Effects of Heating and Cooling Rates on Phase Transformations in 10 Wt Pct Ni Steel and Their Application to Gas Tungsten Arc Welding

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2017-12, Vol.48 (12), p.5890-5910
• Main Authors: Barrick, Erin J., Jain, Divya, DuPont, John N., Seidman, David N.
• Format: Article
• Language: English
• Subjects: Austenite; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cooling; Cooling rate; Deformation resistance; Dilatometry; Gas tungsten arc welding; Hardenability; Heat affected zone; Heat treating; Heating rate; High strength steels; Martensite; Martensitic stainless steels; Martensitic transformations; Materials Science; Metallic Materials; Metallurgy; Microhardness; Microstructure; Nanotechnology; Nickel; Phase transitions; Structural Materials; Surfaces and Interfaces; Temperature; Thin Films; Welded joints
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-017-4379-0

10 wt pct Ni steel is a high-strength steel that possesses good ballistic resistance from the deformation induced transformation of austenite to martensite, known as the transformation-induced-plasticity effect. The effects of rapid heating and cooling rates associated with welding thermal cycles on the phase transformations and microstructures, specifically in the heat-affected zone, were determined using dilatometry, microhardness, and microstructural characterization. Heating rate experiments demonstrate that the Ac 3 temperature is dependent on heating rate, varying from 1094 K (821 °C) at a heating rate of 1 °C/s to 1324 K (1051 °C) at a heating rate of 1830 °C/s. A continuous cooling transformation diagram produced for 10 wt pct Ni steel reveals that martensite will form over a wide range of cooling rates, which reflects a very high hardenability of this alloy. These results were applied to a single pass, autogenous, gas tungsten arc weld. The diffusion of nickel from regions of austenite to martensite during the welding thermal cycle manifests itself in a muddled, rod-like lath martensitic microstructure. The results of these studies show that the nickel enrichment of the austenite in 10 wt pct Ni steel plays a critical role in phase transformations during welding.