel materials Nos. 36 and 37 containing no B, the hard layer is a mixed grain layer, and the fatigue strength is low as compared to that of the above steel materials Nos. 36 and 37. The reason for this is considered that in the steel containing B, since (Fe, Mo, Mn)23(C, B)6 is stably precipitated before induction quenching, reverse transformation in heating of induction quenching occurs non-uniformly, the hard layer is formed of a mixed grain layer, and as a result, the fatigue strength is decreased.
  • In steel materials Nos. 41 and 42, since the heating temperature in induction quenching is too high, the average prior austenite grain diameter becomes coarser and larger, and hence the bending fatigue strength is low.
    TABLE 1
    Steel Composition (percent by mass)
    No. C Si Mn P S Al Cr Mo Cu Ni Co Nb Ti V B Others Remarks
    1 0.52 0.52 0.75 0.015 0.020 0.06 0.14 0.42 — — — — — — — Inventive Steel
    2 0.38 0.54 0.75 0.014 0.021 0.07 0.13 0.33 — 0.15 — — — — — Inventive Steel
    3 0.48 0.55 0.75 0.014 0.021 0.06 0.13 0.31 — — — 0.025 — 0.15 — Inventive Steel
    4 0.48 0.53 0.55 0.013 0.019 0.06 0.12 0.42 0.20 — — 0.031 — — — Bi: 0.12, Inventive Steel
    Pb: 015,
    Zr: 0.002
    5 0.51 0.22 0.75 0.014 0.020 0.07 0.15 0.04 — — — — — — — Comparative Steel
    6 0.48 0.61 0.77 0.013 0.020 0.06 0.14 0.27 — — 0.20 — 0.021 — — Inventive Steel
    7 0.35 0.75 0.78 0.015 0.019 0.06 0.16 0.35 — — — — — — — Ca: 0.002, Inventive Steel
    Mg:
    0.0020
    8 0.55 0.65 0.80 0.012 0.020 0.07 0.14 0.33 0.25 — — — — — — Te: 0.0018 Inventive Steel
    9 0.47 0.54 0.78 0.014 0.021 0.07 0.15 — — 0.20 — — — — — Comparative Steel
    10 0.42 0.53 0.77 0.013 0.020 0.07 0.15 0.80 — 0.02 — — — — — Comparative Steel
    11 0.20 0.51 0.80 0.014 0.018 0.06 0.15 0.36 — — — — — — — Comparative Steel
    12 0.95 0.55 0.75 0.015 0.019 0.07 0.16 0.34 — — — — — — — Comparative Steel
    13 0.52 0.25 0.75 0.010 0.020 0.06 0.14 0.42 — — — — — — — Inventive Steel
    14 0.38 0.18 0.75 0.010 0.021 0.07 0.13 0.33 — 0.15 — — — — — Inventive Steel
    15 0.48 0.15 0.75 0.010 0.021 0.06 0.13 0.31 — — — 0.025 — 0.15 — Inventive Steel
    16 0.48 0.22 0.55 0.010 0.019 0.06 0.12 0.42 0.20 — — 0.031 — — — Bi: 0.12, Inventive Steel
    Pb: 0.15,
    Zr: 0.002
    17 0.51 0.05 0.75 0.010 0.020 0.07 0.15 0.25 — — — — — — — Inventive Steel
    18 0.48 0.22 0.77 0.010 0.020 0.06 0.22 0.27 — — 0.20 — 0.021 — — Inventive Steel
    19 0.35 0.24 0.78 0.010 0.019 0.06 0.16 0.35 — — — — — — — Ca: 0.002, Inventive Steel
    Mg:
    0.0020
    20 0.55 0.15 0.80 0.010 0.020 0.07 0.14 0.33 0.25 — — — — — — Te: 0.0018 Inventive Steel
    21 0.47 0.20 0.78 0.010 0.021 0.07 0.15 — — 0.20 — — — — — Comparative Steel
    22 0.42 0.31 0.77 0.010 0.020 0.07 0.15 0.80 — — — 0.015 — — — Comparative Steel
    23 0.20 0.15 0.80 0.010 0.018 0.06 0.15 0.36 — — — — — — — Comparative Steel
    24 0.95 0.17 0.75 0.010 0.019 0.07 0.16 0.34 — — — — — — — Comparative Steel
    25 0.51 0.25 0.78 0.010 0.019 0.02 0.13 0.41 — — — — — — — Inventive Steel
    26 0.53 0.34 0.77 0.010 0.018 0.06 0.14 0.43 — — — — — — — Inventive Steel
    27 0.53 0.24 0.75 0.010 0.018 0.06 0.05 0.43 — — — — — — — Inventive Steel
    28 0.42 0.51 0.77 0.010 0.023 0.02 0.04 0.45 — — — — 0.021 — 0.0022 Comparative Steel
    29 0.44 0.28 0.87 0.013 0.014 0.03 0.15 0.29 — — — — 0.011 — 0.0018 Comparative Steel
    30 0.42 0.52 0.76 0.011 0.022 0.02 0.05 0.43 — — — — — — — Inventive Steel
    31 0.44 0.29 0.86 0.013 0.015 0.03 0.14 0.30 — — — — — — — Inventive Steel
  • TABLE 2-1
    Total Volume Heating
    Reduction Cooling Volume Fraction Rate in
    Rate from Rate Fraction of Thickness Heating of Heating Thickness
    Steel more than after Hot of Ferrite Pearlite of Ferrite Induction Conditions of of Hard
    Material Steel
    850° C. to Working Structure Structure Structure Quenching Induction Layer
    No. No. 950° C. (%) (° C./s) (vol %) (vol %) (μm) (° C./s) Quenching (mm)
     1 1 85 0.4 64 36 15 600 890° C. × 2s 3.5
     2 1 85 0.3 64 36 15 650 1110° C. × 2s  4.2
     3 1 85 0.5 64 36 15 600  890° C. × 10s 4.8
     4 1 50 0.4 64 36 43 550 890° C. × 2s 4.2
     5 2 85 0.4 46 54 18 550 870° C. × 2s 4.5
     6 3 85 0.4 59 41 17 550 880° C. × 2s 3.7
     7 4 85 0.5 59 41 18 600 925° C. × 2s 4.1
     8 5 85 0.3 63 37 28 550 890° C. × 2s 3.2
     9 6 85 0.4 64 36 21 550 890° C. × 2s 4.0
