/ News & Press / Video / Heat Treatment -The Science of Forging (feat. Alec Steele)

Heat Treatment -The Science of Forging (feat. Alec Steele)

WEBVTT
Kind: captions
Language: en

00:00:06.120 --> 00:00:08.660
Steel is the most important material of human civilization
00:00:08.660 --> 00:00:12.960
For centuries he was the backbone of the human industry
00:00:12.960 --> 00:00:18.590
With the emergence of a large number of iron-making technologies, human civilization has evolved from an agricultural society to an industrialized society today.
00:00:21.060 --> 00:00:25.450
It supports high-rise buildings and paved railway tracks
00:00:25.450 --> 00:00:29.820
It was made into an engine, powering civilization and even the tools used to make these things, and it was also made of steel.
00:00:29.820 --> 00:00:30.840
Even the tools used to make these things are made of steel
00:00:30.840 --> 00:00:34.980
We have previously discussed how the smelting process determines whether the final product is "steel" or "iron"
00:00:34.980 --> 00:00:40.079
And how the exact carbon content of the material greatly affects the properties of the finished product
00:00:43.899 --> 00:00:48.559
Also talked about the evolution of the process, how to make the expensive materials used for swords, armors and tools in the past
00:00:48.559 --> 00:00:53.399
Omnipresent in our daily life
00:00:54.399 --> 00:00:58.789
But I missed out why that trivial carbon has such a big effect on iron
00:00:58.789 --> 00:01:03.030
Making it change from a relatively weak material is enough to start the entire industrial revolution
00:01:03.030 --> 00:01:06.440
And this is exactly what we are going to discuss today
00:01:06.440 --> 00:01:10.360
Much of our knowledge of steel processing comes from generations to generations of blacksmiths
00:01:10.360 --> 00:01:15.030
Craft tools for their village settlements
00:01:15.030 --> 00:01:19.640
Therefore, in order to better understand the magical material "iron" and how the blacksmith carefully changes the properties of iron
00:01:19.640 --> 00:01:22.220
I visited Alec Steele's studio to make a knife of mine from scratch
00:01:22.220 --> 00:01:28.660
We use 1055 steel with 0.55% carbon content for forging
00:01:28.660 --> 00:01:32.670
Place it in a furnace and use a power hammer to forge it into rectangular bars
00:01:32.670 --> 00:01:36.670
So that I can use my thin arm to swing a 3-pound hammer in the next hour
00:01:36.670 --> 00:01:40.220
Forging it more precisely into the shape we want
00:01:40.220 --> 00:01:43.360
After the knife shape is almost completed, we start the grinding and fine-tuning steps.
00:01:43.360 --> 00:01:47.790
After the end of this step, the blade will be ground to complete the final shape.
00:01:47.790 --> 00:01:51.610
But before that, we had to go through a heat treatment process
00:01:51.610 --> 00:01:53.440
To perform some metallurgy witchcraft
00:01:53.440 --> 00:01:57.630
To emphasize how important this step is, we tested 4 samples separately
00:01:57.630 --> 00:02:00.470
They come from the same material and represent different stages in the heat treatment process.
00:02:00.470 --> 00:02:04.250
This sample is before the heat treatment process
00:02:04.420 --> 00:02:05.960
Soon you will see that it is the weakest of all samples.
00:02:05.960 --> 00:02:09.000
And this is a normalised sample. Its yield stress is small and soft.
00:02:09.000 --> 00:02:14.989
It absorbs several times the external force of the hammer to produce plastic deformation.
00:02:14.989 --> 00:02:16.940
This characteristic is not ideal for swords.
00:02:16.940 --> 00:02:20.660
Then we test the samples after quenching
00:02:20.660 --> 00:02:21.939
This is a very dangerous move, do n’t try it at home
00:02:21.939 --> 00:02:25.260
The bursting fragment tore Alec's reflector over a large hole
00:02:25.260 --> 00:02:29.800
Finally, we tested the tempered sample. It absorbed each hammer stroke and produced only a small amount of plastic deformation.
00:02:29.800 --> 00:02:34.829
Only break when we cut a gap to create a stress concentration point
00:02:35.829 --> 00:02:40.420
This material is quite tough and can absorb external forces without permanent deformation.
00:02:40.420 --> 00:02:43.159
At the same time, it is quite hard to prevent the blade from being damaged.
00:02:43.159 --> 00:02:45.659
This is the most ideal material for knife making
00:02:45.659 --> 00:02:50.030
If these terms confuse you, I made a film called Material Properties 101
00:02:50.030 --> 00:02:54.129
You can check out the terms that help you better understand the nature of the material
00:02:54.129 --> 00:02:58.110
So why does heat alone make such a fundamental change in steel?
