Significant Strengthening Effect on Martensitic Stainless Steel by Repetitive High-Stress Loading at Ultralow Temperatur
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pitation-hardening martensitic stainless steels, developed based on super-martensitic stainless steel (SMSS),[1,2] possess high strength, high toughness, excellent corrosion resistance and good weldability. They have been widely used in ultralow temperature applications, such as extreme cold rail transit, ocean engineering and aerospace industries.[3–5] Most investigations of precipitation-hardening martensitic stainless steels are focused on the effect of cryogenic treatment. The influence of cryogenic treatment on the microstructure and mechanical properties of high-vanadium alloy steel,[6] IN718 alloy[7] and 0Cr12Mn5Ni4Mo3Al steel[8] has been studied and reported. It has been found that this treatment can promote the martensitic transformation of residual
HENGCHENG LIAO, HETING XU, and JINGFAN TANG are with the Jiangsu Key Laboratory for Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, 2 Dongnandaxue Road, Nanjing 211189, P.R. China. Contact e-mail: [email protected] SHIHUI HUO, DAOQIONG HUANG, and HUI CHEN are with the Science and Technology on Liquid Rocket Engines Laboratory, Xi’an 710100, P.R. China. Manuscript submitted July 21, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
austenite as well as the precipitation of fine dispersoid particles. The mechanical properties can, therefore, be considerably improved because of the increased volume fraction of martensite and size refinement. Strain-strengthening techniques first appeared in the aerospace field, where austenitic stainless steel was strain strengthened to manufacture propeller tanks on space launch vehicles and satellite launchers at NASA.[9] Since then, the strain-strengthening technique has been widely adopted to improve the strength of many other steels and nonferrous alloys. The strain-strengthening effect is always induced by large or severe plastic deformation, which greatly changes the shape of materials. In this study, the selected S04 steel is a precipitationhardening martensitic stainless steel. The contents of the main elements in wt pct are: C, 0.02; Cr, 13.2; Mo, 5.1; Ni, 6.2; Co, 8.1; Si, 0.3; Mn, 0.3; P, 0.02; S, 0.005 with Fe balanced. Components made of S04 steel are often subject to repetitive trial runs with large loads before serving or accidental overload during service. Thus, it is very important and necessary to evaluate the performances of these components after repetitive trial runs or accidental overload. In our study, a method was designed to simulate this extreme service condition: repetitive high stress loading (RHSL) under a stress around the yield strength of the material. During RHSL, only small plastic deformation occurs that almost doesn’t change the overall shape of materials. However, the influence of small plastic deformation by RHSL on the microstructure and mechanical properties of metallic materials is not well known. We studied and report the effect of RHSL at ultralow temperature on the microstructure and mechanical properties of S04 steel in this work. Round bar
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