| Maraging stainless steels is an category of alloys that consist of ultra-low C,and basic elements of Fe,Cr,Ni and Ti(Al).They can achieve ultra high strength combined with high toughness by heat treatment of martensitic transformation and subsequent aging in which finely dispersed Ni3Ti particles precipitate on the martensite matrix.Maraging stainless steels have been widely used in the high tech industries such as airplane,aerospace,nuclear energy and medical instrument.Surgical suture needle is one of medical consumables in large quantity and is traditionally made of 3Cr13 stainless steel.Brittleness is a serious problem for the traditional 3Cr13 suture needle.Our laboratory has long involved in the study of maraging stainless steel of 00Cr12Ni9Mo4Cu2Ti alloy and attempted its application for the manufacture of suture needle.00Cr12Ni9Mo4Cu2Ti is a maraging stainless steel developed in 1990s by Sandvik,Sweden.It is strengthened by the dispersed precipitation of Ni3Ti nano particles.Recently,A1 element was reported to be additionally added in the alloy to further improve its mechanical properties.In the present study,a group of 00Cr12Ni9Mo4Cu2TiAl alloys was obtained with various Ti/Ti+Al ratio in order to evaluate the performance of the Ti-Al synergistic strengthening of the alloy,with focus on the hardness and toughness after age hardening.The experimental results the Ti-Al maraging stainless steel showed that:(1)The Ti/(Ti+Al)ratio of the alloys plays important role on hardness.The higher the Ti/(Ti+Al)ratio,the higher the hardness and the lower the toughness;(2)The hardness of Ti-Al strengthened martensitic stainless steel increases first and then decreases with the increase of aging temperature,with 475-525°C being the best temperature range for hardness.Toughness increases with the aging temperature first increased and then decreased,with 525-600? being the best temperature range for toughness.From the overall mechanical properties of view,aging treatment at 525 ?can obtain optimal combined strength and toughness.The study of the aging brittleness revealed that:(1)The aging brittleness of 00Cr12Ni9Mo4CuXTiX maraging stainless steel first increases and then decreases with the increase of aging temperature.The maximum value of brittleness(the minimum of the work of rupture)appeared in the range of 425-475 ? while the maximum hardness appeared in the range of 475-525°C.The two temperatures do not coincide at the same range as expected.So,in order to obtain the best performance of the materials,they should be aged at the peak-aging or over-aging regime.The under-aging regime that causes brittleness,should be strictly avoided;(2)Within 30 minutes of aging time,the mechanical properties of OOCr12Ni9Mo4CuXTiX maraging stainless steel appears instable and recoverable fluctuations.Within 120 min,the effect of aging time on the hardness levels off.In this respect,to obtain a more stable toughness,aging time should be at least 60 min or more. |
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