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).

Quenching and tempering (Q&T) allows a wide range of strength and toughness combinations to be produced in martensitic steels. Tempering is generally done to increase toughness, although embrittling mechanisms result in temperature ranges where strength and toughness may decrease simultaneously. Tempered martensite embrittlement (TME) represents one such mechanism, associated with the decomposition of retained austenite and precipitation of cementite during tempering, usually between 250 and 450 °C. The use of induction heating allows for time-temperature combinations, previously unobtainable by conventional methods, that have been shown to improve properties. The present work shows a beneficial effect of rapid tempering in alloy 1045, with an increase in energy absorption of about 50% when measured at room temperature via a three-point bending fracture test in the TME regime. Phase fraction measurements by Mössbauer spectroscopy showed that increased energy absorption was obtained despite essentially complete decomposition of retained austenite during tempering. Scanning electron microscopy (SEM) investigation of the carbide distribution showed refinement of the average carbide size of approximately 15% in the rapid tempered conditions. SEM characterization of the fracture surfaces of the rapid tempered three-point bend samples showed that, despite an increase in energy absorption in the TME regime, increased microscopic ductile fracture appearance was observed only at the highest test temperature.

Quenched and tempered (Q&T) medium-C steels with various V and Mo additions were studied to understand the relationship between alloy carbide precipitation and hydrogen absorption and trapping behaviours. Heat treatments were selected in the temperature range favourable for V carbide formation, 500-600 °C, leading to higher hardness compared to similar V- and Mo-free alloys due to precipitation hardening. Heat-treated coupons were electrochemically charged to introduce hydrogen, and the bulk hydrogen concentration was measured using melt extraction analysis. Hardness and dislocation density were measured for each tempered condition to relate these properties to the hydrogen absorption and trapping behaviours of each material. Results indicate that dislocation density as well as V and Mo carbide precipitation increase the extent of hydrogen absorbed during charging and the amount of hydrogen remaining trapped after holding at ambient temperature for up to 168 h (1 week).

The phase transformation model is coupled with the inverse heat conduction problem (IHCP) to estimate the steel/quenchant interfacial heat flux. Cylindrical steel probes having section thicknesses 25 and 50mm, respectively, and lengths 30mm were made from medium and high carbon steels (AISI 1045 and 52100). The probes were quenched in mineral, neem, and sunflower oils. The cooling curves at the centre and near the surface of steel probes were recorded. The near-surface cooling curve was used as a reference temperature data in the IHCP algorithm for the estimation of surface heat flux, whereas the cooling curve at the centre was used as the boundary condition of the axisymmetric model of the probe. The effect of phase transformation on the metal/quenchant interfacial heat flux was indicated by a kink and rise of heat flux. The increase in the section thickness of the probe from 25 to 50mm decreased the magnitude of the heat flux. Increasing section thickness increases the phase transformation, increasing the resistance to heat flow at the metal/quenchant interface.

Rapid induction hardening of martensitic steel can attain the very high strength levels needed for light-weighting components subjected to high operating stresses. Specimens of martensitic 0.6% C steels were heat treated using a dilatometer to investigate the effects of heating rates of 5 to 500 °C/s to temperatures of 850 to 1050 °C on the transformation to austenite and subsequent transformation to martensite during quenching. Selected specimens were quenched after partial transformation to austenite to assess the initial cementite precipitate size formed in ferrite during heating. Other specimens were isothermally held at the austenitizing temperature to assess cementite dissolution rates. Higher heating rates increased the Ac1 and Ac3 temperatures, and lowered the Ms temperature. Alloy content and prior microstructure also influenced the transformation temperatures.

A hypoeutectoid steel was austenitized at 840 °C for one hour and cooled at two rates. Examination by optical and scanning electron microscopy showed a change in the pearlite microstructure. Cooling in air as compared to furnace cooling reduced the pearlite interlamellar spacing and increased the hardness. The slower cooling resulted in a lower tensile strength, higher tensile elongation, and different fracture appearance.

