CS251460B1 - A method of creating another life cycle of parts made from stabilized austenitic steels - Google Patents

Abstract

The purpose of the solution is the economical use of stabilized austenitic steels with a nickel content of 30 to 34%, namely by restoring their useful properties with regard to their heat-resistant and corrosion-resistant applications; weldability is also restored. Parts made of the above-mentioned steels are annealed in at least one stage, namely in the range of 1,060 to 1,140 °C, then cooled to ambient temperature. By heat treatment in the second stage, other variants of the procedure are applied: annealing in the range of 850 to 950 °C, optionally in the range of 760 to 800 °C; Another variation is two-level annealing in the second stage, whereby annealing in the range of 760 to 800 °C is followed, while leaving the parts in the furnace, by annealing in the range of 630 to 670 °C.

Description

251460

The present invention provides a further life cycle of parts made from stabilized austenitic steels with a nickel content of 30-34%. In applications such as stainless steel and stainless steel, these materials are, in many cases, subjected to a combined load; an example of this is the demands on heat-resistant, gas-resistant corrosion. In the exploitation of the parts produced by these steels, the long-term operation of the steel is progressively degraded, and such changes are significant, especially in the critical region of the art, and the on-going events manifest themselves in a multitude of extremes. Steels are also exposed to thermal shocks in the critical area, but also low-cycle stresses in alternating process runs, often also cyclocycling.

The austenitic eagle's use of austenitics is targeted in two ways; one sauberá effort to prolong life, for example, by MS. AO No. 209 625. restoration of useful properties, the dilutions have to be targeted by narrower points according to the austenitic type groups; Here, the criterion of the content of nickel, an element of the stability of the centered grid, comes to the fore, bearing in mind also its partly opposing phenomena in the set of material properties of austenitic materials. An example of this is the good mechanical properties of nickel alloys by the heat treatment process applied in Sp. st. neither. for gas turbine blades; however, corrosionW. J. McCall (Combustion, April 1971, pp. 27-33) notes in the article that in the case of corrosion, although rarely, its effects on the nickel alloy are destroyed. The data in the article show that restoration of mechanical properties is not complete, and therefore the designation of regeneration is not in use. The procedure is applied at a first stage of 1150 ° C.

Due to the partially irreversible changes in the degraded steel, substitution appears to be a suitable term for thermal processing. The cost of restitution processes is due to the fact that in a few hours the maximum changes that have been made in the steel for several years are to be eliminated, and in the case of stabilized steels, the discrete changes can exhibit positive or negative performance. Thus, V. D. Levin (Issled. After cor. Met., 1951, p. 167-168) found that it was possible to induce intercrystalline. corrosion in titanium-stabilized steel, if it is first extracted at 1300 ° C, cooled with water and then calcined in a critical area. Paradoxically, however, steel with visible carbide aggregates is no longer subject to intercrystalline corrosion if a velmid or, for example, at 650 ° C for 104 h is annealed in the critical region. .

However, also in the critical region, parts of stabilized steels occur, which can only occur after a time of ten times greater than the indicated 104 hours. An example is the case of a radiation section system of a furnace dealkylation unit where the construction material is stabilized steel 21% chromium and 32% nickel. In this piping system, the preceding medium is heated with a molar composition: hydrogen 42%, methane 38%, toluene 16%, the remainder alkane gases, from 490 to 600 CC, at the inlet pressure of 6.1 MPa. The temperature in the radiation section is in the range of 680-700 [deg.] C. The piping system has worked under these conditions at 9.104 h when, during the inspection of the slide, it detected damage to the cracks of the weld seams and at the outlet collector at the points of connection of the outlet tubes. the welds were not successful, and the cracks grew up and formed siefo-guilt. By such degradation of the material properties, the material has been discarded since it has lost its full life; however, in most cases, these materials are discarded before the end of their expected lifetime, namely safety devices.

