This paper reviews several techniques for hardness prediction, from simple to complex, and compares the calculated results to those published previously. Using “old-school” methods based on the Grossman H-Value and Lamont charts, we predict the expected hardness for SAE 1045 and SAE 6140 round bars in three sizes: 1, 3, and 5 in. (25, 75, and 125 mm).

Additively manufactured (AM) metals require a modified heat treatment to accommodate for slight differences in composition caused by powder atomization and cover gas used in the manufacturing process. 17-4PH stainless steel (17-4PH) is a precipitation hardening steel which hardens through the formation of Cu precipitates in a martensitic matrix during aging treatment. The powders used in Laser Powder Bed Fusion (LPBF) fabrication of 17-4PH are typically spray atomized using N 2 cover gas, which is associated with a certain amount of nitrogen uptake. Nitrogen is a potent austenite stabilizer and will lower the martensite start temperature of the steel. To counteract the effect of nitrogen, a sub-zero heat treatment can be introduced to promote a more complete transformation into martensite. In this work, the effect of nitrogen on the heat treatment response of 17-4PH is investigated through comparing standard wrought, nitrogen loaded wrought, and LPBF 17-4PH. In particular, the effect of introducing a subzero treatment is addressed. After quenching from the solutionizing step (austenitization) LPBF fabricated 17-4PH was cold-treated in different combinations of dry ice (-78 °C) and boiling nitrogen (-196 °C). Subsequently, these conditions were aged in the conventional way. The sub-zero treatments were compared with the conventional heat treatment procedure, which does not entail a sub-zero step. In addition, phase transformations (above room temperature) were monitored in-situ using dilatometry. Finally, hardness tests and XRD analysis were performed to characterize the final microstructure. It is demonstrated that sub-zero treatment can be an effective route to address the problems associated with the additional nitrogen present in LPBF 17-4PH fabricated parts.

Carbide free bainitic microstructures can be developed via different thermal processing routes, and the details affect the scale and morphology of the microstructural constituents. In this study, bainitic microstructures are formed by either a controlled cooling process or an austempering process to evaluate the relationship between microstructure and mechanical properties in a 0.2C - 2Mn - 1.5Si - 0.8Cr steel containing small amounts of Nb, Ti, B, and N, and the results are compared to a 4140 steel processed via quenching and tempering. The resulting microstructures are characterized with scanning electron microscopy. When compared to microstructures produced via austempering, microstructures produced with a controlled cool exhibit an increased variety of transformation products, specifically regarding size and distribution of martensite-austenite constituents within a lath-like bainitic ferrite matrix. Nanoindentation testing shows that different transformation products exhibit significantly different local hardness. In all (primarily) bainitic conditions tested for these materials, the martensite/austenite constituent exhibits the highest hardness, followed by the lath bainitic ferrite/retained austenite constituent. Granular bainite and coarse bainitic constituents exhibit the lowest relative hardness in the conditions where they are observed.

Carburizing and induction hardening are two commonly used surface heat treatments that increase fatigue life and surface wear resistance of steels without sacrificing toughness. It is hypothesized that induction hardening following carburizing could yield further increased torsional fatigue performance through reducing the magnitude of the tensile residual stresses at the carburizing case-core interface. If successful, manufacturers could see gains in part performance by combining both established approaches. A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The case microstructure of the heat-treated conditions was primarily tempered martensite and transitioned to a bainitic microstructure around the deepest overall case depth. Material property characterization consisted of radial cross-sectional hardness testing and torsional fatigue testing. The hardness profiles confirmed that the designed case depths were achieved for all conditions. Torsional fatigue testing was conducted using a Satec SF-1U Universal Fatigue Tester. Of the six tested conditions, the condition with the deepest case depths, i.e. carburized to 1.5 mm and induction hardened to 3.0 mm, was expected to have the greatest increase in fatigue performance. However, initial fatigue results potentially indicate the opposite effect as the non-induction hardened samples exhibited longer fatigue lives on average.

Carburization is a common method of hardening steel surfaces to be wear-resistant for a wide range of mechanical processes. One critical characteristic of the carburization process is the increase in carbon content that leads to the formation of martensite in the surface layer. Combustion and spark-OES are two common methods for determination of carbon in steels. However, these techniques do not effectively separate carbon from near surface contaminants, carburized layers, and base material composition. Careful consideration of glow discharge spectroscopy as a method of precisely characterizing carbon concentration in surface layers as part of a production process should be evaluated in terms of how the resulting data align with other common analytical and metallurgical measurements. When used together, glow discharge spectroscopy, optical microscopy, and microhardness testing are all useful, complementary techniques for characterizing the elemental composition, visually observable changes in material composition, and changes in surface hardness throughout the hardened case, respectively. Close agreement between related measurements can be used to support the use of each of these techniques as part of a strong quality program for heat treatment facilities.

