ES2592714T3 - Alloy and article with high heat resistance and high thermal stability - Google Patents

Abstract

Alloy for the manufacture of objects with high resistance to high temperatures and toughness, composed of the following in percentage by weight: ** Table ** as well as impurities inherent in manufacturing.

Description

DESCRIPTION

Alloy and article with high heat resistance and high thermal stability.

The invention relates to an alloy for the manufacture of objects with a high resistance to high temperatures and toughness.

In particular, the invention relates to a steel object for work at high temperatures of high hardness, high heat resistance and high thermal stability.

 10

In general, steels for work at high temperatures can be defined as thermally bondable iron-based alloys, whose increased mechanical properties after heat treatment, especially their high strength and hardness, are maintained at temperatures of up to 500 ° C and more .

In accordance with the increasing requirements of technical development, there is a general demand in 15 materials resistant to high temperatures to continue increasing their quality and, in particular, increasing their resistance to high temperatures with high thermal stability, as well as increasing their toughness .

The usual steels for work at high temperatures are usually iron-based alloys with a carbon content (C) of between 0.3 and 0.4% by weight, whose hardness is increased with a quench by rough cooling by forming martensite in the structure and tempering according to the requirements. The addition of alloy elements, in general by weight percentage, of

 silicon (yes)

       up to 1.5

 chrome (Cr)

 between 2.5 and 5.5

 molybdenum (Mo)

       up to 3.0

 vanadium (V)

       up to 1.0

The iron-based material and the use of a specially configured heat treatment procedure 25 allow an object to be manufactured therefrom that has high values for the desired mechanical properties at an application temperature of up to about 500 ° C. By adding by alloy up to 9% by weight tungsten (W) and up to 3.0% by weight cobalt (Co), the application temperature can be increased somewhat.

 30

Essentially, the hardness at high temperatures is produced in said type of steels by means of a precipitation mechanism, which the expert calls an increase in secondary hardness, in which the finest chromium, molybdenum, tungsten and vanadium carbides are formed in the network of martensite, which is disclosed, for example, documents JP 07228945A and US-A-3453151.

 35

Another increase of a different nature for quenching by sudden cooling of the strength of a material can be achieved by a quenching by precipitation. The prerequisite for precipitation hardening is that the solubility of an alloy additive or alloy elements is reduced with the temperature in the base metal.

In precipitation quenching, the alloyed material is first subjected to a solution annealing treatment with a reinforced cooling carried out below, with which the alloy additive or a phase is totally or partially dissolved and kept in a solution supersaturated A heating carried out at a temperature below the annealing temperature by dissolution causes a dissociation of the supersaturated part of the element (s) or phase (s), which causes a modification of the properties of the material, as a rule an increase in the hardness thereof.

Iron-based materials that can be quenched by precipitation generally have the following alloy contents by weight percentage:

 10

 carbon (C)

 up to 0.05

 manganese (Mn)

 up to 2.0

 chrome (Cr)

 up to 16.0

 molybdenum (Mo)

 up to 6.0

 nickel (Ni)

 up to 26.0

 vanadium (V)

 up to 0.4

 Cobalt (Co)

 up to 10.0

 titanium (Ti)

 up to 3.0

 aluminum (Al)

 up to 0.3

Both iron-based alloys with a formation of martensite in a quench by sudden cooling, as well as those that with the precipitation of elements and phases undergo a change in their mechanical properties, have in common the disadvantage that in the respective area of the composition of the alloy and / or by means of a heat treatment technology only loose properties are improved respectively, such as hardness and stability or temperature resistance, but this leads to a fall in the values of other properties, such as example the toughness of the material, the thermal stability and others.

The object of the invention is to indicate an alloy that allows the overall improvement of the property profile of an object manufactured with it. Accordingly, the task of the invention is to create a steel object for work at high temperatures that simultaneously presents high hardness and high toughness, high resistance to high temperatures and high thermal stability.

The objective of the invention mentioned above is achieved with an alloy composed of the following elements in percentage by weight:

 25

 carbon (C)

 between 0.15 and 0.44

 silicon (yes)

 between 0.04 and 0.3

 manganese (Mn)

 between 0.06 and 0.4

 chrome (Cr)

 between 1.2 and 5.0

 molybdenum (Mo)

 between 0.8 and 6.5

 nickel (Ni)

 between 3.4 and 9.8

 vanadium (V)

 between 0.2 and 0.8

 Cobalt (Co)

 between 0.1 and 9.8

 aluminum (Al)

 between 1.4 and 3.0

 copper (Cu)

       less than 1.3

 niobium (Nb)

       less than 0.35

 iron (Fe)

 rest

as well as impurities inherent in manufacturing.

