CA1184099A - Method of heat treating metal - Google Patents
Method of heat treating metalInfo
- Publication number
- CA1184099A CA1184099A CA000380448A CA380448A CA1184099A CA 1184099 A CA1184099 A CA 1184099A CA 000380448 A CA000380448 A CA 000380448A CA 380448 A CA380448 A CA 380448A CA 1184099 A CA1184099 A CA 1184099A
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- CA
- Canada
- Prior art keywords
- temperature
- seconds
- weld
- affected zone
- hardness
- 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.)
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Classifications
-
- 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
- C21D1/34—Methods of heating
- C21D1/42—Induction heating
-
- 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
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
-
- 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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
ABSTRACT
A method for relieving stress in the micro-structure welds and the heat affected zone in the adjacent base metal in low alloy steel by induction heating in a second post-weld heat treatment. The heated area is monitored with a radiation pyrometer to ensure precise temperature control of the procedure.
A method for relieving stress in the micro-structure welds and the heat affected zone in the adjacent base metal in low alloy steel by induction heating in a second post-weld heat treatment. The heated area is monitored with a radiation pyrometer to ensure precise temperature control of the procedure.
Description
9~
BACXGROUND OF THE INVE~TION
~ he present invention relates to relieving stress in ~le nicros~ctu~e of metal by induction heating, and more particularly to the stress-relief of welds and surrounding areas o~ hase metal in low alloy steels employed in hostile subsurface environments such 2S
are encountered in the petroleum industry.
In many a.reas of the world, hydrogen sulfide, cc-~monly called "sour gas" is encountered ~here a petroleum well is drilled. ~he presence of sour gas in a well dictates a choice of materials which will ~ot be subject to sulfide stress cracking,which ma~ be describea a3 the brittle failure of a metal ~nder the combined action of tensile stress and corrosion in the presence of hydrogen sulfide in an aqueous environment.
The National Association of Corrosion Engineers (NACE) has published a Material Requirement dealing with "Sulfide Stress Cracking Resistant Metallic Materi.al For Oil Field Equipment," NACE Standard MR-01-75 (1980 Revision), which standard is employed as a materials guideline by the petroleum industry ~hen dealing with sour gas. The standard sets forth various requirements for the acceptable perrormance in sour gas , o different ferrous and non-ferrous met21s, fabrication, bolting, platin~s and coatings thereof, as well as r~quirements for various specific components and devices used in ~Jell drilling, testing, producti~n and servicing.
S Low alloy steels, being those containing less t~an about five percent (5~) total alloying elements, are acceptable materials for a sour gas environment pr~vided they meet certain requirements set forth in NACE
Standard MR-Ol 75.
In general, if these steels contain less than one percent (1%) nickel (Ni), they are acceptable provided they are subjected to certain thermal treatments to alter the microstructure o~ the ~e~l. It is emphasized by the NACE Standard that there is a definite correlation between sulfide stress cracking, heat treatment and hardness in metals, which correlation has been proven by extensive laboratory and -field data. Hardness is in part a function of the stress present in the microstructure;
the resistance of the metal to sulfide stress cracking is enhanced by the lowering of hardness by stress relief in ~he l~crostructure through heat treatment. As hardness ~s an accurate, nondestructively generated test parameter, it is extensively used to monitor materials performance.
'l'~he Rockwell "C" Hardness Scale (~RC) as used in the NACE
Skandard is the primary ~asis for determination of an p9~
accept~hle hardness, for sour gas equipment, although it should-be ~nderstood that other hardness scales m~y be employed using suitable conversion factors for . t~orrelation purposes. As a rule, a hardness of .5 .HRC.22 is the maximum hardness allowable by NACE for low-alloy steels and welds thereon in a sour gas ~nvironment. ~ hardness of up to HRC 26 may ~e ~olerated for certain tubular goods, but only if adequate per~ormance is verified with a sulfide stress cracking test, a procedure necessitating additional expense. Therefore, it is desirable to obtain a -hardness of HRC 22, it being understood that this ~lgure may be the average of several tests, as long as the maximum HRC of a specimen does not exceed 23 or 24.
In many instances, a hardness of H~C 22 maximum for steel and welds thereon can be obtained by heat treatiny the material or apparatus in question in a furnace , but in other instances this is impractical, such as where the apparatus is ass~mbled and then welded, the assembly includi.ng components sucll as elastomeric seals, which are destroyed by the high furnace ~emperatures. Likewise, even in the absence of seals, there may be finished surfaces in the apparatus which ~ould be damaged by prolonged exposure to high temper-.atures necessitated by furnace trea-tment. Thus, there presently exists a problem in the production of some material or asse~bly of apparatus to the NACE Standard.
