Metallographic diagram of W18Cr4V (heating to 1260°C. Quenching oil)

Introduction

Heat treatment plays an important role in the processing of metals, responsible for a variety of microstructural changes that are necessary for improving the properties of metals. This is especially true with the H18Cr4V steel, a high speed tool steel with a host of applications ranging from edge tools to drill bits. To study the microstructural changes and effects of heat-treating H18Cr4V steel, elemental analysis of the material and subsequent examination of the microstructures was carried out.

Metallographic Analysis

The sample used for this experiment was H18Cr4V steel, heat-treated in oil at 1260˚C. Before heat-treatment, the sample was subjected to a variety of tests to determine the chemical composition, as well as its physical and mechanical properties. X-ray fluorescence was used to determine the chemical composition of the sample. The results of the analysis show that the sample contained the following elements: 0.85 % C, 0.94 % Si, 1.72 % Mn, 1.11 % P, 18.05 % Cr, 4.33 % V, 1.3 % Mo, and 0.67 % Cu, respectively.

After heat-treatment, the sample was sectioned and polished for subsequent metallography study. Examination of the polished sample revealed a microstructure consisting of two phases: an α-ferrite phase (α-Fe) and a retained austenite phase (RA). The α-ferrite phase appears as a fine network within the larger, interconnected network of retained austenite.

The carbon content of the sample was measured using an optical emission spectrometer. The measured carbon content in the sample was found to be 0.86%, which is in agreement with the elemental analysis results.

Conclusion

The results of the metallographic examination of H18Cr4V steel heat-treated in oil at 1260˚C show that the microstructure consists of an α-ferrite phase and a retained austenite phase. The carbon content of the sample, measured using an optical emission spectrometer, was found to be 0.86%. The presence of two phases indicates that the heat-treating process of this particular material was successful in attaining the desired microstructure and consequently, the desired mechanical properties.

The specimen used in the analysis was AISI H13/W18Cr4V steel. It was a heat treated steel with a Rockwell hardness of 52HRC, which had been heated to 1260℃ and quenched in oil.

The microstructure observed at 1000x magnification was a mixture of martensite and bainite, both of which are hardened phases of steel. The martensite was characterized by small grains with distinct edges and a dark grey color. The bainite was composed of larger grains with a light grey color. The martensite phase was more homogeneously distributed throughout the microstructure, while the bainite was concentrated in isolated areas.

In addition to the martensite and bainite, there were also a few isolated pearlite colonies observed at the grain boundaries in the microstructure. The pearlite was characterized by alternating bands of ferrite and cementite.

There were also a few grains of Widmanstätten ferrite observed in the microstructure, which are part of the structure that forms during quenching and tempering of steel.

The overall microstructural composition of the AISI H13/W18Cr4V steel was composed of martensite, bainite, pearlite and Widmanstätten ferrite. The heat treatme