The Mystery of ASTM A487 Grade 4 Pressure Service Castings

[tc7]

Table 1 of ASTM Grade 4 Class A, B, C, D pressure service castings all indicate the same required heat treatment:
Austenize at 1600?F,
Media: air or liquid
Quenching Cool Below 500°F
Tempering Temperature: 1150°F

Question 1:
There seems to be some steps missing, such as
a. holding time at austenize temperature,
b. are we to air cool or furnace cool until we reach
500°F and then quench ?
c. how long to hold at the tempering temperature?


Table 3 lists a variety of TS/YS combinations:
Class A – 90ksi UTS, 60ksi YS
Class B – 105ksi UTS, 85ksi YS
Class C – 90ksi UTS, 60ksi YS
Class D – 100ksi UTS, 75ksi YS

Question 2:
How does the same heat treatment of Table 1 result in different TS/YS when all classes of Grade 4 have the same chemistry as shown in Table 2?


Question 3:
This A487 in any of its classes doesn't seem to be much different than normalized 4130. What is the advantage?


Thanks for any insight

 

[metengr]

There seems to be some steps missing, such as
a. holding time at austenize temperature,

1 hour/inch of thickness

b. are we to air cool or furnace cool until we reach
500°F and then quench ?

This means you air or liquid cool to below 500 deg F before tempering.

c. how long to hold at the tempering temperature?

1 hour/inch at temperature.

Question 2: How does the same heat treatment of Table 1 result in different TS/YS when all classes of Grade 4 have the same chemistry as shown in Table 2?

Different cooling rates, air versus liquid, and tempering temperatures 1100 deg F versus 1150 deg F results in different properties for the specific class.

Question 3:
This A487 in any of its classes doesn't seem to be much different than normalized 4130. What is the advantage?

Do not understand your question because this specification is for castings, not wrought material.

 

[pwtomlin]

The austenitizing temperature and tempering temperatures listed are both given as minimums. You are allowed to go higher if needed. Classes B and D do not allow for air cool, hence the higher required strength levels. As metengr already said, the quench must take the temperature to below 500 F before tempering. The hour per inch is a good rule of thumb, but I would answer as long as needed to achieve the specified properties. The specification can cover a wide variety of casting sizes and thicknesses, it is up to the foundry to determine the optimal heat treatment.

Question 2 relates back to the fact that both specified temperatures are minimums. You would heat treat different grades (A and C vs B and D, in particular) differently despite the fact that you could have poured the castings with the same chemistry. Obviously, your quench method in coming down from the austenitizing temperature will have a big effect on properties.

Question 3. This standard is for steel castings suitable for pressure service. You can choose to reference it when purchasing steel castings that are going into pressure service. You could also choose to order castings using your own specifications instead.

 

[arunmrao]

Selection of quench media would depend on the section size of the casting to achieve the same properties. The foundry needs to design appropriate heat treatment cycles and procedures in order to achieve the mechanical properties. It is in view of this,that there is a flexiblity provide.

If you need to use 4130 or similar grade,you could specify the properties you need keeping in mind that you are dealing with cast test bars now.