What is CD4MCuN Hardened?

CD4MCuN is a duplex stainless steel alloy that is known for its excellent corrosion resistance properties. It is not typically hardened through traditional heat treatment methods like quenching and tempering, as these methods are not suitable for duplex stainless steels.

Duplex stainless steels like CD4MCuN have a two-phase microstructure consisting of austenitic and ferritic phases. This microstructure provides the alloy with excellent strength and corrosion resistance properties, but it also makes it difficult to harden through traditional heat treatment methods.

Instead of heat treatment, duplex stainless steels like CD4MCuN are typically hardened through cold working or work hardening. This involves subjecting the alloy to mechanical deformation processes like rolling, bending, or forging, which can increase its strength and hardness. The extent of work hardening can be controlled by adjusting the amount and type of deformation applied to the alloy.

However, it is important to note that excessive cold working can also lead to a loss of toughness and ductility, which can make the alloy more susceptible to brittle fracture. Therefore, it is essential to balance the amount of work hardening with the desired mechanical properties and the intended application.

In summary, CD4MCuN is not typically hardened through traditional heat treatment methods like quenching and tempering. Instead, it can be hardened through cold working or work hardening, which involves subjecting the alloy to mechanical deformation processes. It is important to balance the amount of work hardening with the desired mechanical properties and the intended application to avoid excessive loss of toughness and ductility.

How to weld mild steel to stainless steel?

Welding mild steel to stainless steel can be a challenge for new welders who are unsure of their ability to create a high-quality joint between these two dissimilar metals. The properties and compositions of these metals are different, making the welding process more difficult than welding pure stainless steel. In this article, we will discuss the challenges of welding mild steel to stainless steel and provide some tips to ensure a successful weld.

Note: Mild steel (iron containing a small percentage of carbon, strong and tough but not readily tempered), also known as plain-carbon steel and low-carbon steel, is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications.

One of the most critical aspects of welding mild steel to stainless steel is to avoid over-welding and deep penetration. This is because these metals have different melting points and thermal expansion rates, which can cause cracking, distortion, and brittleness in the joint. To prevent these issues, it's important to focus the arc more on the stainless steel portion and maintain low heat.

Related post:

Reasons You Want to Avoid Welding Stainless Steel to Carbon Steel

Maintaining low heat is essential to prevent deep penetration, preserve corrosion resistance, and prevent carbon contamination. To achieve this, you can set the lowest amperage that will melt the filler metal, travel at a fast speed, use stringer beads instead of weaving, use chill bars under or on the metals, and create a symmetrical joint that requires the least amount of weld metal. Despite the uneven angle, pointing the arc towards the stainless steel portion will result in a symmetrical bead with good toe fusion.

Differences between mild and austenitic steel for welding

Property	Mild steel	Austenitic (304) steel
Thermal expansion	65	100
Thermal conductivity	100	33
Electrical resistance	12.5	72
High-temperature strength	900 °F (480 °C)	1300 °F (700 °C )
Tensile strength	60-70ksi	85ksi
Ductility	25	55
Melting point	2800 °F (1540 °C)	2600 °F (1425 °C)
Galvanic corrosion	High	Low

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 Another challenge in welding mild steel to stainless steel is avoiding slag inclusions, which can occur when the welding process produces slag on the bead. To prevent this, the customized angle becomes even more crucial. It's also a good idea to test on similar scrap metals before welding your main project.

Contamination of the stainless steel portion with iron particles is another critical consideration in welding mild steel to stainless steel. Iron particles can cause rusting of the stainless steel portion, leading to corrosion over time. To avoid this, it's essential to use a separate set of tools to clean and bevel the stainless steel portion and avoid scratching it on any carbon steel surfaces, such as the steel portion or the welding table.

In conclusion, welding mild steel to stainless steel can be a challenging task for new welders. It requires a proper understanding of the properties and compositions of these metals and specialized techniques to ensure a successful weld. By following the tips outlined in this article, you can minimize the risks and create a strong, durable joint between these two dissimilar metals.

Reasons You Want to Avoid Welding Stainless Steel to Carbon Steel

When it comes to metalworking, welding is a commonly used technique to join different pieces of metal together. However, welding stainless steel to carbon steel is a particularly difficult task that should be avoided whenever possible. There are several reasons why welding dissimilar metals, such as stainless steel and carbon steel, can lead to problems and potentially compromise the strength and longevity of the finished product.

Difficulty

Combining dissimilar metals adds extra challenges to the welding process. Stainless steel and carbon steel have different properties, including different thermal expansion rates, melting points, and chemical compositions. Welding these two materials together creates a "dissimilar metal weld," which can cause problems such as cracking, distortion, and brittleness.

