UA139982U - METHOD OF HEAT TREATMENT OF CORROSION-RESISTANT PIPES OF AUSTENITE STEEL TO PROVIDE AN INCREASED MECHANICAL POWER COMPLEX - Google Patents

Abstract

The method of the proposed heat treatment of cold-formed pipes made of stainless corrosion-resistant steels of austenitic class type TP304L (domestic analogue: steel grade 03X18H11) and TP316L (domestic analogue: steel grade 03X17H14M3) includes heat treatment of pipes at temperature at least 15%, which allows to provide increased values of yield strength and yield strength while maintaining high plastic performance.

Description

The useful model belongs to pipe production and can be used in the production of seamless cold-formed pipes from corrosion-resistant austenitic steels, intended for product segments in which the material requires increased resistance to high pressure with simultaneously high corrosion and plastic properties.

Today, on the market of seamless stainless pipes, the austenitic chrome-nickel grades of steel TRZO4Y / 1.4301 are most in demand (the domestic analogue is the grade of steel

ОЗХ18НИ11) and TRZ16Й / 1.4401 (domestic analogue - steel grade 0О3Х17НИ14М3). Due to the regulated low carbon content of 0.030 Fo, products made from the above-mentioned grades of steel have high corrosion resistance with a satisfactory set of mechanical properties. In the case of using the generally accepted technology for the production of seamless cold-formed products, the standard heat treatment temperature is 1080 "С, with subsequent holding at the specified temperature and rapid cooling. This standard heat treatment technology allows the production of products with high corrosion resistance, as well as a sufficient set of mechanical properties for the use of the material in the chemical and food industries, as well as for the production of general purpose pipes where resistance to high pressure is not required.

Today, the segment of seamless stainless pipes occupies a leading position in the market of stainless products. Given the dynamics of industrial development, the demand for products with high added value is increasing, in particular, for materials with an increased set of properties and at the same time high corrosion resistance.

For example, in the segment of the automotive industry (fuel bars in fuel systems and other components that require resistance to high pressure), there is a tendency to replace standard grades of the TRZO4Y type with duplex steels, such as OM5 532304 and OM5 531803 / 1.4462. The advantage of duplex grades of steel is higher values of strength and yield strength.

Comparative characteristics are given in Table 1.

Table 1

MPa minimum, MPa minimum, 90 (532304114362. |... 690 | ...777774007 1777117171112г5с2СщС

However, along with the advantages, the following disadvantages of using duplex grades of steel should be noted:

З Low formability and machinability due to the duplex structure: austenite / ferrite;

Tendency to the formation of harmful intermetallic phases, both in the weld zone and in the case of operation at temperatures above 250 "С.

The above-mentioned nuances, characteristic of duplex products, are serious limitations for designers and designers.

The fact that the price of duplex products is at least 30 Fo higher than austenitic products is also important.

To increase operational characteristics while maintaining high plastic characteristics, and, accordingly, good ability to deform, PJSC CENTRAVIS PRODUCTION

UKRAINE" has developed a new heat treatment technology based on the mechanism of weakening of riveted austenitic grades of steel during heating. The use of this technology in the production of cold-formed seamless stainless pipes allows to significantly increase such parameters as strength limit and yield limit while maintaining high plastic properties of finished products.

In the table 2. the requirements of regulatory and technical documentation for austenitic grades of steels such as ТРЗО4Й and ТРЗ16Й, as well as the minimum values of mechanical properties that are ensured in the case of applying the newly developed technology in comparison with the existing production technology, are given:

Table 2 minimum, MPa minimum, MPa minimum, 90 00011117 snuyuchatechnologiyavyrobnitstviya.id//-:/ // 00001111. | 1. Newly developed production technology.

Ensuring (when using new technology) strength characteristics higher than the minimum of 2095 at the strength limit and at least at 4095 at the yield point without loss of plastic properties is a colossal advantage for designers when developing material for projects involving high pressure. Figure 1 shows a cross-sectional view of a pipe.

The dependence of the internal pressure that the pipe (Fig. 1) can withstand with an increase in the strength of the material is described by the OO, Barlow formula, in which: ? - fluid pressure (pounds per square inch), 7 - pipe wall thickness (inches), OD - pipe outer diameter (inches), 5 - material yield strength (pounds per square inch).

An additional advantage of using pipe products with increased strength and yield strength values is the ability to withstand equivalent pressure with the use of pipes with smaller wall thicknesses (7 mm).

The basis of the useful model was the task of improving the method of heat treatment of austenite class pipes using the example of steel grades ТРЗ304И /О3Х18НИ11 and ТРЗ316И /О3Х17Н14М3 due to the reduction of temperature and exposure time when performing heat treatment of pipes on the finished size.

The task is solved in the heat treatment method by lowering the heat treatment temperature on the finished size from 1080 "C to 900 "C and reducing the exposure time by at least 15 95.

The declared parameters of the useful model were obtained experimentally in production conditions.

To carry out the experiment, a repartition pipe blank was taken from the austenitic grade of TRZO4 steel! LZH18NI11 and TRZ16I LZ3X17NI14M3 size 60.3x5 mm.

The scheme of deformation according to redistribution (rolling routes) is given below: 0. 60.3x5 mm 2. 25x2.5 mm KhPT-55 3. 12x1.25 mm KhPT 6-20

Ko) 4. 8x1.25 mm 6/0 hot.

The deformation scheme did not undergo changes and was carried out in accordance with the existing technology.

The temperature of the heat treatment of pipes of the finished size 8x1.25 mm was reduced by 180 C compared to the standard one and amounted to 900 "C (that is, the standard technology provided for the use of a temperature of 1080 C, according to the developed technology: 900 C). The time of holding the pipes at the temperature was also reduced by 16 95 due to increasing the speed of movement of pipes from 0.30 mm/min to 0.36 mm/min. Heat treatment was carried out in a pass-through electric light annealing furnace manufactured by MANI EK.

The complex of mechanical properties was controlled in heat-treated pipes with a finished size of 8x1.25 mm. The results of the control of mechanical properties after the application of the new technology, as well as in comparison with the complex of properties characteristic of the existing technology, are shown in the table. 3.

Table C. . 0.2, .

Steel brand | Size, mm Sv, MPa MPa b, o Notes

Existing technology 1080 "C, M-0.30 mm/min 19 ny

New technology 900 "C, M-0.36 mm/min

NTD requirements Minimum 500 | Minimum 195 | Minimum 35 | 00000000

The results of control of the set of mechanical properties after heat treatment using the new technology at 900 "C meet the requirements of the NTD for all controlled parameters.

In addition, pipes manufactured using the new technology are characterized by increased strength characteristics (strength and yield strength) compared to the existing technology, and, at the same time, plastic properties that meet the requirements of NTD.

Moreover, additional control of plastic properties, namely, tests on flattening and distribution, also demonstrated high plastic properties of pipe samples manufactured according to the new technology. The images of the pipe samples after the distribution and flattening tests are shown in Fig. 2 (a, b) and Fig. 3.

Claims (1)

USEFUL MODEL FORMULA The proposed method of heat treatment of cold-deformed pipes made of stainless corrosion-resistant steels of the TRZO4Y type (domestic analogue: steel grade OZH18NTI1) and TRZ16Y. (domestic analogue: steel grade О3ЖХ17НИ14М3), which includes heat treatment of pipes on the finished size at a temperature of 900 C, and reduction of the holding time by at least 15 95, which allows to ensure increased values of the strength limit and yield limit while simultaneously maintaining high plastic characteristics.