CA1188963A - Method for producing steels having improved resistance to sulfide stress corrosion cracking - Google Patents
Method for producing steels having improved resistance to sulfide stress corrosion crackingInfo
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- CA1188963A CA1188963A CA000381289A CA381289A CA1188963A CA 1188963 A CA1188963 A CA 1188963A CA 000381289 A CA000381289 A CA 000381289A CA 381289 A CA381289 A CA 381289A CA 1188963 A CA1188963 A CA 1188963A
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Abstract
S P E C I F I C A T I O N
Title of the Invention:
METHOD FOR PRODUCING STEELS HAVING IMPROVED
RESISTANCE TO SULFIDE STRESS CORROSION CRACKING
Abstract of the Disclosure:
A method for producing steels having improved resistance to sulfide stress corrosion cracking (SSC), which comprises quenching low-alloy steel containing 0.05 to 0.35%
carbon, 0.01 to 0.30% silicon, 0.15 to 1.50% manganese and 0.005 to 0.10% aluminum with the balance being iron, from the austenite temperature zone so as to convert at least 90% of the steel to a martensitic one and then the steel in a temperature range of from 700°C to Ac1 transformation point for a period of time not longer than 300 seconds, or in a temperature range of from 680°C to 700°C for a period of time ranging from 10 to 300 seconds.
Title of the Invention:
METHOD FOR PRODUCING STEELS HAVING IMPROVED
RESISTANCE TO SULFIDE STRESS CORROSION CRACKING
Abstract of the Disclosure:
A method for producing steels having improved resistance to sulfide stress corrosion cracking (SSC), which comprises quenching low-alloy steel containing 0.05 to 0.35%
carbon, 0.01 to 0.30% silicon, 0.15 to 1.50% manganese and 0.005 to 0.10% aluminum with the balance being iron, from the austenite temperature zone so as to convert at least 90% of the steel to a martensitic one and then the steel in a temperature range of from 700°C to Ac1 transformation point for a period of time not longer than 300 seconds, or in a temperature range of from 680°C to 700°C for a period of time ranging from 10 to 300 seconds.
Description
Background of the Invention:
Field of the Invention:
The present invention relates to production of ste~l~ having a yield point in ~he range of fro~ 60 kgf/mm2 to 80 kgf/~m2 and improved resi~tance to SSC, and particularly relate~ to the principle for improvi~g resistance to such ~tre~ corrosion crackin~ in low-alloyed ~teel~O
Description of the Prior Arts:
It has been well known that pre~ence of hydrogen sulfi~e in fluids rom oil wells have great tende~cies to cause oil pipes through which the fluids flow more susceptible to SSC, which ha~ been imposing severe limitations on the use of high strength steels in th~se applicationæ in particular.
It is a general tendency in the oll indu~try that oil wells are drilled increasingly deeper, and 3teels having high strength ha~ been in steady demands for use i~ such en~ironments contain.ing a high concentration of hydrogen ~ulfide, and hence necessitie~ of i~proving ~h~ resistance of such ~teels to SSC in the~e ~nvixonment~ have ~een increasiny~ ~t i~
a~generally accepted concept that the susceptibility vf steels ~o 5SC increa~P~ as the strength increases.
To meet with the demands mentioned above, a uniformly tempered ~arten~ite ~tructure of ~teels having a y.ield point rang~ng from 60 to 80 ~gf~mm2 obtained by qu~nching and tempering has been considered to be most suitable~ and a ~teel composition containing approximately 1% chromium and 0.5 to 0.75% molybdenum has been regarded as necessary basis for sour service design. However, these conventional knowledges are applicable onl~r when the tempering is done for a long period of time as 0.5 to 1 hour, and are not applicable when the tempering is done in a short time as in an induction heating furnace, and the reason for necessity of the molybdenum has not been fully clarified yet.
Summary of the Invention:
It has now been discovered that even in the case of a short-time tempering an excellent resistance to the SSC
in high-strength steels in particular can be obtained if appropriate tempering conditions are selected.
It has also been found that an excellent resistance to the sulfide stress corrosion cracking can be obtained if the silicon content and the phosphorus content which is pre-sent as impurity in the steel are appropriately controlled and simultaneously appropriate tempering conditions are selected.
