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> 不锈钢定义和特点

  • 分类:标准详解
  • 发布时间:2020-12-31 11:13:43
  • 访问量:0
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THE WASI STAINLESS STEEL ENCYCLOPEDIA
WASI 不锈钢百科全书

Understanding of stainless steel fasteners  不锈钢定义和特点

 

Stainless steel fasteners have the advantages of corrosion resistance, high quality appearance and image, high strength grade, easy to manufacture and weld, no need of painting, electroplating and heat treatment, and can be recycled 100%. Excellent mechanical properties, physical properties, process properties, no matter in the manufacturing, use and treatment of environmental impact and burden are minimal. Although the initial cost is high and the life cycle cost is low, it is the most economical component solution. Chemical industry, energy, machinery, light industry and other industries are widely used.  

不锈钢紧固件具有耐腐蚀的优点,高质量的外观和形象,较高的强度等级,易于制作和焊接,不需要涂漆、电镀和热处理,可以100%的回收再利用等特性。优异的力学性能、物理性能、工艺 性能,无论是在制造、使用和处理时对环境的影响和负担都是最小的。虽然初始成本较高,寿命周期成本较低,但却是最节省的零部件解决方案。化工、能源、机械、轻工等行业得到广泛的应用。

Definition and characteristics of stainless steel 不锈钢的定义和特点

Stainless steel usually refers to the steel which can resist the corrosion of air, water, acid, alkali, salt or other media. According to the alloy composition, stainless steel and acid resistance are emphasized respectively. Although some steels are stainless, they are not necessarily acid resistant. Acid resistant steels are usually stainless.All stainless steel can't cope with all kinds of corrosion. "Stainless steel" is a wrong name, because no one can deal with all corrosive environment, can not rust, the real meaning of stainless steel is "difficult to rust"

不锈钢通常指具有抵抗空气、水、酸、碱、盐或其它介质腐蚀能力的钢,根据合金成分的不同,分别侧重不锈性和耐酸性。有些钢虽然具有不锈性,但不一定耐酸,耐酸钢则通常具有不锈性。所有的不锈钢没有一种能够应付所有的腐蚀环境,都可以不生锈。“不锈钢”是一种错误的名称,因为没有一种能够应付所有腐蚀环境,都可以不生锈的,不锈钢的真正含义只是“难生锈”而已。

The main characteristics of stainless steel are weldability, corrosion resistance, polishing performance and heat resistance (heat resistance means that stainless steel can still maintain its excellent physical and mechanical properties at high temperature). 
不锈钢主要特性表现为焊接性、耐腐蚀性、抛光性能、耐热性能(耐热性能是指高温下不锈钢仍能保持其优良的物理机械性能)。

Compared with carbon steel, the obvious advantages are as follows: 1. Density: the density of carbon steel is slightly higher than that of ferritic and martensitic stainless steel, but slightly lower than that of austenitic stainless steel; 2. Resistivity: the resistivity increases in order of carbon steel, ferritic type, martensitic type and austenitic type stainless steel; compared with carbon steel, austenitic stainless steel has higher resistivity, about 5 times of that of carbon steel; 3. Large coefficient of linear expansion Austenitic stainless steel is the highest and carbon steel is the smallest, which is 40% larger than that of carbon steel, and with the increase of temperature, the value of linear expansion coefficient also increases correspondingly; 4. Carbon steel, ferrite and martensitic stainless steel have magnetism, while austenitic stainless steel has no magnetism, but magnetism will be produced when cold work hardening produces martensitic transformation, which can be eliminated by heat treatment This kind of martensite structure is restored to be nonmagnetic.

与碳钢相比,明显优势为:1.密度:碳钢的密度略高于铁素体和马氏体型不锈钢,而略低于奥氏体型不锈钢;2.电阻率:电阻率按碳钢、铁素体型、马氏体型和奥氏体型不锈钢排序递增;奥氏体型不锈钢与碳钢相比,具有高的电阻率,约为碳钢的5倍;3.线膨胀系数大小的排序也类似,奥氏体型不锈钢最高而碳钢最小,比碳钢大40%,并随着温度的升高,线膨胀系数的数值也相应地提高;4.碳钢、铁素体型和马氏体型不锈钢有磁性,奥氏体型不锈钢无磁性,但其冷加工硬化生成马氏体相变时将会产生磁性,可用热处理方法来消除这种马氏体组织而恢复其无磁性。

