Cr Supermartensitic Stainless Steel Research Articles

Effect of Heat Treatment on Reversed Austenite in Cr15 Super Martensitic Stainless Steel

The effect of different heat treatments on the reversed austenite in Cr15 super martensitic stainless steel was investigated. The experimental results indicate that the microstructure of the steel is composed of tempered martensite and diffused reversed austenite after quenching at 1050 °C and tempering from 550 to 750 °C. The volume fraction and size of reversed austenite increase with increasing tempering temperature and both of them reach the maximum value at 700 °C. The volume fraction and size of reversed austenite decrease when the temperature is above 700 °C. The transmission electron microscope (TEM) results indicate that the orientation relationship between tempered martensite and reversed austenite belongs to Kurdjmov-Sach (K-S) relationship.

Formation of Reversed Austenite in High Temperature Tempering Process and its Effect on Mechanical Properties of Cr15 Super Martensitic Stainless Steel Alloyed with Copper

AbstractFormation mechanism of the reversed austenite of Cr15 super martensitic stainless steel (SMSS) alloyed with copper after high temperature tempering was investigated by means of thermo‐calc software, transmission electron microscope (TEM), and X‐ray diffraction (XRD). The mechanical properties of the SMSS were also tested. The experimental results show that the reversed austenite with low dislocation density is formed at high temperature tempering processing. The transformation of the martensite to reversed austenite is a diffused phase transformation, and the growth of the reversed austenite is closely related to the diffusion process of Ni. The bulk reversed austenite with large amount of stacking faults is formed with the increase of the tempering temperature. The volume fraction of reversed austenite increases at first and then decreases with increasing tempering temperature, and the maximum amount of the reversed austenite is obtained at 650°C. The reversed austenite is unstable at the tempering temperature above 650°C and the martensitic phase transformation will occur at the following cooling process. The mechanical properties of Cr15 super martensitic stainless steel are significantly influenced by the volume fraction of reversed austenite.

Effect of Heat Treatment on Microstructure and Properties of Cr15 Super Martensitic Stainless Steel

The microstructure and mechanical properties of Cr15 super martensitic stainless steel after different heat treatment were studied by SEM and XRD. The results show that the microstructure of steel A and B are lath martensite and retained austenite after quenching. The original austenite grain size increases with the increasing quenching temperature. The microstructure is composed by tempered martensite and reversed austenite after tempering. The amount of reversed austenite in both steels increases first and then decreases with the increasing tempering temperature. Both of the tested steels have the best mechanical properties at 650°C tempering temperature.

Microstructure and mechanical properties of a 15%Cr supermartensitic stainless steel microalloyed with tungsten

The microstructure and mechanical properties of a 15%Cr super martensitic stainless steel microalloyed with tungsten were investigated by means of dilatometer,optical microscopy,transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),energy dispersive spectrometer(EDS),and tensile and hardness tests.The results revealed that a typical biphase structure of tempered martensite and reversed austenite which diffusional distributed in martensite matrix was selected after quenching and tempering.The reversed austenite and martensite matrix meet the K-S relationship.The diffraction pattern calculations and the EDS analysis of TEM confirmed that the nanometer-sized Laves particles and rich copper phase e-Cu precipitated in the matrix during tempering in the investigated steel,which were contributive to improve strength.The steel microalloyed with W showed an improved mechanical property values: 26~36 RC hardness,895~1 009 MPa tensile strength,17%~21% elongation.

Effect of Cu addition on microstructure and mechanical properties of 15%Cr super martensitic stainless steel

The effect of adding different content of Cu (0wt.%, 1.5wt.% and 3wt.%) to the 15%Cr super martensitic stainless steel (SMSS) was investigated using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Its consequence on mechanical properties was examined to clarify the role of Cu in the tested steels. The experimental results indicate that the microstructures of three tested steels are tempered martensite, retained austenite and reversed austenite; two kinds of austenites are dispersedly distributed among martensite matrix. Cu can solute in matrix under quenching condition and can precipitate as Cu-rich nanometer phase (ε-Cu) during tempering. Cu is helpful for the grain refinement and to promote the formation of reversed austenite during tempering. The maximum volume fraction of austenite is 55.9% in the steel with 3wt.% Cu, which is responsible for the improvement of ductility. The results of the mechanical properties tests reveal that the mechanical properties are significantly influenced by the volume fraction of austenite. Cu can cause solid solution strengthening, precipitation strengthening and grain refinement strengthening in SMSS. Cu alloyed super martensitic stainless steel exhibits greatly improved mechanical properties.

