Development of hot stamping grade steel with improved impact toughness by Nb microalloying

Herein, M2 high‐speed steel (HSS) samples with different Ta contents are prepared on #45 steel substrates by a laser additive manufacturing process. The microstructure and mechanical properties of the samples are systematically studied under five different Ta contents. Scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction (XRD) analyses show that the microstructures of the samples comprise equiaxed crystals, cellular dendritic structures, and reticular eutectic carbides. The samples are mainly composed of supersaturated martensite, retained austenite, and MxCy‐type carbides. The microstructures and mechanical properties of the samples are greatly affected by Ta alloying. After the M2 HSS is alloyed with 1 and 2 wt% Ta, obvious grain refinement occurs and the amount of retained austenite decreases; as a result of these microscale changes, the microhardness increases by 2.9% and 7.2%, the impact toughness increases by 12.4% and 17.4%, and the wear resistance increases by 75.74% and 25%.

Section: Resultsmentioning

confidence: 96%

Effect of Tantalum on the Microstructure and Mechanical Properties of M2 High‐Speed Steel Prepared by Laser Additive Manufacturing

Wang

Chen

Zhang

2020

“…The friction coefficients increased rapidly in a short period of time because friction generally goes through three stages, and the first is the running‐in wear stage. [ 18 ] For the small point contact between the grinding ball of Si3N4 (HV = 1700) and the surface of the sample, the actual contact area was small, and micro‐scale peaks on the surfaces were gradually worn away, which led to a rapid increase in the friction coefficient at the beginning. After the increase of the friction coefficient curves of the samples, there was a very short period of decline and a transition to a relatively flat trend when friction and wear entered a stable wear stage.…”

Section: Resultsmentioning

confidence: 99%

“…Adding alloying elements is the method most commonly used by many researchers to improve some performance characteristics. Murugesan et al [ 18 ] refined the grain size and improved the hardness and impact toughness of steel by adding elemental Nb to the steel. Wang [ 19 ] improved the hardness, wear resistance, and impact toughness of M2 HSS by adding different proportions of Ta.…”

Section: Introductionmentioning

confidence: 99%

Effect of Vanadium on Microstructure and Mechanical Properties of M2 High‐Speed Steel Prepared by Laser Metal Direct Deposition Forming

Chen

Zhang

2021

Herein, M2 high‐speed steel containing vanadium is prepared by laser metal direct deposition forming technology, and the effect of vanadium alloying on the microstructure and mechanical properties of M2 HSS is preliminarily explored. Five kinds of M2 HSS samples with different V contents are prepared on substrates of #45 steel. The macromorphology, microstructure, and phase composition of the samples are characterized and analyzed by scanning electron microscopy energy dispersive spectrometry, and X‐ray diffraction. The M2 HSS samples are mainly composed of martensite, residual austenite, and M2C carbides. After adding different proportions of vanadium, because vanadium is a strong carbide forming element, it is easy to combine with carbon to form MC carbide, resulting in the transformation of carbon‐poor matrix from martensite to ferrite, which makes the microhardness of the sample decrease. After alloying with 2, 4, 8, and 12 wt% V, the grain size is significantly refined due to the precipitation of MC carbides at the grain boundaries, which pinned and inhibited the growth of austenite grains. In terms of wear resistance, the amount of wear decreased by 34.41% for the M2 + 2%V sample and increased for the other V‐modified samples relative to M2 HSS. The impact toughness increased by 9.16%, 85.50%, 51.91%, and 25.19%.

“…Applications of Nb in other steel grades provided some evidences about the evolution of toughness. Murugesan et al [ 12 ] studied a low carbon steel sheet with 0.09%Nb at laboratory and found that the toughness increased from 32 to 41 J because of the significant refinement of martensite laths. Zurutuza et al [ 13 ] added 0.026%Nb in a quenched and tempered 15MnB steel and found that the upper‐shelf impact energy increased by 4 J due to microstructural refinement.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Toughness of High‐Temperature Carburizing Gear Steel via Refining Twin Martensite and Retained Austenite by Nb Microalloying

Wan

Jiang

et al. 2022

High‐temperature carburizing technology is replacing traditional carburizing technology due to energy savings and emission reductions. However, further effort is required to understand the mechanical properties for practical high‐temperature carburizing. Herein, the microstructures and mechanical properties of the 20MnCr5 gear steel with different Nb contents after carburizing at the temperature from 900 to 950 °C and the corresponding holding time from 8 to 5 h are investigated. For a given steel, the toughness slightly decreases with the carburizing temperature because of the increase of prior austenite grain size. For high‐temperature carburizing, the impact energy increases from 45.9 to 84 J after Nb microalloying. The toughening mechanism is analyzed through theoretical discussion and various characterizations of fracture morphology and microstructure. It is indicated that the refinement of prior austenite grain caused by the solute drag effect of Nb leads to the refinement of acicular martensite and retained austenite. The combined effect of microstructure refinement results in the significant enhancement of impact toughness and accompanies by coordinated plastic deformation. The fracture spreads along the martensite blocks due to the decrease in the thickness of twin lamellas in acicular martensite, which also contributes to the enhancement of toughness.