Chromium strengthens special steels
Used as an alloying element in special steels, chromium contributes resistance to corrosion, shocks, extreme temperatures and wear, friction hardness and strength. Special steels account for approximately 15% of ferrochrome use today and are used in applications such as industrial tools, cutting tools, injection moulds, camshafts, dies, and mill rollers. Grades of special steels are designed for the specific applications they enable.
Chromium-containing special steels can be broken down in 3 main categories: engineering steels, tool and high-speed steels and chrome-nickel alloys.
Engineering steels
%
of chromium-containing special steels are alloyed engineering steels.
Properties of engineering steels
Chromium alloyed engineering steels play an important role in everything from the automotive industry to power generation, mining and construction. The addition of chromium to engineering steels improves the mechanical properties of the steel, increasing temperature resistance, mechanical strength and hardness.
Increased temperature resistance
Improved mechanical properties
Mechanical strength and hardness
Where engineering steels are used
Sector demand for engineering steels
Automotive
The automotive industry is a major consumer of long engineering steel products such as bearing steels, spring steels, heat treatable steels and case hardening steels as well as flat engineering steel products for automotive sheets.
Mining
High strength and wear resistant steel plate, as well as case hardening and heat treatable steels, represent the main bulk of chromium alloyed engineering steels used in the mining sector.
Case hardening steels can be found in:
- Drivelines of mining equipment
- Heavy duty transmissions
- Earthmoving equipment
- Heavy duty construction cranes.
Heat treatable engineering steels are used in parts for:
- Machine tools
- General mechanical engineering
- Shafts in heavy engines
- Structural components for heavy demands
- Other high strength mechanical engineering components.
Architecture, building and construction
With regard to structural steels, three major steel groups are used; carbon steels, high-strength low-alloy steels (HSLA) and high-strength quenched and tempered alloy steels. Each of these types of steel contain chromium however, quenched and tempered alloy steels can bear up to 3% chromium.
Power
generation
Chromium alloyed engineering steels are used widely in power generation. Here are some of the main applications:
Case hardening steels are used for:
- Gear wheels
- Large components in hydroelectric power stations
- Wind turbine generators
- Propeller drives of drilling rigs
- Steam turbine gears of power stations.
Heat treatable steels are used in:
- Turbine and generator shafts in power stations
- Fastening elements such as high strength bolts.
Chromium alloyed engineering steels are used in:
- Boiler tubes and heat exchanger pipes
- Boiler superheater and reheater cylinders
- Water divider boards in complex fossil-fuelled control plants
- Heat recovery steam generators
- Plate for pressure vessels and high temperature vessels.
Rail infrastructure
Chromium-containing steel is used for railway track rails. The two major chromium-bearing steels used in the manufacturing of rails are R320Cr and R370CrHT, which contain about 0.8-1.2% and 0.4-0.6% chromium, respectively.
Mechanical engineering
Chromium alloyed engineering steels are widely used in mechanical engineering in parts for all kinds of metal transforming machinery including:
- Forging presses
- Metal rolling equipment
- Machine tools
- Mechanical engineering parts
Case hardening steels are used in:
- Coupling parts
- Gears
- Bolts
- Special purpose screws such as self-drilling screws.
Chromium-containing heat treatable steels are used in:
- Machine tools
- High strength mechanical engineering components
- High strength welded components as well as structural components for very heavy demands
- Fastening elements such as high strength bolts, standard bolts, screws and high toughness crank shafts.
Industrial use for engineering steels
Bearing steels
Bearing steels, containing up to 1.8% chromium, are found in almost all rotating or oscillating machine elements – such as shafts, axles or wheels – to support, guide and transfer loads between machine components.
Pressure vessels
Pressure vessels, containing up to 1.5% chromium, are generally for industrial use but are also used in some private sector applications such as hot water storage tanks and diving cylinders.
Typical industrial uses for pressure vessels include distillation towers, hydraulic reservoirs, and containment of liquified gases. Pressure vessels can be used for high-pressure or low-pressure containment as well as cooling and process heating.
Chromium-containing wear resistant steels are used in:
- Cement pouring and forming equipment
- Conveyor system
- Excavation equipment
- Shovels of wheel loaders
- Bodies of trough tipping wagons
- Road machines
- Pulp and paper processing
- Wood processing.
Spring steel
Spring steel, containing between 0.65% and 1.05% chromium, is a wide range of steels used for industrial suspension applications including springs such as cup springs, return springs or suspension springs. These springs usually can be bent, compressed, extended, or twisted continuously and returned to their original shape.
Tool steels
%
of hot working tool steels are used in the automotive and transportation sector (48%) or for industrial purposes (38%).
Properties of tool steels
Properties of hardness, resistance to abrasion, deformation and elevated temperature make tool steels and high-speed steels particularly well suited to being used for tools. High-speed steels are used mainly in the manufacture of cutting tools. In these steels, chromium’s unique properties play a critical role in the hardening mechanism, while at higher temperatures, it contributes to increased strength.
Most tool steels contain chromium.
Hardness
Resistance to deformation
Resistance to abrasion
Resistance to elevated temperatures
Where tool steels and high-speed steels are used
Types of tool steels and their applications
Plastic mould steels
Hot working tool steels
Hot working tool steels are used in applications where the surface temperature generally is above 200°C/392°F. In such applications the tool steels come into contact with hot materials often exceeding 1,000°C. Chromium enables hot working tool steels to withstand the universal mechanical and abrasive stress which tool steels are generally exposed to, as well as the enormous thermal load from hot working.
The automotive and transportation industry (48%) and industrial usage (38%) are the two main end-use areas for hot working alloy tool steels.
Cold working tool steels
Critical properties of cold working tool steels include high hardness, good ductility, low dimensional changes under heat treatment, and adequate machinability.
These steels are used to produce tools that do not generally work at a surface temperature of more than 200°C and are mainly used in metal cutting and metal forming applications (47%) such as cutting, stamping, punching, shearing and blanking. They are also used in non-cutting metal forming applications, such as pressing, bending, forming and deep-drawing (30%).
High speed steels
High speed steels (HSS) are a class of tool steels used for machining and cutting applications at high speeds that require high hot hardness. Usually, high speed steels are alloyed with significant amounts of tungsten, molybdenum, cobalt, vanadium and chromium in addition to iron and carbon.
HSS are used for a variety of purposes including drills commonly found in machine shops, milling of both ferrous and nonferrous materials, cutting knives and blades such as wood chipper, pelletizer knives and cutting wheels as well as in the manufacture of injector needles and nozzles.
HSS cutting knives and blades
Depending on the cutting application there is a wide range of high-speed steel blades and knives used. Knife applications include: pelletizer knives, granulating knives, sheeter knives, slitter knives, rotary cutter knives, planer knives, wood-chipper knives, pipe cutting wheels, shear blades, band knives and circular knives.
HSS other applications
HSS is used in the manufacture of injector needles and nozzles, cutting tools for complex holes or surfaces blanking plus taps and dies.
HSS mills
HSS mills provide good wear resistance and are used for general purpose milling of both ferrous and nonferrous materials. End mills, the most common milling cutters, are available in a wide variety of lengths, diameters, and types. A square end mill is used for most general milling applications, producing a sharp edge at the bottom of pockets and slots.
HSS drills
HSS drills are often found in machine shops with low-volume runs. They are a more economical option in shops where the equipment’s cutting speeds are limited or for applications with heavy interruptions and / or weak setups.
