The Effect of Heat Treatment on the Fracture Toughness and Subcritical Crack Growth Characteristics of a 350-Grade Maraging
The heat treatment response of a 350-grade maraginf steel, with the nominal composition 18.5 Ni, 12 Co. 4.6 Mo, 1.4 Ti, balance le. has been determined in billet and bar form. When ■ged at temperatures below 90(rF, the material was very susceptible to subcritica! crack growth, and premature brittle Iracture occurred in unnotched tension specimens loaded at a slow strain rate in laboratory air. Fracture mechanics was used to interpret this behavior. The introduction of reverted austenite signiticantly decreased the strength level but had little effect on Iracture toughness. The resistance to brittle Iracture of this material is contrasted with that ot high-strength steels currently used by the airplane industry. INTRODUCTION F'he continuing demand lor ultra-high-strength steels prompted the recent development ol two 3S0-grade maraging steels. The development and properties of one alloy nominal composition P.5 Ni. i:.5Co. .VK Mo. 1.7 Ti. 0.15 Al. balance le were recently described ( I ). Vasco Metals, a subsidiary of I eledyne. Inc.. introduced a second alloy that is lower in titanium than the first to avoid segregation problems and has slightly higher nickel and molybdenum contents. Fn this paper, the effect of heat treatment on the fracture toughness and subcritical crack growth resistance of this second alloy is described.
The physical metallurgy of maraging steels
AbstractMaraging steels are a class of high-strength steels characterised by very low carbon contents and the use of substitutional elements to produce age-hardening in iron–nickel martensites. The term 'maraging' was coined from a combination of martensite and age-hardening.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.