The Influence of Heat Treatment on Microstructure and Mechanical Properties of Cr15 Super Martensitic Stainless Steel

The microstructure and mechanical properties of 15Cr super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are lath martensite. With the raising of the quenching temperature, the original austenite grain size increases and the martensite platelet gradually coarsens. The microstructures of the tempered steel are tempered martensite and reversed austenite dispersed in the martensitic matrix.

Role of Nb in low interstitial 13Cr super martensitic stainless steel

Abstract The effect of adding 0.1 wt% Nb to low interstitial (N 0.01 wt%, C 0.01 wt%) 13Cr super martensitic stainless steel (SMSS) on solid phase transformation and microstructures achieved by normalizing and tempering was investigated using dilatometer, electron backscattered diffraction (EBSD), transmission electron microscope (TEM), X-ray diffraction (XRD), and its consequence on mechanical properties was examined to clarify the role of Nb in low interstitial martensitic stainless steel. Nb was found to retard kinetics of reversed austenite formation during tempering and to suppress the occurrence of Cr rich precipitates. The measurement of mechanical properties shows that while the strength properties were significantly increased by nano-scale precipitates enriched in Nb in the steel with 0.10 wt% Nb, the ductility and toughness properties were restored by optimum volume fraction of retained austenite. Excellent strength and adequate toughness properties were obtained by tempering the steel with 0.10 wt% Nb and low interstitial (N 0.01 wt%, C 0.01 wt%) steel at 600 °C.

Modeling of the Stress in 13Cr Supermartensitic Stainless Steel Welds by Artificial Neural Network

In this paper, artificial neural networks (ANN) has been proposed to determine the stresses of 13Cr supermartensitic stainless steel (SMSS) welds based on various deformation temperatures and strains using experimental data from tensile tests. The experiments provided the required data for training and testing. A three layer feed-forward network, deformation temperature and strain as input parameters while stress as the output, was trained with automated regularization (AR) algorithm for preventing overfitting. The results showed that the best fitting training dataset was obtained with ten units in the hidden layer, which made it possible to predict stress accurately. The correlation coefficients (R-value) between experiments and prediction for the training and testing dataset were 0.9980 and 0.9943, respectively, the biggest absolute relative error (ARE) was 6.060 %. As seen that the ANN model was an efficient quantitative tool to evaluate and predict the deformation behavior of type 13Cr SMSS welds during tensile test under different temperatures and strains.

Treatments of Structural Welds using FITNET Fitness-for-Service Assessment Procedure

Recent developments of the advanced welding processes such as laser beam welding (LBW), solid state friction stir welding (FSW) and hybrid welding, numbers of advanced structures are being designed and constructed in industries such as aerospace, power generation, oil and gas transmission and transportation. Development of new structural aluminum and magnesium alloys as well as high strength steels provide further possibilities for the welded structures in similar and dissimilar (material-mix) configurations. Consequently, there is an increasing demand for “Fitness-for-Service” (FFS) assessment of those advanced welded structures by considering the specific features of these weld joints (such as narrow weld width, high strength mis-match, etc.). In year 1999, Structural Integrity Assessment Procedure SINTAP has been developed for analysis of flaws to avoid fracture within the European Commission funded project SINTAP. Recently, the European Community funded project FITNET in the form of a Thematic Network (TN) organisation has completed to review the existing FFS procedures and developed an updated, unified and verified European FITNET FFS Procedure to cover structural integrity analysis to avoid failures due to fracture, fatigue, creep and corrosion. The fracture Module (Section 6) of this new FITNET FFS Procedure, prepared and presented at this conference, FITNET 2006, in three volumes has adopted the SINTAP approach for assessing of the welded structures. This paper describes the FITNET FFS weld assessment route (Option 2 and Option 3) and also aims to demonstrate suitability of weld joint assessment route in prediction of the critical conditions of various advanced welded joints containing flaw. The welded specimens used in this work cover conventional multi-pass welded lnconel-718 turbine blade (T-joint), center cracked wide plates of electron beam welded 13 % Cr supermartensitic stainless steel, laser beam welded shipbuilding C-Mn steel and aluminum alloy as well as welded pipe. The results are showing that the weld strength mismatch analysis option of the FITNET FFS is conservative and degree of conservatism is similar to the analysis options for the homogeneous materials. This provides confidence in the use of the FITNET FFS procedure for assessing of the structural significance of flaws in welded structures.