Abstract

The influence of three multipass cross rolling patterns on the microstructure, mechanical properties and fracture toughness of ferrite-pearlitic pipe steel 09G2S is investigated using mechanical testing, optical metallography, transmission and scanning electron microscopy. Upon all cross-rolling patterns, a change in the parameters of the initial workpiece grain structure is observed with the formation of layered grain size distribution. Near the workpiece surface, the size of globular grains is 1–4 μm, the length of elongated grains in the central part of the workpiece varies from units to tens of μm, and the width varies from 1 to 8 μm. Mechanical tests for uniaxial tension and impact strength are carried out on specimens machined from the central part of the bar. It is established that cross rolling leads to an increase in the yield point and ultimate strength of steel after all investigated patterns with a slight decrease in the overall plasticity. The greatest increase in impact toughness at T = –70°C is observed after controlled cross rolling in the temperature range 850–500°C. Using electron microscopic studies, it is shown that the mechanical behavior of the cross-rolled specimens is associated with structural transformations that occur in steel during rolling and cooling. The main strengthening factor is the refinement of ferrite grains and the formation of a subgrain structure as cross rolled. The increase in impact toughness is associated with a more uniform finely dispersed structure of rolled products, which does not contain cementite and bainite plates. Temperature dependent fracture processes of the initial cross-rolled steel specimens are analyzed based on recorded shock loading diagrams and structures in the rupture areas of Charpy specimens.

中文翻译：

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交叉轧制方式对管钢力学性能和断裂韧性的影响

摘要

利用机械测试，光学金相，透射和扫描电子显微镜研究了三种多道次交叉轧制方式对09G2S铁素体-珠光体管钢的组织，力学性能和断裂韧性的影响。在所有交叉轧制模式下，随着层状粒度分布的形成，观察到初始工件晶粒结构的参数发生了变化。在工件表面附近，球状晶粒的大小为1-4μm，在工件中央部分的细长晶粒的长度从单位变化到数十μm，宽度在1至8μm之间变化。对从钢筋中心部位加工的试样进行了单轴拉伸和冲击强度的机械测试。已经确定，在所有研究的模式之后，交叉轧制会导致钢的屈服点和极限强度增加，而整体塑性略有下降。冲击韧性最大增加在850-500°C的温度范围内进行受控交叉轧制后，观察到T = –70°C。使用电子显微镜研究表明，交叉轧制试样的力学行为与轧制和冷却过程中钢中发生的结构转变有关。主要的强化因素是铁素体晶粒的细化和交叉轧制时形成的亚晶粒组织。冲击韧性的提高与轧制产品更均匀的精细分散结构有关，轧制产品不含渗碳体和贝氏体板。基于夏比试样断裂区域记录的冲击载荷图和结构，分析了初始交叉轧制钢试样的温度相关断裂过程。