Low-alloy bainite ductile iron oil quenching isothermal tempering heat treatment process

Abstract

A low alloy bainite ductile iron oil quenching with temperature isothermal tempering heat treatment process includes: (1) heating a ductile iron work piece to be at 880 to 960 DEG C for the austenization; (2) quenching the work piece in machine oil; (3) taking out the ductile iron work piece when the surface temperature is 150 to 230 DEG C; (4) keeping the ductile iron work piece with temperature and rapidly burying sands for the heat preservation and the tempering for 6 to 8 hours; or burying sands for the heat preservation and the tempering for 1 to 3 hours and then taking the work piece out for the air cooling. Through refractory bricks and molding sands in an insulation packet or a ground pit, the process forms a reasonable temperature gradient from the inside of the ductile iron to the surface, a sands layer, the insulation packet or the ground pit. The slow and stable cooling speed which accords with the requirement is established. The isothermal tempering temperature is effectively controlled. The residue heat after the heat treatment on the ductile iron work piece is used to realize the isothermal transformation from austenite to bainite, which is more beneficial to the formation of bainite tissues. The obtained ductile iron work piece tissues have the advantages of reasonable structure and perfect comprehensive property and are especially applied to gears, crankshafts, grinding balls, etc.

Description

Technical field: [0001] The present invention relates to metallic materials, particularly ductile iron, more particularly low alloy bainitic ductile iron. Background technique: [0002] Low-alloy bainitic ductile iron has high strength, hardness and toughness, and has good casting performance. It is known as one of the major achievements in cast iron metallurgy in the past 40 years. At present, the heat treatment methods for obtaining bainite ductile iron mainly include traditional salt bath isothermal cooling and water medium cooling to control isothermal quenching (CN200510044091.X). Wei Deqiang's "Research and Production of Bainitic Nodular Cast Iron Grinding Ball Material" (Journal of Xiangtan University of Science and Technology 2005.Vol.27No.1: 94-97), discloses the production of heat treatment process using casting waste heat step-by-step isothermal quenching (oil quenching) Low alloy (Mo, M n 、C u 、C r ) The method of ductile iron grinding ball material, using 90...

AI Technical Summary

Problems solved by technology

The isothermal furnace cannot effectively control the holding temperature, which affects the structure and material properties of ductile iron. The residual austenite in the structure increases, and even pearlite transformation occurs. Therefore, when the size of the part is large, the depth of the hardened layer cannot reach Requirements, so that the internal strength, hardness and toughness of the material will be significantly reduced