Stainless steel rust and rust prevention 不锈钢与生锈和防锈

Stainless steel has the ability to resist atmospheric oxidation - that is, it is not rusty, but also has the ability to resist corrosion in the medium containing acid, alkali and salt - namely corrosion resistance. However, the corrosion resistance of the steel varies with its chemical composition, additive state, service condition and environmental medium type. For example, austenitic A2 stainless steel has absolutely excellent corrosion resistance in dry and clean atmosphere, but if it is moved to coastal areas, it will rust quickly in the sea fog rich in salt; while austenitic a4-316 stainless steel performs well.All stainless steel can't cope with all kinds of corrosion. ""Stainless steel"" is a wrong name, because no one can deal with all corrosive environment, can not rust, the real meaning of stainless steel is "difficult to rust"
不锈钢具有抵抗大气氧化的能力-即不锈性,同时也具有在含酸、碱、盐的介质中耐腐蚀的能力-即耐蚀性。但其抗腐蚀能力的大小是随其钢质本身化学组成、加互状态、使用条件及环境介质类型而改变的。例如奥氏体A2不锈钢,在干燥清洁的大气中,有绝对优良的抗腐蚀能力,但将它移到海滨地区,在富有大量盐份的海雾中,很快就会生锈了;而奥氏体A4-316不锈钢则表现良好。所有的不锈钢没有一种能够应付所有的腐蚀环境,都可以不生锈。“不锈钢”是一种错误的名称,因为没有一种能够应付所有腐蚀环境,都可以不生锈的,不锈钢的真正含义只是“难生锈”、“不容易生锈”而已。

Stainless steel is not only rustless, but also antirust. Stainless steel's rust resistance and corrosion resistance are due to the formation of a thin, firm, fine and stable passivation film on the surface of stainless steel. This film can isolate the metal from the external medium, prevent the continuous infiltration and oxidation of oxygen atoms, prevent the metal from further corrosion, and have the ability of self-healing. If this kind of film is damaged, the chromium in the steel will react with the oxygen in the medium The rust resistance and corrosion resistance are relative.
不锈钢不仅不生锈,而且还要防锈。不锈钢的不锈性和耐蚀性是由于其表面上形成的一层极薄而坚固细密的稳定的钝化膜,这层膜使金属与外界的介质隔离,防止氧原子的继续渗入、继续氧化,阻止金属被进一步腐蚀,并且还有自我修复的能力,如果一旦这种薄膜遭到破坏,钢中的铬会与介质中的氧重新生成钝化膜,继续起保护作用,这种不锈性和耐蚀性是相对的。

When the stainless steel in the machining, assembly, welding, weld inspection and other processes bring surface oil and surface damage, these substances damage the surface of the oxide film, reduce the corrosion resistance of stainless steel, stainless steel will occur corrosion, and thus lead to other corrosion, so it is necessary to carry out appropriate anti rust treatment to improve its corrosivity. It has been proved that only after passivation treatment can the surface of stainless steel remain stable for a long time, so that the corrosion resistance can be improved.
当不锈钢在机械加工,组装,焊接,焊缝检查等过程中带来表面油污及表面破坏时,  这些物质破坏其表面的氧化膜,降低了不锈钢的抗腐蚀性,不锈钢就会发生腐蚀,并由此引发其它形成的腐蚀,因此有必要对其进行适当的防锈处理,以提高其腐蚀性。事实证明,不锈钢只有最后经过钝化处理,才能使表面保持长久的钝态稳定,因而才能提高腐蚀性能。

The results show that the corrosion resistance of steel increases with the increase of chromium water content in the weak medium such as atmosphere, water and nitric acid. When the chromium content reaches a certain percentage, the corrosion resistance of steel changes suddenly, that is, from easy to rust to not easy to rust, from non corrosion to corrosion resistance. The stainless steel's stainless steel is also related to the use environment. Different stainless steel should be used in different environments, different application industries and different process requirements.
试验表明,钢在大气、水等弱介质中和硝酸等氧化性介质中,其耐蚀性随钢中铬含水量的增加而提高,当铬含量达到一定的百分比时,钢的耐蚀性发生突变,即从易生锈到不易生锈,从不耐蚀到耐腐蚀。  不锈钢的不锈性,还与使用环境有关,不同的环境、不同的应用行业、不同的工艺要求,要使用不同的不锈钢。

Magnetism of stainless steel 不锈钢的磁性

Most people don't think that stainless steel can be identified by magnet in real life. First of all, zinc alloy and copper alloy can generally imitate the appearance and color of stainless steel, and have no magnetism, so it is easy to be mistaken for stainless steel. Even 304-a2 austenitic steel, which is the most commonly used steel, will have different degrees of magnetism after cold working. So we can't judge the authenticity of stainless steel only by a magnet.
在现实生活中,大多数人都认为不锈钢是没有磁性的,并借助磁铁来鉴别不锈钢,这种方法很不科学。首先锌合金、铜合金一般都可以仿不锈钢的外观颜色,也没有磁性,容易误认为是不锈钢;而即使是我们目前最常使用的304-A2奥氏体钢种,在经过冷加工后,也会出现不同程度的磁性。所以不能只凭一块磁铁来判断不锈钢的真伪。

