F I N E C R Y S T A L S T R U C T U R E OF T H E S U R F A C E L A Y E R

OF S T E E L H A R D E N E D W I T H ROLLERS

(UDC 620.18 : 621.789)

M. E. B l a n t e r , M. G. G a s a n o v , a n d N. A. G u l y a e v a

Al l -Union Cotrespondence Institute of Machine Construction;

Central Scient if ic Research Institute of Machine Construction

Translated from Metal lovedenie i Termicheskaya Obrabotka MetaIlov, No. 3, pp. 13-15, March, 1966

We studied the var ia t ion of the microstrueture and of the fine crystal structure of the surface layer of No. 48

steel hardened with rollers as a function of the pressure on the roller, the number of revolutions of the samples, the rate of motion of the roller, and the number of passes with the rollers.

We studied rods of No. 45 steel with a chemica l composit ion and mechan ica l properties as follows: 0.45% C, 0.2~ Si, 0.8% Mn, 0.02% Ni, 0.07% Cr, up to 0.0~o S and P; a b = 65.5 k g / m m 2, a0. 2 = 38.0 k g / m m 2, 6 = 30%, = 4 4 % , HB 150-160.

Rods normal ized at 840~ were cut to a d iamete r of 17 ram. The samples were roiled with a single roller. Five series of samples were treated. In each series we changed one of the four parameters of the roiling conditions. The conditions of t rea tment and the l imits within which the rolling parameters were changed are given in the table.

The physical widening of the x- ray fringes was studied with the URS-50I-M apparatus (iron K a radiation). The distribution of the intensity of the interference fringes (110) and (220) was recorded au tomat ica l ly at angles 28-= 54-88 and 140-149 ~ respectively. The Ka1-Kaz doublet was separated ana ly t ica l ly [1]. The real physical widening of (110) and (220) fringes was determined by the approximate method, using the (1 + c~) z curves for the fringes of the samples investigated and for the standard [2].

We used the same types of curves for the M(x ) and N(x ) functions character iz ing the distribution of the inten- sity of lines due to second-order stresses and the size of the blocks. The stresses and the sizes of the blocks were

determined by the change in the physical widening of the interference fringes (110) and (220). Third-order stresses were determined by the change in the ratio between the maximum intensity of the (220) fringes and the background

of the same fringe [3].

Some of the rolled samples 5-7 mm long were used to prepare samples for micrographic examinat ion. The samples were cut and polished mechanica l ly . The polishing process was al ternated with etching until a mirror sur- face was at tained which was free of scratches when examined under magnif ica t ion and did not have a bent edge. The samples were etched in a 2% solution of nitric acid in ethyl alcohol. The samples were photographed under the

microscope.

Fig. 1 shows the var ia t ion of the physical widening of the (220) and (110) fringes as a function of the conditions

of t reatment .

It can be seen that with increasing pressure on the roller during rolling and with increasing rates of ro ta t ionof the sample the width of the (220) fringe increases monotonical ly . With increasing numbers of revolutions of the rol ler over the surface and with increasing rates of rotat ion of the roller the width of this fringe first increases to a max imum value and then decreases smoothly. The width of the (110) fringes remains constant independently of the

var ia t ion of a l l the parameters.

Fig. 2 shows the var ia t ion of the ratio between the maximum intensity and the intensity of the background as a function of the rolling conditions. It can be seen that with increasing pressure on the roller this ratio first decreases (first sect ion of the straight line) due to the increase of third-order stresses. At the moment at which the max imum stress in the structure is reached the amount of hea t evolved in the friction area increases sharply, and this decreases the third-order deformat ion and increases the I~20/Iback ratio (the second section of the curve).

188

B i0 -3, tad

.D; ,, i 7g , _ ! ! . . . . .

12

8

#

n ~eo zO// 3a0 ,ag rpm Pressure on the roller

,0 8a czo .~eo Z~e,o,k--g i,iun~ber of revolutions of ~he san"_,-

10 -3, raJ

16 ! : , j 4 ! [ [

+ - 4 , t ! / i i(i~){

0 ~ 2 3 0 5 &' Number of, passes ___--~.

