Hardening plain carbon steel

The hardening of plain carbon steel consists of two stages: first heating to a specific temperature and then cooling rapidly. The cooling process is known as quenching. The correct temperature to which steel must be heated varies with its carbon content (see Fig. 1). Overheating can cause grain growth resulting in weak components.

Temperature (ºC)

0.1

0.3

0.5

0.7

0.9

1.1

% carbon content

Fig. 1. …………………….

The hardness of the heat-treated steel depends on two factors:

1. Type of quenching bath.

This contains either water or quenching oil, depending on the speed of cooling required. The more rapidly a plain carbon steel is cooled, the harder it is. However, overrapid cooling can result in faults, e.g. cracking and distortion. Therefore, the correct quenching bath should be chosen to treat the workpiece as required (see Table 2).

2. The carbon content (see Table 1).

Note

workpiece n – обрабатываемое изделие

Table 1. ………			Table 2. …….
% Carbon Content of Steel	Effect of Hardening		% Carbon Content	Quenching Bath	Required Treatment
0.0 – 0.25	No effect		0.3 – 0.5	oil	toughening
0.3 – 0.5	Some effect: becomes tougher		0.5 – 0.9	oil	toughening
0.5 – 0.9	Good effect: becomes hard		0.5 – 0.9	water	hardening
0.9 – 1.3	Very good effect: becomes very hard		0.9 – 1.3	oil	hardening

Table 3. Requirements for Hardening Plain Carbon Steel

Rеquirements	% Carbon Content	Maximum Temperature, C	Quenching Bath
1. Very hard plain carbon steel component
2. Hard plain carbon steel component
3. Tough plain carbon steel component

5.7. a) Read the text Welding Processes and find a key sentence in each paragraph. Sum up the key sentences and give the main ideas of the text. b) Write out phrases with -ing forms and translate them.

Vocabulary

intimate proximity	—	непосредственная близость
fusion n	—	плавление
interpenetration n	—	взаимопроникновение
weld n	—	сварной шов
riveting n	—	клепка
fusion welding	—	сварка плавлением
filler metal	—	присадочный металл
filler metal feed	—	подача присадочной проволоки
manual welding	—	ручная сварка
semiautomatic welding	—	полуавтоматическая сварка
pressure welding	—	сварка давлением
thermal conductivity	—	теплопроводность
deposited layer	—	наплавленный слой, наплавка
parent metal	—	основной металл, перешедший в шов
fusion line	—	линия сплавления
sound weld	—	качественный сварной шов
heat-affected zone (HAZ)	—	зона термического влияния (ЗТВ)
welded structure	—	сварная конструкция
butt joint	—	стыковое соединение
lap joint	—	соединение внахлестку
T joint	—	Т-образное соединение
corner joint	—	угловое соединение