45# is the grade of steel, which is a high-quality carbon structural steel, corresponding to the Japanese standard S45C, the American standard: 1045, and the German standard C45. It is characterized by higher strength and deformation resistance than ordinary A3 steel.
Chemical composition element ratio (%):
Carbon C: 0.42～0.50;
Chromium Cr: ≤0.25;
Manganese Mn: 0.50～0.80;
Nickel Ni: ≤0.25;
Phosphorus P: ≤0.035;
Sulfur S: ≤0.035;
Silicon Si: 0.17～0.37
Mechanical behavior
σb\Mpa:≥600
σs\Mpa:≥355
δ5\%:≥16
ψ\%:≥40
Hardness\HB:≤197
The recommended heat treatment system for 45 steel specified in the GB/T699-1999 standard is normalizing at 850°C, quenching at 840°C, and tempering at 600°C, and the achieved performance is yield strength ≥ 355MPa.
The GB/T699-1999 standard stipulates that the tensile strength of 45 steel is 600MPa, the yield strength is 355MPa, the elongation rate is 16%, and the area shrinkage rate is 40%.
Heat Treatment Process for Quenching and Tempering of 45# (No.) Steel and 40Cr Steel.
Quenching and tempering is a double heat treatment of quenching and high-temperature tempering, and its purpose is to make the workpiece have good comprehensive mechanical properties.
Quenched and tempered steel has two categories: carbon quenched and tempered steel and alloy quenched and tempered steel. Whether it is carbon steel or alloy steel, its carbon content is strictly controlled. If the carbon content is too high, the strength of the workpiece after quenching and tempering is high, but the toughness is not enough. If the carbon content is too low, the toughness is improved and the strength is insufficient. To obtain good comprehensive performance of the quenched and tempered parts, the carbon content is generally controlled at 0.30~0.50%.
During quenching and tempering, the entire section of the workpiece is required to be quenched, so that the workpiece can obtain a microstructure dominated by fine needle-like quenched martensite. Through high-temperature tempering, a microstructure dominated by uniformly tempered sorbite is obtained. Small factories can’t conduct metallographic analysis for each furnace. Generally, only a hardness test is performed. That is to say, the hardness after quenching must reach the quenching hardness of the material, and the hardness after tempering is checked according to the requirements of the drawing.
The operation of the workpiece quenching and tempering treatment must be carried out in strict accordance with the process documents. We only give some opinions on how to implement the process during the operation.
Quenching and tempering of No. 45 steel
No. 45 steel is a medium carbon structural steel with good cold and hot working properties, good mechanical properties, low price, and wide sources, so it is widely used. Its biggest weakness is low hardenability, and workpieces with large cross-sectional dimensions and relatively high requirements should not be used.
The quenching temperature of No. 45 steel is A3+(30~50) ℃. In actual operation, the upper limit is generally taken. A high quenching temperature can speed up the heating of the workpiece, reduce surface oxidation, and improve work efficiency. To homogenize the austenite of the workpiece, sufficient holding time is required. If the actual furnace load is large, it is necessary to appropriately extend the holding time. Otherwise, there may be insufficient hardness due to uneven heating. However, if the holding time is too long, there will also be coarse grains and serious oxidative decarburization, which will affect the quenching quality. We believe that if the furnace loading is greater than the requirements of the process document, the heating and holding time should be extended by 1/5.
Because of the low hardenability of No. 45 steel, a 10% salt solution with a large cooling rate should be used. After the workpiece enters the water, it should be hardened, but not cold through. If the workpiece is cooled in salt water, it may crack the workpiece. This is because when the workpiece is cooled to about 180 °C, the austenite rapidly transforms into martensite. caused by excessive tissue stress. Therefore, when the quenched workpiece is rapidly cooled to this temperature region, a slow cooling method should be adopted. Since it is difficult to grasp the water temperature, it must be operated by experience. When the workpiece in the water stops shaking, it can be cooled by water and air (if it can be oil-cooled, it is better). In addition, the workpiece should be moved and not static when it enters the water and should be moved regularly according to the geometric shape of the workpiece. The static cooling medium and the static workpiece will cause uneven hardness and uneven stress, which will cause the workpiece to deform and even crack.
The hardness of No. 45 steel quenched and tempered parts after quenching should reach HRC56~59, and the cross-section may be lower, but not lower than HRC48, otherwise, it means that the workpiece has not been fully quenched, and sorbite or even ferrite may appear in the structure The tissue, through tempering, remains in the matrix and cannot achieve the purpose of tempering.
For the high-temperature tempering of No. 45 steel after quenching, the heating temperature is usually 560~600℃, and the hardness is required to be HRC22~34. Because the purpose of quenching and tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide. However, if the drawings have hardness requirements, the tempering temperature must be adjusted according to the requirements of the drawings to ensure the hardness. For example, some shaft parts require high strength, and the hardness requirements are high; while some gears and shaft parts with key grooves need to be milled and inserted after quenching and tempering, so the hardness requirements are lower. Regarding the tempering holding time, it depends on the hardness requirements and the size of the workpiece. We believe that the hardness after tempering depends on the tempering temperature, which has little to do with the tempering time, but it must be back through. Generally, the tempering holding time of the workpiece is always more than an hour.
Application
No. 45 steel is widely used in machinery, without heat treatment: HB≤229; heat treatment: normalizing; impact energy: Aku≥39J; high strength, good plasticity, and toughness, 45# steel after quenching and before tempering, the hardness is greater than HRC55 (up to HRC62) is qualified, after heat treatment, and then tempering can reach HRC42-46, which can not only ensure its good mechanical properties but also obtain the hardness requirements of the surface, used to make small cross-section adjustment with large load Large normalized parts with low-quality parts and less stress, as well as surface quenched parts that do not require high core strength, such as pins, guide posts, watch hands and other components.
Identify the model
- Often by grinding with a grinding wheel to see the spark, the white one is high carbon steel, such as 45# steel, and the red one is A3 steel.
- 45 steel and Q235 materials are ground on the stone, and the Q235 is easy to ground off.
- Hit with a hammer, the marks of 45 steel are much lighter than those of Q235 (A3) because Q235 is much softer than 45 steel.
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