Effect of Heat Treatments on Microstructural Evolution and Tensile Properties of 15Cr12MoVWN Ferritic/Martensitic Steel

Tingwei Ma,Ping Wang,Xianchao Hao

doi:10.3390/met10091271

Abstract

In this study, the phase transformation temperature of 15Cr12MoVWN ferritic/martensitic steel was determined by differential scanning calorimetry to provide a theoretical basis for the design of a heat treatment process. An orthogonal design experiment was performed to investigate the relationship between microstructure and heat treatment parameters, i.e., normalizing temperature, cooling method and tempering temperature by evaluating the room-temperature and elevated-temperature tensile properties, and the optimum heat treatment parameters were determined. It is shown that the optimized heat treatment process was composed of normalizing at 1050 °C followed by air cooling to room temperature and tempering at 700 °C. Under the optimum heat treatment condition, the room-temperature tensile properties were 1014 MPa (UTS), 810.5 MPa (YS) and 18.8% (elongation), while the values are 577.5 MPa (UTS), 469 MPa (YS) and 39.8% (elongation) tested at 550 °C. The microstructural examination shows that the strengthening contributions from microstructural factors were the martensitic lath width, dislocations, M23C6, MX and grain boundaries of prior austenite grain (PAG) in a descending order. The main factors influencing the tensile strength of 15Cr12MoVWN steel were the martensitic lath width and dislocations.

Highlights

Numerous countries promote the design and construction of the fourth-generation nuclear power plants because of increasing fuel consumption [1,2]
From Equation (1), chromium equalization (Creq) for 15Cr12MoVWN steel with the chemical composition in Table 1 is 6.48 wt.%, which is substantially lower than the critical content of 10.0 wt.% to eliminate the δ-ferrite formation
We investigated the evolution of the microstructure of 15Cr12MoVWN steel by DSC and orthogonal design experimental method

Summary

Introduction

Numerous countries promote the design and construction of the fourth-generation nuclear power plants because of increasing fuel consumption [1,2]. Sodium-cooled fast reactor (SFR) is an important type of the fourth-generation nuclear energy and an important direction for Chinese nuclear energy development in the future. 9–12% Cr ferrite martensitic steels have enhanced radiation tolerance, higher thermal conductivity, lower thermal expansion coefficient and low susceptibility to helium embrittlement [4,5,6]. They have been chosen as candidate materials for SFR. DIN 1.4914 or MANET steel with a nominal composition of 0.11C-11.3Cr-0.5Mo-0.3V-0.25Nb-0.03N-0.007B was developed in Germany in the

Results

Discussion

Conclusion