Research On Cryogenic Technology Application In High Alloy Steel

As traditional structure materials, the steel is still irreplaceable in the foreseeable future. In the 21st century, higher requirements are put forward on steel materials strength, service life and reliability, on account of high-rise buildings, large span overloaded bridge, lightweight and fuel-efficient cars, deep well drilling and large diameter oil (gas) pipe, large engineering machinery, large high-performance ships et al. In recent years, cryogenic technology has attracted much attention because liquid nitrogen is wide and non-pollution as cold source, and remarkable effect has been showed in improving steel material comprehensive performance. Because cryogenic technology was widely studied in metal material field, with the dominant tool material high speed steel as research object, the relationship between strong toughness and microstructure of high speed steel under cryogenic treatment will be explored in this paper. In addition, fine-grain strengthening is one of the methods which can improve strength and toughness at the same time among various kinds of strengthening methods. With the progress of technology, the smaller is the minimum grain size to achieve. Cryorolling technology is a new material processing technology developed in recent years, which showed significant effect on such aspects such as refining material microstructure and improving the strong toughness. In view of the austenitic stainless steel was coarse grains and low strength in the regular production, the research idea to realize ultrafine grains through cryorolling and short annealing was presented to increase the strong toughness of austenitic stainless steel greatly. The main contens of this paper are as follows:(1) The different cryogenic treatment processes have been conducted on W6Mo5Cr4V2 high speed steel. Also, the influence of traditional process and cryogenic treatment on the microstructure, content and size distribution of carbides, content of residual austenite have been studied. At the same time, the influence on microstructure between cycle cryogenic treatment and a long time cryogenic treatment have been contrastive analysised. Compared with traditional process, the microstructure of martensitic matrix is refined in cryogenic treatment samples, and the content of residual austenite is reduced. With the decreasing of cryogenic treatment temperature, the size of ultrafine carbides precipitated from matrix decreases. Compared with a long time cryogenic treatment, the matrix microstructure is refined, the size of secondary carbides decreases, the content of carbide precipated is more through cycle cryogenic treatment. The content of secondary carbides, in which was treated at-150℃(123K) by 3 times every 1h, is higher about 8% than samples with a long time cryogenic treatment.(2) The mechanical property tests of different cryogenic treatment have been conducted on high speed steel samples. And the influence of different cryogenic processes on high speed steel hardness, impact toughness and wear resistance has been studied respectively. With the decreasing of cryogenic treatment temperature, the hardness of samples increases. Compared with the traditional process, the hardness increment with -180℃(93K) treatment is 2 times higher than that with -120℃(153K) treatment. The hardness of cycle cryogenic treatment samples is higher than a long time cryogenic treatment. Also, the impact energy and wear resisitence at room temperature is higher after cryogenic treatment.(3) At laboratory conditions, different ways of cryorolling and annealing treatment have been conducted on 304 austenite stainless steel samples, and the influence of cryorolling reduction rate, annealing temperature and time, cycle annealing treatment process on stainless steel microstructure has been studied. Results show that, the grain size increases with the increasing of annealing temperature, and the influence of annealing temperature on grain size is higher than annealing time. The grain size of cycle annealing treatment is smaller than once annealing treatment, the grain size with 65% cryorolling reduction rate, is half of that with once annealing treatment. And the proportion of inversed phase transition increases, grain distribution is more uniform.(4) The mechanical property tests of different cryorolling processes have been conducted on austenite stainless steel samples. The influence of cryorolling process on the strong plastic product, vicker hardness, macro texture and micro texture of stainless steel has been studied respectively. Results show that, the strong plastic product of stainless steel samples increases along with annealing temperature and reduction rate increasing, the strong plastic product of samples with cryorolling and annealing are more than 20000MPa%. With the increasing of annealing temperature, the hardness of samples decreases. The hardness of samples with cryorolling and annealing are more than 280HV10. After annealing treatment, α and γ orientation line density of stainless steel samples are weaken with the increasing of annealing temperature.