Phase Changes in AISI 436L Ferritic Stainless Steel after Nitrogen Permeation Heat Treatment

2007 ◽  
Vol 26-28 ◽  
pp. 1303-1306 ◽  
Author(s):  
Hea Joeng Lee ◽  
Jung Hyun Kong ◽  
Dae Kyoung Yoo ◽  
Young Chul Park ◽  
Jang Hyun Sung
Keyword(s):  
Heat Treatment ◽  
Nitrogen Content ◽  
Stainless Steels ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Phase Changes ◽  
Maximum Hardness ◽  
Surface Layers ◽  
Ferritic Stainless Steels ◽  
Nitride Precipitation

This study examined the phase changes, nitride precipitation and variations in hardness of Fe-18Cr-1Mo-0.2Ti (436L) ferritic stainless steels after a nitrogen permeation heat treatment at temperatures ranging from 1050°C to 1150°C. The strong affinity between nitrogen and Ti/Cr enabled the permeation of nitrogen into the 436L ferritic stainless steels. The nitrogen content of the surface layers ranged from 0.40% to 0.87%, depending on the nitrogen permeation temperatures. The nitrogen-permeated surface layers changed into martensite plus retained austenite(RA) with rod type M2N and square type TiN precipitates. Ups and downs of hardness with increasing depth below the surface was observed, depending on the volume fraction of the RA, nitrogen content and quantity of precipitates. The maximum hardness of the nitrogen permeated surface layer was 700Hv.

The Microstructures and Hardness Analysis of a New Hypereutectoid Mn-Cr-Mo-V Steel

2013 ◽  
Vol 58 (2) ◽  
pp. 563-568
Author(s):  
R. Dabrowski ◽  
E. Rozniata ◽  
R. Dziurka
Keyword(s):  
Heat Treatment ◽  
Chemical Composition ◽  
Liquid Nitrogen ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Chemical Compositions ◽  
Tool Steels ◽  
Maximum Hardness ◽  
Hypereutectoid Steel ◽  
Tempering Temperature

The results of a microstructure and hardness investigations of a new hypereutectoid Mn-Cr-Mo-V steel, imitating by its chemical composition tool steels, are presented in the paper. The microstructure as well hardness changes, caused by austenitising and tempering temperatures were assessed, for samples quenched and sub-quenched in liquid nitrogen, directly after the quenching treatment. Additionally, the influence of the tempering temperature on the volume fraction of the retained austenite was estimated. New hypereutectoid steel, after an appropriate heat treatment obtained the relevant hardness of the tools used in the cold and hot working proces. It was indicated that the steel hardness increases with the increases of the austenitising temperature. At 800ºC the hardness of the quenched samples were equal 895HV, and for the sub-quenched samples 937HV. The maximum hardness, after tempering (746HV), was found at a temperature of 520ºC. It will be possible, in future, to apply this obtained investigation results in designing chemical compositions and microstructures of the new hypereutectoid alloyed steels of properties required by their users.

scholarly journals Surface Modification of a Nickel-Free Austenitic Stainless Steel by Low-Temperature Nitriding

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1845
Author(s):  
Francesca Borgioli ◽  
Emanuele Galvanetto ◽  
Tiberio Bacci
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Austenitic Stainless Steel ◽  
Low Temperature ◽  
Stainless Steels ◽  
Volume Fraction ◽  
Surface Hardness ◽  
Austenitic Stainless Steels ◽  
Surface Layers ◽  
Modified Surface

Low-temperature nitriding allows to improve surface hardening of austenitic stainless steels, maintaining or even increasing their corrosion resistance. The treatment conditions to be used in order to avoid the precipitation of large amounts of nitrides are strictly related to alloy composition. When nickel is substituted by manganese as an austenite forming element, the production of nitride-free modified surface layers becomes a challenge, since manganese is a nitride forming element while nickel is not. In this study, the effects of nitriding conditions on the characteristics of the modified surface layers obtained on an austenitic stainless steel having a high manganese content and a negligible nickel one, a so-called nickel-free austenitic stainless steel, were investigated. Microstructure, phase composition, surface microhardness, and corrosion behavior in 5% NaCl were evaluated. The obtained results suggest that the precipitation of a large volume fraction of nitrides can be avoided using treatment temperatures lower than those usually employed for nickel-containing austenitic stainless steels. Nitriding at 360 and 380 °C for duration up to 5 h allows to produce modified surface layers, consisting mainly of the so-called expanded austenite or gN, which increase surface hardness in comparison with the untreated steel. Using selected conditions, corrosion resistance can also be significantly improved.

