145

c o m p r e s s i o n plane surface this is much less the case, and in the middle much m o r e so. ~R

Consequently, as we move from the center toward the periphery of the cylinder, the angle of dispersion of the orientations gradually decreases, and is least in the middle of the cylinder generator. When plotting pole figures for all the specimens we studied, we found a texture with two crystallographic orientations: 1) strong [111] ~l OH; [112] II PH; [110] tl KH; 2) weak [112] H OH; [111] Jl PH; [110] ~l KIt. As shown by the texture, slip occurs basically on t]he (110) plane and to a considerably l e s s e r extent on the ].11) and (112) planes.

KH

(pM)

Fig. 4. Pole figure (110) of compressed iron for middle of cylinder; reduction ratio 76.6% Figure 5 shows the pole figure of a specimen cut at 4 or 5 m m f r o m the cylinder periphery. The least angle of spread in the crystal orientation is found right in the middle of the cylinder generator (Fig. 6). The pole figures plotted with r e s p e c t to plane (112) also indicate nonuniform flow of the metal through the cylinder. KH

OH

-

~

The experiments showed that as the degree of deformation is increased, the dispersion angles of the texture decrease. The angles also decrease as we go f r o m the center of the cylinder to the periphery, for the same degree of deformation. The experiments show that flow throughout the cylinder is nonuniform. In the middle, the metal flows predominately in a radial direction during deformation, half way along the radius the metal flows in a radial direction, and in a tangential direction, on the generator of the cylinder it flows in a tangertial direction. Consequently, at high dynamic c o m p r e s s i o n ratios the metal flows most intensively along the cylinder generator and, as a result, cracks appear at these points.

0//

Fig. 5. Pole figure (110) of c o m p r e s s e d iron (for middle of cylinder 4 - 5 m m f r o m periphery; 76.6% reduction ratio

KH

Data on the distribution of the deformation texture in a c o m p r e s s e d cylinder correspond to those given in [1]. The poorly-marked texture in the middle of the specimen, where the g r e a t e s t scatter of the crystal axes is observed, is marked by g r e a t e r hardness than in the end sections of the cylinder. It follows f r o m this that the metal hardens to a g r e a t e r extent during high degrees of deformation, provided the deformation texture shows a g r e a t e r spread of the crystal axes. Conversely, the m o r e clearly marked the texture for the same degree of deformation, the lower the mechanical strength of the metal.

REFERENCES

a)

KH b)

Fig. 6. Pole figure (110) of c o m p r e s s e d iron plotted for middle of cylinder right on boundary; a -- reduction ratio 76.6%; b -- 96.6%

1,

S. I. Gubkin, and other. Experimental Problems of Plastic Deformation in Metals, ONTI, 1934.

2.

C. S. Barrett, Structure of Metals, Metallurgizdat, 1948.

WEAR RESISTANCE OF H I G H - M A N G A N E S E STEEL CASTINGS Eng. M. A. GUZOVSKAYA and Cand. Tech. Sci. YA. D. KHORIN (TsNIITMASh) During a study of mining establishments, it was discovered that G13-L steel castings (crusher jaws and cones) subjected to wear and t e a r through impact exhibit varying strength under identical operating conditions. In view of

this we carried out a study of 18 Soviet-made castings and 54 castings made by foreign f i r m s all showing different deg r e e s of strength under identical service conditions. The m a c r o s t r u e t u r e was studied using t r a n s v e r s e templets.

