An AES study of temper embrittlement in a low alloy steel

Abstract

In situ tensile tests were conducted in an Auger spectrometer on specimens of a low alloy steel susceptible to temper embrittlement. The specimens were tested in ultra high vacuum and in a low pressure of high purity hydrogen. Comparisons were made of the stress-strain curves, the fracture modes and the Auger electron spectra obtained from the fracture surfaces. Specimens were tested in the as-quenched martensitic (quenched from 950°C). the unembrittled (tempered at 650°C) and the embrittled (tempered at 500°C) states. Testing in hydrogen changed the mode of fracture, in the asquenched martensitic material, from a normal dimpled rupture to an intergranular, dimpled rupture mode. AES analysis of the intergranular facets showed, with the possible exception of N. no segregation of alloying or embrittling elements. Hydrogen had no major influence on the mode of fracture of samples in the unembrittled or embrittled states. In the temper embrittled material, grain boundary segregation of Sn. P and N together with enhancement of Ni was observed. In all conditions testing in hydrogen had a marked influence in reducing the strain to fracture. Specimens water-quenched from the austenite region were susceptible to intergranular quench cracking. No segregation of impurities was detected on the prior austenite boundaries and it is concluded that the phenomenon of quench cracking is not associated with such segregation.