It has been the skeleton of human industry for centuries, and the advent of the methods

數世紀以來，他是支撐人類工業的骨幹

to mass produce it from iron ore was the impetus to transform human society from a mostly agricultural

而隨著大量製鐵的技術出現，促使了人類文明由農業社會演變為今日的工業化社會

lifestyle to urban industrialisation.

它支撐了高樓大廈，鋪成了鐵路軌道

It forms the backbone of our skyscrapers, it paves the way for our railways, it shapes

它被製成引擎，為文明供給電力 甚至用來製造這些東西的工具，也正是以鋼鐵製成

the engines that powers our society, and the very tools that forge these objects are made

甚至用來製造這些東西的工具，也正是以鋼鐵製成

from steel.

我們先前已經討論過冶煉的過程如何決定最終的成品是為「鋼」或「鐵」

We have spoken before about how the refining processes of iron determines whether the resulting

以及材料中確切的碳含量如何大幅度的影響成品的特性

material will be steel or iron and how the exact percentage of carbon present in the

也談到了製程的演進，如何使過去專為刀劍、鎧甲以及工具製作使用的昂貴材料

material has dramatic results on the final material properties, and how the production

如今在我們的日常生活裡無所不在

methods through time has taken steel from an expensive material reserved for swords,

但我漏提了為何那微不足道的碳對鐵有如此大的影響

armour and toolmaking, to one that has permeated into nearly every technology we use in our

讓它從一個相對較弱的材料搖身一變， 甚至足以開啟整個工業革命

lives.

而這正是我們今天要討論的

But I failed to tell why that simple addition of carbon has such a huge effect on the iron,

我們對於鋼鐵加工的知識 大部分來自鐵匠們一代一代的傳承

turning it from a relatively weak material to one capable of launching an industrial

為他們所在的村莊聚落製作工具

revolution, which is what we are going to learn about today.

因此，為了更了解「鐵」這個神奇的材料 以及鐵匠如何小心翼翼地改變鐵的特性

Much of our knowledge in crafting steel was passed down over the centuries from blacksmith

我拜訪了Alec Steele的工作室 從頭開始製作一把屬於我的刀

to blacksmith, creating tools for their communities, so to learn more about this amazing material

我們使用含碳量0.55%的1055鋼材進行鍛造

and how blacksmiths carefully tailor it's material properties, I visited Alec Steele's

將它置於爐中，並使用動力錘將它鍛造成長方條

workshop to create my own knife from scratch.

好讓我能用我瘦小的手臂 在接下來的一小時裡，努力揮著3磅重的鐵鎚

We started our forging process with round stock 1055 steel with 0.55% carbon content,

將它更精準地鍛造成我們要的刀型

placed it in the forge and gradually shaped it with a power hammer to a rectangular bar

等刀型大致完成後，我們開始研磨及細修的步驟

that could be more precisely shaped into the shape of our blade using a 3 pound hammer

結束這個步驟後的刀胚 會再透過研磨完成最終的刀型

that my wee arms struggled to swing after an hour.

但在那之前，我們得透過熱處理的製程

Once we had roughed out the shape we began to grind and refine our blade.

來施展一些冶金學的巫術

Eventually producing our blade blank that would later be grinded to it's final shape,

為了強調這個步驟有多麼的重要 我們分別測試了4個樣本

but before that could happen we needed to perform some metallurgy wizardry through the

它們來自相同的材料 分別代表了熱處理製程中的不同階段

heat treatment process.

這個樣本為熱處理製程之前

To drive home how important this step is, we tested 4 samples of the same material at

很快你就會看到它是所有樣本裡面強度最弱的

different stages of the heat treatment process.

而這個是正常化(normalised)的樣本 它的降服應力(yield stress)小而較軟

This was our sample before the heat treatment process, which you will quickly see was the

它吸收了幾次的錘擊的外力產生塑性變形(plastic deformation)

weakest of the bunch.

這種特性對於刀劍來說並不理想。

This is the normalised sample, which was ductile with a low yield stress.

接著我們測試經過焠火(quench)硬化後的樣本

It took several hammer blows, which it absorbed through plastic deformation, not ideal characteristics

這是非常危險的舉動，不要在家嘗試

for a sword or knife.

爆裂的斷片把Alec的反光罩扯破了一個大洞

Next we tested our quench hardened sample, which is stupid and dangerous and should not

最後我們測試回火(tempered )後的樣本 它吸收了每一下的錘擊，只產生了些微的塑性變形

be tried at home.

