| At present, the single performance of material is more and more difficult to meet the demand of the society. To combine different materials organicly has became the development trend of future materials. In view of the above trend, this paper designs a new precess to make the steel to produce gradient change by cntroled cooling of unidirectional cooling of steel. Surface profile with high strength, high hardness and high wear resistance organizations, such as the morphology of martensite and bainite, etc.Internal distribution has high toughness, good plastic tissue, such as ferrite andpearlite. The gradient distribution, both sides have their respective advantages of material micro structure and properties. The side of high strength, hardness can meet the demand of strength and wear resistance. High toughness, high ductility side, can meet the demand of toughness and deformation. Although there are differences between both organizations, but the difference is a gradual process. The bond strength between two layers of metallurgy is bond. So the gradient plate is a organic, unfied whole. Low alloy steel has low carbon content which meet the welding performance requirements. Therefore, the organization has a gradient distribution characteristics of thematerial can satisfy the gear, bearing and other parts required, wear resistance, high strength, high toughness, welding deformation, such requirement.This paper analyzes experimental results of transformation in steel during uniaxialcooling process by cooling the experimental steel. The organization of the material, hardness, toughness, lattice constant tensile properties showed a gradient distribution.In the hot rolling one-way control cooling conditions are verified on the law.And analysis of the effect of control rolling on the gradient structure. Finally, with the normal controlled rolling and mechanical properties of coldconditions were compared, analysis the effect of controlled rolling on mechanical properties of gradient materialimpact on the experiment of steel. Check cooling of the cooling rate and cooling temperature gradient distribution.(1) One-way cooling make the cooling rate and cooling temperature gradient distribution. The organization of low alloy steel appears gradient. Along the direction of the thickness,the grain size and microstructure composition be gradient. The more close to the cooling side, the finer the grain be, the more hard organization there is.(2) The gradient distribution of temperature and velocity of cooling make the diffusion rate of carbon and alloying elements be different. Although the microstructure is also a body centered cubic structure of steel, the steellattice constant along the thickness direction of the gradient change. Lattice constant difference between two sides of A# steel reached 0.008 at most.(3) The fast cooling side has higher solid solubility of alloy elements and carbon, finer-grained grain size, more bainite structure. The hardness is gradient in the thickness direction. The hardness of fast cooling side is higher than the slow cooling side water side by about 50MPa.(4) The fast cooling side contains more bainite and other hard organization. Slow cooling side contains more shaping good ferrite and pear lite. Both plasticity and strength are different. The tensile fracture surface of B# test steel shows that both sides of fracture has difference about 1.9μm.Even the fracture mode of D# test steel change from ductile rupture to ductile rupture-cleavage fracture.(5) Compared with the hot rolled homogeneous tissue, hot-rolled gradient of yield strength and tensile strength decreased. The yield strength of D# steel from 692MPa to 497MPa, the tensile strengthdecreased from 935MPa to 920MPa.Compaireed with uniform organization, yield strength of gradient structure yield strength ratiodecreased, yield strength of D# steel ratio decreased from 0.74 to 0.52,which prove that gradient structure has good forming ability. |
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