The Behavior Of Hot Deformation And Heat Treatment Of 13Cr4Ni Martensitic Stainless Steel

13Cr4Ni super martensitic stainless steel has excellent weldability,corrosion resistance and good comprehensive mechanical properties.It is widely used in turbine blades,gas pipelines and offshore platforms.In this thesis,the thermal simulation machine was used to conduct uniaxial and single-pass compression deformation on the material under the deformation conditions of 850~1150? and 0.001~1 respectively.The evolution of the follow stress and microstructure steel during hot deformation were studied.Based on DMM model,the thermal processing diagram was drawn,and the material constitutive equation was established.The microstructure and mechanical properties of 13Cr4 Ni steel after quenching and tempering were studied by optical microscope,scanning electron microscope,XRD diffractor,impact and tensile testing machine.The main results and conclusions are as follow:(1)The follow stress increases with the increase of deformation temperature or strain rate during hot deformation of 13Cr4 Ni steel.When the material deformation in low temperature,the microstructure is the rod-like martensite,while the deformation in high temperature and the slower strain rate,the microstructure is the coarse equiaxed martensite.Both of the two microstructure states are not conducive to the strength and toughness of the material.Analysis the stress-strain curve,thermal deformation structure and thermal processing diagram,fine equiaxed structure can be obtained between the deformation temperature of 1100~1150? and the strain rate of 0.003~1.The Arrhenius hyperbolic sine equation was used to calculate the constitutive equation of 13Cr4 Ni steel under thermal deformation.(2)Study on quenching process.The influence of quenching and cooling on the strength and plasticity of materials was investigated.The influence of quenching temperature between 950?~1020? on the microstructure and mechanical properties of materials was studied.It was found that with the increase of quenching temperature,austenite grains gradually grew and coarsened,the strength of materials first increased and then decreased,and the quenched microstructure was 100% of the lath martensite.(3)Study on the first-stage tempering process of 13Cr4 Ni steel.With the increase of the firs-stage tempering temperature,the content of reverse austenite first increased and then decreased.After tempering at 620?,the volume of reverse austenite reached the maximum value of 8.3%,and when the tempering temperature was increased to 660?,the content of reverse austenite was almost zero.After tempering at 660?,the inverse austenite instability was transformed into fresh martensite.The results of mechanical test show that with the increase of the content of reverse austenite,the plasticity and impact energy of the material increase obviously and the strength decreases obviously.(4)Study on secondary tempering process of 13Cr4 Ni steel.Compared with first-stage tempering,the content of reverse austenite in steel can be greatly increased by secondary tempering.After second-stage tempering at 640?+600?,the maximum content of reverse austenite was 20.3%.EBSD characterization results show that large block inverting austenite is mainly distributed in trifurcated boundary,while the long strip or rod-like reverse austenite is diffusely distributed in matrix.As the content of reverse austenite in 13Cr4 Ni steel was significantly increased by second-stage tempering,its toughness was significantly increased while its strength was significantly decreased.