DIN912 WITH KNURLING 12.9, ML40CR 1

[Joesfast]

Hi every one. I am new to this forum. Has any one heard of a materail ML40CR ? A supplier from China has quoted us for Din 912 which are Socket Screws. These have to be grade 12,9. As far as I can see this material is suitable for 10,9. The supplier has said they heat it up and then it becomes 12,9? Is this possible and what would the drawbacks of using such a material be? These are really odd sizes and I have requested samples which I have sent for testing. I do not want to burn my fingers so I would like to have an experts opinion on whether it is possible to use this material. I have attached the certificate and here it is

http://files.engineering.com/getfil...58d-48f5-9629-da53f766d6f1&file=DOC111111.pdf

Please advise
Thanks

 

[CoryPad]

Never heard of that material before, it is similar to SAE 5140 or 42Cr2 from EuroNorms. The strength meets 12.9 requirements. These parts are suitable for composition and strength.

 

[dbooker630]

I don't know your application but I do not see any heat treat results. While the hardness is satisfactory it is not clear if the minimum tempering temperature (380C) was attained. You can have the lab perform a tempering test, if the hardness drops more than 20 Vickers points the lot was undertempered.

12.9 fasteners are also sensitive to hydrogen embrittlement so you may also want to perform a torque-tension test that your lab should be able to do.

 

[TVP]

ML40CR appears in the Chinese standard GBT 6478 Steel for cold heading. It is a common steel for fasteners in China. It is capable of meeting the requirements of 12.9, but conducting the tempering test may be a good idea.

 

[mrfailure]

First, material meeting 12.9 requirements will, by definition meet 10.9. The only exception could be elongation and reduction of area if machined specimens are tested (10.9 specifies 9%/48% respectively, 12.9 8%/44%).

Also, your material actually does not conform to ML40Cr. Your material is deficient in chrome (ML40Cr requires a minimum Cr content of 0.90%). You instead have an alloy conforming to 40Cr (0.80% - 1.10% Cr), which is identified in a variety of Chinese standards. However, I would not get too hung up on the original alloy. The important fact is that your cap screws are conforming to 12.9.

Aaron Tanzer

http://www.lehightesting.com