Environmental Engineering Reference
In-Depth Information
Figure 7.1
Stress-strain curves of cold-rolled copper with various molten Bi-Pb alloys
at 350°C.
LME cracking originates at the solid-liquid interface, which may be internal
in some cases, e.g., in lead- or tellurium-containing steels. These elements are
added to steel for improvement of machinability, but being low melting, they are
causative factors for LME of the steel component at elevated temperature pro-
cessing or applications.
In most instances, the initiation and propagation of cracks appear to occur
instantaneously. The velocity of crack propagation in LME has been estimated
to be 10-100 cm/s or higher. The fracture may be nucleation-controlled or propa-
gation-controlled. In the former, once a crack is initiated it propagates to failure
in the presence or absence of the liquid metal at the crack tip. In the propagation-
controlled failure, microcracks are formed at some low stress in a liquid metal
environment, but the propagation of these microcracks becomes possible only at
higher stresses. Therefore, in this type of failure, unpropagated microcracks may
be found beside the main fracture.
Specificity of Environment
Like SCC, all liquid metals do not embrittle all solid metals and it appears that
some specificity exists in this regard. For example, liquid mercury embrittles zinc