In accordance with the present invention, there is provided a method for improving sulfide stress corrosion crac~ing resistance of low-alloy steels, which comprises quenchin~ a low-alloy steel containing 0.05 to 0.35% carbon, 0.01 to 0. 303/o silicon, 0.15 to 1.50% manganese and 0.005 to 0.10% aluminum with the balance being iron, and unavoidable impurities, from the austenite temperature zone so as to convert at least 90% of the steel microstructure to a mar-tensite structure, tempering the steel thus quenched in a temperature range of from 700C to the Acl transformation point for a period of time not longer than 300 seconds, or in a temperature range of from 680C to not higher than 700C
for a period of time ranging from 10 to 300 seconds.
Preferably, the low-alloy steel used further contains at least one elemen~ selec-ted from the group con-sisting of chromium in an amount of no more than 1.5%, molybdenum in an amount of no more than 0.4%, boron in an amount of no more than 0.003%, titanium in an amount of no more than 0.03%~ niobium in an amount of no more than 0.05%, vanadium in an amount of no more than 0.1% and nickel in an amount no more than 6%~
According to a preferred embodiment of the invention, the phosphorus content which i3 present in the above steel composition is controlled in correlation with the silicon content' lanthanum may be added to the steel to eliminate adverse effects of the phosphorus content.
Brief Explanation of the Drawings:
Further features and advantages of the invention will become more readily apparent from the following des-cription of preferred embodiments thereof with reference to the appended drawings, in which:
Fig. l is a graph showing the sulfide stress corrosion cracking (SSC property) observed when Steel ~o. l in Table l is tempered. The numerical figures in the graph represent the tempering temperature, and the encircled numerical figures represent the tempering time in second.
Fig. ~ is a graph showing the sulfide stress corrosion cracking (SSC property~ observed when the steel shown in Table 3 is tempered.
Description of Pre~erred Embodiments~
Steel ~o. l having the chemical composition shown in Table 1 is completely hardened into a martensite structure and this martensite steel is tempered for a period of time ranging from lO to 300 seconds by induction heating and the ~e~
relation between the resistance to the SSC and the yield point is shown in Fig. 1. The SSC resistance is evaluated by the fracture strength ~f ~,in NACE) determined by a cons-tant strain rate test (strain rate : 10 6sec. 1) in NACE
solution having a pH value controlled between 3 and 4 (inclusive).
- 4a -~ i tS3 The con~tant ~train rate tea~ method ha~ been establishQd recently by ASTM STP665(1979), as a useful tool to evalua~e the susceptibilit:y o a metallic mater~al to either stress corro~ion cracking or SSC in a given environ-~t.
The test method ha~ bePn i~creasingly adopted in wide application~ for selecting steel materials for various purposes, and ha~ been found to provide good s::orrelation with the conv ntional constant-load ~est~3 and constant-strain tests.
~ he numerical figure~ in Fig. 1 repre~ent the t~mperin~ temperature~, an~ even with 10 ~econd tempering, it is shown that the test ~teel piece ails at af (in ~ACEi) > ay at 700C or higher, namely only after the ~teel is t~ally yield~d in a severe hydrvgen ~ulf ide environm~tl.
shown ~hat when the tempering time i~ not ~horter than 30 seconds~ ~he SSC resistanc~ is improved at 680~C
or higher . Thi~ is attributed f ir~tly to the f act that when the tempering is done at temperatures lower than 680C;
~he grain boundary embrlttlement is enhanc~d due to ~egregation of impuritie~ such as phosphoru~ at the grain boundarie3, and ~econdary thalt the high dislocation de~
due to the insuî f iciell~ tempering, and the f ine prec:ipita tes faciliate t~e hydrogen accumulation at crac:k fxont, thu~
promot~ng ~he SSC. When t~e temperlng is done at 68~C or highe~, the dislocatio~ den~i~y becomes ~uficiently low a~d th~ precipitat0s are unifor~ly disper~ed to reduce the grai~
bounda~y em~rit~lement, so that SSC i~ hard to oacur.
Meanwhile, wh~n thg tempering temp~rature exceeds 7S0C, the SSC re~istance tends to lower ,~gain~ Thls i6 due to the fact that as the t~mperi~g t~mperature exceed~ the Acl point of the ~teel, the ~tructure is partially converted to au~te-nl e by the reverse tran~formation, and thi austenized porti~n ~s transformed into martensi~e and baini~e during cool ng, thu~ inducing the hydrog~n embri~lement.