The fact that it has not been available yet! For example, the repetition of such austenitic steel type can be explained with respect to the composition of the material in question, which is in% by weight. carbon 0.1; silicon 1.0, manganese 1.5; phosphorus 0.03; sulfur 0.02; chromium21; nickel 32; aluminum 0.6; titanium 0.6. The content of the material falls within the area where the respective value of the stratified error energy indicates the slope of the austenitic steel to the hot swelling in the weld joints; This austenitic steel with a chromium content of 18% and nickel of 9% does not have this sensitivity. Even in the case of intercrystalline corrosion, the value of 32% of nickel is in the range of below 28%, where each increase in nickel content has a significant influence on accelerating segregation processes of grain boundaries (LR Scharfstein et al., Brit.Corrosion J., 1, 1965). , pp. 36-41). However, the time factor also explains the difficulty of the issue, as the solution in the first application relates to the construction material observed in the working course for a total duration of 10'h, of which 2.5 .101 h after its restitution. The differences in the material properties, distinguishing the self-stabilized steel from both the nickel and the conventional steel, are further elaborated by the solution. The effects of the restitution process need to be assessed with respect to mainly the application of the corrosion-resistant construction materials. The properties required depend to a large extent on the construction of the zinc boundaries of these steels, depending on the resistance to plastic deformation, the relaxation phenomena, the corrosion behavior, especially the resistance to intercrystalline corrosion. 251460 5

The aforementioned drawbacks in the field of exploited stabilized steels are eliminated in the direction of restitution of the invention, i.e., the further life cycle of the panels made of stabilized caustic steels. The procedure is focused on a typical group characterized by the composition in% mass: carbon max. 0.11 ° / o, chrome 19-23%, nickel 30-34%, aluminum 0.15-0.6%, titanium 0.15 —0, 6%, manganese 1.6% max., Shrub 1.0% max phosphorus 0.03% max sulfur 0.02% max. Parts are annealed at least in one step and then cooled to ambient temperature .

The process according to the invention is characterized by the fact that the parts are heated to a temperature in the region of 1060 ° C - 1140 ° C, where they are left for 20 - 180 minutes and then cooled to ambient temperature with water, complex parts in oil or air. The heating speed of the components is maintained between 30-70 ° C. h_1, i.e. as is customary for high-grade steels. The temperature in the enclosed area and the stamina on it are determined experimentally on the samples of the material under consideration, also with respect to the size. In the case of the need to increase the resistance of the stabilized steel to the intercrystalline corrosion, the parts according to the invention are subjected to a further heat treatment; the second stage is characterized in that the parts are heated to a temperature in the range of 850-950 ° C, which is left for 90-240 minutes and then cooled to ambient temperature, complex in oil, falls in air.

The second stage of the heat treatment according to the invention can be carried out in a similar manner, predominantly for steels with a stabilizing element to carbon ratio below 5 in the case of titanium, below 10 in the case of niobium, even in the lower temperature range, in the range 760 to 800 ° C with a temperature of 2 - 6 h.

For this annealing in the temperature range of 760-800 ° C, further annealing may be applied, which in turn will contribute to increasing the resistance of the stabilized steel to the intergranular corrosion, so that in this embodiment the second stage of the invention has this feature: the parts are heated to temperature in the area of 760-800 ° C, where they remain in shape for 2-6 h, then the furnace is cooled to 630-670 ° C by interruption and annealed at this temperature for 2-4 hours, after which the temperature is reduced again by interruption of heating and at 500 ° C, the parts are removed from the furnace and left outside in the air to cool to ambient temperature.

According to the invention, after the end of the service life of the stabilized steel, its weldability is restored, ie the restored construction material is not susceptible to cracking and can be guaranteed a metal welded connection, so that the welded sites exhibit the necessary strength, toughness, creep resistance, opal and corrosion characteristics , as well as basic material. It is argued that in order to restrain the weldability of the heat-resistant steel, the basis is one-stage heat treatment.

The multistage treatment increases the value of the minimum induction time for the stabilized steel to give rise to the corrosion corrosion in the critical temperature range; after the two-stage treatment, this indicator exceeds 10 h, whereby the application of the two-level annealing in the second stage exceeds 100 h.

According to the above results, the solution according to the invention differs from the above mentioned solutions for nickel alloys as well as the step-by-step processing; the possibility of realizing a substitution in a single stage brings savings in energy, but also in the handling of material, demanding in the case of large apparatuses. Overall, saving time is also significant, and the equivalent of reducing the loss of production unit, for which the apparatuses of these steels are being restored, is equally important.

As an example of a particular embodiment of the process of the invention, the processing of the parts from the radiation section of the furnace serves a dealkylation unit, i. material characterized by the composition in% by weight: carbon 0.1; silicon1.0; manganese 1.5; phosphorus 0.03; sulfur 0.02; chromium21; nickel 32; aluminum 0.6; titanium 0.6. The 16,150 kg device consists of a set of straight tubes, each having a length of 10,970 mm, a diameter of 141 mm and a crest of 15.9 mm. The cumulative action of the individual damage mechanisms resulted in the formation of micro and macrocracks on the knees in the weld area and an outlet collector at the pipe connection point; material lost weldability, so repair was not possible. The metallographic analysis of the sections and the electro-spectroscopic analysis on the extraction replicates revealed intensive precipitation of the carbonic and intermediate phases. The extent of the damage prevented further exploitation of the device, but did not exclude the processing of the structural material according to the invention.

