Welding Procedure Development For A 13Cr-5Ni-2Mo (UNS S41426) Super Martensitic Stainless Steel

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Product Number: 51321-16840-SG

Author: Thanh Nam Vu; Karthik Krishnan; John Sisk

Publication Date: 2021

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To obtain heat affected zone (HAZ) hardness levels below maximums specified in the current (2015) edition of NACE(1) MR0175/ISO(2) 15156-3 for sour service use, welded super martensitic stainless steels (SMSS) need post weld heat treatment (PWHT). PWHT is mainly done by stress relieving or tempering post welding as re-austenitizing, quenching, and tempering is not practical in many applications. Double stress relief thermal cycles may be needed so that any martensite which forms due to transformation during the first stress relief cycle is tempered by the second stress relief cycle. Overall, design of PWHT can be challenging to ensure not only meeting maximum hardness requirements but also ensuring meeting minimum design yield strength. This
study investigates the austenite start and finish (A1 and A3) phase transformation temperatures as a function of heating rate and reports the martensite start and finish temperatures (MS and MF). Phase transformation temperatures in 13Cr-5Ni-2Mo (UNS S41426) alloy are measured using a resistance heating physical simulator coupled with dilatometry. Dilatometry-based phase transformation temperatures are compared with HAZ hardness results in 13Cr-5Ni-2Mo SMSS welds after PWHT. Mechanical properties associated with the different PWHT temperatures are measured to understand the effect of PWHT on design mechanical properties like yield strength.