Welding stainless steel to carbon steel requires precise control of the temperature and heat input to ensure the proper fusion of the two metals. This can be difficult to achieve due to the different properties of each metal. Carbon steel has a lower melting point and is more electrically conductive than stainless steel. Welding stainless steel with resistance welding, for example, heats up the metal much faster than carbon steel. Waiting for the carbon steel to reach weld temperature can cause the stainless steel to overheat and become riddled with hot cracks. Using filler-based welding or preheating the plain carbon steel can mitigate this issue, but these methods aren't foolproof.

Related post:

Differences between Stainless Steel vs Carbon Steel?

How to weld mild steel to stainless steel?

Hot Cracking of the Stainless Steel

Hot cracking is a common issue when welding stainless steel to carbon steel. This occurs because stainless steel is more electrically-resistant than carbon steel, so it heats up faster. Waiting for the carbon steel to reach welding temperature can cause the stainless steel to overheat and become riddled with hot cracks. This problem is particularly prevalent when resistance welding stainless steel to carbon steel. Filler-based welding or preheating plain steel/mild steel can help alleviate this problem, but these methods aren't always sufficient.

Contamination

Welding stainless steel to carbon steel can also result in contamination of the stainless steel with carbon steel particles, which can lead to rust and other forms of corrosion over time.

Thermal Expansion in High-Temperature Service Conditions

This difference in expansion rates between the two metals can cause extra fatigue to the welded joint, reducing the structural integrity and useful life. In high-temperature service conditions, such as in power plants or chemical processing plants, this problem can be particularly acute. The difference in expansion rates between stainless steel and carbon steel can cause the welded joint to become fatigued, leading to structural failure over time.

Increased Bimetallic Corrosion

Stainless steel is resistant to corrosion, whereas carbon steel is not. When these two metals are welded together, the carbon steel can act as a cathode and the stainless steel as an anode in the presence of an electrolyte such as water, leading to corrosion of the stainless steel.

Stainless steel is generally used for its strong corrosion resistance. An uncovered weld of plain carbon steel and stainless steel that is exposed to extremely corrosive conditions, such as immersion in saltwater, could cause corrosion. This is because the intermingling of plain carbon steel particles with the stainless alloy compromises the protective oxide layer of the stainless, allowing rust to form. This type of corrosion is known as bimetallic corrosion and can severely compromise the integrity of the welded joint.

Reduced Weld Strength

Joining dissimilar metals can lead to weaker welds, even with filler-based welding methods. The differences in weld temperatures and operational tolerances alone can easily compromise the strength of the welded joint. Over time, this can lead to failure of the welded joint, which can be dangerous in high-stress applications.

Conclusion

Welding dissimilar metals together are difficult to do right and often produces inferior results compared to using metal alloys that are similar or the same. When it comes to welding stainless steel to carbon steel, there are several reasons why you should avoid it whenever possible. The difficulty of achieving a good weld, the risk of hot cracking, thermal expansion, increased bimetallic corrosion, and reduced weld strength all make it a risky proposition.

Differences between Stainless Steel vs Carbon Steel?

Carbon steel and stainless steel are two common materials used in various applications. Here are some of the main differences between them:

1. Composition: Carbon steel is an alloy of iron and carbon, with a maximum carbon content of 2.1%. Stainless steel is an alloy of iron, carbon, and at least 10.5% chromium, with other elements such as nickel and molybdenum added for specific properties.
2. Corrosion resistance: Carbon steel is susceptible to corrosion and rust, especially in moist or humid environments. Stainless steel has a higher resistance to corrosion due to the presence of chromium, which forms a protective oxide layer on the surface of the material.
3. Strength: Carbon steel has a higher tensile strength and yield strength than stainless steel. However, stainless steel is often used in applications where corrosion resistance is critical, such as in the food and medical industries.

Physical Properties

Physical parameter	Carbon Steel	Stainless Steel
Average Density	The average Density of Carbon Steel is 7850 Kg/m3	The average Density of Stainless Steel is 8000 Kg/m3. So Stainless Steel is slightly heavier than Carbon Steel
Co-efficient of Linear Thermal Expansion	The thermal expansion coefficient for Carbon Steel is usually less than that of stainless steel and varies in the range of (10.8 – 12.5) X 10-6 m/(m °C)	The expansion coefficient of Stainless Steel is comparatively more than that of Carbon Steel. Depending on grade, the coefficient varies in the range of (10-17.3) X10-6 m/(m °C). So, the thermal growth of Stainless Steel is more than Carbon Steel material.
Melting Point	The melting point of Carbon Steel is more than Stainless Steel. Typically Low Carbon Steel has a melting point of 1410 Deg C. The melting point of high Carbon steel ranges between 1425-1540 Deg C.	The melting point of stainless steel varies between 1375 to 1530 Deg C.

