SU1014935A1 - Method for heat treating castings - Google Patents

Abstract

1. METHOD OF THERMAL TREATMENT OF CASTINGS, mainly from steels of austenitic-martensitic class In-I,. ,,,, .. I sa, including homogenizing annealing, hardening, cold working and tempering, aphids, and with the fact that , in order to increase the strength of the steel while maintaining the surface properties of the cast parts, cooling from the temperature of the homogenizing annealing is carried out at a speed of 30-150 ° C / h in the range of 950-650 ° C, and then an additional, vital cold treatment is carried out. 2. The method according to claim 1, which is also distinguished by the fact that the cold treatment is carried out at a temperature of complete martensite transformation.

Description

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The invention relates to the manufacture of cast parts and can be used in the heat treatment of precision castings manufactured by casting on produced models of austenitic-martensitic steel.

The known method of heat treatment of martensitic steels, which allows to increase the strength and ductility in massive sections of details by grinding grains during multiple phase recrystallization. The method includes homogenizing heating from 1180-125 ° C and repeated quenching from 920-1000 С Cl.

There is a method of multiple phase recrystallization of transitional steels (austenitic-martensitic class, carried out by repeated quenching from the steel recrystallization temperature after phase hardening, followed by cold treatment after each quenching.

The closest to the proposed technical essence and the achieved result is a method that includes homogenizing annealing to reduce chemical heterogeneity, repeated quenching with cold treatment after each quenching and tempering 3.

The disadvantage of the heat treatment method is the deterioration of the performance properties of the surface layer of cast parts (corrosion resistance and viscosity) caused by the firing of alloying elements in the process of high temperature heating for quenching. Therefore, in the practice of heat treatment of precision castings, the number of high-temperature heatings is regulated (no more than 2–3 heatings), which guarantees high quality of the surface layer, but does not provide the required grain refinement and increase in strength. properties in castings.

Insufficient grinding of grains in castings after heat treatment according to the method with a regulated amount of high-temperature heatings is associated with a low efficiency of using the first (after homogenizing annealing) heating for quenching. Heating for quenching, carried out directly after cooling from the annealing temperature, practically does not grind the grain in the transitional class of steel, since this heating is carried out from a predominantly austenitic state, t. e. without precursor phase hardening. Thus, when heated under the first quenching, the necessary condition for the recrystallization grinding of the grains — creation of a preliminary

phase hardening of austenite due to martensitic carbon dioxide, / transformation.

The purpose of the invention is to increase the strength of steel while maintaining the performance properties of the surface layer of cast parts.

The goal is achieved according to the method of heat treatment of castings, mainly of austenitic-martensitic steels, including homogenizing annealing, quenching, cold working and tempering, cooling from a temperature of homogenizing annealing is conducted at a speed of 30-150 ° C / h in the EZO-BZO C interval, and then additional cold treatment.

The cold treatment is carried out at a temperature of full martensitic transformation.

Adjustable cooling of castings from a temperature of homogenizing annealing at a rate of 30-150 ° C / h in the range of 950-65 ° C (in the interval of separation of excess carbide and intermetallic phases from austenite) contributes to an increase in the onset of martensitic transformation and destabilization of segregation and residual austenite.

The subsequent martensitic transformation of destabilized austenite during the additional cold treatment ensures the creation of a preliminary phase hardening necessary for recrystallization grinding of the grains during heating for quenching. The cold treatment is carried out at a temperature of complete marceisite transformation, which for transitional steels is typically -50 to 70 ° C.

Combined carrying out controlled cooling from the temperature of homogeneous annealing and subsequent cold treatment is especially effective for grinding grains in massive sections of castings having an increased amount of segregation austenite and the original coarse-crystalline structure.

Cooling from the temperature of the homogenizing annealing at a rate of more than 150 ° C / h does not provide a sufficiently complete separation of excess phases from austenite and a required increase in the point of the beginning of the martensite transformation. Cooling with a speed is no longer advisable, since it requires additional material costs, and there is no significant increase in the point of onset of the martensitic transformation.

The principal difference proposed by the heat treatment method is that the required grinding of grains in castings is not achieved by further increasing the amount of high-temperature heating (quenching), which deteriorates the performance properties of the surface layer of cast parts, but by additional grinding of the grains already during the first heating for quenching.

Pr and measures. Conducted heat treatment of precision castings made by casting on melted models of steel with the following composition, wt.% 1 carbon 0.06}. chromium 13.4} nickel 6.8} molybdenum 0.6} iron and impurities else.

The heat treatment mode of the proposed method includes the following operations: homogenizing annealing at 5 hours; ohl 1zhdnyyb in the range of 950-650C with an average speed, or 30 S / h; cold working at 2.5 hours; quenching from 1000 ° C; 2.5 hours; cold treatment at 2.5 h} tempering at 2.5 h.

In order to obtain comparative data, heat treatment of similar types of castings of the same heat is carried out by means of a known method that differs from the proposed accelerated one. cooling with annealing temperature. (cooling rate in the SSO-SSO C interval), as well as the lack of cold treatment after annealing.

Heat treatment by a known method is carried out with single or double quenching after annealing, followed by cold treatment after each quenching.

Comparative data, control of mechanical properties and grain size of steel in massive sections of castings are given in the table.

As can be seen from the table, thermal

The treatment according to the proposed method increases the strength properties of castings without an additional increase in the number of high-temperature ignition (hardening), t. e. without deterioration

surface properties of the molded parts.

Improving the strength properties of castings while maintaining the quality of the surface layer of cast parts allows

increase technical and economic iiOKazateley machines and mechanisms due to the improvement of their weight characteristics.

Proposed

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Claims (2)

1. METHOD FOR THERMAL TREATMENT OF CASTINGS, mainly from steels of austenitic-martensitic class, including homogenizing annealing, quenching, cold working and tempering, so that in order to increase the strength of steel while maintaining the operation of steel properties of the surface layer of cast parts, cooling from the temperature of homogenizing annealing is carried out at a speed of 30-150 ° C / h in the range of 950-650 ° C, and then additional cold treatment is carried out. 2. The method of pop. 1, distinguishing with the fact that cold treatment is carried out at a temperature of complete martensitic transformation. yoo oo joint venture