Effects of Tempering and Normalizing Heat Treatments on Stress Corrosion Cracking Behaviors of Modified AISI 4340 (300M) Steel in Acidic Chloride Media

Authors: Guma TN, Ajayi EO

DOI Info: N/A

ABSTRACT

Stress corrosion cracking (SCC) is an unpredictable calamitous and highly detested type of corrosion. 300M steel is a special but notable failure-prone structural material by SCC. The aim of this study was to find out SCC mitigation extents of 300M steel by tempering and normalizing heat treatments in seven aqueous media that contained different concentrations of hydrochloric acid (HCl) and sodium chloride (NaCl) up to 17.5%. 56 ASTM E8 standard tensile test samples were produced from procured un-heat-treated 300M steel out of which 14 were heat-treated by tempering and 14 by normalizing. The samples were procedurally cleaned to uniformly smooth surface finishes and each loaded to the same maximum tensile stress of 1427.4 MPa. The loaded samples were immersed in pairs of one tempered with one un-heat-treated and one normalized with one un-heat-treated in each of the seven prepared media under separate constant temperatures of 60 ^oC and 100 ^oC for one hour, and removed for integrity assessment with respect to internal and surface cracks by micro-examination. Results obtained showed no SCC for all the heat-treated samples but multiple trans-granular crack features alongside craters that increased in intensity with the acid and chloride contents and propagated in the matrix structure to the surfaces for the un-heat-treated samples tested at 100 ^oC in media that contained from 14%HCl and 14% NaCl.

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