SU~L~RY OF T~IE INVE~TIO~I
The presen~ invention comprises a method A or thermally treating low alloy steel and welds thereon lusing electrical induction heating, which heating is monitored.using a radiation pyrometer or other suit-able means, th~ induction heating being applied oly to t~e specific area to be stress relieved in a second post-weld heat tre2tment at a temperature approaching the critical point of the treate~ material for a relatively hrief period of time. By employing such a method, seals and other destructible nonmetallic elements as well as finished surfaces in relatively close proximity to the heat treated areas are permitted to remain at a low enough temperature to ensure their integrity.
BRIEF DESCRIPTION OF THE DRAWINGS
The present in~ention will be more readily understood with reference to the description hereafter set forth, in conjunction with the accompanying d~awings wherein~
~lG. 1 is a schematic of an apparatus employed in the practice of the present method, with an apparatus to be hea~ t.reated oriented in position.
FI~. ~ is a drawing depicting the microstructure of the heat arfected zone of the base metal adjacent a fusion ~eld, such as could be found on the apparatus to be treated in FIG. 1, prior to heat treatment.
FIG. 3 is a drawing depicting the microstructure of the heat affected zone of FIG. 2 after heat treat-ment by the method of the present invention.
DESCRTPTION OF TH~ PR~FF,RRED EMBODIMENT
Stress-relief o~ microstructures in metals by heating in a furnace is common in many industries.
iGenerally, the heating takes place over a relatively S long period of time, measured in hours. Induction heating, on the other hand, is usually effected in mi~utes or seconds. Certain variables result in different times and temperatures for obtaining equivalent results from the two types of heating, the la relationship of which has been expressed in the following e~uation:
TI (C + log tI) = TF (C ~ log tF) where TF and tF are the furnace temperature (in degrees Rankinel and time, respectively, known to produce a ~iven hardness ;n a metal, and TI and tF are the equiv-~lent temperatuxe (in degrees Rankine) and time needed to produce that hardness ~ith induction heating. C is a constant which may be empirically determined ~or a given m~tal, and is approximately 15 for steels with 0O25 to 0.50% carbon content. The figures obtained from the above ec~uation for tim~ and tempera-ture to be employed in induction heating of a specific metal are, of course, further refined by empirical testing, FIG. 1 schematically depicts an induction heating apparatus designated generally at 10. Induction heating apparatus 10 comprises generator a~d load coil transformer 12, to which inner induction coils 14 and outer induction coils 16 are connected. A
suitable generator is a Lepel lOOkw generator, Model T-loo-3kcrL~ Precise temperature control at the wor~piece 30 is achieved by use of radiation pyrometer/three mode proportional controller 18, which controls the generator, varying the outpu-t thereof i~ response to the input of infrared sensor 2C, whîch senses the temperature on the workpiece 30. A
suitable pyro~eter/controller is the IRCON, model 6-22F15-01-000-1/620~ ~ portion of tubular workpiece 30 is shown disposed between the inner induction coils 14 and the outer induction coils 16. The t~o coils are employed to avoid a temperature gradient in the T~ork-piece 30, and further temperature uniformity is achieved by mounting the ~orkpiece 30 on a rotating jig~-(not shown~, whe:reby the workpiece 30 is rotated about its longitudinal a~is during the induction heatins procedure.
For t~e sake of illustration, and not by way of limitation, the workpiece 30 shown is a portion of a Halliburton Services F. O. Multiple Stage Cementer, described on page 3347 of ~alliburton Services Sales and Service Catalog Number 40. This type o~ workpiece poses several impediments to furnace stress-relief, namely the presence of elastomeric seals 32 and of finished surface 34. Fusion weld 36 is to be stress relieved with no damage to surface 34 or elastomeric seals 32.
~ The F. O. Multiple Stage Cementer comprises metallic parts of AISI (American Iron and Steel Institute) Grade 4140 low alloy steel. The elastomeric seals 32 have a ma~imum temperature destruction tolerance of 325 F. Finished surrace ~4 will begin to scale at 1050 F. As it is necessary for the opera-tion of the F. O. Multiple Stage Cementer that sleeve ~6 slide within finished surface 34, scaling on surface 34 may result in an inoperative tool. I
there were no seals or finished surfaces, the workpiece could be stress-reIieved by furnace heating for a prolonge~l period at 1300F. However, as the assembled Cementer does include these items, a furnace treatment is impossible. The following procedure, unlike a urnace heat treatment, will result in an assembly and 0 welds thereon with the desired hardnes5 characteristics.
