What Are the Differences Between Carbon Steel and Stainless Steel?

Stainless steel pipe is a kind of hollow steel pipe that is not easy to rust.

Stainless steel pipe

Stainless steel pipe is a kind of hollow steel pipe that is not easy to rust.

Chinese name

Stainless steel pipe

Foreign name

Stainless Steel

Nature

Steel Pipe

is widely used in

Petroleum, chemical, medical,

Scope of application

Used as a pipeline for conveying fluids

Material

304, 316

Classification of stainless steel pipes: stainless steel seamless steel pipes and stainless steel welded steel pipes (slotted steel pipes) are basically two categories. According to the outer diameter of the steel pipe, it can be divided into round pipes and special-shaped pipes. Round steel pipes are widely used, but there are some special-shaped steel pipes such as square, rectangular, semi-circular, hexagonal, equilateral triangle, and octagonal.

For steel pipes subjected to fluid pressure, hydraulic tests and radiographic inspections must be performed to check their pressure resistance and quality. It is qualified that no leakage, soaking or swelling occurs under the specified pressure. Some steel pipes must also be tested according to standards or demander requirements. Hemming test, flare test, flattening test, etc.

Seamless stainless steel pipe, also called stainless steel seamless pipe, is made of steel ingots or solid tube blanks by perforation to make capillary tubes, and then made by hot rolling, cold rolling or cold drawing. The specifications of seamless steel tubes are expressed in millimeters of outer diameter * wall thickness.

The full name of 304 stainless steel pipe is SUS304 stainless steel pipe.

SUS304 stainless steel pipe is a stainless steel pipe made of American grade. The domestic grade is equivalent to 0Cr19Ni9 stainless steel pipe, which is usually replaced by 0Cr18Ni9.

The antirust mechanism of stainless steel is that the alloy elements form a dense oxide film, which blocks oxygen contact and prevents further oxidation. So stainless steel is not "stainless."

There are several reasons for the rust of 304 material:

1. Chloride ion is present in the use environment.

Chloride ions are widely present, such as salt, sweat, sea water, sea breeze, soil, and so on. Corrosion of stainless steel in the presence of chloride ions is fast and even exceeds that of ordinary low carbon steel.

Therefore, there are requirements for the use environment of stainless steel, and it is necessary to wipe frequently to remove dust and keep it clean and dry.

316 and 317 stainless steels (see below for properties of 317 stainless steels) are molybdenum-containing stainless steels. The content of molybdenum in 317 stainless steel is slightly higher than that in 316 stainless steel. Due to the molybdenum in steel, the overall performance of this steel is better than that of 310 and 304 stainless steel. Under high temperature conditions, when the sulfuric acid concentration is lower than 15% and higher than 85%, 316 Stainless steel has a wide range of uses. 316 stainless steel also has good resistance to chloride attack, so it is usually used in the marine environment.

With the development of social economy, the application of stainless steel pipe has also become more and more popular. It is bound to bring about new improvements in various fields.

Theoretical weight of stainless steel pipe: W = outer diameter-wall thickness x wall thickness x 0.02491.

Since the invention of stainless steel at the beginning of this century, stainless steel has combined the image of modern materials and the outstanding reputation in architectural applications, making its competitors envious. Stainless steel does not cause corrosion, pitting, rusting, or abrasion. Stainless steel is also one of the strongest materials in construction metal materials. Because stainless steel has good corrosion resistance, it enables structural components to maintain engineering integrity permanently. Chromium-containing stainless steel also combines mechanical strength and high extensibility, and is easy to process and manufacture components, which can meet the needs of architects and structural designers.

201 serieschrome-nickel-manganese austenitic stainless steel.

300 serieschrome-nickel austenitic stainless steel.

301Good ductility, used for molded products. It can also be hardened by mechanical processing. Good weldability. Abrasion resistance and fatigue strength are better than 304 stainless steel.

302Corrosion resistance is the same as 304, because the carbon content is relatively high and the strength is better.

303It is easier to cut than 304 by adding a small amount of sulfur and phosphorus.

304General model; namely 18/8 stainless steel. The GB grade is 0Cr18Ni9.

309has better temperature resistance than 304.