The advantages resulting from the invention basically focus on the fact that, thanks to the technical measures of alloy, a material has been created in which the dissociation hardening can be superimposed on quenching by sudden cooling or martensitic hardening. Here, the activities of the alloy elements are advantageously selected against carbon and those related to the formation of bonds or phases, such that even at comparatively low austenization temperatures a quenching occurs simultaneously during the bonus the finer secondary precipitations of carbides, in particular of chromium, molybdenum and vanadium carbides, and a tempering by the precipitation of intermetallic phases 10, in particular of Al Fe2Ni, achieving a high hardness at high temperatures together with a high toughness of the material .

According to the invention, it is also possible to perform the complete tempering of large parts better, because the corresponding transformation behavior of the material has been configured from the technical point of view of alloy. Likewise, the resistance to tempering and, consequently, the thermal stability of the bonded material, together with a high hardness, have been considerably improved.

In an iron-based alloy according to the invention, a carbon content of at least 0.15% by weight is provided, so that there is enough precipitate carbide for a desired increase in secondary hardness. Carbon concentrations greater than 0.44% by weight, with the expected elements that form carbides, can form interfering primary carbides that reduce toughness, so that the carbon content must be between 0.15 and 0.44 % in weigh.

The silicon content must be, due to an advantageous composition of the deoxidation product, of at least 0.04% by weight, but on the other hand it must not exceed 0.3% by weight because the higher silicon values negatively influence the toughness of the material.

It is provided according to the invention that the concentration of manganese in the steel is between 0.06 and 0.4% by weight. The lower contents can produce a tendency to break in a hot forming and the upper contents, disadvantages in terms of the hardenability of the material.

The contents of chromium, molybdenum and vanadium are important for a desired formation of secondary hardness of the material during the bonus and must be considered together. Chromium contents of less than 1.2% by weight negatively affect the complete hardenability of the material, while those greater than 5.0% by weight reduce the thermal stability of the material because this reduces the activity of molybdenum.

In molybdenum concentrations below 0.8% by weight, too little of this element dissolves throughout the heat treatment, which leads to low secondary hardness values. An amount 40

greater than 6.5% by weight of molybdenum in steel can produce too much carbide content, which can adversely affect the toughness of the material and can lead to economic disadvantages.

The powerful vanadium carbide former is provided according to the invention with a minimum content of 0.2% by weight, in order to guarantee a sufficient and stable secondary hardening of the steel. Vanadium 5 contents greater than 0.8% by weight, especially with carbon contents in the upper zone of the expected concentration range, can produce a precipitation of primary carbides, so that the toughness properties of the material suddenly worsen.

The effect of niobium, although similar to that of vanadium, is however characterized by a formation of 10 very stable carbides, so that the niobium content should advantageously be below 0.35% by weight.

In order to ensure the desired increase in secondary hardness during a tempering of the martensitic structure of the alloy according to the invention, it therefore has a carbon concentration of between 0.15 and 0.44% by weight, contained in percentage by weight of chromium between 1.2 and 5.0, between 0.8 and 6.5 molybdenum and between 0.2 and 0.8 vanadium.

The nickel concentration of the steel and its aluminum content should be considered with a view to the precipitation kinetics of the Al Fe2Ni type phase for the increase in hardness in a planned heat treatment technology. In nickel contents of less than 3.4% by weight and with an aluminum concentration of less than 1.4% by weight, tempering is restrained by precipitation, so that the increase in additive hardness is low in the material during tempering .

Nickel contents greater than 9.8% by weight displace the γ / α transformation at lower temperatures, which can lead to problems in the treatment of soft annealing of steel, high treatment hardness and disturbances in precipitation kinetics .

Aluminum contents greater than 3.0% by weight disadvantageously promote a high area of DELTA ferrite (δ) in the transformation behavior, a formation of nitrides and decrease the toughness of the alloy material.

Therefore, according to the invention, the nickel content and the aluminum content of the steel in weight percent are in a range between 3.4 and 9.8 nickel and between 1.4 and 3.0 aluminum.

 35

Copper can form unwanted intermetallic phases and its concentration in steel must be less than 1.3% by weight.

In order to further improve the properties profile of the alloy according to the invention, it may be provided that one or more of the following elements are present at the indicated weight percentage concentrations:

 carbon (C)

 between 0.25 and 0.4, preferably between 0.31 and 0.36

 silicon (yes)

 between 0.1 and 0.25 preferably between 0.15 and 0.19

 manganese (Mn)

 between 0.15 and 0.3 preferably between 0.2 and 0.29

 chrome (Cr)

 between 1.9 and 2.9 preferably between 2.2 and 2.8

 molybdenum (Mo)

 between 1.2 and 2.9 preferably between 2.1 and 2.9

 nickel (Ni)

 between 5.0 and 7.6 preferably between 5.6 and 7.1

 vanadium (V)

 between 0.24 and 0.6 preferably between 0.25 and 0.4

 Cobalt (Co)

 between 1.4 and 7.9 preferably between 1.6 and 2.9

 aluminum (Al)

 between 1.6 and 2.9 preferably between 2.1 and 2.8

Thanks to these narrower margins of the content of elements in the chemical compound of steel, the properties of the objects manufactured with it can be further improved.

 5

It is especially important for the mechanical values of the steel to be high as a whole, but in particular also to achieve high tenacity properties of the material, so that the proportion of additives is limited.

In an advantageous configuration of the invention, an alloy containing one or more of the impure elements with the following MAXIMUM concentrations in weight percent is provided:

 phosphorus (P)

 0.02, preferably 0.005

 sulfur (S)

 0.008, preferably 0.003

 copper (Cu)

 0.15, preferably 0.06

 titanium (Ti)

 0.01, preferably 0.005

 niobium (Nb)

 0.001, preferably 0.0005

 nitrogen (N)

 0.025 preferably 0.015

 oxygen (O)

 0.009, preferably 0.002

 calcium (Ca)

 0.003, preferably 0.001

 magnesium (Mg)

 0.003, preferably 0.001

 tin (Sn)

 0.01, preferably 0.005

 Tantalum (Ta)

 0.001, preferably 0.0005

 In order to achieve a particularly pronounced precipitation hardenability of the alloy, superimposed on the secondary hardening by carbides, it may be advantageous that the value of the nickel content broken by the aluminum content corresponds respectively in weight percentage to between 1.8 and 4.2 , Preferably at between 2.1 and 3.9. This avoids an excess of one of the elements that form precipitation.

The task of the invention is resolved according to an improved property profile in a steel object for high temperature work when a starting material manufactured according to a metallurgical fusion process 20 or a powder metallurgical method with a chemical composition previously indicated is molded by forming hot and machined, whose shaped object presents after a hardening heat treatment secondary precipitated carbides, as well as intermetallic precipitation.

The total hardness of the material is advantageously achieved by superimposing the increase in secondary hardness by carbide precipitation and tempering by precipitation. With this you can get

high hardness values of the material, despite the fact that the bonus technology is oriented to achieve a high tenacity of the material and, in comparison with a steel for work at high temperatures according to the state of the art, lower tempering temperatures are used . This lower austenization temperature can also have considerable advantages in terms of reduced deformation in the treatment of bonus parts with complicated shapes. 5

However, if the tempering temperatures are adjusted to a high level, extremely high hardness values of the steel object are achieved, together with the usual good toughness of the material.

 10

When in the structure of the steel object for work at high temperatures there is a ratio of intermetallic precipitations split by secondary carbides precipitated respectively in percentage in volume less than 3.0, preferably 1.0 and less, but greater than 0.38 , the toughness is especially high with high hardness values and the thermal stability moves around up to 50 ° C and more at higher temperatures. fifteen

A steel object for work at high temperatures according to the invention, which presents mixed carbides secondarily precipitated from chromium, molybdenum and vanadium and essentially intermetallic phases of the Al Fe2Ni type in the structure, has a particularly preferred property profile and can be manufactured profitably in conventional tempering facilities at comparatively low temperatures. twenty

A pronounced thermal stability of the object can be achieved when the alloy has a ratio of chromium + molybdenum + vanadium split by carbon, respectively in percentage by weight, greater than 12, but less than 19.

 25

The invention is detailed by way of example in greater detail on the basis of various analysis results and representations.

From an alloy according to the invention A, a conventional steel for work at high temperatures B and a hardened steel by precipitation C (martensitic steel), samples were made, thermally bonded and their material properties analyzed. The alloys have the chemical compositions indicated in Table 1:

Table 1

 Element

 Alloy A Alloy B Alloy C

 C

 0.32 0.36 0.13

 Yes

 0.18 0.40 <0.05

 Mn

 0.25 0.33 <0.02

 Ct

 2.45 4.79 0.11

 Mo

 2.43 2.78 5.26

 Neither

 6.46 0.18 18.01

 V

 0.28 0.62 0.02

 Co

 1.97 <0.05 8.71

 To the

 2.46 0.016 0.13

 Cu

 0.06 0.07 0.06

 Nb

 <0.005 <0.005 <0.005

 Faith

 rest rest rest

 P

 0.008 0.015 <0.005

 S

 0.001 0.001 0.009

 You

 <0.005 <0.005 0.79

 N

 0.0048 0.0068 0.0017

 OR

 0.0022 0.0023 0.0007

 AC

 Mg

 Sn

 <0.005 <0.005 0.009

 Ta

In the material samples, a measurement of the thermal expansion α [10-6 / K] as a function of temperature was performed first, with an initial hardness of the material between 50 and 52 HRC. The values in Table 2 show that, in comparison with a conventional steel for high temperature work B, the alloy according to the invention has a smaller expansion, which also points to a better dimensional stability during a heat treatment.

Table 2

 Temperature [° C]

 A B C

 100 200 300 400 500

 10.8 11.2 11.7 12.2 12.7 11.2 11.61 12 12.5 12.9 9 9.5 9.95 10.44 10.9

 10

 After tempering at approximately 55 HRC approximately of the samples of the alloy according to the invention A and the conventional steel for work at high temperatures B, the hardness profile of the materials was determined as a function of temperature. Here it is of fundamental importance that to achieve this hardness the alloy according to the invention A required an austenization temperature of 990 ° C, while for conventional steel 15 for work at high temperatures B a 1050 ° C was required. As can be seen in Table 3A and Table 3B, the hardness of the composite sample according to the invention A increased as a function of the temperature in a range of between 500 and 600 ° C to values around 60 HRC, while, on the other hand, in the conventional steel for work at high temperatures B a maximum hardness value of 56 HRC at 500 ° C was obtained.

 twenty

Table 3A

 At temperature

    Hardness in HRC

 25 100 200 300 400 500 530 560 590 620 650 680

 54 54 50 51 54 60 60 60 59 55 49 43

Table 3B

 B Temperature

    Hardness in HRC

 25 300 400 500 530 560 590 620 650

 55 52 53 54 53 52 50 47 43

 5

In fig. 1, in graphic representation, the respective hardness profile is shown comparatively as a function of the temperature of the material according to the invention A and of the high temperature steel alloy B according to the state of the art. Starting from the same hardness, which nevertheless is achieved, if necessary, with an advantageous lower austenization temperature, it is produced in the alloy according to the invention A 10 by means of an overlapping precipitation mechanism, in which Al Fe2Ni precipitation is formed in the finest form in the structure, a considerably greater increase in hardness at elevated temperatures of the object, which is also maintained at higher temperatures.

On the basis of an indication of hardness according to Vickers, an analysis of the behavior of the softening of the material as a function of time at a temperature of 650 ° C was carried out.

A determination of the hardness in the sample body at the test temperature was made according to the rebound hardness method (Shore hardness), for whose rebound values so far only a conversion to Vickers hardness values is available.

Starting from approximately the same hardness at room temperature, specifically between 50 and 52 HRC, which was achieved in alloys A, B and C with a composition according to table 1 by different thermal bonus methods (indicated in the annex to analysis, results, sheet 1), a hardness test was carried out over time at 650 ° C.

In comparison with conventional steel for high temperature work B and a 10 C martensitic steel, the alloy according to the invention A presented, at the same starting hardness at 650 ° C, for a period of 1000 minutes, the highest material hardness . After this period, the martensitic steel C had a greater hardness together with a high thermal stability, while the steel for work at high temperatures according to the invention A lost approximately 10% of its hardness until approximately 2000 minutes. The thermal stability of conventional steel for work at high temperatures B was low; the difference in hardness compared to the alloy according to the invention A steadily increased to 1000 minutes.

Claims (12)

image 1 1. Alloy for the manufacture of objects with high resistance to high temperatures and toughness, composed of the following in percentage by weight:  5

 carbon (C)

 between 0.15 and 0.44

 silicon (yes)

 between 0.04 and 0.3

 manganese (Mn)

 between 0.06 and 0.4

 chrome (Cr)

 between 1.2 and 5.0

 molybdenum (Mo)

 between 0.8 and 6.5

 nickel (Ni)

 between 3.4 and 9.8

 vanadium (V)

 between 0.2 and 0.8

 Cobalt (Co)

 between 0.1 and 9.8

 aluminum (Al)

 between 1.4 and 3.0

 copper (Cu)

       less than 1.3

 niobium (Nb)

       less than 0.35

 iron (Fe)

 rest

as well as impurities inherent in manufacturing. 2. Alloy according to claim 1, which contains one or more of the following elements at the indicated weight percent concentrations:

 carbon (C)

 between 0.25 and 0.4

 silicon (yes)

 between 0.1 and 0.25

 manganese (Mn)

 between 0.15 and 0.3

 chrome (Cr)

 between 1.9 and 2.9

 molybdenum (Mo)

 between 1.2 and 2.9

 nickel (Ni)

 between 5.0 and 7.6

 vanadium (V)

 between 0.24 and 0.6

 Cobalt (Co)

 between 1.4 and 7.9

 aluminum (Al)

 between 1.6 and 2.9

3. Alloy according to claim 1, containing one or more of the following elements at the indicated weight percent concentrations:  fifteen

 carbon (C)

 between 0.31 and 0.36

 silicon (yes)

 between 0.15 and 0.19

 manganese (Mn)

 between 0.2 and 0.29

 chrome (Cr)

 between 2.2 and 2.8

 molybdenum (Mo)

 between 2.1 and 2.9

 nickel (Ni)

 between 5.6 and 7.1

 vanadium (V)

 between 0.25 and 0.4

 Cobalt (Co)

 between 1.6 and 2.9

 aluminum (Al)

 between 2.1 and 2.8

4. Alloy according to one of claims 1 to 3, which contains one or more of the impure elements with the following MAXIMUM concentrations by weight percentage:

 phosphorus (P)

 0.02

 sulfur (S)

 0.008

 copper (Cu)

 0.15

 titanium (Ti)

 0.01

 niobium (Nb)

 0.001

 nitrogen (N)

 0.025

 oxygen (O)

 0.009

 calcium (Ca)

 0.003

 magnesium (Mg)

 0.003

 tin (Sn)

 0.01

 Tantalum (Ta)

 0.001

5. Alloy according to one of claims 1 to 3, containing one or more of the impure elements with the following MAXIMUM concentrations by weight percentage:

 phosphorus (P)

 0.005

 sulfur (S)

 0.003

 copper (Cu)

 0.06

 titanium (Ti)

 0.005

 niobium (Nb)

 0.0005

 nitrogen (N)

 0.015

 oxygen (O)

 0.002

 calcium (Ca)

 0.001

 magnesium (Mg)

 0.001

 tin (Sn)

 0.005

 Tantalum (Ta)

 0.0005

6. Alloy according to one of claims 1 to 5, wherein the value of the nickel content split by the aluminum content is equivalent, respectively in weight percentage, to between 1.8 and 4.2:  10 Ni = between 1.8 and 4.2 To the 7. Alloy according to one of claims 1 to 5, wherein the value of the nickel content split by the aluminum content is equivalent, respectively, by weight percentage, to between 2.1 and 3.9: 15 Ni = between 2.1 and 3.9 To the 8. Alloy according to one of claims 1 to 7, wherein in its chemical composition it has a ratio of chromium + molybdenum + vanadium broken by carbon, respectively in percentage by weight, greater than 12, but less than 19:  5 9. Steel object for work at high temperatures of high hardness, high heat resistance and high thermal stability, in which a starting material manufactured according to a metallurgical fusion process or a powder metallurgical method, with a chemical composition specified in the preceding claims, It is molded by hot forming and machining, whose shaped object presents 10 after a hardening heat treatment precipitated secondary carbides, as well as intermetallic precipitation. 10. Steel object for work at high temperatures according to claim 9, which presents in the structure a ratio of intermetallic precipitations split by precipitated secondary carbides, respectively in percentage by volume, less than 3.0. 11. Steel object for work at high temperatures according to claim 9, which presents in the structure a ratio of intermetallic precipitations split by precipitated secondary carbides, respectively in percentage by volume, of 1.0 and less, but greater than 0.38 . twenty 12. Steel object for work at high temperatures according to one of claims 9 to 11, which presents mixed carbides secondarily precipitated from chromium, molybdenum and vanadium and intermetallic phases of the type Al Fe2Ni in the structure.   25