EP0682123A1 - Method of manufacturing carburized steel products - Google Patents

Method of manufacturing carburized steel products Download PDF

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Publication number
EP0682123A1
EP0682123A1 EP94106435A EP94106435A EP0682123A1 EP 0682123 A1 EP0682123 A1 EP 0682123A1 EP 94106435 A EP94106435 A EP 94106435A EP 94106435 A EP94106435 A EP 94106435A EP 0682123 A1 EP0682123 A1 EP 0682123A1
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EP
European Patent Office
Prior art keywords
boron
carburized
treated steel
hardening depth
steel
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.)
Withdrawn
Application number
EP94106435A
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German (de)
French (fr)
Inventor
Jee Yong-Kwon
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.)
Volvo Construction Equipment Korea Co Ltd
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Samsung Heavy Industries Co Ltd
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Publication date
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Priority to EP94106435A priority Critical patent/EP0682123A1/en
Priority to JP6113560A priority patent/JPH07300661A/en
Publication of EP0682123A1 publication Critical patent/EP0682123A1/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces

Definitions

  • the present invention is concerned with a method of manufacturing carburised steel products with an increased hardening depth.
  • the power transmitting components such as gears are heat-treated with carburization for surface hardening considering the strength and wear durability required by the transmitted load, where the required hardening depths are properly designed by the transmitted loads. Particularly the increased hardening depth is required for the large scale gear on which high loading transmission torque is acted.
  • the hardening depth is limited during carburization heat-treatment due to the material properties characterized by the alloy elements of the steel composition, and particularly this phenomenon becomes more apparent in the large scale gears(Ref. Fig. 1).
  • Fig. 1 represents the change in hardening depth with the gear diameter and quenching rate of heat treatment.
  • the hardening depth increases with the quenching rate, and under the given quenching rate, the hardening depth decreases as the given diameter increases. Accordingly, unless the hardening depth is good enough in case of large scale high loading gears, the case crushing on spalling as indicated by Fig. 2 occurs.
  • a method of manufacturing a carburized steel product comprising a step of a carburization heat treatment using a boron treated steel, thereby a hardening depth is increased.
  • the said heat treatment is performed at temperature range 925 ⁇ 1050°C for at least 15 hours.
  • the said boron treated steel comprising, 0.18 ⁇ 0.35 wt% of C, 0.06 ⁇ 0.3 wt% of Si, 0.5 ⁇ 1.5 wt% of Mn, ⁇ 1 wt% of Cr, ⁇ 0.02 wt% of S, ⁇ 0.03 wt% of P, 0.01 ⁇ 0.08 wt% of Al, ⁇ 0.05 wt% of Ti, ⁇ 0.012 wt% of N2, ⁇ 0.003 wt% of O2 and 0.0005 ⁇ 0.003 wt% of B.
  • the present invention makes use of the following characteristics of boron(B) treated steel; (i) since the boron(B) treated steel does not comprises the expensive transition metal elements such as Ni, Cr, and Mo, or comprises these metal elements by the minimum amount, carbon(C) can be permeated more readily into the steel during carburization treatment, and on the other hand, (ii) the use of boron(B) and the minimum amount of alloying elements make it possible to increase the hardenability and hardening depth of the carburized products.
  • the carburization temperature is below 920°C, the carburized depth does not increase.
  • the carburization rate increases above 920°C.
  • the carburization temperature exceeds 1050°C, the grains grow and become coarsend resulting in the deterioration of the durability properties such as impact strength of the heat-treated product. Accordingly, the carburization heat treatment should be performed in the said temperature range of 920°C ⁇ 1050°C.
  • the alloying elements such as Al, Ti added by small amounts contribute to lowering the grain growth, and the repeat quench is performed in order to prevent further the grains from coarsening in the said temperature range.
  • the said repeat quench makes the coarsend grains redistributed finely, allowing the grain growth to be affected little by the maximum carburization temperature.
  • the specimens( ⁇ 25x40mm) are made using boron(B) treated steel with chemical composition as shown in Table 1, carburized at 930°C for the times as shown in table 2 and 3 respectively, quenched at 850°C, and then annealed at 180°C for 2 hrs. Comparing the hardening depth of boron treated steel with that of the conventional carburized steels used for gears, it is noted that the hardening depth of the carburized boron treated steel is 1.5 times deeper than that of the other alloy steels. However, if the same experiments as above is performed at 920°C, it is noted that the increase in the hardening depth does not occur although the carburization is performed for the times as long as those in table 3. That is, unless the carburization temperature is above 920°C, the effect of boron treatment does not become apparent on the increase in carbon permeability and hardening depth.
  • the hardening depths can be deeper than in the conventional alloy steels resulting in the improvement of the strength of high loading carburized products such as large scale gears and screws, particularly the fracture strength like case crushing.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

