**4.4 Microstructure of laser micromachining**

**Figure 18** shows the cross-section micrograph of laser-micromachined specimen. Obviously, the processed substrate is altered and can be detected directly. The smoother processed surface is achieved by laser micromachining with the microstructure variation as shown in **Figure 18a** labeled as zone A. Zone A, known as the hardened layer, distributes certainly enlarged and spheroidized carbide particles (high magnification in **Figure 18a**). Compared with **Figure 18a** and **b**, there are finer spheroidized carbide particles distributed in the matrix of ferrite as shown in zone B. Consequently, the property of the processed surface of the mold or die is improved to meet well with the practical applications. The heat-affected zone (HAZ), zone C, is shown in **Figure 18b** and **c**. The microstructure of the substrate, zone D, is shown in **Figure 18c**. Comparing **Figure 18c** with **Figure 3**, the microstructure does not change and keeps the same. Furthermore, the microstructure shown in zone C is almost the same as that shown in zone D, which means the energy input into the substrate by laser micromachining is too low to effectively change the mechanical property of materials. Additionally, the average thickness of zone A and zone B is �40 μm as shown in **Figure 18a**, while the average thickness of zone A is about 10 μm. As a result, the machined surface is suitable for microindustry application.
