Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 1 – Microstructural analysis

Abstract

Specimens of 16Cr -5Ni -1Mo stainless steel were solution treated at 1050°C for 1 h followed by heating in the temperature range 400 -750°C for different holding times (1 -16 h). After heat treatment, optical microscopy, scanning (SEM) and transmission (TEM) electron microscopy, and X-ray diffraction examinations were conducted. The microstructure of all aged specimens was found to consist of martensite with variable fractions of d ferrite and reversed austenite. Very ne precipitates of Mo carbides were revealed in the specimens aged at 475°C. The specimens aged at 625°C showed a decrease in the dislocation density and a high volume fraction of austenite and precipitation of Fe 2 Mo Laves phase was detected by X-ray analysis. Above 625°C, Cr 23 C 6 and TiC became the predominate carbides heterogeneously precipitated in the martensitic matrix. Partial transformation of reversed austenite to unaged martensite was observed at temperatures above 625°C.MST/5714

Microstructure and Properties of 15Cr‐5Ni‐1Mo‐1W Martensitic Stainless Steel

“…Tungsten and Molybdenum are added as solid solution strengthener. In addition, Mo also imparts strength by formation of fine Mo 2 C in the temperature range of 450–500°C . Nevertheless, both these elements form Laves phase (Fe 2 W, Fe 2 Mo), when aged at 550–650°C for prolonged time .…”

“…Use of cryo treatment is well known for high carbon MSS used in wear applications . These heat treatments are used for accomplishing specific functions (i) ST (950–1050°C) to achieve supersaturated solid solution which facilitates proper precipitation; (ii) CT (−70 to −196°C) to achieve fully martensite structure which ensures dimensional stability and imparts strength; (iii) Aging (400–500°C) to improve the strength by formation of precipitates of Cu, Ni 3 Ti, Ni 3 Mo, Mo 2 C, NiAl . Few martensitic stainless steels based on Fe‐15Cr‐(X)Ni with the addition of Mo, Cu, and Al were extensively studied for microstructure and properties after different heat treatment .…”

Kinetics analysis of two-stage austenitization in supermartensitic stainless steel

“…The excellent strength and toughness properties are obtained through inter-critical annealing (tempering below A 3 temperature) to promote the formation of lamellar reversed austenite on high-and low-angle boundaries of lath martensite [4][5][6][7]. The annealing leads to an effective decrease of the average grain size and to a "composite structure" of hard tempered martensite and soft austenite.…”

Formation and stabilization of reverted austenite in supermartensitic stainless steel

“…The alloy grade became popular in the oil and gas industry as a low cost alternative to highly alloyed duplex stainless steels in pipeline applications [2]. The strength and toughness of the material is based on formation of reversed austenite from lath martensite during inter-critical annealing [3][4][5][6]. Annealing leads to effective grain refinement by formation of a two phase structure of soft austenite and hard tempered martensite.…”