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.

Effects of Water Jet Height and End Dipping on the Cooling Rate and Hardenability in the Jominy End Quench Test

The effects of water jet height and end dipping on cooling rate and hardenability in the Jominy end quench test were investigated to understand the Jominy test in more detail. Experimental tests were conducted under end dipping cooling condition as well as for specific water jet heights of 35, 65, and 100 mm. The thermal behavior and mechanical properties of the Jominy specimen with region were evaluated using thermocouples and hardness measurements, respectively. The effect of the water jet height on the thermal and hardness behaviors was not large; especially, the influence of water jet height was negligible when the water jet height was over 50 mm. These observations indicate that the uncertainty of the water jet height is not important during the standard Jominy end quench test. Meanwhile, during the standard Jominy test, we cannot neglect the heat flow along the radial direction of the specimen because the temperature difference between the center and surface area was not small; the maximum temperature difference was approximately 50 °C. Based on the comparative study between the standard Jominy cooling and the end dipping cooling processes, the thermal gradient along the radial direction of the specimen can be reduced with the more stable cooling condition on the Jominy end. However, the effect of temperature deviation along the radial direction of the Jominy specimen on the hardness distribution along the longitudinal direction was not large, which shows the high reliability of the Jominy end quench test.

Increasing Hardenability and Hardness of Quenching and Tempering Alloys by Substituting Chromium with Manganese

This study investigates the influence of the substitution of chromium (-0.8 wt.−%) by manganese (+1.3 wt.−%) in a standard quench and tempering steel and the predictability of property changes through simple simulations, only dependent on the chemical composition. The substitution of chromium by manganese leads to an increased hardness (+50 HV10) and a reduction of the critical cooling speed from 19 K s−1 for the reference alloys to 9 K s−1 for the new alloy and a nearly constant hardness of (600 HV10) after Jominy-test. The commercial software JMATPRO is used to simulate and predict key properties for the industrial production. It is shown that a successful simulation of phase transformation temperatures and the general directions of change can be predicted, but more complex properties like critical cooling rates or hardenability need more sophisticated methods.

Pengaruh jarak nozzle penyemprot terhadap kemampukerasan baja komersil dengan metode jominy test

Steel is the material most widely used in the industry. To avoid wear and tear on steel, it is necessary to do heat treatment to improve the mechanical properties of the steel according to its application in the field. The increase in hardenability in metals can be determined by doing a hardenability test, namely the Jominy test method. The Jominy test is a method to determine the hardness value of metal using ASTM standards. This research was conducted with varying the distance of the nozzle of the sprayer to the lower end of the specimen, namely 10 mm, 12.5 mm, and 14 mm with a long spraying time of 15 minutes. The heat treatment process at temperature of 780oC and 90 minutes holding time. The averagehardness value of specimen number one (10 mm spraying distance) is 45.43 kgf, specimen number two (12.5 mm spraying distance) is 45.68 kgf, and specimen number three (14 mm spraying distance) is 44.31 kgf. The highest hardness value was specimen number two, there was an increase of 1.87 kgf (4.02%), according to ASTM standards where the spraying distance was 12.5 mm.Keywords: Steel, spraying distance, Jominy test.

Adjustment of Isothermal Transformation Diagrams Using Finite-Element Optimization of the Jominy Test

A practical method for adjusting and optimizing isothermal transformation (IT) diagrams using the Jominy test is presented. The method is based on a finite-element optimization procedure, which iteratively minimizes the error between the target phase fractions and the corresponding finite-element solutions at the sample points using an optimization tool. A standard Jominy test of AISI 52100 bearing steel is used to investigate the feasibility and reliability of the method. Three optimization parameters for each IT diagram curve are mathematically applied to the modified Kirkaldy model. These parameters are the design variables in the optimization. The curves obtained from the modified Kirkaldy model are used as the initial guesses in the optimization and they approach the experimental IT diagram by minimizing the error. Good agreement is observed between the optimized diagram and the experimental diagram reported in the literature. The predicted phase fractions using the experimental IT diagram, the IT diagram obtained from the modified Kirkaldy model, and those obtained from the optimized model are compared and demonstrate that the adjustment or optimization procedure significantly improves the accuracy of the predicted phase fraction of the model. The applicability of the method is investigated in a practical case study.

Effect of boron microaddition on hardenability of new-developed HSLA-type steels

Purpose: The paper presents the results of investigations on the effect of 0.003% boron microaddition on the hardenability of new-developed HSLA-type steels. In order to prevent the binding of the boron microaddition with nitrogen in BN nitrides, Ti microaddition at concentrations of 0.033% and 0.028% was also added into the tested steels. Design/methodology/approach: Evaluation of hardenability of the investigated steels was carried out on the basis of the Jominy test and the analytical method, according to the ASTM 255-89 standard, taking into account the effect of the boron microaddition. Additionally, developed of the CCT-diagram of investigated steel. A DIL 805A/D dilatometer with a LVDT-type measuring head was used to carry out the dilatometric test. Findings: Microaddition of boron, introduced into steel in a concentration of 0.003% along with Ti microaddition shielding (in concentration of 0.033% in steel A and 0.028% in steel B), advantageously improves hardenability. This is reflected in calculated ideal critical diameter DIB, which is equal 163 mm for steel A and 155 mm for steel B. The form of curves of phase transformations of supercooled austenite is typical for steels with microaddition of boron, with similar chemical composition. Research limitations/implications: Due to similar chemical composition of investigated steels, the kinetics of phase transformations of austenite, supercooled under continuous cooling, was determined for steel B containing 0.28% C, 1.4% Mn, 0.3% Si, 0.26% Cr, 0.22% Mo and Nb, Ti, V and B microadditions at 0.027%, 0.028%, 0.019% and 0.003% respectively. Practical implications: Tested steels have high hardenability and show the full usability for production of forged parts with the method of thermomechanical treatment, i.e., hot- deformed in the temperature range adjusted to the type of microadditions added to steel, with direct quenching of forgings from finishing forging temperature. The results of the tests may be useful for developing the parameters of heat treatment and thermomechanical treatment of investigated steels. Originality/value: The hardenability of new-developed HSLA-type steels was determined.

PENGARUH VARIASI HOLDING TIME TERHADAP KEMAMPUKERASAN BAJA MENGGUNAKAN ALAT UJI JOMINY

Kemampukerasan adalah kemampuan suatu material untuk dapat dikeraskan sampai kedalaman tertentu dengan cara perlakuan panas dengan properti mekanik, hingga terbentuk martensit pada proses pendinginan untuk mencapai kekerasan tertentu. Salah satu metode pengujian hardenability yaitu jominy test (Van Vlack, 1991). Uji jominy merupakan sebuah metode untuk mengetahui kemampuan pengerasan logam (baja). Pengujian jominy tes dilakukan berdasarkan standard ASTM A255. Pengujian dilakukan mengunakan baja ST 42 dengan panjang 100 mm dan diameter 25.4 mm dengan spesimen uji sebanyak 3 buah. Hasil pengujian spesimen 1 dengan holding time 30 menit menghasilkan nilai kemampukerasan 43,7 HRB, untuk spesimen 2 dengan Holding Time 60 menit menghasilkan nilai kemampukerasan 43,7 HRB, sedangkan pada spesimen 3 dengan holding Time 90 menit menghasilkan nilai kemampukerasan 47 HRB. Semakin lama dilakukan holding Time pada spesimen maka nilai kekerasan yang dihasilkan akan lebih tinggi.