Influence of solution annealing temperature and cooling medium on microstructure, hardness and corrosion resistance of martensitic stainless steel X46Cr13

Abstract

The corrosion behavior of carbon containing martensitic stainless steels depends strongly on the applied heat treatment which determines the distribution of carbon and chromium in the microstructure. This work's focus is on the effect of solution annealing on microstructure, hardness and the resulting corrosion resistance of the martensitic stainless steel X46Cr13. Solution annealing was performed at selected temperatures based on thermodynamic calculations of the chromium and carbon contents in solid solution and the chemical composition of the remaining carbides as function of temperature. The corrosion resistance was investigated with electrochemical potentiodynamic reactivation (EPR) and the KorroPad (KP) technique. The results indicate a large influence of the solution treatment temperature, duration and cooling rate on passivation behavior and pitting corrosion resistance. Higher solution annealing temperatures increase the amount of chromium and carbon dissolved in solid solution resulting in easier passivation and higher hardness. If diffusion is enabled by slow air-cooling, chromium depletion was detected causing high susceptibility to pitting corrosion.

Investigations proofing the passive layer stability of stainless steels

“…The presented investigations and the many practical applications the KorroPad technique proved to be excellently suitable for describing the passive layer stability. Compared to other established methods to describe the corrosion resistance like salt spray and electrochemical tests the short testing time and the non‐destructive type of the KorroPad test are advantageous.…”

Dynamics of Tempering Processes in Stainless Steel

“…During a heat treatment Cr diffuses from the carbides into the ferritic matrix and are replaced by Fe from the matrix [2]. Rosemann et al performed Thermocalc calculation for carbide composition which shows at 500 °C that 10% of the mass in carbides is replaced by Fe at the expense of Cr.…”

“…The material was rolled into sheets with thickness of 0.45 mm at the manufacturer. For sample preparation, the samples of 1x1 cm 2 were cut out of the sheet with an abrasive saw. The samples were mechanically polished up to 0.04 μm sized particles for EBSD analysis.…”

“…By scanning the same area for whole duration of the experiment the microstructural and crystallographic orientation changes were tracked. The selected area of 20x20 μm 2 was scanned in a hexagonal grid with a step size of 0.4 μm. Each scan took 2 minutes to complete.…”

“…The oxidation process at the surface is in particular relevant for the corrosion resistance of stainless steel [2]- [4]. Several high temperature experimental methods exist to explore the mechanisms behind surface oxidation.…”