DE1267853C2 - HIGH-STRENGTH STEEL ALLOY WITH PRIORLY MARTENSITIC STRUCTURE - Google Patents

Description

The invention relates to a high strength steel alloy with predominantly martensitic structure and the following composition:

0.15 until O.65 "/ _O Carbon, 7th until 12 ° / o Nickel, 0.2 until 7 ⁰ Zo Cobalt, 0 until 2 ⁰ Zo Manganese, 0 until 2 ° / o Aluminum, 0 until 3 ⁰ Zo Silicon, 0 until l ° / o Chrome, 0.2 until 0.4 ° / ₀ Molybdenum, 0 until 0.35 ° / ₀ Vanadium, 0 until 0.4 "/ ο Niobium, 0 until 0.04 ° / ₀ Sulfur, 0 until 0.04 "Z _n Phosphorus,

Remainder iron with incidental impurities,

the chromium, vanadium and niobium content individually or in groups being at least 0.12% and the molybdenum can be partially replaced by tungsten in a weight ratio of 3: 1.

The strength of steel alloys depends on the composition and the heat treatment 5 or without mechanical processing.

From the French patent 1 246 567 steel alloys are already known that by mixing of powders of various elements, such as carbon, nickel, manganese, cobalt, etc., subsequent pressing

ίο to the desired shape and subsequent sintering at a temperature in the range from 650 to 76O ⁰ C are produced. The steel alloys produced by these powder metallurgy techniques contain manganese in an amount of 0.4 to 1 percent by weight and molybdenum in an amount of 0.5 to 5 percent by weight and, as an optional additive, KobaU in an amount of 0 to 3 percent by weight. The steel alloys produced by this process, however, only have low tensile strengths in the range of about 30 to 50 kg / mm ² .

In contrast, the high-strength steel alloy according to the invention has a predominantly martensitic structure which is achieved in that the steel is poured from the molten state and then rolled or forged. As a result of the predominantly martensitic structure, the steel alloy according to the invention has an extremely high tensile strength, which is in the range from 140 to 210 kg / mm ² . In contrast to the known steel alloy, the manganese contained in the steel alloy is only an optional additive which is not necessary to achieve the high strength properties. In contrast, the cobalt additive, which is optional in the known steel alloy, is a necessary component according to the invention, which is added in an amount of 0.2 to 7 percent by weight, preferably 1 to 4 percent by weight, in order to achieve high strength properties. French patent specification 1,082,372 describes non-magnetic, austenitic steel alloys which contain manganese in an amount between 0.5 and 20 percent by weight and nickel in an amount of up to 12 percent by weight. The total content of nickel plus manganese therein is in the range of about 15 to 20 percent by weight.

In contrast, the steel alloy according to the invention has a predominantly martensitic structure, and the content of the only optional additive manganese is a maximum of 2 percent by weight, whereas nickel is an essential component of the invention Steel alloy is. The total content of nickel and manganese is reached in the steel alloy according to the invention a maximum of 14 percent by weight compared to the 15 to 20 percent by weight in the known steel alloy. The previously known steel alloys were preferred if the martensite formation did not begin, d. H. processed at a temperature not above the "Ms" line, whereby this Deformation area has proven to be impractical for many alloys because the lower part of the loop is in this way the ZTU curve shifted significantly to the left and the specimen only reached room temperature with difficulty cool down Iiei3 without the original austenite being converted into other non-martensitic products, such as bainite, and this transformation results in the achievement of high tensile strength and notched impact strength values prevented.