只有在我們切割了一個缺口 產生應力集中點(stress concentration point)時才斷裂

This fractured explosively and tore a hole through Alec's reflector.

這樣的材料相當強韌 能吸收外力而不會產生永久的形變

Finally we tested the tempered material, which absorbed every hammer blow with minimal plastic

同時也相當堅硬，能讓刀刃不至於損壞

deformation and only broke when we cut a notch into the material to create a stress concentration

這是製刀最理想的材料

point.

如果這些名詞讓你感到困惑的話，我做了一部影片叫做Material Properties 101

This material is tough, capable of absorbing energy without deforming permanently, and

你可以去看看，幫助你更了解材料性質的術語

hard allowing it to resist damage to the cutting edge.

那麼，為何僅僅是加熱就能讓鋼鐵產生如此根本的改變呢

It is the ideal material for a blade.

這就是鐵碳合金的魔法

If any of these terms confused you, I created a video called Material Properties 101 that

我們可以透過特定的加熱與冷卻流程 小心地控制材料內部的金屬晶體結構組成

you can check out to get a better understanding of material property terminology.

首先讓我們來看看在鐵中添加碳如何影響其結晶組織(crystalline structure)

So how can the same steel alloy change so radically by simply applying heat?

未含碳的純鐵會形成稱作體心立方晶體(body centred cubic )的晶體結構

Well this is the magic of the iron carbon alloy.

由八個鐵原子分別位於角落，包圍著中間一個鐵原子

We can careful control how the internal metallic crystal structure forms with heating and cooling

每個晶體結構都有一個最容易產生變形的方向

cycles.

稱為滑移面(slip plane)

First let's see how adding carbon to iron affects it's crystalline structure.

對體心立方晶體而言，滑移面是左圖的這個面

With no carbon present pure iron will form a crystal structure called body centred cubic

體心立方晶體的金屬如鐵、鎢等通常較硬、延展性較差

with an iron atom at each of the eight corners and another in the centre.

相較於面心立方晶體結構的金屬如鋁、鉛、金等而言

Each crystal structure has a direction it most easily wants to deform, called a slip

當金屬冷卻時 這些結晶從各個成核點(nucleation points)開始增長

plane.

沿著相同的滑移面方向形成晶粒(grain)

For body centred cubic the slip plane occurs along this planes.

然而相鄰的晶粒不一定擁有相同方向的滑移面

Metals with Body centred cubic crystals like iron and tungsten tend to be harder and less

我們用2維的方式想像一下，當施加外力時

malleable than metals with face centred cubic crystals like aluminium, lead and gold.

晶粒會想朝某個特定方向滑移 並把力傳給此方向上的下一個晶粒

When a metal is cooling, these crystals grow from individual nucleation points and form

然而這個晶粒的滑移面角度並不相同 因此必須施加更大的外力

grains where each grain has the same orientation of slip plane but neighbouring grains may

才足以產生形變

not have the same slip plane.

這就好像試著要推動鐵軌上的火車 推的卻是側邊

Let's think about this 2 dimensionally, when a force is applied, the grain wants to

這樣要讓它移動是很困難的

slip in a particular direction, and passes the force onto the next grain in that direction

因此越大量且越小的晶粒組成的材料就越強韌

too, but this grains slip plane is at a different angle, so that force needs to be greater in

當冷卻時，純鐵通常擁有一樣的晶體結構

order to cause deformation.

其晶體結構並不會因熱處理產生有意義的改變

It's like trying to push a train down a railway track, by pushing on its side.

這時鐵碳合金就派上用場了

It's not going to go anywhere easily.

要探討這點，我們先來看看碳鋼的相圖(phase diagram)

So smaller and more numerous grains results in a stronger material.

在這個相圖中，X軸是碳含量的百分比

Pure iron tends to always has the same crystal structure as it cools and it's crystal structure

Y軸則是攝氏溫度

doesn't change meaningfully with heat treatment.

這告訴我們在不同溫度及碳含量底下金屬的結晶組織

This is where alloying with carbon comes in.

在我們的左手邊是純鐵，如我們先前所解釋的

To explore this let's look at our phase diagram for carbon steel.

形成單一的結晶組織，稱為肥粒鐵(ferrite)

On this diagram we have our carbon content percentage on the x-axis and the temperature

當我們移動到相圖的右手邊 形成肥粒鐵的結晶越來越少

of the metal on the y-axis.

