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Tool steel

Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures (red-hardness). Tool steel are generally used in a heat-treated state.

With a carbon content between 0.7% and 1.4%, tool steels are manufactured under carefully controlled conditions to produce the required quality. The manganese content is often kept low to minimize the possibility of cracking during water quenching. However, proper heat treating of these steels is important for adequate performance, and there are many suppliers who provide tooling blanks intended for oil quenching.

Tool steels are made to a number of grades for different applications. Choice of grade depends on, among other things, whether a keen cutting edge is necessary, as in stamping dies, or whether the tool has to withstand impact loading and service conditions encountered with such hand tools as axes, pickaxes, and quarrying implements. In general, the edge temperature under expected use is an important determinant of both composition and required heat treatment. The higher carbon grades are typically used for such applications as stamping dies, metal cutting tools, etc.

Tool steels are also used for special applications like injection molding because the resistance to abrasion is an important criterion for a mold that will be used to produce hundreds of thousands of parts.

Water-hardening grades
W-grade tool steel gets its name from its defining property of having to be water quenched. W-grade steel is essentially high carbon plain-carbon steel. This type of tool steel is the most commonly used tool steel because of its low cost compared to other tool steels. They work well for small parts and applications where high temperatures are not encountered; above 150 °C (302 °F) it begins to soften to a noticeable degree. Hardenability is low so W-grade tool steels must be quenched in water. These steels can attain high hardness (above HRC 60) and are rather brittle compared to other tool steels.

The toughness of W-grade tool steels are increased by alloying with manganese, silicon and molybdenum. Up to 0.20% of vanadium is used to retain fine grain sizes during heat treating.

Typical applications for various carbon compositions are:

0.60—0.75% carbon: machine parts, chisels, setscrews; properties include medium hardness with good toughness and shock resistance.
0.76—0.90% carbon: forging dies, hammers, and sledges.
0.91—1.10% carbon: general purpose tooling applications that require a good balance of wear resistance and toughness, such as drills, cutters, and shear blades.
1.11—1.30% carbon: small drills, lathe tools, razor blades, and other light-duty applications where extreme hardness is required without great toughness.

Air-hardening grades
The first air hardening grade tool steel was mushet steel, which was known as air-hardening steel at the time.

A2 is the most common air hardening grade currently used.


Cold-working grades
Grade-O refers to oil hardening tool steels, while grade-A refers to air hardening tool steels. These tool steels are used on larger parts or parts that require minimal distortion during hardening. The use of oil quenching and air hardening helps reducing distortion as opposed to higher stress caused by quicker water quenching. More alloying elements are used in these steels, as compared to water-hardening grades. These alloys increase the steels' hardenability, and thus require a less severe quenching process. These steels are also less likely to crack and are often used to make knife blades.

D-grade tool steels contain between 10% and 18% chromium. These steels retain their hardness up to a temperature of 425 °C (797 °F). Common applications for these grade of tool steel is forging dies, die-casting die blocks, and drawing dies. Due to high chromium content, certain D-grade tool steel grades are often considered stainless or semi-stainless tool steels.


Composition
Here are composition for some of the most common cold-working tool steels, quantities of minor ingredients may vary slightly with manufacturer:

O-1 steel contains 0.90% carbon 1.0%-1.4% manganese, 0.50% chrome, 0.50% nickel, and 0.50% tungsten. It is a very good cold work steel and also makes very good knives.

A-2 steel contains 1.0% carbon, 5.0% chromium, and 1.0% molybdenum.

D-2 steel is a semi-stainless alloy containing 1.5% carbon and 11-13% chromium; additionally it is composed of 0.45% manganese, 0.03% phosphorus, 0.02% sulfur, 0.30% nickel, 1.10% vanadium, 0.7% molybdenum, and 0.60% silicon. D2 is very wear resistant but not as tough as lower alloyed steels. It is widely used for shear blades, planer blades and industrial cutting tools, sometimes used for knives.


Shock resisting grades
S-grade tool steel are designed to resist shock at both low and high temperatures. A low carbon content is required for the necessary toughness (approximately 0.5% carbon). Carbide-forming alloys provide the necessary abrasion resistance, hardenability, and hot-working characteristics. This family of steels displays very high impact toughness and relatively low abrasion resistance, it can attain relatively high hardness (HRC 58/60). This type of steel is used in applications such as jackhammer bits.


High speed grades
T-grade and M-grade tool steels are used for cutting tools where strength and hardness must be retained at temperatures up to or exceeding 760 °C (1,400 °F). M-grade tool steels were developed to reduce the amount of tungsten and chromium required.