So how does the magnetism of stainless steel come from? Generally speaking, austenitic stainless steel (represented by 304) is non-magnetic, but may also have weak magnetism, while ferrite and martensite are generally magnetic. There are some kinds of stainless steel (such as 304, etc.) classified as "non-magnetic stainless steel", which means that its magnetic index is lower than a certain value, that is to say, the general stainless steel has more or less certain magnetism. In addition, as mentioned above, austenite is non-magnetic or weakly magnetic, while ferrite and martensite are magnetic. Due to composition segregation or improper heat treatment during smelting, a small amount of martensite or ferrite will appear in Austenitic 304 stainless steel, so weak magnetism will appear in 304 stainless steel. In addition, the microstructure of 304 stainless steel will also transform to martensite after cold working. The larger the cold working deformation is, the more martensitic transformation will be, and the stronger the magnetic properties will be. In order to completely eliminate the magnetism of 304 stainless steel, the stable austenite structure can be restored by high temperature solution treatment, so as to eliminate the magnetism. Therefore, the magnetism of materials is determined by the regularity of molecular arrangement and the isotropy of electron spin. We think that it is the physical properties of materials, while the corrosion resistance of materials is determined by the chemical composition of materials, which is not related to the magnetic properties of materials.
那么不锈钢的磁性究竟是怎么来的? 通常来说,奥氏体不锈钢(以304为代表)是无磁性的,但是也可能带有弱磁性,而铁素体和马氏体一般都是带有磁性的。 不锈钢里面有一些钢种(如304等)分类为“无磁性不锈钢”的是指其磁性指标低于某个值而已,也就是说,一般不锈钢都或多或少带有一定的磁性。 此外,上面提到奥氏体是无磁或者弱磁性,而铁素体和马氏体是带磁性的,由于冶炼时成分偏析或热处理不当,会造成奥氏体304不锈钢中出现少量的马氏体或铁素体组织,这样304不锈钢中就会出现弱磁性。另外,304不锈钢经过冷加工,组织结构也会向马氏体转化,冷加工变形越大,马氏体转化越多,磁性也会越强。 想要完全消除304不锈钢的磁性,可以通过高温固溶处理恢复稳定奥氏体组织,从而消除磁性。 因此材料的磁性是由分子排布是否规则及电子自旋的同向性决定的,我们认为是材料的物理性能,而材料的耐腐蚀性能则是由材料的化学成分决定的,是材料的化学性能,与材料是否有磁性无关。

According to newest ISO 3506-6:2020, the magnetic permeability of materials relates to their ability to be attracted by a permanent magnet or influenced by a magnetic field. Ferritic, martensitic, duplex and non-austenitic precipitation hardening stainless steels are usually classified as "magnetic" since they exhibit a strong response ( or pull ) to a magnetic field e.g. a handheld magnet.By comparison, austenitic stainless steels are classified as non-magnetic, however, cold working during fastener manufacture can induce some residual magnetism. This residual magnetism can then be lowered e.g. by a specific heat treatment process. For some applications, it is necessary to use a stainless steel which has very low permeability. A limit is usually specified, the lowest relative magnetic permeability of a paramagnetic material would tend to 1,0 (i.e. the magnetic response of the material is the same as "free space" or a complete vacuum). The best austenitic stainless steel types for low permeability applications are those with high austenite stability as these have low permeability in both the annealed or cold worked conditions. For example, the nitrogen containing steels such as 1.4311(A2L) and 1.4406(A4L) or the high nickel types such as 1.4845 ( see Annex A) are considered suitable. Where specific non-magnetic properties are necessary, the advice of a stainless steel materials expert should be sought before determining the specification and agreement between the purchaser and supplier established at the time of the order.
按照最新ISO 3506-6:2000版本,材料的磁导率与它们被永磁体吸引或受磁场影响的能力有关。铁素体、马氏体、双相和非奥氏体沉淀硬化不锈钢通常被归类为“磁性”,因为它们可以被磁场(例如手持式磁铁)吸引(或拉扯),相比之下,奥氏体不锈钢被归类为无磁性的,然而,紧固件制造过程中的冷加工会产生一些残余磁性,生产过后可以通过特定的热处理工艺来减弱这些残余磁性。对于某些应用,有必要使用渗透性很低的不锈钢。通常规定一个极限,顺磁性材料的最低相对磁导率趋于1,0(即材料的磁响应与“自由空间”或完全真空相同)。用于低渗透性应用的最佳奥氏体不锈钢类型是那些具有高奥氏体稳定性的不锈钢,因为这些钢在退火或冷加工条件下都具有低渗透性。例如,含氮钢如1.4311(A2L)和1.4406(A4L)或高镍钢如 1.4845(见材料篇表)被认为是合适的。

