Influence Of Different Additives On Microstructure And Properties Of Stainless Steel Specimens By Laser Rapid Forming

With the development of society and the improvement of science and technology, allwalks of life to flourish, to meet requirements of the various fields of military, civil,aerospace and so on, people put forward a higher challenge on the properties of thematerial, it is very urgentment to produce the high-properties materials that can meet theneeds of various industries. Laser rapid forming is began to be developed in the1990s,it isa new type of modern advanced manufacturing technology, it can quickly achieve highproperties dense metal parts of the complex structure of near-net shape without mold,combined with the technology molding process has the characteristics of rapid heating andrapid cooling, the manufactured parts generally have a fine microstructure and higherdensity, the comprehensive mechanical properties compared to the same conventionalcasting machining parts have greater advantage, more can meet the properties requirementsfor different service environment on the material.This article is mainly aimed at microstructure, static mechanical properties and fatigueproperties of specimens made of304austenitic stainless steel powder through laser rapidforming technology, which is added trace CH compounds, borax and a small amount ofNi60AA powder in different proportion. After the304austenitic stainless steel specimensof laser rapid forming were studied, and it is found that the comprehensive mechanicsproperties is relatively good, while the hardness is slightly low. The laser rapid formingexperiment of420martensitic stainless steel powder is proposed in order to meet the otherrequirements of high hardness occasions, and surface rockwell hardness is studied beforeand after the high frequency forging. The microstructure was observed by OM and SEM in304stainless steel specimens; Using vickers microhardness tester to study the vickersmicrohardness of304stainless steel specimens;Using rockwell hardness tester to study the surface rockwell hardness of420martensitic stainless steel specimens before and after thehigh frequency forging；Using universal testing machine to study the tensile strength andelongation of304stainless steel specimen， and analyse morphology by SEM andcomponent by the spectrum analyzer of the fracture of the tensile specimens；Using fatiguetesting machine to study the fatigue properties of304stainless steel specimens. Theexperimental results showed that:(1)From the microstructure figures of304austenitic stainless steel specimen of laserrapid forming, we can see that the microstructure of the specimens of304stainless steel isalong the direction of temperature gradient dendritic growth of rules and some fine grainarea without adding Ni60AA powder; However, the microstructure of the specimens of304stainless steel with adding Ni60AA powder is mainly presented herringbone, and itssecond phase is obvious.(2) With304austenitic stainless powder added into the CH compounds, the vickersmicrohardness of specimens of304austenitic stainless steel of laser rapid forming isgreatly improved, and with the increase of the content of CH compound,vickersmicrohardness of the specimens also are improved accordingly. However, on the basis ofadding CH compounds, when the mixed powder is added into a certain amount of Ni60AApowder, vickers microhardness of the specimens obtain further improvement again, andwith the increase of content of Ni60AA powder, vickers microhardness of the specimensare improved accordingly.(3) Before micro forging, the hardness of ratio of different components of420stainless steel specimens have a very big difference, and as the decrease of percentage of420powder in the molding powder, the surface rockwell hardness of the specimengradually decline. However, after high frequency micro forging processing, the averagesurface rockwell hardness value of ratio of different components of420stainless steelspecimens is improved and exceed55HRC. (4)With304austenitic powder added to CH compounds, the tensile strength ofspecimens and elongation have been greatly improved, and tensile specimens happenedgreat plastic deformation before fracture which belongs to ductile fracture; However, onthe basis of adding CH compounds, when the mixed powder is added into a certain amountof Ni60AA powder, the tensile strength has been greatly improved again, and with theincrease of Ni60AA content in the specimen, the tensile strength of specimen is higher andhigher, while the elongation is more and more lower. The tensile specimen has little or noplastic deformation before fracture which belongs to brittle fracture.(5) The specimens of304stainless steel with adding Ni60AA powder have a low loadcoefficient, but its Fatigue strength is almost equal with the ordinary304stainless steelsheet and the specimens made of pure304stainless steel powder. The fatigue strength ofthe forming specimen of304stainless steel added CH compounds and borax is487MPa to505.26MPa, which is higher than the ordinary304stainless steel sheets more than13%,and its load coefficient is0.8~0.83.