Alloy cast steels

Alloy cast steels find use in the production of castings which must have improved mechanical properties, enhanced resistance to wear, corrosion, heat, and so forth. The alloying elements commonly used here are Cr, Ni, Mo, V or Si, and Mn.

Manganese cast steels come in three types, low-alloy (up to 2 %Mn), medium-alloy (2.5-4% Mn), and high-alloy (up to 20% Mn). Low-alloy steel shows improved mechanical properties, as against common carbon steel, and compares with the latter in casting properties. Medium-alloy steel has enhanced wear resistance and high strength, but low plastic properties. This steel is suitable for gears, cams, and other parts operating under friction conditions.

High-alloy steel (up to 13% Mn) enjoys the most extensive applications. It is well stable to wear under impact loads. The uses include track shoes of crawler-mounted machines, excavator bucket teeth, and others. An increased manganese content imparts fluidity to steel, but raises its shrinkage and tendency to form hot cracks and oxide spots in castings.

Chromium cast steels come in low-alloy (1 or 2% Cr), medium-alloy (3 to 5% Cr), and high-alloy grades (30% Cr).

Low-alloy steel works well in abrasion, has high strength, but insufficient ductility. Small percentages of molybdenum, vanadium, and tungsten added to low-chromium steel raise its ultimate strength to 1,862 MPa. Medium-alloy steels have increased strength at high temperatures and resist well the attack by some chemical substances. High-alloy steels feature enhanced high-temperature strength at temperatures approaching 1,100°C.

Chromium cast steels exhibit low fluidity. High-chromium steels have high shrinkage and tendency to develop cracks and shrinkage cavities. Overheating before pouring and an increased pouring rate (double the pouring rate for carbon steel), make chromium steel fill better the molds.

Chromium-nickel cast steels have high strength, increased ductility, corrosion resistance, and high-temperature strength. Low-alloy steels of this type contain 1 or 2% Cr, 1.5 to 3% Ni, 0.2 to 0.5% C. They show enhanced strength.

Chromium-nickel corrosion-resistant steels are highly heat resistant. They contain 0.1-0.4% C, 0.8-1% Si, 0.4-0.6% Mn, 17-19% Cr, and 7-9% Ni. Examples of uses are parts of steam and gas turbines and other parts designed for high-temperature service.

Chromium-nickel cast steels are inferior to common carbon steels in fluidity. In order that they fill better the molds, these steels need overheating and high speeds of pouring. Solidification of castings gives rise to a coarse-grained macrostructure which fosters hot cracking. For this reason, in running the castings from chromium-nickel steels, it is advisable to resort to multiple gating to avoid local overheating, use well deformable cores and molds, and choose the correct pouring temperature for every casting.

Silicon cast steels exhibit an increased wear resistance and chemical stability. Low-alloy steels of this type contain up to 2% Si, and high-alloy steels up to 20% Si. High-alloy steels are very hard and brittle, and low-alloy steels are highly susceptible to hot cracking, which necessitates molds and cores of good deformability and slow and uniform cooling of castings.

Industry also employs copper cast steels for the production of cast crankshafts, pistons, and other parts, and tungsten cast steels for cutting tools. Tungsten cast steels have low fluidity and increased shrinkage.

Task 1

Find in the text English equivalents to the following words and word combinations.

механічні властивості, легуючі елементи, бути придатним до, ударне навантаження, гусеничний, придавати (наділяти), усадка, оксидна плівка, стирання (зношування), ковкість, усадкові порожнини, бути гіршим (за якістю), наповнювати форму, крупно зерниста структура, бажано, уникати, рівномірне охолодження.

Task 2

Match the following words with their translation:

A	B
1. crankshaft	a) затвердіння
2. piston	b) колінчатий вал
3. brittleness	c) зношення
4. deformability	d) поршень
5. fluidity	e) текучість
6. solidification	f) крихкість
7. casting	g) виливок
8. wear	h) здатність до деформації

Task 3

Fill in the correct words from the list below. Use each word only once.

spots, plastic, wear, cast, applications, pouring, strength,

crawler, overheating, friction, properties, solidification,

1. most extensive …	7. correct … temperature
2. … before pouring	8. resistance to …
3. manganese … steels	9. increased …
4. oxide … in castings	10. improved mechanical …
5. … of castings	11. …mounted machines
6. low … properties	12. under … conditions

Task 4

Give Ukrainian equivalent to the following words and word combinations.

production of castings, alloying elements, low-alloy steel, wear resistance, low plastic properties, gears, cams, friction conditions, extensive applications, impact loads, ultimate strength, crawler-mounted machines, excavator bucket teeth, insufficient ductility, low fluidity, shrinkage, pouring rate, steam and gas turbines, molds, multiple gating, chemical stability, tungsten.

Task 5

Fill in the gaps with the verbs given below used in the proper tense form.

to raise, to have, to need, to be, to work, to give, to enjoy, to be suitable

1. In order that they fill better the molds, these steels _____ overheating and high speeds of pouring.

2. Medium-alloy steels _____ for gears, cams, and other parts operating under friction conditions.

3. Low-alloy steel _____ well in abrasion, has high strength, but insufficient ductility.

4. An increased manganese content imparts fluidity to steel, but _____ its shrinkage and tendency to form hot cracks.

5. Alloy cast steels find use in the production of castings which _____ improved mechanical properties, enhanced resistance to wear, corrosion, heat, and so forth.

6. Solidification of castings _____ rise to a coarse-grained macrostructure which fosters hot cracking.

7. High-alloy steel _____ most extensive applications.

8. Chromium-nickel cast steels _____ inferior to common carbon steels in fluidity.

Task 6

Translate the following word combinations into Ukrainian paying attention to the Past Participle.

elements used, improved mechanical properties, enhanced wear resistance, tungsten added, enhanced strength, increased ductility, parts designed for, used elements, cracks developed, applied loads, solidified castings, raised temperature, examples given in the report.

Task 7

Make up sentences from the given words. Start with the underlined word.

1. suitable Medium-alloy operating for is, cams, other and parts friction under gears conditions.

2. manganese form The addition hot of the tendency to in castings cracks raises.

3. are steels production crankshafts pistons, used for the Copper of and other parts cast.

Task 8

Answer the following questions:

1. What alloying elements are mentioned in the text “Alloy cast steels”?

2. What steel works well in abrasion?

3. What steels can resist the effect of some chemical substances?

4. Why are chromium-nickel corrosion-resistant steels used for steam and gas turbines?

5. Where are copper and tungsten steels used?

Task 9

Fill in the table using the information from the text above.

steel	good properties	poor properties	usage
Manganese low alloy medium alloy high-alloy
Chromium low-alloy medium-alloy high-alloy
Chromium-nickel
Silicon
Copper
Tungsten

Дата добавления: 2015-07-20