Method for determining temperature of full polymorphous transformation of heat-resistant two-phase titanium alloys of (alpha+beta)-martensitic class

FIELD: metallurgy.

SUBSTANCE: method for determining temperature of full polymorphous transformation of heat-resistant two-phase titanium allows of (α+β)-martensitic class is proposed, which involves preliminary preparation of a specimen by means of multistage heat treatment of the latter, which is performed immediately in a differential thermal analysis (DTA) instrument in atmosphere of cleaned argon and its investigation using DTA method. Heating of the alloy specimen to single-phase β-area, supercooling below temperatures of active diffusional decay of β solid solution, short-term exposure and repeated heating to the single-phase area is performed. Fixation of dependence of a DTA signal on temperature and calculation of values of derivative of DTA signal on temperature is performed, and temperature of completion of full polymorphous transformation is determined as per maximum on the curve of the first derivative of DTA signal at repeated high-temperature heatinge.

EFFECT: improving determination accuracy of temperature of full polymorphous transformation in heat-resistant two-phase titanium alloys.

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The invention relates to the field of research of processes of polymorphic transformations in metals and solid-phase metal alloys and can be used, for example, in the technical control of metallurgical plants producing titanium and alloys based on it.

The temperature of polymorphic transformation (temperature end of the polymorphic transformation temperature TPP) is the temperature above which the alloy structure is absent α-phase and the alloy consists of stable β-solid solution.

Modes of thermomechanical processing, namely, the heating temperature and deformation processing, industrial grades of alloys based on titanium have

Tn=(TPP±N)°C,

where Tn- temperature/strain specific melting alloy;

TPPthe temperature of complete melting polymorphic transformation, changing within the brand alloy in a certain range;

N is the Offset from TPP. N does not depend on the chemical composition of the melt and within the brand alloy is constant.

Thus, to select a specific temperature heating/deformation of the alloy necessary information about TPPused for melting. In addition, in most cases, the overheating of the alloy above TPPthe final stages of processing is unacceptable as it results in the it to a significant growth of the original β-grains and deterioration of mechanical properties of the semi-finished product.

There is a method of determining the temperature of polymorphic transformation (TPP) titanium alloys by the method of trial sakaluk [1]. The essence of this method consists in fixing the structure of the alloy after quenching with heating at successively higher temperatures in the region of the α+β→β transition.

This method is very time-consuming, requires making a large number of special designs, sophisticated laboratory equipment and, in addition, are not known with great precision, and high performance.

There is also known a method of determining the temperature TPPin two-phase titanium alloys, including heat samples for hardening to a predetermined temperature, determining their microstructure and identifying dependencies between the heating temperature for quenching and number of primary α-phase [2].

Using this method, you can determine the temperature TPPby quenching and study of the microstructure of a single sample, but the main disadvantages are that it is still very time consuming and not very accurate and high performance.

In addition, well-known simplified metallographic method for the determination of TPPbased on deep etching of the samples after quenching with different temperatures in the interval of occurrence of polymorphic transformation. At this surface the samples, hardened from the α+β region becomes opaque and after quenching from the β-region remains shiny [1].

The main disadvantage of this method is its applicability only to alloys (α+β)-class, and relatively low precision.

Sometimes applied the settlement method of determining TPP[1] according to chemical analysis. For this purpose experimental dependences of TPPalloy on the concentration of alloying elements.

Also known a more General approach for the analytical determination of TPPmelting based on the concentration of alloying elements for industrial titanium alloys of any brand [3].

The disadvantages of calculation methods for the determination of TPPis the use of experimental correlation dependences, as well as the absence of common regression coefficients for all of the used alloying elements and impurities.

In addition, there is a method of determining the temperature TPPtwo-phase titanium alloys by fixing the temperature of the free deflection, which corresponds to TPPfixed sample under continuous heating contact method [4].

There is also known a method of determining the end temperature of the α+β→β transformation using the method of acoustic emission [5]. The essence IU the ode is to measure the radiated acoustic emission and the analysis of its activity during continuous heating of the sample. The fixing temperature TPPproduced by abrupt reduction in the activity of acoustic emission.

Lack of data is the need to use equipment that is not produced commercially, which seriously reduces the possibility of using these methods in industry, in particular in the technical control of metallurgical industries, since it is difficult to ensure reproducibility and repeatability of results.

Also known application of the dilatometric method for determining the temperature of the end of the α+γ→γ transformation (AC3in steels, which is the analogue of temperature TPPin alloys based on titanium [6, 7].

