中碳冷镦钢的室温压缩变形及其不均匀应变硬化行为
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摘要
对SWRCH45K中碳冷镦钢在万能材料试验机上进行室温压缩变形,观察了压缩试样表面质量及其内部组织,以及分析了压缩试样侧表面赤道位置的轴向与周向应变。结果表明:该钢在压缩变形过程中,压缩载荷先随位移的增加而稳定增大,当位移大于7. 5 mm时,压缩载荷急剧增大;随压下量的增加,压缩试样的鼓度值先增大后减小。载荷和鼓度值在位移7. 5 mm时,同时出现变化趋势的改变,这是由于压缩变形的不均匀应变硬化所致,即在位移小于7. 5 mm的压缩变形过程中,大变形区位于试样的中心位置,其应变硬化程度高;而在随后的位移大于7. 5 mm的压缩变形过程中,该区将因应变硬化程度高、其进一步变形所需变形力大而不再是变形程度最大的区域,其应变硬化程度的增幅减小,相反此前试样内变形程度小的难变形区和小变形区因应变硬化程度小、其进一步变形的变形力小而产生较大的变形,其应变硬化程度的增幅大幅度增加。
Compression deformation at room temperature of medium carbon cold heading steel SWRCH45 K was conducted by universal testing machine,the surface and internal microstructures of compression samples were observed,and the axial strain and circumferential strain at the equator position on the side surface of compression samples were analyzed. The results show that in the compression deformation process,firstly the compression load increases steadily with the increase of displacement,when the displacement is greater than 7. 5 mm,it increases rapidly,and the drum-shape value of compression samples first increases and then decreases with the increase of displacement.When the displacement is 7. 5 mm,the changes in trends occur simultaneously. The reason for this phenomenon is regarded as the uneven strain hardening of compression deformation. When the compression deformation under the condition of the displacement less than 7. 5 mm,the large forming region is located at the center of the compression sample,and the strain hardening is relatively large. While in subsequent compression deformation of the displacement greater than 7. 5 mm,it no longer is the maximum forming region due to high strain hardening and large deformation force to deform further,and the increase in the degree of strain hardening is reduced. On the contrary,the large deformation is produced at the previous difficult deformation region and small forming region due to the lower strain hardening and deformation force to deform further,and the increase in the degree of strain hardening is improved significantly.
Compression deformation at room temperature of medium carbon cold heading steel SWRCH45 K was conducted by universal testing machine,the surface and internal microstructures of compression samples were observed,and the axial strain and circumferential strain at the equator position on the side surface of compression samples were analyzed. The results show that in the compression deformation process,firstly the compression load increases steadily with the increase of displacement,when the displacement is greater than 7. 5 mm,it increases rapidly,and the drum-shape value of compression samples first increases and then decreases with the increase of displacement.When the displacement is 7. 5 mm,the changes in trends occur simultaneously. The reason for this phenomenon is regarded as the uneven strain hardening of compression deformation. When the compression deformation under the condition of the displacement less than 7. 5 mm,the large forming region is located at the center of the compression sample,and the strain hardening is relatively large. While in subsequent compression deformation of the displacement greater than 7. 5 mm,it no longer is the maximum forming region due to high strain hardening and large deformation force to deform further,and the increase in the degree of strain hardening is reduced. On the contrary,the large deformation is produced at the previous difficult deformation region and small forming region due to the lower strain hardening and deformation force to deform further,and the increase in the degree of strain hardening is improved significantly.
引文
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[12]许树勤,陈志英,张善元.镦粗试验中鼓度与摩擦的相关性研究[J].锻压技术,2004,29(5):46-48.Xu S Q,Chen Z Y,Zhang S Y. Research on the relation betweenbulging and friction in cylinder upsetting[J]. Forging&StampingTechnology,2004,29(5):46-48.
[2]王宏亮,车安,袁野,等.冷镦钢盘条表面质量改进研究[J].金属制品,2018,44(1):53-58.Wang H L,Che A,Yuan Y,et al. Study on surface quality im-provement of cold heading steel wire rod[J]. Metal Products,2018,44(1):53-58.
[3]李文奇.冷成形工艺在汽车行业的应用[A].第十一届中国钢铁年会[C].北京,2017.Li W Q. Application of cold forming technology in automobile in-dustry[A]. The 11th China Iron and Steel Annual Conference[C]. Beijing,2017.
[4] Eom J G,Sonb Y H,Jeong S W,et al. Effect of strain hardeningcapability on plastic deformation behaviors of material during metalforming[J]. Materials and Design,2014,54(2):1010-1018.
[5] Li Z,Wu D,Lu W. Effects of rolling and cooling conditions onmicrostructure and mechanical properties of low carbon cold head-ing steel[J]. Journal of Iron and Steel Research,International,2012,19(11):64-70.
[6] Sabih A,Nemes J A. Internal ductile failure mechanisms in steelcold heading process[J]. Journal of Materials Processing Tech-nology,2009,209(9):429-431.
[7]郭泽尧,彭碧辉. SWRCH45K冷镦钢盘条显微组织均匀性研究[J].金属制品,2013,39(4):43-46.Guo Z Y, Peng B H. Research on microstructure uniformity ofSWRCH45K cold heading wire rod[J]. Metal Products,2013,39(4):43-46.
[8]李勇,战东平,韩作宽,等. 45钢Φ10 mm材冷镦裂纹的分析和工艺改进措施[J].特殊钢,2009,30(1):50-51.Li Y,Zhang D P,Han Z K,et al. An analysis on cold upsettingcrack of 0. 45C steelΦ10 mm products and process improvedmeasures[J]. Special Steel,2009,30(1):50-51.
[9]嵇国金,彭颖红,阮雪榆.金属自由镦粗的实验研究[J].金属成形工艺,1999,(5):23-26.Ji G J,Peng Y H,Ruan X Y. Experimental study on metal freeupsetting[J]. Metal Forming Technology,1999,(5):23-26.
[10] Lee P W,Kuhn H A. Fracture in cold upset forging-a criterionand model[J]. Metallurgical Transactions, 1973, 4(4):969-974.
[11] Dodd B,白以龙.关于镦粗锻造中自由表面开裂的综述[J].力学学报,1981,17(5):474-485.Dodd B,Bai Y L. A review of free surface cracking in upset forg-ing[J]. Chinese Journal of Theoretical and Applied Mechanics,1981,17(5):474-485.
[12]许树勤,陈志英,张善元.镦粗试验中鼓度与摩擦的相关性研究[J].锻压技术,2004,29(5):46-48.Xu S Q,Chen Z Y,Zhang S Y. Research on the relation betweenbulging and friction in cylinder upsetting[J]. Forging&StampingTechnology,2004,29(5):46-48.