This paper reports on a study to investigate the creation of a mixed microstructure consisting of proeutectoid ferrite, bainite, and austenite in a medium carbon high silicon steel. The microstructure was produced through the use of a continuous cooling process at a moderate cooling rate from the austenitizing temperature range to room temperature. The investigation also examined the influence of this microstructure on the mechanical properties of the material. Test results indicate that the developed steel has better mechanical properties compared to commercially available dual phase steels.

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 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.

Nitrogen (N 2 ) atmospheres with different, not always optimized levels of reducing and carburizing gases are often used to prevent decarburizing and oxidation of steel parts during annealing in continuous furnaces. The type and concentration of these additives in N 2 should correlate to the extent of air leakage into furnace, entrainment of air with loaded parts, steel composition, and complex reaction kinetics in the gradients of oxygen (O 2 ) and temperature existing between the entrance and hot zones of the furnace. This study explores the effect of small, 0.1 vol.% - 0.4 vol.% propane (C 3 H 8 ) additions on composition of air-contaminated N 2 atmosphere in the temperature range of 500°C - 860°C. Microstructures are presented for AISI 1045 steel exposed to the atmospheres produced. Atmosphere compositions compared include those produced by a new type of plasma activated, in-situ reformer for N 2 -diluted C 3 H 8 . The latter method extends the atmosphere protection to the lower range of annealing temperatures. Present results may assist heat treaters in optimizing their neutral hardening operations.

An attempt was made to characterize microstructure, mechanical properties and cleanliness of continuous cast as rolled billets versus microstructure, mechanical properties and cleanliness of the forging in normalized condition, upset forged from AISI 41B30 modified chemistry billets. Two forgings were compared, one in as forged condition and one in normalized or heat treated condition. Upsets were produced by upsetting only one end of the billet by hydraulic press. Samples from cold portion of the forgings, near the flange location and from flanges were taken and examined. Results of microstructure, mechanical properties and hardness are presented. Normalizing cycle did not improve mechanical and impact properties. Low impact and ductile properties are results of Widmanstätten structure and continue to be present in the final product. Low impact and ductile properties of this structure might not be the best solution for dynamically loaded parts.

It is well known that petroleum oil base stocks possess a number of limitations, such as being non-renewable, but even more importantly, they are considered relatively toxic with limited biodegradability. One class of base stock that is renewable with excellent biodegradability characteristics and that is generally, but not always, non-toxic is animal and seed oils. The quenching performance of many different animal and vegetable oil compositions has been reported in the literature. However, as a class, they suffer from generally poor thermal oxidative stability, even when containing oxidation inhibitors, when compared to quenchants derived from petroleum oil. This factor limits their potential commercial utility. One method of addressing this problem is to chemically modify the vegetable oil to produce increased resistance to thermal-oxidative degradation. This work discusses the physical properties and quenching performance of epoxidized soybean oil-based formulations and the resulting metallurgical properties, hardness, and microstructures obtained. These results have not been reported previously.

The effect of forging temperature and temperature before quenching on microstructure is studied. This is related to the mechanical properties like tensile strength, yield strength and impact toughness. It was observed that martensitic needles in direct quenched parts were slightly longer than the normal hardened and tempered parts. This was attributed to the coarser prior austenite grain size, resulting in fewer nucleation sites in case of direct quenched parts.

Microalloying of medium carbon bar steels is a common practice for a number of traditional components; however, use of vanadium microalloyed steels is expanding into applications beyond their original designed use as controlled cooled forged and hot rolled products and into heat treated components. As a result, there is uncertainty regarding the influence of vanadium on the properties of heat treated components, specifically the effect of rapid heat treating such as induction hardening. In the current study, the torsional fatigue behavior of hot rolled and scan induction hardened 1045 and 10V45 bars are examined and evaluated at effective case depths of 25, 32, and 44% of the radius. Torsional fatigue tests were conducted at a stress ratio of 0.1 and shear stress amplitudes of 550, 600, and 650 MPa. Cycles to failure are compared to an empirical model, which accounts for case depth as well as carbon content.