EP0079864B1 - Process for high-temperature carburizing treatment of track bushes for tractors or tracked vehicles, with carburizing atmosphere produced in situ, direct quenching, annealing at ends and total stress relieving - Google Patents
Process for high-temperature carburizing treatment of track bushes for tractors or tracked vehicles, with carburizing atmosphere produced in situ, direct quenching, annealing at ends and total stress relieving Download PDFInfo
- Publication number
- EP0079864B1 EP0079864B1 EP82830210A EP82830210A EP0079864B1 EP 0079864 B1 EP0079864 B1 EP 0079864B1 EP 82830210 A EP82830210 A EP 82830210A EP 82830210 A EP82830210 A EP 82830210A EP 0079864 B1 EP0079864 B1 EP 0079864B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- bushes
- carburizing
- temperature
- furnace
- chamber
- 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.)
- Expired
Links
- 238000005255 carburizing Methods 0.000 title claims description 40
- 238000010791 quenching Methods 0.000 title claims description 14
- 230000000171 quenching effect Effects 0.000 title claims description 11
- 238000000034 method Methods 0.000 title claims description 10
- 238000011065 in-situ storage Methods 0.000 title claims description 4
- 238000011282 treatment Methods 0.000 title description 11
- 238000000137 annealing Methods 0.000 title 1
- 238000004519 manufacturing process Methods 0.000 claims description 11
- 238000001816 cooling Methods 0.000 claims description 9
- 229910000734 martensite Inorganic materials 0.000 claims description 7
- 238000005496 tempering Methods 0.000 claims description 7
- 239000000567 combustion gas Substances 0.000 claims description 4
- 230000006698 induction Effects 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 229910000712 Boron steel Inorganic materials 0.000 claims description 2
- 239000000839 emulsion Substances 0.000 claims description 2
- 238000000605 extraction Methods 0.000 claims description 2
- 239000002912 waste gas Substances 0.000 claims description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 239000003981 vehicle Substances 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 235000019362 perlite Nutrition 0.000 description 1
- 239000010451 perlite Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000002569 water oil cream Substances 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Classifications
-
- 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
- C23C8/80—After-treatment
-
- 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
- C21D1/78—Combined heat-treatments not provided for above
-
- 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
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
- C21D9/14—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes wear-resistant or pressure-resistant pipes
Definitions
- the invention refers to the production of bushes for the tracks of tracked vehicles in general, such as tractors and earthmoving machinery, more precisely, the invention refers to a production process in which the bushes are carburized at high temperature in a carburizing atmosphere produced in situ (using techniques which are already known as such but which have never been applied simultaneously to the items in question), and then are individually quenched and finally undergo a tempering of the ends and a total stress relief.
- the bush rotatably coupled to a pin, forms the articulated junction element between the track links.
- the technological properties the bush must have in order to withstand such use conditions include high surface hardness combined with good tensile strength, good fatigue strength and good impact strength. These properties are ensured by specifications that call for a completely martensitic structure in the centre and on the surface, 5-8 ASTM austenitic grain, surface hardness in excess of 55 HRC, centre hardness of 32-44 HRC and surface hardnes at the ends of 35-46 HRC.
- Attainment of the desired mechanical properties is an essential condition for the production of parts, such as bushes, subject to wear and decidedly unusual stresses, when in use.
- parts such as bushes
- parts such as bushes
- wear and decidedly unusual stresses when in use.
- a number of treatments of great interest from the technical and economic aspects were already known, such as high-temperature carburizing and direct quenching, it had hitherto been considered impossible or anyway too complex and costly to apply them to the production of track bushes for tracked vehicles (henceforth simply referred to as bushes).
- the bush-manufacture cycles generally comprised a carburizing treatment at a temperature of 960 ⁇ 10°C in carburizing furnaces with natural gas fed directly into the retort.
- Such unwanted structures could be avoided by a high complicated treatment involving, after carburization, a slow cooling in carburizing furnace to about 600°C, followed by a transfer to suitable chamber for further cooling to about 300°C; then air cooling to room temperature, followed by heating to 820-860°C, and quenching in water oil emulsion; then tempering of bushes ends at 550-600°C in induction furnace and subsequent cooling to obtain a surface hardness of 35-46 HRC; at last total stress relieving in soaking pit at 180-200°C for 1-2 hours.
