Heat Treatment 3

[PVRV]

Is Quenching & Tempering a permissable alternative to Normalizing?
bearing in mind that the plates in question will be subject to fabricaton (rolling & welding) subsequently stress-relieving.

Cheers

 

[sayee1]

What is the plate material? the question on replacing NR by Q&T would be dependant on material! A word of caution on the PWHT though, if Q&Ted plates, then the SR(PWHT) temperature should be lower than the tempering temperature in case of most specifications. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[PVRV]

a)
A516 Gr. 60

b)
Loss of tempering effect; I see where you are coming from please note SAW will be employed after rolling the plates. Is that another concern?

 

[Metalguy]

This depends in part on the thickness of the plates and the quenching medium. 516 is a good grade of carbon steel, and if the thickness is over ~1.5" or so, even quenching in water will still give you pearlite. It will be finer pearlite than normalizing, which is good.

BUT, hardening (quenching) temps. are lower than normalizing temps., and you will not get the same amount of microstructure refinement-if that's a concern.

 

[PVRV]

Metalguy,

a)
The quenching medium is water

b)
The quenching temperature is about 1652 F

c)
The tempering temperature is about 1160 F

d)
The thickness is 1.35"

With appreciation,

 

[sayee1]

What consumables aree you planning to use for the SAW? With the thickness being just 1.35" and the SR time around 1 1/2 hr(~1 hr/inch), I don't think the properties of a typical 70 ksi wire flux combination should cause any problem. The tempering temperature being 626 Degrees C, it should not be a problem to SR @610 Degrees C. So from welding point of view not a constraint.
For my understanding though, I would love to know why you need to substitute NR with Q&T? Is it client requirement or restriction of the heat treatment facilities etc.?
Metalguy,
Finer pearlite and coarser microstructure by Q&Ting as compared to NRing----- What would be the impact on the mechanical properties Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[Metalguy]

The stated quenching temp. is almost as high as a normalizing temp. so I don't think you'll have a microstructural problem from this. However, there is another concern with the water quenching, given the thickness. You do NOT want to form martensite/bainite, and the C and Mn are the two elements of concern. *IF* they are on the low side of the spec. you should be OK, but if near the high limit you *could* have a problem. The Mn range is pretty high, and it has a drastic effect on hardenability. A cold water quench would also be worse than if the water were near ~90 deg F. (steam blanketing).

Fine pearlite is almost always preferred-better mech. properties, except for creep (IIRC).

 

[Metalguy]

Oops, coarse grains (large grain size) helps creep strength. I'll look up the effect of pearlite spacing on creep when I get a few minutes.

 

[PVRV]

a)
Would it worthwhile to conduct tensile testing with the following provisions:

1. Cut the specimen at the area of concern (neck of the tensile specimen), join it by SAW, back chip on other side and place a SMAW weld. (typical to main weld seams of the Pressure Vessel)

2. Preform item 1) in addition to stress releiving; prior
to tensile testing.

3. Machine the tensile specimen at mid-section (thickness)
with provisions for item 1) & 2) above.

4. Conduct hardness reading across the plates through thickness.

Or perhaps just reject the plates

b)
As for exchanging Q&T with Normalizing; I was worried about a lower grade material being used. But the tempering temperature is so high that any hardening effect would not be that substantial and I am concerned of why Q&T has been preformed seems more of a hassle.

With Appreciation

 

[Metalguy]

I think all you need to do is run a few hardness checks on the surface of the plates, and compare them with the interior hardness. *IF* you have "transformed" steel, the outside will be noticeably harder. If they are similar, they should be fine.

You could also mount,polish and etch a piece and see what microstructure you have.

 

[ellynn]

1) I have Pipe A672 Gr.B60 CLASS 22(stress relieved)with thickness 42.30mm and 48.50mm (ASTM Specification A515 Gr.60).
2) The minimum Design Metal Temperature is 0°C (Design T.427°C Max.)as per our class.
3) According to ASTM A515 para.5 (2in and under in thickness mat be ordered normalized or stress relieved, or both).
4) Following to B31.3 Fig.323.2.2A (curve B) it is necessary to impact tested this material.

My question is: the material must be stress relieved or normalized.

Thank you for your help.
Ellynn

 

[stanweld]

SA-516 para. 5.4 permits cooling at faster rates than obtainable in air for improvement in toughness if approved by the purchaser and the material is subsequentyly tempered in the range of 1100 F to 1300 F. Quenching and tempering from the normalizing temperature is, therefore, permitted.
Generally one would only do this if the material were thick - on the order of 3" or greater to meet ASME Code impact properties at -50 F.

 

[stanweld]

Ellynn:
The heat treating requirements of A-672 apply to the pipe after forming and welding. Class 22 requires uniformly heating the pipe within the post weld heat treatment temperature range for a minimum of 1 hr per inch of thickness or 1 hr, whichever is greater. In order to assure meeting the toughness requirements of FIG. 323.2.2A Curve B, I would advise that the pipe be ordered as Class 42 - normalized and tempered. The impact test properties may also be met by manufacturing A-672 pipe from A-515-60 plate, previuosly normalized, followed by tempering per Class 22 as stated above.