Microstructure and Tensile Properties of TRIP-Aided Steel Sheet Subjected to Hot-Rolling and Austempering

2021 ◽  
Vol 1016 ◽  
pp. 732-737
Author(s):  
Junya Kobayashi ◽  
Hiroto Sawayama ◽  
Naoya Kakefuda ◽  
Goroh Itoh ◽  
Shigeru Kuraoto ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Hot Rolling ◽  
Manufacturing Process ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Isothermal Holding ◽  
High Strength ◽  
Isothermal Transformation ◽  
Transformation Process ◽  
Steel Sheets

Various high strength steel sheets for weight reduction and safety improvement of vehicles have been developed. TRIP-aided steel with transformation induced plasticity of the retained austenite has high strength and ductility. Conventional TRIP-aided steels are subjected to austempering process after austenitizing. Generally, elongation and formability of TRIP-aided steel are improved by finely dispersed retained austenite in BCC phase matrix. The finely dispersed retained austenite and grain refinement of TRIP-aided steel can be achieved by hot rolling with heat treatment. Therefore, the improvement of mechanical properties of TRIP-aided steel is expected from the manufacturing process with hot rolling and then isothermal transformation process. In this study, thermomechanical heat treatment is performed by combining hot rolling and isothermal holding as the manufacturing process of TRIP-aided steel sheets. The complex phase matrix is obtained by hot rolling and then isothermal holding. Although the hardness of the hot rolled and isothermal held TRIP-aided steel is decreased, the volume fraction of retained austenite is increased.

Comparison of Microstructure and Mechanical Behavior of the Ferritic Stainless Steels ASTM 430 Stabilized with Niobium and ASTM 439 Stabilized with Niobium and Titanium

2016 ◽  
Vol 879 ◽  
pp. 1651-1655 ◽  
Author(s):  
Leandro Paulo de Almeida Reis Tanure ◽  
Cláudio Moreira de Alcântara ◽  
Tarcísio Reis de Oliveira ◽  
Dagoberto Brandão Santos ◽  
Berenice Mendonça Gonzalez
Keyword(s):  
Stainless Steels ◽  
Lower Cost ◽  
Volume Fraction ◽  
Austenitic Stainless Steels ◽  
Total Elongation ◽  
Drawing Ratio ◽  
Limit Drawing Ratio ◽  
Soaking Time ◽  
Ferritic Stainless Steels ◽  
Cold Rolled

The use of Ferritic Stainless Steels has become indispensable due its lower cost and the possibility to replace austenitic stainless steels in many applications. In this study, cold rolled sheets of two stabilized ferritic stainless steels with 85% thickness reduction were annealed by applying a heating rate of 24 oC/s and a soaking time of 24 s. The niobium stabilized ferritic stainless steel type ASTM 430 (430Nb) was annealed at 880 oC while the niobium and titanium bi-stabilized steel ASTM 439 was annealed at 925 oC. The annealed samples were tensile tested and due to the smaller grain size, steel 430Nb, showed a higher yield stress and a higher total elongation. Concerning drawability the steel ASTM 439 presented a better performance with higher average R-value, lower planar anisotropy coefficient and a greater value for Limit Drawing Ratio (LDR). These results are explained in terms of the differences in size and volume fraction of precipitates between the two steels.

Effects of Heat Treatment on Microstructure of High-Strength Manganese-Silicon Steels

2017 ◽  
Vol 270 ◽  
pp. 239-245
Author(s):  
Dagmar Bublíková ◽  
Štěpán Jeníček ◽  
Kateřina Opatová ◽  
Bohuslav Mašek
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Microstructure Evolution ◽  
Retained Austenite ◽  
Volume Fraction ◽  
High Strength ◽  
Quenching And Partitioning ◽  
Alloying Additions ◽  
New Procedures ◽  
Strength And Ductility

Today’s advanced steels are required to possess high strength and ductility. This can be accomplished by producing appropriate microstructures with a certain volume fraction of retained austenite. The resulting microstructure depends on material’s heat treatment and alloying. High ultimate strengths and sufficient elongation levels can be obtained by various methods, including quenching and partitioning (Q&P process). The present paper introduces new procedures aimed at simplifying this process with the use of material-technological modelling. Three experimental steels have been made and cast for this investigation, whose main alloying additions were manganese, silicon, chromium, molybdenum and nickel. The purpose of manganese addition was to depress the Ms and Mf temperatures. The Q&P process was carried out in a thermomechanical simulator for better and easier control. The heat treatment parameters were varied between the sequences and their effect on microstructure evolution was evaluated. They included the cooling rate, partitioning temperature and time at partitioning temperature. Microstructures including martensite with strength levels of more than 2000 MPa and elongation of 10–15 % were obtained.

Estimating Volume Fractions of Microstructural Constituents in Austempered High Silicon Alloyed GJS 600-10 Ductile Iron through Magnetic Measurements (VSM)

2017 ◽  
Vol 907 ◽  
pp. 50-55
Author(s):  
Yakup Yürektürk ◽  
Murat Baydogan
Keyword(s):  
Heat Treatment ◽  
Ductile Iron ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Magnetic Measurements ◽  
Ferritic Matrix ◽  
Volume Fractions ◽  
High Silicon ◽  
New Generation

In this paper, austempering heat treatment was applied to a new generation high silicon GJS 600-10 grade ductile iron with an initial ferritic matrix. Different austempering temperatures of 270, 330 and 390°C were applied after austenitizing at 975°C for 120 min. Depending on the austempering temperatures, lower and upper ausferritic microstructures were obtained. Results showed that volume fraction of the retained austenite in the ausferritic microstructures, which was estimated by VSM technique is well correlated with those estimated by XRD technique.

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