Effect of niobium and austenitizing temperature on the microstructures and properties of spray-deposited AISI M3:2 high speed steel

The microstructure and properties of niobium-containing AISI M3:2 high speed steels (HSSs) fabricated by spray forming and traditional casting have been investigated. The results show that fine and uniformly-distributed grains without macrosegregation appeared in the as-deposited HSSs that differ from those of as-cast HSSs. Nb mostly appears in primary MC carbides, whereas it contributes less to the formation of M6C carbides. The high stabilization of Nb-rich MC carbides can pin the grain boundaries during high-temperature austenitizing process, thus conferring a fine grains and raising the content of dissolved alloying elements. Enhanced precipitation strengthening and fine dispersion of NbC carbides throughout the matrix contribute to the high hardness and red hardness of Nb-containing HSS.

Austempering and Bainitic Transformation Kinetics of AISI 52100

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.

Effect of Different Parameters of Quenching and Tempering Process on SS410 Grade Martensitic Stainless Steel

This paper reports the influence of different chemical composition, austenitizing temperature, quenching rate and tempering temperature on the mechanical properties and microstructure of martensitic stainless-steel SS 410 grade. For calculating general material properties such as hardness and yield strength of SS 410 grade, JMatpro software is used. Analysis of SS 410 grade has been done for austenitizing temperature ranging from 9250C to 10100C followed by tempering whose temperature ranges from 2050C to 6050C.The proper practices of quenching and tempering should be performed ensuring the suitable microstructure of the steels. To get fully Martensite, quenching has to be done at least at 0.40C/s or more than that. The results also shows that composition of carbon has great effect on transition temperature Ms and Mf of martensitic stainless steel 410 grade as compared to chromium. Air cooling or oil quenching this type steels from austenite phase results in microstructure consists of mainly hard and brittle martensite, small amount of retained austenite. Subsequent tempering process reduces hardness and increases ductility and toughness.

Jominy End Quench Test of Martensitic Stainless Steel X30Cr13

In this study, the influence of thermal treatments on the properties of the martensitic stainless steel X30Cr13 (EN 10088-3: 1.4028) were investigated. These steels are characterized by a high hardness as well as corrosion resistance and can be specifically adjusted by heat treatment. In particular, the austenitizing temperature ϑA and cooling rate T˙ affect the hardness and corrosion properties of martensitic stainless steels. In order to investigate these influences, the Jominy end quench tests were performed at varying austenitizing temperatures. The aim is to determine the hardness and corrosion properties as a function of the austenitizing temperature and the cooling rate. The austenitizing temperature strongly influences the solubility of alloying elements within the austenitic lattice as well as the grain size, and thus affects both precipitation and phase transformation kinetics. In consequence, different austenitizing temperatures lead to different macroscopic material properties, like hardness and pitting corrosion potential. The heat treatment was simulated using finite element (FE) method and compared with time-temperature sequences measured at different locations of the Jominy end quench sample using thermocouples. That allows determining the cooling rate T˙ between 800∘C and 500∘C and to assign it to each location of the Jominy end quench sample. The numerical estimations were in close conformity with the experimental values. By assigning the hardness and pitting corrosion potentials to the respective cooling rates as a function of the austenitizing temperature, it is possible to determine optimum process windows for the required properties.

Effect of Heat Treatment on Microstructure and Mechanical Properties of High-Strength Steel for in Hot Forging Products

High-strength steel is widely used in hot forging products for application to the oil and gas industry because it has good mechanical properties under severe environment. In order to apply to the extreme environment industry requiring high temperature and high pressure, heat treatments such as austenitizing, quenching and tempering are required. The microstructure of high-strength steel after heat treatment has various microstructures such as Granular Bainite (GB), Acicular Ferrite (AF), Bainitic Ferrite (BF), and Martensite (M) depending on the heat treatment conditions and cooling rate. Especially in large forged products, the difference in microstructure occurs due to the difference in the forging ratio depending on the location and the temperature gradient according to the thickness during post-heat treatment. Therefore, this study attempted to quantitatively analyze various phases of F70 high-strength steel according to the austenitizing temperature and hot forging ratio using the existing EBSD analysis method. In addition, the correlation between microstructure and mechanical properties was investigated through various phase analysis and fracture behavior of high-strength steel. We found that various microstructures of strength steel depend on the austenitizing temperature and hot forging ratio, and influence the mechanical properties and fracture behavior.