The object of the invention was to develop a steel alloy in which during machining

at high temperature for the conversion into high- something cobalt in the alloy diminished because of it temperature structure, such as ferrite and / or pearlite, only a cobalt the amount of retained austenite is kept to a minimum, small displacement of the lower portion of the further must in the composition at least Conversion curve from austenite to bainite to the left about 0.12% of a metal such as chromium, molybdenum, As a result, steel alloys with vanadium and niobium should be present. It was a high tensile strength and notch toughness produce graphite formation during heat treatments, which presumably let, which does not prevent the shortcomings of previous steel loans based on the influence of nickel, have alloys. This task was also carried out with the In addition, according to the invention, higher percent finding of the high-strength steel sets according to the invention on one or more of the elements carbon alloy With a predominantly martensitic structure, io material, chromium or silicon have higher percentages solved. Cobalt and / or nickel to achieve the best techno-

In the case of compositions with low carbon properties, be assigned,
Material content of about 0.15 to 0.35% must be cobalt in carbon contributes to increasing the predetermined amount in steel to achieve a high strength and hardness. It varies in the given tensile strength. In the case of a combined area and only to explain its settlements with larger proportions of carbon, the mode of action is subdivided into the following areas:
Chromium and / or silicon are larger amounts of χ _of q ^ _b i _s 9350,
Nickel and / or cobalt for balancing of the alloy _yon d _{0 '35 to} r / 5 ° /'"and
tion and to achieve the properties according to the invention ' _o ' r to 065 <V
shafts required. 20 *

F i g. 1 shows a diagram showing the ratio of the alloys in the lower carbon range

from carbon to cobalt indicates that generally have good weldability and attainment

Different strengths in the finished products have a high notched impact strength, so that they are z. B.

is required; the strengths are not only due to the hull for underwater vehicles

the composition, but also through which 25 are reversible; they show after the heat treatment

Quenching and tempering intended; a 0.2 proof stress of 105 to 170 kg / mm ² and one

F i g. Figure 2 shows a curve for a steel alloy tensile strength of about 125 to 210 kg / mm ² . composition. In Fig. 2 also shows the alloys with a medium carbon content when working in different temperature ranges after the heat treatment, as will be explained in more detail later. 30 higher 0.2 yield strength from 165 to 190 kg / mm ²

The in F i g. The curves shown in FIG. 1 represent sub and tensile strengths of 200 to 240 kg / mm ² ; you are

search results of alloys with about 8 to also weldable and have a high notch impact

9% nickel, but with different amounts of toughness.

Carbon and cobalt represent. For this purpose, the alloys in the higher carbon range are

numerous samples each at a temperature of 35 after the heat treatment quite hard and

about 800 to 815 ⁰ C austenitized, then in oil on have a very high 0.2 yield strength and tensile strength

Quenched at room temperature, further to the temperature and a medium notched impact strength. Particular

temperature of liquid nitrogen cooled and alloys in the lower carbon range of this

then tempered for 1 hour at 315 ° C. Group are weldable. Your 0.2 proof stress is

The in Fig. Curves shown in 1 are indicative of 40 at 185 to 210 kg / mm ² and their tensile strength at

for examining the numerous aggregates of 225 to 245 kg / mm ² .

Subsidence under the given conditions. According to the invention, nickel is about 7 to about 12%

at a different tempering temperature, e.g. at 200 ^c C, and preferably at about 7.5 to about 9.5%,

the numerous curves would be steeper. The first is the toughness and strength of the

Transition in the curves from a ratio of alloys; secondly, the insensitivity of the

moderately straight line in the bent sections in alloys against embrittling agents, such as. B.

lower part of FIG. 1 would, however, among all um- silicon, carbon, phosphorus and sulfur, and

would be around 3% cobalt. thirdly, increase the hardenability of the alloy.

If the nickel content was changed to about 8 to 9 ° / _c , the curves in FIG. 1 so shifted 50 of the alloy, the amount of retained austenite increases, so that larger amounts of carbon remain in the during the transformation into martensite. Relation to Smaller Amounts of Nickel Used This is for any given level of carbon that would be used, for each percent change in case and an undesirable structural component. This change in the nickel content of 0.02% in the effect becomes more pronounced the more carbon-carbon content. 55 substance is present. This endeavor to restore austenite

If the treatment conditions change, the addition of cobalt counteracts

Omitting the cooling on the temperature of worked.

liquid nitrogen before tempering would cobalt in the alloy should be about 0.2 to about 7, the resulting body has a lower tensile strength preferably from about 1 to 4%, may be contained, include, but the curves would in grol.en and ^fi o Its purpose is to reduce reslausleness by making it all of the same general shape. At the Ms temperature increased. The higher the A / .s-Tempe steels with retained austenite a part of this value can be, the more austenite will tend to transform into martensil at a later date. B. Room temperature, which is associated with a volume increase, is then always below an A / s temperature.

