Water- grade tool steel

W-grade tool steel has got such a name because it must be water quenched. W-grade steel is essentially high carbon steel. This type of tool steel is the most commonly used tool steel because of its low cost compared to other tool steels. It works well for small parts and applications where high temperatures are not encountered; at above 150 °C (302 °F) it begins to soften to a noticeable degree. Hardenability is low so W-grade tool steels must be quenched in water. These steels can attain high hardness and are rather brittle compared to other tool steels.

The toughness of W-grade tool steels is increased by alloying with manganese, silicon and molybdenum. Up to 0.20% of vanadium is used to retain fine grain sizes during heat treating.

Typical applications for various carbon compositions are:

• 0.60–0.75% carbon: machine parts, chisels, setscrews; properties include medium hardness with good toughness and shock resistance.
• 0.76–0.90% carbon: forging dies, hammers, and sledges.
• 0.91–1.10% carbon: general purpose tooling applications that require a good balance of wear resistance and toughness, such as drills, cutters, and shear blades.
• 1.11–1.30% carbon: small drills, lathe tools, razor blades, and other light-duty applications where extreme hardness is required without great toughness.

The first air hardening grade tool steel was mushet steel, which was known as air-hardening steel at the time.

A2 is the most common air hardening grade currently used.

Grade-O refers to oil hardening tool steels, while grade-A refers to air hardening tool steels. These tool steels are used for parts that require minimal distortion during hardening. These steels are also less likely to crack and are often used to make knife blades.

D-grade tool steels contain between 10% and 18% chromium. These steels retain their hardness up to a temperature of 425 °C (797 °F). Common applications for this grade of tool steel is forging dies, die-casting die blocks, and drawing dies. Due to high chromium content, certain D-grade tool steels are often considered to be stainless or semi-stainless.

Unit 12

1. Memorize the following words:

latter alloy steel tungsten exist prolong retard replace excel favour abrasion rate device purpose scaling shortcoming permeability engineering power impart growth as regards permanent

последний из упомянутых легированная сталь вольфрам существовать продлевать замедлять заменять превосходить благоприятствовать стирание скорость устройство цель окалина, накипь недостаток магнитная проницаемость техника, технология энергия придавать рост, увеличение что касается постоянный

останній із згаданих легована сталь вольфрам існувати подовжувати сповільнювати, затримувати заміняти перевершувати сприяти стирання швидкість пристрій мета окалина, накип недолік магнітна проникність техніка, технологія енергія надавати ріст, збільшення що стосується постійний

1. Practise the reading of the following words:

Permeability, engineering, power, purpose, abrasion, excel, favour, chromium, tungsten, vanadium, titanium, cobalt, intercrystalline, niobium, zirconium, structural, quality, superhigh, turbine, manufacture, measuring, thermal, valuable, exceptionally, nitric.

1. Read and translate the text:

Alloy steel

Alloy steels are those which in addition to carbon contain some alloying elements imparting them certain distinctive properties. The main alloying elements of these steels are: chromium, nickel, tungsten, vanadium, molybdenum and also silicon and manganese in large propotions. Alloy steels possess the properties that do not exist in carbon steels. Moreover, they do not have the shortcomings of the latter. The effects of alloying elements on the properties of alloy steels are the following.

1. Chromium increases hardness and strength of steel but decreases ductility. The steel with over 18% chromium becomes corrosion-resistant.
2. Nickel imparts higher strength, ductility and corrosion resistance to steel. It also raises the impact strength.
3. Tungsten has the property of adding hardness to steel.
4. Vanadium makes steel stronger and harder and also gives it higher resistance to impacts, abrasion and rupture.
5. Cobalt imparts higher temperature strength and permeability.
6. Molybdenum increases hardness, elasticity and strength as well as oxidation resistance at high temperatures.
7. Silicon contained in a proportion of over 1% adds strength, raises elasticity, acid resistance and permeability.
8. Manganese added in an amount of 1% and over prolongs wear life without decreasing ductility.
9. Aluminum gives higher resistance to scaling.
10. Titanium adds strength and reduces intercrystalline corrosion.
11. Niobium favours the growth of corrosion resistance and acid resistance.
12. Zirconium imparts strength and retards grain growth.
13. Copper reduces corrosion.

By the amount of alloying elements added to steels they are low-alloy, medium-alloy and high-alloy steels containing up to 3%, from 3 to 10%, and over 10%, respectively. As regards the purpose they have to serve, alloy steels fall into three categories: structural steels, tool steels and special steels with specific physical and chemical properties.

Structural steels come as good-quality, high-quality and superhigh-quality steels. They find wide application in industry, for example, for the manufacture of bolts, springs, automobile parts, shafts, axles, connecting rods, gears, turbine components and many others.

Alloy tool steels are used for the manufacture of cutting, measuring, impact and stamping tools. The tools made of these steels considerably excel in quality the tools of carbon steels, as they are harder and more resistant to wear. Cutting tools withstand high temperatures without reduction in hardness, so they can work at high cutting rates.

Special alloy steels are widely used in power engineering, rocket engineering, turbine technology, gas and oil producing industry. This group of steels includes magnet and nonmagnetic steels, steels with high electrical resistance, and steels with specific thermal and elastic properties. Magnet steels go into the production of permanent magnets, electromagnets, rotors and stators. Nonmagnetic steels replace expensive nonferrous metals in precision instruments where the material magnetization can affect the accuracy of readings. Alloy steels with specific thermal properties have exceptionally high elasticity and durability and are valuable for the production of various springs and membranes for watches, instruments and other devices.

Steels with specific chemical properties are getting more and more important as chemical, oil-and-gas and other industries require more and more metal resistant to attack by corrosive atmosphere. Thus, steels containing large amounts of chromium and nickel are used to produce parts intended to work in nitric, sulfuric, phosphoric and other acids.

1. Find in the text English equivalents for the following words and word-combinations:

За кількістю легуючих елементів, постійні магніти, що стосується цілей, більш того, на додаток до, відповідно, перевершувати за якістю, частини, призначені для роботи в кислотах, виключно висока еластичність, без зниження твердості, сприяє зростанню, точність показань.

1. Answer the following questions:

1. What steels are called alloy steels?

2. What is the purpose of adding alloying elements to steel?

3. How do alloy steels differ from carbon steels?

4. What metals can be alloying elements for steel?

5. What is the effect of aluminum as an alloying element?

6. What amount of alloying elements can high-alloy steel contain?

7. How are alloy tool steels used?

8. In what fields are special alloy steels used?