Study On Stress Relaxation Effect And Low Temperature Performance Of Induction Tempered Q550D Steel

Q550D steel is a kind of micro-alloy low carbon bainite steel with high strength, goodtoughness, strong wear resistance and corrosion resistance, excellent low temperaturetoughness, processability and welding performance, etc. They are widely used in engineeringmachinery, coal machinery, shipbuilding and steel structure, etc. Tempering after quenchingis an important heat treatment process which is used to increase the toughness, eliminateinternal stress, improve dimensional stability and uniformity of the steel. The traditionaltempering is proceeding in the box type resistance furnace, gas furnace, or infrared furnace.Its tempering time is long, energy consumption is high, operation is complicated. The qualitycan’t be guaranteed due to the space limitations of the tempering furnace in batch processing.The production efficiency is low, the production cost is high. It can’t adapt to the currentconcept of environmental protection and energy saving production. Therefore, as the heattreatment equipment upgrading, the research and development of the induction temperingwhich can adapt to the continuous and rapid production requirements of temperingtechnology are vitally significant.The research object is Q550D steel in this study. Q550D steel plate after quenchingtreatment is tempering under different process parameters of the traditional tempering(tempering in box type resistance furnace) and induction tempering. The microstructure,room temperature mechanical properties, the stress relaxation effect, low temperatureperformance of steel samples between the contrast experiments using two kinds oftechnology will be analyzed and researched.In the study, the organization form of Q550D steel samples through inductiontempering process is more uniform, the size of the precipitates is smaller, the dispersiondegree is higher, and the stability of the organization is also very good. After inductiontempering, the hardness reduced gradually with the rise of temperature, but the impacttoughness at room temperature gradually increased with the increase of the temperature. Both are higher than the same temperature tempered samples of traditional tempering.In terms of stress relaxation effect, induction tempering process in the process oftempering shorten the stress relaxation effective time significantly, make the stress relaxationprocess can be done in a shorter period of time in induction tempering. Compared with thetraditional technology, the whole of tempered steel stress relaxation effect is better, theelimination of stress concentration area is more obvious, the heat preservation time is lessthan traditional tempering several times. It is greatly strengthened the effect of temperingstress relaxation and efficiency.Tempering at450℃, induction tempering process effectively reduces the brittle-ductiletransition temperature of Q550D steel. The average Ak of induction tempering samples issignificantly higher than traditional tempered samples in-40℃low temperature impact test.According to the SEM images of the impact fracture, the traditional tempering samples areoccurred brittle fracture, the induction tempering sample is ductile fracture, inductiontempering process make Q550D steel retained excellent low-temperature impact toughness,avoid the brittle fracture in low temperature effectively.