Study on SLM Forming Process, Residual Stress and Thermal Fatigue of 24CrNiMo Alloy Steel.

Yongsheng Zhao,Chenggang Ding,Yong Chen,Hui Chen

doi:10.3390/ma14164383

Yongsheng Zhao, Chenggang Ding + Show 2 more

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https://doi.org/10.3390/ma14164383

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Abstract

The selective laser melting (SLM) forming process of 24CrNiMo alloy steel was optimized by orthogonal experiment. The density and microstructure of the sample were analyzed, and the optimized process parameters were as follows: laser power 300 W, scanning speed 530 mm/s. The 24CrNiMo alloy steel samples were prepared with optimized parameters. The relationship between residual stress and thermal fatigue and the effect of stress-relieving annealing (SR) on residual stress were analyzed. The density of the sample was found to increase at first and then to decrease with the increase of laser power and then to decrease with the increase of scanning speed. Increasing the laser power and scanning speed widened and deepened the weld. Under the optimized process window, the formability of 24CrNiMo alloy steel samples was improved significantly. The residual stress distribution was tensile stress, which had a negative effect on the thermal fatigue properties of the sample. After SR, the residual stress changed to compressive stress, which had a positive effect on the thermal fatigue properties of the samples. Compared with the deposited state, the thermal fatigue cracks were significantly shortened after SR, which was able to further promote the improvement of thermal fatigue performance. The gradient residual stress test showed that the gradient residual stress in the edge region and the central region of the deposited sample had the same trend, and decreased gradually from the surface layer to the base layer.

Highlights

The 24CrNiMo low alloys, as a branch of Cr-Ni alloys, have been widely applied in the braking systems of the high-speed trains [1,2,3] due to their high corrosion resistance and excellent wear resistance [4] as well as their thermal fatigue resistance [5]
The results showed that the residual stress and distortion of all specimens focused on the effects of process parameters such as laser power, scanning rate and scansubjected to rescanning strategy were more serious than those of specimens without rescanning strategy on the microstructure and residual stress of 24CrNiMo alloy steel, but there ning strategy [20]
Alloy Steel shows test results of the first orthogonal. It can be the sample increases atdensity first and decreases with the increasetest of laser power in the seen that the density of the three groups of samples numbered

Summary

Introduction

The 24CrNiMo low alloys, as a branch of Cr-Ni alloys, have been widely applied in the braking systems of the high-speed trains [1,2,3] due to their high corrosion resistance and excellent wear resistance [4] as well as their thermal fatigue resistance [5]. With the increase in the speed of a high-speed train, the performance requirements of the brake disc [6] are improved . Some studies have shown that [7] the residual stress has an important influence on the thermal fatigue performance of the parts. The measurement of the residual stress of the brake disc is of great significance in evaluating the performance and service life of the brake disc

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Results

Conclusion