多數形成一種鐵碳合金，通常稱為雪明碳鐵(cementite)

This tells us the crystalline structure of the metal at various temperatures and carbon

現在如果我們從溫度軸往上移動 我們會看到這些代表轉變溫度(transition temperature )的線條

contents.

在這裡鋼的結晶組織開始轉變為新的結晶組織

On the left hand side we have pure iron, which as we explained earlier forms only one crystal

稱為沃斯田鐵(Austenite)

structure, called ferrite.

再繼續往上 這邊我們看到的線條代表金屬轉變為液態

As we move across the diagram to the right hand side, less and less of the crystal structure

沃斯田鐵與肥粒鐵的主要差別在於它形成了我們先前看過的面心立方晶體

forms ferrite, and more forms an iron carbide alloy, commonly called cementire.

而肥粒鐵則是體心立方晶體

Now if we move up in temperature we start to see these lines that represent transitional

儘管沃斯田鐵的排列方式相較體心立方晶體更為密集，

temperatures, where the crystal structures of the steel begin to transform into a new

它仍然擁有足夠的間隙 讓較鐵原子小的碳原子，能舒服的容身其中

crystal structure called Austenite.

讓沃斯田鐵相較於肥粒鐵，有較高的碳可溶度(solubility)

Moving further up again we see lines representing the transition of the material to a liquid

利用以上這些資訊，現在讓我們拿0.55%的1055鋼材

state.

看看它在我們的熱處理過程中，從頭到尾是如何轉變的

Austenites primary difference to ferrite is that it forms that face centred cubic crystal

第一個步驟叫正常化(normalisation)

structure that we saw early, while ferrite is body centred cubic.

正常化的主要功用是釋放在鍛造過程中產生的內應力(internal stresses)與應變(strains)

And while this packing pattern is denser than body centred cubic, it does open up spaces

讓鋼材回復到其原先的結晶組織

in the crystal structure that interstitial carbon atoms, which are smaller than iron,

它就像鋼材的「重啟」按鈕 讓鋼材產生整齊、平均的晶粒大小與分佈

can snuggly fit.

增加它的強度

Allowing austenite to have a higher solubility to carbon over ferrite.

這裡我們將刀胚放在鋼管中， 避免刀胚直接接觸火源

Using all of this information, let's take our 1055 steel with 0.55% carbon content and

而是從鋼管散發出的較平均的輻射熱

see how it transforms from the start of our heat treatment cycle to the end.

一旦它達到轉變溫度，我們讓它定溫停留一段時間

The first step is called normalisation.

讓結晶組織有足夠時間排列完成

Normalisation is primarily functions to relieve internal stresses and strains that formed

正常化的下一步是讓鋼材在空氣中徐冷

during the forging process and return the material to its original crystal structure

這時鋼材中的碳含量會決定這時會發生什麼事

before forging began.

如果我們拿含碳量0.8%的碳鋼 等等，我們需要大一點的圖

It's effectively a reset button for the steel and creates nice even grain size and

如果我們拿含碳量0.8%的碳鋼， 讓它冷卻並通過轉變溫度

distribution, increasing its strength.

沃斯田鐵與其中的碳會緩慢的轉變為肥粒鐵與雪明碳鐵的混合

Here we placed the knife blank inside a steel tube to prevent the metal from receiving heat

這樣的層狀(laminar)結構稱為波來鐵(pearlite)

directly from the flame, but instead a more even radiative heat from the tube.

波來鐵僅在碳含量0.8%時形成

Once it reaches this transition temperature we let it soak to give the crystal structure

現在如果我們拿碳含量0.2%的碳鋼，

time to settle.

讓它徐冷至這邊第一個轉變溫度

The next step in normalising is to allow the steel to slowly air cool.

此時肥粒鐵首先開始形成，由於肥粒鐵是純鐵

What happens now depends on the carbon content.

所以當肥粒鐵形成，碳含量會開始上升，這樣的轉變會一直持續

If we take a 0.8% carbon steel, no hang on we're gonna need a bigger graph for this,

直到剩餘的沃斯田鐵有足夠0.8%的碳 並由此開始形成波來鐵

If we take a 0.8% carbon steel and cool it to it's through transitional temperature

這會形成一個由顏色較淡的肥粒鐵為主

the austenite and the interstitial carbon will slowly transform to a mixture of ferrite

周圍則是較黑的波來鐵的結晶組織

and cementite, which takes this laminar structure called pearlite.

