DE2720805C2 - Process for the production of work pieces from alloy steel - Google Patents

Description

is defined where Z "is the constriction of a specimen not electrolytically loaded with hydrogen and L ₁ . mean the constriction of a specimen loaded electrolytically mk hydrogen.

2. The method according to claim I, characterized in that that a steel of the composition:

0.15 - 0.30 ",, C.

0.1-0.5% Si.

0.5 - 1% Mn.

2-3% Cr.

0.25 - 0.5% Mon.

0.5-1% Ni.

0 - 0.1% V and / or 0 to 0.07% Nb.

Balance Fe and inevitable impurities
used and produces workpieces with a thickness of 25 to Ml mm

3 The method according to claim 1, characterized in that that a steel of the composition:

0.15 - 0.30% C.

0.1-0.5%, Si.

0.5 - 1.5% Mn.

1-2% Cr.
0.5 - KMo,

Balance Fe and inevitable impurities
and produces workpieces with a thickness of 20 to 50 mm.

4. The method according to any one of claims I to 3, characterized in that the cooling with takes place at a speed of 100,000 'CVh.

5 The method according to any one of claims 1 to 4. characterized in that the heat treatment After welding the workpiece, a third step for relaxation in a metallurgical egg ■ \ nLet the temperature be the same or a maximum of 20 C lower temperature.

(1 Use of workpieces produced according to the method according to any one of claims I to 5 for The invention relates to a method of the type required in the preamble of claim 1 and the use of the workpieces manufactured afterwards.

The invention is particularly applicable to steel workpieces with a very high yield strength up to about 930 MPa, either in hydrogen or in hydrogenated gases under pressure or in the presence of by chemical Reactions generated nascent hydrogen work, as is the case, for example, with workpieces, those of crack formation due to stress corrosion in liquid or practically saturated with hydrogen sulphide (H.S) Having to withstand media under pressure.

These steels are intended to be used in the manufacture of forged, rolled or welded workpieces can be used.

Rope has been tried for several years. To manufacture steels, which retain sufficient mechanical properties if those made from these steels Work pieces in a hydrogenated atmosphere or in the presence of nascent hydrogen. One actually had especially in the oil wells, an embrittlement of the steel and a risk of cracking of the Workpiece due to stress corrosion, especially in liquid or a significant proportion of hydrogen sulfide containing gaseous medium found. Therefore, the FR-PS 10 77 011 describes a steel for Manufacture of deep oil wellbore tubing. the particular have a certain aluminum content.

Although this research is quite old, it had to do with resistance to cracking in the present Steels developed by hydrogen have rather limited mechanical properties, and most importantly a yield strength not exceeding 640 MPa. Well, such mechanical properties are common to petroleum well pipes sufficient for other applications, e.g. B. Bottles for the transport of hydrogen under pressure, not sufficient. To obtain improved mechanical

V) see properties, such a steel must have a martensitic tempering structure, and so far it has been assumed. that a martensite structure with good resistance to stress corrosion would be incompatible in the presence of hydrogen ["Material test." I.

5-, (1959), No. I. Pages 3. 9. IO |. So it seemed impossible. Steels with high mechanical properties but still suitable for working in the presence of hydrogen to manufacture

Accordingly, it is known from Uj-PS 28 95 XM.

ho an unkilled steel in the preamble of the claim I mentioned / nsammenci / iint! hot 9? s to I 100 (to austenitize, quench and then anneal at 725 to X (Kl C. but a structure is obtained that is on a leash

_h -, n uniformly in the Fcrritnialrlx verioili -.-. izlohulisiert Karhldtcilchcn is composed.

Finally Is from the FR-PS ?! (> (> 5X ^ cm procedure which in the preamble of claim I \ <> rausi: esctz-

th type known, with the Ausienislerungs- and event temperatures ^ n 800 to 1100 C or 625 to 750 "C are used and the quenching is only as fast is carried out so that a bainite structure is produced. The workpieces produced in this way have a maximum yield strength of 687 MPa and a tensile strength of 853 MPa.

Despite the above-mentioned opinion, which is generally widespread in specialist circles, that a martensite structure with a good Resistance to stress corrosion in the presence of hydrogen was incompatible the applicant researches to create chairs with improved mechanical properties at the same time and the suitability for use in the presence of hydrogen.

The invention is based on the object of providing a method of the prerequisite in the preamble of claim I. Kind of evolving like that. that workpieces with higher values of the yield point and tensile strength and at the same time good resistance to cracking due to stress corrosion in the presence of hydrogen are available.