Type of stainless steel 不锈钢种类

According to the structure, there are five basic types of stainless steel: martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, duplex stainless steel and precipitation hardening stainless steel.
按组织结构不锈钢有五个基本的种类:马氏体不锈钢、铁素体不锈钢、奥氏体不锈钢、双相不锈钢、沉淀硬化型不锈钢。

Among them, the austenitic stainless steel materials commonly used for fasteners have the best comprehensive properties, which not only has sufficient strength, but also has excellent plasticity, but also has low hardness, which is one of the reasons why they are widely used. The tensile strength, yield strength and hardness of austenitic stainless steel increase with the decrease of temperature, while the plasticity decreases with the decrease of temperature. The tensile strength increases uniformly in the temperature range of 15 ~ 80 ° C. More importantly, with the decrease of temperature, the impact toughness decreases slowly, and there is no brittle transition temperature. So stainless steel can keep enough plasticity and toughness at low temperature. The heat resistance of stainless steel refers to the performance of oxidation resistance or gas corrosion resistance under high temperature, namely thermal stability.
其中紧固件常用的奥氏体不锈钢材料的综合性能最好,既有足够的强度,又有极好的塑性同时硬度也不高,这也是它们被广泛采用的原因之一。奥氏体型不锈钢同绝大多数的其它金属材料相似,其抗拉强度、屈服强度和硬度,随着温度的降低而提高;塑性则随着温度降低而减小。其抗拉强度在温度15~80°C范围内增长是较为均匀的。更重要的是:随着温度的降低,其冲击韧度减少缓慢,并不存在脆性转变温度。所以不锈钢在低温时能保持足够的塑性和韧性。不锈钢的耐热性能是指高温下,既有抗氧化或耐气体介质腐蚀的性能即热稳定性。

Stainless steel is divided into Cr, Cr Ni, Cr Ni Mo, Cr Mn Ni,Common alloy elements in stainless steel: C, Cr, Ni, Mn, Si, N, Nb, Ti, mo.Austenite forming elements : C、Ni、Mn 、N、Cu.Ferrite forming elements : Cr、Si、Ti、Nb、Al、Mo.
不锈钢按照合金元素种类划分:Cr、Cr-Ni、Cr-Ni-Mo、 Cr-Mn-Ni,不锈钢中常见的合金元素有 C、Cr、Ni、Mn、Si、N、Nb、Ti、Mo。奥氏体形成元素 :C、Ni、Mn 、N、Cu等,铁素体形成元素 :Cr、Si、Ti、Nb、Al、Mo等。

Different categories have different characteristics and application fields. For details, please refer to the introduction of stainless steel materials.
不同的类别,有不同的特性及应用领域,详情请见不锈钢材料介绍

General standards of delivery of stainless steel fasteners 不锈钢紧固件常见工业标准主要包括以下几个方面

■  不锈钢紧固件产品尺寸方面的标准:具体规定产品基本尺寸方面的内容;带螺纹的产品,还包括螺纹的基本尺寸、螺纹收尾、肩距、退刀槽和倒角、外螺纹零件的末端尺寸等方面内容。
■  不锈钢紧固件产品技术条件方面的标准。具体又包括以下几个方面内容的标准:
a) 紧固件产品公差方面的标准:具体规定产品尺寸的公差和形位公差方面的内容。
b) 紧固件产品机械性能方面的标准:具体规定产品机械性能等级的标记方法以及机械性能项目和要求方面的内容;有的紧固件产品则将此项内容改为产品材料性能或工作性能方面的内容 。
c) 紧固件产品表面缺陷方面的标准:具体规定产品表面缺陷种类和具体要求等方面的内容。
d) 紧固件产品的表面处理方面标准:具体规定产品表面处理种类和具体要求等方面的内容。
e) 不锈钢紧固件产品试验方面的标准:具体规定上述各种性能要求试验方面的内容。
■  不锈钢标准件产品验收检查、标志与包装方面的标准:具体规定产品出厂验收时抽查项目合格质量水平和抽样方案,以及产品标志方法和包装要求方面的内容。
■  紧固件产品标记方法方面的标准:具体规定产品完整标记方法和简化标记方法方面的内容。
■  不锈钢紧固件其他方面的标准:如紧固件术语方面的标准,紧固件产品重量的标准等。
详见不锈钢紧固件制造和交付的通用标准介绍

 

THE WASI STAINLESS STEEL ENCYCLOPEDIA

 

WASI不锈钢百科全书

 

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