將這些顯微組織與其他兩個比較，我們可以看到碳對顯微組織的影響

Pearlite only forms at a 0.8% carbon solution

這是純鐵，其為100%的肥粒鐵，顏色較淡，甚至可以看到晶界(grain boundaries)

Now if we take a 0.55% 0.2% steel, like the one we used.

這是含碳量0.5%的碳鋼，與我們所使用的很像 在此僅有非常少量的肥粒鐵形成

And slowly cool it, to its first transitional temperature here.

便進入波來鐵的形成階段

Where ferrite first begins to form, ferrite is pure iron so as it forms the carbon percentage

而這是含碳量0.8%的碳鋼

begins to rise, this will continue to happen until the remaining austenite has a carbon

在這裡整個結晶組織為波來鐵，在我們先前展示的500倍放大的照片中

percentage of 0.8% and it will then form pearlite from this point on.

你甚至可以輕易看到其中的層狀組織

This forms a crystal structure dominated by ferrite, showing here as a lighter colour,

波來鐵如何影響鋼鐵強度目前所知仍有限

surrounded by the darker pearlite.

它對鋼鐵的剛性影響不大 然而波來鐵的含量增加

Comparing these microstructures to another 2 we can see the effect carbon has on the

對材料的降服點(yield point)有戲劇性的影響 令其能吸收更多能量而不產生永久的形變

microstructure.

但我們的確能透過接下來的步驟增加材料的剛性與硬度

Here we have pure iron, with 100% ferrite, showing as this light colour, you can even

假如我們將鋼材重新加熱到形成沃斯田鐵 但這次，不是讓它徐冷而是浸入油中快速冷卻

see the grain boundaries.

而是浸入油中快速冷卻，順便燒燒手毛

This is a 0.5% carbon steel similar to ours, where a very small amount of ferrite formed

在高溫沃斯田鐵中散佈的碳原子

before we reaching the point of pearlite formation, and this is 0.8% carbon steel where the entire

無法自晶格(crystal lattice)中擴散出去形成雪明碳鐵， 而困在其中

structure is pearlite, with our previous example showing pearlite under 500 times magnification

形成一個新的結晶組織稱為麻田散鐵(martensite)

where you can readily see that laminar structure.

這個結晶組織內部有很大的拉力

How Pearlite strengthens steel is not well understood.

部分來自於困在結晶組織中的碳原子導致晶格變形

It has little effect on the steels stiffness, but increasing the pearlite content has dramatic

也因為在快速冷卻的過程中，表面的冷卻速度較內部快許多

effects on the materials yield point, making it much more capable of absorbing energy without

這導致了材料內部的張力

permanently deforming.

這種內部的應變讓其他的形變較難產生

But we can increase the materials stiffness and hardness with our next step.

但這並不會讓材料變得更加強韌

If we heat the metal back up to form austenite once again, but this time instead of letting

它只代表材料在斷裂前不會延展或彎曲

it cool slowly, we rapidly cool it in oil, while casually burning your arm hair off and

但當斷裂發生時，所有內在的張力在爆裂的一瞬間釋放

barely flinching, the carbon atoms that spread out throughout the hot austenite structure

如果你有看過Smarter Every Days的頻道裡 魯珀特之淚(Saint Rupert’s Drop)的影片

cannot diffuse out of the crystal lattice to form cementite, and instead gets stuck

你可以看到同樣的原理在極慢動作下呈現

in solution, creating a new crystal structure called martensite.

這個材料特性叫做硬度， 我們希望我們的刀鋒夠硬，在切割時不會受損

This crystal structure has a huge amount of internal stretching.

但我們不希望整把刀都如此的硬

In part because the carbon trapped within the crystal structure causes the crystal lattice

這樣一來它無法吸收太大的力量

to deform, but also because during the rapid cooling the surface cooled much faster than

它必透過加熱與形變來消耗一些內部的應力

the internal material.

這時最後一個步驟就派上用場了 稱為回火(tempering)

This causes internal tension in the material.

回火這個步驟透過加熱到特定溫度，讓被困住的碳能夠脫離

These internal strains make it harder for additional deformation to occur, but this

我們僅用了烤箱，設定200度C 其中的碳再度聚合形成雪明碳鐵

does not make the material stronger.

但與先前形成波來鐵不同

It simply means it will not stretch and bend before breaking, and when it finally does

它聚合成被肥粒鐵包圍的小球

fracture all of this internal tension is suddenly released in an explosive expansion.