    10 7 90 0.4 42 58 26 550 910° C. × 2s 4.5
    11 8 85 0.4 68 32 18 550 900° C. × 2s 4.1
    12 9 85 0.4 58 42 32 550 870° C. × 1s 3.8
    13 10 85 0.5 0 0 — 550 900° C. × 2s 4.5
    14 11 85 0.3 77 23 25 550 880° C. × 2s 1.0
    15 12 85 0.4 0 2.5 — 550 880° C. × 2s 4.0
    16 13 85 0.4 64 36 18 550 890° C. × 2s 3.5
    17 13 85 0.4 64 36 18 550 1110° C. × 2s  4.2
    18 13 85 0.4 64 36 18 550  890° C. × 10s 4.8
    19 13 50 0.4 64 36 36 550 890° C. × 2s 4.8
    20 14 85 0.4 46 54 21 550 870° C. × 1s 4.5
    21 15 85 0.3 59 41 16 550 880° C. × 2s 3.7
    22 16 85 0.5 59 41 20 550 925° C. × 2s 4.1
    Average
    Prior
    Austenite Degree of
    Grain Presence of Mixed Bending
    Diameter (Fe, Mo, Mn)23 Grain Fatigue Total
    Steel of Hard (C, B)6 before Status of Strength Hole
    Material Layer Induction Hard [1 × 108] Depth
    No. (μm) Quenching Layer (MPa) (mm) Remarks
     1 1.9 No Low 734 6111 Example
     2 14.2 No Low 495 6515 Comparative
    Example
     3 12.9 No Low 571 5737 Comparative
    Example
     4 14.0 No Low 501 3401 Comparative
    Example
     5 2.9 No Low 704 6226 Example
     6 2.7 No Low 744 6203 Example
     7 1.7 No Low 752 5982 Example
     8 13.1 No Low 431 7102 Comparative
    Example
     9 3.6 No Low 688 6311 Example
    10 2.2 No Low 705 6465 Example
    11 2.4 No Low 719 5958 Example
    12 17.0 No Low 467 7001 Comparative
    Example
    13 1.0 No Low 831 2557 Comparative
    Example
    14 3.9 No Low 481 8018 Comparative
    Example
    15 2.4 No Low 765 2714 Comparative
    Example
    16 2.3 No Low 702 6560 Example
    17 16.0 No Low 482 6560 Comparative
    Example
    18 13.5 No Low 503 5217 Comparative
    Example
    19 12.6 No Low 520 3524 Comparative
    Example
    20 3.2 No Low 697 7450 Example
    21 3.1 No Low 730 6630 Example
    22 1.9 No Low 745 8350 Example
  • TABLE 2-2
    Total Volume Heating
    Reduction Cooling Volume Fraction Rate in
    Rate from Rate Fraction of Thickness Heating of Heating Thickness
    Steel more than after Hot of Ferrite Pearlit of Ferrite Induction Conditions of of Hard
    Material Steel
    850° C. to Working Structure Structure Structure Quenching Induction Layer
    No. No. 950° C. (%) (° C./s) (vol %) (vol %) (μm) (° C./s) Quenching (mm)
    23 17 85 0.4 63 37 18 550 890° C. × 2s 3.8
    24 18 85 0.4 59 41 18 550 890° C. × 2s 4.0
    25 19 85 0.4 42 58 20 550 910° C. × 2s 4.5
    26 20 85 0.3 68 32 17 550 900° C. × 2s 4.1
    27 21 85 0.4 58 42 26 550 870° C. × 1s 3.8
    28 22 85 0.4 0 0 — 550 900° C. × 2s 4.5
    29 23 85 0.4 77 23 27 550 880° C. × 2s 1.0
    30 24 85 0.5 0 25 — 550 880° C. × 2s 4.0
    31 25 85 0.4 63 37 20 550 890° C. × 2s 3.4
    32 26 85 0.4 65 35 18 550 890° C. × 2s 3.6
    33 27 85 0.4 65 35 19 550 890° C. × 2s 2.5
    34 28 85 0.4 0 0 — 550 890° C. × 2s 4.0
    35 29 85 0.4 0 0 — 550 890° C. × 2s 4.0
    36 30 85 0.4 50 50 16 550 890° C. × 2s 4.0
    37 31 85 0.4 50 50 16 550 890° C. × 2s 4.0
    38 1 85 0.4 63 37 15 800 890° C. × 2s 3.5
    39 1 85 0.4 62 38 14 350 890° C. × 2s 3.5
    40 1 85 0.4 65 35 14 150 890° C. × 2s 3.5
    41 1 85 0.4 63 37 13 150 1050° C. × 2s  3.4
    42 1 85 0.4 62 38 13 150 1010° C. × 2s  3.4
    43 1 85 0.4 64 36 15 150 980° C. × 2s 3.5
    Average
    Prior
    Austenite Degree
    Grain Presence of of Mixed Bending
    Diameter (Fe, Mo, Mn)23 Grain Fatigue
    Steel of Hard (C, B)6 before Status of Strength Total Hole
    Material Layer Induction Hard [1 × 108] Depth
    No. (μm) Quenching Layer (MPa) (mm) Remarks
    23 3.6 No Low 685 8650 Example
    24 3.7 No Low 672 6620 Example
    25 2.5 No Low 697 8420 Example
    26 2.6 No Low 708 6700 Example
    27 19.0 No Low 456 6720 Comparative
    Example
    28 1.0 No Low 810 3560 Comparative
    Example
    29 4.2 No Low 470 9410 Comparative
    Example
    30 2.5 No Low 745 2170 Comparative
    Example
    31 2.8 No Low 695 6480 Example
    32 2.5 No Low 710 6720 Example
    33 2.2 No Low 700 6750 Example
    34 2.5 Yes High 735 2620 Comparative
    Example
    35 2.3 Yes High 751 2819 Comparative
    Example
    36 2.5 No Low 765 6430 Example
    37 2.5 No Low 782 6320 Example
    38 1.8 No Low 745 6120 Example
    39 2.0 No Low 731 6070 Example
    40 2.4 No Low 715 6140 Example
    41 13.5 No Low 567 6130 Comparative
    Example
    42 12.8 No Low 585 6120 Comparative
    Example
    43 11.1 No Low 605 6150 Example