T1 (also known as 18-4-1) is a common T-grade alloy. Its composition is 0.7% carbon, 18% tungsten, 4% chromium, and 1% vanadium. M2 is a common M-grade alloy.


Hot-working grades
H-grade tool steels were developed for strength and hardness during prolonged exposure to elevated temperatures. All of these tool steels use a substantial amount of carbide forming alloys. H1 to H19 are based on a chromium content of 5%; H20 to H39 are based on a tungsten content of 9%-18% and a chromium content of 3%-4%; H40 to H59 are molybdenum based.


Special purpose grades
P-grade tool steel is short for plastic mold steels. They are designed to meet the requirements of zinc die casting and plastic injection molding dies.
L-grade tool steel is short for low alloy special purpose tool steel. L6 is extremely tough.
F-grade tool steel is water hardened and substantially more wear resistant than W-grade tool steel.

[edit] Other tool steels
Silver steel is a common tool steel in the UK that is roughly equivalent to drill rod in the US.

工具钢
  工具钢是用以制造切削刀具、量具、模具和耐磨工具的钢。工具钢具有较高的硬度和在高温下能保持高硬度得红硬性,以及高的耐磨性和适当的韧性。
  工具钢一般分为碳素工具钢、合金工具钢和高速工具钢。
  碳素工具钢的主要生产品种、性能和用途
  一、生产品种
  热轧棒材 圆钢直径或方钢边长8mm-80mm
  锻制棒材 圆钢直径或方钢边长50mm-150mm
  冷拉棒材圆钢直径8mm-40mm
  热轧钢板 厚度0.7mm-15mm
  冷拉钢带厚度0.10mm-3.60mm
  冷拉钢丝圆钢丝直径0.050mm-16mm
  热轧扁钢 厚度*宽度 3mm-30mm*(10、12、14、16、18、20、22、25、28、30、32、35、38、40、45、50、55、60、65、90、100、160)mm
  锻制扁钢 厚度*宽度 10mm-65mm*(40、45、50、55、60、65、70、80、90、100、110、120、130、150、170、180、190、200)mm
  二、性能和用途
  T7、T7A 亚共析钢。具有较好的塑、韧性和强度,以及一定的硬度,能承受震动和冲击负荷,但切削能力差。用于制造承受冲击负荷不大,且要求具有适当硬度和耐磨性,及较好的韧性的工具,如锻模、凿子、锤、冲头、金属剪切刀、扩孔钻、钢印、木工工具、风动工具、机床顶尖、钳工工具、钻凿工具、较钝的外科医疗用具等。
  T8、T8A 共析钢。淬火加热时容易过热,变形也大,塑性和强度比较低,不宜制造承受较大冲击的工具,但经热处理后有较高的硬度和耐磨性。用于制造切削刃口在工作时不变热的工具,如木工工具、风动工具、钳工工具、简单模具、铆钉冲模、中心孔铳和冲模、切削钢材用工具、轴承、刀具、铝锡合金压铸板和型芯,以及各类弹簧等。
