Prasonk Sricharoenchai

Two body type abrasion wear behaviour in hypoeutectic 16%Cr cast irons with Mo

Abstract Hypoeutectic 16%Cr cast irons, both Mo free and 1–3%Mo containing specimens were prepared to investigate their abrasion wear behaviour. Annealed specimens were hardened at 1323 K and then tempered at three temperatures from 673 to 873 K for 7·2 ks, the temperature giving the maximum hardness (HTmax) and the lower and higher temperature, (L-HTmax, H-HTmax). The abrasion wear behaviour was investigated using a two body type Suga abrasion wear tester. A linear relation was obtained between wear loss and wear distance. The highest wear resistance or the lowest wear rate (R W) was obtained in H Tmax specimens except for the Mo free specimen. The lowest wear resistance or the highest R W was obtained in H-HTmax specimens. The R W was decreased with an increase in macrohardness. The lowest R W appeared around 25% retained austenite (V γ ). The R W was decreased with an increase of Mo content, and the V γ value at the minimum R W shifted to the high V γ side.

Effect of Reheat Treatment on Microstructural Refurbishment and Hardness of the As-cast Inconel 738

Abstract This work investigates the effect of rejuvenation heat treatment conditions for refurbishment of the long-term serviced gas turbine blades, which were made of as-cast nickel base superalloy grade, Inconel 738. The reheat treatment conditions consist of solutionizing treatments at temperatures of 1,438, 1,458 and 1,478 K for 14.4 ks and aging treatments at temperatures of 1,133, 1,148 and 1,163 K for 43.2, 86.4, 129.6 and 172.8 ks. The results show that increase in aging times results in continuous increase of size and area fraction of gamma prime (γ′) particles. The higher solutionizing temperature leads to the lower area fraction and smaller size of gamma prime particles. Regarding the microstructure characteristics, the most proper reheat treatment condition should be solutionizing at temperature of 1,438 K for 14.4 ks and aging at temperature of 1,133 K for 172.8 ks, which provides the highest area fraction of gamma prime particles in proper size.

Effect of molybdenum content on subcritical heat treatment behaviour of hypoeutectic 16 and 26 wt-% chromium cast irons

Abstract Hypoeutectic high chromium cast irons containing 16 and 26 wt-%Cr, with and without Mo, were prepared to clarify the variation of hardness and volume fraction of retained austenite (Vγ) during subcritical heat treatment. As cast specimens were held at temperatures between 773 and 973 K for 21··6 ks (6 h) and air cooled with a fan. Hardness and Vγ values were measured in all specimens. In the subcritically heat treated state, secondary hardening similar to hardened tempered alloy cast irons and steels was observed. Vγ decreased gradually with rising temperature. The maximum hardness levels following subcritical heat treatment were obtained at temperatures between 823 and 873 K. The greatest improvement, an increase of 140 HV30, was obtained in 16 wt-%Cr cast iron with 3 wt-%Mo.

Improvement of Oxidation Behavior at 1,073 and 1,173K of Austenitic Stainless Steels by Addition of Ni

This work studied the effect of Nickel addition to improve the oxidation behavior of austenitic stainless steels at 1,073 K and 1,173 K. The results show that Nickel increases the oxidation resistance of the austenitic stainless steels. The compositions of oxide scale also change form only Cr2O3 to be Cr2O3, Fe2O3, NiFe2O4 and Ni (Cr2O4). The oxidation behavior follows the parabolic rate law; W = ktn, where W = weight gain (g/cm2), t = time (s), k is the exponential rate constant and n is the exponent of growth rate. The n values are between 0.47-0.88.

Effect of Sub-Critical Heat Treat Parameters on Hardness and Retained Austenite in Mo-Containing High Chromium Cast Irons

Subcritical heat treatment of austenite in alloyed cast iron, treated at a temperature below pearlite transformation (A1), has been used to improve matrix hardness without conventional hardening heat treatment. Two series of hypoeutectic 16 and 26 wt% Cr cast irons containing 0, 1, 2 and 3 wt% molybdenum (Mo) were used to investigate the behavior of hardness and retained austenite during subcritical heat treatment. An as-cast test piece was held at subcritical temperatures in 50K intervals from 773K (500C, 932F) to 873K (600C, 1112F) for 21.6 ks to 64.8 ks and then cooled to room temperature by fan cooling. Hardness and volume fraction of retained austenite (Vγ) were measured. In the as-cast state, the hardness decreased gradually but the Vγ increased greatly as Mo content increased in both 16 and 26 wt% Cr cast irons. In the state of subcritical heat treatment, the hardness increased first and then decreased with an increase in holding time. This phenomenon is due to a hardening caused by the precipitation of secondary carbides and by martensite transformation from the destabilized austenite during cooling. At the same Mo content, the degree of hardening was greater in the 16 wt% Cr cast iron than in the 26 wt% Cr cast iron. The Vγ decreased with an increase in both holding time and holding temperature. The maximum hardness in the subcritical heat treatment (HSTmax) was obtained when the specimens were treated at temperatures from 823K (550C, 1022F) to 873K (600C, 1112F) for 50.4 ks. The HSTmax increased gradually in the 16 wt% Cr cast iron but it changed little in the 26 wt% Cr cast iron when Mo content was increased. The highest value of HSTmax, 760 HV30, was obtained in the 16 wt% Cr cast iron with 3 wt% Mo where the Vγ was less than 10%.