Prior to assembly, the metallic parts o~ the F. O.
Multiple Stage Cementer, comprising fine grain seamless, hot finished and normali~ed AISI Grade 4140 low alloy steel, are subjected to stress-relief heating in a ~5 furnace at 130G F for several hours. Subsequently .
the desired finished surface 34 is-machined, and the tool is assembled with elastorneric seals 32. A-t that point, fusion weld 36 is made by, for example, a submerged arc welding process (SAW), with a preheat at the weld point of 700 F, an-interpass temperature of 650 F during t~e welding process, followed by cooling to below the Ms te~perature, the temperature of which martensite begins to form,which is approcimately 500 F.
The interpass ternperature lowers the cooling rate of the metal to an acceptable level, minimizing residu.l stresses in the microstructure. Subsequently, the weld is subjected to a first postheat at 800F. A
low alloy steel electrode comprising less than 1%
nickel ~Ni) is employed in the SA~ process, being an r~r~
ASME (American Society of Mechanical Engineers) SF A5.28 ER80S-D2. Such electrodes are available from Union Carbide Corporation Linde Division as Linde 83, or Page Dlvision of Acco as Page 18. The weld flux employed may be a neutral Fxxx, classes per AWS (American Welding Society) A5.17-76 or A5.23-77. A sui.table flux is Lincoln Electric 880 Flu~.
5ubse~uent to the first postheat, the workpiece 30 is coole~ and placed on a jig, which orients the work-piece 30 between inner induction coils 14 and outer inductiorl coils 16 of induction heating apparatus 10.
The workpiece 30 is slowly rotated on the jig about its axis between the two coils during which rotation the weld 36 is then subjected to a second postheat at substantially 1340F for 900 seconds. The temperature ls measured by sensor 20 at t~e metal surace of the workpiece 30. Radiation pyrometer~
three mode proportional controller 18 maintains this temperature in an accurate manner by controlling the output of generator and load coil transformer 12 to induction coils 14 and 16. ~s 1340 F is close to the critical temperature of 135~F for AISI Grade 4140 low alloy steel, it is imperative that the stress-relief temperature ~e closely monitored to avoid a supercritical temperature in the metal.
Actu21 empirical testing of AISI Grade 4140 specimens welded and subjected to a second postheat according to these specifications has shown the hardness of the heat-affected zone (HA~) in the base metal adjacPnt the weld to under HRC 23 after stress- ~--relief. Test specimens were stressed to lO0~ of their txansverse tensile yield strength, with the maximum stress loc~ted across the fusion zone of the weld, and subjected to a 5% sour brine corrodent at atmospheric pressure at 65F temperature for 30 days.
All speclmens resisted sulfide stress cracking for the 30 day period.
Re~ering to FIGS. ~ and 3 of the drawings, which are representative of the microstructure of the HAZ of base metal adjacent a weld at 200 x magnification on an F~ O. Multiple S-tage Gementer, it can be seen in FIG. 2 that there was a modera-tely stressed microstructure in the HA2 after the first post-weld heating, comprising martensite as well as bainlte, the latter of which appears as groups of needle-like structures; FIG. 3, depicting the HAZ adjacent the weldment after the second postheat, shows a much more refined grain structure in the HAZ, with attendant lowered stress level. The HAZ
har,lness was reduced from HRC 29 measured in FIG. 2, to HRC 20 measured in FIG. 3. During the stress relief-process, the maximum temperature at g.5 inches from the ~eld alony the outer case of the F. O. Multiple Stage Cementer was 295F, belo~ the destruction temperature of the elasto~eric seals 32, and well below scaling temperature for finished surface 34.
It should be noted that the preheat employed in the SAW process contributes to the success of the subsequent second postheat as it enhances the formation of bainite ~0 (designated as B in FIG.2) along with the martensite of the microstructure, thus reducing the initial hardness of the HA~.
It may also be noted that the temperatures and times given in the above illustration are variable to a certain ~5 e~tent for the desired results. For e~ample (again assuming AI5I Grade 41~0 low alloy steel), a preheat as low as substanti~lly 675F or as high as substantially 800F may be employed, with acceptable results. The higher prehea~ temperature of 800Y will result in less martensite formation and a softer post-weld micro-structure, but the lower temperatures will produceacceptable results. Likewise, a first postheat o substantially 775F to substantially 900F may be utilized. The first postheating is the least critical of the heating steps, being used to drive off monatonic hydrogen ~rom the weldmen-t. Similarly, the interpass temperature of 650F is 2n approximation, the important consideration being the reduction of the cooling rate at the weld area to an acceptable area.