Ac~ording to the prasen~ invention, the ~mpering ~emperature is limlted to the range of rom 700-C to the Acl point in case the holding ~im~ ig not longer than 30 seconds and llmited to ~he range of from 6800C to the ~cl point in ca~e ~he holding time i~ 30 ~econds or lo~ger for ~h~ ahove reasons, It ls prefarable that the quenching is under a cond~tio~ which provide.s fully martensite structure, but presence of the other ~tructures not more than 10~ may be penmitted becau~e it has no tangible adverse efect on the SSC resi~ta~ce. ~hough there ~ 9 ~0 specîfic limitation on the austeni2i~y co~dltio~, it ~B preferable for austenite grains to be a~ fln~ a~ possible, because a finer austenite grain in general increa3es ~he resistance to SSC.
~ eason~ ~or th~ limitatiGn i~ ~he chemical composition of the ~teel~ ~o which ~he presen~ in~ention is applied will be explained b810w.
In order ~o maintain th~ strength level at a yield pvint ranging from 60 to 80 kgfm~2. 0.05 to O ~ 35% oarb~n and 0.15 to 1~5~ mangane~ are es~ential. Silicon is requtred in a~ ~mount vf at lea~ 0.01% for deox~dation of the steel, ~ 6 --and more tha~ 0~3~ on i~ not egpecially required. In Al-killed steels, 0.005 to 0.31.% aluminum is usually requiredO
In order to obtai~ fine au~tenite grains and to maintain the strength le~el in the range of from 60 to 80 kyf/mm2 (yield polnt), it is desirable ~o add at lea~t one of not larger than lo5% chromi~m, not larger than 0,4~ molybden~LI~ not larger than O.003~ boron, not larger than 0.03% titanium, not larger than 0.l% vanadium, a~d not larger than 6% nickel in addition to ~he above ba~ic ~teel compositionO It is al~o known that addition o~ not largar than 0~5~ copper, and not larger tha~ l.0% cobal~ are effecti~e to improve th~ SSC
re~istance, and therefor~, it may be advantageous to add the~e elements in th~ basic steel composition a~ defined above.
Fur~her ac~ording ~o ~he present invention, a~
mentioned hereinbefore; a ~mall amount of lanthanum i~ added to the steel to ~fficiently ix ~he pho8phoru~ content and pxevent the grain boundary cracki~g without danger of increased intervention of hydrogen into the steel 50 ~hat the excellent SSC property call be obtained.
The prese~ inventor~ have investig~ted the cri~ical phosphorus content at grain boundaries for pre~enting the integranular ~ulfide stre~ corrosion cracking t and have found that the pho~phoru~ co~tent mu~t be lowered ~o a8 to sati~fy ~h~ foll~wl~g condition~ determined by the inter~
rela~io~ am~g the ~ilicon and pho~phoru~ content~ an~ th~
te~pering tempexature~
[Si~ ~ 0~ 05) x lP3 ~ ~. û0375 when the tempering temperature i~ 700C ox higher ( lSi~ ~ 0.05) x lP3 < 0.00075 when the tempering temperature i~ 650 to 700C (exclusive) where~rl Si and P are in weight per c:ents ~ owever, i~ is practically very difficult and ~rery exp~n~ive to re~5uce the phosphorus content as above.
Mearlwhile, it ha~ been found that lanthanum is effectiv~ ~o lower the pho~phoNs content at grain boundaries because it E ixe~ pho~phoru~ as LaP, and the amo~mt of lanthanuin requ~ xed :for thi~ purpo~ed i~ determined by the ollowing conditioIl~; J on the l~a~i~ of.the fact t~lat lanthanum fixes about 1~4 . 596 P per 196 of lanthanum.
tPl - 1 ~ 3 _ 003~5 when the temperi~g te~nper~-4 . 5 ~;il +0 0 05 ture is 7 00C or higher lp] ~ I,al c~ 00075 wh}~n the t~pering tempera-4 o 5 lSil -tO. o5 ture is 650 to 7005:~ (exclusi~) wherein LR i~ express~d by weight per c~nt 5ince lanthanum is a strong sul~id~ ~orT~er as well a~; a strong oxide formQx, it i~ neces~a~y ~o fully de:3xide ~he steel prior to the addition of lan~ha3lu~n. In this connection it i8 desirable ~o add Ca and RE~A ~rare earth metal elemerlts) ~uch a~3 Ce to the steel beforehanLd.
