Control method of as-cast condition heavy section ferrite-based nodular iron casting graphite nodule and matrix structure

Abstract

The invention discloses a control method of an as-cast condition heavy section ferrite-based nodular iron casting graphite nodule and a matrix structure. The control method comprises the following steps of: manufacturing a weight panel according to the shape of a spheroidizing packet; selecting pig iron, foundry returns, scrap steels and silicon irons to prepare materials; scaling the spheroidizing packet by using smelted molten iron more than or equal to 1500 DEG C; adding a spheroidizing agent, a nucleating agent, scrap iron, the weight panel, pig iron and Sb into a packet pit in sequence to carry out spheroidizing; adding an inoculation agent which accounts for 0.1-0.2% of molten iron by weight into the surface of the molten iron after the spheroidizing; stirring and scattering slag removers on the surface of the molten iron; after the spheroidizing, pouring the molten iron into a phenolic sand molded sand box which is prepared in advance so as to be cast and molded, wherein the molten iron needs to be breaded along with the flow, the breading quantity is 0.2% of the weight of a cast piece, and the box is opened after being molded and cooled to be less than 300 DEG C. The mechanical performance of the central part of a body of the material under the cast mode is as follows: the extension strength sigma b is not less than 380MPa, the surrendering strength sigma 0.2 is not less than 230Pa, and the cut-off ductility delta is not less than 20%.

Description

technical field [0001] The invention relates to a method for controlling graphite balls and matrix structure of as-cast thick-section ferrite-based ductile iron castings, in particular to a control method for spheroidization and inoculation treatment, belonging to the field of large-scale iron castings. Background technique [0002] Due to its good toughness and casting performance, ductile iron has a simple production method and its output has increased year after year. However, for ductile iron castings with thick and large cross-sections, due to the large modulus, slow cooling, long solidification time, a series of defects such as graphite distortion, few graphite balls and thick graphite balls are prone to appear in the center of wall thickness or hot joints. casting properties. For the ferrite-based structure required by the QT400-18 material in the as-cast state, due to the small number and coarseness of graphite spheres, the amount of pearlite in the casting increase...

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Problems solved by technology

However, for ductile iron castings with thick and large cross-sections, due to the large modulus, slow cooling, long solidification time, a series of defects such as graphite distortion, few graphite balls and thick graphite balls are prone to appear in the center of wall thickness or hot joints. Casting properties

For the ferrite-based structure required by the QT400-18 material in the as-cast state, due to the small number and coarseness of graphite spheres, the amount of pearlite in the casting increases and the strength increases, but the elongation decreases, and the toughness of the material does not meet the requirements, especially low temperature impact toughness

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