00:02:58.110 --> 00:03:01.120
This is the magic of iron-carbon alloys
00:03:01.120 --> 00:03:06.260
We can carefully control the composition of the metal crystal structure inside the material through specific heating and cooling processes
00:03:07.360 --> 00:03:11.180
First let's see how adding carbon to iron affects its crystalline structure
00:03:11.180 --> 00:03:15.739
Pure iron without carbon forms a crystal structure called body centred cubic
00:03:15.739 --> 00:03:19.379
Eight iron atoms are located at the corners and surround the middle iron atom
00:03:19.379 --> 00:03:23.890
Each crystal structure has a direction that is most prone to deformation
00:03:23.890 --> 00:03:24.950
Known as slip plane
00:03:24.950 --> 00:03:28.580
For a body-centered cubic crystal, the slip surface is the one on the left
00:03:28.580 --> 00:03:32.900
Body-centered cubic crystal metals such as iron, tungsten, etc. are usually harder and less ductile
00:03:32.900 --> 00:03:37.870
Compared to metals with a face-centered cubic crystal structure such as aluminum, lead, gold, etc.
00:03:37.870 --> 00:03:41.909
These crystals start to grow from various nucleation points as the metal cools
00:03:41.909 --> 00:03:46.540
Grains are formed along the same slip plane direction
00:03:46.540 --> 00:03:48.099
However, adjacent grains may not have the same sliding surface.
00:03:48.099 --> 00:03:51.739
Let ’s imagine it in two dimensions. When an external force is applied,
00:03:51.739 --> 00:03:53.000
The grain will want to slide in a certain direction and transfer the force to the next grain in this direction
00:03:53.000 --> 00:04:01.260
However, the slip angle of this grain is not the same, so a larger external force must be applied.
00:04:01.260 --> 00:04:02.760
Is enough to cause deformation
00:04:02.760 --> 00:04:06.989
It's as if trying to push the train on the rails is pushing the side
00:04:06.989 --> 00:04:08.909
It's difficult to make it move like this
00:04:08.909 --> 00:04:12.569
Therefore, the larger and smaller the grain size, the stronger the material.
00:04:12.569 --> 00:04:17.070
When cooled, pure iron usually has the same crystal structure
00:04:17.070 --> 00:04:19.769
Its crystal structure does not change meaningfully due to heat treatment
00:04:19.769 --> 00:04:21.989
Then iron-carbon alloy comes in handy
00:04:21.989 --> 00:04:25.270
To explore this, let's take a look at the phase diagram of carbon steel.
00:04:25.270 --> 00:04:29.320
In this phase diagram, the X axis is the percentage of carbon content
00:04:29.320 --> 00:04:31.250
Y-axis is Celsius
00:04:31.250 --> 00:04:34.870
This tells us the crystalline structure of the metal at different temperatures and carbon contents
00:04:35.870 --> 00:04:39.000
On our left hand side is pure iron, as we explained earlier
00:04:39.000 --> 00:04:41.580
Forms a single crystalline structure, called ferrite
00:04:41.580 --> 00:04:45.461
As we move to the right-hand side of the phase diagram, less and less crystals of iron are formed
00:04:45.461 --> 00:04:50.550
Most form an iron-carbon alloy, commonly known as cementite
00:04:50.550 --> 00:04:54.370
Now if we move up from the temperature axis we will see these lines representing the transition temperature
00:04:54.370 --> 00:04:58.330
Here the crystalline structure of the steel begins to transform into a new crystalline structure
00:04:58.330 --> 00:05:00.830
Called Austenite
00:05:00.830 --> 00:05:05.460
Moving on, the lines we see here represent the transition from metal to liquid
00:05:06.460 --> 00:05:10.330
The main difference between Vosstian iron and fat iron is that it forms the face-centered cubic crystal we have previously seen
00:05:10.330 --> 00:05:13.840
The fat iron is a body-centered cubic crystal
00:05:13.840 --> 00:05:17.770
Although Vostian irons are arranged more densely than body-centered cubic crystals,
00:05:17.770 --> 00:05:21.770
It still has enough space for carbon atoms smaller than iron atoms to fit comfortably in it.
