bainitic heat treatment of 1045

[petedie]

Hello,

in our manufacturing process we use 19mm high by 3mm thick heat treated 1045 steel cutting knifes. These knifes have been harden to 36-38 HRc using bainitic hardening process. Recently we'd received a material batch where one side of the knife measured 35 HRc and the other 28 HRc, but when we had cross sectional micro hardness test done, we did not see this large gradient. In fact the hardness barely changed from one side to the other. What could be causing this discrepancy between the two tests and why would the surface hardness for such a thin material be so different.

Thanks
Pete

 

[Guest102023]

It is not impossible that hardness testing was done in error. The Rockwell test is prone to error on the low side if the sample is not flat on the underside. The technician should have noticed the discrepancy from the usual result and checked his work before reporting.

Further than this, you would have to do some metallography to compare the surface with the core, but you have already done this. A frequent cause of low surface hardness is decarburization, which you would have spotted by metallography.

 

[TVP]

I concur with brimstoner: error in the Rockwell testing is one possibility, as is surface decarburization. How close to the surface was the micro hardness performed?

 

[petedie]

Initially we believed that the Rockwell tester was wrong so we had it calibrated and samples retested. The result were the same. We also tried scale A(60kg load) hardness test and results were not as skewed but there was a difference between the two sides. It seems that the more you indent the surface the larger the spread. Could surface decarb cause this? TVP I'm not sure what you're asking but the micro hardness test was done with a 500g weight....