High strength carbon steel, treated with a high surface hardness and strength, but ductility, toughness is poor, moderate machinability, weldability, poor hardenability, water quenching has a tendency to crack formation. Material Name: High quality carbon structural steel Grade: 55 Standard: GB / T 699-1999 Features and Scope: general use after normalizing or quenching, used as requiring high strength and wear resistance or flexibility, dynamic load and impact load small parts, such as gears, rims, flat springs, crankshafts, etc., but also for casting. 2 Chemical Composition: Carbon C: 0.52 ~ 0.60 "Si Si: 0.17 ~ 0.37 Mn Mn: 0.50 ~ 0.80 Sulfur S: ≤0.035 phosphorus P: ≤0.035 chromium Cr: ≤0.25 Ni Ni: ≤0.30 copper Cu: ≤0.25 3 uses function test shaft parts, structural features and technical requirements shaft parts is one of the typical machine parts often encountered it is mainly used to support transmission and four tensile mechanical properties σb (MPa):. ≥645 (66) yield strength σs (MPa): ≥380 (39) Elongation δ5 (%): ≥13 Reduction of area ψ (%): ≥35 Hardness: no heat treatment, ≤255HB; annealed steel, ≤217HB sample size: Test Sample size is 25mm heat treatment and microstructure specifications: Heat treatment specifications: normalizing, 820 ℃; quenching, 820 ℃; tempering, 600 ℃ Delivery status: to no heat treatment or heat treatment (annealing, normalizing or tempering) Status delivery requirements heat treatment delivery should be specified in the contract, not indicated by not heat treatment delivery delivery status of steel hardness HBS10 / 3000, ≤ | no heat treatment of steel: 255 delivery status of steel hardness HBS10 / 3000, ≤ | annealed steel: 217