8 LaN(;e, Some Rcuiarkable Steel Crystals. 



columnar formation. In both cases there is uniformity 

 of orientation along a main long axis. Rhead believes 

 that the difference of conductivity between the solid 

 growth and the liquid mass is responsible for the uni- 

 formity of orientation in the former case, and certainly 

 the chilling effect of the mould produces the same result 

 in the latter case. 



You will notice that the columnar crystals do not 

 appear to have much cohesion, and, in fact, the surface 

 cracks often observed in rolling or forging ingots usually 

 pass between these crystals. 



It will be observed that there is no regularity in the 

 size or formation of these columns ; the lateral growths 

 are irregular, so that the columns interrupt each other in 

 their growth at different distances from their main axis, 

 and there is also no relation in the angles of the lateral 

 growths of the neighbouring crystals. In fact, the crystal 

 growths follow the ordinary law of chemical solutions. 

 When a crystal starts from a point it grows in all directions 

 until interfered with by the growth of adjacent crystals. 

 For the same reason, slow cooling results in large crystals, 

 and quick cooling in small crystals. The columnar 

 structure is due to the rapid absorption of heat by the 

 sides of the mould, tending to make the steel crystallise 

 in long prisms at right angles to the surface, although 

 naturally the crystal grains tend to an equiaxed forma- 

 tion. As the walls thicken, and the flow of heat lessens, 

 the prismatic tendency weakens, and there is a sudden 

 change from the prismatic to the equiaxed formation. 

 There is also, as before remarked upon, the interstratal 

 action of the liquid core. 



These remarks as to the formation of a columnar 

 structure during solidification hold good for any steel 

 casting whether in an iron or a sand mould ; and at all 



