Heat treatment method of medium carbon manganese steel two-phase region subcritical normalizing refining structure

Abstract

The invention relates to a heat treatment method of a medium carbon manganese steel forging refining structure. On the current market, a heat treatment process of normalizing at the temperature of 30-50 DEG C above Ac3 is adopted in a conventional method for treating the medium carbon manganese steel forging refining structure, for example, 070M55 medium carbon manganese steel forging is subjected to normalizing treatment at the temperature of 840 DEG C according to the standard of BS970-1983, the forging cannot meet standard requirements for plasticity and toughness indexes due to coarse crystal grain and network structure. The normalizing method adopted in the invention comprises the following steps: firstly heating to a sub-temperature range slightly below the Ac3 of steel at the rate of less than or equal to 80 DEG C per hour, namely the upper limit temperature of a ferrite and austenite two-phase region, holding the temperature according to the standard of 40-60mm per hour, cooling in a furnace to the temperature 20-30 DEG C above Ac3 of the steel, holding the temperature at the lower limit temperature of the ferrite and austenite two-phase region according to the standard of 25-35mm per hour and carrying out air cooling outside the furnace. The heat treatment method has the characteristics that the crystal grain can be remarkably refined; the defects of the network structure, the coarse crystal grain and the like of ferrite are eliminated, so that the mechanical property indexes of plasticity, toughness and the like of the medium carbon manganese steel are increased.

Description

technical field [0001] The invention relates to a heat treatment method for large-scale carbon-manganese steel forgings in the iron and steel metallurgy industry, in particular to a heat treatment method for medium-carbon-manganese steel forgings. After the medium carbon manganese steel undergoes sub-temperature normalizing heat treatment in the two-phase zone, the grains are obviously refined, and the plasticity and toughness are significantly improved. Background technique [0002] After forging large-scale medium-carbon manganese steels at home and abroad, they are all subjected to Ac3+30~50℃ full austenitization temperature normalizing treatment, such as 070M55 medium carbon manganese steel adopts 840℃ full austenitization heat preservation according to BS970-1983 standard Post-air cooling heat treatment method. In this method, during the heat treatment process, especially for large-scale forged materials, due to the long holding time, the grains will grow, and it is ea...

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Problems solved by technology

[0003] The purpose of the present invention is to overcome the shortcomings of the conventional heat treatment process for medium-carbon manganese steel, and provide a heat treatment method for sub-temperature normalizing in the two-phase region of medium-carbon manganese steel to refine the microstructure, aiming at solving the problem of network structure, rough The mechanical properties of medium carbon manganese steel are reduced due to phenomena such as crystallization or mixed crystals, but the heat treatment method of the present invention can significantly refine the grains, eliminate the phenomena of network structure, coarse grains or mixed crystals, and especially improve the plasticity and toughness. Significantly improved, thereby improving the mechanical properties

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