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Welding-Induced Brittleness Susceptibility in Mo-V-Ti-N Microalloyed Steel and Metallurgical Methods for Restraint

Author: XuWenWen
Tutor: WangQingFeng
School: Yanshan University
Course: Materials Science
Keywords: VN micro-alloyed steel Welding Heat-affected zone Notch toughness Fracture M - A component Multi-phase structure Micro-hardness
CLC: TG142.15
Type: Master's thesis
Year: 2009
Downloads: 100
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Abstract


In this paper , in order to study the low-carbon Mo - V - Ti - N micro- alloy structural steel welding embrittlement tendency and its suppression method to prepare a typical increase in N ( 120ppm ) plus B alone ( 12 ppm ) and Nb ( 210 ppm 17 ppm ) composite Add the three trials steel and prepared samples of each test steel in different T8 / 5 ( 100s ) under simulated coarse grain heat affected zone ( CGHAZ ) by Gleeble3500 thermal simulation mechanism . For each sample observation optical microstructure , and Statistics morphology parameters ; structure of martensite - austenite ( MA ) component brittle phase transmission ( TEM ) was observed ; nanoindentation test MA and near the substrate marks hardness ; tested -20 ° C in the V-notch ( CVN ) impact energy of the sample , scanning ( SEM ) morphology of fracture and secondary cracks was observed . The results showed that , in the Mo-V-Ti-N steel CGHAZ the multiphase organization formed with MA . Its microstructure, hardness and fracture characteristics is increased trend follower t8 / 5 : reduce the number of bainitic ferrite (BF) and acicular ferrite (AF) , first eutectoid ferrite (PF) the increase in the number ; the morphology of the MA from the strip to the massive evolution , the size increases , the degree of dispersion decreases , the internal structure of the evolution of the twinned martensite from the retained austenite to martensite , the difference in hardness of the matrix near the increase ; CVN impact energy is reduced , the fracture morphology of quasi-cleavage brittle fracture evolution from the dimple ductile fracture . Further, in a very small amount of boron added to the Mo - V- Ti - N steel , by inhibiting the transformation of the PF , and promote acicular ferrite and granular bainite is formed , so that the MA can t8 / of 5 under CGHAZ in decreased size reduction , improved dispersion , impact toughness improvement . Therefore , Mo-V - Ti - N steel welding embrittlement tendency to vary depending on the the element MA containing CGHAZ multiphase organization of the micro - structure and micro-hardness characteristic , adding trace suppression method is the use of small heat input welding or steel in boron.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Steel > Microstructure and properties of steel > Analysis of the steel test
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