146

CHARACTERISTICS OF FOREIGN-MADE CASTINGS

Groqp of castings

Macro-

structure

[ structure M~e*o- 'i U~..~/ ~[ Chemical compositionin % --i '~'~ 'p ' ~ ~! [ Grain Carbide~ ~,~1 readingreading~ ~ = c Mn si [ p

Crasher linings

Fine

3--4i 1--2p5~-%?0--1.2 11--13,5 0-3--0,6i0,01--0,07

13.all-milI / amngs

Fine

2 3 1--2 15-25 0,9--1,2 10 13 0.2--0,610.04--0.10

Cold compacting i [ presstools [

Fine

3 5 1--5 2--4 1.2--1,4 10--14 0,1--0,8,0.03--0.0{i

] Centerpieces

Mean

Tracks

I i

1

Not Ii 1--5 determined

[I--212--30 1,1--1.3 2--5

1--20 1,0--1.3

11--I4 0.2--0,8i10,04--0.07 11--14 i

--

O.04--0AO

r

The m i c r o s e e t i o n s w e r e etched in a solution p r e h e a t e d to 50 - 80 ~ containing 50 m l HCL, 25 ml HNO3, 50 ml H20 and 12 g Cr207. The oxide f i l m formed during etchIng was l u b r i c a t e d with another solution (500 ml HC1, 50 ml HC1, 50 ml HNO3, 50 ml H20 and 35 g Cr207), a f t e r which the s e c t i o n was washed with a soda solution, cold and w a r m w a t e r and then dried. The i m p a c t toughness was d e t e r m i n e d with s p e c i m e n s cut f r o m the zones lying next to the working s u r f a c e and p o s s e s s i n g identical m i c r o s t r u c t u r e . The m i c r o s t r u c t u r e was brought out on s e c t i o n s made f r o m the two h a l v e s of the ruptured i m p a c t s p e c i m e n s . As the e t c h e r we used a 370 alcohol solution of HNO 3. The e t c h e r r e s i d u e was washed off with alcohol. We studied the m i e r o s t r u c t u r e on unctched cuts with a magnification of 100, and on etched cuts with a magnification of 100 and 135 ~ The g r a i n s i z e was a s s e s s e d on the GOST State Standard s c a l e (5639-51), while the amount of carbide was m e a s u r e d with the Scale used by the TU Ural coach making plant. The content of carbon, silicon, sulphur and phosphorous was d e t e r m i n e d by c h e m i c a l a n a l y s i s , while the m a n g a n e s e content was d e t e r m i n e d by quantitative s p e c t r a l a n a l y s i s . The data obtained f r o m our study of the c a s t i n g s a r e shown in the Table. It i s c l e a r f r o m t h i s table that not one of the analyzed c h a r a c t e r i s t i c s uniquely defines the w e a r r e s i s t a n c e of the castings. The quality of the c a s t i n g s i s a function of a number of f a c t o r s all put together. The m a c r o s t r u e t u r e has a c o n s i d e r a b l e effect on w e a r r e s i s t a n c e . The nature of the m i c r o s t r u e t u r e i s d e t e r m i n e d by the p a i r i n g t e m p e r a t u r e , hence, it is r e c o m m e n d e d that the s t e e l be poured at m i n i m u m t e m p e r a t u r e (according to the shape of the casting). The different amounts of carbon, manganese, phosphorous and sulphur in the c a s t i n g s studied has no effect on t h e i r w e a r r e s i s t a n c e ; foreign c a s t i n g s show a m a x i m u m carbon content of 1.2 - 1.370, phosphorous 0.06 - 0.07. Silicon does have an effect on w e a r r e s i s t a n c e - h i g h - s t r e n g t h c a s t i n g s contain 0.36 - 0.8870 Si, and l o w - s t r e n g t h castings O. 57 - i. 1370. It is generally recognized [i], [2], that high-manganese steel of good quality should have a fine-grain austenitie structure with a small amount of free carbide. W e should point out the erroneous nature of the view that the structure of high-grade steel, as brought out by etching with a n i t r i c acid solution in i s o a m y l alcohol, shows a secondary network in the a u s t e n i t i c g r a i n s , p a r t i c u l a r l y noticable when the b e a m i s defoeused [2]. We have obs e r v e d t h i s s t r u c t u r e many t i m e s at a magnification of 1350