According to the invention, this task is carried out by the im characterizing part of claim 1 specified features solved.

Surprisingly, it has been shown that a deterrent over the critical martensiiischen speed and a careful determination of the minimum tempering temperature Yield limit values and tensile strength wedge values at the same time in the stressed area in the finished workpieces, which are far above those according to FR-PS 21 66 585, and a very low degree of embrittlement enable.

Refinements of the method according to the invention are characterized in subclaims 2 to 5.

The subject of the invention is also in the Unier claim 6 claimed use of the workpieces produced according to the invention.

The invention will now be described on the basis of several non-restrictive examples and the single figure. die grapi,; sch as abscissa the tempering temperature in C and as ordinate the yield point R, in MPa and den Shows degree of embrittlement F in% and reproduces the curve of corresponding curves for steels according to the invention.

Steels were made with different compositions, which were adjusted within very precise limits, in order to form sheets of different thicknesses between 25 and 60 mm. A certain number of test pieces were made from each steel. which has been subjected to the heat treatment defined above, the tempering temperature being within the specified limits. varied. The test pieces were subjected to an embrittlement test by cathodic hydrogen according to the following method: v *

Tensile test samples are placed as cathodes in an electrolysis system with acidified water (solution with 10% pure hydrochloric acid); the calhodic cavity protects the sample against corrosion; on the other hand, nasal hydrogen is released on the upper surface of the sample w. Part of this nascent hydrogen penetrates into the metal. After 48 hours of such a charge, the sample is broken in the tensile test, and its lacing! Heim Bruch becomes hereditary with the infiltration of a comparative prediction, which was not swirled into a milk load with ^tr "hydrogen"'Hniirunu' ki with W aterOfl bulking l'rohe less than that of the comparison sample (ductility loss of the metal due to hydrogen). A degree of embrittlement by hydrogen is defined with the formula

Z-- - Z.

where Z, “the constriction of the unloaded comparative sample and Z, the constriction of the loaded sample. The greater the F % , the more susceptible the metal is to being embrittled by the hydrogen.

It can be assumed that the degree of embrittlement to achieve a satisfactory reverberation is not 30 " may exceed which value is apparently variable as a function of the conditions of use.

One of the features of the invention is based above all on the fact that certain compositions have been defined for which the curve representing the degree of embrittlement depending on the starting temperature shows a sharp drop at about 600 ° C. such as _: .; E. that from a fairly precise tempering temperature, which can be determined from WO C., the degree of embrittlement fell to a satisfactory value in the order of magnitude of 25 ". and remained at this level up to the transition point Λ. The only figure shows the F- and R, curves for the steels according to the invention The curves drawn for each exact composition would have the general shape of the curve types shown in the diagram.

Thanks to systematic embrittlement tests, you can do so define a minimum tempering temperature from which the degree of embrittlement is satisfactory.

Since the yield point R ,, as a function of the tempering temperature up to the transition point A, ■ ·. it is possible to reduce the tempering temperature within these limits to choose which allows to obtain the necessary mechanical properties. However it is. ever more one increased mechanical properties' .inter Aims to limit the tempering temperature, all the more important to control the degree of embrittlement, which can become unacceptable in a very narrow temperature range can.

In addition to this specification of the tempering temperature, there is the need to preserve a martensitical structure thanks to an extremely rapid cooling, which in any case must be above the critical speed of martensllic deterrence. In general, cooling is carried out at a rate of the order of 100,000 ⁰ CVh.

Up until now it was thought that it was impossible. a Niartensitic structure to be used in the presence of hydrogen, since such steels can break spontaneously under relatively low loads. However, the applicant arrived at this result by precisely adjusting the contents of the various steel constituents. < ⁽ⁱ e apparently react to each other.

It has been so determined to be used in steel rather narrow limits inside which is however sen two steel can be defined ^f miilien.

In the first case, the steels have a chromium content of 2 to .V \ and contain vanadium and / or niobium. Their composition is as follows
0.15 (i.30 'C.
0.1 0.v> SI.
0.5 I- Mn.
1. &Quot; ■ Cr.

11.25 0.5 ■ Mon.

• 1.5 I ¹ ·. Ni.

0 0.1 N. Y and / or his Ο.ΙΓ Nb.

Resl lc and unavoidable impurities.
This steel can now be used to manufacture workpieces with a thickness ranging from 25 to 60 mm.
The eradicating chairs were made:

Hey i spie I I

Is samples were made from a steel that is a Sheet metal with a thickness of M) mm hildelc Lind I gcw ichtnia-UiB) the following composition:

(1.23 "C 0.271 Si. 0.7 .li Mn. 0.77», \; | _ i, 7.V "Cr. 0.34% Mo. remainder Fe and modest yeast-impurities.