- the object of this invention is to simplify and reduce the cost of making bushes through a series of measures aimed at simplifying the plant reducing carburizing times, eliminating the heating for quenching and reducing energy consumption, particularly as regards methane, but maintaining the most suitable internal structure of the bushes.
- the present invention provides for the use of techniques that, although actually known, such as high-temperature carburizing with furnace- produced atmosphere and direct quenching, are applied in an original manner to a product such as bushes and incorporated for the first time simultaneously in an optimized treatment cycle.
- the process for the production of track bushes for tracked vehicles, from low-carbon boron steel, having a martensitic structure in the centre and on the surface with 5-8 ASTM austenitic grain, centre hardness between 32 and 44 HRC, surface hardness over 55 HRC and hardness of ends between 35 and 46 HRC, according to present invention comprises the following steps:
- the carburizing temperature is preferably between 950 and 980°C.
- the ends are preferably tempered in an induction furnace at a temperature of 550-600°C.
- the manufacture cycle of the invention allows to save energy and to operate rapidly.
- the saving in time is also marked. Indeed, if a carburizing depth of about 2.5 mm is chosen, with the traditional carburizing temperatures between 900 and 930°C the carburizing time ranges from 20 to 30 hours, which is almost twice that needed with the process as per the present invention.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Heat Treatment Of Articles (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
Description
- The invention refers to the production of bushes for the tracks of tracked vehicles in general, such as tractors and earthmoving machinery, more precisely, the invention refers to a production process in which the bushes are carburized at high temperature in a carburizing atmosphere produced in situ (using techniques which are already known as such but which have never been applied simultaneously to the items in question), and then are individually quenched and finally undergo a tempering of the ends and a total stress relief.
- The bush, rotatably coupled to a pin, forms the articulated junction element between the track links.
- During the relative movement between two connected track elements the pin rotates inside the bush with sliding friction and is subject to high dynamic loads applied directly to the bush by the driving sprocket. The variable temperatures under which earthmoving machinery operates further increase the stress on the bushes.
- The technological properties the bush must have in order to withstand such use conditions include high surface hardness combined with good tensile strength, good fatigue strength and good impact strength. These properties are ensured by specifications that call for a completely martensitic structure in the centre and on the surface, 5-8 ASTM austenitic grain, surface hardness in excess of 55 HRC, centre hardness of 32-44 HRC and surface hardnes at the ends of 35-46 HRC.
- These requisites are obtainable by using a low-carbon steel (0.13-0.24% C) containing boron (0.0005-0.003% B) with 0.60-0.90% Mn and 0.10-0.30% Si, both forthe extrusion and for the machining processes of manufacture. Other elements such as aluminium, for instance, are preferentially added in the quantities normally required for the purpose of inhibiting the growth of austenitic grain during high-temperature carburizing.
- However, the above steel composition is not a limiting factor as regards this invention; indeed, any steel capable of meeting the technical requirements indicated earlier is suitable for treatment by the present invention.
- Attainment of the desired mechanical properties is an essential condition for the production of parts, such as bushes, subject to wear and decidedly unusual stresses, when in use. For these reasons, although a number of treatments of great interest from the technical and economic aspects were already known, such as high-temperature carburizing and direct quenching, it had hitherto been considered impossible or anyway too complex and costly to apply them to the production of track bushes for tracked vehicles (henceforth simply referred to as bushes). In fact, with the higher temperatures involved in high-temperature carburizing, not only is there the risk of uncontrolled grain growth (a risk that in the case in point is controlled by the special inhibitors mentioned above), but there is also the risk that they may create temperature profiles and hence stresses in the pieces during cooling, such as to result in distortion and rupture or at least to lead to lack of uniformity of properties. Then again, direct quenching, which uses the residual carburizing heat, performed hitherto either on very small parts treated en bloc or even sometimes on large parts, treated singly right from the carburizing heating phase, seemed difficult to apply to parts such as bushes, which are too small to be suitable for individual treatment right from the carburizing process, but too large to support direct quenching treatment en masse, since any differences in packing them into the baskets can easily cause differences in cooling rates and hence in the mechanical properties, among distant parts of the bush or between the outer and inner surfaces thereof.
