Improvement of ASTM A53 Steel Durability Using Agrowastes as Carburizing Agent

The importance of steel in manufacturing and construction over the past century cannot be over-emphasized and easy accessibility couple with excellent mechanical properties make it preferable over others. However, the problem of durability has posed a serious concern as majority of steel application are meant for long term use. Several attempts have been made to improve the durability of steel in the past and increase of carbon content in low carbon steel was found to be a suitable agent. Although getting carbon is not the challenge rather obtaining it from a sustainable source that has zero environment impact. This research identified two separate agrowaste that has high carbon content the issue of sustainability brought about the development of carburizing agent from agrowaste that are easily accessible namely palm kernel and eggshell which is employed in this research. The use of agrowaste was found to be effective as there was notable increase in grain structure of the carburized steel when compared to the control sample without carburized agent in it.

Effect of Heat Treatment on the Structure and Properties of the Carburized Layer of the Legs of Three-Ball Drill Bits

The effect of time-temperature parameters of heat treatment on the structure and properties of carburized case and the core of 19CrMnNiMo steel was studied. The critical points were determined by dilatometric analysis: Ac1 = 740°C, AC3 = 835°C. It was established, that after carburizing at 940 °C, prequench to 890 °C with oil cooling, quenching at 790 °C and tempering at 180 °C, martensite structure of carburized case with uniformly distributed carbides and the least amount of retained austenite is formed. The hardness of carburized case decreases smoothly from the surface into the depth, in proportion to the decrease in the carbon concentration and amounts to 60-50 HRC. The technological process of heat treatment of drill bit legs made of 19CrMnNiMo carburized steel providing minimal amount of retained austenite in structure, absence of carbide network and combination of optimum mechanical properties which is proved by a real on-site experiment is developed. Temperature conditions of carburizing, quenching and low tempering are recommended for the production of legs of roller bits.

Isothermal Heat Treatment of the Low-Carbon Martensitic Steel

A study of the low-carbon steel with high hardenability was carried out. The steel contained the following alloying elements, wt. %: C – 0.20; Cr – 2.0; Mn – 2.0; Si – 1.04 Ni – 1.0; Mo – 0.3. The quenching – partitioning treatment of the studied steel was implemented. The microstructure of the steel consisted of the tempered martensite laths, bainite and martensite-austenite regions. The amount of the residual austenite and the carbon concentration in the residual austenite were estimated. The possibility of the quenching – partitioning treatment of the carburized steel was shown.

Microstructure, Hardness, and Tensile Properties of Vacuum Carburizing Gear Steel

We investigated the effects of the austenitizing temperature on the microstructure, hardness, and tensile properties of case-carburized steel after vacuum carburization at 930 °C and then re-austenitization at 820–900 °C followed by oil quenching and tempering. The results show that fractures occurred early with the increase in the austenitizing temperature, although all the carburized specimens showed a similar case hardness of 800 HV0.2 and case depth of 1.2 mm. The highest fracture stress of 1919 MPa was obtained for the experimental steel when the austenitizing temperature was 840 °C due to its fine microstructure and relatively high percentage of retained austenite transformed into martensite during the tensile tests. We also found that the stress–strain behavior of case-carburized specimens could be described by the area-weighted curves of the carburized case and the core in combination. The strain hardening exponent was about 0.4 and did not vary with the increase in the austenitizing temperature. We concluded that the optimum austenitizing temperature was around 840 °C for the experimental steel.

Prediction of Residual Stress of Carburized Steel Based on Machine Learning

In recent years, the number of machine learning applications (especially those involving deep learning) applied to predicting and discovering material properties has been increasing. This paper is based on using microstructure and carbon content to train machine learning models to predict the residual stress of carburized steel. First, a semantic segmentation model of the material organization structure (SegModel-MOS) was constructed based on the AlexNet network and initially trained on the PASCAL VOC2012 dataset. Then, the trained model was fine-tuned on an enhanced homemade dataset consisting of optical microstructures. The experimental results show that SegModel-MOS can distinguish acicular martensite, retained austenite, and lath martensite in microstructures. Finally, we used both support vector machine (SVM) and decision tree (DT) algorithms to establish a mapping relationship between the microstructure, carbon content, and residual stress to predict the residual stress of steel from its microstructure and carbon content. The experiments verified that the prediction model constructed in this study exhibits high accuracy and can directly predict residual stress without requiring any long-term measurements. Thus, the developed model provides a new approach to the study of residual stress in steel.

Development of Nanobainitic Microstructures in Carbo-Austempered Cast Steels: Heat Treatment, Microstructure and Properties

Carburizing implies the existence of a carbon gradient from the surface to the core of the steel, which in turn will affect both the critical temperature for austenite formation and the kinetics of the bainitic transformation during the austempering treatment. Therefore, for future development of carbo-austempered steels with nanobainitic microstructures in the case, it is key to understand the effect of such carbon gradient has on the final microstructure and the mechanical properties reached by the heat treatments used. This work was divided into two parts, firstly two alloys with similar carbon content to those at the surface and center of the carburized steel were used to establish the optimal heat treatment parameters and to study bainite transformation kinetics by high resolution dilatometry. In a second step, a carburized alloy is produced and subjected to the designed heat treatments, in order to evaluate the microstructure and mechanical properties developed. Results thus obtained are compared with those obtained in the same carburized alloy after following the most common quench and temper treatment.