What is the meaning behind the stipulated range of chemical composition of a steel alloy?
What is the meaning behind the stipulated range of chemical composition of a steel alloy?
(OP)
Hi,
The range of chemical composition of steel or an alloy has always been stipulated. But, on what basis the RANGE of chemical composition was defined?
I have a Cr-Mn Forged Steel Shaft, where its Chromium (0.9 to 1.5wt%) and Molybdenum (0.15 to 0.3wt%) contents are marginally higher than the stipulated range. What I have got for Cr was 1.6wt% and Mo was 0.6wt%. I know that Cr and Mo are good for corrosion resistance, the more the better. However, will the higher than the stipulated range for both Cr and Mo affect the fatigue strength of the shaft? In other words, can the excessive Cr and Mo cause the shaft to become more susceptible to fatigue?
The range of chemical composition of steel or an alloy has always been stipulated. But, on what basis the RANGE of chemical composition was defined?
I have a Cr-Mn Forged Steel Shaft, where its Chromium (0.9 to 1.5wt%) and Molybdenum (0.15 to 0.3wt%) contents are marginally higher than the stipulated range. What I have got for Cr was 1.6wt% and Mo was 0.6wt%. I know that Cr and Mo are good for corrosion resistance, the more the better. However, will the higher than the stipulated range for both Cr and Mo affect the fatigue strength of the shaft? In other words, can the excessive Cr and Mo cause the shaft to become more susceptible to fatigue?
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
To which material code or standard are you referring ?
ASTM ? ASME ? ISO? EN ?... or something else ?
Supposedly these standards were developed by authorities who put reasonable limits on chemical composition for various reasons.
Limitations on steel chemical composition can be placed for a variety of reasons including long component life, corrosion resistance, creep resistance and to facilitate steel production and quality product. There are several other reasons ...
As a reponsible engineer designing a robust quality product, you are not required to use a steel that meets any international code or standard.
..... but, then again ... you must stand by your decision and explain this to your client
.... and if there is a failure, you cannot blame the quality of manufacture
.... you are responsible
How do others feel about this important issue ???
MJCronin
Sr. Process Engineer
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
The original material specification sets limits on the original heat (melt) chemistry.
These limits for steels are often based on hardenability and heat treatment response resulting in specific structure and properties.
For a product chemistry there are allowances a little bit outside of these ranges.
More is not better.
The right amounts (and relationships to each other) are critical so that you end up with what was intended.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
Please, request for all elements within tolerance range as given in the standard.
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
On the other hand, if early failure is a real risk, don't mess around with out-of-spec material. There are limits because having the right mix of alloying elements maximizes the desired grain structure, but too much can create new phases and interstitials that can be very bad. The test results may also indicate a process that's not sufficiently controlled.
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
Cr and Mo in low alloy steels are there for hardenability; they do not impart much in the way of aqueous corrosion resistance at low or ambient temperature. The benefits of a protective Cr oxide scale (i.e. 'stainless') do not kick in until > 10%.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?
To Ironic Metallurgist,the specified carbon content is 0.48%max and the chemical analysis result shows that it is within the specification.
RE: What is the meaning behind the stipulated range of chemical composition of a steel alloy?