回火也減輕了因急速冷卻導致的內在張力

If you have watched Smarter Every Days video on the Saint Rupert's Drop, you will have

這降低了硬度，但增加了韌性

seen this principle demonstrated in incredible slow motion.

這創造了一個性質介於正常化與焠火硬化之間的鋼材

This material property is called hardness, and we want our cutting edge to be hard to

他有足夠的韌性可以承受錘擊而不會碎裂

resist damage when cutting, but we do not want our entire blade to be hard as it will

而又足夠強韌而不會永久的變形 同時又擁有足夠的硬度確保刀鋒無損

not be able to absorb a lot of energy.

熱處理的流程賦予我們的鋼材完美的特性，

It needs to be able to dissipate some of that energy through heat and deformation.

而這幾乎全部取決於我們所使用的鋼材品質

This is where the final step of the process comes in, called tempering.

與Alec學習這些技術非常有趣 我也極力推薦你一定要到他的頻道看看

Tempering raises the temperature enough to allow the carbon trapped in solution to escape,

他對工作的態度非常了不起 啟發我今年開始學習一些新的技術

we just used an oven set at 200 degree, the carbon then coalesces to form cementite once

我希望從學習如何使用arduino設計程式與創造機器人開始

again, but instead of forming pearlite like before.

我在skillshare上找到的這個課程 對所有想學習這個技術的人來說，是個很棒的起跑點

It gathers in globules surrounded by ferrite.

Skillshare擁有包含了圖像設計、動畫、網頁開發

Tempering also relieves some of that internal tension caused by the rapid cooling.This reduces

音樂、攝影、遊戲設計等等數千個課程

the hardness, but increases toughness.

現今的社會 你幾乎可以透過網路自學所有技術 而Skillshare正是這樣一個非常棒的地方

This produces a material that has the perfect balance of characteristics between the normalised

在專業、可理解，且有清楚學習曲線的課程中，

material and the hardened material.

你可以盡情投入並開始學習你熱愛的工作

It is ductile enough to absorb hammer blows without shattering, but strong enough to not

高級會員每個月10美元起 就可無限制的訪問所有課程

permanently deform, and with enough hardness to ensure it doesn't gather damage on the

但只要你使用這個網址登錄，就可享前三個月99分美元的價格

cutting edge.

這項優惠原先只到一月底截止

This process gave our steel the perfect material properties and a lot of that is thanks to

但我與Skillshare協調，為各位將這項優惠延長到二月十五日

the quality of the steel we started off with.

在這三個月中，你可以輕易的學到那些所需的技術，開啟新的興趣或生意

Learning these skills with Alec was a lot of fun and I highly recommend you check his

所以問問你自己吧

channel out.

你一直拖延沒去學的技術是什麼

His incredible attitude to work really inspired me to start learning some new hands on skills

你一直夢想著要完成，但不確定自己是否辦得到的計劃是什麼

this year and I am hoping to start that off by learning how to programme and create robotics

何不馬上開始，用以下網址登錄Skillshare

with an arduino.

你不但沒有損失，還會獲得寶貴的生活技能

This course I found on skillshare is the perfect jumping off point for anyone looking to learn

一如往常的，謝謝觀賞 也感謝我所有的Patreon支持者

the same skills.

如果你想要從我這了解更多的話， 我的twitter, facebook和instagram網址如下

Skillshare is home to thousands of other classes in graphic design, animation, web development,

music, photography, video game design and more.

These days you can teach yourself pretty much any skill online and Skillshare is a fantastic

place to do it.

With professional and understandable classes, that follow a clear learning curve, you can

dive in and start learning how to do the work you love.

. A Premium Membership begins around $10 a month

for unlimited access to all courses, but you can get your first 3 months for just 99 cent

if you sign up with this link.This offer was supposed to be only valid until the end of

Jan, but I talked to Skillshare and was able to get this extended for ye until Feb 15.

In those 3 months you could easily learn the skills you need to start a new hobby or business.

So ask yourself right now.

What skill have you been putting off learning.

What project have you been dreaming of completing, but you aren't sure if you have the skills

to do it.

Why not start right now and sign up to Skillshare using the link below.

You have nothing to lose and a valuable life skill to gain.

As usual thanks for watching and thank you to all my Patreon supporters.

If you would like to see more from me, the links to my twitter, facebook and instagram

pages are below.