Laizhou Dingtai Machinery Co., Ltd.

　　The main reasons for the generation of white iron castings include chemical composition imbalance, excessive cooling rate, insufficient inoculation treatment, microelement segregation, and improper process control. The following is a detailed analysis:

　　Chemical Composition Imbalance

　　Insufficient carbon and silicon content: Insufficient carbon equivalent (CE) will weaken the graphitization ability and promote the formation of cementite (Fe₃C).

　　Excessive manganese and anti-graphitization elements: Excessive manganese content (>1.7×S%+0.3) or excessive sulfur, phosphorus, oxygen, etc., will inhibit graphite precipitation.

　　Influence of harmful trace elements: Trace elements such as Pb, Bi, and Te, even in trace amounts, will significantly increase the tendency towards white iron.

　　Excessive Cooling Conditions

　　Too low pouring temperature or too fast cooling rate: Increased undercooling during iron solidification leads to the formation of non-graphite phases (such as cementite or martensite). For example, high moisture content in molding sand, poor permeability of the mold, and local rapid cooling will all exacerbate white iron formation.

　　Casting Design Defects: Unreasonable gating system design (such as small pouring gate, poor venting) or sudden changes in casting wall thickness easily lead to local white iron formation.

　　Problems in Melting and Inoculation Treatment

　　Improper use of spheroidizing agent and inoculant: Excessive residual magnesium or rare earth, or inoculation decay (such as insufficient in-stream inoculation), will both inhibit graphite spheroidization.

　　Poor melting quality: Severe oxidation of molten iron, low tapping temperature leading to element loss, or the use of high-hardness recycled materials (such as HB>250) may all trigger hereditary white iron.

　　Influence of Gas and Segregation

　　Excessive hydrogen and oxygen content: Gas accumulation during solidification (such as hydrogen enrichment in the center of the casting) will hinder graphitization.

　　Composition segregation: Such as the inverse segregation of carbon (low carbon content in the central region) or local enrichment of rare earths and magnesium, leading to cementite precipitation.

　　Process Control Defects

　　Insufficient pouring time and pressure: Too fast pouring speed or insufficient pressure prevents gas from escaping, forming pores and accompanied by white iron.

　　Improper heat treatment: Insufficient annealing time or poor temperature control cannot completely decompose cementite.