00:05:23.310 --> 00:05:27.150
Allows Vostian Iron to have higher carbon solubility compared to Fertilized Iron
00:05:27.150 --> 00:05:32.919
Using the above information, let us now take 0.55% of 1055 steel
00:05:32.919 --> 00:05:37.080
See how it changed from start to finish during our heat treatment
00:05:37.080 --> 00:05:39.259
The first step is called normalisation
00:05:39.259 --> 00:05:43.300
The main function of normalization is to release internal stresses and strains generated during forging
00:05:43.300 --> 00:05:47.400
Return the steel to its original crystalline structure
00:05:48.860 --> 00:05:53.540
It's like steel's `` restart '' button to make steel have a neat, average grain size and distribution
00:05:53.540 --> 00:05:55.460
Increase its strength
00:05:55.460 --> 00:05:59.150
Here we place the blank in the steel pipe to avoid direct contact with the source of fire
00:05:59.150 --> 00:06:03.810
But the more average radiant heat emitted from the steel pipe
00:06:03.810 --> 00:06:07.151
Once it reaches the transition temperature, we let it stay for a while
00:06:07.151 --> 00:06:08.560
Allow sufficient time for the crystalline structure to complete
00:06:08.560 --> 00:06:12.349
The next step in normalization is to cool the steel in the air
00:06:12.349 --> 00:06:14.970
The carbon content of the steel at this time will determine what will happen at this time
00:06:14.970 --> 00:06:21.370
If we take carbon steel with carbon content of 0.8% and so on, we need a bigger picture
00:06:21.370 --> 00:06:25.780
If we take a carbon steel with 0.8% carbon content, let it cool and pass the transition temperature
00:06:25.780 --> 00:06:30.120
Vostian iron and the carbon in it will slowly transform into a mixture of ferrous iron and Xueming carbon iron
00:06:30.120 --> 00:06:34.319
Such a laminar structure is called pearlite
00:06:34.319 --> 00:06:37.870
Polaite is formed only at a carbon content of 0.8%
00:06:37.870 --> 00:06:40.460
Now if we take carbon steel with 0.2% carbon content,
00:06:40.460 --> 00:06:43.639
Let it cool down to the first transition temperature here
00:06:43.639 --> 00:06:48.340
At this time, the fertile iron began to form first, because the ferrous iron was pure iron.
00:06:48.340 --> 00:06:52.849
So when the fertilized iron is formed, the carbon content will start to rise, and this transformation will continue.
00:06:52.849 --> 00:06:57.389
Until the remaining Vostian iron has enough 0.8% carbon and from this it begins to form Pola.
00:06:57.389 --> 00:07:01.629
This will form a lighter-colored fat iron
00:07:01.629 --> 00:07:03.430
Surrounded by darker crystalline iron
00:07:03.430 --> 00:07:07.710
Comparing these microstructures with the other two, we can see the effect of carbon on the microstructure
00:07:08.889 --> 00:07:14.800
This is pure iron, which is 100% fat iron, with a lighter color, and even grain boundaries can be seen
00:07:14.879 --> 00:07:20.110
This is a carbon steel with a carbon content of 0.5%. It is very similar to what we use. Only a small amount of ferrous iron is formed here.
00:07:20.110 --> 00:07:22.500
Into the formation stage of Pola
00:07:23.000 --> 00:07:25.000
And this is carbon steel with 0.8% carbon content
00:07:25.300 --> 00:07:30.590
Here the entire crystalline structure is boron iron, in the 500x magnified photo we showed earlier
00:07:30.590 --> 00:07:33.300
You can even easily see the layered structure inside
00:07:33.300 --> 00:07:35.990
How Pole-Iron influences steel strength is still limited
00:07:35.990 --> 00:07:40.689
It has little effect on the rigidity of steel, however, the content of boron iron increases
00:07:40.689 --> 00:07:44.840
Dramatic impact on the yield point of a material allows it to absorb more energy without permanent deformation
00:07:46.409 --> 00:07:50.569
But we can indeed increase the stiffness and hardness of the material through the next steps
00:07:50.569 --> 00:07:54.979
Suppose we reheat the steel to form Vostian Iron, but this time, instead of letting it cool down slowly, we immerse it in oil and quickly cool
00:07:54.979 --> 00:07:59.400
Instead, immerse it in oil and quickly cool it.
00:07:59.400 --> 00:08:04.159
Carbon atoms scattered in hot Vostian iron
00:08:04.159 --> 00:08:08.080
Unable to diffuse out of the crystal lattice to form citronite and become trapped in it
00:08:08.080 --> 00:08:12.060
Formation of a new crystalline structure called martensite
00:08:12.060 --> 00:08:15.100
There is a lot of tension inside this crystalline structure
00:08:15.100 --> 00:08:18.810
Partly from the carbon atoms trapped in the crystalline structure causing the lattice to deform
00:08:18.810 --> 00:08:23.159
Because the surface cools much faster than the inside during the rapid cooling process.
