SU1680783A1 - Rolled stock heat-treatment method - Google Patents

Abstract

The invention relates to ferrous metallurgy and can be used in the manufacture and heat treatment of rolled wire mainly from low carbon silicon-manganese steels. The purpose of the invention is to increase the technological plasticity of the rod. The method includes austenitizing the rolled wire, cooling to the bainite transformation temperature at a rate of 3-5 ° C / s and final cooling first with a speed of 0.01-0.10 ° C / s to a temperature of 500-530 ° C and further - with arbitrary speed. This cooling mode allows to obtain the ferritic-quasi-eutectoid structure of the rod. 1 tab.

Description

The invention relates to ferrous metallurgy and can be used in the manufacture and heat treatment of rolled wire mainly from low carbon silicon-manganese steels.

The purpose of the invention is to increase the technological plasticity of the rod.

According to the proposed method of heat treatment of a rod, mainly from silicon-manganese steels, including austenitization, accelerated cooling to the temperature of the beginning of bainite transformation and final cooling, accelerated cooling is performed at a speed of 3-5 ° C / s, and final cooling is performed at a rate of 0.01 -0.10 ° С / s up to 500-530 ° С and further - with an arbitrary speed.

During heat treatment according to the proposed method, cooling modes from the austenitic state in the first cooling stage at a rate of 3-5 ° C / s are prevented

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the precipitation along the grain boundaries of structurally free cementite in the temperature range of 600-750 ° C is crushed, and in the second stage of cooling at a rate of 0.01-0.10 ° C / s to 500-530 ° C / s, bainite is prevented from forming. Since cooling at the specified rate ensures that the cooling curve passes over the start line of the bainite transformation and upon reaching 500-530 ° C, the transformation of austenite is completely completed with the formation of a ferritic quasi eutectoid (pearlite) structure, which increases the technological plasticity of the rod.

Thus, during heat treatment of rod of low-carbon silicon-manganese steels according to the proposed method, in which accelerated cooling from the austenitic state is performed at a speed of 3-5 ° C / s to the temperature of the beginning of bainitic

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first, at the rate of 0.01–0.10 ° C / s to 500–530 ° C and then at an arbitrary rate, a ferritic quasi-eutectoid structure is formed, which provides an increase in the technological plasticity of the rod.

If accelerated cooling is performed at a rate of more than 5 ° C / s, with further cooling in the second stage, part of the austenite undergoes transformation by an intermediate mechanism, as a result, the technological plasticity of the wire rod deteriorates. If accelerated cooling is performed at a rate of less than 3 ° C / s, structural-free cementite is released at the grain boundaries, which also leads to a deterioration of the technological plasticity of the rod.

If the final cooling is performed at a rate of more than 0.10 ° C / s, then the cooling curve crosses the temperature Ac2 and bainite forms in the structure - the process plasticity decreases. If the cooling rate is less than 0.02 ° C / s, then the amount of perlite increases, and perlite cementite acquires a rougher plate shape, which also impairs technological ductility.

If cooling is completed above 530 ° C, then with further cooling it is possible to release bainite, which reduces process ductility, and if below 500 ° C. This does not change qualitatively, however, the process of heat treatment is lengthened.

Example. Samples of rod of steel grade 08G2S with a diameter of 8 mm are subjected to heat treatment according to the proposed and known methods

When implementing this method, the samples are heated to 930 ° C, held for 10 minutes, and then cooled first at a rate of 80 ° C / s to the temperature at which the bainite transformation begins (615 ° C), then to room temperature at a rate of 5 ° C / s .

Some samples thermoabout the proposed method. They are also subjected to austenitization at 930 ° C, then cooled at a rate of 2 to 6 ° C / s to the temperature at which the bainite transformation begins, and then at a rate of 0.009 to 0.20 ° C / s to 480 to 540 ° C. Final cooling to room temperature is carried out in air.

Specimens processed according to the known and proposed methods are subjected to microstructural studies, mechanical properties and technological plasticity (using the draft test method).

Heat treatment modes and research results are presented in the table.

Research has shown that the proposed method of heat treatment of rolled wire compared to the known method allows a significant increase in the technological plasticity of the metal, which significantly increases the yield of the material during further processing and in the production of, for example, steel wire.

Claims (1)

The method of heat treatment of rolled metal, mainly rods of low carbon silicon-manganese steels, including austenitizing, cooling to bainite transformation temperature and final cooling, characterized in that in order to increase the technological plasticity of the rod, cooling to bainite transformation temperature is performed at a speed of 3 - 5 ° C / s, and the final cooling is carried out first at a rate of 0.01-0.1 ° C / s to 500-530 ° C and then at an arbitrary speed.