- Up to now, as it is stated in Metal Science and Heat Treatment, vol. 21, No 7, 1979, pages 609-611, the bush-manufacture cycles generally comprised a carburizing treatment at a temperature of 960±10°C in carburizing furnaces with natural gas fed directly into the retort.
- By using such manufacturing cycles carburizing times last 20-28 hours.
- Then, as stated in the same reference cited above, a carburizing in fluidized bed was tested with temperature ranging between 930 and 960°C. It was found that the use of said fluidized bed reduced the carburizing times. However improvements of the inner structure of the bushes were not satisfactory because the bushes were not characterized by a completely martensitic structure, showing small quantities of cementite, austenite and/or perlite.
- Such unwanted structures could be avoided by a high complicated treatment involving, after carburization, a slow cooling in carburizing furnace to about 600°C, followed by a transfer to suitable chamber for further cooling to about 300°C; then air cooling to room temperature, followed by heating to 820-860°C, and quenching in water oil emulsion; then tempering of bushes ends at 550-600°C in induction furnace and subsequent cooling to obtain a surface hardness of 35-46 HRC; at last total stress relieving in soaking pit at 180-200°C for 1-2 hours.
- The complexity of the cycle is evident, particularly the effects on its economy of the treatment times and the four heatings, three of which at high temperature.
- Recent events which caused such a vertiginous rise in energy costs have resulted in a very decided deterioration in the situation. However, it does not appear that any significant changes have occured so far in the specific field of bush manufacture.
- The object of this invention is to simplify and reduce the cost of making bushes through a series of measures aimed at simplifying the plant reducing carburizing times, eliminating the heating for quenching and reducing energy consumption, particularly as regards methane, but maintaining the most suitable internal structure of the bushes.
- The present invention provides for the use of techniques that, although actually known, such as high-temperature carburizing with furnace- produced atmosphere and direct quenching, are applied in an original manner to a product such as bushes and incorporated for the first time simultaneously in an optimized treatment cycle.
- The process for the production of track bushes for tracked vehicles, from low-carbon boron steel, having a martensitic structure in the centre and on the surface with 5-8 ASTM austenitic grain, centre hardness between 32 and 44 HRC, surface hardness over 55 HRC and hardness of ends between 35 and 46 HRC, according to present invention comprises the following steps:
- -preheating of bushes in a pretreatment chamber of the furnace fed by combustion gases from the successive carburizing chamber;
- -transfer of the track bushes to carburizing chamber, where the carburizing atmosphere is producted in situ, and where the track bushes are carburized at a temperature in excess of 900°C;
- -extraction of said bushes one at a time and direct individual quenching;
- -tempering of ends of said bushes and emulsion cooling;
- -total stress relieving of bushes for 1-2 hours at 180―200°C in continuous furnace fed by hot waste gases from carburizing furnace.
- The carburizing temperature is preferably between 950 and 980°C.
- After direct quenching of the bushes the ends are preferably tempered in an induction furnace at a temperature of 550-600°C.
- The manufacture cycle of the invention allows to save energy and to operate rapidly.
- The following example illustrates the present invention.
- A series of charges of bushes each weighing 2000 kg, all of the same type of steel, was treated at 950°C and 980°C to obtain carburizing depths of between 2 and 3 cm. The treatment times were then varied, while the other parameters remained the same for each change, namely: quench temperature 850°C; tempering of ends in induction furnace 570°C, stress relieving for two hours at 180°C.
- The results obtained can be summarized as follows.
- -Carburizing temperature: 950°C
- -Carburizing time (steady state): 12 hours
- -Quench temperature: 850°C
- -Tempering: 2 hours at 180°C
- -Austenitic grain: 5.5 in centre, 7 in carburized layer (ASTM)
- -Structure: martensitic
- -Surface hardness: 60 MRC
- -Centre hardness: 41 MRC
- -Surface hardness of ends: 40 HRC
- -Effective depth at 50HRC; 2.2 mm
- -Carburizing temperature: 980°C
- -Carburizing time (steady state): 10 hours
- -Quench temperature: 850°C
- -Tempering: 2 hours at 180°C
- -Austenitic grain: 5 in centre and 7 in carburized layer (ASTM)
- -Structure: martensitic in centre; martensitic with residual austenite in carburized zone
- -Surface hardness: 61 HRC
- -Centre hardness: 42HRC
- -Surface hardness of ends: 41 HRC
- -Effective depth at 50 HRC: 2.5. mm
- The ensemble of specific techniques seIeεted- furnace producted carburizing atmosphere and direct quenching-and the high recovery of residual heat from the carburizing gas, permits an enetgy saving in excess of 200 Nm3 of methane per tonne of charge, equal to 40% of an identical treatment using endogas, and this despite the higher carburizing temperature.
