oka137
Materials
- Jul 23, 2011
- 3
Last week my company had some problems regarding the hardness of bearing steel after heat treatment. Bearing ring , AISI 52100, (inner and outer) was found after heat treatment process, having low hardness.
Before HT : 8 - 13 HRc
After HT : 61 - 64 HRc
Problem Ring : 18 - 22 HRc
After searching the whole day, we cannot find where the problem came from ; is it from the HT machine that have some trouble, or human error that makes the ring does not proceed do HT process?
We conducted three methods of investigations : using Back-Scatter to find the retained austenite, etching with nital to find the microstructure, and simulation on line.
The assumption was, if using EBSD we find significant peaks of Fe-C, than we can conclude that the ring follows the HT process, but if not, then it must be something else. Our first suspect were the grain consisting of Fe - Cr - Ni, the compound of stainless steel formed on 300 degree celcius.
We did not found any Fe - Cr - Ni compound, but we found a high ammount of Fe - Cr - O compound, so we suspect the ring had been heat treated under the eutectoid temperature, say 700 degree celcius, and the cooling rate is not fast enough to make tempered martensite.
Due to our limited optical microscop, we cannot determine the grain and the phase. The etchant available is only Picral and Nital, no Zephiran Chloride available.
I would like to ask any opinion about this. Is there something wrong in our investigation methods? or is the etchant not significant enough (i really think it is)? or our conclusion is wrong?
Thanks =D
Before HT : 8 - 13 HRc
After HT : 61 - 64 HRc
Problem Ring : 18 - 22 HRc
After searching the whole day, we cannot find where the problem came from ; is it from the HT machine that have some trouble, or human error that makes the ring does not proceed do HT process?
We conducted three methods of investigations : using Back-Scatter to find the retained austenite, etching with nital to find the microstructure, and simulation on line.
The assumption was, if using EBSD we find significant peaks of Fe-C, than we can conclude that the ring follows the HT process, but if not, then it must be something else. Our first suspect were the grain consisting of Fe - Cr - Ni, the compound of stainless steel formed on 300 degree celcius.
We did not found any Fe - Cr - Ni compound, but we found a high ammount of Fe - Cr - O compound, so we suspect the ring had been heat treated under the eutectoid temperature, say 700 degree celcius, and the cooling rate is not fast enough to make tempered martensite.
Due to our limited optical microscop, we cannot determine the grain and the phase. The etchant available is only Picral and Nital, no Zephiran Chloride available.
I would like to ask any opinion about this. Is there something wrong in our investigation methods? or is the etchant not significant enough (i really think it is)? or our conclusion is wrong?
Thanks =D