This invention is concerned with the processing method of carburized product with an increased hardening depth, in which boron treated steel comprising by weight percent 0.18∼ 0.35 % C, 0.06∼0.3 % Si, 0.5∼1.5 % Mn, <1 % Cr, <0.02 % S, <0.03 % P, 0.01∼0.08 % Al, <0.05 % Ti, <0.012 % N₂, <0.003 % O₂ and 0.0005∼0.003 % B is carburized at the temperature range of 925∼1050°C. As described in the above, if the steel products made of boron treated steel are

Description

    Background of the invention 1. Field of the invention
  • The present invention is concerned with a method of manufacturing carburised steel products with an increased hardening depth.
    • 2. Description of the prior arts
  • It is generally known that the power transmitting components such as gears are heat-treated with carburization for surface hardening considering the strength and wear durability required by the transmitted load, where the required hardening depths are properly designed by the transmitted loads. Particularly the increased hardening depth is required for the large scale gear on which high loading transmission torque is acted. However, in the conventional steel alloy materials for carburized gears, the hardening depth is limited during carburization heat-treatment due to the material properties characterized by the alloy elements of the steel composition, and particularly this phenomenon becomes more apparent in the large scale gears(Ref. Fig. 1).
  • Fig. 1 represents the change in hardening depth with the gear diameter and quenching rate of heat treatment.
  • It is noted that the hardening depth increases with the quenching rate, and under the given quenching rate, the hardening depth decreases as the given diameter increases. Accordingly, unless the hardening depth is good enough in case of large scale high loading gears, the case crushing on spalling as indicated by Fig. 2 occurs.
    • Summary of the invention
  • It is an object of the present invention to provide a method of manufacturing carburized steel products which not only increases the carbon permeability during carburization heat treatment, but increases the hardening depth and thereby improves the strength and wear durability of the carburized steel products by using boron treated steel in which the hardening depth can be made deeper than in the conventional steels for gears due to the effect of boron(B) element.
  • According to one aspect of the present invention, there is provided a method of manufacturing a carburized steel product, comprising a step of a carburization heat treatment using a boron treated steel, thereby a hardening depth is increased.
  • It is preferrable that the said heat treatment is performed at temperature range 925∼1050°C for at least 15 hours.
  • It is also preferrable that the said boron treated steel comprising, 0.18∼0.35 wt% of C, 0.06∼0.3 wt% of Si, 0.5∼1.5 wt% of Mn, <1 wt% of Cr, <0.02 wt% of S, <0.03 wt% of P, 0.01∼0.08 wt% of Al, <0.05 wt% of Ti, <0.012 wt% of N₂, <0.003 wt% of O₂ and 0.0005∼0.003 wt% of B.
    • Description of the preferred embodiments
  • The present invention makes use of the following characteristics of boron(B) treated steel; (i) since the boron(B) treated steel does not comprises the expensive transition metal elements such as Ni, Cr, and Mo, or comprises these metal elements by the minimum amount, carbon(C) can be permeated more readily into the steel during carburization treatment, and on the other hand, (ii) the use of boron(B) and the minimum amount of alloying elements make it possible to increase the hardenability and hardening depth of the carburized products.
  • In order to increase the hardening depth of the said boron(B) treated steel, it should be carburized at 925 ∼ 1050 °C for the necessary time to achieve the carburisation depth required for the final heat treated product. THis indicates that the hardening characteristics of boron(B) treated steel is associated with the fact that carbon(C) permeability into the surface of boron(B) treated steel increases apparently above on a certain temperature.
