The austenite grain size (AGS) developed immediately before final cooling by quenching or other means is known to exert a substantial effect on the resistance to fracture in the final part. SAE 1045 steels containing Al, V, and V+Nb and a nonmicroalloyed steel were preconditioned by various thermomechanical treatments and then assessed for AGS by several methods defined in ASTM E112-13. Test results show that the microalloys present, the test method selected to evaluate the AGS, and the condition of the steel prior to conducting the grain size tests all have substantial effects on the measured AGS. The results demonstrate that for a meaningful AGS specification and test result, it is necessary to specify the precondition of the steel, the test method, and the test conditions.

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.

High entropy alloys (HEA) are an exciting new class of alloys composed of several metallic elements with equiatomic or near-equiatomic composition to maximize configurational entropy, leading to desirable properties. However, during solidification, as in casting or welding processes, elements segregate, creating local regions of distinct composition. In conventional alloy systems, homogenization heat treatments are used to remove this segregation effect. This study examines the conditions of the heat treatment needed in HEA alloys. First, the solidification behavior of equiatomic alloy composition AlCoCrCuFeNi is modeled using the Scheil module within Thermo-Calc along with the TCHEA2 database. Energy dispersive spectroscopy (EDS) is performed across the dendrite arms of the as-melted HEA to compare with the Scheil calculations. The resulting dendritic and interdendritic compositions are used as inputs in Thermo- Calc to determine the stable phases as a function of temperature. Selected heat treatments are conducted on the as-melted HEA to compare with the calculation results.

Martensitic steels must be tempered to increase their toughness and ductility. The tempering process requires heating from room temperature to the desired tempering temperature. In this paper, the effects of heating rates on carbide precipitate size distribution, chemistry, and precipitate density will be discussed. As-quenched martensite in AISI 4140 steel was heated to selected tempering temperatures in air furnaces as well as by induction. The heating rates for tempering vary from 30 seconds to 20 minutes. The experimental results are presented, and carbides were characterized using an extraction technique.

Extension of the service life for high temperature structural alloy RA602CA is the goal for the project described in this paper. The performance of alloy RA602CA and aluminized RA602CA in a gas carburization furnaces were studied for periods up to two years. Aluminizing treatments (widely used in aerospace industry, especially in turbine blade applications) were also studied in this project. Carbon has very low solubility in alumina, so aluminizing could be a good method for protecting RA602CA alloys. Microstructural development during the carburizing process is presented, and the degradation of chromium oxide as well as alumina oxides is identified. The weight gain of RA602CA compared to similar alloys is discussed.

The 13% Cr 0.2%C steel is extensively used in OCTG application. This steel was examined in the double hardened condition at 1040°C/OQ followed by 980°C/OQ as against conventional hardening treatment at 980°C/OQ. It was observed that the double hardening heat treatment resulted in higher carbon dissolution in the matrix without any residual grain boundary necklace carbides while single hardening at 980°C shows remnant grain boundary carbide. Double hardening heat treatment was found to refine the grain size by recrystallization of the defects introduced in first hardening. During double tempering heat treatment, the carbides in the 980°C treatment were coarse and found to nucleate along grain boundary. The double hardened sample on tempering showed an even distribution of carbide throughout without grain boundary carbide. The double hardened sample show improved strength and toughness compared to the single hardened sample at similar tempering conditions. The microstructural analyses at various stages of processing have been correlated to the mechanical properties obtained.

Recent destructive analysis of six ASTM A350 LF2 flanges has revealed vastly different low temperature (-50°F) Charpy impact toughness from 4 J (3 ft-lbs) to greater than 298 J (220 ft-lbs). These relatively low strength flanges, minimum 248 MPa (36 ksi) yield and 483-655 MPa (70-95 ksi) tensile strength, had nominally the same yield and UTS despite the difference in toughness. Detailed chemical and microstructural analysis was undertaken to elucidate the cause of the toughness range. The majority of the flanges had aluminum additions and a fine grain size with the toughness differences mostly explained by the cooling rate after normalizing with the still air cool showing the lowest toughness and the fastest air cooled sample the highest. For flanges of this strength level a quench and temper operation is not required to obtain good low temperature toughness but forced air cooling after normalizing is a minimum cooling rate to ensure good toughness and overall strength.

The heat-treating industry is in need of heat-treatment furnace materials and fixtures that have a long service life and reduced heat capacity. Failure mechanisms on the effect of prolonged exposure to carburization heat treatment have been investigated. RA330, RA602CA, 304L, 316L and Inconel 625 alloys were selected to study the anti-corrosion properties. The alloys were exposed to 0.7%C carburizing atmosphere at around 900°C for 3 months, 6months, and 12months. Based on microstructural analysis of components that were used until failure in carburization furnace application, it was found that the primary reason for failure was the excessive carburization that leads to “metal dusting” and subsequent cracking. In addition, metallographic analysis indicated that “flake offs” of Fe-Cr-Ni alloys were mainly graphite and chromium carbides. In this paper the failure analysis of industrial components will be presented. In addition, the preliminary analysis of microstructural development during long term exposure experiments in an industrial carburizing furnace will be presented. These samples were characterized using optical and scanning electron microscope and x-ray diffraction.

This paper presents the results of an experimental investigation of the effect of three types of post-heat treatments: 1) solution treatment and aging, 2) stress relieving, and 3) annealing on the corrosion behavior of Ti-6Al-4V fabricated via direct metal laser sintering (DMLS). The microstructure and phase evolution as affected by heat treatment temperature were examined through scanning electron microscopy and via x-ray diffraction. The Vicker’s microhardness, as it was affected by various heat treatments, was compared. The corrosion behavior of the specimens was measured electrochemically in simulated body fluid at 37°C. It was found that the nonequilibrium α’ phase with a small amount of β nuclei was formed in the as-fabricated sample. Heat treatments allow the formation of the β phase and the agglomeration of β precipitates to occur at elevated temperatures. Transformed β phase with various morphologies was observed as a result of the heat treatments. Different degrees of improvement in the corrosion resistance were observed in the solution-treated and aged samples, 650 °C stress relieved, and annealed samples.

As part of a project to identify nondestructive techniques to determine the surface hardness and case depth of carburized steel, Meandering Winding Magnetometers (MWM) measurements were evaluated. MWM technology is based on eddy current testing. Compared to traditional eddy current testing, MWM measurements integrate the generating coil and detection coil into a thin, flexible sensor that can be applied to complex geometries. Conductivity and permeability are measured with MWM equipment to evaluate the properties of carburized steel. For this study, samples of 8620 were carburized to selected hardness and case depths. MWM technology was determined to be an effective method to detect surface hardness. The results of this study are presented and discussed in this paper.

Grain growth during heat treatment can affect mechanical properties. A large grain size can result in a lower strength and susceptibility to brittle failure. In order to control the prior austenite grain size, the effect of Austenitizing temperatures and holding times on the grain size and hardness in 4140 steel was experimentally investigated. Samples were heat treated at 900, 1000, and 1100 °C, and held for 1, 4, and 9 hours. After austenitizing, samples were cooled in the furnace to 850 °C before they were quenched in water at room temperature. Each sample was cut, mounted, and polished. Rockwell hardness and microhardness tests were performed on each sample. A Picric etch was used for grain size analysis. The grain size was measured following the E112 standard test method. It was found that the prior austenite grain size increased with temperature and time according to the standard grain growth model. It was also found that the as-quenched hardness decreased with an increase in grain size.