It is shown that the phenomenological relation da/dN=C[((△K)~2-K_2~2)/(K_1~2-(△K)~2)]~p proposed by us in 1974, agrees fairly well with existing experimental data giving the whole variation of da/dN with △K provided that R=K_(min)/K_(max) is kept constant, p are around unity and C≌3×10~(-3)—10~(-2)mm/cycle.

Based upon dislocation theory the stress intensity factors can be calculated. The dislocation density distribution function (?) (x) is easily obtained by solving the integral equation with the Chebyshev polynomials. Some stress intensity factors thus calculated for practical cases have been found to agree fairly well with the results obtained by the conventional fracture mechanics.

The development of computer controlled tandem rolling process calls for a mathematical expression to represent the condition of inequality of mass flow constant. From the condition of dynamic equilibrium, a differential equation of tension is given as:dσ_i/dt=E/l[V′_(i+1)-V_i][1+σ_i/E]Based upon the physical rules in industrial practice and in experiments, for example, the law of volume constancy, the linear relation between forward slip and tension, the following equations are derived.The equation of the state of tandem rolling:(?)=-τ~(-1)Aσ+E/lBUThe equation of the dynamic state of tension:σ(t)=e~(-~(r-1))Atσ_0+A~(-1)[I-e~(-~(r-1))At]W~(-1)△VThe equation of the static state of tension:σ=A~(-1)m~(-1)qThe equation of tension represents the relation between tension, thickness, velocity of roll and time of the tandem rolling process. It implies that the tandem rolling process is an asymtotically stable, controllable and measurable dynamic system.

A crystallographic investigation of a Mg 6%Ga alloy during aging was performed by X-ray diffraction methods, together with hardness measurements and metallographic observations, The aging process of this alloy at 190℃ may be devided into three staps:1. Precipitation of β′. An orthorhombic transition phase β′ is precipitated at the initial stage of aging. Its lattice constants are: aβ′=9.1(?), bβ′=6.2(?), cβ′=24.6(?), and the orientation relationships with the matrix (M) are aβ′∥[0001]M, bβ′∥[2(?)0]M, cβ′∥[01(?)0]M.A preliminary determination showst hat the thin plates of the transition phase are parallel with {10(?)0} and {11(?)0} planes of the matrix.2. Precipitation of β. The equilibrium phase β precipitated out in a Widmanstatten form in the matrix has a composition of Mg_5Ga_2, with lattice constants aβ=13.72(?), bβ=7.02(?), cβ= 6.02(?). The orientation relationships between β and the matrix are: aβ/[0001]M, bβ∥[2110]M, cβ∥[0110]M. Dispersion hardening always accompanies this precipitation, and the habit plane in the matrix was found to be (0001)M.3. Overaging. The Widmanstatten structure of the equilibrium phase in the matrix disappears, and there is no definit orientation relationship between β and the matrix.

δ-ferrite in 0Cr17Mn14Mo2N stainless steel formed at 1050—1350℃ was measured quantitatively by metallographic methods, and the distribution of alloy elements between δ-ferrite and austenite was determined by electron-probe and electrolytic extraction phase analysis. It was found that the amount of δ-ferrite increases from 23% at 1050℃ to 42% at 1350℃. As to be expected, the concentration difference of Cr, Mn, Mo between δ-ferrite and austenite became increasingly smaller as the solution temperature was increased.After reheating in the range of 550—950℃, several types of transformation in δ ferrite including δ→γ′, δ→κ(χ)+γ′ and δ→δ′+κ(χ) may take place, and phases like Cr_2(CN), (CrFe)_7C_3, Cr_(23)C_6, χ and σ were found to appear. Both the type and product of transformation varied with the temperature of solution treatment and the subsequent isothermal heating. The high Mn content (14%) in steel promoted the formation of χ-phase expressed as Fe_(31)Cr_(14)Mn_(8.5)Mo_(4.5), and its cell constant was α_0~(552)=8.86(?).The kinetics of isothermal transformation in δ ferrite is of the C-curve type with its nose for δ→κ(χ)+γ′ at 850℃.

In certain conditions, hot cracks eccurred in continuous casting billets of a 0.45% C steel. It was observed that such cracks were practically healed by rolling when the reduction ratio attained about four. Inclusion clusters and segregation of phosphorous in the neighbourhood of the above cracks as elongated streaks were often present and aligned with the rolling direction. In view of these, dark etching lines resembling cracks could occur on deep macro-etching. This sort of inhomogeneity hardly affected the longitudinal mechanical properties of therolling products, although the transverse ductility was appreciably lowered.

An investigation has been carried out on the so-called intergranular cracks appearing in the central part of a macroetched transverse section of a 20Cr2Ni4A steel billet. It is shown that this in fact was a kind of acid-etching phenomenon, due to low-melting inclusions at the interdendritic boundaries appearing as cracks. The above observation was further substantiated in laboratory ingots by the introduction of certain low-melting inclusions into experimental melts.

In view of the well-known embrittlement associated with welded Al-Cu joints, a low temperature friction welding process for joining aluminum to copper has been considered. This process is characterized by the joint action of a lower rotating speed and a moderately high axial welding pressure so as to keep the temperature by friction at the weld interface never raised above that of the eutectic point (548℃) in Al-Cu system, and at the same time to obtain a sufficient plastic de-formation at the friction surfaces of the joint. As a result, the many unsatisfactory features such as low mechanical strength and poor toughness of the weld joint generally associated with the conventional friction welding for dissimilar metals were much improved. Tests for hot stability, aging properties and practical applications also proved that the joint quality fully satisfied the technical requirements.

1. Effect of rare earth elements on the properties of steel2. Functions of rare-earth in steel2.1 Cleaning effect and modification of inclusion morphology(1) Deoxidation(2) Desulphurization and sulphide-control(3) Others2.2 Alloying effect and its interaction with interstitials3. Methods of addition of rare-earth elements in steelmaking4. Blockade of ladle nozzle during teeming