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高速工具钢低倍组织检验随着机械工业的发展,现代金属的切削加工广泛采用较高的切削速度和大进刀量的快速切削方法,这就要求刃具材料必须具有较高的红硬性及耐磨性。
另外,随着切削速度和进刀量的增大,刃具负荷增加,对于刃具材料的强度和韧性也提出越来越高的要求。
碳素工具钢及低合金工具钢已经不能适应对刃具的高要求,而必须使用高碳高合金工具钢及特殊合金来制造刃具。
高速工具钢是含有W、Mo、Cr、V等合金元素的高碳高合金工具钢,因其具有较高的硬度、较高的耐磨性和红硬性,被广泛用于制造各种中、高速的切削刀具,成为目前应用最广泛的钢种之一。
而高速工具钢的锻造,对于刃具制造来说,又是十分重要的一道工序,因为其锻造性能的好坏,不但直接影响到刃具的质量,而且还影响到生产成本。
高速工具钢低倍组织的优劣,对其锻造性能又将产生较大的影响。
因此,对于高速工具钢低倍组织的检验结果的准确与否,就显得尤为重要。
常规试验高速工具钢低倍组织检验是根据国标GB226-77《钢的低倍组织及缺陷酸蚀试验法》规定,采用热酸浸蚀法。
酸蚀检验的腐蚀属于电化学腐蚀。
钢的化学成分不均匀性和缺陷之所以能用浸蚀来显示,是因为它们以不同的速度与浸蚀剂起反应。
表面缺陷、夹杂物、偏析区等被浸蚀剂有选择性的浸蚀,表现出可见的浸蚀特征。
对于高速工具钢而言,最常用的浸蚀剂成分是1∶1(溶剂比)的盐酸(相对密度1.19)水溶液,酸蚀温度为(75±5)℃,酸蚀时间为15～40min。
试样经酸蚀实验后,规定不得有肉眼可见的缩孔、气泡、翻皮、内裂及夹杂物等缺陷存在,并且按照国标GB1979-80《结构钢低倍组织缺陷评级图》对照进行评定中心疏松、一般疏松和偏析的级别。
采用这种常规的试验方法对高速工具钢的低倍组织进行检验,操作起来比较容易,设备也比较简单,但是作者认为在实际操作中可能会出现一些问题。
常规试验可能出现的问题酸蚀试验主要受到以下几个因素的影响:浸蚀剂成分、酸蚀时间、酸蚀温度及试样浸蚀面的光洁度。
贵州大学实验报告（小三号，加黑）
学院：材料与冶金专业：材料科学与工程班级：材料081
图5-1 不同浇铸条件下铝锭的宏观组织
℃浇铸，3mm厚铁模 b）800℃浇铸，10mm厚铁模 c）680℃浇铸，100mm厚铁模加硅铁粉
图5-2 钢中常见的低倍缺陷
a）一般疏松 b）方框偏析 c）皮下气泡 d）白点 e）缩孔残余
次消光和发亮现象。
对于
透明的，各向同性的球形夹物，
SiO 2，在明场下呈深灰 图5-3 钢中的非金属夹杂
Al 2O 3 b ）MnS c ）TiN d ）玻璃质SiO 2明场下光环特征 e ）玻璃质SiO 2，偏
图5-4 偏振光装置示意图
几种非金属夹杂物的特征
暗场偏振光
，不规则外形小颗粒成群分布，透明、淡黄色透明，弱各向异性
注：各学院可根据教学需要对以上栏目进行增减。
表格内容可根据内容扩充。
对使用低倍评级图评定低倍缺陷“点状偏析”的看法曾文涛谷强(抚顺特殊钢公司辽宁抚顺113001)摘要叙述了低倍缺陷“点状偏析”在低倍酸浸试片上的评定特征,以及从有关标准对该缺陷表述进行识别和评定。
关键词点状偏析评定标准在钢材作低倍检验时,常出现对“点状偏析”的评定有争议,尤其是对大尺寸钢材的低倍试样的评定该缺陷为常有。
点状偏析在低倍检验的同行内常简称为“点偏”。
如何使用标准评级图对“点偏”这一缺陷评定,谈谈个人的看法与讨论。
1 准确评定“点状偏析”的重要性低倍缺陷的准确评定,是关于钢材的合理使用及判废的大问题。
尤其是“点状”这种低倍缺陷,在常用的GB3077-88合金结构钢技术条件中就明确规定:优质钢,一般点状偏析、边缘点状偏析不得大于1级,高级优质钢和特高级优质钢不允许有一般点状偏析和边缘点状偏析。
国军标GJB1951-94航空用优质合金结构钢棒规范规定:“钢棒的横截面酸浸低倍试片上不允许有肉眼可见的点状偏析。
”从这些产品标准中,可以看出“点偏”作为低倍组织的一种缺陷,在某些技术中以允许的缺陷而被接收,但要求级别较严,仅允许1、2级。
而在一些技术条件中以不允许存在的缺陷而被否定。
“点偏”这种低倍缺陷不同于缩管、翻皮、夹杂等不允许缺陷,在酸浸试片上特征明显,而容易与“疏松”这些低倍组织缺陷混淆。
这样就存在着允许缺陷和不允许缺陷分不清、判别不明存在异议、关系到钢材合格与判废的大问题,因此准确评定“点偏”是低倍组织评定的一个主要检验。
所以有必要正确认识“点偏”这种低倍缺陷。
2 从有关标准上理解和认识“点状偏析”当我们进行低倍组织评定时,主要的依据就是检验标准,在有关的产品的技术条件中,具体规定了低倍检验标准:如GJB1951-94应用了GB1979-80结构钢低倍组织缺陷评级图,所以有必要对低倍评级检验标准作进一步的了解。
目前,我国GB1979-80标准是钢材宏观检验的基础标准,除结构钢的低倍组织评定使用它外,其它某些钢种也参照使用它。
低倍标准应用
1引用标准
目前应用的标准有9个：
1.1GB/T1979-2001：结构钢低倍组织缺陷评级图(Standard diagrams for macrostructure and defect of structural steels)
1.2GB 1814-79：钢材断口检验法
1.3GB226-91：钢的低倍组织及缺陷酸蚀检验法(Etch test macrostructure and defect of steels)
1.4GB/T15711-1995；钢材塔形发纹酸浸检验方法（Steel products Methodfor etch test of tower sample）
1.5YB 4002-91: 连铸钢方坯低倍组织缺陷评级图
1.6JIS G 0553：1996：钢的低倍组织试验方法
1.7JIS G0556：1998：钢中发纹宏观试验方法
1.8JIS G 0560：1998：Method of sulphur print for steel(钢的硫印方法)
1.9ASTM E381-01:Standard Method of Macroetch Testing Steel Bars,Billets,Blooms,and Forgings
2检验项目
常规低倍检验项目及各标准的规定见表1。
1 适用于碳素钢、低合金钢、弹簧钢（锻、轧坯）。
2 适用于连铸生产的碳素钢及低合金钢等方坯横截面腐蚀低倍组织的缺陷。
方坯横截面尺寸范围为边长90~200mm。
Standard diagrams for macrostructure and defect of structuralsteels1Classification of defects and Features1.1General porosityFeatures: In the acid leaching test,the microstructure is not dense, the dark and void is dispersed in the whole cross section. Scotoma is round or oval shaped. The voids are not regular under the observation of magnifying glass. These dark spots and voids usually appear in between the dendrite and the coarse spindle shaft,loose area is dark but the axis area is light. When the difference between the light and the dark area is little, the pit is not produced.Evaluation principle：According to the number, scattered throughout the cross section of the scotoma and the size of the voids and their distribution, And consider the thickness of the dendritic crystal.1.2Center porosityFeatures: The distribution of voids and scotoma was focused in