Question:Can you please explain the effect on hardenability by chromium in
medium-carbon steels?
Answer:As you most likely know, carbon, and to a lesser extent manganese, have
the greatest effect on hardenability in steels. Still, chromium does have an
influence, which can be summarized below:
“Chromium (Cr) is one of the most versatile and widely used alloying
elements in steel. It is considered a mild hardenability agent, improves wear
resistance (generally via hard and stable chromium carbides), promotes the
retention of strength at elevated temperatures, provides resistance to
softening during tempering and, depending on amount, provides resistance to
corrosion and oxidation. It is not as strong a hardenability agent as either
manganese (Mn) or molybdenum (Mo).”[1]
It is less cost effective (hardenability gain/cost) than Mn but more
cost effective than Mo.
This may be seen in Table 1, which collectively provides important information
on the effect of carbon, the primary alloying elements and the significant
effect of grain size (which is often overlooked).[2]
“Due to the strengthening effect at higher temperatures and the
resistance to softening during tempering, Cr-containing steels will require
higher tempering temperatures and/or times than for plain-carbon steels. These
effects increase with increasing Cr content.”[1]
Chromium and chromium–nickel steels are susceptible to both temper
embrittlement and tempered-martensite embrittlement.[1]
When comparing steels from two different heats of the same or
essentially the same grade of steel, caution must be exercised to evaluate all
of the following: relative carbon contents; relative levels and associated
hardenability effects of the various primary and residual alloying elements; and the grain sizes of
the two materials. If one heat has a coarser grain size, via killing method
and/or processing history, it will have an innate hardenability advantage. This
is readily seen by studying Table 1.
Comments (0)