摘要采用拉伸冷作硬化虽然能显著提高金属的强度，但是材料的塑性变化不够充分，影响强化效果，更有甚者会使金属产生颈缩现象及造成材料的初始损伤。因此，采用拉伸冷作硬化产生的应变强化和塑性变形是很不充分的。现有试验研究及分析结果表明，采用扭转冷作硬化能够使金属材料得到更加充分的强化，且在较大幅度提高钢材的强度的同时能够保证材料的截面积几乎不发生变化，得到明显优于拉伸冷作硬化的硬化效果。86046

本文以单位长度扭转角为硬化程度指标，并基于准静态拉伸，扭转和冲击实验，得到了未经强化和不同扭转硬化程度下的Q235钢的抗拉强度、规定非比例延伸强度、断面收缩率、断后伸长率及不同温度下的冲击韧性等性能参数。实验结果表明，扭转硬化能显著地提高Q235钢的拉伸强度，其中对规定塑性延伸强度的提高幅度可达到一倍以上；其塑性性能的下降呈现两头剧烈而中间平缓的“三段式”模式，其中第二阶段中塑性下降平缓，而强度提高显著，可得到较好的扭转硬化效果且兼顾塑性性能。基于拉伸实验数据，本文还构建（拟合）了Q235低碳钢在常温常态下拉伸强度、塑性性能与扭转硬化程度的关系函数。

在相同温度条件下，随着硬化程度的不断增加，低碳钢的冲击韧性逐渐下降，而且在硬化到一定程度后，材料的冲击韧性会突然急剧下降，突变点对应的扭转角随着温度的降低，不断变小。在扭转硬化程度相同时，随着温度的不断降低，低碳钢的冲击韧性也逐渐下降。

此外，为了得到Q235钢较优的冲击韧性，应控制其处在0°C和单位长度相对扭转角为5°/mm这两种条件下。

毕业论文关键词：Q235钢；扭转强化；拉伸实验；强度性能；塑性性能；冲击韧性

Abstract Although the tensile work hardening can significantly improve the strength of the metal, but the plastic of material changes insufficiently, influence hardening effect, and some even make the necking phenomenon and initial damage of materials。 Thus, the strain hardening and plastic deformation produced by tensile work hardening are very insufficient。 Experimental research and analysis results show that torsion work hardening can more fully strengthen the metal material, and significantly increase the strength of steel。 At the same time it also ensures that the cross-sectional area of the material is hardly changed and be significantly better than tensile work hardening。 

Therefore, Experimental study on tensile mechanical properties of Q235 steel with/without torsion hardening using quasi-static tensile, torsion and impact experiment were presented in this paper, including tensile strength, proof strength,plastic extension, percentage reduction of area, percentage elongation after fracture and impact toughness of different temperature。 The torsion angle within unit length was employed as indicator。 Experimental results show that tensile strength of Q235 steel increases significantly after torsion hardening。 The proof strength,plastic extension increases by one hundred percent。 The decrease of plastic property exhibits a ‘three-stage mode’。 In the second stage, the plastic property decreases stably but the strength increases significantly。 And it’s easy to keep a balance between strength and plastic。 Hence, the second is the prior stage。 Based on the data of tensile experiment, the functions among tensile strength, plastic property and degree of torsion hardening  of Q235 steel were also build at the quasi-static condition。

And at the same temperature, with the degree of hardening increasing, the impact toughness of low-carbon steel gradually decreased。 After a certain extent of hardening, the impact toughness of the material will be suddenly and sharply drop, mutation point corresponding torsion angle with the temperature decreasing and gradually advance。 At the same degree of twist, with the temperature decreasing, the impact toughness of low carbon steel gradually decreased。 In addition, in order to get the prior impact toughness of Q235 steel, both conditions are 0°C and 5°/mm of the torsion angle within unit length。