How is Stainless Steel Made?

Stainless steel (Stainless Steel) is an abbreviation for stainless acid-resistant steel. Steels that are resistant to weakly corrosive media such as air, steam, and water, or stainless steel are called stainless steel. The type of steel that is corroded is called acid-resistant steel.

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Stainless steel (Stainless Steel) is an abbreviation for stainless acid-resistant steel. Steels that are resistant to weakly corrosive media such as air, steam, and water, or stainless steel are called stainless steel;

The invention and use of stainless steel goes back to

Stainless steel is often divided into:

stainless steel

Due to the different uses of each product, its processing technology and quality requirements of raw materials are also different. Generally speaking, different stainless steel products require different raw material thickness tolerances, such as second-class tableware and insulation cups. Thickness tolerances are generally higher, -3 ~ 5%, while first-class tableware thickness tolerances are generally required- 5%, steel pipe requirements of -10%, hotel refrigerator freezer material thickness tolerance requirements of -8%, dealers' requirements for thickness tolerances are generally between -4% ~ 6%. At the same time, the different domestic and foreign sales of the product will also lead to different customer requirements for raw material thickness tolerances. The thickness tolerance requirements of general export product customers are relatively high, while domestic sales enterprises have relatively low thickness tolerance requirements (mostly due to cost considerations), and some customers even require -15%.

DDQ (deep drawing quality) material: refers to materials used for deep drawing (punching), which is what we call soft materials. The main characteristics of this material are higher elongation ( 53%) and hardness. Low ( 170%), the internal grain grade is between 7.0 and 8.0, and the deep drawing performance is excellent. Many companies producing thermos bottles and pots generally have higher processing ratios (BLANKING SIZE / product diameter), and their processing ratios are 3.0, 1.96, 2.13, and 1.98, respectively. SUS304DDQ materials are mainly used for these products that require higher processing ratios. Of course, products with a processing ratio exceeding 2.0 generally require several passes to complete. If the raw material extension cannot be achieved, the product is prone to cracks and punctures when processing deep-drawn products, which affects the qualification rate of the finished product, and of course increases the cost of the manufacturer;

General material: It is mainly used for materials other than DDQ. This material is characterized by relatively low elongation ( 45%) and relatively high hardness ( 180HB). The internal grain size is between 8.0 and 9.0. Compared with DDQ materials, its deep-drawing performance is relatively poor. It is mainly used for products that can be obtained without stretching, such as spoons, spoons, forks, electrical appliances, and steel pipes for tableware. But it has an advantage compared with DDQ material, that is, the BQ property is relatively good, which is mainly due to its slightly higher hardness.

Stainless steel sheet is a not expensive material, but customers have very high requirements for its surface quality. Stainless steel sheets will inevitably have various defects in the production process, such as scratches, pits, sand holes, dark lines, creases, pollution, etc., so their surface quality, such as scratches, creases, etc. are high-grade materials. It is not allowed to occur, and defects such as pits and sand holes are never allowed in spoons, spoons, forks, and during production, because it is difficult to throw it away during polishing. Need to determine the quality level of the table according to the degree and frequency of the appearance of various defects, so as to determine the product level.

Compared with carbon steel

1.Density

The density of carbon steel is slightly higher than that of ferritic and martensitic stainless steel, and slightly lower than that of austenitic stainless steel;

2. Resistivity

Resistivity in ascending order of carbon steel, ferritic, martensitic and austenitic stainless steels;

3. The order of the linear expansion coefficients is similar, with the highest austenitic stainless steel and the smallest carbon steel;

4. Carbon steel, ferritic and martensitic stainless steels are magnetic, while austenitic stainless steels are non-magnetic, but when they are cold-work hardened to produce martensitic transformation, they will have magnetic properties. Heat treatment can be used to eliminate this martensite The tissue while recovering its non-magnetism.

Compared with carbon steel, austenitic stainless steel has the following characteristics:

1) High resistivity, about 5 times that of carbon steel.

2) The large linear expansion coefficient is 40% larger than that of carbon steel, and as the temperature increases, the value of the linear expansion coefficient increases accordingly.

3) Low thermal conductivity, about 1/3 of carbon steel.

Most of the use requirements are to maintain the original appearance of the building for a long time. Be sure to

Antibacterial stainless steel

Tested by authoritative units, the antibacterial stainless steel has a killing rate of more than 99% against E. coli and Staphylococcus aureus, and it also has a significant killing effect on other bacteria such as Candida albicans and Fusarium oxysporum. Antibacterial and antibacterial durability. Tests by the National Institute of Drug and Biological Products Inspection show that antibacterial stainless steel fully meets national technical standards in terms of toxicity and human safety. While imparting antibacterial properties to stainless steel, the material's mechanical, corrosion resistance, hot and cold working, welding and other properties are comparable to the original stainless steel.

The successful development of antibacterial stainless steel provides a broad space for the development of antibacterial products. The development potential of antibacterial stainless steel products is huge, and the market prospect is extremely broad. In today's society, many domestic manufacturers have expressed strong interest in antibacterial stainless steel, and the research group is actively seeking support for conducting a pilot test, and strive to turn this result into a commodity as soon as possible.

