What effect does Chromium content of 0.5% in Low alloy steel have?

[Abhijeet242]

Especially in case of A216, Cr content is restricted max. to 0.5%. Chromium is stable carbide former. Which carbide is formed in case of this Steel, C₂₃C⁶ or Cr₇C₃?
What effects does the normalizing and tempering has?

 

[Dhurjati Sen]

Cr has substituted Fe and is acting as ferrite stabilizer only.

It is reducing the austenite region thereby increasing the ferrite region.

Try to obtain Fe-Cr equilibrium diagram and have a look.

Coming back to your questions, no carbides are formed in this case.

As austenite region has reduced, the normalizing range has got squeezed compared to plain carbon steel.

Again, tempering would not have significant difference when compared to plain carbon steel.

DHURJATI SEN

 

[weldstan]

This is a low carbon steel casting spec which permits residual Cr up to 0.5%. It will have no real effect on heat treatment specified within the specification or when welded to other parts to various ASME Codes where PWHT is required.

 

0.5% Cr by itself doesn't have much effect on carbon steel, including weld filler metals. Which is why there isn't a standard AISI or PV steel containing only 0.5% Cr - such a steel offers no unique properties that would justify a creating a new grade of low alloy steel.
In the past little while I have been trying to convince a CPWE at a major EPC that this amount of Cr does NOT make steel into a Chrome-Moly grade.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[bobjustbob]

Like others have said the Cr will not have much of an affect on plain WCC or WCB grades in A216. It could cause an issue with exceeding the upper UTS if you are making WCA, depending on the rest of the chemistry. It will raise your carbon equivalent. If S11 or S16 are called out or the part needs to meet NACE requirements this could cause an issue.

The temper does not do much after the normalize. It could help your elongation or reduction of area but I have never seen the need.

 

Fun fact: Chromium in Iron has a negative solution hardening effect at low concentrations.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."