The critical martensitical speed of this steel is 17,000 (7h (/ between SsO and 600 (I. which means that a martensitic quenching in the core is a! IlcL'h ¹ ; to / u 60 πιπί thickness '.' Den ein.es kuivlrmitrri- .ils up to 9s mm diameter /ulill.lt.

This steel was subjected to the following heat treatment, which gave it <. \. T ·· Martensius lie.

i step

\ usienitisieriing at a temperature of 875 "('during 1 h. then cooling in water (quenching with about UKIOf) O CYh ι

? .. Schriti:

Tempering at graduated temperatures from 600 to "00 C for 1 hour.

The structure of the steel treated in this way consists of an occasion martensli. the one from glowing. fine and is formed regularly in a matrix of free ferrite divided carbides. This deluge is made by etching 'Int a solution of picric acid in alcohol clearly visible ocmpower.

Treated like this: Steel was subjected to the embrittlement -Ii ^ "by kaihodic hydrogen to the top subject to the method explained.

\ ^H a tempering temperature wm 610 C the comparison pT ^ '\ lung is satisfactory degree, but it is in practice · .or / u / ieher ,. choose a temperature of 620 C / u.

The mechanical properties are then as follows: Yield strength R = 765 MPa

Tensile strength ^: -it R. = 883 MPa

1 in ^ cord /. ■ = 67>

Impact strength KCA '-20 f. "= 154 J / _C m ^!

for the same act of deterrence. However, with tempering limited to 600 ° C. , the mechanical properties would be changed little (R "=" 85 MPa). However, a degree of embrittlement F above 80 ° would have been obtained, i.e. a very unfavorable degree of embrittlement.

On the other hand, one poses. when a steel of the same composition is subjected to a heat treatment which does not allow a martensite structure to be obtained. 7. B. austenitizing at a temperature of ¹ ^ 10 C for 1 h with subsequent cooling at a rate of the order of 3000 C / h and finally, as above, tempering at temperatures graded from 600 to 700 = C during 1 h. states that the tempering temperature required to obtain a satisfactory degree of embrittlement is 650 ^: C. however the mechanical properties are then much lower:
Yield strength R ₁ = 640 MPa

Z.ugl'esligkell R "7S < Ml'a

1 inschnürunu Z '2

KCΛ ' L 20 C 225 J'cm''

In the case of this steel, one notices that the essential requirement is an increase in the yield strength by 125 MPa while at the same time maintaining a good resistance to embrittlement due to water spray Adjustment of the composition and the heat treatment made possible
in

Example Il

Fs were pi..hen from a steel following! Weight composition produced
i> 0.1X5 C n.225'i. Si. 0.605> Mn. o.Mio Ni, 2.3- (r. 0.340t mol. O.OsOi Y. remainder Fe and unavoidable Y-impurities

The critical speed of martensitic action is 65 0OO CIi. which the feeling of a : o martensltischen Ciefiiuc · - in the K: rn of a sheet up to 20 mm thick or a round material up to 45 mm in diameter / uläl.lt.

Diener steel has undergone the following heat treatment unlerworlen:

^: 'I. step:

Austenitization at a temperature of ¹ MO C would take ml / h. Subsequent cooling in <k Grolk order v <, r. 100,000 CVh.

in 2 step:

Graduated Anlallhoharullunaen from 600 to 700 C ι 1 h>

The structure is a -NnLissmartensite.

One observes that 1 is the lowest event temperature. j ·) ah which achieves a satisfactory degree of embrittlement. 610 C is. but it is advisable to choose a minimum temperature of 620 C. The mechanical properties are then as follows:
Yield strength R. = ⁽ »io MPa

Jd tensile strength R .. - ΐη · '· 0 MPa

Constriction Z ^ = ■> "

Impact strength KC · '^ - 20' C = Ί52 J / cm "

For the same quenching treatment, but ^{tempering limited to 1} ° C, the degree of embrittlement due to hydrogen is 10VH with a value of the yield strength of 945 MPa. which is very inconvenient.

Example III

Samples were made from a steel of the following chemical Weight composition produced '

0.260 "C. 0.225% Sl. 0.680 ^ Mn. 0.82O ^ Ni. 2.49. Cr. 0.350% Mo. 0.060% V. remainder Fe and inevitable Y'er-5i impurities.