316After 304, the second most widely used steel type is mainly used in the food industry and surgical equipment. The addition of molybdenum makes it a special structure resistant to corrosion. Because it has better resistance to chloride corrosion than 304, it is also used as "marine steel". SS316 is usually used in nuclear fuel recovery equipment. 18/10 grade stainless steel usually also meets this application level. [1]

Model 321Similar to 304 except that the addition of titanium reduces the risk of corrosion of the material's welds.

400 Series-Ferritic and Martensitic Stainless Steel.

408Good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.

409The cheapest model (British and American), usually used as automobile exhaust pipe, is a ferritic stainless steel (chrome steel).

410Martensite (high-strength chromium steel), has good wear resistance and poor corrosion resistance.

416The addition of sulfur improves the processability of the material.

420 "Blade grade" martensitic steel, similar to the earliest stainless steel of Brinell high chromium steel. Also used in surgical knives, it can be made very bright.

430Ferritic stainless steel, for decoration, such as for car accessories. Good moldability, but poor temperature resistance and corrosion resistance.

440High-strength cutting tool steel, which contains slightly higher carbon, can obtain higher yield strength after appropriate heat treatment, and hardness can reach 58HRC, which is among the hardest stainless steels. The most common application example is a "shaving blade". There are three commonly used models: 440A, 440B, 440C, and 440F (easy to process).

500 SeriesHeat-resistant chrome alloy steel.

600 SeriesMartensitic precipitation hardened stainless steel.

630The most commonly used precipitation hardening stainless steel model, also commonly called 17-4; 17% Cr, 4% Ni.

[(Outer diameter-wall thickness) * wall thickness] * 0.02491 = kg / meter (weight per meter)

1. The power supply with vertical external characteristics is adopted, and the positive polarity is adopted when the direct current is used (the welding wire is connected to the negative electrode).

2. Generally suitable for welding of thin plates below 6mm. It has the characteristics of beautiful welding seam formation and small welding deformation.

3. The protective gas is argon with a purity of 99.99%. When the welding current is 50 ~ 50A, the argon flow is 8 ~ 0L / min, and when the current is 50 ~ 250A, the argon flow is 2 ~ 5L / min.

4. The length of the tungsten electrode protruding from the gas nozzle is preferably 4 ~ 5mm. It is 2 ~ 3mm in the place with poor shielding such as fillet welding and 5 ~ 6mm in the depth of the slot. The distance from the nozzle to the work is generally not More than 5mm.

5. In order to prevent the occurrence of welding pores, the welding site must be cleaned if there is rust, oil, etc.

6. Welding arc length. When welding ordinary steel, it is better to be 2 ~ 4mm, and when welding stainless steel, it is better to be ~ 3mm. If it is too long, the protection effect is not good.

7. To prevent the back surface of the bottom bead from being oxidized during butt bonding, the back surface also needs to be protected by gas.

8. In order to protect argon well from welding pool and facilitate welding operation, the tungsten electrode centerline and the welding workpiece should generally maintain an angle of 80 ~ 85 °, and the angle between the filler wire and the workpiece surface should be as small as possible. Generally it is about 0 °.

9. Windproof and ventilation. Where there is wind, take measures to block the net, and indoors should take appropriate ventilation measures.

1. Low temperature embrittlement --- In low temperature environment, the deformation energy is small. In a low-temperature environment, the phenomenon that the elongation and the reduction in area are reduced is called low-temperature embrittlement. Mostly produced on the body-centered cubic structure of the ferrite series.

2. Low temperature processing --- quenching the martensitic stainless steel from the austenitizing temperature and then cooling it to a very low temperature to promote the quenching method of producing martensite. Suitable for stainless steels that easily produce retained austenite.

At low temperature, the stainless steel tube will have great changes in resistance, linear expansion coefficient, thermal conductivity, mass melting and magnetic properties. Resistance, linear expansion coefficient becomes smaller at low temperature; thermal conductivity and mass heat capacity decrease sharply at low temperature; Young's modulus (longitudinal elastic modulus) increases at the same time as temperature decreases. Because the austenite series stainless steel pipe has a low temperature (Subzreo temperature) Ms point (the temperature at which martensite transformation starts or the temperature at which martensite is formed), martensite can be formed when it is kept below the Ms point. The formation of martensite at low temperatures makes SUS304 (18Cr-8Ni), a representative type of austenitic stainless steel, non-magnetic at normal temperature, but becomes magnetic at low temperatures.

