Effect of Titanium Addition on As-Cast Structure and High-Temperature Tensile Property of 20Cr-8Ni Stainless Steel for Heavy Castings

20Cr-8Ni stainless steel is used to manufacture heavy castings in industrial practice. Owing to the slow solidification rate of heavy castings, the as-cast structure is usually coarse, which reduces the mechanical properties. To refine the solidification structure, the effect of titanium addition on the as-cast structure and high-temperature tensile property was investigated in the laboratory. The ingots with 0.0036, 0.2, and 0.45 mass percent titanium were produced in the laboratory. On the basis of experiment and thermodynamic calculation through Thermo-Calc software, the typical inclusions changed from dual phase Si-Mn-Ti oxides to pure TiN or complex Ti2O3 + TiN with titanium content increasing. The equiaxed grain ratio of ingot increased from 51 percent to nearly 100 percent, and the size of equiaxed grain decreased owing to heterogeneous nucleation of δ-Fe. Besides, the equilibrium solidification model changed from the FA model to the F model, and the mass fraction of ferritic phase in ingots increased from 24.8 to 42.6 percent. As a result, the yield strength and ultimate tensile strength of ingots increased gradually, but the tensile elongation changed little owing to the increase of ferritic phase mass fraction and decrease of equiaxed grain size.

Stereological Analysis of Carbides in Hypoeutectic Chromium Cast Iron

The results of research on stereological parameters of carbides in modified hypoeutectic chromium cast iron were shown in the paper. The effect of distance the casting heat centre of casting to the carbide phase morphology was examined. The samples for metallographic examination were taken from various locations of the model casting prepared in a special tester. This model casting was designed to simulate the solidification of heavy castings. Using the proposed methodology the relation of the distance from the model mould and the size, perimeter, length, width and the shape factor of carbides was examined. During the analysis, the values of stereological parameters of carbides changed on various sections of the model casting.

Development of a 90°/180° Upender for Large and Heavy Workpiece by Using Airbags-Drived Flipping Worktable

There is a serious security problem in the process of workpieces flipping, which restricts the increase of production capacity in manufacturing process of large workpieces applied in nuclear power equipment. The shapes and characteristics of flipping workpieces were analyzed; the general model of workpieces outer contour was established. The design goals of heavy castings and forgings cold-work turnover mechanism were formulated based on the requirements of turning process, then the basic constraint-face was build and the geometric constraint-model was uniformed. A novelty 3- DOF planar serial mechanism of heavy upender was proposed whose overall configuration consists of three movements, that is roll, mobile, folding turn, which can realize the double function of turning 90 ° and 180 ° of large workpiece as hollow cylindrical, conical and spherical crown three types. On this basis, the airbags-drived flipping worktable was designed; Topological optimization of flipping worktable was further conducted. Its key technology will provide useful ideas and references for the development of large heavy duty positioner and turnover machine with its other related equipment.

Influence of Compound Deoxidation of Steel with Al, Zr, Rare Earth Metals, and Ti on Properties of Heavy Castings

Influence of Compound Deoxidation of Steel with Al, Zr, Rare Earth Metals, and Ti on Properties of Heavy Castings Heavy steel castings deoxidized with aluminium are sometimes brittle intercrystalline failed during their service along primary grain boundaries what is initiated by aluminium nitrides and so called conchoidal fractures are formed. The tendency to forming the conchoidal fractures depends in particular on cooling rate (the casting modulus), aluminium and nitrogen contents in steel. During deoxidation, when manufacturing heavy castings, the elements with high affinity to nitrogen, zirconium or titanium, are added to steel that would decrease nitrogen activity by the bond on stable nitrides. The formation of stable nitrides should reduce the tendency of steel to the formation of conchoidal fractures. Deoxidation was thermodynamically analyzed at presence of the mentioned elements. For particular conditions a probable course of deoxidation was estimated at test castings. The deoxidation course was checked by microanalysis of deoxidation products (inclusions). For service and experimental castings the anticipated composition of inclusions was compared. It has been proved that in heavy castings with high aluminium contents in steel under studied conditions neither the addition of zirconium nor of titanium nor of rare earth metals will prevent the formation of conchoidal fractures.

NI-HARD

NI-HARD is a white cast iron alloyed with nickel and chromium to give high hardness and outstanding resistance to abrasion. The structure consists of hard carbide matrix rendered martensitic by the nickel content. The wearing faces of heavy castings may be chilled, thus giving a white iron face, backed by grey cast iron where the metal has cooled more slowly. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on casting, heat treating, machining, and joining. Filing Code: CI-9. Producer or source: Allen-Sherman-Hoff Pump Company.