According to the experimentally determined modes, heat treatment was carried out. In view of the width of the whole system, it was necessary to divide it; dividing lines with straight-line connections of the knee section napriam. The pieces were fed into the furnace at a temperature of about 320 ° C, then the heating rate was about 50 ° C. h_1; after reaching the prescribed temperature of 1100 ° C it did not follow the stamina for 30 minutes, then cooling the air. After the restitution of the parts, the crack was repaired by welding, the parts were inserted into the radiation section, and welded there. The reconstructed lifecycle has worked the construction material for 3 years and continues to work seamlessly. In a further embodiment of the exemplary embodiment, a sample of the steel pipe system annealed in said first stage at 1100 degrees Celsius with a duration of 30 minutes is subjected to

Claims (4)

251460 7 l and in the second annealing step at 870 rC the form of 2 h and then cooled in the air. In the minimum indication induction], the susceptibility to intergranular corrosion in the critical region was shown to be as follows: 10 h. In an exemplary conversion of the titanium-to-carbon targeting process to below 5, steel specimens, characterized by the main ingredients, were processed in carbon: 0.07; chromium 21.3; nickel 33.2, aluminum 0.2; titanium 0.3. Samples were taken from the tube, which in the critical region exceeded 4 x 10 < 1 > h, working at a radiation section of the furnace at a temperature of about 680 [deg.] C. and at a temperature of about 515 degrees Celsius. In the first step, the samples were calcined at 1100 ° C for 30 minutes and then cooled in air. In the second stage, annealing was carried out for 150 minutes at 780 ° C (after this annealing two samples were removed from the furnace and cooled in air), the furnace temperature was further annealed at 650 degrees Celsius for 3 hours; At 500 ° C, the samples were removed from the furnace and cooled in air. The samples showed the following values for at least a time to develop intergranular corrosion in the critical region: less than 1 h after single-stage annealing, after annealing at 780 ° C the value exceeded 10 h, after annealing at 650 ° C it exceeded 100 h The limiting condition for selecting the parts for the application of this method is that such parts may not be rebuilt in the field of operation. conuate throughout the volume and in which the creep mechanism does not reach the end stage; It may be necessary to remove the surface layer from which the impurities of the deeper layers such as carbon, sulfur, nitrogen and the like can diffuse in the heat treatment of the workpiece. The process of the invention can be applied in a wide range of applications in the chemical, petrochemical, metallurgical, food, pharmaceutical and energy industries with the aim of restituting apparatuses from these high-alloy steels. OBJECT A method for forming a further life cycle of parts made of stabilized austenitic steels containing max. 0.11% carbon, 19-23% chromium, 30-34% nickel, 0.15-0.6% aluminum, 0 , 15 to 0.6% titanium, max 1.6% manganese, max. 1.0% silicon, max 0.03% amax phosphorus. 0.02% sulfur, the parts being annealed at least in one stage and then cooled to ambient temperature, characterized in that the dielcesa is heated to 1060 to 1140 ° C, respectively, for 20 to 180 minutes and then cooled to ambient temperature, in oil or air. 2. A method of forming a further life cycle of parts according to claim 1, wherein in the second annealing step the parts are heated to a temperature of 850 to 950 [deg.] C. on which they are left for 90 to 240 minutes and then the invention is cool to ambient temperature with water, optionally oil or air. 3. The method of forming an additional life cycle of parts according to claim 1, wherein in the second annealing step the parts are heated to a temperature of 760 to 800 ° C, where they are left for 2 to 6 hours and then cooled to ambient temperature. water, possibly oil or air. 4. The method of forming a further life cycle of parts according to claim 1, wherein in the second annealing step the parts are heated to a temperature of 760-800 ° C, where they are left for 2 to 6 hours, then interrupted by heating. the furnace is cooled to 630 to 670 ° C and annealed at this temperature for 2-4 hours, after which the temperature is lowered and at 500 ° C the parts are removed from the furnace and cooled to ambient temperature. Severografia, n. P., Závod 7, Most Price 2,40 Kcs