SU490848A1 - Method of spheroidizing treatment of martensitic steels - Google Patents

Description

one

The invention relates to the field of heat treatment and can be used to intensify the technological process of manufacturing products from martensitic steel.

At present, high strength steels of martensitic class (for example, 28KhSSNL1VFA ZZHZNSMVFA, 38X5 MFSA, -12X2H5CMA, etc.) are widely used for the manufacture of various machines and structures of responsible purpose.

These steels, when cooled in air or with a furnace (after hot processing or heating to austenitization temperatures during heat treatment), have a martensite structure with high hardness (48-52 HRc units). In order to carry out cold processing, dressing or machining of such products, they are subjected to heat treatment in order to spheroidize carbides.

The known method of spheroidizing treatment of steels of martensitic class consists in tempering at temperatures below the Aci point by 30-50 ° C. For example, in nickel-containing steels, Aci is low (steel with 5% Ni has Aci 650 ° C). Due to the low temperature of the heating during tempering, the spheroidization process is slow and the holding time is 20-30 hours.

The disadvantage of this treatment mode is the long duration of the spheroidization processes and the associated delay of the thermal equipment.

In order to accelerate the process of spheroidization of carbides, steel is aggreaded to a temperature of Asz + 50 ° C, forced to a temperature of Aci - + - 40 ° C, deformed with continuous cooling in the range (Aci + 40 ° C) + (Aci--60 ° C) , cooled in air, and subjected to tempering at a temperature of Aci-30 + 50 ° C for 4-6 hours.

The proposed method can also be carried out using heating under hot processing, as a result of which, after hot working (rolling, forging), products with a fine-grained structure are obtained. Subsequent tempering leads to carbide coarsening. In so doing, the required hardness is obtained, at which the product is satisfactorily deformed and processed.

The described method was tested on pipes. Pipes of steel of martensitic class 3835MSFA and 42Х2Н5СМА are processed according to the following technology: they are heated in a furnace to an austenitization temperature of 1050–950 ° C, podstuzhivayut to, rolled on a mill with continuous cooling in the temperature range 800-700 0 with a total deformation of 30-40%, then cooled in air. The resulting pipe with a hardness of 39-41 units. HRc is subjected to tempering in order to enlarge the cartillo ° 38Kh5MSFA steel — at a temperature of lovoT JA T L1, it is 4 hours, steel 42X2H5CMA is at 630 ° C (Aci-650C), holding for 6 hours. The hardness 5 of the metal of the finished pipe is 23-27 units. HRc, while after normal processing, steel 42X2N5CMA even after holding for 40 hours at 630 ° C has a hardness of 33 units. HRc.The subject matter of the invention 1. The method of spheroidizing treatment of steels of martensitic class, including tempering at Acj- (30 + 50 ° C) differs because in order to accelerate the process of carbide spheroidization, steel is heated to Asz + 50 ° C, heat up to Aci + 40 ° C, deform with continuous cooling in the range (Aci + 40 ° C) + (Aci-60 ° C), cool in air and leave to leave for 4-6 hours. 2. The method according to l. 1, characterized in that the deformation of continuous cooling and iri is carried out in the temperature range 800-700 ° C with a total degree of deformation of at least 30%.