00:08:24.780 --> 00:08:27.360
This causes tension within the material
00:08:27.360 --> 00:08:31.430
This internal strain makes other deformations more difficult to produce
00:08:31.430 --> 00:08:33.450
But this does not make the material more tough
00:08:33.450 --> 00:08:37.670
It simply means that the material will not stretch or bend until it breaks
00:08:37.670 --> 00:08:42.029
But when the fracture occurs, all the internal tension is released at the instant of burst
00:08:42.029 --> 00:08:45.230
If you have watched Saint Rupert's Drop videos on Smarter Every Days' channel
00:08:45.230 --> 00:08:48.839
You can see the same principle is presented in extreme slow motion
00:08:48.839 --> 00:08:53.110
This material property is called hardness, and we want our blades to be hard enough that they will not be damaged during cutting.
00:08:53.110 --> 00:08:57.440
But we don't want the whole knife to be so hard
00:08:57.440 --> 00:08:59.910
This way it cannot absorb much power
00:08:59.910 --> 00:09:03.839
It must consume some internal stress through heating and deformation
00:09:03.839 --> 00:09:07.640
At this point the last step comes in handy called tempering
00:09:07.640 --> 00:09:11.730
This step of tempering allows the trapped carbon to escape by heating to a specific temperature
00:09:11.730 --> 00:09:16.400
We only used the oven and set the carbon at 200 ° C to re-aggregate to form citronite.
00:09:16.400 --> 00:09:19.320
But different from the previous formation of Plei iron
00:09:19.320 --> 00:09:21.980
It aggregates into small balls surrounded by fat iron
00:09:21.980 --> 00:09:26.320
Tempering also reduces the internal tension caused by rapid cooling
00:09:26.320 --> 00:09:28.740
This reduces hardness but increases toughness
00:09:28.740 --> 00:09:32.560
This creates a steel with properties between normalization and hardening
00:09:34.540 --> 00:09:38.339
He has enough toughness to withstand hammering without breaking
00:09:38.339 --> 00:09:42.089
It is strong enough without permanent deformation and has sufficient hardness to ensure that the blade is not damaged
00:09:43.290 --> 00:09:47.420
The heat treatment process gives our steel perfect properties,
00:09:47.420 --> 00:09:50.360
And it all depends on the quality of the steel we use
00:09:50.360 --> 00:09:54.060
Learning these techniques with Alec is very interesting and I highly recommend you to check out his channel
00:09:55.060 --> 00:09:58.800
His attitude towards work is amazing and inspired me to start learning some new techniques this year
00:09:58.800 --> 00:10:02.740
I want to start by learning how to design programs and create robots with arduino
00:10:04.139 --> 00:10:07.760
This course I found on skillshare is a great starting point for anyone who wants to learn this technology
00:10:09.399 --> 00:10:13.800
Skillshare includes graphic design, animation, web development
00:10:13.800 --> 00:10:16.839
Thousands of courses in music, photography, game design and more
00:10:16.839 --> 00:10:21.000
In today's society, you can learn almost all the technology by yourself online. Skillshare is such a great place.
00:10:22.240 --> 00:10:26.050
In courses that are professional, understandable, and have a clear learning curve,
00:10:26.050 --> 00:10:28.709
You can devote yourself and start learning the work you love
00:10:28.709 --> 00:10:33.000
Unlimited access to all courses for premium members starting at $ 10 per month
00:10:33.000 --> 00:10:36.510
But as long as you use this URL to log in, you can enjoy the price of 99 cents for the first three months
00:10:36.510 --> 00:10:40.860
This offer originally only lasted until the end of January
00:10:40.860 --> 00:10:45.310
But I coordinate with Skillshare to extend this offer to February 15th for you
00:10:45.310 --> 00:10:50.190
In these three months, you can easily learn the required technology and start a new interest or business.
00:10:50.190 --> 00:10:51.970
So ask yourself
00:10:51.970 --> 00:10:53.800
What is the technology that you have been delaying?
00:10:53.800 --> 00:10:56.940
You've always dreamed of getting it done, but you're not sure what you can do
00:10:57.940 --> 00:11:00.820
Why not start right away and log in to Skillshare at
00:11:00.820 --> 00:11:04.350
Not only do you not lose, you also gain valuable life skills
00:11:04.350 --> 00:11:07.970
As always, thanks for watching and thanks to all my Patreon supporters
00:11:07.970 --> 00:11:11.089
If you want to learn more from me, my twitter, facebook and instagram URLs are as follows

Sales phone