  T8Mn、T8MnA 共析钢。具有较高的淬透性和硬度,但塑性和强度较低。用于制造断面较大的木工工具、手锯锯条、刻印工具、铆钉冲模、发条、带锯锯条、圆盘锯片、煤矿用凿、石工用凿等。
  T9、T9A 过共析钢。具有较高的硬度,但塑性和强度较低。用于制造要求较高硬度且有一定韧性的各种工具,如刻印工具、铆钉冲模、压床模、冲头、木工工具、农机切割零件、凿岩工具和铸模的分流钉等。
  T10、T10A过共析钢。晶粒细,在淬火加热时(温度达800℃)不致过热,仍能保持细品粒组织;淬火后钢中有未溶的过剩碳化物,所以具有比T8、T8A钢更高的耐磨性,但韧性较低。
  用于制造切削刃口在工作时不变热的工具,不承受冲击负荷而具有锋利刃口和少许韧性的工具,如加工木材用工具、手用横锯、手用细木工具、机用细木工具、麻花钻、拉丝模、冲模、冷镦模、螺丝锥、扩孔刀具、搓丝板、车刀、刨刀、铣刀、货币压模、小尺寸断面均匀的冷切边及冲孔模、低精度形状简单的卡板、钳工刮刀、硬岩石钻子、制铆钉和钉子用工具、螺丝刀、锉刀、刻纹用凿子、切纸和烟叶用刀具等。
  T11、T11A 过共析钢。具有较好的综合力学性能(如硬度、耐磨性和韧性等),晶粒更细,在加热时对晶粒长大和形成碳化物网的敏感性小。用于制造在工作时切削刃口不变热的工具,如锯、錾刀、丝锥、锉刀、刮刀、发条、仪规、扩孔钻、板牙、切烟叶用刀具、尺寸不大和断面无急剧变化的冷冲模及木工刀具等。
  T12、T12A 过共析钢。由于碳含量高。淬火后仍有较多的过剩碳化物,所以硬度和耐磨性高,但韧性低,且淬火变形大。不适于制造切削速度高和受冲击负荷的工具。用于制造不受冲击负荷,切削速度不高,切削刃口不变热的工具,如车刀、铣刀、钻头、铰刀、扩孔钻、丝锥、板牙、刮刀、量规、刀片、小型冲头、钢锉、锯、发条、切烟叶用刀具,及断面尺寸小的冷切边模和冲口模等。
  T13、T13A 过共析钢。由于碳含量高,淬火后有更多的过剩碳化物,所以硬度更高,韧性更差;又由于碳化物数量增加且分布不均匀,故力学性能较差。不适用于制造承受冲击负荷和较高速度的切削工具。
  用于制造不受冲击负荷,但要求极高硬度的金属切削工具,如剃刀、刮刀、拉丝工具、锉刀、刻纹用工具、钻子,以及坚硬岩石加工用工具和雕刻用工具等。
  合金工具钢
  合金工具钢的淬硬性、淬透性、耐磨性和韧性均比碳素工具钢高,按用途大致可分为刃具、模具和量具用钢3类。其中碳含量高的钢(碳质量分数大于0080%)多用于制造刃具、量具和冷作模具,这类钢淬火后的硬度在HRC60以上,且具有足够的耐磨性;碳含量中等的钢(碳质量分数0.35%~0.70%)多用于制造热作模具,这类钢淬火后的硬度稍低,为HRC50~55,但韧性良好。
  高速工具钢
  高速工具钢主要用于制造高效率的切削刀具。由于其具有红硬性高、耐磨性好、强度高等特性,也用于制造性能要求高的模具、轧辊、高温轴承和高温弹簧等。高速工具钢经热处理后的使用硬度可达HRC63以上,在600℃左右的工作温度下仍能保持高的硬度,而且其韧性、耐磨性和耐热性均较好。退火状态的高速工具钢的主要合金元素有多、钼、铬、钒,还有一些高速工具钢中加入了钴、铝等元素。这类钢属于高碳高合金莱氏体钢,其主要的组织特征之一是含有大量的碳化物。铸态高速工具钢中的碳化物是共晶碳化物,经热压力加工后破碎成颗粒状分布在钢中,称为一次碳化物;从奥氏体和马氏体基体中析出的碳化物称为二次碳化物。这些碳化物对高速工具钢的性能影响很大,特别是二次碳化物,其对钢的奥氏本晶粒度和二次硬化等性能有很大影响。碳化物的数量、类型与钢的化学成分有关,而碳化物的颗粒度和分布则与钢的变形量有关。钨、钼是高速工具钢的主要合金元素,对钢的二次硬化和其他性能起重要作用。铬对钢的淬透性、抗氧化性和耐磨性起重要作用,对二次硬化也有一定的作用。钒对钢的二次硬化和耐磨性起重要作用,但降低可磨削性能。
  高速工个钢的淬火温度很高,接近熔点,其目的是使合金碳化物更多的溶入基体中,使钢具有更好的二次硬化能力。高速工具钢淬火后硬度升高,此为第一次硬化,但淬火温度越高,则回火后的强度和韧性越低。淬火后在350℃以下低温回火硬度下降在350℃以上温度回火硬度逐渐提高,至520~580℃范围内回火(化学成分不同,回火温度不同)出现第二次硬度高峰,并超过淬火硬度,此为二次硬化。这是高速工具钢的重要特性。