Fig. 1. Subrnicrostructure of G13-L steel, x 1350a -- s t e e l without carbide (1 point); b -- s t e e l with c a r b i d e s (3 points) in anstenite s t e e l (see Fig. a) and in s t e e l containing carbide (see Fig. b) after n o r m a l etching. In the case of m o s t of the foreign forgings studied, (with the exception of t r a c k s and tools for compacting p r e s s e r s ) , the i m p a c t toughness amounts to 15 - 25 k g m / e m 2 , while for Soviet-made c a s t i n g s with a r e l a t i v e l y h i g h - s t r e n g t h it i s 10 - 20 k g m / e m 2 . The i m p a c t toughness of castings with low w e a r r e s i s t a n c e does not exceed 10 k g m / e m 2 in most c a s e s , though it i s s o m e t i m e s 2 - 4 k g m / c m 2 . In this way, an i n c r e a s e in i m p a c t toughness helps to i m p r o v e the w e a r resistance.

147

3. The c a s t i ngs m u s t be i ns pe c t e d for m i c r o s t r u c t u r e and i m p a c t toughness.

CONCLUSIONS

1. To i m p r o v e the w e a r r e s i s t a n c e of p a r t s made of G13-L s t e e l , the l a t t e r has to be p a i r e d at as low a t e m p e r a t u r e as p o s s i b l e . 2. Castings (drag buckets, c r u s h e r cones and front ladle walls) should not contain m o r e than 0.06 - 0.07% P and 0.5% - 0.6% St.

REFERENCES 1.

I. L Subbctin, "Muscovite i n d u s t r y " , No. 2, 1929.

2.

I. S. Roginskiy, " M e t a l l u r g " , No. 3, 1932.

RESISTANCE OF METALS A N D A L L O Y S TO L O W DEGREES OF PLASTIC F L O W A. G. RAKHSHTADT

One of the i m p o r t a n t c h a r a c t e r i s t i c s of many c o n s t r u c tion m a t e r i a l s i s r e s i s t a n c e to low d e g r e e s of p l a s t i c flow, which i s c h a r a c t e r i z e d by the y i e l d point or proportion a l i t y l i m i t . The reg ion of e l a s t i c deformation, however, can be much m o r e r e l i a b l y d e t e r m i n e d by the e l a s t i c l i m i t1. Many m o n o c r y s t a l s have a " c l e a r l y pronounced" a bs olute e l a s t i c l i m i t , i . e . , a s t r e s s below which t h e r e is n e i t h e r r e s i d u a l deformation, nor any other i r r e v e r s i b l e change [1]. The opinion is commonly held that in the case of p o l y c r y s t a l line s p e c i m e n s the absolute e l a s t i c l i m i t i s e i t h e r totall y lack ing, or i s so s m a l l that it is of no p r a c t i c a l i m p o r t a n c e , The publications [2] - [6] have shown, however, that when the r e s i d u a l elongation (up to 1 - 2 x 10-4) is d e t e r m i n e d a c c u r a t e l y , the e l a s t i c l i m i t (e0.0002 or %.0004 ) for a n u m b e r of s t e e l s i s close to the y i e l d point [2] - [4]. Repeated loadings up to s t r e s s e s beyond a0. 0002 cause a f r e s h inc r e a s e in r e s i d u a l deformation {approximately in equal portions); r e p e a t e d loadings below this l i m i t do not lead to the a c c u m u l a t i o n of any a p p r e c i a b l e r e s i d u a l deformation [2] (Fig. 1). g2a %c 6tempering 425~

g,:.0%c;

tempering 370~

10a~

a 20 40 -200 20 ,~0 ~20

a)

b)