Steel-made items given. This un- cobalt also serves to increase strength

desired effect of the later transformation of the alloy without significant loss of toughness,

Austenite becomes martensite due to the presence of particularly low carbon steels

v>

salary. Therefore, certain minimum areas must form the bay area 17 by him. The quantities marked with Ms will be present when the carbon is in the line indicating the temperature for the beginning of the lower range. Transformation of austenite into martensite. Above cobalt, the hot hardness of steel continues to increase. This line runs a horizontal line A ₁ , which and increases its tempering resistance, particularly in FIG. 5, the lower end temperature of a critical zone connection with silicon. Steels containing cobalt can indicate. The upper end temperature of this critical zone, therefore at relatively high temperatures, is indicated by line A ₃ . In this one or more phases can be tempered and still retain the critical zone with the desired strengths. In addition, cobalt reduces its equilibrium with austenite, while in addition the further possibility of a quenching io above the ^ ₃ -line only austenite can exist. Crack formation, ie the crack formation that occurs due to the machining of the steel changes according to the invention in the dimensions due to the re-alloying is based on a cold working basis, conversion of austenite into martensite. Nevertheless, it increases at relatively high temperatures, which is also due to the insensitivity to certain substances which make the term "hot-cold processing" brittle, such as B. carbon and 15 can be. The machining is limited to the silicon, and in this sense works in a similar way to the area above the nose of the curve, as is the case with nickel. the transformation of austenite into the transformation manganese has a similar influence on the hardness products of higher temperatures,
of steel like silicon. When processing at temperatures substantially above silicon has the general task of reducing the temperature to half room temperature and in the area for which the tempering reaction at tempering temperatures of 315 ° C. has numerous ZTU curves in FIGS. 2 are drawn, and to delay below. The silicon content is set on the machining itself a shift of the maximum 3 ° / ₀ , because larger amounts result than the development of the ZTU curves, whereby the cause of undesired brittleness of the steel shift is also shown in the drawing. To see are. 25 to obtain a product that does not prevent the tendency to graphitization and conversion products is contaminated by any chromium, but increases the hardness. substantially pure of martensite with a minimum molybdenum acts similarly to chromium * z "d is in amount of retained austenite, it has proven to be notwen amounts of 0.2 to 0.4 ° /" added, it may be partially proved dig, according to the present invention to proceed with tungsten in a weight ratio of 3: 1 30. The term "martensite" should be replaced here. However, denote a martensite-like product, the sulfur and phosphorus are undesirable. 04 ° / _{0 has} not been exceeded.

Vanadium is used for grain refinement, hardening. 2 will be editing in any case

and to prevent graphite formation. Its preferred range due to a practically horizontal wave is 0.05 to 0.15 ° / ₀ . line showing that the machining of aluminum acts as a grain refiner and as a deoxygenation agent carried out at a single given temperature. It also increases under certain circumstances, although the actual machining would also increase the strength of the alloy. a steady reduction in temperature by-niobium can be performed in the steel alloy 40 according to the invention, which z. B. be present by touching the completely missing or only with about 0.4 weight to be processed material with a proportionate percentage of the entire alloy. It can prevent coarsening of the grain using colder processing tools of suitable design. In any case, the FIG. 2 Increase the hardenability of the alloy and its machining time by increasing the position and length. the horizontal logarithmic timescale, determined. According to the invention, vanadium, aluminum, this initial cooling before machining, and / or silicon can be wholly or partially replaced by titanium, which is replaced by a sloping line from a zirconium and / or rare earth metals. relatively high austenitizing temperature. The behavior of the steel according to the invention is indicated, is and must be sufficiently followed on the basis of the ZTU curves in FIG. 2 are carried out for a short time, so that this is merely an explanation. The alloy composition of FIG. 2 Cooling as such no conversion into any i is the following: substantial amount of the treated material in the

one or another type of conversion products, di <

Carbon 0.42 55 is not austenite and undesirable takes place Nickel 8.52 in Fig. 2 is a ZTU curve that has no « Cobalt 3.80 Bay 17 between an upper and a lower one Manganese 0.24 lobes 15 and 16 respectively. The temperature of the