The use of the dilatometric method for determining the temperature TPPtwo-phase titanium alloys is complicated by the low volume effect in the course of the α+β→β transformation.

Also known applications of the methods of differential thermal analysis and differential scanning calorimetry (DSC) to determine the end temperature of polymorphic transformation in alloys based on titanium [8, 9].

It is known [8...10] noted that when using thermal analysis techniques such as DTA and DSC, recorded in experiments curves continuous heating is strongly influenced by the original structure of the research is imago sample, in particular, the morphology of the α-phase in the alloy structure. In particular, if the structure of a large primary precipitates of α-solid solution instrumentally recorded temperature end of the α+β→β transformation is higher than the equilibrium TPPdetermined by metallographic techniques. Accordingly, for each melt of the alloy is necessary to use different heating rates in order instrumentally recorded temperature was correlated with temperature TPPdetermined by metallographic techniques trial sakaluk.

The technical task of the invention is to improve the accuracy and productivity of determining the temperature of polymorphic transformation of two-phase titanium alloys by the method of differential thermal analysis.

To solve this technical problem, a method for determining the temperature of complete polymorphous transformation of two-phase heat-resistant titanium alloys (α+β)-martensitic class, including preliminary training patterns of the alloy and its study by the method of differential thermal analysis (DTA) under continuous heating of the sample alloy and wherein the preliminary preparation of the structure is realized by means of multi-stage heat treatment of the sample that Provo is drawn directly into the device DTA in the atmosphere of purified argon, moreover, preliminary multistage thermal treatment includes rapid heating in single-phase β-region, subcooling temperatures below the active diffusion decay β-solid solution, short-term exposure and re-heating in single-phase region with a predetermined controlled speed, during which spend fixation according to the DTA-signal from the temperature and the calculation of values of the derivative DTA signal, and the temperature of the end of the full polymorphic transformation is determined by the maximum on the curve of the first derivative DTA signal at repeated high-temperature heating.

The invention is illustrated graphic materials, in which figure 1 shows a diagram of the temperature profile DTA experiments, figure 2 - microstructure of samples alloy VT3-1, quenched from different temperatures, figure 3, 4 - areas DTA-curves of repeated continuous high-temperature heating of the samples of the alloy VT3-1 and VTM and calculated according to the partial derivatives DTA signal from the temperature.

The order of operations in the specified way of determining the full temperature of polymorphic transformation alloy VT3-1 is as follows:

1. The sample melting alloy is placed into the measuring cell of the device DTA.

2. The heat chamber of the measuring device is filled with an inert atmosphere, the quality of the solid fuel which is used argon technical purity additionally purified by the adsorption method, moreover, in a heat chamber of the device during the whole experiment must be supported gauge pressure (relative to atmospheric) controlled atmosphere.

3. The sample of the alloy is heated in a single-phase β-region with the maximum sold used by the device speed.

4. The sample directly after heating pereohlajdenia up to temperatures of 600...650°C (below the interval of the high-temperature decomposition of β-solid solution most heat-resistant two-phase α+β alloys martensitic class) with the most-sold rate on your device differential thermal analysis.

5. The sample is aged at a temperature of hypothermia in a few minutes to equalize the temperature in his section.

6. After isothermal aging re-heating of the sample alloy in single-phase β-region with speed, selectable individually for each grade of alloy.

7. After the experiment is calculated partial derivate of the first order numerical method the original DTA-signal time.

8. The temperature of the end of polymorphic transformation after processing according to the specified mode is determined by the maximum on the curve private derivative of the first order.

This technical solution is confirmed investigated the s of the bottoms of two-phase titanium alloys martensitic class VTM and VT3-1.

Metallographic studies have established that the temperature TPPthe investigated melts (by the method of trial sakaluk) equal 973°C and 980°C for alloy VT3-1 and VTM respectively (figure 1). In the proposed method: TPPalloy VT3-1 is 977°C and 982°C for alloy VTM.

A sample of the alloy dimensions 3×3×3 mm (D×V×W) is placed in the measuring cell device DTA NETZSCH STA 449C Jupiter" (maximum speed of heating and cooling to 50°/min) and processed according to the mode, the circuit of which is shown in figure 1. When processing are recorded according to the DTA-signal from the temperature at various speeds and re-heating in single-phase β-region (3, 4).

After the experiment is performed numerical calculation of the partial derivate of the first order initial DTA-signal time and the build dependencies of the values derived from the current temperature.

