LCB heat treatment for reduced UTS 1

[Lyrl]

We are a commercial heat treat company. One of our customers occasionally has us process A352/LCB castings (with which we have very limited experience) and has complained that the UTS after our heat treatment is too high (around 92 ksi, I think, with a requirement of 90 ksi max - no idea what the minimum is). We were told "all the other test results are good". Our current process (I have no idea how it was originally set up) is
1650°F, oil quench
Temper 1300°F, cool to 1100°F, oil quench

Any thoughts on reducing the UTS without significantly adversely affecting the other properties? We have the capability for high-pressure gas quench, if doing that instead of the oil quench would help.
Also, any idea if the cool to 1100° after the temper or the oil quench after the temper have any purpose?

 

[jwhit]

With the heat treatment you are using, I wouldn't expect the problem to be heat treat specific. Your temps look good. Usually when there is an issue with excess tensile strength in LCB it is related to running the carbon to the high side of the spec. Where notch toughness is concerned, it is better to reduce the carbon, with the quench 0.18-0.22 is good and run the Mn to the high end. What kind of residuals are they seeing in the chemistry? I'd be looking at V, Nb and B in particular and Ti if it is excessively high. You can bump your temper to 1350f max if need be, but it seems to me that is compensating for a chemistry that is just a little off. Unless the casting is extremely heavy walled the oil quench out of the temper isn't necessary to achieve the 13 ft lb minimum Cv required by A352 for LCB. We normalize at 1725-1750,then re-austenitize at 1650, water quench then temper followed by air cool. This is the process for LCB that most foundries use. The hardenability of LCB shouldn't be significant enough to require an oil quench out of the austenitize.

 

[arunmrao]

jwhit, has provided several useful posts on this topic in this forum. Pl, perform a search and then EUREKA!!

A commercial heat treater getting involved for this alloy, is quite a challenge . I would not stick my neck on the deliverables, for the foundry knows best, all that might have gone wrong.

http://www.eng-tips.com/search.cfm?...tings&t=&h=&searchSite=1&searchArea=1&d=1&s=1

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[weldstan]

The oil quench from 1100F will increase ultimate tensile strength versus air cooling from the 1350 F max temper.

 

[jwhit]

arun, Thank you for the compliment, the recognition is appreciated, esp. since in the work environment I get the "are you nuts" kind of looks for these things. The price for having mainly OJT knowledge and no degree,I guess.

 

[Lyrl]

We changed the temper from 1300-1100-oil quench to 1350-cool (rate not important), which is much cheaper for us (can be run in equipment without a quench and is a shorter process). Our customer is a small casting house, and I think they could adjust their chemistry, but it's a little awkward for the heat treater to tell the casting house their chemistry is wrong, so we tried the temper change first. They loved the results!

Thank you for all the responses, it was very helpful in understanding this material and our options for processing it, and it's great that both us and our customer benefit from the process changes!

 

[jwhit]

When they have it in metal, you have to work with what you've got. Going forward, you may suggest they take a look at this post or some of the others on LCB/LCC and let them figure out on their own that they can in fact help themselves out by juggling composition a little.