._ ~
i3 Regarding the quenching/ it is de~irable to select the quenching conditions so as to convert at least 90-~ of the microstructure into martensite structure. There i5 no specific limitation on khe austeniæing condition during the quenching, hut it îs pxeferable that the austenit~
grains are as fine as possible, because a finer austenite grain in general reduces the tendency of the hydrogen embrittlement.
Description of Preferred Embodiments:
The present invention will be better understood from the following embodiments.
Example 1:
Staels No.2 and No.3 shown in Table 1 were tempered at various temperatures for 30 seconds, and the resultant SSC resistance axe shown in Table 2. Steel No.2 which is within the scope of the present invention shows a yield point xanging from 60 to 70 kgf/mm2 and a fracture strength ~
(as defined hereinbefore~ much higher than the yield point a~. Steel No~3 has a higher strength due to the ti~anium addition, but shows a satisfactory SSC resistance when treated according to ~he present invention.
Example ~:
As silown in Fig. 2, steel NoOl in Table 3 contains a relatively small amount of phosphorus as 0~01~, but ails to give a satisfactory SSC property. On the other hand, as illustrated by Steel NoO 2 in Table 3, a satisactory SSC
property of af in NACE > ay (20ne not susceptible to crackin~
is obtained wh~n 0.05% La is added to 0.2% Si steels, and ~s ill~strated by Steel No, 3 in Table 3 an excellent SSC property can be obtained when 0.03% La is added to 0.05% Si steels~
As i.llustrated by the above examples, an excellent resistance to the sulfide ætress corrosion cracking can be assured when lanthanum is added to the steels under the conditions definPd by ~he present invention.
Table 1 Chemical Compositions of Test Pieces (in weight per cent~
.
Steel No. C ¦ si ¦ Mn ¦ P ~ S Cr ~ Mo i Ti I -- r 1 0.13l 0.~5 0.50 0.010~ 0.002' 1.1 ~0.12 '0~02
Field of the Invention:
The present invention relates to production of ste~l~ having a yield point in ~he range of fro~ 60 kgf/mm2 to 80 kgf/~m2 and improved resi~tance to SSC, and particularly relate~ to the principle for improvi~g resistance to such ~tre~ corrosion crackin~ in low-alloyed ~teel~O
Description of the Prior Arts:
It has been well known that pre~ence of hydrogen sulfi~e in fluids rom oil wells have great tende~cies to cause oil pipes through which the fluids flow more susceptible to SSC, which ha~ been imposing severe limitations on the use of high strength steels in th~se applicationæ in particular.
It is a general tendency in the oll indu~try that oil wells are drilled increasingly deeper, and 3teels having high strength ha~ been in steady demands for use i~ such en~ironments contain.ing a high concentration of hydrogen ~ulfide, and hence necessitie~ of i~proving ~h~ resistance of such ~teels to SSC in the~e ~nvixonment~ have ~een increasiny~ ~t i~
a~generally accepted concept that the susceptibility vf steels ~o 5SC increa~P~ as the strength increases.
To meet with the demands mentioned above, a uniformly tempered ~arten~ite ~tructure of ~teels having a y.ield point rang~ng from 60 to 80 ~gf~mm2 obtained by qu~nching and tempering has been considered to be most suitable~ and a ~teel composition containing approximately 1% chromium and 0.5 to 0.75% molybdenum has been regarded as necessary basis for sour service design. However, these conventional knowledges are applicable onl~r when the tempering is done for a long period of time as 0.5 to 1 hour, and are not applicable when the tempering is done in a short time as in an induction heating furnace, and the reason for necessity of the molybdenum has not been fully clarified yet.
Summary of the Invention:
It has now been discovered that even in the case of a short-time tempering an excellent resistance to the SSC
in high-strength steels in particular can be obtained if appropriate tempering conditions are selected.
It has also been found that an excellent resistance to the sulfide stress corrosion cracking can be obtained if the silicon content and the phosphorus content which is pre-sent as impurity in the steel are appropriately controlled and simultaneously appropriate tempering conditions are selected.
