Medium-carbon steel has a carbon content of 0.25 – 0.60 wt.% and a manganese content of 0.60 – 1.65 wt.%. The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure.
Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened.
Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.
Medium-carbon steel has approximately 0.3–0.6% carbon content. These alloys may be heat-treated by austenitizing, quenching, and then tempering to improve their mechanical properties. They are most often utilized in the tempered condition, having microstructures of tempered martensite. Medium-carbon steel balances ductility and strength and has good wear resistance. This grade of steel is mostly used in the production of machine components, shafts, axles, gears, crankshafts, coupling and forgings, could also be used in rails and railway wheels and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, and toughness.
For example, a 1040 steel is a plain carbon steel containing 0.40 wt% C. Typical uses of this type of steel include machine, plow, and carriage bolts, tie wire, cylinder head studs, and machined parts, U-bolts, concrete reinforcing rods, forgings.
Medium carbon steel is a grade of ferrous metal, meaning that it contains iron. There are vast applications, and thus, benefits, of this highly ductile and strong alloy. Continue reading to learn more about medium-carbon steel, including its most common applications, and what you can do with your leftover scrap metal.
The uses for medium-carbon steel are defined by the requirement for a high tensile strength and ductility that, despite its brittleness when compared to other forms of steel, make it the preferred choice. Between 0.3 and 0.7 percent carbon is added during the manufacturing process to create a medium or mid-range steel product. This specific range of carbon is combined with a process of quenching (i.e., cooling the steel from the outer surface to the inner) and tempering to create a structure that has a consistent tensile strength (referred to as Martensite) throughout the body.
Medium carbon steel has carbon content between 0.25% and 0.65%. It can be easily heat treated for added strength with very low risk of Hydrogen Embrittlement after plating. It has a tensile strength between 100,000 psi and 120,000 psi (690 MPa to 830 MPa).
SAE Grade 5 (metric class 8.8) is generally made from medium carbon steel with AISI grades 1038, 1040, 1045, 1541, 5132, and 5135 falling into this category.
The demand for medium carbon low alloy steels is progressively increasing in automotive, aerospace, defense, and other industries. The reason behind this is their superior mechanical properties, excellent fracture toughness, and high fatigue resistance and wears resistance. These properties are attributed to the lathα′ and retained γ phases in their microstructure developed by the heat–treatment process. Quenching and tempering (QT) process is one of the widely used heat–treatment processes in the manufacturing industry. Quenching process develops carbon supersaturated α′ phase, while subsequent tempering diffuses excess carbon of α′ phase into retained γ phase.
Lath martensitic transformation during the QT process divides the prior γ grain into many packets and further subdivided each packet into blocks of parallel aligned laths. As both the packet and block exhibit high angle grain boundaries, these are considered to have a significant impact on the mechanical properties of steel.
It has been reported that properties achieved by QT processes can be further improved by grain size reduction, which is possible through microalloying, cyclic heat–treating and controlling starting microstructure during the manufacturing of steel. Cyclic heat–treating is one of the most suitable, easier, and economical method involves the repetition of QT processes. Few investigations have been conducted on cyclic heat–treatments by repeating QT processes twice (DQT). The DQT cyclic heat–treatment involves austenitizing, oil quenching, intermediate low–temperature tempering, re–austenitizing, and second oil quenching followed by moderate temperature tempering.
Medium carbon low alloy steel having a specific composition was produced and cast in the laboratory. This steel was subjected to cyclic heat–treatments including conventional single (SQT), double (DQT), and triple (TQT) quenching and tempering processes. Microstructure analysis and mechanical test results were obtained to validate the microstructure/mechanical properties relationship. Fractography was also performed to evaluate the fracture mechanism. Immersion corrosion analysis was carried out in 5 wt% NaCl solution and morphology, elemental composition and distribution of corrosion products were studied.
Medium carbon steels for high-strength; high-fatigue-resistant applications have been traditionally hardened by austenitizing, quenching to martensite, and tempering. When high strength and moderate toughness are required, tempering is performed at low temperatures, around 200 °C (390 °F), and when moderate strengths and high toughness are required, tempering is performed at high temperatures, around 500 °C (930 °F). In order to provide for good hardenability and through-section hardening, steels subjected to hardening heat treatments are alloyed with significant percentages of chromium, nickel, and/or molybdenum.
This class of steels uses microalloying to develop extra strength in ferrite/pearlite microstructures produced directly on cooling from forging temperatures. Microadditions of vanadium and niobium, below 0.20%, are less expensive than substantial alloying additions of chromium, nickel, and molybdenum used for hardenable steels, and the fact that good strengths are achieved by direct cooling after forging without subsequent multistep heat treatment adds to reduced costs and increased productivity.