  • If the carburization temperature is below 920°C, the carburized depth does not increase. The carburization rate increases above 920°C. However, if the carburization temperature exceeds 1050°C, the grains grow and become coarsend resulting in the deterioration of the durability properties such as impact strength of the heat-treated product. Accordingly, the carburization heat treatment should be performed in the said temperature range of 920°C∼1050°C.
  • During carburization treatment, the alloying elements such as Al, Ti added by small amounts contribute to lowering the grain growth, and the repeat quench is performed in order to prevent further the grains from coarsening in the said temperature range.
  • The said repeat quench makes the coarsend grains redistributed finely, allowing the grain growth to be affected little by the maximum carburization temperature.
  • The following example is submitted to illustrate the processing method and the effects thereof but not to limited this invention.
    • Example
  • The specimens(⌀25x40mm) are made using boron(B) treated steel with chemical composition as shown in Table 1, carburized at 930°C for the times as shown in table 2 and 3 respectively, quenched at 850°C, and then annealed at 180°C for 2 hrs. Comparing the hardening depth of boron treated steel with that of the conventional carburized steels used for gears, it is noted that the hardening depth of the carburized boron treated steel is 1.5 times deeper than that of the other alloy steels. However, if the same experiments as above is performed at 920°C, it is noted that the increase in the hardening depth does not occur although the carburization is performed for the times as long as those in table 3. That is, unless the carburization temperature is above 920°C, the effect of boron treatment does not become apparent on the increase in carbon permeability and hardening depth.
  • In order to confirm the said effect, the conventional alloy steel and the boron treated steel of this invention have been heat heated at the condition as shown in table 4 with the difference in hardening depth shown in Fig. 3 and 4 respectively. As shown in Fig. 3, it can be seen that the hardening depth of conventional carburized product(t1) is less than that of the boron treated steel of this invention(t2).
    Figure imgb0001
     Table 2
    Carburization Temp. Time (hr) Hardening Depth(HV 513)
    SCM 21 SNCM 21 Boron Treated Steel
    930°C 1.5 0.7mm 0.7mm 1.0mm
    3 0.9mm 0.9mm 1.3mm
    4 1.1mm 1.0mm 1.4mm
    5 1.1mm 1.2mm 1.7mm
    Table 3
    Carburization Temp. Time (hr) Hardening Depth(HV 513)
    SCM 21 SNCM 21 Boron Treated Steel
    930°C 1.5 0.8mm 0.9mm 1.1mm
    5 1.1mm 0.9mm 1.2mm
    7 1.6mm 1.5mm 1.6mm
    9 1.9mm 1.7mm 1.9mm
    Table 4
    Treatment Temperature Time CP
    Holding 950°C 1Hr 0
    Carburization 950°C 12Hr 1.0
    Diffusion 950°C 10Hr 0.8
    Quenching 860°C 1Hr -
    Annealing 180°C 3Hr -
  • As described in the above, if the steel products made of boron treated steel are carburized at the proper temperatures, the hardening depths can be deeper than in the conventional alloy steels resulting in the improvement of the strength of high loading carburized products such as large scale gears and screws, particularly the fracture strength like case crushing.

Claims (5)

  1. A method of manufacturing a carburized steel product, comprising a step of a carburization heat treatment using a boron treated steel, thereby a hardening depth is increased.
  2. The method of claim 1, wherein said heat treatment is performed at temperature range 925∼1050°C.
  3. The method of claim 1, where in said boron treated steel comprising, 0.18∼0.35 wt% of C, 0.06∼0.3 wt% of Si, 0.5∼1.5 wt% of Mn, <1 wt% of Cr, <0.02 wt% of S, <0.03 wt% of P, 0.01∼0.08 wt% of Al, <0.05 wt% of Ti, <0.012 wt% of N₂, <0.003 wt% of O₂ and 0.0005∼0.003 wt% of B.
  4. The method of claim 1, wherein further comprising a step of a repeat quenching is performed after the carburization heat treatment at the said temperature range.
  5. The carburized steel product manufactured by claims 1 , 2, 3 and 4.
EP94106435A 1994-04-25 1994-04-25 Method of manufacturing carburized steel products Withdrawn EP0682123A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP94106435A EP0682123A1 (en) 1994-04-25 1994-04-25 Method of manufacturing carburized steel products
JP6113560A JPH07300661A (en) 1994-04-25 1994-04-28 Production of carburized article, and carburized article produced thereby

