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Method of thermal processing of high-strength maraging steel articles

Method of thermal processing of high-strength maraging steel articles
IPC classes for russian patent Method of thermal processing of high-strength maraging steel articles (RU 2344182):
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FIELD: technological processes, metal processing.

SUBSTANCE: invention concerns engineering industry and can be applied in various industry spheres for thermal processing of maraging steel articles, such as "08Х15Н5Д2Т", "06Х14Н6Д2МБТ", "10Х14Н4АМ3" and "07Х16Н6". To enhance resilience an article is annealed at 650-670°C for 6-10 hours, further is heated to 1000-1070°C for tempering in furnace, matured for 2-3 hours and cooled down in oven to 880- 900°C first, with maturing at that temperature for 2.5-3 hours, then cooled down in water, blazed off and aged.

EFFECT: enhanced resilience.

2 tbl, 2 dwg

 

The invention relates to mechanical engineering and can be used in various industries during heat treatment of parts made of Maraging steels, for example, AND, AND, HAS and HN.

The known method of heat treatment of parts made of high-strength Maraging steel, which consists in annealing at 660°C for 6 h and quenched with 1000°at an exposure of 3 h with cooling water to a darkening of the surfaces of parts, hereinafter on the air, followed by aging after machining parts (Potac AM high-Strength steel. M.: metallurgy, 1972, p.146).

The disadvantage of this method is the reduction of mechanical and corrosion properties. In particular, the value of impact strength on specimens with a crack at -70°to CRP is 0,015 MJ/m2. Reduced corrosion properties occurs due to the presence of carbide precipitates at the boundaries of austenite grains on individual batches of metal.

The closest in technical essence to the claimed method of heat treatment is a method of thermal treatment of products made of high-strength Maraging steels, including annealing at 650-670°C for 6...10 hours, heating for hardening up to 1000...1070°within 2 to 3 hours, vacation and aging (USSR Author's certificate No. 333204, C21D 1/78, 6/00, 1972.

The disadvantage of the prototype is that it does not allow to exclude the appearance of the structure of steel carbide precipitates at the grain boundaries, which is accompanied by the appearance of fragile zones in the fractured samples.

The proposed method for heat treatment of Maraging steels provides improved impact strength at room and low temperatures.

The technical result, which directed the inventive method, is provided by annealing at 650...670°C for 6...10 hours by heating for hardening up to 1000...1070°With over 2...3 hours and cooled with the furnace up to 880 900...°aged at this temperature for 2.5 to 3 hours, and then in the water, tempering and aging.

The inventive method includes the following sequence of operations:

1. Annealing at 650...670°C for 6...10 hours;

2. Tempering: heating to 1000 1070...°C, holding for 2 to 3 hours, cooling the oven to 880 900...°C, holding for 2.5-3 hours with subsequent cooling in water;

3. Cold treatment at a temperature of -70°aged 2 hours;

4. Vacation at 340 360...°With over 2...3 hours;

5. Aging after machining parts according to the appropriate technology for each specific grade of steel.

Read more the essence of the proposed method is illustrated by a photo:

- figure 1 shows the microstructure of the article is whether HR after the heat treatment by known techniques by A.S. No. 333204;

- figure 2 shows the microstructure of a steel IN after the heat treatment by the present method.

Carrying out annealing at a temperature of 650...670°C for 6...10 hours provides the regulation of the amount of residual austenite before quenching steel. In addition, when the annealing temperature less than 650°there is in the structure of carbide steel mesh. When the annealing temperature 670°With the decrease of corrosion resistance of steel. When the exposure time less than 6 hours marked lowering of corrosion resistance of steel. When increasing the exposure time of the annealing more than 10 hours there has been a sharp decrease in the corrosion resistance of steel due to carbide precipitation.

Heating for hardening determines the level of mechanical properties of steel. When the heating temperature for quenching are less than 1000°With a decrease of the tensile strength of steel. When the hardening temperature of 1070°With the strength of steel increases, however, decreases dramatically toughness values.

When the exposure time during heating for quenching are less than 2.5 hours, the decrease of the corrosion resistance of steel by forming a grid of carbides at the grain boundaries. Increasing the exposure time during heating for quenching over 3 hours followed by a sharp decrease in the relative elongation of the steel.

During slow cooling from 1000...107° With up to 890°is the loss of small number of particles of carbide phase type (FeCr)23With6at the grain boundaries of the austenite, which is provided by the difference in solubility of the elements at 1000 and 890°C. Allocation, are in fine form, coagulated during subsequent exposure at 890°thereby minimizing the energy of grain boundaries, which reduces the speed of diffusion processes during subsequent cooling.

Studies have shown that the increase in temperature of more than 900°With, for example up to 950°With, does not give a positive effect, as insufficient proportion of the emitted particles, leading to a decrease in the energy of the border. Reducing the temperature below 880°To cause a significant amount of coagulated carbides.

No carbide precipitates during cooling with 880 900...°confirmed by metallographic (figure 2), electron microscopy, x-ray and microengineering analysis.

Conducted thermal treatment of parts made of Maraging steel AND, at which point the beginning of carbide precipitates is 950°With the end of the carbide precipitates 650°C, the temperature at which the martensite transformation 130°C. the Parts were processed by the modes given in table 1. The test results presented in table 2.

Corrosion rack is to be evaluated when the extract in solution composition: CuSO 4- 110 g/DM3; N2SO4- 55 g/DM3and test base of 10 hours.

Using the proposed method of heat treatment of parts made of high-strength Maraging steels provides the receiving structure without carbide precipitates, increased corrosion resistance and improved reliability of the product in use.

The method of thermal treatment of products made of high-strength Maraging steels, including annealing at 650-670°C for 6-10 h, heating for hardening in the oven until 1000-1070°S, shutter speed within 2-3 h and cooled first with oven until 880-900°aged at this temperature for 2.5-3 h, and then water, tempering and aging.

 

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