It should also be understood that the critical temperature given for AISI Grade 4140 low alloy steel maX ~ary appreciably from 1354 F, depending upon the exact chemical composition of the bar stock obtained.
The critical temperature may range from 1340F to 1395F, thus allowing some minor variation of the induction ~0 ~eatin~ postheat temperature. For example, a minimum time of 350 seconds at substantially 1335F may be employed, and acceptable results obtaired. The second posthea~ temperature of 1340F may also be modified down~ard somewhat, for example to substantially 1310F, for a tii~e of substantially 900 seconds. Below this temperature, the time for heating becomes too lony rrom an economic standpoin~. Furthermore, it is desirable to maintain hardness in the ran~e of HRC
18-22, to pr~serve the mechanical properties of the weld material and surrounding base metal in the HAZ, which too long a heating time may prevent. Equip-.
ment use~ in sour gas in the petroleum industry must meet the API (~nerican Petroleum Institute) L-80 tensile requirements, as well as the L-80 hardness 1~ requirement of HRC ~3 maximum. The minimum acceptable tensile yield strength is 80,000 psi.
Reduction of hardness to below substantially 18 HRC
will result in failure to meet this requirement~
While it may not be necessary for the weldment itself 1~ to meet this requirement, if the hardness in the HAZ
is reduced below substantially 18 HRC, the base metal in the HAZ will fail at too low a stress.
It should also be noted that the use of tempera-tures in ~he second postheat below substantially 1310F
in the instances where seals, finished surfaces or other destructi~le elements are present~ may result in damage to those elements due to the necessarily longer time exposure at what must still be a high temperature, to achieve the desired results.
~hile reference has been made to the specific example of treating AISI Grade 4140 low alloy steel, ,~
it should be understood that the present invention is not so limited. Other low all~y steels, as well as some carbGrl steels, are susceptible to treatment in a similar fashion.
It is thus apparent that the present invention comprises a new and different method for heat treating metals which will be subject to a sour gas environment ~hen furnace heating is unworkable. Additionally, the procedure may be accomplished in a very short lQ period of time, with high quality control and uni~ormity.
The ~ethod, of course, while illustrated with respect to welds and surrounding H~Z in base metal, is not so limited; rather it is applicable wherever precise, localiz.ed heat treating to relieve stress in the micro-structure of metals is desired. It will be readily apparent to one of ordinary skill in the art that modifications, additions, and substitutions to the disclosed method can be made, the invention being limited only by the spirit and scope of the appended ~laims.
p ..
BACXGROUND OF THE INVE~TION
~ he present invention relates to relieving stress in ~le nicros~ctu~e of metal by induction heating, and more particularly to the stress-relief of welds and surrounding areas o~ hase metal in low alloy steels employed in hostile subsurface environments such 2S
are encountered in the petroleum industry.
In many a.reas of the world, hydrogen sulfide, cc-~monly called "sour gas" is encountered ~here a petroleum well is drilled. ~he presence of sour gas in a well dictates a choice of materials which will ~ot be subject to sulfide stress cracking,which ma~ be describea a3 the brittle failure of a metal ~nder the combined action of tensile stress and corrosion in the presence of hydrogen sulfide in an aqueous environment.
The National Association of Corrosion Engineers (NACE) has published a Material Requirement dealing with "Sulfide Stress Cracking Resistant Metallic Materi.al For Oil Field Equipment," NACE Standard MR-01-75 (1980 Revision), which standard is employed as a materials guideline by the petroleum industry ~hen dealing with sour gas. The standard sets forth various requirements for the acceptable perrormance in sour gas , o different ferrous and non-ferrous met21s, fabrication, bolting, platin~s and coatings thereof, as well as r~quirements for various specific components and devices used in ~Jell drilling, testing, producti~n and servicing.
S Low alloy steels, being those containing less t~an about five percent (5~) total alloying elements, are acceptable materials for a sour gas environment pr~vided they meet certain requirements set forth in NACE
Standard MR-Ol 75.