Silicon <0.10 nose of the curve lobe 16 approximately at point 29 isi

Chromium 0.18 60 critical here, with the processing of the fiction Molybdenum 0.38 according to steel alloy at temperatures above hold Vanadium 0.10 the temperature of point 19 is carried out Sulfur <0.10 must. According to the teachings of the state of Technil Phosphorus <0.010, processing was carried out at temperatures corresponding to Remainder iron with incidental impurities. 65 corresponding to the bay section 17, after the path a

with the processing carried out in the bay

The ZTU curve denoted by 14 shows one can, however, the inevitable shift lower tab 15 and an upper tab 16, exercise of the lower tab 15 from the fully distinguished

Neten position of the curve 14 in the position shown in dashed lines at 30 results. This is not a serious problem in the case of light or relatively thin samples, but it can cause very great difficulties in the case of relatively heavy or thick samples. The curve path α and the shifted position 30 indicate the conditions that can be obtained when using heavy samples. The cooling portion 31 of path a will cut through the displaced flap 30; this results in contamination of the sample by undesired conversion products. In FIG. 2, path b lies in the critical zone, ie between temperatures A ₁ and A ₃ , which in this case also lies within the range of the present invention, since the processing section of this path lies completely above temperature nose 29 of upper curve 16. Under these circumstances, the lower tab 15 is only shifted from the position shown in full extension to the position shown by the dashed curve line 32, so that the processing can be finished as shown in the drawing, and the product afterwards can be cooled or quenched along line 33 without intersecting any portion of dashed curve 32 and therefore no introduction of any conversion products, ie lower temperature conversion products such as bainite, into the finished material. The finished material consists practically entirely of martensite with a very small amount of retained austenite.

The machining at a temperature above the height indicated by the line A ₃ , ie in the stable austenite zone, corresponds to the path c, with quenching taking place immediately after the machining and actually having to start at the time zero, provided, of course, that the machining itself is not excessively elongated and there is no excessive period of time between the completion of the machining and the start of the quenching process.

After the samples have been quenched, usually in air or in oil at least to room temperature, a further part of the retained austenite can be converted into martensite by means of strong cooling, for example by reducing the temperature to any achievable low temperature, including e.g. . B. immersing the object in liquid nitrogen; This reduces the temperature of the product to the boiling point of liquid nitrogen, ie about -200 ^° C. There are other liquid gases as well, including CO ₂ , He, H ₂ or O ₂ . can be used for cooling.

For the maximum conversion from austenite to martensite can be a repetitive or cyclic Processes are advantageously used in which cooled, then heated to about the tempering temperature and cooled again and is hypothermic. Usually, with about two such loops, the greatest possible conversion is obtained, since there are additional loops, although they may increase the amount of conversion desired To a certain extent, increase * one in proportion to the cost of carrying it out cause little improvement.

Through the specified hot-cold processing

certain physical or mechanical properties are significantly improved.

It is also found that the effect of mechanical deformation or machining to a certain extent The circumference is proportional to the amount of such deformation or processing to which the sample is subjected will is. In order to achieve an actual and noticeable minimum improvement, the Deformation at least 10%, based on the

ίο physical dimensions of the specimen prior to such deformation. However, this is a minimum requirement; the maximum is much higher, with a practical machining margin or preferred deformation amount on the order of 50 to 90 degrees / ₀ .

Machining can be done in a number of ways, all of which are generally applicable to the mechanical processing of steel and its alloys known under other conditions are. According to the invention this can, for. B. by a forging or crushing operation, by mechanical Rolling, extrusion, wire drawing and any other known method for Machining of metals can be carried out. A desirable feature of the steel alloy of the invention is that the manufactured products have a very high toughness, as is evident from their Notch Tensile Strengths is displayed.