Claims (16)

1. A steel material for induction quenching, comprising 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, wherein the steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the maximum thickness of the ferrite structure is 30 μm or less, and an average prior austenite grain diameter of a hard layer after induction quenching is 12 μm or less.
2. The steel material for induction quenching according to claim 1, further comprising at least one element selected from the group consisting of 1.0% or less of Cu, 3.5% or less of Ni, 1.0% or less of Co, 0.1% or less of Nb, 0.1% or less of Ti, and 0.5% or less of V on a mass basis.
3. The steel material for induction quenching according to claim 1, further comprising at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.
4. The steel material for induction quenching according to claim 2, further comprising at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.
5. An induction quenched member formed from the steel material for induction quenching according to claim 1, wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.
6. An induction quenched member formed from the steel material for induction quenching according to claim 2, wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.
7. An induction quenched member formed from the steel material for induction quenching according to claim 3, wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.
8. An induction quenched member formed from the steel material for induction quenching according to claim 4, wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.
9. A method for manufacturing a steel material for induction quenching, comprising:
a step of hot working steel at a total reduction rate of 80% or more in a temperature region of more than 850° C. to 950° C., the steel comprising 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, and
a step of cooling the steel treated by the hot working to 600° C. or less at a cooling rate of less than 0.6° C./sec.
10. The method for manufacturing a steel material for induction quenching, according to claim 9, wherein the steel further comprises at least one element selected from the group consisting of 1.0% or less of Cu, 3.5% or less of Ni, 1.0% or less of Co, 0.1% or less of Nb, 0.1% or less of Ti, and 0.5% or less of V on a mass basis.
11. The method for manufacturing a steel material for induction quenching according to claim 9, wherein the steel further comprises at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.
12. The method for manufacturing a steel material for induction quenching according to claim 10, wherein the steel further comprises at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.
13. A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to claim 1, which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
14. A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to claim 2, which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
15. A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to claim 3, which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
16. A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to claim 4, which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.
US10/555,511 2003-09-29 2004-07-16 Steel product for induction hardening, induction-hardened member using the same, and methods for production them Abandoned US20070000582A1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
JP2003338634 2003-09-29
JP2003339634 2003-09-30
JP2004181467 2004-06-18
JP2004181467 2004-06-18
PCT/JP2004/010570 WO2005031020A1 (en) 2003-09-29 2004-07-16 Steel product for induction hardening, induction-hardened member using the same, and methods for producing them

