【正文】 st speed, quenching cooling after only extremely thin surface oxidation, are pale, parts, and still beautiful color saved a great deal of nitrogen and inert gas, so that treatment costs will decline further. Vacuum lowpressure carburizing bined with highpressure gas quenching is an advanced carburizing today, it has carburizing speed, excellent carbide organization ,quenching cracking and little deformation, saving energy and carburizing agent raw materials, carburized parts surface quality is good, be helpful for environmental protection etc. (Ⅱ ) heat treatment equipment: The trend of foreign heat treatment furnace development: (1) stove based on the power is increasing, oil for heat treatment furnace ratio decreasing. (2) To product surface quality request more strictly controlled atmosphere heat treatment furnace, this occupies an important position still. (3) Lining tends to use of lightweight materials, the application in resistance furnace with heatresistant ponent and nonmetallic furnace the proportion of heating elements increase gradually. (4) The microputer and PLC accelerates the development of heat, and have with the other automation line of automatic heat treatment process of trend. eccentric shaft failure forms and preventing measures Shaft loading: fatigue, impact, tensile, pression, bending, twisting, cutting, wear, surface changes, size changes, etching, corrosion and other failure modes. (1) eccentric shaft under heavy load at work, subject to bending stress, wear and tear in the neck, by the main have occurred wear fracture and axial crack two circumstances parts (2) axial crack, axial crack is eccentric shaft parts mon failure form, this crack except material adverse outside, main is caused by excessive heat surface tension stress caused by its quenchhardening ability, due to merger part weeks than axial tensile stress surface , and material surface tensile stress of lateral performance under longitudinal, prevent such hardening layer, and promptl y tempering. (3) Axis failure form: There are insufficient due to fatigue resulting fatigue fracture, static strength due to lack of plastic deformation or brittle fracture, wear, and exceed the allowable range of deformation and vibration. (4) axial fracture is mainly reverse fatigue fracture. Chapter II Theoretical analysis Heat Treatment of eccentric shaft Unified Digital Code: A20202 【 Chemical Composition】 ⑷ (mass fraction) (%) C: ~ Si: ~ M n: ~ Cr: ~ 【 Mechanical properties 】 Sample blank size (mm): 15 Heat buried: The first quenching temperature: 880 ℃ 。 Coolant: water, oil The second quenching temperature: 780 ~ 820 ℃ 。 Coolant: water, oil Tempering heating temperature: 200 ℃ 。 Coolant: water, air Tensile strength ≥ 835MPa Yield point: ≥ 540MPa LaSalle epigastria long rate: ≥ 10% Section shrinkage: ≥ 40% Shock absorption≥ 47J impact energy Brinell hardness (annealed or high temperature tempering state): ≤ 179 【 Main Special items】 Compared with the 15Cr steel , it has higher strength and its quenchhardening ability in oil critical quenching, up to 4 ~ 22mm diameter appearing in water to critical quenching of 11 ~ diameter 40mm lottery, but the firmware is poor, when the steel carburizing Grains are still growing tendency, when the direct quenching temperature on impact toughness of greater impact, so the secondary quenching after carburizing need to improve the toughness of the Ministry of parts heart, no temper brittleness。 steel, plastic strain of cold high in the cold state The following drawing。 machinability high temperature in the state of normalizing or quenching and good, but after annealing poor。 welding is good, generally do not need heat treatment after welding, but the thickness of the parts is greater than 15mm to be preheated before welding to the 100 to 150 ℃ . 【 examples Of Application】 This kind of steel is used mostly manufacturing heart the demand is higher, intensity of surface bear wear, section 30mm below in plex shape and load or small carburized parts (oil quenching machine), such as: transmission gear, gear axle, CAM, worm, etc. For small and high heat treatment deformation wear parts, carburizing should highfrequency surface after quenching, such as modulus is less than 3 gear wheel, bearing etc. 20Cr can also be used in conditioning condition, used to make the speed of work and under moderate impact load large parts, this steel also can be used as low carbon steel, martensitic quenching further increased the yield strength and steel tensile strength. Chapter Ⅲ experimental materials and experimental methods : Material for this study is the eccentric shaft 20Cr, 20Cr is the carbon content of % for the carburization of low carbon steel, 20Cr steel than carbon steel carbon content of the same strength and hardenability were clearly high, oil quenching to the semimartensitic hardenability of hardness for the φ20 ~ 23mm. Compared with the 15Cr steel has high strength and hardenability, the critical quenching diameter, oil is about 422mm, the water is about 1140mm, poor toughness, good welding, after welding as not need heat treatment. Uses: Most of hardened steel used for the manufacture of the Ministry of the heart require a higher strength, to withstand the friction surface, crosssectional size or shape of the 30mm less plex and less load carburized parts (oil quenching), such as machine transmission gear, gear shaft, cam, worm, etc., on the requirements of small and high heat deformation resistance of the parts after carburizing and high frequency surface hardening, such as modulus ≤ 3mm of gears, shafts and spline shaft. It can also be used in the quenched state, for the manufacture of mediumvelocity impact load larger