B e i s ρ i each 1 1

The various compositions are listed in Table 1.

In Tables II and III, with reference to the samples specified in Table I, certain properties of the materials with the corresponding compositions are shown. For Tables II and III , the tensile strength, yield strength, tensile strength and elongation in each case on a flat sample about 2 mm thick, about 7.5 mm wide and sufficient length for a central test section (between the clamping sections) of about 50 mm length determined.
The treatment levels were as follows:

a) Austenitizing down to one temperature Table!! and III;

b) The samples were then quenched in oil at about room temperature (24 ^C C), then

c) cools to a temperature of about -5 ° C for 2 hours,

d) then tempered at 205 T for the results listed in Table II and tempered at 315 ^C C for the results listed in Table III, and that for 1 hour each time, then took place Cooling to room temperature in air, then tempering again at the same temperature Tempering temperature for 1 hour and then cooling in air to room temperature;

e) the samples were then finish ground to the desired exact dimensions of the test pieces,

f) the chips caused by the grinding were removed by tempering to 10 ⁼ C, the is below the tempering temperature specified for each sample, and

g) the test results were given in Tables Ii and III combined.

309 641 / 46-

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Table I.

10

Per
be C. Ni Co Mn Si Cr Mon V Al Nb S. P. preferably low C content a 0.23 9.5 2 0.20 0.20 0.25 0.30 0.10 0.01 0 0.01 0.01 preferably medium C content b 0.40 9 3 0.20 0.20 0.20 0.25 0.10 0.01 0 0.01 0.01 preferably high C content C. 0.62 7.7 5 0.20 0.20 0.10 0.20 0.10 0.01 0 0.01 0.01 preferably low C content d 0.15 8.75 3.50 0.30 0.20 0.32 0.35 0.008 0 0 0.005 0.006 preferably high C content e 0.65 8.82 6.80 0.46 0.21 0.30 0.31 0.11 0 0 0.008 0.007 low Ni content f 0.42 7th 0.48 0.33 0.15 0.10 0.23 0.13 0.3 0 0.006 0.005 high Ni, low Si content G 0.45 12th 5 0.14 0.005 0.30 0.34 0.15 0 0 0.007 0.007 high Mn content H 0.25 10 1.25 2 0.23 0.35 0.29 0.07 0.09 0 0.023 0.014 high Nb content + sample b i 0.40 9 3 0.20 0.20 0.20 0.25 0.10 0.01 0.4 0.01 0.01 low Nb content + sample b j 0.40 9 3 0.20 0.20 0.20 0.25 0.10 0.01 0.04 0.01 0.01 high Al content ■ + - sample b k 0.40 9 3 0.20 0.20 0.20 0.25 0.10 2 0 0.01 0.01

Table II

sample Austenitic
temperature 0.2 yield strength tensile strenght strain
(%in ' Constriction RC hardness Notch pull
strength ("C) (kg / mm ⁸ ) (kg / mm ² ) 50 mm) (%) (kg / mm ^s ) a 870 136.5 161.7 8th 48 46.5 > 136.5 b 790 172.2 203.9 7th 35 54 210.9 C. 845 207.3 232 5 25th 56 70.3 d 900 116 136.5 8th 60 41 > 116 e 845 209.5 235.5 6th 30th 56.5 70.3 f 815 165.2 196.8 7th 40 54 182.8 G 790 175.8 203.9 7th 40 54.5 179.3 H 845 147.6 168.7 7th 50 46 > 147.6 i 815 175.8 207.3 7th 40 54.5 210.9 j 815 173.7 205.3 7th 37 54 > 210.9 k 815 172.2 203.9 6th 35 54.5 161.7

