ASTM A536 70-50-05

[QC1971]

I have a question regarding the mechanical testing results for A536 70-50-05 material. I have a supplier who does both seperate and cast on samples however their acceptance criteria for cast on samples is significantly lower than what A536 specifies for 70-50-05. Where A536 calls for a tensile of 485 MPa and a yeild of 345 MPa the supplier accepts tensiles of 379 MPa and yeilds of 272 MPa for their cast on samples. If the cast on samples have significantly lower properties than are specified how can the material be considered 70-50-05 when the mechanical properties are what A536 bases its classifications on? Thanks in advance for your replies.

 

[arunmrao]

The difference in mechanical properties as noted by you is because of the differences in cooling rate between the separately cast and integrally cast test samples.

Have you been able to refer to the explanation provided in the standard in Appendix X1 Mechanical properties of castings.. I provide an extract below.

" The mechanical properties of iron castings are influenced by cooling rate during and after solidification,by chemical composition,by heat treatment, by the design and nature of the mild,by the location and effectiveness of gates and risers and by certain other factors.
The cooling rate in the mild and therefore the properties developed in any particular section are influenced by cores, chills and chaplets, changes in section thickness and the existence of bosses ----. Because of the interactions of these factors,no precise quantitative relationship can be stated between the properties of the iron in various locations of the same castings or between the properties of a casting and those of a test specimen cast from the same iron. "

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"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[QC1971]

I understand that materials can have different properties due to variations in their thermal treatments. The issue is that A536 classifies materials based on their mechanical properties, it allows for cast on samples or seperately cast samples but the same property values apply to both samples. In this case the supplier has created their own acceptance standard for cast on samples that is significantly lower than what A536 specifies for 70-50-05 material.

If we were talking minor differences we would not be having this discussion, but 106 MPa (15,375 psi) tensile and 73 MPa (10,588 psi) yeild are pretty significant differences.

A536 para. 6.3 states that the manufacturer shall maintain controls and documentation to assure the purchaser that the properties determined from the test coupons / bars are representative of the castings. How can they be representative of the castings if you expect this much difference in mechanical properties.

My only concern is that the components were designed based on the properties of 70-50-05 material but the actual product is not close to the required properties. I feel that an evaluation of the materials actual properties vs. design requirements is needed to determine if it is fit for purpose.

 

[arunmrao]

QC1971,

I appreciate your concerns, and they are valid . However,the supplier is right in stating that the melt has qualified,but unfortunately ,the casting has not, due to reasons discussed above.

Did you have an opportunity to discuss this aspect with the vendor. Perhaps he might have factored by adding some alloying elements or a thermal treatment.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[mrfailure]

QC1971,

I think you are entirely right in your perspective. Test coupons cast at the time of casting are representative of the casting, BUT properties of the actual casting do have to meet them. From the perspective of a test lab that sometimes analyzes such castings after service (often as part of failure investigations), I would be very alarmed if the actual casting did not meet 70-50-5 requirements because these are, as you discussed, the basis for use in design. In your shoes I would change suppliers to one who can meet these requirements for the actual casting.

 

[QC1971]

I have read A536 numerous times and this morning I set down and read it again and I may have found my answer.

4.1 states that "the iron represented by the test specimens shall conform to the requirements as to tensile properties presented in tables 1 and 2".

What do you guys think?

 

[arunmrao]

Yes,you are right and the same was stated by me in my previous post.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year