Publications (1)

Publication Number Publication Date
US20070000582A1 true US20070000582A1 (en) 2007-01-04

Family

ID=34395620

Family Applications (1)

Application Number Title Priority Date Filing Date
US10/555,511 Abandoned US20070000582A1 (en) 2003-09-29 2004-07-16 Steel product for induction hardening, induction-hardened member using the same, and methods for production them

Country Status (6)

Country Link
US (1) US20070000582A1 (en)
EP (1) EP1669468B1 (en)
KR (1) KR100726251B1 (en)
DE (1) DE602004032363D1 (en)
TW (1) TWI276690B (en)
WO (1) WO2005031020A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110002807A1 (en) * 2009-01-16 2011-01-06 Nippon Steel Corporation Steel for induction hardening
US10260123B2 (en) * 2014-07-03 2019-04-16 Nippon Steel & Sumitomo Metal Corporation Rolled steel bar for machine structural use and method of producing the same
US10266908B2 (en) * 2014-07-03 2019-04-23 Nippon Steel & Sumitomo Metal Corporation Rolled steel bar for machine structural use and method of producing the same
US10808304B2 (en) 2016-07-19 2020-10-20 Nippon Steel Corporation Steel for induction hardening

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI384077B (en) * 2008-10-01 2013-02-01 China Steel Corp Anti-tempering softening treatment of high-carbon tool steel and its manufacturing method
JP6614238B2 (en) * 2015-08-10 2019-12-04 日本製鉄株式会社 Product member manufacturing method and product member
KR102440498B1 (en) * 2016-12-19 2022-09-06 현대자동차주식회사 High durable outer wheel of constant velocity joint and manufacturing method thereof
JP7127999B2 (en) * 2017-03-27 2022-08-30 株式会社神戸製鋼所 Steel for forgings, forged steel crank throws and forged journals for assembled crankshafts

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5279688A (en) * 1989-12-06 1994-01-18 Daido Tokushuko Kabushiki Kaisha Steel shaft material which is capable of being directly cut and induction hardened and a method for manufacturing the same