- The saving in time is also marked. Indeed, if a carburizing depth of about 2.5 mm is chosen, with the traditional carburizing temperatures between 900 and 930°C the carburizing time ranges from 20 to 30 hours, which is almost twice that needed with the process as per the present invention.
cooling in a third chamber of the furnace, to a temperature of 820-860°C, maintained by means of combustion gas leaving the carburizing chamber;
Claims (3)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IT4955281 | 1981-10-23 | ||
IT49552/81A IT1171606B (en) | 1981-10-23 | 1981-10-23 | PROCESS FOR HEAT TREATMENT OF CEMENTATION AT HIGH TEMPERATURE WITH CEMENTING ATMOSPHERE PRODUCED IN SITU DIRECT HARDENING AT THE ENDS OF TOTAL DISTENSION OF BUSHINGS FOR TRACTOR CATALOGS OR TRACKED VEHICLES |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0079864A1 EP0079864A1 (en) | 1983-05-25 |
EP0079864B1 true EP0079864B1 (en) | 1987-11-25 |
Family
ID=11271005
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP82830210A Expired EP0079864B1 (en) | 1981-10-23 | 1982-07-21 | Process for high-temperature carburizing treatment of track bushes for tractors or tracked vehicles, with carburizing atmosphere produced in situ, direct quenching, annealing at ends and total stress relieving |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0079864B1 (en) |
BR (1) | BR8206000A (en) |
DE (1) | DE3277732D1 (en) |
IT (1) | IT1171606B (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS60138065A (en) * | 1983-12-27 | 1985-07-22 | Chugai Ro Kogyo Kaisha Ltd | Gas carburizing and quenching method and continuous gas carburizing and quenching equipment |
JPH02169375A (en) * | 1988-12-21 | 1990-06-29 | Topy Ind Ltd | Crawler bushing and manufacture thereof |
JPH03285020A (en) * | 1990-03-31 | 1991-12-16 | Topy Ind Ltd | Manufacture of bushing for crawler |
IT1288690B1 (en) | 1996-11-14 | 1998-09-23 | Bruno Girardello | PROCEDURE FOR THE HEAT TREATMENT OF BUSHINGS ESPECIALLY FOR TRACKED AND SIMILAR VEHICLES |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE632935C (en) * | 1931-05-16 | 1936-07-16 | Benno Schilde Maschb Akt Ges | Process and device for surface carbonization of iron and steel |
US3227586A (en) * | 1963-08-19 | 1966-01-04 | Caterpillar Tractor Co | Track pin bushing |
CH615948A5 (en) * | 1974-03-18 | 1980-02-29 | Hawera Probst Kg Hartmetall | |
US4049473A (en) * | 1976-03-11 | 1977-09-20 | Airco, Inc. | Methods for carburizing steel parts |
US4152177A (en) * | 1977-02-03 | 1979-05-01 | General Motors Corporation | Method of gas carburizing |
-
1981
- 1981-10-23 IT IT49552/81A patent/IT1171606B/en active
-
1982
- 1982-07-21 EP EP82830210A patent/EP0079864B1/en not_active Expired
- 1982-07-21 DE DE8282830210T patent/DE3277732D1/en not_active Expired
- 1982-10-14 BR BR8206000A patent/BR8206000A/en unknown
Non-Patent Citations (1)
Title |
---|
Industrial Heating, september 1984, pages 22-23 * |
Also Published As
Publication number | Publication date |
---|---|
BR8206000A (en) | 1983-09-13 |
IT1171606B (en) | 1987-06-10 |
DE3277732D1 (en) | 1988-01-07 |
IT8149552A0 (en) | 1981-10-23 |
EP0079864A1 (en) | 1983-05-25 |
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