| Physical Properties | Metric | English | Comments |
|---|---|---|---|
| Density | 7.75 – 7.89 g/cc | 0.280 – 0.285 lb/in³ | Average value: 7.85 g/cc Grade Count:914 |
| Particle Size | 6.7 – 12 µm | 6.7 – 12 µm | Average value: 9.27 µm Grade Count:12 |
| Mechanical Properties | Metric | English | Comments |
| Hardness, Brinell | 126 – 578 | 126 – 578 | Average value: 247 Grade Count:831 |
| Hardness, Knoop | 145 – 616 | 145 – 616 | Average value: 276 Grade Count:838 |
| Hardness, Rockwell B | 71 – 112 | 71 – 112 | Average value: 94.8 Grade Count:779 |
| Hardness, Rockwell C | 9.0 – 71 | 9.0 – 71 | Average value: 25.9 Grade Count:703 |
| Hardness, Vickers | 131 – 614 | 131 – 614 | Average value: 265 Grade Count:838 |
| Tensile Strength, Ultimate | 450 – 2730 MPa | 65300 – 396000 psi | Average value: 987 MPa Grade Count:835 |
| Tensile Strength, Yield | 245 – 1740 MPa | 35500 – 252000 psi | Average value: 685 MPa Grade Count:828 |
| Elongation at Break | 5.0 – 34.2 % | 5.0 – 34.2 % | Average value: 18.9 % Grade Count:819 |
| Reduction of Area | 20 – 71.4 % | 20 – 71.4 % | Average value: 49.7 % Grade Count:526 |
| Modulus of Elasticity | 187 – 213 GPa | 27100 – 30900 ksi | Average value: 203 GPa Grade Count:899 |
| Bulk Modulus | 152 – 163 GPa | 22000 – 23600 ksi | Average value: 160 GPa Grade Count:863 |
| Poissons Ratio | 0.28 – 0.30 | 0.28 – 0.30 | Average value: 0.290 Grade Count:884 |
| Fatigue Strength | 138 – 614 MPa | 20000 – 89100 psi | Average value: 370 MPa Grade Count:13 |
| Fracture Toughness | 80.9 – 143 MPa-m½ | 73.7 – 130 ksi-in½ | Average value: 120 MPa-m½ Grade Count:4 |
| Machinability | 40 – 80 % | 40 – 80 % | Average value: 60.1 % Grade Count:641 |
| Shear Modulus | 72.0 – 82.0 GPa | 10400 – 11900 ksi | Average value: 79.6 GPa Grade Count:891 |
| Izod Impact | 9.00 – 135 J | 6.64 – 99.6 ft-lb | Average value: 45.7 J Grade Count:256 |
| Charpy Impact | 10.8 – 65.0 J | 8.00 – 47.9 ft-lb | Average value: 31.7 J Grade Count:8 |
| Electrical Properties | Metric | English | Comments |
| Electrical Resistivity | 0.0000166 – 0.0000263 ohm-cm | 0.0000166 – 0.0000263 ohm-cm | Average value: 0.0000213 ohm-cm Grade Count:795 |
| Thermal Properties | Metric | English | Comments |
| CTE, linear | 10.4 – 15.1 µm/m-°C | 5.78 – 8.39 µin/in-°F | Average value: 12.9 µm/m-°C Grade Count:592 |
| Specific Heat Capacity | 0.470 – 0.519 J/g-°C | 0.112 – 0.124 BTU/lb-°F | Average value: 0.477 J/g-°C Grade Count:616 |
| Thermal Conductivity | 21.9 – 52.0 W/m-K | 152 – 361 BTU-in/hr-ft²-°F | Average value: 47.7 W/m-K Grade Count:710 |
| Processing Properties | Metric | English | Comments |
| Processing Temperature | 166 – 838 °C | 331 – 1540 °F | Average value: 600 °C Grade Count:8 |
| Component Elements Properties | Metric | English | Comments |
| Aluminum, Al | 0.020 – 1.15 % | 0.020 – 1.15 % | Average value: 0.324 % Grade Count:4 |
| Boron, B | 0.00050 – 0.0030 % | 0.00050 – 0.0030 % | Average value: 0.00175 % Grade Count:43 |
| Carbon, C | 0.10 – 1.29 % | 0.10 – 1.29 % | Average value: 0.418 % Grade Count:952 |
| Chromium, Cr | 0.13 – 4.5 % | 0.13 – 4.5 % | Average value: 0.829 % Grade Count:597 |
| Cobalt, Co | 4.5 – 8.0 % | 4.5 – 8.0 % | Average value: 6.60 % Grade Count:5 |
| Copper, Cu | 0.20 – 0.50 % | 0.20 – 0.50 % | Average value: 0.300 % Grade Count:9 |
| Iron, Fe | 78.7 – 100 % | 78.7 – 100 % | Average value: 97.4 % Grade Count:952 |
| Manganese, Mn | 0.10 – 3.0 % | 0.10 – 3.0 % | Average value: 0.913 % Grade Count:949 |
| Molybdenum, Mo | 0.030 – 4.25 % | 0.030 – 4.25 % | Average value: 0.266 % Grade Count:476 |
| Nickel, Ni | 0.15 – 10 % | 0.15 – 10 % | Average value: 1.13 % Grade Count:294 |
| Phosphorus, P | 0.0080 – 0.40 % | 0.0080 – 0.40 % | Average value: 0.0363 % Grade Count:918 |
| Silicon, Si | 0.050 – 2.2 % | 0.050 – 2.2 % | Average value: 0.292 % Grade Count:666 |
| Sulfur, S | 0.0020 – 0.50 % | 0.0020 – 0.50 % | Average value: 0.0546 % Grade Count:921 |
| Vanadium, V | 0.030 – 1.0 % | 0.030 – 1.0 % | Average value: 0.176 % Grade Count:57 |