The critical martensite quenching speed is 20 500 ⁼ C / h. which allows a martensite structure to be obtained inside a sheet metal up to 57 mm thick or in a round material up to 90 mm in diameter.
This steel was subjected to the following heat treatment:

1st step:

Austenitization at a temperature of 910 ⁵ C for 1 hour, then cooling of an order of magnitude

of 100,000 = C / h.

2nd step:

Tempering treatments graded from 600 to 700 ^{c C (1}

The structure is an analogue type

Effort observed dall the / in order to echo a satisfactory Degree of scorching required tempering tempera-IIir 625 C is

The mechanical properties slml then loigciiiic. ^: Yield point R ₁ . ■ -: 9.12 Ml'a

/ ugfestlgkcit R "= 10.10 Mi'a

! ■ insi.hr ,, · ung / ■ = 64 \.

Impact strength KCV - ■ || .ij / cnr

for the same horror treatment. However, ^{tempering limited to ln} (100 ° C) is the initial ridge due to hydrogen 100> at a yield point value of ¹ MPa, which is very unfavorable.

Example IV

Samples of a steel were made of the following chemical Weight composition made:

0.250 C. 0.245% Sl. 0.720 'Mn. 0.8.15 '\ Ni. 2.46 '* Cr. 0.145% Mon. 0.060% V. Remainder Ie and, n \ ermeUlllchc conditions. 2 <i

The critical market quenching speed is 2100ITCVh. which allows the maintenance of a human lie in the core of a sheet up to 55 mm thick or a round material up to 85 mm in diameter. 2i

This steel was subjected to the following heat treatment:

I step:

During cooling at a temperature of 910 ° C I h. then cooling in the order of 100,000 "CVh.

2nd step:

Tempering treatments graded from 600 to "Ό0 C (1 hl.

The lie is an occasional martensite.

It has been observed that the foremost a satisfactory Degree of embrittlement required tempering temperature is 620 C.

The mechanical properties are then as follows: w Yield strength R, = 932 MPa

Tensile strength R.,. = 1060 MPa

Constriction Z = 64%

Impact strength KCV = 118J / cm ²

■ 4t

For the same quenching treatment. however, with a tempering limited to 600 ° C, the degree of embrittlement is by hydrogen 80% at a yield point of 1005 MPa. which is unfavorable.

A second steel group was also determined with a chromium content of 1 to 2% and a molybdenum content from 0.5 to 1%. Their composition is as follows:

0.15-0.30% C,

0.1-0.5% Si, 0.5-1.5% Mn.

1 - 2% Cr,

0.5 - 1% Mon.

Balance Fe and inevitable impurities.
For example, the following steels were produced:

Example V

Samples were made from a steel of the following chemical weight composition:

0.257% C, 0.235% Si, 0.665% Mn. 0.080% Nl, 1.50% Cr, 0.750% Mo, the remainder Fe and unavoidable impurities.

The critical speed of this M.lrtensltahschic ^l Suhl 9.1 500 "(Vh, which up to 2.1 mn 'thickness or a Rundmaterlals zuliißt obtaining a niartensülschen Gcfüges in the core of a sheet up to 40 mm diameter.

This steel was subjected to the following heat treatment:

1st step:

Austenitizing at a temperature of 910 "C during I h. then cooling in the order of magnitude of HIO (IOO CVh.

2 step:

\ on 600 to 700 "C graded special occasions Il hl

The structure is an occasional martensite.

It was observed that to obtain a satisfactory Degree of embrittlement required tempering temperature is 620 C.

The mechanical properties are then as follows: Stretched ounce R, - 920 MPa '

Tensile strength R ". = 1020 MPa

Constriction /. % = 65 ¹ V,

Impact strength KCV + 2 <> C = 137 J / cnr

For the same quenching treatment. However, with an annealing limited to 600 "C, if the mechanical properties are little changed (R,. = 990 MPa). the degree of embrittlement in the order of magnitude from 45'V. what is not very cheap.

Example Vl

Samples were made from a steel with the following chemical weight composition:

0.255% C. 0.270% Si. 1.24%, Mn. 0.10% Ni. 1.49% Cr. 0.765% Mo. balance Fe and unavoidable impurities.

The critical Martensitabschreckgeschwindlgkeit is 24OOO ^c C / h, Jie obtaining permits a mancnsltischen Ciefüges in the core of a sheet thickness to 50 mm or a Rundmaterlals up to 80 mm diameter.

This steel was subjected to the following heat treatment:

1st step:

Austenitizing at a temperature of 910 ° C during 1 h, then cooling in the order of 100,000 ° C./h.

2nd step:

Tempering treatments graded from 600 to 700 ^r C (lh).