In accordance with the present invention, there is provided a method for improving sulfide stress corrosion crac~ing resistance of low-alloy steels, which comprises quenchin~ a low-alloy steel containing 0.05 to 0.35% carbon, 0.01 to 0. 303/o silicon, 0.15 to 1.50% manganese and 0.005 to 0.10% aluminum with the balance being iron, and unavoidable impurities, from the austenite temperature zone so as to convert at least 90% of the steel microstructure to a mar-tensite structure, tempering the steel thus quenched in a temperature range of from 700C to the Acl transformation point for a period of time not longer than 300 seconds, or in a temperature range of from 680C to not higher than 700C
for a period of time ranging from 10 to 300 seconds.
Preferably, the low-alloy steel used further contains at least one elemen~ selec-ted from the group con-sisting of chromium in an amount of no more than 1.5%, molybdenum in an amount of no more than 0.4%, boron in an amount of no more than 0.003%, titanium in an amount of no more than 0.03%~ niobium in an amount of no more than 0.05%, vanadium in an amount of no more than 0.1% and nickel in an amount no more than 6%~
According to a preferred embodiment of the invention, the phosphorus content which i3 present in the above steel composition is controlled in correlation with the silicon content' lanthanum may be added to the steel to eliminate adverse effects of the phosphorus content.
Brief Explanation of the Drawings:
Further features and advantages of the invention will become more readily apparent from the following des-cription of preferred embodiments thereof with reference to the appended drawings, in which:
Fig. l is a graph showing the sulfide stress corrosion cracking (SSC property) observed when Steel ~o. l in Table l is tempered. The numerical figures in the graph represent the tempering temperature, and the encircled numerical figures represent the tempering time in second.
Fig. ~ is a graph showing the sulfide stress corrosion cracking (SSC property~ observed when the steel shown in Table 3 is tempered.
Description of Pre~erred Embodiments~
Steel ~o. l having the chemical composition shown in Table 1 is completely hardened into a martensite structure and this martensite steel is tempered for a period of time ranging from lO to 300 seconds by induction heating and the ~e~
relation between the resistance to the SSC and the yield point is shown in Fig. 1. The SSC resistance is evaluated by the fracture strength ~f ~,in NACE) determined by a cons-tant strain rate test (strain rate : 10 6sec. 1) in NACE
solution having a pH value controlled between 3 and 4 (inclusive).
- 4a -~ i tS3 The con~tant ~train rate tea~ method ha~ been establishQd recently by ASTM STP665(1979), as a useful tool to evalua~e the susceptibilit:y o a metallic mater~al to either stress corro~ion cracking or SSC in a given environ-~t.
The test method ha~ bePn i~creasingly adopted in wide application~ for selecting steel materials for various purposes, and ha~ been found to provide good s::orrelation with the conv ntional constant-load ~est~3 and constant-strain tests.
~ he numerical figure~ in Fig. 1 repre~ent the t~mperin~ temperature~, an~ even with 10 ~econd tempering, it is shown that the test ~teel piece ails at af (in ~ACEi) > ay at 700C or higher, namely only after the ~teel is t~ally yield~d in a severe hydrvgen ~ulf ide environm~tl.
shown ~hat when the tempering time i~ not ~horter than 30 seconds~ ~he SSC resistanc~ is improved at 680~C
or higher . Thi~ is attributed f ir~tly to the f act that when the tempering is done at temperatures lower than 680C;
~he grain boundary embrlttlement is enhanc~d due to ~egregation of impuritie~ such as phosphoru~ at the grain boundarie3, and ~econdary thalt the high dislocation de~
due to the insuî f iciell~ tempering, and the f ine prec:ipita tes faciliate t~e hydrogen accumulation at crac:k fxont, thu~
promot~ng ~he SSC. When t~e temperlng is done at 68~C or highe~, the dislocatio~ den~i~y becomes ~uficiently low a~d th~ precipitat0s are unifor~ly disper~ed to reduce the grai~
bounda~y em~rit~lement, so that SSC i~ hard to oacur.