The course polymorphic α+β→β transformation during heating takes place with absorption of energy (i.e., the polymorphic transformation process is endothermic) [11], therefore under continuous heating of the sample alloy on the DTA curve in the temperature range of polymorphic transformation is fixed endothermic effect. Thus, the dependences of the private values of the derivative DTA temperature in the temperature range downward in the Twi endothermic effect observed local maximum.

Joint analysis of the obtained dependences of the derivative DTA signal from the temperature shows that for alloy VT3-1, the rate of repeated high-temperature heating 20°/min provides the ability to define TPPwith an accuracy not lower than the accuracy of the method of trial sakaluk - 3. For alloy VTM - speed re-heating, provide the calculation of the TPPthe proposed method is 50°/min

Example.

Samples of alloy VT3-1 and VTM was placed in the measuring cell device simultaneous thermal analysis NETZSCH STA 449C Jupiter" and processed according to the mode, the circuit of which is shown in figure 1. When the treatment was carried out recording dependencies DTA signal from the temperature at various speeds and re-heating in single-phase β-region. After the experiment was conducted numerical calculation of the partial derivatives of the first order initial DTA-signal time and built according to the values derived from the current temperature (figure 3, 4) for all investigated heating rates. Through joint analysis of the obtained dependences of the derivative DTA signal from the temperature were selected speed reheating samples for the determination of TPPthe proposed method is 20°/min for alloy VT3-1, 50°/min for alloy VTM.

The proposed method of determining the temperature of polymorphic transformation in dujfasp the x titanium alloys can improve the accuracy of determining the end temperature of polymorphic transformation heat-resistant two-phase titanium alloys (α+β)-martensitic class.

Sources of information

1. Metallography of titanium alloys. Edited Anoshkina NF, Bochvar GA, Livanov, VA and other M, metallurgy, 1980, p.36.

2. Copyright certificate №394709, G01N 25/02, 1973, No. 34, p.142.

3. B.A. Kolachev, SHE Egorova, S. B. Belov. The relation of the temperature of the α+β→β transition of industrial titanium alloys and their chemical composition / Metallography and heat treatment of metals. 2008. No. 8 (638), p.10...14.

4. RF patent 2248539, G01K 9/00, G01N 25/02.

5. The invention application EN 2010134056, 13.08.2010.

6. Ryzhkov M.A., A.A. Popov, Methodological issues of building thermokinetic diagrams of transformation of undercooled austenite in low-alloy steels / metal Science and heat treatment of metals. No. 12 (666). 2010. p.37...41.

7. ASTM A 1033-04. Standard Practice for Quantitative Measurement and Reporting of Hypereutectoid Carbon and Low-Alloy Steel Phase Transformations. ASTM, 2004. 14 p.

8. TIAN Fei, ZENG Wei-dong, MA Xiong, SUN Yu, ZHOU Yi-gang. Measurement of beta transus temperature of BT25 titanium alloy by physical analysis and metal lographic observation methods / Transactions of Materials and Heat Treatment. 2011. Issue 5.

9. Carton M., Jacques, P., Clement N., Lecomte-Beckers J. Study of Transformations and Microstructural Modifications in Ti-LCB and Ti-555 Alloys Using Differential Scanning Calorimetry / Ti-2007 Science and Technology. 2007. pp.491...494.

10. A.I of Gadaev, A.G. Illarionov, A.A. Popov, M.A. Ryzhkov, E.V. Kolosova, M.A. Popov, PS Altman, NN. Bondaruk. Using the method of thermal analysis to determine the full temperature of polymorphic transformation of two-phase titanium alloy and the VA / Scientific and technical journal "Titan". 2010. No. 1. P.24-30.

11. Handbook of thermal analysis and calorimetry: Principles and Practice / Michael E. Brown. London: Chapman and Hall, V.2. 1998. - 725 p.

The method of determining the temperature of complete polymorphic transformation heat-resistant two-phase titanium alloys (α+β)-martensitic class, including preliminary training patterns of the alloy and its study by the method of differential thermal analysis (DTA) under continuous heating of the sample alloy, are cleansed by the fact that the preliminary preparation of the structure is realized by means of multi-stage heat treatment of the sample, which is carried out directly in the device DTA in the atmosphere of purified argon, and the preliminary multi-stage heat treatment includes rapid heating in single-phase β-region, subcooling temperatures below the active diffusion of the decay d-solid solution, short-term exposure and re-heating in single-phase region with predetermined controlled speed, which are fixed according to the DTA-signal from temperature and determine the value of the derivative DTA signal, and the temperature of the end of the full polymorphic transformation is determined by the maximum on the curve of the first derivative DTA signal at repeated high-temperature heating.



 

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