Toshio Shiota

Influences of graphite shapes on wear characteristics of austempered cast iron

Abstract Dry slip–rolling contact wear test and wet slip–rolling contact fatigue test of several austempered cast irons with various graphite shapes were conducted by using a Nishihara-type wear-testing machine. The influences of the graphite shapes on the wear and fatigue characteristics of cast iron were investigated. Changing graphite shape from spheroidal to flake was found to result in a considerable increase in wear loss in both dry and wet conditions. Decrease in graphite nodularity results increase in wear loss at the initial wear stage. It is because lower graphite nodularity results in a shorter average matrix distance between graphites and also a larger stress concentration factor at graphite tips. The pitting phenomenon is easier to occur in sample with lower graphite nodularity.

Mechanical characteristics of spheroidal graphite cast irons containing Ni and Mn with mixed ferrite and bainitic ferrite microstructure

Abstract This study aims to clarify the influence of additive elements of Ni and Mn on tensile and impact properties of three kinds of spheroidal graphite cast irons (SG irons), which are as cast, annealed and austempered samples. Spheroidal graphite cast irons with Ni (0–4˙5 mass-%) and Mn (0–0˙5 mass-%) melted by a high frequency induction furnace and cast into a Y block CO2 mould with 30 mm in thickness. From the viewpoint of heat treatment, tensile strength and hardness of SG irons become larger in the order of ferritised<as cast<austempered ones. Matrix structures of SG irons, which are conducted to austempering treatment from α and γ mixture range, consists of bainitic ferrite with high toughness. Austempered SG iron with 3%Ni in 0˙1%Mn series is found to become higher tensile strength compound with elongation and toughness of 901 MPa, 17% and 915 kJ m−2.

Effects of heat treatment on the thermal expansion characteristics and mechanical properties in low expansion austenitic cast iron

Several kinds of heat-treatments were applied to a low thermal expansion austenitic flake graphite and spheroidal graphite cast irons. The effects of heat treatment on the average coefficient of li...

Notch Effects on Impact and Bending Characteristics of Spheroidal Graphite and Compacted Vermicular Graphite Cast Irons with Various Matrices

The object of this study is to find out and evaluate systematically how the basic factors such as graphite-shape, external notch and matrix-characteristic affect the impact and bending characteristics of cast irons. The Spheroidal Graphite (SG) and Compacted Vermicular graphite (CV) cast iron samples were prepared, and their matrixes were modified into ferritic, pearlitic and bainitic in order to make the various kinds of samples whose graphite-shape and matrix vary widely. From each sample we produced five kinds of Charpy-type specimens by adding five kinds of notches whose stress concentration factor (α) varied from 1.0 (un-notched) to 4.8. The Charpy impact value decreases greatly in the range of α from 1 to 2.3 but decreases slightly in the range of α larger than 2.3. No influence to the fracture energy in the range of α larger than 2.3. Increasing of α results in moderate elevation of transition temperature of Charpy impact value and the transition temperature of CV cast ion is lower than that of SG one. The impact value in brittle fracture region of the cast iron samples were recognized to be a little bit larger than that of cast steel sample, and it was considered to be caused by graphite which act as a kind of buffer effect against crack growth in brittle fracture.

Low thermal-expansion gray cast iron strengthened by crystallizing dispersed carbide particles

Low thermal-expansion gray cast iron with high strength and hardness was produced by dispersing carbide particles by means of alloying carbide-stabilizing elements such as Nb, Cr, W, V, Ti and Mo up to 5 at.%. Increasing the alloying content of each element results in increasing the area fraction of carbide and decreasing in that of the graphite fraction, and it results in remarkable increasing in hardness. Tensile strength increases remarkably with increasing in alloying content of Cr or V, but it becomes maximum at some 1 at.% in the case of W or Nb. The increasing in tensile strength and hardness was discussed from such viewpoints as increasing in area fraction of carbide and increasing in effective sectional area ratio resulted from decreasing in area fraction of graphite. The coefficient of mean linear thermal-expansion at 373K increases largely with increasing alloying contents in the case of Cr, W or Mo, but it increases only slightly in the case of Ti, V or Nb.