Meanwhile, wh~n thg tempering temp~rature exceeds 7S0C, the SSC re~istance tends to lower ,~gain~ Thls i6 due to the fact that as the t~mperi~g t~mperature exceed~ the Acl point of the ~teel, the ~tructure is partially converted to au~te-nl e by the reverse tran~formation, and thi austenized porti~n ~s transformed into martensi~e and baini~e during cool ng, thu~ inducing the hydrog~n embri~lement.
Ac~ording to the prasen~ invention, the ~mpering ~emperature is limlted to the range of rom 700-C to the Acl point in case the holding ~im~ ig not longer than 30 seconds and llmited to ~he range of from 6800C to the ~cl point in ca~e ~he holding time i~ 30 ~econds or lo~ger for ~h~ ahove reasons, It ls prefarable that the quenching is under a cond~tio~ which provide.s fully martensite structure, but presence of the other ~tructures not more than 10~ may be penmitted becau~e it has no tangible adverse efect on the SSC resi~ta~ce. ~hough there ~ 9 ~0 specîfic limitation on the austeni2i~y co~dltio~, it ~B preferable for austenite grains to be a~ fln~ a~ possible, because a finer austenite grain in general increa3es ~he resistance to SSC.
~ eason~ ~or th~ limitatiGn i~ ~he chemical composition of the ~teel~ ~o which ~he presen~ in~ention is applied will be explained b810w.
In order ~o maintain th~ strength level at a yield pvint ranging from 60 to 80 kgfm~2. 0.05 to O ~ 35% oarb~n and 0.15 to 1~5~ mangane~ are es~ential. Silicon is requtred in a~ ~mount vf at lea~ 0.01% for deox~dation of the steel, ~ 6 --and more tha~ 0~3~ on i~ not egpecially required. In Al-killed steels, 0.005 to 0.31.% aluminum is usually requiredO
In order to obtai~ fine au~tenite grains and to maintain the strength le~el in the range of from 60 to 80 kyf/mm2 (yield polnt), it is desirable ~o add at lea~t one of not larger than lo5% chromi~m, not larger than 0,4~ molybden~LI~ not larger than O.003~ boron, not larger than 0.03% titanium, not larger than 0.l% vanadium, a~d not larger than 6% nickel in addition to ~he above ba~ic ~teel compositionO It is al~o known that addition o~ not largar than 0~5~ copper, and not larger tha~ l.0% cobal~ are effecti~e to improve th~ SSC
re~istance, and therefor~, it may be advantageous to add the~e elements in th~ basic steel composition a~ defined above.
Fur~her ac~ording ~o ~he present invention, a~
mentioned hereinbefore; a ~mall amount of lanthanum i~ added to the steel to ~fficiently ix ~he pho8phoru~ content and pxevent the grain boundary cracki~g without danger of increased intervention of hydrogen into the steel 50 ~hat the excellent SSC property call be obtained.
The prese~ inventor~ have investig~ted the cri~ical phosphorus content at grain boundaries for pre~enting the integranular ~ulfide stre~ corrosion cracking t and have found that the pho~phoru~ co~tent mu~t be lowered ~o a8 to sati~fy ~h~ foll~wl~g condition~ determined by the inter~
rela~io~ am~g the ~ilicon and pho~phoru~ content~ an~ th~
te~pering tempexature~
[Si~ ~ 0~ 05) x lP3 ~ ~. û0375 when the tempering temperature i~ 700C ox higher ( lSi~ ~ 0.05) x lP3 < 0.00075 when the tempering temperature i~ 650 to 700C (exclusive) where~rl Si and P are in weight per c:ents ~ owever, i~ is practically very difficult and ~rery exp~n~ive to re~5uce the phosphorus content as above.
Mearlwhile, it ha~ been found that lanthanum is effectiv~ ~o lower the pho~phoNs content at grain boundaries because it E ixe~ pho~phoru~ as LaP, and the amo~mt of lanthanuin requ~ xed :for thi~ purpo~ed i~ determined by the ollowing conditioIl~; J on the l~a~i~ of.the fact t~lat lanthanum fixes about 1~4 . 596 P per 196 of lanthanum.
tPl - 1 ~ 3 _ 003~5 when the temperi~g te~nper~-4 . 5 ~;il +0 0 05 ture is 7 00C or higher lp] ~ I,al c~ 00075 wh}~n the t~pering tempera-4 o 5 lSil -tO. o5 ture is 650 to 7005:~ (exclusi~) wherein LR i~ express~d by weight per c~nt 5ince lanthanum is a strong sul~id~ ~orT~er as well a~; a strong oxide formQx, it i~ neces~a~y ~o fully de:3xide ~he steel prior to the addition of lan~ha3lu~n. In this connection it i8 desirable ~o add Ca and RE~A ~rare earth metal elemerlts) ~uch a~3 Ce to the steel beforehanLd.
