Size Distribution Of Inclusions Research Articles

Effect of composition and thermal treatment on the overheating characteristics of low-alloy steels

The overheating characteristics of several commercial and experimental low-alloy steels have been investigated. Overheating is characterized by the appearance of ductile intergranularfacets onfracture surfaces caused by the precipitation of a-MnS particles at prior austenite grain boundaries. The cooling rate through the overheating rangeproduced a marked variation in the size and dispersion of intergranular a-MnS particles. Cooling rates in the range 10°-400°C/min produced the most severe grain-boundary embrittlement and were consistent with an MnS particle size of 1–2 μm for a commercial En39B steel. A marked refinement in the size distribution of inclusions was apparent following overheating treatments on all steels and was due to the solution and reprecipitation of the sulphide inclusions. Rare-earth-treated En39B steels, when subjected to high-temperature ‘overheating’ treatments, contained no areas of intergranular failure on impact fracture surfaces and no marked deterioration in mechanical properties was observed following such treatments. A critical Ce/S ratio of ∼2:1 resulted in the complete modification of MnS inclusions to rare-earth sulphides and oxysulphides. Values below this critical level resulted in the presence of ‘free MnS’ which dissolved and reprecipitated at prior austenite grain boundaries following overheating treatments.

A mathematical model to predict the growth and elimination of inclusions in liquid steel stirred by natural convection

A model is developed to predict the rate of removal and the change in the size distribution of inclusions in a melt stirred by natural convection. Difficulties in obtaining an exact solution to the problem due to lack of adequate knowledge for the velocity fields in the melts are discussed. The model is based on Smoluchowski’s Theory of Gradient Collision to obtain the probability of collision between two inclusions under an arbitrarily chosen velocity gradient. Initial size distributions obtained in experimental heats are used as the input to the model. Various conditions are proposed by which inclusions are removed from the melt. The rates of removal are compared with the experimentally obtained rate of removal of oxides. It is observed that a boundary layer effect and the presence of a thin liquid metal film prevent rapid removal of inclusions from the stirred melts. Inclusion size distribution predicted by the model agrees qualitatively with the experimentally observed size distribution. It is postulated that the surface forces play a significant role in coalescence and assimilation of inclusions. Finally, the application of similar models to understand the removal of inclusions in such processes as argon sparging, solidification, degassing and electroslag remelting are advocated.

鋼中析出物介在物抽出分離残さの超音波ふるいわけ法

In order to measure the size distribution of precipitates and inclusions in steels and to analyze them after classification by the sizes, a wet method was developed for sieving under ultrasonic vibration the residues which were chemically extracted from steels. Ultrasonic vibration prevented small particles of the residues from aggregation and accelerated sieving.Metallic sieves with openings of from 20 to 2 μ were made by electroplating coarse copper sieves with nickel and platinum. A suitable apparatus to this sieving method was made.This method was applied to synthetic chromium carbide and the residues extracted from zirconium steel by the acid dissolution method. The reproducibility of sieving was satisfactory. The analytical results of the sieved residues were also discussed.By this method, about 50 mg of the extracted residues can be sieved in about 25 min with 5, 10, 15 and 20 μ sieves.

Measurement of the Size Distribution of Nonmetallic Inclusions in Steel

Measurement of the Size Distribution of Nonmetallic Inclusions in Steel

Corrigenda to “Measurement of the Size Distribution of Nonmetallic Inclusions in Steel” [Trans. ISIJ, 8 (1968), No. 3, pp. 181–185

Corrigenda to “Measurement of the Size Distribution of Nonmetallic Inclusions in Steel” [Trans. ISIJ, 8 (1968), No. 3, pp. 181–185