In general, if these steels contain less than one percent (1%) nickel (Ni), they are acceptable provided they are subjected to certain thermal treatments to alter the microstructure o~ the ~e~l. It is emphasized by the NACE Standard that there is a definite correlation between sulfide stress cracking, heat treatment and hardness in metals, which correlation has been proven by extensive laboratory and -field data. Hardness is in part a function of the stress present in the microstructure;
the resistance of the metal to sulfide stress cracking is enhanced by the lowering of hardness by stress relief in ~he l~crostructure through heat treatment. As hardness ~s an accurate, nondestructively generated test parameter, it is extensively used to monitor materials performance.
'l'~he Rockwell "C" Hardness Scale (~RC) as used in the NACE
Skandard is the primary ~asis for determination of an p9~
accept~hle hardness, for sour gas equipment, although it should-be ~nderstood that other hardness scales m~y be employed using suitable conversion factors for . t~orrelation purposes. As a rule, a hardness of .5 .HRC.22 is the maximum hardness allowable by NACE for low-alloy steels and welds thereon in a sour gas ~nvironment. ~ hardness of up to HRC 26 may ~e ~olerated for certain tubular goods, but only if adequate per~ormance is verified with a sulfide stress cracking test, a procedure necessitating additional expense. Therefore, it is desirable to obtain a -hardness of HRC 22, it being understood that this ~lgure may be the average of several tests, as long as the maximum HRC of a specimen does not exceed 23 or 24.
In many instances, a hardness of H~C 22 maximum for steel and welds thereon can be obtained by heat treatiny the material or apparatus in question in a furnace , but in other instances this is impractical, such as where the apparatus is ass~mbled and then welded, the assembly includi.ng components sucll as elastomeric seals, which are destroyed by the high furnace ~emperatures. Likewise, even in the absence of seals, there may be finished surfaces in the apparatus which ~ould be damaged by prolonged exposure to high temper-.atures necessitated by furnace trea-tment. Thus, there presently exists a problem in the production of some material or asse~bly of apparatus to the NACE Standard.
SU~L~RY OF T~IE INVE~TIO~I
The presen~ invention comprises a method A or thermally treating low alloy steel and welds thereon lusing electrical induction heating, which heating is monitored.using a radiation pyrometer or other suit-able means, th~ induction heating being applied oly to t~e specific area to be stress relieved in a second post-weld heat tre2tment at a temperature approaching the critical point of the treate~ material for a relatively hrief period of time. By employing such a method, seals and other destructible nonmetallic elements as well as finished surfaces in relatively close proximity to the heat treated areas are permitted to remain at a low enough temperature to ensure their integrity.
BRIEF DESCRIPTION OF THE DRAWINGS
The present in~ention will be more readily understood with reference to the description hereafter set forth, in conjunction with the accompanying d~awings wherein~
~lG. 1 is a schematic of an apparatus employed in the practice of the present method, with an apparatus to be hea~ t.reated oriented in position.
FI~. ~ is a drawing depicting the microstructure of the heat arfected zone of the base metal adjacent a fusion ~eld, such as could be found on the apparatus to be treated in FIG. 1, prior to heat treatment.
FIG. 3 is a drawing depicting the microstructure of the heat affected zone of FIG. 2 after heat treat-ment by the method of the present invention.
DESCRTPTION OF TH~ PR~FF,RRED EMBODIMENT
Stress-relief o~ microstructures in metals by heating in a furnace is common in many industries.
iGenerally, the heating takes place over a relatively S long period of time, measured in hours. Induction heating, on the other hand, is usually effected in mi~utes or seconds. Certain variables result in different times and temperatures for obtaining equivalent results from the two types of heating, the la relationship of which has been expressed in the following e~uation:
TI (C + log tI) = TF (C ~ log tF) where TF and tF are the furnace temperature (in degrees Rankinel and time, respectively, known to produce a ~iven hardness ;n a metal, and TI and tF are the equiv-~lent temperatuxe (in degrees Rankine) and time needed to produce that hardness ~ith induction heating. C is a constant which may be empirically determined ~or a given m~tal, and is approximately 15 for steels with 0O25 to 0.50% carbon content. The figures obtained from the above ec~uation for tim~ and tempera-ture to be employed in induction heating of a specific metal are, of course, further refined by empirical testing, FIG. 1 schematically depicts an induction heating apparatus designated generally at 10. Induction heating apparatus 10 comprises generator a~d load coil transformer 12, to which inner induction coils 14 and outer induction coils 16 are connected. A
suitable generator is a Lepel lOOkw generator, Model T-loo-3kcrL~ Precise temperature control at the wor~piece 30 is achieved by use of radiation pyrometer/three mode proportional controller 18, which controls the generator, varying the outpu-t thereof i~ response to the input of infrared sensor 2C, whîch senses the temperature on the workpiece 30. A
suitable pyro~eter/controller is the IRCON, model 6-22F15-01-000-1/620~ ~ portion of tubular workpiece 30 is shown disposed between the inner induction coils 14 and the outer induction coils 16. The t~o coils are employed to avoid a temperature gradient in the T~ork-piece 30, and further temperature uniformity is achieved by mounting the ~orkpiece 30 on a rotating jig~-(not shown~, whe:reby the workpiece 30 is rotated about its longitudinal a~is during the induction heatins procedure.