About ferrite at low temperature

(1) Output hit a record high. From January to June 2013, the country's cumulative production of crude steel was 390 million tons, a year-on-year increase of 7.4%, an increase of 5.6 percentage points from the same period last year. In the first 6 months, the average daily output of crude steel was 2.154 million tons, equivalent to an annual output of 786 million tons of crude steel. Among them, in February it reached a record high of 2.208 million tons. Although it declined in March-June, it remained at a high level of more than 2.1 million tons. In terms of provinces and regions, the crude steel output of Hebei and Jiangsu increased by 6.8% and 13.2% year-on-year respectively from January to June. The combined new production of the two provinces accounted for 42.4% of the national increase of 26.94 million tons. Provinces such as Henan and Yunnan also increased output by more than 1 million tons. In terms of different types of enterprises, from January to June, the crude steel output of key large and medium-sized steel companies increased 5.5% year-on-year, which was 2 percentage points lower than the national average increase, but 60% of the increase in output was still from key large and medium-sized steel companies.

(2) Low steel prices. From January to June 2013, the overall performance of the domestic steel market was sluggish. With the substantial release of crude steel production capacity, the market supply and demand has fallen into an imbalance, and steel prices have entered a downward channel and have fallen weakly for more than 4 months. As of July 26, 2013, the steel price index had dropped to 100.48 points, which was lower than 6.6 points at the beginning of the year. The prices of the eight steel varieties that the Iron and Steel Industry Association focused on have all fallen to varying degrees from the beginning of the year, with an average decrease of 5.7%. In terms of different types, the prices of construction wires and rebars, which accounted for a large proportion of China's steel production, fell by 4.9% and 6.7%, and the prices of plate and hot rolled coil fell by 5.7% and 9.7%, respectively.

(3) The export of steel products has grown rapidly. The imbalance between supply and demand in the domestic steel market has stimulated exports. From January to June, China exported 30.69 million tons of steel products, an increase of 12.6% year-on-year; imported steel products were 6.83 million tons, a decrease of 1.8%, and imported steel billets and ingots were 320,000 tons, an increase of 50%. Converting billets into crude steel, the cumulative net export was 25.06 million tons, a year-on-year increase of 17.3%, accounting for 6.4% of China's crude steel output. From the perspective of export prices, the average export price of rods and wires for the first six months of the year was US $ 624.3 / ton, a year-on-year decrease of 18%; sheet materials were US $ 835.2 / ton, a year-on-year decrease of 2.8%.

(4) Steel mills and social stocks are operating at high levels. The contradiction between market supply and demand has spread to the circulation field, and domestic steel stocks have continued the growth trend at the end of the previous year. On March 15, it reached a record high of 22.52 million tons, an increase of 3.51 million tons from the previous year's highest point, of which 14.32 million tons of construction steel stocks, accounting for 63.6% of the total inventory. After that, as seasonal consumption increased, the inventory gradually dropped, and it fell to 15.4 million tons on July 26. Oversupply in the market has also pushed up steel plant inventory. In mid-March, the steel stocks of key enterprises reached a historical record of 14.51 million tons, a year-on-year increase of 29.7%. In late June, it fell to 12.68 million tons, which is still a 29.9% increase from the beginning of the year, compared with 2012 The year-on-year growth was 11.4%.

(E) The profit level of steel mills has been decreasing month by month. In the first half of 2013, the metallurgical industry realized a profit of 73.69 billion yuan, an increase of 13.7% year-on-year, of which the ferrous metal smelting and rolling processing industry realized a profit of 45.44 billion yuan, an increase of 22.7% year-on-year. From January to May, the profitability of key large and medium-sized iron and steel enterprises is far lower than the overall level of the industry, and it has shown a downward trend from month to month. Although the profit has increased by 34%, it is only 2.8 billion yuan, and the sales profit margin is 0.19%. In May of that month, 86 key large and medium-sized steel companies only realized a profit of 150 million yuan, which has been a sequential decline for 5 consecutive months, of which 34 companies lost money, with a loss of up to 40%.

(6) The growth rate of investment in fixed assets in the steel industry dropped significantly. From January to June 2013, the investment in fixed assets in the steel industry was 303.5 billion yuan, an increase of 4.3% year-on-year, of which ferrous metal smelting and rolling investment was 235.6 billion yuan, an increase of 3.3% year-on-year, down 6.1 percentage points from the same period in 2012; The selected investment was 67.9 billion yuan, a year-on-year increase of 7.8%, and the growth rate fell sharply by 15 percentage points.