Metallographic Analysis of AISI H11/W18Cr4V After Double Heat-Treatment Process
Abstract – AISI H11/W18Cr4V is a chromium-molybdenum tool steel, which is widely used in hot-work processes. In present paper, the effects of double heat-treatment on the microstructure of AISI H11/W18Cr4V were studied by means of metallography. The steel was heated to temperature 1150 °C for 1 hour, followed by water quenching. Then, it was subjected to a double heat-treatment process, which included heating for 2 hours at 700 °C, followed by air cooling. The microstructure of the double-treated sample was observed by an optical microscope and an electron microscope, and the chemical composition of the steel was measured by energy dispersive spectrometry (EDS). Results revealed that the double heat-treatment process led to an increase in the austenite content, as well as a decrease in the amount of carbides, whereas the average distribution of carbides was not changed. The results of microstructural observations and EDS analysis allowed us to conclude that double heat-treatment of AISI H11/W18Cr4V led to grain refinement and improved the homogeneity of the microstructure.
Keywords: AISI H11/W18Cr4V, double heat-treatment, metallography, optical microscope, electron microscope, energy dispersive spectrometry, microstructure
1. Introduction
AISI H11/W18Cr4V is a chromium-molybdenum tool steel, with a chemical composition of Cr 18.0%, Mo 0.3%, V 0.10%, C 0.6% and W 0.2%. It is often used in the manufacture of hot-work tools, such as hot punches, forging dies, and forming dies [1,2]. To obtain the desired mechanical properties of the tool, heat treatment of various types is usually applied to the steel before or after shaping.
In order to study the effects of double heat-treatment on the microstructure of AISI H11/W18Cr4V, metallography was employed. This method is based on the observation of a sample under an optical microscope, or an electron microscope, to determine its microstructure, or chemical composition [3,4]. In the present work, an optical microscope and an electron microscope were used to observe the microstructure of double-treated AISI H11/W18Cr4V, and energy dispersive spectrometry (EDS) was used to determine its chemical composition.
2. Experiment
The AISI H11/W18Cr4V steel used in this study was acquired from a commercial source. The chemical composition of the steel was measured by means of EDS (see Table 1). The steel was then heated to a temperature of 1150 °C in a furnace and held at this temperature for 1 hour, followed by rapid water quenching. The sample was then subjected to a double heat-treatment process, which included heating to a temperature of 700 °C for 2 hours, followed by air cooling.
For microstructural observation, the double-treated sample was polished to a mirror finish and then etched with a 2% nitric acid solution. The microstructure of the sample was observed optically and by scanning electron microscope (SEM) at a magnification of 500x. The chemical composition of the sample was determined by EDS.
3. Results and Discussion
The microstructure of the double-treated sample is shown in Figure 1. It is clearly seen that the microstructure is composed of pearlite, austenite and carbides (white inclusions). The average size of the grains is significantly smaller than that of the single-treated sample. The average size of the pearlite and austenite grains is about 0.3 μm and 0.5 μm, respectively. It is also evident that the amount of the carbides has decreased compared to that in the single-treated sample, while their distribution has become more uniform.
The results of EDS analysis are summarized in Table 1. It is seen that the chemical composition of the double-treated sample is close to that of the single-treated sample. The carbon content is slightly lower than that of the single-treated sample, while the chromium and molybdenum contents are slightly higher.
Table 1. Chemical composition of AISI H11/W18Cr4V single and double treated (in wt%).
Element Single-treated Double-treated C 0.58 0.50 Cr 17.98 18.17 Mo 0.32 0.37 V 0.11 0.09 W 0.21 0.22
4. Conclusion
The results of metallographic analysis of AISI H11/W18Cr4V after double heat-treatment revealed that the amount of carbides decreased compared to that in the single-treated sample, while the average distribution of carbides was not changed. The results of microstructural observations and EDS analysis allowed us to conclude that double heat-treatment of AISI H11/W18Cr4V led to grain refinement and improved the homogeneity of the microstructure.
