Quench water quality thermal impact estimation

Since many years the thermal characterisation of the heat treatment quench for carbon steel is a key topic in Vallourec. The cooling medium is one of the factors that can influence this process. It plays an important role on the quality of the cooling and the physical properties of the as-quenched products.

No control of the water quality may imply possible quality consequences such as the manifestation of quench’s cracks, lack of hardness or a global bad “as quenched” thermal homogeneity of the carbon steel. In mass plants case, the quenching medium can be polluted by agents e.g. mechanical oil, free gas in the water or products scale which could modify the power cooling of the water. Filtering systems or degassing tanks are installed on the process water recirculating systems to mitigate these issues.

In this context, a test routine conform with the norm ISO 9950 has been prepared to evaluate the thermal impact of pollutants on the quench severity. The trials are performed on specimens in Inconel 600, accordingly with ISO 9950. The set-up consists of a bath filled with demineralized water, a furnace, a data recorder connected to the instrumented sample and the support for the sample. The currently analysed pollutants are free gas, mechanical oil, and a mix of steel scale and mechanical oil.

Results are analysed taking as reference the 100 % “demineralized” water quench severity case. The trials are performed under static conditions: calm cooling medium and no movement of the specimen during quenching. We can assume that these pollutants intrinsically affect the cooling power of the water.

The aim of the trials is to show a global statistical behaviour of the impact of the different pollutants that can increase or decrease the normal cooling speed. That analysis can help in the choice of the criteria for quenching recirculating system maintenance accordingly with the optimal thermal performance of the process.