L ] - - ,

fl 6# O~ 1,2 1,~' f,O ~.ate 'of m~tion of the roller ,

ram/revolu t ion

Fig. 1. Variation of the physical widening of the (220) and (110) fringes as a function of: 1) pressure on the rol ler ; 2) number of revolutions of the sample; 3) rate of motion of the sample; 4) number of passes.

kate of mot ion of ihe roller, I ( 2 z 0 ) mm/revo lu ~ion

0,4 o,s ,,~ ~,6 Iback " ~ I [ i ': ! ]

c 1 / i i I

I ~ - - J / - I I ! ! k , " - ~ / - - 2 3 ! ~ I ; T-a§247

~o 80 12o eG0 kg pressure on the rol ler

1,2 ~ I

1 2 3 N Number of passes of the roller

Fig. 2. Variation of the ratio between the max imum intensity of the (220) l ine

and the intensity of the background as a function of t reatment conditions. The notations are the same as in Fig. 1.

TABLE i

~ d Roi l ing c0nditions

n in I S in P in kg revs /min l m m / r e v

80;0200 185 0,1 120--600 0,1

1 0 0 1 8 5 0 , 0 8 - - 2 100 185 0, 1

N

1 1 1

1--6

Fig. 3. Variation of the microstructure of the surface layer with the pressure on the rol ler during treatment. x 500. a) 3 0 k g ; b ) 7 0 k g ; c ) 1 0 0 k g ; d ) 150kg ;e )200 kg.

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As the pressure on the roller is increased, the temperature prevents the deve lopment of third-order stresses, and therefore there is no deformat ion during subsequent increase of the pressure on the rolIer. The dependence of the rat io between the max imum intensity and the intensity of the background on the rate of rotat ion of the samples dur- ing roiling is the same as during the var ia t ion of the pressure on the roller.

Third-order deformat ion decreases with increasing rates of motion of the roller down to 0.2 ram/revolut ion. Beginning with 0.2 and up to 0.8 ram/revolu t ion the third-order stresses increase, With further increase in the rate of mot ion of the roller these stresses remain constant.

If the number of passes is no more than two then the I220/Iback ratio remains almost unchanged. Further in-

crease in the number of passes leads to a continuous increase in the I220/Iback rat io, i .e . , beginning with the second pass of the roller , the third-order stresses decrease. This is due to the fact that beginning with the third pass the gra in size becomes very smal l and the second and third-order stresses increase. At the same t ime, the thick surface layer loosens and the recrys ta l l iza t ion temperature decreases. Also, during friction of the surface the crystal la t t ice is continuously rebuil t ( tempering) and the stresses of the second and third order are par t ia l ly rel ieved.

Fig. 3 shows that with increasing pressure the depth of the deformed layer in which the grains are fragmented and elongated increases, In the case of roll ing under a pressure of 30 kg the pear l i t i c - fe r r i t i e structure of the outer layers is great ly deformed. The grains are fragmented and elongated, Under a load of 70 kg the structural changes are the same but the depth of the deformed layer is greater. Under a load of 100 kg the depth of the deformed layer is not much greater but the grains on the surface are less elongated than under smal ler loads. As the load is increased to 150-200 kg the depth of the deformed layer increases and the grains become "rounded ~, part icularly under a load

of 200 kg. Also, under this load the surface of the sample begius to peel off.

With increasing numbers of revolutions up to 185 rpm the depth of the deformed layer first increases and then remains almost constant. At the rate of 480-600 rpm the grains become round, but this occurs not at the surface i tself but in the presurface layer.

With increasing numbers of passes the depth of the deformed layer increases. After three passes the surface layer begins to pee i off in places; after six passes loosening and scaling occur at a cer ta in distance from the surface.

Thus, t rea tment with rollers leads to f ragmentat ion and elongat ion of graim and the surface of the t reated

articles is damaged (scaling and loosening).

C O N C L U S I O N S

1. The physical widening of the (220) fringe increases continuously with increasing pressure on the roller and the number of revolutions of the sample. The increase in the rate of motion of the roller and of the number of passes of the rol ler is character ized by curves with a maximum corresponding to smal l values of these parameters.

2. The increase in the pressure on the roller, the number of revolutions of the samples, and the rate of motion

of the rol ler leads first to a decrease of the I220/Iback ratio and then to its increase up to a l imi t value or to a de - crease after the max imum value is reached (for a given rate of motion of the roller). The ratio between the inten- sities increases continuously with increasing numbers of passes of the roller beginning with the third pass.

3. An increase in the intensity of roi l ing leads first to an improvement of the orientat ion and to fragmentaion of grains at the surface and then to scal ing with subsequent peeling of the deformed layer from the surface of the

sample.

1o

2.

3.

L I T E R A T U R E C I T E D

W. Rachinger, Journ. Scienr. Instrum., 25, No. 7 (1948). G. V. Kurdynmov and L. I. Lysak, ZhTF, 17 (1947). L. L Mirkin and Ya. S. Umanskii, FMM, 9, No. 6 (1960).

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