For t~e sake of illustration, and not by way of limitation, the workpiece 30 shown is a portion of a Halliburton Services F. O. Multiple Stage Cementer, described on page 3347 of ~alliburton Services Sales and Service Catalog Number 40. This type o~ workpiece poses several impediments to furnace stress-relief, namely the presence of elastomeric seals 32 and of finished surface 34. Fusion weld 36 is to be stress relieved with no damage to surface 34 or elastomeric seals 32.
~ The F. O. Multiple Stage Cementer comprises metallic parts of AISI (American Iron and Steel Institute) Grade 4140 low alloy steel. The elastomeric seals 32 have a ma~imum temperature destruction tolerance of 325 F. Finished surrace ~4 will begin to scale at 1050 F. As it is necessary for the opera-tion of the F. O. Multiple Stage Cementer that sleeve ~6 slide within finished surface 34, scaling on surface 34 may result in an inoperative tool. I
there were no seals or finished surfaces, the workpiece could be stress-reIieved by furnace heating for a prolonge~l period at 1300F. However, as the assembled Cementer does include these items, a furnace treatment is impossible. The following procedure, unlike a urnace heat treatment, will result in an assembly and 0 welds thereon with the desired hardnes5 characteristics.
Prior to assembly, the metallic parts o~ the F. O.
Multiple Stage Cementer, comprising fine grain seamless, hot finished and normali~ed AISI Grade 4140 low alloy steel, are subjected to stress-relief heating in a ~5 furnace at 130G F for several hours. Subsequently .
the desired finished surface 34 is-machined, and the tool is assembled with elastorneric seals 32. A-t that point, fusion weld 36 is made by, for example, a submerged arc welding process (SAW), with a preheat at the weld point of 700 F, an-interpass temperature of 650 F during t~e welding process, followed by cooling to below the Ms te~perature, the temperature of which martensite begins to form,which is approcimately 500 F.
The interpass ternperature lowers the cooling rate of the metal to an acceptable level, minimizing residu.l stresses in the microstructure. Subsequently, the weld is subjected to a first postheat at 800F. A
low alloy steel electrode comprising less than 1%
nickel ~Ni) is employed in the SA~ process, being an r~r~
ASME (American Society of Mechanical Engineers) SF A5.28 ER80S-D2. Such electrodes are available from Union Carbide Corporation Linde Division as Linde 83, or Page Dlvision of Acco as Page 18. The weld flux employed may be a neutral Fxxx, classes per AWS (American Welding Society) A5.17-76 or A5.23-77. A sui.table flux is Lincoln Electric 880 Flu~.
5ubse~uent to the first postheat, the workpiece 30 is coole~ and placed on a jig, which orients the work-piece 30 between inner induction coils 14 and outer inductiorl coils 16 of induction heating apparatus 10.
The workpiece 30 is slowly rotated on the jig about its axis between the two coils during which rotation the weld 36 is then subjected to a second postheat at substantially 1340F for 900 seconds. The temperature ls measured by sensor 20 at t~e metal surace of the workpiece 30. Radiation pyrometer~
three mode proportional controller 18 maintains this temperature in an accurate manner by controlling the output of generator and load coil transformer 12 to induction coils 14 and 16. ~s 1340 F is close to the critical temperature of 135~F for AISI Grade 4140 low alloy steel, it is imperative that the stress-relief temperature ~e closely monitored to avoid a supercritical temperature in the metal.
Actu21 empirical testing of AISI Grade 4140 specimens welded and subjected to a second postheat according to these specifications has shown the hardness of the heat-affected zone (HA~) in the base metal adjacPnt the weld to under HRC 23 after stress- ~--relief. Test specimens were stressed to lO0~ of their txansverse tensile yield strength, with the maximum stress loc~ted across the fusion zone of the weld, and subjected to a 5% sour brine corrodent at atmospheric pressure at 65F temperature for 30 days.
All speclmens resisted sulfide stress cracking for the 30 day period.
