SU1423609A1 - Method of heat treatment of cryogenic equipment articles made of martensitic-ageing steels - Google Patents

Abstract

The invention relates to metallurgy, and more specifically to methods for heat treatment of products from martensite-aging steels, designed to operate at cryogenic temperatures under conditions of a complex stress state. The aim of the invention is a significant increase in ductility and the provision of high strength characteristics. The method includes threefold hardening and aging, with the second hardening being carried out from the intercritical temperature range, and the third one from the Ac temperature C40-° C. The use of the proposed method allows to significantly increase the ductility and operational reliability of highly stressed structures made of martensite-aging: steels. 2 tab. Id (L

Description

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The invention relates to metallurgy, in particular, to methods for heat treatment of products made from martensitic steels, designed to work at cree (temperature 1H111x temperatures under complex stress conditions.

The purpose of the invention is a substantial plasticity and the provision of high strength characteristics.

The method includes triple hardening and aging, with the second hardening being carried out from the intercritical temperature range, and the third from the temperature Ac, -f (AO-100) ° C.

P r and m er. Heat-treated were subjected to thin-walled tubular products made of steel X11H10M2T.

Heat treatment was carried out in the following modes: 1st heating to, Exposure for 0.6 hours, cooling in water, 2nd heating to 600-650 ° C, holding for 2 hours, air cooling, 3rd heating to 740-800 ° C, pulling out for 2 hours, cooling in water and aging at 500-525 C for 2 hours.

Table 1 shows the heat treatment modes and the data on the amount of reverse austenite fd, its strength yield strength and the value of the maximum uniform plastic deformation p at the test temperature of the steel X11H10M2T heat-treated according to the proposed (mode 1-5) and known (mode 6 -8, triple hardening and aging) methods. Heat treatment according to a known method is at the same time the regimes, and exit - dimi beyond the boundary conditions of the proposed method.

As can be seen from the data presented in Table 1, structurally substantiated (by the amount of austenite e) specification of temperature, second hardening limits and upper limit of third hardening heating temperature, modes 1-3 allowed Ka4ecTBeHH (j new for martensite-aging articles to combine strength and ductility characteristics at cryogenic test temperatures, associated with a more than 20 times increase in deformability, approaching the level of austenitic steel, while simultaneously exceeding their yield strength by 4 times .

Outside the proposed method with a lower limit of temperature

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A quenching hinge T of a known method (mode 6) austenite in the steel structure is formed in a small amount, insufficient to delay after the third hardening even at a temperature Tj close to the lower limit of the proposed method. Associated with the inherent phase-hardened martensite, which forms during the third quenching, a slight decrease in the temperature of the onset of transformation upon reheating, leads to the formation of austenite in the structure of aged steel. However, in its structural SOS10JANIZO and colttaism, it cannot ensure the realization of the objective of the proposed method and instead of fp 16-20% (mode 1-5), Ep 0.75%.

At the upper limit of the second batch temperature T of a known method (recovery 7), a small amount (up to 5%) of phase-riveted residual austenite and martensite forms in the steel structure. The presence of residual austenite broadens the temperature range of the f-T dependence upon reheating, resulting in an amount of β-phase after the third quenching to be increased to 1-8%. the onset of b.- j transformation into the temperature range of hardening aging. However, its structural - state and quantity does not provide for the plasticization of steel, and the development of the aging process contributes to a sharp increase in its deformability (Cf 0.5%). Upper limit tempera; that -. The third hardening T of the known method (mode 3) causes the decomposition of austenite, which is retained after the second hardening, and, consequently, leads to a sharp decrease in the deformability of the steel during the subsequent strengthening aging

(ep 0.5%).

The new temperature proposed in the inventive method is the 1-1st indicator for estimating the temperature limits T, T (d) d, ax (formation temperature of the maximum amount of stabilized austenite), as well as the temperature criterion Ac used, for evaluating the temperature limits Tj depend on : The way of the character of the alloying of martisite and steel and steel

(Table 2), which allows the proposed method to be extended to other steels of the class under consideration.

The use of the proposed heat treatment method allows significantly (by a factor of 20) to increase the resource of low-temperature plasticity (p 16-20% after treatment according to a known method. 6p 0.5-0.75%). The relevance and practical value of the proposed method are enhanced for thin-walled elemental structures operating at cryogenic temperatures, as a rule, under conditions of a complex stress state. The decrease in the deformability for such products when the test temperature is lowered and during the transition from the linear to flat stress state necessitates a significant increase in the plasticity resource at high strength indices. Providing, as a result of the implementation of the proposed method, a sharp increase in the ductility resource to the level of austenitic steels while exceeding their limit

a yield of more than 4 times makes it possible to expand the field of application of martensitizing steels in the case of highly stressed structural elements; 1; cryogenic technology with a significant increase in their bearing capacity, operational reliability and durability.

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Claims (1)

Invention Formula C-features of heat treatment of products of cryogenic technology from martensitic aging steels, including multiple quenching and aging, characterized in that, in order to increase ductility and ensure high strength characteristics, the second quenching is carried out from the intercritical temperature range in the T range (f; ) ± 25 ° С, the third - from the temperature Ac, -t- (40-100) С, and aging is carried out at temperatures of 25,500-525 ° C, providing the content in the steel of 25-35% austenite, where T (d) max. temperature of formation of the maximum amount of stabilized, annogo austenite. n ON 1L about CM 1L m G- VC f in 1L (N About u-i r c " about 1L CHO oh oh oh oh vo irv LOfc1 / 1 ON o o o o o about 1L f about VO v About vO "3 about n ABOUT) about gt vO CN to 1L CN 00 oh oh 00 About 1L f about 1L f about 1L oo about m 1L four 1L about p sh G-4 OSM oh x 1L ABOUT about g 1L tM (M o m l about  1L about OS at about so 1L f o 1A23609 table 2 Temperature intervals of austeite formation (2 2 h) X16N5DZ 625 X12N10MT .600  X11H10M2T 625 X13H9D2MT 620 XI8M3T 650 X18K9M5T 650