The structure is an occasional martensite.

It was observed that the time required to obtain a satisfactory degree of embrittlement tempering temperature 620 ^c C.

The mechanical properties are then as follows: Streckerenze R „= 920 MPa

Tensile strength R = 1020 MPa

Constriction Z% = 65%

Impact strength KCV +20 ⁰ C = 142 J / cm ²

For the same quenching treatment, but with a tempering limited to 600 ° C., one obtains at a yield point of 100 MPa a less favorable degree of embrittlement of 50%.

In all examples, the minimum tempering temperature allowed to obtain the best mechanical properties was used specified. It is obvious that one

if ηι, ιη less high figurines' resound. a higher, after all only> Kirch die I mw andlun -. 'slempcralur A,, limited tempera uir can choose. »; I> ilen Viii ι A lint that in.m --ie need not enclose with a mi great precision. because it 's in this area Irei cin <Sprödigkcit by W'.is- - crMofl aiiknmd a / ti niediigen Anlaßtempei ■ lir Ul Sn put r in thanks to a sorglältigen and accurate choice eggs / u .ammensctzung a Abschreckstahl ago. who can withstand exposure to high temperatures and, while maintaining high mechanical shapes, adopts a thermodynamically stable lie, i.e., resistance to stress corrosion in the presence of water slurry is required.

The choice of chemical composition, the The temperature and the degree of tempering to be carried out within the precise specified limits must be carried out Take into account:

the quenching possibilities of the workpiece with special consideration of the shape and the thickness of the workpiece, ti ie (.lie determination of a theoretical Thickness depends on the clic critical closing speed: it really is It is essential that the cooling is sufficiently rapid. a quenching at a speed above the critical martensite speed of the used To secure steel:

the desired mechanical shapes (yield point, tensile strength), but the maximum limit is about ^ι ) Μ) MPa / 1 to ensure good resistance to embrittlement by water! / u preserve.

It should also be noted that the factory gaps made from the steels defined in this way can be subjected to welding processes. This is essential - ic an I lUspannungsbehaiidlung is at a '■■ "to subdue • special" high · femperatur equal or del than 20 C below the metallurgical lemperatur the starting ¹ ·.'. However, it is never below (■ 25 C.

Of course, the answers are all those given Examples are not limited, which only served to explain particular execution errors. These chemical compositions and store temperatures and signs. which are given in the examples. Minnen, on the other hand, especially as a function The shapes of the workpiece and the twisted figurines. However, it can simply be varied within the narrow limits given above; so must the frightful speed always the appearance of a niartensitisclien (enable ielüges.

finally (iegenstatul tier l'rlinden also uie in ile steels with the described gearshifts i.e. manufactured workpieces. Fin such steel can be at different Application lines can be used, uie /. ».:

Devices for transport or storage. even under high pressures, hydrogen or water slippery conditions Gases! /. B. Frdgas). the Schwelelwassersloll contain otler not, being tlie constructions can be fixed or movable containers. Valves or the moving parts of turbo compressors '' Flemenie tier Gchüiserräder: wheel hubs, flanges. Shovels).

I lememe for the exploitation of the oil or gas deposits at great depths, such as B. the pipes or the pipe joints

It is clear that other applications ii.i Area of discovery.

1 sheet of drawings

Claims (1)

Patent claims: I. Process for the production of workpieces with good strength properties and resistance to cracking due to stress corrosion in the presence of hydrogen from a non-killed steel, consisting of 0.15 to 0.3'fe carbon, 0.1 to 0.5% silicon, 0, 5 to 1.5% manganese, 1 to 3% chromium, 0.25 to 1% molybdenum, 0 to 1% nickel, 0 to 0.1% iu vanadium and / or niobium and the remainder iron with the usual production-related impurities which the workpieces at 875 to 950 ^; C austenitized. quenched and finally annealed for tempering at 620 to 725 ° C, characterized in that the workpieces are quenched after austenitizing at a speed above the critical martensitic speed and tempered in such a way that the minimum tempering temperature is in the range from 620 to 725 ° C is determined by the stipulation that in the finished workpiece the yield point R ₁ , in the range from 740 to 932 MPa, the tensile strength R _m in the range from 880 to 1080 MPa and a degree of embrittlement F are - 30%, where F by the equation ρ% = χ 100 Devices for the transport or storage of hydrogen or hydrogen-containing gases, e.g. B. natural gas, with or without hydrogen sulfide content, for valves or moving parts of turbo compressors or for pipes or pipe connections to exploit the oil or gas storage huts in large Lows.