The development of non-quenched steel has gone through three stages.
The development of non-quenched steel has gone through three stages. The first generation of non-quenched steel is ferrite.Pearlite type non-quenched steel.The second generation is bainian type non-quenched steel.the third generation is low carbon martensionic type non-quenched steel.
Ferrite – pearlescent non – tempered steel.
At present, the largest amount of non – tempered steel, about 60% of the total amount.Compared with tempered steel, it has more strength than toughnes.So it is necessary to improve the toughness under the condition of guaranteeing the strength.
Development of non-quenched steel-Nippon steel
The Nippon steel researchers found,by properly controlling the production process.the austenite crystals were allowed to form a large number of ferrite nucleating cores.Then ferrite is formed not only in grain boundary, but also in austenitic crystal package.
These fine, evenly distributed ferrites make the steel remarkably more ductile.
Bayesian type non-tempered steel
It is a kind of strength and toughness is very good non quenched and tempered steel.In order to make the air cooling after forging can get bainite organization, after joined the molybdenum, manganese, boron in steel and other alloy elements.
The effect of manganese
When the content of it to a certain extent can make austenitic isothermal transformation curve is in the shape of epsilon to separate the steel C curve up and down;Boron can significantly delay ferrite transformation.
The combination of molybdenum of development of non-quenched steel
To boron or manganese – boron results in the bainite structure of steel over a wide cooling range.At the same time, manganese can reduce the phase change temperature.improve the toughness and enhance the strength.
Elements such as vanadium and chromium,they are usually added to low carbon bainitic steel,For makeing up for the decrease in strength caused,by the decrease in carbon content.
Martensioned non tempered steel
(1)
In 1988, an American steel company,first proposed the concept.third-generation non-tempered steel with low carbon tempered martensitic structure.
Similar to bainitic non-quenched steel, low carbon martensitic non-quenched steel has high toughness,as well as high strength.It has already been used in automobile walking parts and construction machinery.
(2)
At the same time, after the development and application of ferrite – pearlite (f-p), bainite (B), martensitic (M) non-quenched steel, ferrite – bainitic (F- B), ferrite – martensitic (F- M), composite phase non-quenched steel is gradually developed,and used because of low cost and excellent performance.
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