._ ~
i3 Regarding the quenching/ it is de~irable to select the quenching conditions so as to convert at least 90-~ of the microstructure into martensite structure. There i5 no specific limitation on khe austeniæing condition during the quenching, hut it îs pxeferable that the austenit~
grains are as fine as possible, because a finer austenite grain in general reduces the tendency of the hydrogen embrittlement.
Description of Preferred Embodiments:
The present invention will be better understood from the following embodiments.
Example 1:
Staels No.2 and No.3 shown in Table 1 were tempered at various temperatures for 30 seconds, and the resultant SSC resistance axe shown in Table 2. Steel No.2 which is within the scope of the present invention shows a yield point xanging from 60 to 70 kgf/mm2 and a fracture strength ~
(as defined hereinbefore~ much higher than the yield point a~. Steel No~3 has a higher strength due to the ti~anium addition, but shows a satisfactory SSC resistance when treated according to ~he present invention.
Example ~:
As silown in Fig. 2, steel NoOl in Table 3 contains a relatively small amount of phosphorus as 0~01~, but ails to give a satisfactory SSC property. On the other hand, as illustrated by Steel NoO 2 in Table 3, a satisactory SSC
property of af in NACE > ay (20ne not susceptible to crackin~
is obtained wh~n 0.05% La is added to 0.2% Si steels, and ~s ill~strated by Steel No, 3 in Table 3 an excellent SSC property can be obtained when 0.03% La is added to 0.05% Si steels~
As i.llustrated by the above examples, an excellent resistance to the sulfide ætress corrosion cracking can be assured when lanthanum is added to the steels under the conditions definPd by ~he present invention.
Table 1 Chemical Compositions of Test Pieces (in weight per cent~
.
Steel No. C ¦ si ¦ Mn ¦ P ~ S Cr ~ Mo i Ti I -- r 1 0.13l 0.~5 0.50 0.010~ 0.002' 1.1 ~0.12 '0~02
2 ~4 20 0.25 1.~0 0.011l O.
L o. ~5 ~ 25 0~010l o o~ 0.20 0.0 Table 2 Results of Constant Strain-Rate Ten~ile __ Tests in Oil and in NACE Solution .
~\ ¦ in Oil SolutionRemark~
ing~ ~
Cbndit~Qns\ I ~y I ~B ¦ ~f 650CI 70 1 75 68I S~eel No. 2 Comparative 680C~8 i 72 70Steel ~o. 2 Present ! Invention 710C ~6 , 70 68 Steel No. 2 Present , ¦ Invention il. _ I _ 650C 79 1 84 ¦ 71 Steel No. 3 Comparative 680C 78 ! 83 1 80 ! S~eel No. 3 Present i Invention 710C 74 7~ 76 S~eel No. 3 Presen~
Invention _ _ _ Tempered for 30 seconds a~, ~B~ af : in kg /mm Table 3 Chem.ical CQmpositions of ~est Pieces teel llo. ~ C I Si I Mnl P I S I -Ti I -~a I -Ca- !
_ 1 0.~10~2 1.2 0~0~l 0.G03 _ -2 0.210.2 1.2 0.0~ 0.003 _ 0O05 0~00~ ,
L o. ~5 ~ 25 0~010l o o~ 0.20 0.0 Table 2 Results of Constant Strain-Rate Ten~ile __ Tests in Oil and in NACE Solution .
~\ ¦ in Oil SolutionRemark~
ing~ ~
Cbndit~Qns\ I ~y I ~B ¦ ~f 650CI 70 1 75 68I S~eel No. 2 Comparative 680C~8 i 72 70Steel ~o. 2 Present ! Invention 710C ~6 , 70 68 Steel No. 2 Present , ¦ Invention il. _ I _ 650C 79 1 84 ¦ 71 Steel No. 3 Comparative 680C 78 ! 83 1 80 ! S~eel No. 3 Present i Invention 710C 74 7~ 76 S~eel No. 3 Presen~
Invention _ _ _ Tempered for 30 seconds a~, ~B~ af : in kg /mm Table 3 Chem.ical CQmpositions of ~est Pieces teel llo. ~ C I Si I Mnl P I S I -Ti I -~a I -Ca- !