Precipitation hardening stainless steel

It has good formability and good weldability, and can be used as an ultra-high-strength material in the nuclear industry, aviation and aerospace industries.

According to the composition, it can be divided into Cr series (400 series), Cr-Ni series (300 series), Cr-Mn-Ni (200 series), heat-resistant chromium alloy steel (500 series) and precipitation hardening series (600 series).

200 series: chromium-manganese-nickel

201, 202, etc .: Manganese-nickel substitutes have relatively poor corrosion resistance, and are widely used as cheap substitutes for the 300 series in China

300 series: chrome-nickel austenitic stainless steel

301: Good ductility, used for molded products. It can also be hardened by mechanical processing. Good weldability. Better abrasion resistance and fatigue strength

Numbering and representation of steel

Use the international chemical element symbol and the country's symbol to represent the chemical composition, and use the Arabic letters to represent the content of the composition:

Such as: China, Russia 12CrNi3

Use fixed digits to represent steel series or numbers; such as: US, Japan, 300 series, 400 series, 200 series;

Use the Latin alphabet and sequence to form the serial number, only for the purpose.

Chinese numbering rules

Use element symbols

Use, Chinese Pinyin, Open hearth steel: P, Boiling steel: F, Calm steel: B, Class A steel: A, T8: Special 8, GCr15: Ball

Alloy steel,

Stainless steel corrosion

Electrochemical or chemical reactions occur on metal surfaces exposed in a corrosive environment, and they are uniformly corroded. The corrosion-resistant part of the stainless steel surface passivation film forms a pitting reaction due to the self-excitation reaction, generates small pores, and adds chlorine ions close to form a strong corrosive solution, which accelerates the corrosion reaction rate. And stainless steel inside

whether

The development of stainless steel industry in China is relatively late. Since the founding of the People s Republic of China and before the reform and opening up, the demand for stainless steel in China has been mainly based on cutting-edge industrial and defense applications. After the reform and opening up, the rapid development of the national economy and the significant improvement in people's living standards have stimulated the demand for stainless steel. After entering the 1990s, China's stainless steel industry has entered a period of rapid development, and the growth rate of stainless steel demand is much higher than the global level. Since 1990, the global apparent stainless steel consumption has increased at an average annual rate of 6%. In the 10 years of the 1990s, China s apparent stainless steel consumption has been 2.9 times the world s average annual growth rate. In the 21st century, China's stainless steel industry has grown rapidly.

From 2000 to 2006, the average annual growth rate of China's stainless steel consumption was above 21.17%. Among them, in 2001, China s apparent stainless steel consumption reached 2.05 million tons, surpassing the United States and becoming the world s largest stainless steel consumer. In 2008, China s apparent stainless steel consumption reached 6.400 million tons, a year-on-year decrease of 5.17%.

In November 2011, China's stainless steel output increased by 11.1% to 12.5 million tons. The production of stainless steel products was 338,800 tons, a year-on-year increase of 65.25%. Among them, Guangdong Province is the main production base of stainless steel products in China, with an output of 1.837 million tons, a year-on-year increase of 41.76%, accounting for 78.62% of the country's total output.

Stainless steel is the world's most widely used steel surface treatment method with the best performance-price ratio.

With the implementation of the western development strategy, projects such as West-to-East Power Transmission, West-to-East Gas Transmission, South-to-North Water Diversion, Three Gorges Project, Rural Power Network and Urban Power Grid Reform have been launched, and China's hot-dip galvanizing industry has entered a new round of high-speed progression stage.

The supply of chromium and nickel in the raw materials of the stainless steel industry in China is oversupplied abroad, but in short supply in China; stainless steel is overcapacity, oversupply, and frequent fluctuations in profitability. As the competition in the stainless steel industry continues to intensify, mergers and acquisitions and capital operations between large stainless steel manufacturers are becoming more frequent. Domestic excellent stainless steel manufacturers are paying more and more attention to the research of the industry market, especially the changes in the development environment and customer demand trends. In-depth research. Because of this, a large number of domestic excellent stainless steel brands have risen rapidly and gradually become the leader in the stainless steel industry!

Operation of the steel industry

(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 in 2012. 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.

Theoretical weight calculation of stainless steel products

Reference formula for stainless steel plate / steel strip: stainless steel plate weight (kg) = length (m) * width (m) * thickness (mm) * density (g / cm³) .

Stainless steel round bar / wire reference formula: Stainless steel round bar weight (kg) = (diameter (mm) / 2) * (diameter (mm) / 2) * * length (m) * density (g / cm³) / 1000 .

Stainless steel round pipe reference formula: stainless steel round pipe weight (kg) = ((outer diameter (mm) / 2) * (outer diameter (mm) / 2)-(inner diameter (mm) / 2) * (inner diameter (mm) / 2)) * * length (m) * density (g / cm³) / 1000 ; ** wall thickness (mm) = (outer diameter (mm)-inner diameter (mm)) / 2.

