AISI 8640 material standard 1

[Dalinus]

Hello all,

our customer demands casting made of steel AISI 8640, Q+T to 269-331 BHN. No other mechanical properties were demanded, and when we asked for them, the response was that "The hardness required is 269-331 BHN and the remaining as per standard AISI 8640".
I googled 50 pages, but except chemical composition there were no mechanical properties others than for bars, pipes..., and none matching 269-331 BHN.

My question is, is there AISI 8640 standard which contains mechanical properties matching demanded hardness?
I would like to buy it, but I dont like buying pig in a poke.

I apologize for maybe stupid question, but I am still a little bit confused about the connections between AISI, SAE, ASTM, ASM and others American organizations, standards and material designations.

Dalin

 

[jwhit]

If they really want 8640 material there are 2 options. ASTM A148 Gr. 135-125 or 150-135 could be used as they are open chemistries except for P & S, alternatively, the ICI 8640 composition could be used. ICI gives a typical range of mechanical properties that can be attained by varying the temper. The AISI composition should be modified slightly for casting use regardless. Typically the C range is opened up slightly to .35 to.45 and a higher Si content is allowed for fluidity. Customers and design personnel should keep in mind that when shifting from wrought product to cast, they need to make some allowances for varying the material from what they are used to in order to aid the manufacturing process. Too many minds think that metal is metal and that is all there is to it.

 

[jwhit]

One thing I neglected to state about the ICI specs is that they are appropriate if this is an Investment Casting.

 

[arunmrao]

The customer has rightly asked you to offer him a casting with chemistry of 8640 and heat treated to 269-331 BHN. 8640 steel is not a cast grade material and attempting to achieve those properties in a casting is near impossible.

Cast microstructures have several impurities and coarse grains structure. I have had several such requests for casting in EN24 grade steel (NiCrMo steel). The hardness is specified and chemistry confirmed.

Can you describe the casting for the benefit of understanding.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[OGMetEngr]

The AISI designation only locks in the chemical composition. The hardness range you stated could be achieved but it would depend entirely on the size of the casting. Very large thickness castings will not be able to do this. Also, regardless of size, toughness will be low.

Take a look at ASTM A732 chemical compositions, you may find something very close to 8640 there.

 

[tbuelna]

As others noted AISI 8640 only covers chemistry. And also as noted, a steel alloy of this composition would be difficult cast reliably using common foundry processes. Based on the description of your customer's PO requirements, you might interpret it to mean only the raw material melted to produce the casting must meet AISI 8640 chemistry, rather than the finished casting itself. Your foundry could simply buy some AISI 8640 bar and melt it down.

The non-specific requirement for determining the 269-331BHN also makes things very easy. This is a fairly modest strength level and should be easy to achieve with any type of casting using this material. Especially since the mechanical properties of the heat treated casting can be taken anywhere you choose.

 

[Dalinus]

Thank you all for your responses.

The casting is about 3.8 tons with maximum wall thickness about 100 mm.
The calculated DI is between 66-161 mm, so I will go to upper range of chemistry.

With mass about 6t with risers and gating system I will do it on EAF, so chemistry is no problem.

As for ASTM A732, it looks like 14Q has similar chemical composition (except lower C contetnt) and can get to desired hardness range.

I suppose oil or salt quenching from 860°C and tempering at +/- 600°C. I will do trials on blocks before.

Dalin