Effective heat treatment is essential for optimizing the properties of steels in various applications. Understanding the evolution of steel microstructure during intrinsic or post-heat treatment, along with managing distortions and residual stresses, is crucial for ensuring component usability. In laser-based additive manufacturing, high temperature gradients and cooling rates induce residual stresses, impacting the heat-affected zones. However, there remains a gap in understanding how stress influences precipitation during heat treatment, particularly regarding transformation-induced plasticity (TRIP), where a stress triggers deformation during phase transformation. This study aims to investigate TRIP effects during the aging of maraging steels, commonly employed in laser-based powder bed fusion. During the experiments, the steels were continuously aged under varying compression stresses. By isolating TRIP strain from total strain, the study establishes a relationship between maximum TRIP strain after phase transformation and applied stress, defining specific TRIP constants for each steel. The presence of TRIP strain has been confirmed during short time continuous aging treatments, indicating its significance even in the initial stages of the heat treatment process. While the applied stress level does not affect hardness, significant differences in maximum hardness values after aging were observed among the investigated materials. Furthermore, a comparative analysis of different maraging steels revealed a positive correlation between the TRIP constant and the amount of precipitation, and consequently, hardness. These findings confirm the role of TRIP in precipitate formation in maraging steels and provide a foundation for further understanding and predicting post-heat treatment material states.

The work presented in this paper addresses a data gap that continues to be a hinderance to users of precipitation modeling tools, particularly those based on Langer-Schwartz theory. Thermodynamic and kinetic data required for precipitation models can be obtained from CALPHAD databases, but interfacial energies between the bulk and precipitate phases are not available for many alloy systems. In this work, a number of matrix-precipitate interfacial energies have been determined for influential precipitates in alloys of industrial importance, for example, carbides in Grade 22 low-alloy steels, delta phase in Ni 625 and 718, S-phase in Al 2024, and Q’ and β’’ in Al 6111.

Steels hardened by copper precipitation are the focus of many research programs. Most of this effort is devoted to development of low-carbon steels. Precipitation strengthening of ferrite is used for steel strengthening without losing the capability of deep drawing before the precipitation hardening. This article shows the results of precipitation strengthening in low alloyed steel containing 0.2% carbon. The steel composition is aimed at developing weldable high-strength steel for demanding structural applications. Copper precipitation was exploited to strengthen different types of microstructures. Quenching and ageing and isothermal austenite decomposition into bainite were used to develop copper precipitation. Mechanical properties and microstructure were compared. Tensile tests were performed and hardness was measured. Copper precipitation was documented by FEG SEM microscopy.

A precipitation hardenable semi-austenitic stainless steel AISI 632 grade was austenitized according to industrial specifications and thereafter subjected to isothermal treatment at sub-zero Celsius temperatures. During treatment, austenite transformed to martensite. The isothermal austenite-to-martensite transformation was monitored in situ by magnetometry and data was used to sketch a TTT diagram for transformation. As an alternative treatment, after austenitization the material was immersed in boiling nitrogen and up-quenched to room temperature by immersion in water prior to be subjected to isothermal treatment. Magnetometry showed that the additional thermal step in boiling nitrogen yields a minor increment of the fraction of martensite, but has a noteworthy accelerating effect on the transformation kinetics, which more pronounced when the isothermal holding is performed at a higher temperature. Data is interpreted in terms of instantaneous nucleation of martensite during cooling followed by time dependent growth during isothermal holding.

Precipitation-hardening stainless steels are iron-nickel chromium alloys containing precipitation hardening elements such as aluminum, titanium, niobium and copper. In this work, heat treatment of a novel precipitation hardening stainless steel using niobium as a forming element for the hardening precipitates in order to increase its surface hardness and wear resistance was performed. The steel composition was 0.03C - 0.22Si - 17.86Cr - 3.91Ni - 2.19Mo - 1.96Nb (in wt%). The samples were solubilized at 1100 °C for 2 hours. Cooling was done in oil and the samples were subsequently aged at 500, 550 and 600 °C. The solubilized samples exhibited an average hardness of 30 HRc and after the aging treatments, the hardness increased to 46 HRc. The hardness increases during the aging treatments were very fast. A 5 minute treatment achieved hardness levels that were close to the maximum obtained for this alloy. Niobium was an efficient precipitation hardeners forming a Laves phase of the type Fe 2 Nb.

There is considerable interest in nitriding austenitic stainless steels under conditions where nitrogen is primarily in solid solution. Supersaturation with nitrogen significantly increases hardness and induces high residual compressive stresses. This paper explores the relationship between nitrogen content, layer morphology, and properties. It examines Nitrex’s Nano-S nitriding processes performed at various times to achieve different nitrogen levels in austenitic AISI 304 stainless steel. The research also includes 410 grade martensitic stainless steel and 17-4 precipitation-hardened steel, with results yet to be determined. Based on these results, optimal nitriding conditions to achieve the desired properties will be recommended.