Heat Treatment and Austenitization Temperature Effect on Microstructure and Impact Toughness of an Ultra-High Strength Steel

Heat treatment parameters were varied to determine the effect of normalizing and austenitizing temperature on the properties of an ultra-high strength wrought steel. Normalizing temperature did not have a significant effect on strength and ductility. Higher normalizing temperatures led to an increase in final prior austenite grain size and a slight loss in toughness. Austenitizing temperature of 825 °C was insufficient to produce a fully austenitic structure prior to quenching and led to sub-par impact behavior. The best properties were obtained after austenitizing at 915 °C followed by water quenching; the resulting quasi static properties were shown to be a yield strength of 1380 MPa with an ultimate tensile strength of 1670 MPa and 12.5% total ductility. Charpy V-notch impact properties as high as 52 J at −40 °C and 75 J at 25 °C and the behavior were achieved using higher austenitizing temperatures as well.

Microstructural Changes During Short-Term Heat Treatment of Martensitic Stainless Steel—Simulation and Experimental Verification

Short-term heat treatments of steels are used for tools and cutlery but also for the surface treatment of a variety of other workpieces. If corrosion resistance is required, martensitic stainless steels like AISI 420L or AISI 420MoV are typically used. The influence of short-term heat treatment on the different metastable states of the AISI 420L steel was examined and reported in this article. Starting from a defined microstructural state, the influence of a short-term heat treatment is investigated experimentally with the help of a quenching dilatometer and computer assisted simulations are carried out. With the results obtained, a simulation model is built up which allows to compute the microstructural changes during a short-term heat treatment to be evaluated without the need for an experiment. As an indicator, the value of the martensite start temperature is calculated as a function of different holding times at austenitizing temperature. The martensite start temperature is measured by dilatometry and compared to calculated values. Validation of simulated results reveals the potential of optimizing steel heat treatment processes and provides a reliable approach to save time, resources and energy.

Artificial Neural Networks-Based Prediction of Hardness of Low-Alloy Steels Using Specific Jominy Distance

Successful prediction of the relevant mechanical properties of steels is of great importance to materials engineering. The aim of this research is to investigate the possibility of reducing the complexity of artificial neural networks-based prediction of total hardness of hypoeutectoid, low-alloy steels based on chemical composition, by introducing the specific Jominy distance as a new input variable. For prediction of total hardness after continuous cooling of steel (output variable), ANNs were developed for different combinations of inputs. Input variables for the first configuration of ANNs were the main alloying elements (C, Si, Mn, Cr, Mo, Ni), the austenitizing temperature, the austenitizing time, and the cooling time to 500 °C, while in the second configuration alloying elements were substituted by the specific Jominy distance. Comparing the results of total hardness prediction, it can be seen that the ANN using the specific Jominy distance as input variable (runseen = 0.873, RMSEunseen = 67, MAPE = 14.8%) is almost as successful as ANN using main alloying elements (runseen = 0.940, RMSEunseen = 46, MAPE = 10.7%). The research results indicate that the prediction of total hardness of steel can be successfully performed only based on four input variables: the austenitizing temperature, the austenitizing time, the cooling time to 500 °C, and the specific Jominy distance.

Effect of Alloying Additives and Microadditives on Hardenability Increase Caused by Action of Boron

The presented work was aimed at evaluating influence of boron on hardenability of steel quantitatively and evaluating this effect during complex use of boron with other alloying additives like chromium, vanadium and titanium. For this purpose, eight melts with variable chemical compositions were prepared. From the ingots, cylindrical specimens with normalized dimensions according to EN ISO 642:1999 were cut out and subjected to full annealing at 1200 °C and to normalizing at 900 °C. Such specimens were subjected to the hardenability Jominy test. In order to distinguish the influence of boron on hardenability of a given melt and thus to eliminate the differences resulting from its chemical composition, grain size and austenitizing temperature, the obtained ideal critical diameter was corrected and the boron effectiveness factor was determined. The performed examinations and analyses showed that inadequate quantities of microadditives result in losing the benefits coming from introduction of boron as the hardenability-improving element and can even result in a reduction of hardenability of the boron-containing steel.