Response of a DIN 18MnCrSiMo6-4 Continuous Cooling Bainitic Steel to Different Plasma Nitriding Gas Mixtures

The authors have conducted a comparative analysis of diffusion layers of steels of various structural classes manufactured by complex technology including laser remelting of powder material and plasma nitriding. Parameters of diffusion layers of bainitic steel (Fe – 0.09 % C – 1 % Cr – 2 % Ni – 1 % Mo – 1 % Cu) and martensitic steel (Fe – 0.25 % C – 13 % Cr – 2 % Ni) manufactured by direct laser deposition (DLD) and austenitic steel (Fe – 0.03 % C – 17 % Cr – – 14 % Ni – 3 % Mo) manufactured by selective laser melting (SLM) were investigated. During plasma nitriding at 540 °C for 24 h of martensitic and austenitic steels, diffusion layer of 140 – 160 μm was formed, additionally maximum microhardness of surface layer was 800 HV0.1 and 1050 HV0.1 and it is almost constant on thickness of 100 μm. Diffusing layer of bainitic steel is 900 μm and its microhardness monotonously decreases from the surface. Reinforcing phases of nitrided layer were determined by X-ray analysis: γ′ (Fe4N) is fixed in the bainitic steel, γ′ and CrN are fixed in martensitic and austenitic steels. Moreover on the surface of austenitic steel solid nitrided layer is formed. The influence of heat treatment after laser remelting of powder material was also studied. It was determined, that despite decreasing of crystal structure defects after heat treatment, the thickness of nitrided layer changes slightly. Also the authors have investigated the influence of porosity of austenitic steel on the thickness of nitrided layer. It was shown, that porosity of 0.5 – 2.0 % doesn’t result in changing of diffusion layer’s thickness.

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Continuous cooling transformation behaviour and bainite formation kinetics of new bainitic steel

Materials Science and Technology ◽

10.1080/02670836.2016.1224608 ◽

2016 ◽

Vol 33 (4) ◽

pp. 454-463 ◽

Cited By ~ 8

Author(s):

Y.-F. Zheng ◽

R.-M. Wu ◽

X.-C. Li ◽

X.-C. Wu

Keyword(s):

Bainitic Steel ◽

Continuous Cooling Transformation ◽

Transformation Behaviour ◽

Continuous Cooling ◽

Formation Kinetics ◽

Kinetics Of

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Dynamic continuous cooling transformation, microstructure and mechanical properties of medium-carbon carbide-free bainitic steel

High Temperature Materials and Processes ◽

10.1515/htmp-2020-0051 ◽

2020 ◽

Vol 39 (1) ◽

pp. 304-316

Author(s):

Xi Chen ◽

Fuming Wang ◽

Changrong Li ◽

Jing Zhang

Keyword(s):

Cooling Rate ◽

Retained Austenite ◽

Charpy Impact ◽

Granular Bainite ◽

Morphology Evolution ◽

Bainitic Steel ◽

Cooling Process ◽

Medium Carbon ◽

Continuous Cooling ◽

Lath Bainite

AbstractThe effects of the cooling rate after hot deformation on phase transformation, the microstructure of the designed nonquenched and tempered medium-carbon carbide-free bainitic steel have been investigated during the dynamic continuous cooling process. The results show that with the increase of the cooling rate, the morphology of the carbide-free bainite of the experimental steel evolves from granular bainite to lath bainite. Meanwhile, the hardness increases, and the amount of the retained austenite decreases with the increase of the cooling rate. Besides, the morphology evolution of the retained austenite from block to film is revealed by EBSD. Moreover, 0.5°C/s is considered to be the favorable cooling rate to obtain the best strength–toughness matching. Furthermore, the semi-industrial experimental results proved that the tensile strength, yield strength and Charpy impact energy were 1,298 MPa, 847 MPa and 38 J, respectively.

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Continuous Cooling Transformation Behavior and Kinetic Models of Transformations for an Ultra-Low Carbon Bainitic Steel

Journal of Iron and Steel Research International ◽

10.1016/s1006-706x(13)60035-7 ◽

2012 ◽

Vol 19 (12) ◽

pp. 73-78 ◽

Cited By ~ 8

Author(s):

Zhi-min Zhang ◽

Qing-wu Cai ◽

Wei Yu ◽

Xiao-lin Li ◽

Li-dong Wang

Keyword(s):

Kinetic Models ◽

Bainitic Steel ◽

Low Carbon ◽

Transformation Behavior ◽

Continuous Cooling Transformation ◽

Continuous Cooling

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The Impact of Retained Austenite on the Mechanical Properties of Bainitic and Dual Phase Steels

Journal of Materials Engineering and Performance ◽

10.1007/s11665-021-06547-w ◽

2022 ◽

Author(s):

Bogusława Adamczyk-Cieślak ◽

Milena Koralnik ◽

Roman Kuziak ◽

Kamil Majchrowicz ◽

Tomasz Zygmunt ◽

...

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Transformation Temperature ◽

Retained Austenite ◽

Tensile Tests ◽

Total Elongation ◽

Isothermal Transformation ◽

Bainitic Transformation ◽

Bainitic Steel ◽

Continuous Cooling

AbstractThis paper presents the microstructural changes and mechanical properties of carbide-free bainitic steel subjected to various heat treatment processes and compares these results with similarly treated ferritic–pearlitic steel. A key feature of the investigated steel, which is common among others described in the literature, is that the Si content in the developed steel was >1 wt.% to avoid carbide precipitation in the retained austenite during the bainitic transformation. The phase identification before and after various heat treatment conditions was carried out based on microstructural observations and x-ray diffraction. Hardness measurements and tensile tests were conducted to determine the mechanical properties of the investigated materials. In addition, following the tensile tests, the fracture surfaces of both types of steels were analyzed. Changing the bainitic transformation temperature generated distinct volume fractions of retained austenite and different values of mechanical strength properties. The mechanical properties of the examined steels were strongly influenced by the volume fractions and morphological features of the microstructural constituents. It is worth noting that the bainitic steel was characterized by a high ultimate tensile strength (1250 MPa) combined with a total elongation of 18% after austenitizing and continuous cooling. The chemical composition of the bainitic steel was designed to obtain the optimal microstructure and mechanical properties after hot deformation followed by natural cooling in still air. Extensive tests using isothermal transformation to bainite were conducted to understand the relationships between transformation temperature and the resulting microstructures, mechanical properties, and fracture characteristics. The isothermal transformation tests indicated that the optimal relationship between the sample strength and total elongation was obtained after bainitic treatment at 400 °C. However, it should be noted that the mechanical properties and total elongation of the bainitic steel after continuous cooling differed little from the condition after isothermal transformation at 400 °C.

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