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2725747B2 (en) * 1990-11-16 1998-03-11 大同特殊鋼株式会社 Steel for induction hardening
JPH0517821A (en) * 1991-07-12 1993-01-26 Nippon Steel Corp Production of induction hardened parts minimal in quenching crack
JP3208960B2 (en) * 1993-10-20 2001-09-17 株式会社神戸製鋼所 High surface fatigue strength parts for machine structural use and their manufacturing method
JPH0853714A (en) * 1994-08-09 1996-02-27 Kobe Steel Ltd Shaft parts for machine structural use excellent in torsional fatigue strength
JP3432950B2 (en) * 1995-04-17 2003-08-04 新日本製鐵株式会社 Steel material for induction hardened shaft parts that has both cold workability and torsional fatigue strength characteristics
JP3562192B2 (en) * 1997-01-31 2004-09-08 Ｊｆｅスチール株式会社 Component for induction hardening and method of manufacturing the same
JP3809004B2 (en) * 1998-02-24 2006-08-16 新日本製鐵株式会社 Induction quenching steel with excellent high strength and low heat treatment strain characteristics and its manufacturing method
JP4435953B2 (en) * 1999-12-24 2010-03-24 新日本製鐵株式会社 Bar wire for cold forging and its manufacturing method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5279688A (en) * 1989-12-06 1994-01-18 Daido Tokushuko Kabushiki Kaisha Steel shaft material which is capable of being directly cut and induction hardened and a method for manufacturing the same

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110002807A1 (en) * 2009-01-16 2011-01-06 Nippon Steel Corporation Steel for induction hardening
US10260123B2 (en) * 2014-07-03 2019-04-16 Nippon Steel & Sumitomo Metal Corporation Rolled steel bar for machine structural use and method of producing the same
US10266908B2 (en) * 2014-07-03 2019-04-23 Nippon Steel & Sumitomo Metal Corporation Rolled steel bar for machine structural use and method of producing the same
US10808304B2 (en) 2016-07-19 2020-10-20 Nippon Steel Corporation Steel for induction hardening

Also Published As

Publication number Publication date
KR100726251B1 (en) 2007-06-08
EP1669468B1 (en) 2011-04-20
WO2005031020A1 (en) 2005-04-07
TWI276690B (en) 2007-03-21
EP1669468A1 (en) 2006-06-14
KR20060016788A (en) 2006-02-22
DE602004032363D1 (en) 2011-06-01
TW200512302A (en) 2005-04-01
EP1669468A4 (en) 2007-03-07

Similar Documents

Publication Publication Date Title
EP1669469B1 (en) Steel parts for machine structure, material therefor, and method for manufacture thereof
JP6057014B2 (en) Induction hardening steel
EP2418296A1 (en) Steel for case hardening which has excellent cold workability and machinability and which exhibits excellent fatigue characteristics after carburizing and quenching, and process for production of same
WO2012046779A1 (en) Case hardened steel and method for producing the same
JP6384629B2 (en) Induction hardening steel
JP6384628B2 (en) Induction hardening steel
WO2018016506A1 (en) Steel for induction hardening
US7678207B2 (en) Steel product for induction hardening, induction-hardened member using the same, and methods producing them
JP3932995B2 (en) Induction tempering steel and method for producing the same
EP3330398B1 (en) Steel pipe for line pipe and method for manufacturing same
JP3738004B2 (en) Case-hardening steel with excellent cold workability and prevention of coarse grains during carburizing, and its manufacturing method
US20070000582A1 (en) Steel product for induction hardening, induction-hardened member using the same, and methods for production them
JP4528363B1 (en) Case-hardened steel with excellent cold workability, machinability, and fatigue characteristics after carburizing and quenching, and method for producing the same
JP3978111B2 (en) Carburizing steel with excellent torsional fatigue properties
JP4488228B2 (en) Induction hardening steel
JP4344126B2 (en) Induction tempered steel with excellent torsional properties
JP3739958B2 (en) Steel with excellent machinability and its manufacturing method
JP5443277B2 (en) High-strength steel with excellent machinability and method for producing the same
JP7436779B2 (en) Steel for carburized gears, carburized gears, and method for manufacturing carburized gears
JP6922415B2 (en) Carburized parts
JP2019218586A (en) Steel for carburization and component
JP7368697B2 (en) Steel for carburized gears, carburized gears, and method for manufacturing carburized gears
JPH11270531A (en) High strength bolt having good delayed fracture characteristic and manufacture thereof
JPH0987801A (en) Steel product for machine structural use excellent in machinability and quenching crack resistance, and its production
JPH0967642A (en) Steel material for machine structural use, excellent in cold workability, and its production

Legal Events

Date Code Title Description
AS Assignment

Owner name: JFE STEEL CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MATSUZAKI, AKIHIRO;OMORI, YASUHIRO;KUROSAWA, NOBUTAKA;AND OTHERS;REEL/FRAME:017322/0158;SIGNING DATES FROM 20051114 TO 20051116

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION