DE1962504A1 - Process for the heat treatment of steel - Google Patents

Description

Mitsubishi Jukogyo Kabushiki Kaisha \ £ OEZ. 1969 Tokyo, Japan -

Process for the heat treatment of steels

The invention relates to a method for heat treatment of steel, which gives the steel high material strength and, to an appropriate extent, internal friction or intrinsic friction be awarded.

In modern rotary machines such as turbines and compressors grain i, the blades are exposed because of the enlargement of the machines and the speed increase increasingly a large centrifugal force. To ensure a quick development of this Rotationsmaschi- must therefore a blade material are created rien, which can withstand a stress caused by centrifugal force. In addition to being strong, this blade material must also have appropriate internal friction, since the blade is subject to a certain driving force when the centrifugal force is high. The reason for this is as follows: When designing a turbine or compressor blade, a corresponding opposing plane is generally taken into account in order to avoid dangerous resonances under special drive conditions it is practically impossible to constructively avoid all conceivable resonances. In practice, therefore, a counter-plane is only specified in the design to produce a really dangerous resonance, while no counter-plane is determined for the other, less dangerous, resonances

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Damping capacity of a scii ^ fel together, i.e. in the sense a 'vibrator,' in which the vibration amplitude is small there is a large damping capacity. So it varies the area of dangerous resonance with the damping capacity of a blade, the number or size of the dangerous to be avoided by constructive means The greater the damping capacity, the smaller the resonance is. The damping capacity of such a blade depends largely on the internal friction of the blade material away. For this reason, a blade material must have a corresponding internal friction around the blade from harmful resonance as a result of the action of a certain To protect driving force "

So far, 13 Cr-type stainless steel has been used as a material for workpieces that must have a large internal friction. Steels of this type, however, have a tendency to reduce internal friction quickly if the strength is increased by changing the composition or by improving the heat treatment _e The limit value up to which steels of this type can be used as a material with high internal friction is therefore generally at a tensile strength of 90 kg / mm or less. In view of these difficulties, a tough steel suitable for turbine blades has been proposed (Japanese Patent Application No. 75390/65) which has a tensile strength of 100-130 kg / mm ² and a has high internal friction. Although this tough steel generally has a good internal coefficient of friction, it has been found in later tests that the internal friction properties change with even slight fluctuations in the melting conditions and that some of these steels show only a very small amount of internal friction.

Surprisingly, it has now been found, according to the invention, while ensuring a high internal friction of materials, that the above- mentioned steel and other steels can be given a stable, high internal friction by means of a special heat treatment «

The object of the invention is therefore primarily to create a method for the heat treatment of steel, by means of which its internal friction is stabilized to a suitable value 0.06 $ O, up to 1.0 $ Si, up to 1.0 $ Mn, 3 10 $ Hi, 8 - 1796 Cr, 4 - 10 $ Co, 2 - 5 $ Mo or W as a substitute for Mo im Ratio 2: 1, other impurities, aggregate elements and remainder]? E is first cooled from the austenitic temperature to a temperature between the beginning and the end of the martensite transition range, the structure being at least partially converted into martensite, then the steel again to a temperature is heated temperature range in which the previously formed primary martensite only partly, preferably, converted to a considerable extent in the austenite, the steel thereon for transforming the rest austenite to martensite and finally the overall t cools sec undary martensite is subjected to precipitation hardening «With unlimited tensile ^strength: the proportion of martensite formed first can go up to 100

mm is sufficient. The precipitation hardening can be omitted. However, if the yield point is to ^{reach 100-130 kg / mm 2} for the particular advantages of the invention, the resulting proportion of primary martensite must be controlled, for example to at least $ 20, normally to $ 50, in order to achieve a sufficiently high internal friction .

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. A feature of the invention is that the inventions according to Applied steel is subjected to the heat treatment to be described below, in principle in such a way that in it at the same time two or more different hardness phases, including a very soft phase, are present.

When the said steel is cooled from the low austenitic temperature, martensitic deformation occurs if the cooling rate is about 10 ⁰ O per hour or more, below this cooling rate

^ however, only a correspondingly lower rate of martensite formation. The characteristic feature of this transformation is that the size of the transformation largely depends on the temperature and is hardly influenced by time. More specifically, said steel is cooled from a temperature above the austenite transition end point to a suitable temperature below that at which the martensite deformation begins and above that at which this deformation ceases, whereby at least a portion of the austenite is converted into martensite. Thereupon the steel ^{is heated to a temperature of 600 - 700 0} O above the martensite transition point.

Bt temperature heated to soften the martensite. Simultaneously on the other hand, the residual austenite remains partially unchanged and practically free from a change of state in Dependence on the time and will the martensite deformation caused by the subsequent cooling at a corresponding temperature. The one at the beginning of the heat treatment formed martensite is hereinafter referred to as "primary martensite" denotes, while that of the remaining austenite after reheating or tempering the primary martensite formed martensite is called "secondary martensite" will.

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ORIGINAL INSPECTED

If the tempering or tempering temperature of the primary martensite is higher than the upper martensite transition point, the primary jiartensite (above Ac ₁ in the present steel) is partially converted, for example up to 50 $, or completely into austenite. According to the invention, in order to ensure adequate tempering of the primary marcensite, a tempering temperature is used, if necessary, such that at least part of it is reshaped.

In this case, it becomes that formed from the primary martensite Austenite is partially or> completely converted into martensite by subsequent cooling. Although this mar- " tensite has a tendency to retain the residual austenite and has a fairly low precipitation hardness ability, its properties are similar to those of secondary martensite. In some cases it is required, depending on the material used to promote the cooling to a temperature below room temperature in order to achieve a Satisfactory regulation or control of the proportion of the primary material and the transformation of the secondary material to ensure sits after tempering or tempering. The residence time at each temperature must, however, depending on the naoh The dimensions of the piece to be subjected to the heat treatment must be so long that the temperature is evenly distributed reached over the entire interior of the workpiece; will. This residence time can be used without affecting the Material properties vary in the range of 1 to 10 hours.

If the steel obtained in this way, which has a microstructure of primary and secondary Martenite, is kept for 1 to 100 hours at a temperature of 400-5OQ ⁰ O, the primary Marteneitpha experiences over-

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aging does not change the hardness during the previous intermediate heating, i.e. it remains as soft as it is, while the secondary martensite phase experiences aging hardening over a phase that is practically the same as the phase obtained during normal hardening, whereby the necessary hardness and strength of the steel are increased overall. In this state, the steel shows a strength based on the heat treatment and chemical composition as well as high internal friction properties _e

In the case of the steel subjected to the aforementioned heat treatment, the internal friction is generally greater, the greater the amount of primary martensite and the higher the Tempering or tempering temperature was. On the other hand, on the other hand, the strength or hardness is reduced. In this case can reduce the strength or hardness to a certain extent by increasing the amount of aggregate on a hardening element, like molybdenum, are suppressed in order to reduce the ability of the secondary Increase martensite phase.

The proportion of primary martensite in the steel should also expedient taking into account the chemical composition, the required material strength and the internal friction of the steel can be determined. Since the deformation properties of the primary martensite are lower Variation in chemical composition must change the amount of chemical constituents for example by measuring the thermal expansion curve of each individual melt precisely. With such control of the proportion of primary martensite due to a change in the conditions of the seashell »collecting

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Changes in the steel only have a minor effect. The tempering temperature of the primary martensite is set as high as possible in order to reduce the hardness of the primary martensite as much as possible to keep it low. This pail is also preferred the martensite initial temperature by measuring the austenite transition temperature Each melt is determined. A temperature value is preferably chosen as this temperature in which the transformation of the primary martensite 50 $ or is less.

In the following the invention is explained in more detail in an exemplary embodiment, without
wanting to restrict.

in more detail, explained without, however, the invention leg on it Table 1 is the chemical composition of a steel indicated, that by ordinary heat treatment none great internal friction can be imparted. A sample consisted of a piece of steel that was in a basic

High-frequency melting furnace cast into a casting of 30 kg · » sen, forged into a rod with a square cross-section of 40 χ 40 mm and cut into pieces was. In this regard, the mechanical properties and the internal friction properties are each Sample for each heat treatment illustrated in Pig * 2. In Fig. 2, the heat treatment · No. 1 means the Samples A, B ... E a known heat treatment, while the other positions the heat treatment according to the invention indicate. The internal friction is duroh measurement of the natural visual vibration attenuation curve of a sample in shape of a tuning fork is determined by calculation based on the thus measured value. The maximum logarithmic The damping ratio and the resulting load or stress represent a maximum value of the. logarithmic damping ratio within a

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Measuring range and a load or stress in the respective time. According to Fig. 1, in which the vertical Coordinate the logarithmic damping ratio and the horizontal coordinate the maximum bending load (in kg / mm), achieves the real internal friction curve does not have a maximum value at a certain load, but simply increases with increasing load, so that the logarithmic damping ratio on the side- a white> The increased load has a correspondingly higher value.

0 Tabel 1 Sl Mn . Hi Or Mon Oo _W sample 0.03 0.09 0.34 6.17 12.40 3.80 7.37 . 0.02 0.14 0.07 5.50 11.83 3.47 6.14 '- A. 0.03 Chemical composition (weight-90 0.28 0.44 6.01 11.58 3.16 6.39 B. 0.03 0.31 0.19 5.42 12.12 2.71 6.86 σ • 0.03 0.26 0.35 5.76 12.21 - 7.02 4, D. E.

In the embodiment mentioned, the invention according to the method according to FIG. 2 evidently none so great influence on a sample that gives great internal friction by ordinary known heat treatment can be improved, while each sample can be remarkably improved by the ordinary heat treatment only very little internal friction can be imparted; Besides that the internal friction is stabilized at an appropriate optimum value by the method according to the invention.

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0098 86/1291 originally inspected

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Although the above. Embodiment samples used have the chemical composition given in Table 1, the steels used according to the invention are not limited to this, but can have the following composition: less than 0.06 $ O, less than 1.0 $ Si, less than 1.0 t Mn, 3 - IO96 M, 8j *, 17 # Or, 4 - 10 $ Go, 2 - 5 $ Mo or ¥ as Ersata. for Mo in the ratio 2; 1, other impurities, aggregate elements and the remainder Fe. Elements that can be added either alone or in a mixture as additives in such a proportion that they do not impair the properties of the steel are, for example, Ti, Al, Zr, TS-, Os, Hf, Oa, B, etc.

Although the invention has been described in preferred exemplary embodiments is described in detail, certain changes and modifications are of course possible for the person skilled in the art, without departing from the scope of the invention.

As can be seen from the foregoing description, the invention thus provides a method of heat treatment of steels, which gives the steel high material strength and internal friction can be imparted to an appropriate optimum extent.

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Claims (1)

196250Λ -to- Claim . Process for the heat treatment of steel with essentially the following composition: 0 s less than 0, Si = less than Mh = less than 1, Ni = about 3 - _ Or = about 8 « w Go "= about 4 -, Mo = about 2 - 5 ^ as well Impurities and remainder Fe, characterized in that the steel is first cooled from the • austenitic temperature to a temperature at which it is completely or partially converted to martensite, then the steel is heated again to a temperature at which the primarily formed martensite is softened and becomes necessary, a part can regress thereof to austenite, in turn, the steel thereon to the martensite transition region is cooled to the remaining undjfeder ψ demapped Instenit in secondary martensite reshape and to form a mixed structure containing at least two phases, the martensite formed primarily and the martensite re-formed from the remaining and / or re-formed austenite, and that this secondary formed martensite is finally subjected to precipitation hardening. 008686/1291 Blank page