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP94106435A EP0682123A1 (en) 1994-04-25 1994-04-25 Method of manufacturing carburized steel products
JP6113560A JPH07300661A (en) 1994-04-25 1994-04-28 Production of carburized article, and carburized article produced thereby

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EP0682123A1 true EP0682123A1 (en) 1995-11-15

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4938414A (en) * 1972-08-15 1974-04-10
JPS5794516A (en) * 1980-12-05 1982-06-12 Toyota Motor Corp Method for heat treatment on low-carbon boron steel
JPS5798657A (en) * 1980-12-06 1982-06-18 Nisshin Steel Co Ltd Carburizing steel with superior workability and carburizability
JPS58164758A (en) * 1982-03-25 1983-09-29 Daido Steel Co Ltd Carburizing steel
JPS58221263A (en) * 1982-06-15 1983-12-22 Nisshin Steel Co Ltd Special steel with superior workability and heat treatability and its manufcture
JPS59136416A (en) * 1983-01-22 1984-08-06 Daido Steel Co Ltd Manufacture of parts for carburization
US4495004A (en) * 1983-10-20 1985-01-22 Italtractor Itm Spa Process for high-temperature carburizing treatment of track bushes for tractors or tracked vehicles
JPH02185954A (en) * 1989-01-11 1990-07-20 Sumitomo Metal Ind Ltd Carburized and case-hardened steel and its production

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4938414A (en) * 1972-08-15 1974-04-10
JPS5794516A (en) * 1980-12-05 1982-06-12 Toyota Motor Corp Method for heat treatment on low-carbon boron steel
JPS5798657A (en) * 1980-12-06 1982-06-18 Nisshin Steel Co Ltd Carburizing steel with superior workability and carburizability
JPS58164758A (en) * 1982-03-25 1983-09-29 Daido Steel Co Ltd Carburizing steel
JPS58221263A (en) * 1982-06-15 1983-12-22 Nisshin Steel Co Ltd Special steel with superior workability and heat treatability and its manufcture
JPS59136416A (en) * 1983-01-22 1984-08-06 Daido Steel Co Ltd Manufacture of parts for carburization
US4495004A (en) * 1983-10-20 1985-01-22 Italtractor Itm Spa Process for high-temperature carburizing treatment of track bushes for tractors or tracked vehicles
JPH02185954A (en) * 1989-01-11 1990-07-20 Sumitomo Metal Ind Ltd Carburized and case-hardened steel and its production

Non-Patent Citations (7)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Derwent World Patents Index; AN 74-80131V C46, "carbirised steel for motor-driven link chains" *
DATABASE WPI Derwent World Patents Index; AN 84-228686 C37, "carbirised steel parts prodn." *
PATENT ABSTRACTS OF JAPAN vol. 14, no. 458 (C - 0766) 3 October 1990 (1990-10-03) *
PATENT ABSTRACTS OF JAPAN vol. 6, no. 180 (C - 125) 14 September 1982 (1982-09-14) *
PATENT ABSTRACTS OF JAPAN vol. 6, no. 186 (C - 126) 22 September 1982 (1982-09-22) *
PATENT ABSTRACTS OF JAPAN vol. 7, no. 285 (C - 201) 20 December 1983 (1983-12-20) *
PATENT ABSTRACTS OF JAPAN vol. 8, no. 67 (C - 216) 29 March 1984 (1984-03-29) *

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Publication number Publication date
JPH07300661A (en) 1995-11-14

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