Table III

sample Austenitic
temperature 0.2 yield strength tensile strenght strain
(% in Constriction RC hardness Notch pull
strength ( ⁰ O (kg / mm ⁸ ) (kg / mm ² ) 50 mm) ("/ ·) 0cg / mm ^a ) a 87ü 136.5 154.7 8th 50 46 > 136.5 b 790 161.7 175.8 7th 51 51 > 182.8 C. 845 179.3 196.8 6th 53 53 -140.6 d 900 116 126.6 8th 63 40 > 116 e 845 182.8 189.8 6th 40 53.5 -v 140.6 f 815 161.7 182.8 7th 50 51 > 182.8 G 790 167.3 189.8 7th 45 52 > 182.8 H 845 150.2 161.7 7th 53 45 > 151.2 i 815 165.2 189.8 7th 45 51.5 > 175.8 j 815 161.7 182.8 7th 42 51 > 175.8 k 815 189.8 210.9 5 35 54 105.5

Example 2

This example is intended to carry out hot-cold machining in the area on which the Invention with reference to FIG. 2, illustrate.

This procedure is not only applicable to all of the alloy compositions mentioned, but also to compositions known generally as hardenable steel alloys are applicable.

Table IV
Mechanical properties of hot-cold machined steels

Austenitic
tization Ver
forming Ver Tempering 0.2- train Deh A- hardness 67 Notch pull sample Tem
temperature Tem
temperature ΙΟΓ-
mung temperature Yield point strength tion scnnu-
tion 61 strength ( ⁰ C) ( ⁰ C) (%) ("C) (kg / mm ² ) (kg / mm ² ) ( ⁰ A,) (° / o) 47 59 (kg / mm ⁵ ) a 870 732 10 1 h - 204 147.6 154.7 7th 40 52.5 - 61.5 870 732 80 immediately deterred 168.9 176.8 5 21.8 49.5 870 732 80 1 h - 204 154.8 167.8 5 31.2 50 > 155.4 870 732 90 1 h - 204 161.8 175.8 6th 36 55 > 161.7 b 790 732 10 1 h - 204 179.3 209.5 7th 36 790 704 80 immediately deterred 177.2 274.2 56.3 790 704 80 1 h -121 182.8 267.2 105.5 790 704 80 lh - 204 196.8 228.5 56 > 210.9 790 732 90 1 h - 204 207.3 239 6th 40 - premature break > 2O7.3 C. 845 732 10 1 h - 204 too brittle - 6th 845 732 80 immediately deterred 207.3 316.4 5 35.2 845 732 80 1 h - 204 218 288.2 5 ~ 182, p 845 732 80 lh -315 210.9 253.1 5.5 ~ 182.f 845 732 90 1 h - 204 232 295.2 > 186.

1 sheet of drawings

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Claims (6)

Patent claims: 1.-High strength steel alloy, featured due to a predominantly martensitic structure and the following composition: 0.15 until 0.65% carbon, 7th until 12% nickel, 0.2 until 7% cobalt, 0 until 2 ° / ₀ manganese, 0 until 2% aluminum, 0 until 3 ° / ₀ silicon, 0 until l ° / ₀ Chiom, 0.2 until 0.4 ° / "molybdenum, 0 until 0.35 ° / ₀ vanadium, 0 until 0.4% / ₀ niobium, 0 until 0.04 _^0/0 sulfur, 0 until 0.04 ° / ₀ .Phosphor, Remainder iron with incidental impurities, the chromium, vanadium and niobium content, individually or in groups, being at least 0.12 "/ o and the molybdenum is partially replaced by tungsten in a weight ratio of 3: 1 can. 2. Steel alloy according to claim 1, characterized in that it is 7.5 to 9.5%> Contains nickel and 1 to 4% cobalt. 3. Steel alloy according to claim 1 or 2, characterized in that it is at least 0.12% Contains chrome. 4. Steel alloy according to claims 1 to 3, characterized in that it is 0.05 to 0.15% Contains vanadium. 5. Steel alloy according to claims 1 to 3, characterized in that higher percentages higher percentages of cobalt and / or nickel of carbon, chromium and / or silicon assigned. 6. Steel alloy according to claims 1 to 4, characterized in that vanadium, aluminum and / or silicon in whole or in part with titanium, zirconium and / or rare earth metals are replaced.