~

The s e r e s u l t s s u g g e s t that t h e r e i s an e l a s t i c Hmit ~0 s i m i l a r to the absolute l i m i t , but which can be d e t e r m i n e d with a c e r t a i n r e s i d u a l deformation t o l e r a n c e conditioned by the a c c u r a c y of the m e a s u r e m e n t 2. As d i s t i n c t from the conventional e l a s t i c l i m i t , however, t h i s c h a r a c t e r i s t i c i s not found f r o m one, but f r o m two independent quantities, s i n c e the r e s i d u a l de forma t i on cannot be detected by m e a s u r e m e n t with the p r e s e t a c c u r a c y , and does not a c c u m u l a t e during mul t i pl e loading, w h e r e a s above the l i m i t ~0 i t builds up with each loading. It may be c ons i de re d that below a 0 t h e r e i s a l s o r e s i d u a l deformation, but that above t hi s s t r e s s , i t i n c r e a s e s in jumps of at l e a s t a fa c t or of 10 (see Fig. l c ). Thus, a s d i s t i n c t f r o m the conventional e l a s t i c l i m i t , the quantity ~0 shows the beginning of one type of a t h e r m a l p l a s t i c flow. It i s often difficult to d e t e r m i n e the e l a s t i c t h r e s h o l d during t e n s i o n t e s t s by f i r s t - k i n d r e s i d u a l s t r e s s e s . The s e ma y even lead to shortening of the s p e c i m e n s (Figs. l b and c) when the s t r e s s e s a r e l e s s than a0- F u r t h e r m o r e , i t m u s t be taken into account t ha t the s t a r t of a t h e r m a l p l a s t i c flow can only be detected if the s p e c i m e n i s not loaded for too long a period, s i n c e if the loading t i m e i s f a i r l y long, the e l a s t i c aftereffect, s t r e s s r e l a x a t i o n and so on, begin to have a m a r k e d effect. Hence, the conditions for detecting the e l a s t i c t h r e s h old have to be s e l e c t e d for each group of a l l o y s in a c c o r d ance with the s t r u c t u r e , c o r r e s p o n d i n g t e m p e r a t u r e and t e s t t i m e . F or the mome nt the e x i s t e n c e of an e l a s t i c t h r e s h o l d at 20 ~ has been found in s t e e l s a ft e r annealing and n o r m a l i z i n g [3], quenching and t e m p e r i n g [2], and a l s o in copper [6], and a l umi num and i t s a l l oys [5].

D

5L

-2a

and M. A. SHTREMEL

fO

c)

50

,~a' 10 -~ ~re~/O

Fig. 1. D e t e r m i n a t i o n of e l a s t i c l i m i t by s u c c e s s i v e unloadings [2] (10 loadings each at points A, B, C, D, E and F)

1) Conditional p r o p o r t i o n a l i t y l i m i t ffp and e l a s t i c l i m i t a e a r e d i s t i n g u i s h e d by p r e s e t t i n g a t o l e r a n c e for r e s i d u a l def ormation, but, m o r e i m p o r t a n t , by the fact that (~p i s det e r m i n e d f r o m the deviation of the s t r a i n d i a g r a m a(e) f r o m the line cr = Ee, while a is d e t e r m i n e d f r o m the p r e s e n c e of r e s i d u a l deformation a f t e r unloading.

The s t a r t of a t h e r m a l p l a s t i c flow above the e l a s t i c i t y t h r e s h o l d l e a d s to c o n s i d e r a b l e v a r i a t i o n in the coefficient of expansion [7], [8], t h e r m a l capacity [9], and other c h a r a c t e r i s t i c s (Fig. 2). P l a s t i c flow at n o r m a l t e m p e r a t u r e s i s produced by a d i s l o c a t i o n m e c h a n i s m in which the d i s l o c a t i o n s multiply and move a c r o s s the c r y s t a l during the application of s t r e s s e s . O r d e r l y s y s t e m s , m o s t often in the form of t r i m e n s i o n a l networks [10, 11], the nodes of which a r e anchored, f o r m i n the c r y s t a l before the de forma t i on of the d i s l o c a t i o n begins.

2) Hence, the t e r m " a bs ol ut e e l a s t i c l i m i t " is tmacceptable It i s b e t t e r to call eO the e l a s t i c threshold.