Re~ering to FIGS. ~ and 3 of the drawings, which are representative of the microstructure of the HAZ of base metal adjacent a weld at 200 x magnification on an F~ O. Multiple S-tage Gementer, it can be seen in FIG. 2 that there was a modera-tely stressed microstructure in the HA2 after the first post-weld heating, comprising martensite as well as bainlte, the latter of which appears as groups of needle-like structures; FIG. 3, depicting the HAZ adjacent the weldment after the second postheat, shows a much more refined grain structure in the HAZ, with attendant lowered stress level. The HAZ
har,lness was reduced from HRC 29 measured in FIG. 2, to HRC 20 measured in FIG. 3. During the stress relief-process, the maximum temperature at g.5 inches from the ~eld alony the outer case of the F. O. Multiple Stage Cementer was 295F, belo~ the destruction temperature of the elasto~eric seals 32, and well below scaling temperature for finished surface 34.
It should be noted that the preheat employed in the SAW process contributes to the success of the subsequent second postheat as it enhances the formation of bainite ~0 (designated as B in FIG.2) along with the martensite of the microstructure, thus reducing the initial hardness of the HA~.
It may also be noted that the temperatures and times given in the above illustration are variable to a certain ~5 e~tent for the desired results. For e~ample (again assuming AI5I Grade 41~0 low alloy steel), a preheat as low as substanti~lly 675F or as high as substantially 800F may be employed, with acceptable results. The higher prehea~ temperature of 800Y will result in less martensite formation and a softer post-weld micro-structure, but the lower temperatures will produceacceptable results. Likewise, a first postheat o substantially 775F to substantially 900F may be utilized. The first postheating is the least critical of the heating steps, being used to drive off monatonic hydrogen ~rom the weldmen-t. Similarly, the interpass temperature of 650F is 2n approximation, the important consideration being the reduction of the cooling rate at the weld area to an acceptable area.
It should also be understood that the critical temperature given for AISI Grade 4140 low alloy steel maX ~ary appreciably from 1354 F, depending upon the exact chemical composition of the bar stock obtained.
The critical temperature may range from 1340F to 1395F, thus allowing some minor variation of the induction ~0 ~eatin~ postheat temperature. For example, a minimum time of 350 seconds at substantially 1335F may be employed, and acceptable results obtaired. The second posthea~ temperature of 1340F may also be modified down~ard somewhat, for example to substantially 1310F, for a tii~e of substantially 900 seconds. Below this temperature, the time for heating becomes too lony rrom an economic standpoin~. Furthermore, it is desirable to maintain hardness in the ran~e of HRC
18-22, to pr~serve the mechanical properties of the weld material and surrounding base metal in the HAZ, which too long a heating time may prevent. Equip-.
ment use~ in sour gas in the petroleum industry must meet the API (~nerican Petroleum Institute) L-80 tensile requirements, as well as the L-80 hardness 1~ requirement of HRC ~3 maximum. The minimum acceptable tensile yield strength is 80,000 psi.
Reduction of hardness to below substantially 18 HRC
will result in failure to meet this requirement~
While it may not be necessary for the weldment itself 1~ to meet this requirement, if the hardness in the HAZ
is reduced below substantially 18 HRC, the base metal in the HAZ will fail at too low a stress.
It should also be noted that the use of tempera-tures in ~he second postheat below substantially 1310F
in the instances where seals, finished surfaces or other destructi~le elements are present~ may result in damage to those elements due to the necessarily longer time exposure at what must still be a high temperature, to achieve the desired results.
~hile reference has been made to the specific example of treating AISI Grade 4140 low alloy steel, ,~
it should be understood that the present invention is not so limited. Other low all~y steels, as well as some carbGrl steels, are susceptible to treatment in a similar fashion.
It is thus apparent that the present invention comprises a new and different method for heat treating metals which will be subject to a sour gas environment ~hen furnace heating is unworkable. Additionally, the procedure may be accomplished in a very short lQ period of time, with high quality control and uni~ormity.
The ~ethod, of course, while illustrated with respect to welds and surrounding H~Z in base metal, is not so limited; rather it is applicable wherever precise, localiz.ed heat treating to relieve stress in the micro-structure of metals is desired. It will be readily apparent to one of ordinary skill in the art that modifications, additions, and substitutions to the disclosed method can be made, the invention being limited only by the spirit and scope of the appended ~laims.
p ..
