硼含量3.29%高硼不锈钢的微观组织和性能研究

Study on microstructure and properties of high boron stainless steel with 3.29%boron content

本文采用粉末冶金技术制备了硼含量为3.29%的高硼不锈钢,并与硼含量0.3%和1.9%的高硼不锈钢进行了对比,研究了其微观组织、物相、硼元素在组织中的分布及对合金性能的影响。试验结果表明:粉末冶金工艺制备合金的硼相晶粒呈不规则的长条形,硬质的含硼相为Fe_(1.1)Cr_(0.9)B_(0.9),合金的抗拉强度达到了900 MPa、伸长率为1.0%。

The objective of the study was to prepare the borated stainless steel(BSS)containing with 3.29%boron,to test BSS powder morphology and eutectic melting points,and observe phases,microstructure,elemental distribution and mechanical properties of BSS alloy.These characteristics were compared with two grades of BSS alloy with lower boron content(0.29%and 1.86%)which correspond to standard A887304B and 304B7 respectively issued by American Society of Testing Materials(ASTM).The Fe-Cr-Ni austenite steel powder with boron was obtained by atomization equipment.Fe-B,Fe-Cr and other raw materials were put into the melting furnace to melt and then were ejected to make the powder.The morphology of the BSS powder was observed by scanning electron microscope(SEM)and the eutectic melting point was analyzed by differential scanning calorimetry(DSC).The gas atomization powder obtained was passed through the 74μm sieve.The powder was placed in the capsules.Filled with BSS powder,the capsules were heated to 500°C in the atmospheric oven and degassed to 10−3 Pa to reduce oxidation of the powder.The capsule was placed in the hot isostatic pressing(HIP)furnace and then heated up,elevated pressure and held at sintering temperature and maximum pressure(110 MPa)for 2 h.Coupons of three BSS alloys were evaluated by quantitative X-ray diffraction(XRD)phase analysis.Microstructures were observed by SEM and energy-dispersive spectroscopic(EDS)analysis.Strength and ductility of specimens were tested according to Chinese Standard GB/T 228.1.The eutectic liquid phase point of BSS with 3.29%boron occurs at 1181.4°C tested by DSC.The BSS alloy with 3.29%boron prepared by PM comprised two main phases:the cubic austenite phase is 66%;the orthorhombic Fe_(1.1)Cr_(0.9)B_(0.9) boron phase is 34%.The boron phase grains of BSS with 3.29%boron have irregularly shaped grains,many of which are already in contact and joined together,while the grains of the low content boron BSS alloys have the regular shape and are separated from each other.The element boron fluctuates between 9.0%and 16.6%in the boron-containing phase of BSS,so the boron distribution of BSS is uneven.The BSS containing 3.29%boron have the tensile strength of 900 MPa and the elongation of only 1.0%,while 304B7 BSS have tensile strength of 720 MPa and elongation of 13.0%and 304B sample have tensile strength of 770 MPa and elongation of 20.5%.The tensile strength of BSS with lower boron content below 2.25%is similar,but elongation decreases with the increase of boron content;however,the strength of BSS with 3.29%boron is greater than that of low boron alloys by more than 100 MPa,but elongation decreases to only 1%.BSS alloys consist of two phases,the boron-containing phase content increases as the boron content of the alloy increases.As the boron content increases,the grains of the boron-bearing phase become irregular and the connections between grains increase.The BSS alloy containing 3.29%boron is brittle material.