and Soft States in Metals. 271 
and crystalline. The phase theory of hardening shows that 
these three types of structure must be present in any mass of 
metal which has been subjected to overstrain, and that their 
existence does not necessarily depend on the presence of several 
crystalline phases such as occur in iron and steel. The granules, 
which are always present in the most perfectly flowed metal, 
may be regarded as minute cells encased in the hardened 
phase. The larger crystalline aggregates may also be so 
regarded, for they also are encased. The increased rigidity 
of the hardened metal results from this partitioning up of the 
whole mass by thin rigid cell-walls which enclose and protect 
their contents of plastic phase from further deformation and 
transformation. 
57. When a greater stress is applied to the hardened mass, 
the rigidity of the cellular structure has to be overcome before 
further yielding can take place. When this structure breaks 
down, the plastic phase which is thereby reached is set -in 
motion, and forms itself into a new set of protecting partitions. 
It appears to me that only in this way can we account for the 
immediate and marked increase of rigidity which results from 
the transformation of a relatively small amount of the softened 
hase. 
? 58. The breaking down of tenacity and elasticity under 
frequent repetitions or reversals of stress is more easy to 
understand when it is recognized that every movement of the 
crystalline elements over each other, however slight, must 
lead to the transformation of the C into the A phase. The 
hardened surfaces or partitions thus produced, after being 
frequently broken down and remade, must eventually arrive 
at a stage when the plastic material in their neighbourhood 
is all used up. The movement will then tend to open up 
partings which, in the absence of fresh plastic material, will 
remain open, and will form the starting-point of fissures at 
which rupture will ultimately take place. 
59. In the commercial forms of iron and steel the presence 
of other constituents in various phases will complicate the 
effects; but even in such cases the phase transformation 
C——> M——-A must play a leading part in the structural 
changes which take place. very crystalline phase, whatever 
its constituents, must either be rigid enough to resist defor- 
mation ; or if deformation takes place, it must be partially 
converted into the amorphous phase, An eutectic in which 
erystalline grains are embedded may become so hardened by 
flow, as to supply a rigid cellular structure enclosing the 
grains. Or the amorphous eutectic may be so fragile as to 
lead to the breakdown of the whole structure. 
