A comparative study on surface topography and microhardness of laser polished-hardened AISI D2 tool steel

Abstract

In this work, a laser polishing-hardening (LPH) method with integration and high efficiency for the treatment of AISI D2 tool steel was proposed, and the effects of laser hardening (LH), laser polishing (LP) and LPH treatments on the surface topography and microhardness were examined. The results show that LH method had a negligible effect on the surface roughness of the treated sample, while the surface roughness Ra of LP and LPH specimens was reduced by 74.6% and 80.9% respectively, indicating that the milled surface topography had been significantly improved, especially LPH was more effective in reducing the roughness. Besides, the polishing efficiency of LPH was 10 times that of LP approach. In terms of hardness improvement, the near-surface microhardness of LH and LPH samples increased by 1.5 times and 1.3 times respectively, and the effective hardened zone (EHZ) depth was 0.42 mm and 0.24 mm respectively, demonstrating that these two laser processing methods had a beneficial effect on the cross-section microhardness of D2 tool steel, while the increase of LP on the microhardness was insignificant. The comprehensive analysis of the surface morphology and microhardness of LPH specimen indicates that LPH was a feasible laser surface treatment method for D2 tool steel. On the premise of ensuring a high surface finish, the polishing efficiency can be remarkably improved, the subsurface microhardness and EHZ depth of processed specimen can be also significantly enhanced, which provided a feasible idea for the application of laser surface treatment technology in industrial mold production.

Control of the metallographic and mechanical properties of Cr8 cold-work die steel by laser continuous/dispersed quenching

“…During the rapid cooling process, more carbon atoms diffuse out of the crystal at a high diffusion rate, resulting in the precipitation of nanoscale carbides at the martensitic boundaries. This is consistent with the distribution of precipitated carbides[5].…”

“…Cr8 steel (ASTM D3M) is a commonly used alloy tool steel, due to its high hardenability and excellent comprehensive mechanical properties, which widely was used in the manufacture of cold-work mold, such as draw dies, stamping dies, cold extrusion dies and powder compacting dies, etc [1][2][3][4]. Meanwhile, it is also placed on high expectation in the modern high-performance vehicle high-strength steel parts stamping production [2,5]. During actual use, the surface of the mold to withstand the impact and high stress can easily give rise to fatigue fracture and small chipping [6][7][8][9].…”