跟著回火溫度的進步，普通來說，鋼的強度目標降服點（σ s ）、抗拉強度（σ b ）不斷降落，而塑性目標伸長率（δ）、斷面壓縮率（ψ）不斷上升。在350℃擺布回火時，鋼的彈性極限到達極大值，在400℃以上回火時，鋼的伸長率（δ）、斷面壓縮率（ψ）上升非常顯著。45鋼淬火后的強度并不高，且塑性很差。如在200?300℃回火得到回火馬氏體，且由于內應力消除，使其強度到達極大值；在350?500℃回火，構造為回火屈氏體，彈性極隈非常高，韌性也較好！在450?600℃回火，得到的構造為回火索氏體，具有良好的概括力學機能，即較高的強度與良好的塑性、韌性相配合。
When the quenched steel is tempered, the mechanical function has also changed accordingly due to changes in the structure.
The change law of hardness of tempered steel forging round manufacturers during tempering. The general change trend is that as the tempering temperature rises, the hardness of the steel falls. However, when the high carbon steel with more carbon content is tempered at 100 °C, the hardness increases slightly, which is caused by the segregation of carbon atoms in martensite and the precipitation of ε-carbide. When tempered at 200 to 300 ° C, the hardness drop is moderated. This is due to the fact that on the one hand, the martensite is interpreted, the hardness is lowered, and on the other hand, the retained austenite is transformed into the lower bainite or the tempered martensite, so that the hardness is increased, and the effects of the two are summarized. After the tempering temperature exceeds 300 ° C, the ε-carbide is transformed into cementite, the coherent trunk system is destroyed, and the cementite cluster grows, causing the hardness of the steel to fall linearly.
The alloying elements in the steel can reduce the tendency of the middle hardness drop in the tempering process to a certain extent, and improve the tempering consolidation. The strong carbides cause the elements to precipitate the dispersed extra-carbons during the tempering at the temperature, which causes the hardness of the steel to rise significantly, resulting in secondary toughness.
(2) Strength and toughness
With the progress of tempering temperature, in general, the steel strength target drop point (σ s ) and tensile strength (σ b ) continue to fall, while the plastic target elongation (δ) and section compression ratio (ψ) keep rising. . When the tempering is performed at 350 ° C, the elastic limit of the steel reaches a maximum value, and when tempered at 400 ° C or more, the elongation (δ) and the section compression ratio (ψ) of the steel rise significantly. The strength of 45 steel after quenching is not high, and the plasticity is very poor. For example, tempered martensite is obtained by tempering at 200~300 °C, and its strength reaches a maximum value due to the elimination of internal stress; tempering at 350~500 °C, the structure is tempered troostite, and the elastic enthalpy is very high. , toughness is also better! Tempered at 450~600 °C, the structure is tempered sorbite, with good general mechanical function, that is, high strength is matched with good plasticity and toughness.