Alloy steels

Alloy steels are those whose composition includes not only iron and carbon, but also an additional element or more. The object is to give to carbon steel a microstructural condition in which the alloy is in solid solution with both alpha аnd gamma iron, so that its strength and hardness are improved.

To predict the effect of any alloy on steel, equilibrium diagrams are used showing its iron-iron carbide relations. The microstructural effects are that alloy steels need less carbon for a pearlitic structure than carbon steels, while the tempe­ratures at which various heat treatments can be employed are rather different from those of carbon steels. There is another important point. Alloy steels are found to harden at lower cri­tical rates, so that the mass of the piece is less important than in carbon steels. It therefore becomes possible to obtain a much more uniform miегоstructure with work of large dimensi­ons.

Consequently, it is often possible for alloy steels to become martensitic in structure with a less drastic form of quenching, oil being substituted for water, with much less danger of crack formation and distortion.

Boron, lanthanum, cerium, etc., known as rare earth metals, are usually added in minute amounts to the melt to give certain properties and to deoxidize and desulphurize the molten metal.

Ex. 30. Разберите каждое предложение и переведите, обращая особое внимание на причастие, герундий, инфинитив и модальные глаголы:

1. Of all the elements alloyed with iron carbon is considered to be the most important one for controlling hardness, strength and wear resistance. 2. Steel to be quench hardened is to be heated to the hardening temperature recommended and held for a sufficient1 period to allow steel to be fully austenitized. 3. High hardness produced by quenching steel being accompanied by excessive brittleness, the task of the designer is to obtain the desired hardness without losing too much of toughness. 4. To select the proper medium steel should be quenched in to obtain the desired degree of hardness the designer is to remember that steel must be quenched rapidly enough to completely suppress the formation of pearlite. 5. The increase in volume during the transformation of austenite setting up very high stresses, there is always a danger of cracking or warping in water-quenched steel containing over 0,55 per cent carbon. 6. To remove residual stresses the yield stress is to be lowered by raising the tempe­rature to that at which residual stresses are expected to produ­ce plastic flow. 7. Stress relief involving the conversion of elastic to plastic strain, some distortion always accompanies the process. 8. If produced by plastic deformation such as for­ming, machining and grinding, internal stresses can be removed by an annealing process known as stress relief. 9. When nucleated new crystals contain very few dislocation, the process of crys­tal growth continuing until all cold worked material has been absorbed. 10. A redistribution of stress within a component to be stress-relieve has been found to occur as the surface layers are removed by machining. 11. By adding reinforcing metals in the form of very fine filaments called “whiskers” to a setter matrix the resulting metal can be given strength approaching the theoretical limit of atomic cohesion. 12. With whiskers possessing very high strength being obtainable in relatively minute quantities, methods are being developed to produce them in experimental amounts.

LIST OF TERMS

A

abrasion - стирание износ

acid – кислота

alumina - глинозем

annealing - отжиг

full a. - полный отжиг

process а. – промежуточный отжиг

antimony - сурьма

arsenic - мышьяк

austenitizing - аустенитизация

B

batch - партия

brine - солевой раствор

brittle - -хрупкий

C

carburizing – цементация, науглероживание

gas с. - газовая цементация

pack с. - цементация в карбюризаторе (твердом)

liquid с. - цементация в жидком карбюризаторе

chlorine - хлор

coarse – крупный

cohesion - сцепление

cold-worked - холоднодеформированный, наклепанный

composite - композит, компози­ционный

contract – сокращать(ся), отжимать(ся)

crack - трещина, трескаться

creep – ползучесть

cut – резать

D

dense - плотный

distortion - искажение, деформация

distribution - распределение

draw - волочить, протягивать

die - штамп

dilute - малоконцентрированный, разбавленный dimension – размер

dispesion - дисперсия

ductile - тягучий, ковкий, пластичный

E

edge - кромка

elastic - упругий

electroplating - гальванопокрытие

elongation - удлинение

expand – расширяться

F

failure – разрушение, разрыв, повреждение

fiber - волокно

f. reinforcement - упрочнение волокнистыми материалами

filament - нить

film - пленка

forming - пластическая обработка

G

grade - сорт, качество

grind - шлифовать

H

harden – закалять, упрочнять

hold - выдерживать

I

imperfection - дефект

L

layer — слой

M

machine (v.) - подвергать механической обработке

machinery steel - конструкционная сталь

magnitude - величина

matrix - матрица

medium (Pl.media) - среда

melt - расплав

N

nitriding - азотирование

nucleus (pl.nuclei) - зд.центр

nucleate - зарождаться

О

oil - масло

Q

quench - закалять, быстро охлаждать; закалка

R

refine - очищать

reflectivity – отражательная способность

relief – снятие

relieve - снимать

rupture - разрыв, излом

S

section - сечение

heavy section – большое сечение

thin-section - малое сечение

sheet - лист

sodium - натрий

specific - удельный

spray - струя, распылять, обрызгивать

spring - пружина

strain - деформация

stress - напряжение

compressive s. - сжимающее напряжение

tensile s. - растягивающее напряжение

yield s. - напряжение текучести

T

technique - метод

tempering - отпуск

tool - инструмент

tough - вязкий

transformation – превращение

U

uniform - однородный

W

warp- коробиться

wear - износ

winding - обмотка

whiskers - усы

wire - проволока, провод

workpiece - заготовка, деталь