Combination of High Yield Strength and Improved Ductility of 21Cr Lean Duplex Stainless Steel by Tailoring Cold Deformation and Low-Temperature Short-Term Aging

Proper matching of cold-rolled deformation and low-temperature short-term aging can simultaneously enhance the strength and ductility of the lean duplex stainless steel. To investigate this, the microstructure evolution of cold-rolled and aging steels was observed by using scanning electron microscopy, transmission electron microscopy and electron backscattered diffraction. Additionally, the phase volume fraction was measured using X-ray diffraction. In this study, it was observed that the elongation of 21Cr lean duplex stainless steel significantly increased to 16.7% after undergoing moderate cold deformation (~ 40% reduction) and subsequent aging treatment at 550 ℃ for 30 min. Remarkably, the material still maintained a high yield strength of 1045 MPa. Such an excellent mechanical property was attributed to a unique microstructure combination of fine α'-martensite, twins, coarsened austenite resulting from partial martensite reverse transformation, and two-phase fine layered structure. The result of this study may open up new horizons for the alloy development in order to overcome the low ductility of cold-rolled high-strength lean duplex stainless steel.

Designing gradient nanograined dual-phase structure in duplex stainless steel for superior strength-ductility synergy

Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel,thus facilitating a superior strength-ductility synergy:a yield strength of 1009.5 MPa being two times higher than that of the as-received sample,a total elongation of 23.4%and a uniform elongation of 5.9%.This novel structure is produced through a processing route of ultrasonic severe surface rolling and annealing,which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite.During the tension deformation of gradi-ent nanograined dual-phase structured duplex stainless steel,a significant accumulation of geometrically necessary dislocations occurs.These dislocations are formed to accommodate the deformation incompat-ibility caused by the layer-by-layer difference in strength and hardness of individual phase domains,as well as the inherent difference in properties between the austenite and ferrite domains.This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties.Our study provides a new avenue to develop advanced steels with high strength and ductility.

High-Temperature Creep Behavior and Microstructural Evolution of a Cu-Nb Co-Alloyed Ferritic Heat-Resistant Stainless Steel

The creep behavior of Fe–17 Cr–1.2 Cu–0.5 Nb–0.01 C ferritic heat-resistant stainless steel was investigated at temperatures ranging from 973 to 1123 K and stresses from 15 to 90 MPa.The evolution of precipitates after creep deformation was analyzed by scanning electron microscopy,energy dispersion spectrum,and transmission electron microscopy.The minimum creep rate decreased with the decrease in the applied load and temperature,thereby extending the rupture life.Cu-rich phase and Nb-rich Laves particles were generated in dominant quantities during the creep process,and the co-growth relationship between them could be detected.Creep rupture was featured by ductile fracture with considerable necking.As increasing the temperature and decreasing the stress,the softening of the metal matrix was accelerated,showing more obvious plastic fl ow.The true stress exponent and activation energy were 4.9 and 375.5 kJ/mol,respectively,indicating that the creep deformation was dominated by the diffusion-controlled dislocation creep mechanism involving precipitate-dislocation interactions.Based on the creep rupture data obtained,the Monkman–Grant relation and Larson-Miller parameter were established,which described the creep rupture life for the studied steel well.

Achieving Superior Strength and Ductility of AlSi10Mg Alloy Fabricated by Selective Laser Melting with Large Laser Power and High Scanning Speed

AlSi10Mg alloy was prepared by selected laser melting(SLM)in a high laser power range 300–400 W.The effects of energy density on the relative density,microstructure and mechanical properties of the SLMed AlSi10Mg alloy were studied.The results showed that the SLMed AlSi10Mg alloy fabricated at a laser power of 400 W and a scanning speed of 1800 mm/s had a relative density of 99.4%,a hardness of 147.8 HV,a tensile strength of 471.3 MPa,a yield strength of 307.1 MPa,and an elongation of 9.6%,exhibiting excellent comprehensive mechanical properties.The unique combination of the melt pool structure and microstructure caused by the large laser power and fast scanning was responsible for the excellent performance.The wide and shallow melt pool structure with few defects and proper overlapping between the continuous melt pools were obtained.The growth of columnar crystals was inhibited by a large proportion of equiaxed grains formed at the border of melt pools,and numerous sub-structures were observed within theα-Al grains.This study provided a more efficient process parameters for the preparation of the SLMed AlSi10Mg alloy.The enhanced mechanical property will help to broaden the application of the AlSi10Mg alloy in industry.

Cu-rich nanoprecipitates modified using Al to simultaneously enhance the strength and ductility of ferritic stainless steel

1. Introduction Nanoprecipitation strengthening has always been a concern in steel materials, and this approach is one of the most proven and effective strengthening methods [1–3]. However, the increase in strength due to the nanoprecipitates often corresponds to a decrease in ductility [4,5], and this conflicting relationship between strength and ductility has attracted the attention of researchers,who have sought to find a balance between strength and ductility [6–8].