Precipitation behaviour and strengthening mechanisms of V-bearing 1800 MPa grade hot-stamping steel

Abstract

Achieving strength-ductility synergy of hot-stamping steel via microalloying technology has attracted great attention due to their pronounced precipitation strengthening. Nevertheless, the precipitation behaviours and characteristics have not been clearly unveiled. In this work, the effects of V content on the microstructure and mechanical properties of 1800 MPa grade hot-stamping steel are systematically studied. Massive V contained precipitates develop after hot-rolling and coiling, which refine the martensitic microstructure and retain in the matrix after austenitizing and quenching. The refined martensite with massive precipitates is responsible for the good mechanical properties. Generally, the tensile strength decreases slightly with increasing V content from 0.04% to 0.2%, as V consumes C in the martensite matrix by forming carbides and promoting precipitate coarsening.

Multi-Scale Microstructural Tailoring and Associated Properties of Press-Hardened Steels: A Review

“…Generally, the steel grade and strength level of traditional Mn-B steel is determined by the C content, as presented in Table 1 . For example, 30MnB5 and 34MnB5 have C contents of 0.30–0.31 wt% and 0.33–0.34 wt%, respectively, and their corresponding tensile strength can reach 1880 MPa and 1980 MPa [ 20 , 39 ]. More recently, there have also been considerable research efforts devoted to developing PHS with even higher strength, such as 0.38% C content corresponding to a tensile strength of 2181 MPa [ 10 ].…”

“…These elements are strong carbide formers [ 45 , 46 ] and tend to segregate [ 47 ] at interphase, which can cause a precipitation-strengthening effect and solute drag in PHS [ 48 ]. In our recent work, the precipitation behavior of microalloying elements in PHS is unveiled [ 20 ]. It is found that the microalloyed carbides mainly precipitate during hot rolling and coiling, as a result of the low solid solubility of microalloying carbides in ferrite.…”

“…Furthermore, other examples also show that increasing microalloying elements may harm mechanical properties [ 34 , 40 , 55 , 56 ]. Recent work on V-bearing PHS has shown that increasing the V content from 0 to 0.2% can consume more C in the solid solution of martensite matrix and cause precipitate coarsening, resulting in reduced strength [ 20 ]. Additionally, Zhang et al [ 54 ] suggested that the grain refinement resulting from microalloying carbonitride is another critical factor affecting strength.…”

“…In addition to multiple interfaces, a high density of dislocations at the level of 10 15 m −2 is another significant feature, and this provides a maximum strengthening effect for PHS. Specifically, dislocation strengthening can contribute to a strength increase of 700–1000 MPa [ 20 , 34 ]. Hence, as with most martensitic steel, high-density dislocations are crucial to the attainment of high strength [ 35 ].…”

“…Hence, as with most martensitic steel, high-density dislocations are crucial to the attainment of high strength [ 35 ]. In addition to grain refinement strengthening and dislocation hardening, the main strengthening mechanisms are precipitation hardening, principally from microalloying carbides and solid-solution strengthening predominantly caused by interstitial C element [ 20 ]. Therefore, the high strength of PHS results from the synergistic effect of multiple strengthening mechanisms.…”