Claims (6)
1. A method of achieving a microstructure hardness of at least substantially 18, and no more than substantially 23 on the Rockwell "C" scale in the heat affected zone surround-ing a weld in AISI Grade 4140 low alloy steel, comprising:
reducing the temperature of said heat affected zone to less than substantially 500°F; and locally heating said heat affected zone at a sub-critical temperature of at least substantially 1310°F for at least substantially 350 seconds.
reducing the temperature of said heat affected zone to less than substantially 500°F; and locally heating said heat affected zone at a sub-critical temperature of at least substantially 1310°F for at least substantially 350 seconds.
2. The method of claim 1, wherein said subcritical temperature is at least substantially 1335°F.
3. The method of claim 1, wherein said time of at least substantially 350 seconds is no more than substantially 900 seconds.
4. The method of claim 1, wherein said time is sub-stantially 900 seconds.
5. The method of claim 1, wherein said subcritical temperature is substantially 1340°F and said time is sub-stantially 900 seconds or less.
6. A method of stress-relieving the heat affected zone surrounding a weld in low alloy steel while maintaining a microstructure hardness of at least substantially 18 and no more than substantially 23 on the Rockwell "C" scale in said heat affected zone, comprising:
induction heating said weld and surrounding heat affected zone at a subcritical temperature of between sub-stantially 1310°F and substantially 1340°F for a period of between substantially 350 seconds and substantially 900 seconds.
induction heating said weld and surrounding heat affected zone at a subcritical temperature of between sub-stantially 1310°F and substantially 1340°F for a period of between substantially 350 seconds and substantially 900 seconds.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000462087A CA1190457A (en) | 1980-07-07 | 1984-08-29 | Method of heat treating metal |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16673980A | 1980-07-07 | 1980-07-07 | |
| US166,739 | 1980-07-07 |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000462087A Division CA1190457A (en) | 1980-07-07 | 1984-08-29 | Method of heat treating metal |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184099A true CA1184099A (en) | 1985-03-19 |
Family
ID=22604517
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000380448A Expired CA1184099A (en) | 1980-07-07 | 1981-06-23 | Method of heat treating metal |
Country Status (8)
| Country | Link |
|---|---|
| AU (1) | AU7262281A (en) |
| BR (1) | BR8104297A (en) |
| CA (1) | CA1184099A (en) |
| DE (1) | DE3125450A1 (en) |
| GB (1) | GB2079659B (en) |
| IT (1) | IT1137291B (en) |
| NL (1) | NL8103201A (en) |
| NO (1) | NO812301L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2146435B (en) * | 1983-09-07 | 1987-02-18 | Atomic Energy Authority Uk | Temperature control during annealing |
| DE102006033299A1 (en) * | 2006-07-17 | 2008-01-24 | Rolls-Royce Deutschland Ltd & Co Kg | Process for repairing a BLISK compressor rotor |
| DE102007014637A1 (en) * | 2007-03-23 | 2008-10-02 | Ab Skf | Edge layers inductive heating device for e.g. track element of taper roller of taper roller bearing, has induction heads formed in extending manner, and movable concerning their radial distance to principal axis of workpiece |
| DE102008014165A1 (en) | 2008-03-14 | 2009-09-24 | Ab Skf | Apparatus for heating and method for heating |
| DE102010044799A1 (en) * | 2010-09-09 | 2012-04-26 | Benteler Automobiltechnik Gmbh | Multipart stabilizer, has two stabilizer components material-conclusively coupled with each other by thermal joining and circulating joining seam, and stabilizer profile manufactured as tubing profile and/or profile made of full material |
-
1981
- 1981-06-23 CA CA000380448A patent/CA1184099A/en not_active Expired
- 1981-06-27 DE DE19813125450 patent/DE3125450A1/en not_active Withdrawn
- 1981-07-01 GB GB8120379A patent/GB2079659B/en not_active Expired
- 1981-07-03 NL NL8103201A patent/NL8103201A/en not_active Application Discontinuation
- 1981-07-06 BR BR8104297A patent/BR8104297A/en unknown
- 1981-07-06 NO NO812301A patent/NO812301L/en unknown
- 1981-07-07 IT IT22798/81A patent/IT1137291B/en active
- 1981-07-07 AU AU72622/81A patent/AU7262281A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| IT8122798A0 (en) | 1981-07-07 |
| NO812301L (en) | 1982-01-08 |
| DE3125450A1 (en) | 1982-03-18 |
| BR8104297A (en) | 1982-03-23 |
| NL8103201A (en) | 1982-02-01 |
| AU7262281A (en) | 1982-01-14 |
| IT1137291B (en) | 1986-09-03 |
| GB2079659A (en) | 1982-01-27 |
| GB2079659B (en) | 1985-05-22 |
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