Structure Of Lower Bainite Research Articles

Effect of Copper on the Toughness of Ductile Cast Iron with Lower Bainite Structure

Effect of Copper on the Toughness of Ductile Cast Iron with Lower Bainite Structure

Characteristic features of the failure of heat-treated leaf spring steels 65G and 60S2A

1. Spring steels 65G and 60S2A with a lower-bainite structure (isothermal hardening) are characterized by intercrystallite fracture and a discontinuous, intermittent failure, which corresponds to the serrated section on the failure diagram. In the steel with a structure of tempered martensite (quenching+tempering), failure occurs monotonically. 2. It can be assumed on the basis of analysis of the structure of the isothermally treated steel that discontinuous crack growth may be caused by the martensitic transformation of sections of residual austenite under stress in the crack tip. 3. The crack resistance of the isothermally treated steel is lower, and the resilience and relative elongation higher than those in the quenched and tempered steel.

鋼のオーステナイト相の変態によって生成する各種組織の研削特性 恒温変態によって生ずるベーナイト組織の被研削性 Ｉ

In the present study, isothermal transformation temperature, θISO of the carbon steel was changed and grinding force, grinding temperature, grinding ratio, surface roughness, and thickness of ground surface layer of the upper and lower bainite steel were investigated. The results are as follows: (1) Grinding force, grinding temperature and thickness of ground surface layer reduce to the minimum around the boundary temperature θISO of upper and lower bainite structure, whereas grinding ratio increases around this temperature. (2) Both scratching force, P of the material to be cut and energyfor plastic deformation, W, reduce at the boundary temperature of upper and lower bainite structure. This temperature correspond to that stated in (1), at which grindability is most improved. (3) The thickness of plastic deformation of the ground surface layer is most reduced around the boundary temperature of upper and lower bainite structure. Similarly, plastic flow in the direction of grinding is minor around this temperature. The changes are observed corresponding to the temperature at which concavo-convex of tensile fracture faces and sizes of dimple patterns abruptly reduce. (4) Grinding damages such as grinding burns, swell out residual of the grinding surface, etc., are most alleviated at the boundary temperature of upper and lower bainite structure.

Effect of isothermal transformation temperature on the fine structure of steel 12Kh1MF

1. Isothermal treatment of steel 12Kh1MF at 350–500°C leads to the formation of a structure consisting of upper and lower bainite. At 500° the structure consists primarily of upper bainite, and at 350° of lower bainite. 2. With tempering of the steel with a structure of upper and lower bainite at 730° for 3 h the dislocations undergo redistribution of the polygonization type within ferrite needles, with development of a cellular substructure. The acicular structure of the matrix is retained in this case. The density and evenness of the distribution of carbides is higher in upper bainite than in lower bainite. 3. Steel 12Kh1MF with a structure of upper bainite is more susceptible to recrystallization as compared with a structure of lower bainite, which is responsible for the higher heat resistance of the latter.

Creep Rupture Strength of the Specimens from Actual Turbine Rotor Shaft

Creep rupture test were conducted at 538°C (1000°F), 565°C (1050°F) and 593°C (1100°F) on the 1Cr-11/4 Mo-1/4V steel which is used as the high- and medium-pressure turbine rotor shaft up to 1100mm diameter.Specimens were taken out of inner and outer part of an actual rotor, having radial, tengential and longitudinal direction, respectively.Test results are summarized as follows:(1) The longitudinal specimen has about 10% higher creep rupture strength than radial specimen which has higher strength than tangential specimen also by about 10% in terms of 1000 to 10000 hour creep rupture stress at each temperature.(2) Specimens from outer part of rotor show lower rupture strength than specimens from inner part. Though both inner and outer part have the bainite microscopic structure, the inner part has the upper bainite structure and the outer part has the lower bainite structure, since the cooling rate at quenching is slower in the inner part.The present result which shows that the upper bainite has better creep rupture strength than the lower bainite is in conformity with the previous results on small specimens.(3) The creep rupture stress of the notched specimen is higher than that of the smooth specimen in a short time range of testing and lower in a long time range.This intersecting of the rupture stress vs. time-curve for the notched and the curve for the smooth occurs at a shorter time of testing and when the testing temperature is made higher.(4) Comparing with the results of the tests by Werner et al.2), Conrad et al.4) and Rankin et al.5) on the 1 Cr-11/4 Mo-1/4V steel turbine rotor shaft, the present result shows nearly similar creep rupture strength to their results, and speaking at some length, the present data show a little lower strength in short time range and a little higher strength in long time range than theirs.(5) Elongation at creep rupture in the present test is similar to or a little higher than Rankin's.The specimen from inner part of a rotor gives longer rupture time but shorter elongation at rupture than the specimen from outer part.