Mechanical Properties

Mechanical properties	Carbon Steel	Stainless Steel
Yield Strength	Low Carbon Steel: 180 to 260 MPa; High carbon Steel: 325 to 440 Mpa.	Ferritic Steel: 280 Mpa; Austenitic Steel: 230 MPA; Martensitic Steel: 480 MPA
Tensile Strength	Low Carbon Steel: 325 to 485 MPa; High carbon Steel: 460 to 924 Mpa.	Ferritic Steel: 450 Mpa; Austenitic Steel: 540 MPA; Martensitic Steel: 660 MPA
Elastic Modulus	2100000 Mpa	1900000 MPa
Shear Modulus	81000 Mpa	740000 MPa
Poisson’s Ratio	0.3	0.27

Other differences

Stainless Steel	Carbon Steel
Thermal conductivity is comparatively lower	Higher thermal conductivity.
Excellent wear resistance	Poor wear resistance.
Heat treatment of Stainless steel is difficult	Carbon Steel can easily undergo heat treatment.
Stainless Steel is easily cleanable	The cleanability of carbon steel is less than stainless steel.

4. Cost: Carbon steel is generally less expensive than stainless steel, although the cost can vary depending on the specific grades and applications.
5. Appearance: Stainless steel has a shiny, polished appearance and is often used in decorative applications. Carbon steel has a more matte finish and is often used in industrial applications.
6. Which is better carbon steel or stainless steel? It depends on the application and cost. For applications in a corrosive environment, stainless steel performs better than carbon steel due to its higher resistance to corrosion. For high-temperature and very low-temperature applications, stainless steel is preferred due to its better performance at extreme temperatures. However, for normal applications, carbon steel is often considered better as it is less expensive and has higher tensile strength than stainless steel. Ultimately, the choice between carbon steel and stainless steel depends on the specific needs of the application, including factors such as temperature, corrosion resistance, and cost.

Overall, the choice between carbon steel and stainless steel depends on the specific requirements of the application, such as the level of corrosion resistance, strength, and cost.

Difference Between Stainless Steel 321 and 347

ASTM A213 321 321H 347 347H Chemical Composition:

Grade	321	321H	347	347H
UNS Designation	S32100	S32109	S34700	S34709
Carbon (C) Max.	0.08	0.04–0.10	0.08	0.04-0.10
Manganese (Mn) Max.	2.00	2.00	2.00	2.00
Phosphorous (P) Max.	0.045	0.045	0.04	0.04
Sulphur (S) Max.	0.03	0.03	0.03	0.03
Silicon (Si) Max.	1.00	1.00	0.75	0.74
Chromium (Cr)	17.0–20.0	17.0–20.0	17.0–20.0	17.0–20.0
Nickel (Ni)	9.0–12.0	9.0–12.0	9.0–13.0	9.0–13.0
Molybdenum (Mo)	–	–	–	–
Nitrogen (N)	–	–	–	–
Iron (Fe)	Bal.	Bal.	Bal.	Bal.
Other Elements	Ti=5(C+N) to 0.70%	Ti=4(C+N) to 0.70%	Cb+Ta=10xC-1.0	Cb+Ta=10xC-1.0

A limitation with 321 is that titanium does not transfer well across a high temperature arc, so is not recommended as a welding consumable. In this case grade 347 is preferred – the niobium performs the same carbide stabilisation task but can be transferred across a welding arc. Grade 347 is therefore the standard consumable for welding 321. Grade 347 is only occasionally used as parent plate material.

Like other austenitic grades, 321 and 347 have excellent forming and welding characteristics, are readily brake or roll formed and have outstanding welding characteristics. Post-weld annealing is not required. They also have excellent toughness, even down to cryogenic temperatures. Grade 321 does not polish well, so is not recommended for decorative applications.

TP321 Stainless Steel Tubes

Features:

TP321 is a stabilized stainless steel that offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperature in the chromium carbide precipitation range from 800 °F to 1500°F (427°C to 816°C). Alloy 321 stainless steel tubing is stabilized against chromium carbide formation by the addition of titanium.

TP347H Stainless Steel Tube:

Features:
It is a stable austenitic heat-strength steel. It has good heat strength and resistance to intergranular corrosion, good welding performance, and good corrosion resistance in alkali, seawater and various acids.347H and 347HFG in higher elevated temperature allowable stresses for these stabilized alloys for ASME Boiler and Pressure Vessel Code applications.

Application:
Heat exchangers for large boiler superheater tubes, reheater tubes, steam lines and petrochemicals. The allowable oxidation temperature in boiler tubes is 750 °C.