• Categories
• Deformación (Mecánica)
• Fundición (Metalurgia)
• Fundición
• Acero
• Elasticidad (Física)

Citation preview

  John Barr  

DESIGN OF MACHINE MEMBERS

This book is produced in full compliance with the government's regulations for conserving paper and other essential materials.

PRODUCT DEVELOPMENT SERIES TEXTS AND REFERENCE WORKS OUTLINED

BY T!1E FOLLOWING COMMITTEE

K. H.

CONDIT,

Chairman and Consulting Editor

Dean, School of Engmeermg, Princeton University.

E. P.

BULLARD

President of The Bullard Company.

G. 1\1.

EATON

Sales Engmeer of Spang, Chalfant, Inc. FRANCIS

C.

FRARY

Director, Aluminurr Research Laboratories, Aluminum Company of America.

F.

v. LARKIN

Director, Industrial :E-

'."

.... H

SEC.

11]

ENGINEERING MATERIALS

13

members. The alloying elements usually used are nickel, chromium, manganese, molybdenum, vanadium, and combinations of these. 10. Wrought Steel. This is the most common material found in machine members, except cast iron. The mechanical working in the manufacturing process refines the structure and produces a more uniform steel having greater strength, greater toughness, and more durability than is obtained in castings. The properties of the steels vary greatly with the carbon content and with the form in which the carbon occurs, the beneficial effects of alloying materials depending to a large extent on their action on the carbon. Low-carbon steels, containing up to 0.30 per cent of carbon. are soft, very ductile, easily machined, easily welded by any process, and, since the carbon content is low, unresponsive to heat-treatment. Medium-carbon steels, containing from 0.30 to 0.50 per cent carbon, are stronger and tougher than the lowcarbon steels, machine well, and respond to heat-treatment. High-carbon steels, containing over 0.50 per cent carbon, respond readily to heat-treatment. In the heat-treated state, they may have very high strengths combined with hardness, but are not so ductile as the medium-carbon steels. In the higher carbon ranges, the extreme hardness is accompanied by excessivE brittleness. The higher the carbon content, the more diffi.culi it is to weld these steels. 11. Alloy Wrought Steel. The principal alloying elements usec in steel are nickel, chromium, vanadium, molybdenum, manga· nese, and to a lesser extent, copper, tungsten, cobalt, beryllium boron, and silver. Alloys are used to effect increased strength increased elastic ratio, increased hardness without loss of ductil ity, more uniform structure, better machinability, and bette: resistance to fatigue and corrosion. The proper combination o these properties depends not only on the chemical composition, but largely on the heat-treatment, without which the alloy steels are not greatly s~perior to the plain carbon steels. The effects of heat-treatment' on a typical alloy steel are shown in Fig. 2. With proper alloying and heat-treating, ultimate strengths of over 300,000 psi and yield stresses of over 250,000 psi. are obtainable. Many of the alloy steels are expensive, and their use is therefore limited.

>-' ,..,..

TABLE 3.-PROPERTIES OF TYPICAL ALLOY STEELS

EndurModulus of elast1c1ty Brmell Elonance hard- \ \ gat10n hm1tin Remarks and sugness Material, alloy and S A.E. No. In Tens10n and Shear gested uses Tension Shear Tension Shear reversed num2 Int compression bending G 81 ber % E ------------1---1---1---1---J---l---I I 1---1-------Nickel: S.A E. 2320, water quenched .... 77,000 55,0001 50,000 30,000 49,000 143 30,000,0001 12,000,000 30 Casehardenmg stock 140,000 98,000 110,000 65,000 68,000 277 18 for heavy parts. Nat desirable for thin sections '----•----•----•----•----1---1 I I 01! quenched 75,000 54 ' 0001 48 '000 29,000 46,000 140 30 Gears 30. 000' 0001 12 '000 '000 130,000 90,000 100,000 60,000 50,000 262 18

Ultnnate strnngth

..

S.A.E. 2340, water quenched

Yield stress

••

95' 0001 60. 0001 65. 000 175,000 110,000 150,000

••

38,000 87,000

...

53,000 75,000

183 340

'----•----•----•----•----1---1 oil quenched

93,0001 59,0001 62,000 165 ,000 105 ,ODO 148 ,000

---------------1 Nickel-chromium. ' S A.E. 3120, water quenched

36,000 85,000

55,000 75,000

183 330

l----1----1----1----1---1 86,000 140,000

60,000! 57 ,0001 98,000 115,000

34.000 68,000

55,000

77,000 120,000

55,000 82,000

29,000 57 ,000

46,000 48,000

174

58,000 269 ----•----•----•----•----1---1 oil quenched

---------------1 S A E. 3220, water quenched

163

I

80,000 ~6,000 53,000 55' 000 107 '000 130. 000

36,000 83,000

58,000 72,000

I

187 331

30 16

Forgings, axles

30' 000' 0001 12' 000' 000

17

Gears

51,000 65,000

174 311

~ ~

~ ~

:;,..

~

14 I

I

34 15

30, 000' 0001 12' 000' 000

I

1---------

I

30

30' 000. 0001 12 '000 '000

Heavy sections requiring medium depth casehardemng

5 ~

Vi

18

I 30' 000' 0001 12 '000 '000

!---------

I

33 16

Massive sections requiring

31,000 95,000

~

~

J

241

1----1----1----1----1---1 87,000 60,000 60,000 165,000 115,000 143,000

'

oil quenched.

48,000 96,000

30' 000' 0001 12 '000 '000

C'

30. 000. 0001 12 '000. 000

30 20

deep

hardenmg

case-

0::i: ;..

~ >-< >-