Reference formula for stainless steel square tube : stainless steel square tube weight (kg) = (section length (mm) * 2-section width (mm) * 2-wall thickness (mm) * 4) * wall thickness (mm) * length (m) * Density (g / cm³) / 1000 .

Reference formula for stainless steel equilateral angle steel : stainless steel equilateral angle steel weight (kg) = (section side length (mm) * 2-side thickness (mm) * length (m) * density (g / cm³) / 1000 ; ** [ 1] According to the national standard GB / T706-2008 for isolateral angle steel, the calculation formula for the actual weight of angle steel is more complicated. Because GB / T706-2008 indicates the angle of the inner arc radius (r1) and the inner arc radius ( r) Not as a delivery condition, and combined with the actual delivery status of the angle steel in production and circulation, this reference formula is given; [2] According to the formula for the calculation of the area of the equilateral angle steel in GB / T706-2008: S = d * (2 * bd) + 0.215 * (r²-2r1²), accurate theoretical weight of stainless steel equilateral angle steel (kg) = cross-sectional area S (mm²) * length (m) * density (g / cm³) / 1000.

Stainless steel unequal angle steel reference formula: stainless steel equal angle steel weight (kg) = (section side length 1 (mm) + section side length 2 (mm)-side thickness (mm)) * length (m) * density (g / cm³) / 1000 ; ** [1] According to the national standard GB / T706-2008 for unequal side angle steel, the formula for calculating the actual weight of angle steel is more complicated. Since GB / T706-2008 indicates that the inner arc radius (r1) and the inner arc radius (r) of the end of the angle steel section are not used as delivery conditions, this is given in combination with the actual delivery status of the angle steel in production and circulation. Reference formula; [2] According to the calculation formula of unequal-angle angle steel cross-section area given in GB / T706-2008: S = d * (B + bd) + 0.215 * (r²-2r1²), accurate stainless steel unequal-angle angle steel Theoretical weight (kg) = cross-sectional area S (mm²) * length (m) * density (g / cm³) / 1000.

Reference formula for stainless steel channel : stainless steel channel weight (kg) = (section height (mm) * section waist thickness (mm) + (section leg width (mm)-section waist thickness (mm)) * section average leg thickness (mm ) * 2) * length (m) * density (g / cm³) / 1000 ; [1] According to the national standard GB / T706-2008 for channel steel, the formula for calculating the actual weight of channel steel is more complicated. As specified in GB / T706-2008, the inner arc radius (r1) and inner arc radius (r) of the end of the channel section are not regarded as the delivery conditions. Based on the actual delivery status of the channel in production and circulation, This reference formula is given; [2] According to the formula for calculating the cross-section area of channel steel given in GB / T706-2008: S = h * d + 2 * t * (bd) +0.349 (r²-r1²), accurate stainless steel groove Theoretical weight of steel (kg) = cross-sectional area S (mm²) * length (m) * density (g / cm³) / 1000.

Reference formula of stainless steel I-beam : stainless steel I-beam weight (kg) = (section height (mm) * section waist thickness (mm) + (section leg width (mm)-section waist thickness (mm)) * section average leg thickness (mm) * 2) * length (m) * density (g / cm³) / 1000 ; [1] According to the national standard of I-beam GB / T706-2008, the formula for calculating the actual weight of I-beam is more complicated. Because GB / T706-2008 indicates that the inner arc radius (r1) and inner arc radius (r) of the end of the I-beam section are not used as delivery conditions, the actual delivery status of the I-beam in production and circulation is combined. , Give this reference formula; [2] According to the calculation formula of I-section area given in GB / T706-2008: S = h * d + 2 * t * (bd) +0.615 (r²-r1²), accurate Theoretical weight of stainless steel I-beam (kg) = cross-sectional area S (mm²) * length (m) * density (g / cm³) / 1000.

Stainless steel L-shaped steel reference formula: Stainless steel L-shaped steel weight (kg) = (long side width (mm) * long side thickness (mm) + (short side width (mm)-long side thickness (mm)) * short side thickness (mm )) * Length (m) * density (g / cm³) / 1000 ; [1] According to the national standard GB / T706-2008 for L-shaped steel, the formula for calculating the actual weight of L-shaped steel is more complicated. Although GB / T706-2008 does not indicate the inner arc radius (r1) and inner arc radius (r) of the end of the L-shaped steel section, they are not used as delivery conditions, but the actual delivery status of the L-shaped steel in production and circulation is combined. , Give this reference formula; [2] According to the calculation formula of L-shaped steel cross-sectional area given in GB / T706-2008: S = B * D + d * (bD) + 0.215 * (r²-r1²), accurate stainless steel Theoretical weight of L-shaped steel (kg) = cross-sectional area S (mm²) * length (m) * density (g / cm³) / 1000.

Stainless steel square steel reference formula: stainless steel square steel weight (kg) = section length (mm) * section width (mm) * length (m) * density (g / cm³) / 1000 .

Reference formula for stainless steel wire rope : Stainless steel wire rope weight (kg) = diameter (mm) * diameter (mm) * hundred-meter factor * length (m) / 100 .