the central part of acid leaching test piece. The main difference between center porosity and the general general porosity is scotoma exists only in the center of gap, and not spread over the whole cross section.Evaluation principle：According to the number and the size of the voids, scotoma and intensity.1.3 Ingot segregationFeatures：In the acid leaching test, the corrosion depth is deep, it consists of dark spots and voids,the same shape of the cross section of the ingot type, generally shape of square.Evaluation principle：Evaluate the degree of the organization and the width of the frame. When necessary, can measure the distance between segregation box margins and test block plane.1.4Spot segregationFeatures：In the acid leaching test piece with different shape and size of the dark spots. No matter whether bubbles exist with the dark spots, the dark spots are defined as spotted segregation. When the speckle is distributed in the whole cross section, it is called the common spot segregation, when the spots are on the edge of the test piece, it is called edge spot segregation.Evaluation principle：According to the number and the size of the voids, scotoma and intensity.4.5 Bright bandFeatures：In the acid leaching test piece,the organization of the dense bright white or light white box with strong anti corrosion ability.Evaluation principle：When assessment is needed,record the bright band width and the distance to the nearest test frame margin with the surface.1.6Central segregationFeatures：In the acid leaching test piece, the central part of the surface of thecorrosion is dark, sometimes dark spots have gray ribbons and porosity around. Evaluation principle：Assess according to spot size and quantity to of the central dark area.1.7Cap segregationFeatures：In the central part of the acid leaching test piece, a dark and easily corroded metal area is presented.Evaluation principle：Assess according to the area size of the dark area.1.8subsurface bubbleFeatures：In acid leaching test piece, scattered or clustered distribution of slender cracks or with circular holes in the sibsurface.Most elongated cracks are perpendicular to the surface of the steel (Billet).Evaluation principle：Measure the most distance between the bubble and the steel (Billet) surface.1.9Residual shrinkage holeFeatures: Irregular cracks or voids wrinkle in center area of acid leaching test piece (in most cases),serious porosity above or around, inclusion (slag inclusion) and composition segregation, etc.Evaluation principle：define according to the size of the crack or the hole.1.10skull patchFeatures：In the acid leaching test piece, there is a bright white curved strip or irregular dark lines, and there are air holes and inclusions in it or around it. Some are composed with dense voids and inclusions.Evaluation principle：Measure the largest distance between skull patch and the steel surface(Billet) or the skull patch length.1.11White spotsFeatures：Appearance of a small serrated pattern in the edge region of the acid leaching test plate. Radial shaped, concentric circle or irregular shape distribution. Round or oval highlights or small cracks are existed in the longitudinal fracture according to the different orientation.Evaluation principle：define with the crack length and the numbers.1.12Axial intergranular fractureFeatures：Such defects generally occur in high alloy stainless steel (such as Cr5M0、lCrl3、C r25……）. Sometimes high alloy structural steel like 18Cr2Ni4WA will occur. In the acid leaching test piece, fork shape or small winding appearance, stripes of spider web shaped by the axis of the billet。
