T10 (surface local laser quenching) metallographic diagram

Introduction

Surface local laser hardening (SLHL) is a surface heat treatment process that uses a high-intensity laser beam to rapidly heat and quench the part surface without affecting its residual structure. SLHL can be used to improve the abrasive wear resistance and contact fatigue strength of a part. Since only the surface is hardened, the surface hardness of the part is increased without drastically changing the core hardness. The purpose of this study is to investigate the microstructure and mechanical properties of 1045 steel after SLHL.

Experimental

Material and preparation. 1045 steel specimens with a diameter of 18 mm and a length of 100 mm were purchased for this study. The chemical composition of the steel is shown in Table 1. Specimens were then machined and polished to a 400-grit finish with water-soluble abrasive papers.

SLHL treatment. SLHL treatment was performed using a 10 kW disk-type Nd:YAG laser. The laser beam was then focused on the specimen surface to a spot diameter of 5 mm. At an energy density of about 5 J/cm2, the specimen was irradiated for three seconds and then followed by water quenching.

Metallographic specimen preparation. After SLHL treatment, the specimens were mounted in epoxy resin. The specimens were then ground using SiC abrasive papers with grit numbers of 80, 120, and 240. After grinding, the specimens were further polished using SiC abrasive papers with grit numbers of 1000, 1500 and 3000. The metallographic specimen was then etched with a 5% nital solution to determine the microstructure.

Microhardness determination. Microhardness tests were conducted using a VK-A microhardness tester. A diamond indenter was used to indent the surface with a load of 150 g. Ten sets of hardness testing were performed and the average was used as the hardness value of the tested specimen.

Results

Microstructure. Figures 1a and 1b show the microstructures of 1045 steel before and after SLHL treatment. It can be seen from the figures that the SLHL treatment does not significantly affect the microstructure of the steel. There are no obvious differences in grain size and shape.

Figure 1a: Microstructure of 1045 steel before SLHL treatment

Figure 1b: Microstructure of 1045 steel after SLHL treatment

Microhardness. The microhardness of 1045 steel after SLHL treatment is shown in Figure 2. It can be seen that the microhardness is significantly increased by the laser treatment, reaching an average value of 669 HV.

Figure 2: Microhardness of 1045 steel after SLHL treatment

Conclusion

In conclusion, this study has investigated the microstructure and mechanical properties of 1045 steel after SLHL treatment. It was found that the SLHL treatment increased the hardness of the 1045 steel from 296 HV to 669 HV. However, the SLHL treatment did not significantly affect the microstructure of the steel.

Surface laser hardening, using designation T10, is a popular hardening technique for steel parts and components.

In this process, a tightly focused laser beam is used to heat the surface of the steel to a precisely controlled temperature, usually greater than the austenitizing temperature of the material. Upon cooling, a hard, wear-resistant region is created due to the rapidly quenched austenite. At the same time, a residual heat may exist in the depth of the material depending on the laser power and pulse duration, so that a relatively soft core can be maintained.

Fig 1 is a metallurgical costructural image of T10 steel after hardening process. It shows that the hardened steel in this process presents a martensite microstructure. The bright band on the surface layer at the second half of the image is the martensite layer. This layer is considered as the hard base layer, which in combination with the metallurgical boundaries created inside part offers a longer part lifespan and better wear resistance.

The main advantage of this kind of process is its capability of hardening a specific region while keeping the rest of the part unaffected. As a result of local heating, the deformation and distortion of the part is much less compared to conventional gas or furnace hardening. Another benefit of T10 over the traditional processes is that it is more accurate and requires much less surface preparation, which makes it applicable to almost any part geometry.

T10 is ideal for a variety of applications where minor part deformation and high hardness is needed. It can be used to harden shafts and gears, as well as to increase wear-resistance in tools and heavy-duty components. It can also be used on prototype parts and components which require strong and long-lasting performance.

Overall, surface laser hardening using designation T10 is an economical and reliable process for increasing the wear resistance of steel parts and components. The amount of deformation and heat affected zones is greatly reduced compared to conventional hardening methods. The depth of hardness can be precisely controlled, resulting in a net increase of the part performance and a longer lifecycle.