Prevention of weld-decay in austenitic stainless steel by using surface mechanical attrition treatment

Majid Laleh,Farzad Kargar,Alireza Sabour Rouhaghdam

doi:10.1186/2228-5326-2-37

Abstract

Surface mechanical attrition treatment (SMAT) was applied to the samples of a type AISI 304 stainless steel in order to induce grain refinement as well as formation of twins. Transmission electron microscopy and X-ray diffraction analysis results showed that the average grain size at the surface of the SMATed sample was about 10 nm. The untreated and SMATed samples were then welded using a one-pass gas tungsten arc procedure. The heat-affected zone (HAZ) of the samples was examined by optical microscopy and corrosion tests. Results of the double loop electrochemical potentiokinetic reactivation tests showed that the degree of sensitization in the HAZ for the SMATed sample was very low as compared to that of the untreated one. The pre-SMATed sample was resistant to intergranular corrosion. This is mainly due to the formation of high density of twins which are not prone to carbide precipitation because of their regular and coherent atomic structure and extreme low grain boundary energy as compared with those of other grain boundaries.

Highlights

Austenitic stainless steels are widely used in a wide range of applications such as steam generating plants, chemical reactors, and nuclear plants due to their excellent corrosion resistance, good mechanical properties, and good weldability at elevated temperatures
Austenitic stainless steels possess excellent resistance to general corrosion; when they are subjected to a treatment like welding in the temperature range between 500°C and 800°C, they suffer from corrosion in forms of intergranular corrosion and intergranular stress corrosion cracking
The full width of half maximum (FWHM) of the diffraction peaks for the SMATed sample is much broader than that of the asreceived sample, which came from the influence of grain refinement

Summary

Introduction

Austenitic stainless steels are widely used in a wide range of applications such as steam generating plants (as piping and superheating tube materials), chemical reactors, and nuclear plants due to their excellent corrosion resistance, good mechanical properties, and good weldability at elevated temperatures. Austenitic stainless steels possess excellent resistance to general corrosion; when they are subjected to a treatment like welding in the temperature range between 500°C and 800°C, they suffer from corrosion in forms of intergranular corrosion and intergranular stress corrosion cracking. This is generally attributed to sensitization as a result of chromium depletion which in turn is due to the chromium carbide precipitation in the grain boundaries [1,2,3,4,5]. Sensitization as a serious and momentous problem during welding of stainless steel has not been completely prevented by conventional techniques such as reduction of carbon content (below 0.03 wt.%), addition of strong was made to evaluate the effect of nano grains and twins formation in the 304 stainless steel (by using SMAT) on the prevention of weld-decay

Methods

Results

Conclusion