A micro-alloyed 1045 steel was commercially rolled into 54 mm diameter bars by conventional hot rolling at 1000 °C and by lower temperature thermomechanical rolling at 800 °C. The lower rolling temperature refined the ferrite-pearlite microstructure and influenced the microstructural response to rapid heating at 200 °C·s -1 , a rate that is commonly encountered during single shot induction heating for case hardening. Specimens of both materials were rapidly heated to increasing temperatures in a dilatometer to determine the A c1 and A c3 transformation temperatures. Microscopy was used to characterize the dissolution of ferrite and cementite. Continuous cooling transformation (CCT) diagrams were developed for rapid austenitizing temperatures 25 °C above the A c3 determined by dilatometry. Dilatometry and microstructure evaluation along with hardness tests showed that thermomechanical rolling reduced the austenite grain size and lowered the heating temperature needed to dissolve the ferrite. With complete austenitization at 25 °C above the A c3 there was little effect on the CCT behavior.

This paper presents a method for calculating quench severity based on hardness profile matching. The new method has the potential to eliminate the need for Jominy end-quench testing as required in the traditional Kern approach. To assess the accuracy of the proposed method, a test bar and Jominy bar were machined from 2-in. bar stock and heat treated in accordance with ASTM A255. The test bar was quenched in a draft-tube system with a water velocity of 6 ft/s. An excel workbook was programmed to calculate the quenched hardness profile based on prior austenite grain size and steel chemistry. The calculations were in good agreement with measured Jominy hardness as were the quench severities determined by the Kern method and the proposed hardness profile matching technique.

This work investigates the effect of boriding and thermo-reactive deposition on 15B30 steel. The results presented in the paper show that these thermochemical treatments produce boride and carbide rich layers that improve surface hardness and wear resistance, and they do so without the adverse effects of adding more boron to the alloy.

Rene 65 is a nickel-based superalloy used in aerospace components such as turbine blades and disks. The microstructure in the as-received condition of the superalloy consists of about 40% volume fraction of gamma prime precipitates, which is so strong that thermomechanical processing is problematic. The aim of this work is to find a heat treatment to reduce hardness for manufacturing purposes without changing grain size in the final application. For the design of the heat treatments, Taguchi’s L8 matrix is used and the factors that are examined include cooling rate, hold temperature, hold time, and cooling method to room temperature.

Vanadium microalloying additions are common in medium carbon ferrite-pearlite steel shafts. The increased load capacity provided by vanadium carbonitride precipitation is beneficial in many applications. Induction hardening can further increase the surface strength of a component; however, the implications of the vanadium carbonitride precipitates on microstructural evolution during induction hardening are unclear. Evidence that vanadium microalloying influences the microstructural evolution of the induction hardened case as well as the case/core transition regions are presented in the current study. Vanadium increases the amount of non-martensitic transformation products in the case while decreasing austenite formation kinetics in the case/core transition region. Observations in induction-hardened shafts were supported by Gleeble physical simulations of computer simulated thermal profiles. Characterization was conducted using scanning electron microscopy, dilatometry, and microhardness testing.

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate.

Hardness bench testing is a simple and universally accepted practice for checking induction hardened parts and is performed in literally thousands of manufacturing facilities. There are trained metallurgical professionals who have spent years studying and training in this art. However these days many new users are given only the basics during a quick show and tell: this paper is intended for these up and coming heat treaters or quality engineers. The presentation will reveal simple to understand rules for proper work piece cutting, surface preparation, and other factors in the preparation of induction hardened samples for bench hardness testing. Selection of the best RC scale to use based on the part configuration and size will be reviewed.

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.

The latest generation of eddy current test instruments and probes enables manufactures to perform 100% in-line inspection of heat treated components reducing warranty, scrap, and testing costs. The implementation of multi-frequency testing in conjunction with simplified user interfaces, allows these manufacturers to quickly create tests that effectively reject components with metallurgical defects such as misplaced case, shallow case, short quench, and ground out condition. In a study performed with a powder metal gear manufacturer, eddy current testing demonstrated more consistent results than Rockwell hardness (HRB) testing.

This study evaluated the suitability of a new furnace and quench tank facility for heat treating blowout preventer (BOP) bodies in the oil well industry. A challenging 19.5T single-bore BOP body that previously failed to meet hardness consistency requirements was selected for comprehensive analysis. The research aimed to address historical heat treatment challenges by utilizing fluid flow analysis for optimal quench tank positioning and surface thermocouples to verify temperature uniformity during austenitization. Brinell hardness testing revealed significant improvements in hardness consistency after treatment, concluding that the new heat treatment facility will substantially enhance the manufacturer’s ability to meet stringent customer specifications for BOP bodies.

Fully automated Vickers measurement systems with image analysis have been commonly used for over 20 years to measure case depth in carburizing, nitriding, and surface hardening processes. One of the most frequently discussed issues is the reproducibility of results both within individual systems and between different systems. This paper presents examples from industrial users to illustrate the ongoing challenges with these systems and the main points of discussion. The examples highlight the difficulties that arise even when systems operate within the accepted accuracy range of existing standards. Additionally, the paper will discuss future challenges and potential improvements for automatic hardness test systems.