The difference between Class 1 and Class 2 SA-387

[Paulettaa]

Dear All

I want to know what is the difference between class 1 and class 2 in SA-387. As per the specification, there is no difference in chemical composition of these two classes. However, there is difference between the two classes in terms of their mechanical strength.
In table3 of the specification Note A, it is mentioned that the values are not applicable to annealed materials. So can we say that the difference between class 1 and class 2 is that class 1 is normalized and tempered and class 2 is annealed?
And finally in the heat treatment section of the specification there is a third heat treatment which is accelerated cooling from the austenitizing temperature by air blasting or liquid quenching followed by tempering. Is this heat treatment also class 1?

Warm Regards

 

[mk3223]

IMO, the strength differences between SA-387 Class 1 and 2 material can be resulted from the minor differences of the chemical composition as well as the heat treatment process. Basically, the selection of either class material is based on the mechanical strength at the elevated temperature service. And, the prices of two classes material are also different.

 

mk3223,

Composition is the same regardless of Class, and there is no reference to Class in Table 1. However manufacturers might adjust composition to optimize the final properties for a given heat treatment (although always within the limits of Table 1).

I have struggled with this question when encountering these alloys, because SA-387 does not explicitly link Class (UTS) with specific heat treatments. I have only ever worked with Class 1, the lowest minimum UTS level, which corresponds to the annealed (softest) condition.

We expect harder/stronger steel with more aggressive heat treatments. Quenched & tempered gives the highest hardness and is considered Class 2. I am not sure where the intermediate heat treatment of normalizing & tempering fits Class-wise, but I suspect it falls into Class 2.

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