A Study On Mechanical Properties Of 40crni2mo Steel At Low Temperatures

40CrNi2Mo steel is a kind of medium carbon low alloy high strength steel, it is widely used in mechanical parts and structural parts.For steel containing Cr, Mo, Ni elements, its hardenability is better than others, when processing generally through annealing to reduce hardness, conventional heat treatment is mainly quenching and tempering.With industrial development, more and more to be quenched and tempered steel used in low temperature environment, and steel under low temperature environment will change the organization, which will bring tremendous damage for production and life. Visibly, study for the mechanical properties of 40CrNi2Mo steel under low temperature environment appears particularly important for outdoor machinery at low temperature areas.Based on the modal 40CrNi2Mo tempered steel for research object, low-temperature tensile test method for performance, this article used low tensile test method for performance study, and get law of the main properties (σs,σb,ψ,δ) for 40CrNi2Mo steel changing along with temperature. Series impact tests method was carried out to measure the series impact energy, thus giving a brittle transition temperature curve. The ductile-brittle transition temperature of the steel was determined according to the integrated energy consumption and fracture morphology of the tested samples. Used 40Cr,45 tempered steel as sample to take comparative tests of performance.(1) Yield strength and tensile strength of the 40CrNi2Mo steel elevate as the temperature reduces, contraction of area and elongation percentage reduce as the temperature reduces, and they change as linear relationship with the temperature. In addition, the article has also extracted the expression which is about yield strength and ultimate strength of the 40CrNi2Mo steel changing along with temperature.(2) Through taking the comparative tests of performance for the 40Cr,45 tempered steel , get the conclusion that: Yield strength and tensile strength of tempered steel elevate as the temperature reduces, and change as linear relationship with the temperature; elongation after fracture and contraction of area reduce as the temperature reduces, which indicates that: with the temperature reduces, plastic of tempered steel declines.(3) By series impact tests method, detected that ductile-brittle transition temperatures of the 40CrNi2Mo steel, 40Cr steel and 45 steel are -125℃, -50℃and -40℃respectively.