  高速工个钢除了具有高的硬度、耐磨性、红硬性等使用性能外,还具有一定的热塑性、可磨削性等工艺性能。
  多系高速工具钢主要合金元素是钨,不含钼或含少量钼。其主要特性是过热敏感性小,脱碳敏感性小、热处理和热加工温度范围较宽,但碳化物颗粒粗大,分布均匀性差,影响钢的韧性和塑性。
  钨钼系高速工具钢的主要合金元素是钨和钼。其主要特性是碳化物的颗粒度和分布均优于钨系高速工具钢,脱碳敏感性和过热敏感性低于钼系高速工具钢,使用性能和工艺性能均较好。
  钼系高速工具钢的主要合金元素是钼,不含钨或含少量钨。其主要特性是碳化物颗粒细,分布均匀、韧性好,但脱碳敏感性和过热敏感性大、热加工和热处理范围窄。
  含钻高速工具钢是在通用高速工具钢的基础上加入一定量的钴,可显著提高钢的硬度、耐磨性和韧性。
  粉未高速工具钢是用粉未冶金方法产生的。首先用雾化法制取低氧高速工具钢预合金粉未,然后用冷、热静压机将粉未压实成全致密的钢坯,再经锻、轧成材。粉未高速工具钢的碳化物细小、分布均匀,韧性、可磨削性和尺寸稳定性等均很好,可生产用铸锭法个可能产生更高合金元素含量的超硬高速工具钢。粉未高速工具钢可分为3类,第一类是含钴高速工具钢,其特点是具有接近硬质合金的硬度,而且还具有良好的可锻性、可加工性、可磨性和强韧性。第二类是无钴高钨、钼、钒超硬高速工具钢。第三类是超级耐磨高速工具钢。其硬度不太高,但耐磨性极好,主要用于要求高耐磨并承受冲击负荷的工作条件。
  工具钢的特性
  (1) 硬度
  工具钢制成工具经热处理后具有足够高的硬度,如用于金属切削加工的工具一般在HRC60以上。工具在高的切削速度和加工硬材料所产生高温的受热条件下,仍能保持高的硬度和良好的红硬性。碳素工具钢和合金工具钢一般在180℃~250℃、高速工具钢在600℃左右的工作温度下,仍能保持较高的硬度。红硬性对热变形模具和高速切削刀具用钢是非常重要的性能。
  (2) 耐磨性
  工具钢具有良好的耐磨性,即抵抗磨损的能力。工具在承受相当大的压力和摩擦力的条件下,仍能保持其形状和尺寸不变。
  (3) 强度和韧性
  工具钢具有一定的强度和韧性,使工具在工作中能够承受负荷、冲击、震动和弯曲等复杂的应力,以保证工具的正常使用。
  (4) 其他性能
  由于各种工具的工作条件不同,工具用钢还具有一些其他性能,如模具用钢还应具有一定的高温力学性能、热疲劳性、导热性和耐磨腐蚀性能等。
  工具钢除了具有上述使用性能外,还应具有良好的工艺性能。
  (1) 加工性
  工具钢应具有良好的热压力加工性能和机械加工性能,才能保证工具的制造和使用。钢的加工性取决于化学成分、组织的质量。
  (2) 淬火温度范围
  工具钢的淬火温度应足够宽,以减少过热的可能性。
  (3) 淬硬性和淬透性
  淬硬性是钢在淬火后所能达到最高硬度的性能。淬硬性主要与钢的化学成分特别是碳含量有关,碳含量越高,则钢的淬硬性越高。
  淬透性表示钢在淬火后从表面到内部的硬度分布状况。淬透性的高低与钢的化学成分、纯洁度、晶粒度有关。
  根据用于制造不同的工具,对这两种性能各有一定的要求。
  (4) 脱碳敏感性
  工具表面发生脱碳,将使表面层硬度降低,因此要求工钢的脱碳敏感性低。在相同的加条件下,钢的脱碳敏感性取决于其化学成分。
  (5) 热处理变形性
  工具在热处理时,要求其尺寸和外形稳定。
  (6) 耐削性
  对很制造刀具和量具用钢。要求具有良好的磨削性。钢的磨削性与其化学成分有关,特别是钒含量,如果钒质量分数不小于0.50%则磨削性变坏。
高速工具钢和合金工具钢工艺及参数上的区别
  高速工具钢也是一种合金工具钢,其中含有C,Mn,Si,Cr,V,W,Mo,Co.而它能用来做高速旋转切割工具,能耐磨,耐高温,就是其中Cr,V,W,Mo得比例比较大(你也是同行,这里就不细讲了),以 W12Cr4V5Co5为例,Cr->3.75%-5%,V->4.5%-5.25%,W->11.75%-13%.其中Cr和V得比例不得低于3%。P和S得含量不得大于0.030%。
  合金工具钢的加工方法主要是压力加工钢和切削工具钢。合金工具钢种类和多,有冷作,热作,无磁,塑料模具钢等等,同时Cr和V得比例不能过低。

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