_ 1 0.~10~2 1.2 0~0~l 0.G03 _ -2 0.210.2 1.2 0.0~ 0.003 _ 0O05 0~00~ ,
3 0.2~0.05 1.2 0.Dl ~ 0 02 ¦ 0.03 -_ ~ I
Claims (3)
1. A method for improving sulfide stress corrosion cracking resistance of low-alloy steels, which comprises quenching a low-alloy steel containing 0.05 to 0.35% carbon, 0.01 to 0.30% silicon, 0.15 to 1.50% manganese and 0.005 to 0.10% aluminum with the balance being iron, and unavoidable impurities, from the austenite temperature zone so as to convert at least 90% of the steel microstructure to a martensite structure, tempering the steel thus quenched in a temperature range of from 700°C to the Acl transformation point for a period of time not longer than 300 seconds, or in a temperature range of from 680°C to not higher than 700°C
for a period of time ranging from 10 to 300 seconds.
for a period of time ranging from 10 to 300 seconds.
2. A method according to claim 1, wherein the low-alloy steel used further contains at least one element selected from the group consisting of chromium in an amount of no more than 1.5%, molybdenum in an amount of no more than 0.4%, boron in an amount of no more than 0.003%, titanium in an amount of no more than 0.03%, niobium in an amount of no more than 0.05%, vanadium in an amount of no more than 0.1%
and nickel in an amount no more than 6%.
and nickel in an amount no more than 6%.
3. A method according to claims 1 or 2, wherein the silicon content and phosphorus content present as impurity are controlled so as to satisfy the following conditions:
when the tempering tempera-ture is 700°C or higher when the tempering temperature is 650 to 700°C (exclusive) wherein the La content includes O and P, Si and La are in weight %
and the steel is subjected to a short time tempering for not longer than 300 seconds in a temperature range of from 650°C to the Ac1 transformation point.
when the tempering tempera-ture is 700°C or higher when the tempering temperature is 650 to 700°C (exclusive) wherein the La content includes O and P, Si and La are in weight %
and the steel is subjected to a short time tempering for not longer than 300 seconds in a temperature range of from 650°C to the Ac1 transformation point.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9304480A JPS5719321A (en) | 1980-07-08 | 1980-07-08 | Improvement for sulfide stress corrosion cracking of low alloy steel |
| JPSHO55-93044 | 1980-07-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188963A true CA1188963A (en) | 1985-06-18 |
Family
ID=14071499
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000381289A Expired CA1188963A (en) | 1980-07-08 | 1981-07-07 | Method for producing steels having improved resistance to sulfide stress corrosion cracking |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5719321A (en) |
| CA (1) | CA1188963A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101418416B (en) | 2007-10-26 | 2010-12-01 | 宝山钢铁股份有限公司 | Yield strength 800MPa grade low welding crack sensitivity steel plate and its manufacturing method |
| CN102814630B (en) * | 2012-09-19 | 2013-06-05 | 南通超达机械科技有限公司 | Method for improving mold hardness of EPP foaming mold |
| CN105603315B (en) * | 2016-03-24 | 2017-07-18 | 攀钢集团攀枝花钢铁研究院有限公司 | A kind of hot rolling production method of V, Ti, Cr, Ni, Cu microalloy high strength steel |
| CN105624552B (en) * | 2016-03-24 | 2017-08-01 | 攀钢集团攀枝花钢铁研究院有限公司 | A kind of V, Ti, Cr, Ni, Cu microalloy high-strength steel and its smelting method |
| CN113403530A (en) * | 2021-05-22 | 2021-09-17 | 江苏铸鸿重工股份有限公司 | High-strength corrosion-resistant alloy steel forged circle and preparation method thereof |
-
1980
- 1980-07-08 JP JP9304480A patent/JPS5719321A/en active Granted
-
1981
- 1981-07-07 CA CA000381289A patent/CA1188963A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0127126B2 (en) | 1989-05-26 |
| JPS5719321A (en) | 1982-02-01 |
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